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• F{"o}rster, S., Schmidt, L.K., Kopic, E., Ansch{"u}tz, U., Huang, S., Schl{"u}cking, K., K{"o}ster, P., Waadt, R., Larrieu, A., Batistič, O., Rodriguez, P.L., Grill, E., Kudla, J., Becker, D. (2019) Wounding-Induced Stomatal Closure Requires Jasmonate-Mediated Activation of GORK K+ Channels by a Ca2+ Sensor-Kinase CBL1-CIPK5 Complex, Dev Cell, 48(1), 87–99, available: https://doi.org/10.1016/j.devcel.2018.11.014.
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  Guard cells integrate various hormone signals and environmental cues to balance plant gas exchange and transpiration. The wounding-associated hormone jasmonic acid (JA) and the drought hormone abscisic acid (ABA) both trigger stomatal closure. In contrast to ABA however, the molecular mechanisms of JA-induced stomatal closure have remained largely elusive. Here, we identify a fast signaling pathway for JA targeting the K+ efflux channel GORK. Wounding triggers both local and systemic stomatal closure by activation of the JA signaling cascade followed by GORK phosphorylation and activation through CBL1-CIPK5 Ca2+ sensor-kinase complexes. GORK activation strictly depends on plasma membrane targeting and Ca2+ binding of CBL1-CIPK5 complexes. Accordingly, in gork, cbl1, and cipk5 mutants, JA-induced stomatal closure is specifically abolished. The ABA-coreceptor ABI2 counteracts CBL1-CIPK5-dependent GORK activation. Hence, JA-induced Ca2+ signaling in response to biotic stress converges with the ABA-mediated drought stress pathway to facilitate GORK-mediated stomatal closure upon wounding.

  @article{Forster:2019:Dev-Cell:30528785, abstract = {Guard cells integrate various hormone signals and environmental cues to balance plant gas exchange and transpiration. The wounding-associated hormone jasmonic acid (JA) and the drought hormone abscisic acid (ABA) both trigger stomatal closure. In contrast to ABA however, the molecular mechanisms of JA-induced stomatal closure have remained largely elusive. Here, we identify a fast signaling pathway for JA targeting the K+ efflux channel GORK. Wounding triggers both local and systemic stomatal closure by activation of the JA signaling cascade followed by GORK phosphorylation and activation through CBL1-CIPK5 Ca2+ sensor-kinase complexes. GORK activation strictly depends on plasma membrane targeting and Ca2+ binding of CBL1-CIPK5 complexes. Accordingly, in gork, cbl1, and cipk5 mutants, JA-induced stomatal closure is specifically abolished. The ABA-coreceptor ABI2 counteracts CBL1-CIPK5-dependent GORK activation. Hence, JA-induced Ca2+ signaling in response to biotic stress converges with the ABA-mediated drought stress pathway to facilitate GORK-mediated stomatal closure upon wounding.}, author = {F{\"o}rster, S and Schmidt, L K and Kopic, E and Ansch{\"u}tz, U and Huang, S and Schl{\"u}cking, K and K{\"o}ster, P and Waadt, R and Larrieu, A and Batistič, O and Rodriguez, P L and Grill, E and Kudla, J and Becker, D}, journal = {Dev Cell}, keywords = {myown}, month = {jan}, number = 1, pages = {87-99}, title = {Wounding-Induced Stomatal Closure Requires Jasmonate-Mediated Activation of GORK K+ Channels by a Ca2+ Sensor-Kinase CBL1-CIPK5 Complex}, volume = 48, year = 2019 }

  %0 Journal Article %1 Forster:2019:Dev-Cell:30528785 %A F{"o}rster, S %A Schmidt, L K %A Kopic, E %A Ansch{"u}tz, U %A Huang, S %A Schl{"u}cking, K %A K{"o}ster, P %A Waadt, R %A Larrieu, A %A Batistič, O %A Rodriguez, P L %A Grill, E %A Kudla, J %A Becker, D %D 2019 %J Dev Cell %N 1 %P 87-99 %R 10.1016/j.devcel.2018.11.014 %T Wounding-Induced Stomatal Closure Requires Jasmonate-Mediated Activation of GORK K+ Channels by a Ca2+ Sensor-Kinase CBL1-CIPK5 Complex %U https://www.ncbi.nlm.nih.gov/pubmed/30528785 %V 48 %X Guard cells integrate various hormone signals and environmental cues to balance plant gas exchange and transpiration. The wounding-associated hormone jasmonic acid (JA) and the drought hormone abscisic acid (ABA) both trigger stomatal closure. In contrast to ABA however, the molecular mechanisms of JA-induced stomatal closure have remained largely elusive. Here, we identify a fast signaling pathway for JA targeting the K+ efflux channel GORK. Wounding triggers both local and systemic stomatal closure by activation of the JA signaling cascade followed by GORK phosphorylation and activation through CBL1-CIPK5 Ca2+ sensor-kinase complexes. GORK activation strictly depends on plasma membrane targeting and Ca2+ binding of CBL1-CIPK5 complexes. Accordingly, in gork, cbl1, and cipk5 mutants, JA-induced stomatal closure is specifically abolished. The ABA-coreceptor ABI2 counteracts CBL1-CIPK5-dependent GORK activation. Hence, JA-induced Ca2+ signaling in response to biotic stress converges with the ABA-mediated drought stress pathway to facilitate GORK-mediated stomatal closure upon wounding.

• Hedrich, R., Mueller, T.D., Becker, D., Marten, I. (2018) Structure and Function of TPC1 Vacuole SV Channel Gains Shape, Mol Plant, 11(6), 764–775, available: https://doi.org/10.1016/j.molp.2018.03.017.
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  @article{RN122, author = {Hedrich, R. and Mueller, T. D. and Becker, D. and Marten, I.}, journal = {Mol Plant}, keywords = {imported}, number = 6, pages = {764-775}, title = {Structure and Function of TPC1 Vacuole SV Channel Gains Shape}, type = {Journal Article}, volume = 11, year = 2018 }

  %0 Journal Article %1 RN122 %A Hedrich, R. %A Mueller, T. D. %A Becker, D. %A Marten, I. %D 2018 %J Mol Plant %N 6 %P 764-775 %R 10.1016/j.molp.2018.03.017 %T Structure and Function of TPC1 Vacuole SV Channel Gains Shape %U https://www.ncbi.nlm.nih.gov/pubmed/29614320 %V 11
• Kudla, J., Becker, D., Grill, E., Hedrich, R., Hippler, M., Kummer, U., Parniske, M., Romeis, T., Schumacher, K. (2018) Advances and current challenges in calcium signaling, New Phytol, 218(2), 414–431, available: https://doi.org/10.1111/nph.14966.
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  @article{RN124, author = {Kudla, J. and Becker, D. and Grill, E. and Hedrich, R. and Hippler, M. and Kummer, U. and Parniske, M. and Romeis, T. and Schumacher, K.}, journal = {New Phytol}, keywords = {imported}, number = 2, pages = {414-431}, title = {Advances and current challenges in calcium signaling}, type = {Journal Article}, volume = 218, year = 2018 }

  %0 Journal Article %1 RN124 %A Kudla, J. %A Becker, D. %A Grill, E. %A Hedrich, R. %A Hippler, M. %A Kummer, U. %A Parniske, M. %A Romeis, T. %A Schumacher, K. %D 2018 %J New Phytol %N 2 %P 414-431 %R 10.1111/nph.14966 %T Advances and current challenges in calcium signaling %U https://www.ncbi.nlm.nih.gov/pubmed/29332310 %V 218
• Dindas, J., Scherzer, S., Roelfsema, M.R.G., von Meyer, K., Muller, H.M., Al-Rasheid, K.A.S., Palme, K., Dietrich, P., Becker, D., Bennett, M.J., Hedrich, R. (2018) AUX1-mediated root hair auxin influx governs SCF(TIR1/AFB)-type Ca(2+) signaling, Nat Commun, 9(1), 1174, available: https://doi.org/10.1038/s41467-018-03582-5.
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  @article{RN123, author = {Dindas, J. and Scherzer, S. and Roelfsema, M. R. G. and von Meyer, K. and Muller, H. M. and Al-Rasheid, K. A. S. and Palme, K. and Dietrich, P. and Becker, D. and Bennett, M. J. and Hedrich, R.}, journal = {Nat Commun}, keywords = {imported}, number = 1, pages = 1174, title = {AUX1-mediated root hair auxin influx governs SCF(TIR1/AFB)-type Ca(2+) signaling}, type = {Journal Article}, volume = 9, year = 2018 }

  %0 Journal Article %1 RN123 %A Dindas, J. %A Scherzer, S. %A Roelfsema, M. R. G. %A von Meyer, K. %A Muller, H. M. %A Al-Rasheid, K. A. S. %A Palme, K. %A Dietrich, P. %A Becker, D. %A Bennett, M. J. %A Hedrich, R. %D 2018 %J Nat Commun %N 1 %P 1174 %R 10.1038/s41467-018-03582-5 %T AUX1-mediated root hair auxin influx governs SCF(TIR1/AFB)-type Ca(2+) signaling %U https://www.ncbi.nlm.nih.gov/pubmed/29563504 %V 9
• Nishiyama, T., Sakayama, H., de Vries, J., Buschmann, H., Saint-Marcoux, D., Ullrich, K.K., Haas, F.B., Vanderstraeten, L., Becker, D., Lang, D., Vosolsobe, S., Rombauts, S., Wilhelmsson, P.K.I., Janitza, P., Kern, R., Heyl, A., Rumpler, F., Villalobos, L., Clay, J.M., Skokan, R., Toyoda, A., Suzuki, Y., Kagoshima, H., Schijlen, E., Tajeshwar, N., Catarino, B., Hetherington, A.J., Saltykova, A., Bonnot, C., Breuninger, H., Symeonidi, A., Radhakrishnan, G.V., Van Nieuwerburgh, F., Deforce, D., Chang, C., Karol, K.G., Hedrich, R., Ulvskov, P., Glockner, G., Delwiche, C.F., Petrasek, J., Van de Peer, Y., Friml, J., Beilby, M., Dolan, L., Kohara, Y., Sugano, S., Fujiyama, A., Delaux, P.M., Quint, M., Theissen, G., Hagemann, M., Harholt, J., Dunand, C., Zachgo, S., Langdale, J., Maumus, F., Van Der Straeten, D., Gould, S.B., Rensing, S.A. (2018) The Chara Genome: Secondary Complexity and Implications for Plant Terrestrialization, Cell, 174(2), 448–464 e24, available: https://doi.org/10.1016/j.cell.2018.06.033.
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  @article{RN121, author = {Nishiyama, T. and Sakayama, H. and de Vries, J. and Buschmann, H. and Saint-Marcoux, D. and Ullrich, K. K. and Haas, F. B. and Vanderstraeten, L. and Becker, D. and Lang, D. and Vosolsobe, S. and Rombauts, S. and Wilhelmsson, P. K. I. and Janitza, P. and Kern, R. and Heyl, A. and Rumpler, F. and Villalobos, Liac and Clay, J. M. and Skokan, R. and Toyoda, A. and Suzuki, Y. and Kagoshima, H. and Schijlen, E. and Tajeshwar, N. and Catarino, B. and Hetherington, A. J. and Saltykova, A. and Bonnot, C. and Breuninger, H. and Symeonidi, A. and Radhakrishnan, G. V. and Van Nieuwerburgh, F. and Deforce, D. and Chang, C. and Karol, K. G. and Hedrich, R. and Ulvskov, P. and Glockner, G. and Delwiche, C. F. and Petrasek, J. and Van de Peer, Y. and Friml, J. and Beilby, M. and Dolan, L. and Kohara, Y. and Sugano, S. and Fujiyama, A. and Delaux, P. M. and Quint, M. and Theissen, G. and Hagemann, M. and Harholt, J. and Dunand, C. and Zachgo, S. and Langdale, J. and Maumus, F. and Van Der Straeten, D. and Gould, S. B. and Rensing, S. A.}, journal = {Cell}, keywords = {myown}, number = 2, pages = {448-464 e24}, title = {The Chara Genome: Secondary Complexity and Implications for Plant Terrestrialization}, type = {Journal Article}, volume = 174, year = 2018 }

  %0 Journal Article %1 RN121 %A Nishiyama, T. %A Sakayama, H. %A de Vries, J. %A Buschmann, H. %A Saint-Marcoux, D. %A Ullrich, K. K. %A Haas, F. B. %A Vanderstraeten, L. %A Becker, D. %A Lang, D. %A Vosolsobe, S. %A Rombauts, S. %A Wilhelmsson, P. K. I. %A Janitza, P. %A Kern, R. %A Heyl, A. %A Rumpler, F. %A Villalobos, Liac %A Clay, J. M. %A Skokan, R. %A Toyoda, A. %A Suzuki, Y. %A Kagoshima, H. %A Schijlen, E. %A Tajeshwar, N. %A Catarino, B. %A Hetherington, A. J. %A Saltykova, A. %A Bonnot, C. %A Breuninger, H. %A Symeonidi, A. %A Radhakrishnan, G. V. %A Van Nieuwerburgh, F. %A Deforce, D. %A Chang, C. %A Karol, K. G. %A Hedrich, R. %A Ulvskov, P. %A Glockner, G. %A Delwiche, C. F. %A Petrasek, J. %A Van de Peer, Y. %A Friml, J. %A Beilby, M. %A Dolan, L. %A Kohara, Y. %A Sugano, S. %A Fujiyama, A. %A Delaux, P. M. %A Quint, M. %A Theissen, G. %A Hagemann, M. %A Harholt, J. %A Dunand, C. %A Zachgo, S. %A Langdale, J. %A Maumus, F. %A Van Der Straeten, D. %A Gould, S. B. %A Rensing, S. A. %D 2018 %J Cell %N 2 %P 448-464 e24 %R 10.1016/j.cell.2018.06.033 %T The Chara Genome: Secondary Complexity and Implications for Plant Terrestrialization %U https://www.ncbi.nlm.nih.gov/pubmed/30007417 %V 174

• Fasbender, L., Maurer, D., Kreuzwieser, J., Kreuzer, I., Schulze, W.X., Kruse, J., Becker, D., Alfarraj, S., Hedrich, R., Werner, C., Rennenberg, H. (2017) The carnivorous Venus flytrap uses prey-derived amino acid carbon to fuel respiration, New Phytologist, 214(2), 597–606, available: https://doi.org/10.1111/nph.14404.
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  * The present study was performed to elucidate the fate of carbon (C) and nitrogen (N) derived from protein of prey caught by carnivorous Dionaea muscipula. For this, traps were fed 13C/15N-glutamine (Gln). * The release of 13CO2 was continuously monitored by isotope ratio infrared spectrometry. After 46 h, the allocation of C and N label into different organs was determined and tissues were subjected to metabolome, proteome and transcriptome analyses. * Nitrogen of Gln fed was already separated from its C skeleton in the decomposing fluid secreted by the traps. Most of the Gln-C and Gln-N recovered inside plants were localized in fed traps. Among nonfed organs, traps were a stronger sink for Gln-C compared to Gln-N, and roots were a stronger sink for Gln-N compared to Gln-C. A significant amount of the Gln-C was respired as indicated by 13C-CO2 emission, enhanced levels of metabolites of respiratory Gln degradation and increased abundance of proteins of respiratory processes. Transcription analyses revealed constitutive expression of enzymes involved in Gln metabolism in traps. * It appears that prey not only provides building blocks of cellular constituents of carnivorous Dionaea muscipula, but also is used for energy generation by respiratory amino acid degradation.

  @article{NPH:NPH14404, abstract = {* The present study was performed to elucidate the fate of carbon (C) and nitrogen (N) derived from protein of prey caught by carnivorous Dionaea muscipula. For this, traps were fed 13C/15N-glutamine (Gln). * The release of 13CO2 was continuously monitored by isotope ratio infrared spectrometry. After 46 h, the allocation of C and N label into different organs was determined and tissues were subjected to metabolome, proteome and transcriptome analyses. * Nitrogen of Gln fed was already separated from its C skeleton in the decomposing fluid secreted by the traps. Most of the Gln-C and Gln-N recovered inside plants were localized in fed traps. Among nonfed organs, traps were a stronger sink for Gln-C compared to Gln-N, and roots were a stronger sink for Gln-N compared to Gln-C. A significant amount of the Gln-C was respired as indicated by 13C-CO2 emission, enhanced levels of metabolites of respiratory Gln degradation and increased abundance of proteins of respiratory processes. Transcription analyses revealed constitutive expression of enzymes involved in Gln metabolism in traps. * It appears that prey not only provides building blocks of cellular constituents of carnivorous Dionaea muscipula, but also is used for energy generation by respiratory amino acid degradation.}, author = {Fasbender, Lukas and Maurer, Daniel and Kreuzwieser, Jürgen and Kreuzer, Ines and Schulze, Waltraud X. and Kruse, Jörg and Becker, Dirk and Alfarraj, Saleh and Hedrich, Rainer and Werner, Christiane and Rennenberg, Heinz}, journal = {New Phytologist}, keywords = {myown}, number = 2, pages = {597–606}, title = {The carnivorous Venus flytrap uses prey-derived amino acid carbon to fuel respiration}, volume = 214, year = 2017 }

  %0 Journal Article %1 NPH:NPH14404 %A Fasbender, Lukas %A Maurer, Daniel %A Kreuzwieser, Jürgen %A Kreuzer, Ines %A Schulze, Waltraud X. %A Kruse, Jörg %A Becker, Dirk %A Alfarraj, Saleh %A Hedrich, Rainer %A Werner, Christiane %A Rennenberg, Heinz %D 2017 %J New Phytologist %N 2 %P 597--606 %R 10.1111/nph.14404 %T The carnivorous Venus flytrap uses prey-derived amino acid carbon to fuel respiration %U http://dx.doi.org/10.1111/nph.14404 %V 214 %X * The present study was performed to elucidate the fate of carbon (C) and nitrogen (N) derived from protein of prey caught by carnivorous Dionaea muscipula. For this, traps were fed 13C/15N-glutamine (Gln). * The release of 13CO2 was continuously monitored by isotope ratio infrared spectrometry. After 46 h, the allocation of C and N label into different organs was determined and tissues were subjected to metabolome, proteome and transcriptome analyses. * Nitrogen of Gln fed was already separated from its C skeleton in the decomposing fluid secreted by the traps. Most of the Gln-C and Gln-N recovered inside plants were localized in fed traps. Among nonfed organs, traps were a stronger sink for Gln-C compared to Gln-N, and roots were a stronger sink for Gln-N compared to Gln-C. A significant amount of the Gln-C was respired as indicated by 13C-CO2 emission, enhanced levels of metabolites of respiratory Gln degradation and increased abundance of proteins of respiratory processes. Transcription analyses revealed constitutive expression of enzymes involved in Gln metabolism in traps. * It appears that prey not only provides building blocks of cellular constituents of carnivorous Dionaea muscipula, but also is used for energy generation by respiratory amino acid degradation.
• Scherzer, S., Shabala, L., Hedrich, B., Fromm, J., Bauer, H., Munz, E., Jakob, P., Al-Rascheid, K.A.S., Kreuzer, I., Becker, D., Eiblmeier, M., Rennenberg, H., Shabala, S., Bennett, M., Neher, E., Hedrich, R. (2017) Insect haptoelectrical stimulation of Venus flytrap triggers exocytosis in gland cells, Proceedings of the National Academy of Sciences, available: https://doi.org/10.1073/pnas.1701860114.
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  The Venus flytrap Dionaea muscipula captures insects and consumes their flesh. Prey contacting touch-sensitive hairs trigger traveling electrical waves. These action potentials (APs) cause rapid closure of the trap and activate secretory functions of glands, which cover its inner surface. Such prey-induced haptoelectric stimulation activates the touch hormone jasmonate (JA) signaling pathway, which initiates secretion of an acidic hydrolase mixture to decompose the victim and acquire the animal nutrients. Although postulated since Darwin’s pioneering studies, these secretory events have not been recorded so far. Using advanced analytical and imaging techniques, such as vibrating ion-selective electrodes, carbon fiber amperometry, and magnetic resonance imaging, we monitored stimulus-coupled glandular secretion into the flytrap. Trigger-hair bending or direct application of JA caused a quantal release of oxidizable material from gland cells monitored as distinct amperometric spikes. Spikes reminiscent of exocytotic events in secretory animal cells progressively increased in frequency, reaching steady state 1 d after stimulation. Our data indicate that trigger-hair mechanical stimulation evokes APs. Gland cells translate APs into touch-inducible JA signaling that promotes the formation of secretory vesicles. Early vesicles loaded with H+ and Cl− fuse with the plasma membrane, hyperacidifying the “green stomach”-like digestive organ, whereas subsequent ones carry hydrolases and nutrient transporters, together with a glutathione redox moiety, which is likely to act as the major detected compound in amperometry. Hence, when glands perceive the haptoelectrical stimulation, secretory vesicles are tailored to be released in a sequence that optimizes digestion of the captured animal.

  @article{Scherzer17042017, abstract = {The Venus flytrap Dionaea muscipula captures insects and consumes their flesh. Prey contacting touch-sensitive hairs trigger traveling electrical waves. These action potentials (APs) cause rapid closure of the trap and activate secretory functions of glands, which cover its inner surface. Such prey-induced haptoelectric stimulation activates the touch hormone jasmonate (JA) signaling pathway, which initiates secretion of an acidic hydrolase mixture to decompose the victim and acquire the animal nutrients. Although postulated since Darwin’s pioneering studies, these secretory events have not been recorded so far. Using advanced analytical and imaging techniques, such as vibrating ion-selective electrodes, carbon fiber amperometry, and magnetic resonance imaging, we monitored stimulus-coupled glandular secretion into the flytrap. Trigger-hair bending or direct application of JA caused a quantal release of oxidizable material from gland cells monitored as distinct amperometric spikes. Spikes reminiscent of exocytotic events in secretory animal cells progressively increased in frequency, reaching steady state 1 d after stimulation. Our data indicate that trigger-hair mechanical stimulation evokes APs. Gland cells translate APs into touch-inducible JA signaling that promotes the formation of secretory vesicles. Early vesicles loaded with H+ and Cl− fuse with the plasma membrane, hyperacidifying the “green stomach”-like digestive organ, whereas subsequent ones carry hydrolases and nutrient transporters, together with a glutathione redox moiety, which is likely to act as the major detected compound in amperometry. Hence, when glands perceive the haptoelectrical stimulation, secretory vesicles are tailored to be released in a sequence that optimizes digestion of the captured animal.}, author = {Scherzer, Sönke and Shabala, Lana and Hedrich, Benjamin and Fromm, Jörg and Bauer, Hubert and Munz, Eberhard and Jakob, Peter and Al-Rascheid, Khaled A. S. and Kreuzer, Ines and Becker, Dirk and Eiblmeier, Monika and Rennenberg, Heinz and Shabala, Sergey and Bennett, Malcolm and Neher, Erwin and Hedrich, Rainer}, journal = {Proceedings of the National Academy of Sciences}, keywords = {myown}, title = {Insect haptoelectrical stimulation of Venus flytrap triggers exocytosis in gland cells}, year = 2017 }

  %0 Journal Article %1 Scherzer17042017 %A Scherzer, Sönke %A Shabala, Lana %A Hedrich, Benjamin %A Fromm, Jörg %A Bauer, Hubert %A Munz, Eberhard %A Jakob, Peter %A Al-Rascheid, Khaled A. S. %A Kreuzer, Ines %A Becker, Dirk %A Eiblmeier, Monika %A Rennenberg, Heinz %A Shabala, Sergey %A Bennett, Malcolm %A Neher, Erwin %A Hedrich, Rainer %D 2017 %J Proceedings of the National Academy of Sciences %R 10.1073/pnas.1701860114 %T Insect haptoelectrical stimulation of Venus flytrap triggers exocytosis in gland cells %U http://www.pnas.org/content/early/2017/04/13/1701860114.abstract %X The Venus flytrap Dionaea muscipula captures insects and consumes their flesh. Prey contacting touch-sensitive hairs trigger traveling electrical waves. These action potentials (APs) cause rapid closure of the trap and activate secretory functions of glands, which cover its inner surface. Such prey-induced haptoelectric stimulation activates the touch hormone jasmonate (JA) signaling pathway, which initiates secretion of an acidic hydrolase mixture to decompose the victim and acquire the animal nutrients. Although postulated since Darwin’s pioneering studies, these secretory events have not been recorded so far. Using advanced analytical and imaging techniques, such as vibrating ion-selective electrodes, carbon fiber amperometry, and magnetic resonance imaging, we monitored stimulus-coupled glandular secretion into the flytrap. Trigger-hair bending or direct application of JA caused a quantal release of oxidizable material from gland cells monitored as distinct amperometric spikes. Spikes reminiscent of exocytotic events in secretory animal cells progressively increased in frequency, reaching steady state 1 d after stimulation. Our data indicate that trigger-hair mechanical stimulation evokes APs. Gland cells translate APs into touch-inducible JA signaling that promotes the formation of secretory vesicles. Early vesicles loaded with H+ and Cl− fuse with the plasma membrane, hyperacidifying the “green stomach”-like digestive organ, whereas subsequent ones carry hydrolases and nutrient transporters, together with a glutathione redox moiety, which is likely to act as the major detected compound in amperometry. Hence, when glands perceive the haptoelectrical stimulation, secretory vesicles are tailored to be released in a sequence that optimizes digestion of the captured animal.

• Ankenbrand, M.J., Weber, L., Becker, D., F{"o}rster, F., Bemm, F. (2016) TBro: visualization and management of de novo transcriptomes, Database (Oxford), 2016, available: https://doi.org/10.1093/database/baw146.
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  RNA sequencing (RNA-seq) has become a powerful tool to understand molecular mechanisms and/or developmental programs. It provides a fast, reliable and cost-effective method to access sets of expressed elements in a qualitative and quantitative manner. Especially for non-model organisms and in absence of a reference genome, RNA-seq data is used to reconstruct and quantify transcriptomes at the same time. Even SNPs, InDels, and alternative splicing events are predicted directly from the data without having a reference genome at hand. A key challenge, especially for non-computational personnal, is the management of the resulting datasets, consisting of different data types and formats. Here, we present TBro, a flexible de novo transcriptome browser, tackling this challenge. TBro aggregates sequences, their annotation, expression levels as well as differential testing results. It provides an easy-to-use interface to mine the aggregated data and generate publication-ready visualizations. Additionally, it supports users with an intuitive cart system, that helps collecting and analysing biological meaningful sets of transcripts. TBro's modular architecture allows easy extension of its functionalities in the future. Especially, the integration of new data types such as proteomic quantifications or array-based gene expression data is straightforward. Thus, TBro is a fully featured yet flexible transcriptome browser that supports approaching complex biological questions and enhances collaboration of numerous researchers. DATABASE URL: : tbro.carnivorom.com.

  @article{Ankenbrand:2016:Database-Oxford:28025338, abstract = {RNA sequencing (RNA-seq) has become a powerful tool to understand molecular mechanisms and/or developmental programs. It provides a fast, reliable and cost-effective method to access sets of expressed elements in a qualitative and quantitative manner. Especially for non-model organisms and in absence of a reference genome, RNA-seq data is used to reconstruct and quantify transcriptomes at the same time. Even SNPs, InDels, and alternative splicing events are predicted directly from the data without having a reference genome at hand. A key challenge, especially for non-computational personnal, is the management of the resulting datasets, consisting of different data types and formats. Here, we present TBro, a flexible de novo transcriptome browser, tackling this challenge. TBro aggregates sequences, their annotation, expression levels as well as differential testing results. It provides an easy-to-use interface to mine the aggregated data and generate publication-ready visualizations. Additionally, it supports users with an intuitive cart system, that helps collecting and analysing biological meaningful sets of transcripts. TBro's modular architecture allows easy extension of its functionalities in the future. Especially, the integration of new data types such as proteomic quantifications or array-based gene expression data is straightforward. Thus, TBro is a fully featured yet flexible transcriptome browser that supports approaching complex biological questions and enhances collaboration of numerous researchers. DATABASE URL: : tbro.carnivorom.com.}, author = {Ankenbrand, M J and Weber, L and Becker, D and F{\"o}rster, F and Bemm, F}, journal = {Database (Oxford)}, keywords = {myown}, title = {TBro: visualization and management of de novo transcriptomes}, volume = 2016, year = 2016 }

  %0 Journal Article %1 Ankenbrand:2016:Database-Oxford:28025338 %A Ankenbrand, M J %A Weber, L %A Becker, D %A F{"o}rster, F %A Bemm, F %D 2016 %J Database (Oxford) %R 10.1093/database/baw146 %T TBro: visualization and management of de novo transcriptomes %U https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5199188/ %V 2016 %X RNA sequencing (RNA-seq) has become a powerful tool to understand molecular mechanisms and/or developmental programs. It provides a fast, reliable and cost-effective method to access sets of expressed elements in a qualitative and quantitative manner. Especially for non-model organisms and in absence of a reference genome, RNA-seq data is used to reconstruct and quantify transcriptomes at the same time. Even SNPs, InDels, and alternative splicing events are predicted directly from the data without having a reference genome at hand. A key challenge, especially for non-computational personnal, is the management of the resulting datasets, consisting of different data types and formats. Here, we present TBro, a flexible de novo transcriptome browser, tackling this challenge. TBro aggregates sequences, their annotation, expression levels as well as differential testing results. It provides an easy-to-use interface to mine the aggregated data and generate publication-ready visualizations. Additionally, it supports users with an intuitive cart system, that helps collecting and analysing biological meaningful sets of transcripts. TBro's modular architecture allows easy extension of its functionalities in the future. Especially, the integration of new data types such as proteomic quantifications or array-based gene expression data is straightforward. Thus, TBro is a fully featured yet flexible transcriptome browser that supports approaching complex biological questions and enhances collaboration of numerous researchers. DATABASE URL: : tbro.carnivorom.com.
• Jaślan, D., Mueller, T.D., Becker, D., Schultz, J., Cuin, T.A., Marten, I., Dreyer, I., Schönknecht, G., Hedrich, R. (2016) Gating of the two-pore cation channel AtTPC1 in the plant vacuole is based on a single voltage-sensing domain, Plant Biology, 18(5), 750–760, available: https://doi.org/10.1111/plb.12478.
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  * The two-pore cation channel TPC1 operates as a dimeric channel in animal and plant endomembranes. Each subunit consists of two homologous Shaker-like halves, with 12 transmembrane domains in total (S1-S6, S7-S12). In plants, TPC1 channels reside in the vacuolar membrane, and upon voltage stimulation, give rise to the well-known slow-activating SV currents. * Here, we combined bioinformatics, structure modelling, site-directed mutagenesis, and in planta patch clamp studies to elucidate the molecular mechanisms of voltage-dependent channel gating in TPC1 in its native plant background. * Structure-function analysis of the Arabidopsis TPC1 channel in planta confirmed that helix S10 operates as the major voltage-sensing site, with Glu450 and Glu478 identified as possible ion-pair partners for voltage-sensing Arg537. The contribution of helix S4 to voltage sensing was found to be negligible. Several conserved negative residues on the luminal site contribute to calcium binding, stabilizing the closed channel. * During evolution of plant TPC1s from two separate Shaker-like domains, the voltage-sensing function in the N-terminal Shaker-unit (S1-S4) vanished.

  @article{PLB:PLB12478, abstract = {* The two-pore cation channel TPC1 operates as a dimeric channel in animal and plant endomembranes. Each subunit consists of two homologous Shaker-like halves, with 12 transmembrane domains in total (S1-S6, S7-S12). In plants, TPC1 channels reside in the vacuolar membrane, and upon voltage stimulation, give rise to the well-known slow-activating SV currents. * Here, we combined bioinformatics, structure modelling, site-directed mutagenesis, and in planta patch clamp studies to elucidate the molecular mechanisms of voltage-dependent channel gating in TPC1 in its native plant background. * Structure-function analysis of the Arabidopsis TPC1 channel in planta confirmed that helix S10 operates as the major voltage-sensing site, with Glu450 and Glu478 identified as possible ion-pair partners for voltage-sensing Arg537. The contribution of helix S4 to voltage sensing was found to be negligible. Several conserved negative residues on the luminal site contribute to calcium binding, stabilizing the closed channel. * During evolution of plant TPC1s from two separate Shaker-like domains, the voltage-sensing function in the N-terminal Shaker-unit (S1-S4) vanished.}, author = {Jaślan, D. and Mueller, T. D. and Becker, D. and Schultz, J. and Cuin, T. A. and Marten, I. and Dreyer, I. and Schönknecht, G. and Hedrich, R.}, journal = {Plant Biology}, keywords = {myown}, number = 5, pages = {750–760}, title = {Gating of the two-pore cation channel AtTPC1 in the plant vacuole is based on a single voltage-sensing domain}, volume = 18, year = 2016 }

  %0 Journal Article %1 PLB:PLB12478 %A Jaślan, D. %A Mueller, T. D. %A Becker, D. %A Schultz, J. %A Cuin, T. A. %A Marten, I. %A Dreyer, I. %A Schönknecht, G. %A Hedrich, R. %D 2016 %J Plant Biology %N 5 %P 750--760 %R 10.1111/plb.12478 %T Gating of the two-pore cation channel AtTPC1 in the plant vacuole is based on a single voltage-sensing domain %U http://dx.doi.org/10.1111/plb.12478 %V 18 %X * The two-pore cation channel TPC1 operates as a dimeric channel in animal and plant endomembranes. Each subunit consists of two homologous Shaker-like halves, with 12 transmembrane domains in total (S1-S6, S7-S12). In plants, TPC1 channels reside in the vacuolar membrane, and upon voltage stimulation, give rise to the well-known slow-activating SV currents. * Here, we combined bioinformatics, structure modelling, site-directed mutagenesis, and in planta patch clamp studies to elucidate the molecular mechanisms of voltage-dependent channel gating in TPC1 in its native plant background. * Structure-function analysis of the Arabidopsis TPC1 channel in planta confirmed that helix S10 operates as the major voltage-sensing site, with Glu450 and Glu478 identified as possible ion-pair partners for voltage-sensing Arg537. The contribution of helix S4 to voltage sensing was found to be negligible. Several conserved negative residues on the luminal site contribute to calcium binding, stabilizing the closed channel. * During evolution of plant TPC1s from two separate Shaker-like domains, the voltage-sensing function in the N-terminal Shaker-unit (S1-S4) vanished.
• Bemm, F., Becker, D., Larisch, C., Kreuzer, I., Escalante-Perez, M., Schulze, W.X., Ankenbrand, M., de Weyer, A.-L.V., Krol, E., Al-Rasheid, K.A., Mithöfer, A., Weber, A.P., Schultz, J., Hedrich, R. (2016) Venus flytrap carnivorous lifestyle builds on herbivore defense strategies, Genome Research, 26(6), 812–825, available: https://doi.org/10.1101/gr.202200.115.
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  @article{Bemm_2016, author = {Bemm, Felix and Becker, Dirk and Larisch, Christina and Kreuzer, Ines and Escalante-Perez, Maria and Schulze, Waltraud X. and Ankenbrand, Markus and de Weyer, Anna-Lena Van and Krol, Elzbieta and Al-Rasheid, Khaled A. and Mithöfer, Axel and Weber, Andreas P. and Schultz, Jörg and Hedrich, Rainer}, journal = {Genome Research}, keywords = {myown}, month = {may}, number = 6, pages = {812–825}, publisher = {Cold Spring Harbor Laboratory Press}, title = {Venus flytrap carnivorous lifestyle builds on herbivore defense strategies}, volume = 26, year = 2016 }

  %0 Journal Article %1 Bemm_2016 %A Bemm, Felix %A Becker, Dirk %A Larisch, Christina %A Kreuzer, Ines %A Escalante-Perez, Maria %A Schulze, Waltraud X. %A Ankenbrand, Markus %A de Weyer, Anna-Lena Van %A Krol, Elzbieta %A Al-Rasheid, Khaled A. %A Mithöfer, Axel %A Weber, Andreas P. %A Schultz, Jörg %A Hedrich, Rainer %D 2016 %I Cold Spring Harbor Laboratory Press %J Genome Research %N 6 %P 812--825 %R 10.1101/gr.202200.115 %T Venus flytrap carnivorous lifestyle builds on herbivore defense strategies %U https://doi.org/10.1101%2Fgr.202200.115 %V 26

• Gonz{’a}lez, W., Valdebenito, B., Caballero, J., Riadi, G., Riedelsberger, J., Mart{’i}nez, G., Ram{’i}rez, D., Z{\’u}{\~{n}}iga, L., Sep{’u}lveda, F.V., Dreyer, I., Janta, M., Becker, D. (2015) K2P channels in plants and animals, Pfl{"u}gers Archiv - European Journal of Physiology, 467(5), 1091–1104, available: https://doi.org/10.1007/s00424-014-1638-4.
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  Two-pore domain potassium (K2P) channels are membrane proteins widely identified in mammals, plants, and other organisms. A functional channel is a dimer with each subunit comprising two pore-forming loops and four transmembrane domains. The genome of the model plant Arabidopsis thaliana harbors five genes coding for K2P channels. Homologs of Arabidopsis K2P channels have been found in all higher plants sequenced so far. As with the K2P channels in mammals, plant K2P channels are targets of external and internal stimuli, which fine-tune the electrical properties of the membrane for specialized transport and/or signaling tasks. Plant K2P channels are modulated by signaling molecules such as intracellular H+ and calcium and physical factors like temperature and pressure. In this review, we ask the following: What are the similarities and differences between K2P channels in plants and animals in terms of their physiology? What is the nature of the last common ancestor (LCA) of these two groups of proteins? To answer these questions, we present physiological, structural, and phylogenetic evidence that discards the hypothesis proposing that the duplication and fusion that gave rise to the K2P channels occurred in a prokaryote LCA. Conversely, we argue that the K2P LCA was most likely a eukaryote organism. Consideration of plant and animal K2P channels in the same study is novel and likely to stimulate further exchange of ideas between students of these fields.

  @article{González2015, abstract = {Two-pore domain potassium (K2P) channels are membrane proteins widely identified in mammals, plants, and other organisms. A functional channel is a dimer with each subunit comprising two pore-forming loops and four transmembrane domains. The genome of the model plant Arabidopsis thaliana harbors five genes coding for K2P channels. Homologs of Arabidopsis K2P channels have been found in all higher plants sequenced so far. As with the K2P channels in mammals, plant K2P channels are targets of external and internal stimuli, which fine-tune the electrical properties of the membrane for specialized transport and/or signaling tasks. Plant K2P channels are modulated by signaling molecules such as intracellular H+ and calcium and physical factors like temperature and pressure. In this review, we ask the following: What are the similarities and differences between K2P channels in plants and animals in terms of their physiology? What is the nature of the last common ancestor (LCA) of these two groups of proteins? To answer these questions, we present physiological, structural, and phylogenetic evidence that discards the hypothesis proposing that the duplication and fusion that gave rise to the K2P channels occurred in a prokaryote LCA. Conversely, we argue that the K2P LCA was most likely a eukaryote organism. Consideration of plant and animal K2P channels in the same study is novel and likely to stimulate further exchange of ideas between students of these fields.}, author = {Gonz{\'a}lez, Wendy and Valdebenito, Braulio and Caballero, Julio and Riadi, Gonzalo and Riedelsberger, Janin and Mart{\'i}nez, Gonzalo and Ram{\'i}rez, David and Z{\'u}{\ {n}}iga, Leandro and Sep{\'u}lveda, Francisco V. and Dreyer, Ingo and Janta, Michael and Becker, Dirk}, journal = {Pfl{\"u}gers Archiv - European Journal of Physiology}, keywords = {myown}, number = 5, pages = {1091–1104}, title = {K2P channels in plants and animals}, volume = 467, year = 2015 }

  %0 Journal Article %1 González2015 %A Gonz{'a}lez, Wendy %A Valdebenito, Braulio %A Caballero, Julio %A Riadi, Gonzalo %A Riedelsberger, Janin %A Mart{'i}nez, Gonzalo %A Ram{'i}rez, David %A Z{\'u}{\~{n}}iga, Leandro %A Sep{'u}lveda, Francisco V. %A Dreyer, Ingo %A Janta, Michael %A Becker, Dirk %D 2015 %J Pfl{"u}gers Archiv - European Journal of Physiology %N 5 %P 1091--1104 %R 10.1007/s00424-014-1638-4 %T K2P channels in plants and animals %U http://dx.doi.org/10.1007/s00424-014-1638-4 %V 467 %X Two-pore domain potassium (K2P) channels are membrane proteins widely identified in mammals, plants, and other organisms. A functional channel is a dimer with each subunit comprising two pore-forming loops and four transmembrane domains. The genome of the model plant Arabidopsis thaliana harbors five genes coding for K2P channels. Homologs of Arabidopsis K2P channels have been found in all higher plants sequenced so far. As with the K2P channels in mammals, plant K2P channels are targets of external and internal stimuli, which fine-tune the electrical properties of the membrane for specialized transport and/or signaling tasks. Plant K2P channels are modulated by signaling molecules such as intracellular H+ and calcium and physical factors like temperature and pressure. In this review, we ask the following: What are the similarities and differences between K2P channels in plants and animals in terms of their physiology? What is the nature of the last common ancestor (LCA) of these two groups of proteins? To answer these questions, we present physiological, structural, and phylogenetic evidence that discards the hypothesis proposing that the duplication and fusion that gave rise to the K2P channels occurred in a prokaryote LCA. Conversely, we argue that the K2P LCA was most likely a eukaryote organism. Consideration of plant and animal K2P channels in the same study is novel and likely to stimulate further exchange of ideas between students of these fields.

• Anschütz, U., Becker, D., Shabala, S. (2014) Going beyond nutrition: Regulation of potassium homoeostasis as a common denominator of plant adaptive responses to environment, Journal of Plant Physiology, 171(9), 670–687, available: https://doi.org/http://dx.doi.org/10.1016/j.jplph.2014.01.009.
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  @article{ANSCHUTZ2014670, author = {Anschütz, Uta and Becker, Dirk and Shabala, Sergey}, journal = {Journal of Plant Physiology}, keywords = {myown}, number = 9, pages = {670 - 687}, title = {Going beyond nutrition: Regulation of potassium homoeostasis as a common denominator of plant adaptive responses to environment}, volume = 171, year = 2014 }

  %0 Journal Article %1 ANSCHUTZ2014670 %A Anschütz, Uta %A Becker, Dirk %A Shabala, Sergey %D 2014 %J Journal of Plant Physiology %N 9 %P 670 - 687 %R http://dx.doi.org/10.1016/j.jplph.2014.01.009 %T Going beyond nutrition: Regulation of potassium homoeostasis as a common denominator of plant adaptive responses to environment %U http://www.sciencedirect.com/science/article/pii/S0176161714000340 %V 171

• Latz, A., Mehlmer, N., Zapf, S., Mueller, T.D., Wurzinger, B., Pfister, B., Csaszar, E., Hedrich, R., Teige, M., Becker, D. (2013) Salt Stress Triggers Phosphorylation of the Arabidopsis Vacuolar K+ Channel TPK1 by Calcium-Dependent Protein Kinases (CDPKs), Molecular Plant, 6(4), 1274–1289, available: https://doi.org/http://dx.doi.org/10.1093/mp/sss158.
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  @article{LATZ20131274, author = {Latz, Andreas and Mehlmer, Norbert and Zapf, Simone and Mueller, Thomas D. and Wurzinger, Bernhard and Pfister, Barbara and Csaszar, Edina and Hedrich, Rainer and Teige, Markus and Becker, Dirk}, journal = {Molecular Plant}, keywords = {myown}, number = 4, pages = {1274 - 1289}, title = {Salt Stress Triggers Phosphorylation of the Arabidopsis Vacuolar K+ Channel TPK1 by Calcium-Dependent Protein Kinases (CDPKs)}, volume = 6, year = 2013 }

  %0 Journal Article %1 LATZ20131274 %A Latz, Andreas %A Mehlmer, Norbert %A Zapf, Simone %A Mueller, Thomas D. %A Wurzinger, Bernhard %A Pfister, Barbara %A Csaszar, Edina %A Hedrich, Rainer %A Teige, Markus %A Becker, Dirk %D 2013 %J Molecular Plant %N 4 %P 1274 - 1289 %R http://dx.doi.org/10.1093/mp/sss158 %T Salt Stress Triggers Phosphorylation of the Arabidopsis Vacuolar K+ Channel TPK1 by Calcium-Dependent Protein Kinases (CDPKs) %U http://www.sciencedirect.com/science/article/pii/S1674205214609163 %V 6
• Dadacz-Narloch, B., Kimura, S., Kurusu, T., Farmer, E.E., Becker, D., Kuchitsu, K., Hedrich, R. (2013) On the cellular site of two-pore channel TPC1 action in the Poaceae, New Phytologist, 200(3), 663–674, available: https://doi.org/10.1111/nph.12402.
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  * The slow vacuolar (SV) channel has been characterized in different dicots by patch-clamp recordings. This channel represents the major cation conductance of the largest organelle in most plant cells. Studies with the tpc1-2 mutant of the model dicot plant Arabidopsis thaliana identified the SV channel as the product of the TPC1 gene. By contrast, research on rice and wheat TPC1 suggested that the monocot gene encodes a plasma membrane calcium-permeable channel. * To explore the site of action of grass TPC1 channels, we expressed OsTPC1 from rice (Oryza sativa) and TaTPC1 from wheat (Triticum aestivum) in the background of the Arabidopsis tpc1-2 mutant. Cross-species tpc1 complementation and patch-clamping of vacuoles using Arabidopsis and rice tpc1 null mutants documented that both monocot TPC1 genes were capable of rescuing the SV channel deficit. * Vacuoles from wild-type rice but not the tpc1 loss-of-function mutant harbor SV channels exhibiting the hallmark properties of dicot TPC1/SV channels. When expressed in human embryonic kidney (HEK293) cells OsTPC1 was targeted to Lysotracker-Red-positive organelles. * The finding that the rice TPC1, just like those from the model plant Arabidopsis and even animal cells, is localized and active in lyso-vacuolar membranes associates this cation channel species with endomembrane function.

  @article{NPH:NPH12402, abstract = {* The slow vacuolar (SV) channel has been characterized in different dicots by patch-clamp recordings. This channel represents the major cation conductance of the largest organelle in most plant cells. Studies with the tpc1-2 mutant of the model dicot plant Arabidopsis thaliana identified the SV channel as the product of the TPC1 gene. By contrast, research on rice and wheat TPC1 suggested that the monocot gene encodes a plasma membrane calcium-permeable channel. * To explore the site of action of grass TPC1 channels, we expressed OsTPC1 from rice (Oryza sativa) and TaTPC1 from wheat (Triticum aestivum) in the background of the Arabidopsis tpc1-2 mutant. Cross-species tpc1 complementation and patch-clamping of vacuoles using Arabidopsis and rice tpc1 null mutants documented that both monocot TPC1 genes were capable of rescuing the SV channel deficit. * Vacuoles from wild-type rice but not the tpc1 loss-of-function mutant harbor SV channels exhibiting the hallmark properties of dicot TPC1/SV channels. When expressed in human embryonic kidney (HEK293) cells OsTPC1 was targeted to Lysotracker-Red-positive organelles. * The finding that the rice TPC1, just like those from the model plant Arabidopsis and even animal cells, is localized and active in lyso-vacuolar membranes associates this cation channel species with endomembrane function.}, author = {Dadacz-Narloch, Beata and Kimura, Sachie and Kurusu, Takamitsu and Farmer, Edward E. and Becker, Dirk and Kuchitsu, Kazuyuki and Hedrich, Rainer}, journal = {New Phytologist}, keywords = {myown}, number = 3, pages = {663–674}, title = {On the cellular site of two-pore channel TPC1 action in the Poaceae}, volume = 200, year = 2013 }

  %0 Journal Article %1 NPH:NPH12402 %A Dadacz-Narloch, Beata %A Kimura, Sachie %A Kurusu, Takamitsu %A Farmer, Edward E. %A Becker, Dirk %A Kuchitsu, Kazuyuki %A Hedrich, Rainer %D 2013 %J New Phytologist %N 3 %P 663--674 %R 10.1111/nph.12402 %T On the cellular site of two-pore channel TPC1 action in the Poaceae %U http://dx.doi.org/10.1111/nph.12402 %V 200 %X * The slow vacuolar (SV) channel has been characterized in different dicots by patch-clamp recordings. This channel represents the major cation conductance of the largest organelle in most plant cells. Studies with the tpc1-2 mutant of the model dicot plant Arabidopsis thaliana identified the SV channel as the product of the TPC1 gene. By contrast, research on rice and wheat TPC1 suggested that the monocot gene encodes a plasma membrane calcium-permeable channel. * To explore the site of action of grass TPC1 channels, we expressed OsTPC1 from rice (Oryza sativa) and TaTPC1 from wheat (Triticum aestivum) in the background of the Arabidopsis tpc1-2 mutant. Cross-species tpc1 complementation and patch-clamping of vacuoles using Arabidopsis and rice tpc1 null mutants documented that both monocot TPC1 genes were capable of rescuing the SV channel deficit. * Vacuoles from wild-type rice but not the tpc1 loss-of-function mutant harbor SV channels exhibiting the hallmark properties of dicot TPC1/SV channels. When expressed in human embryonic kidney (HEK293) cells OsTPC1 was targeted to Lysotracker-Red-positive organelles. * The finding that the rice TPC1, just like those from the model plant Arabidopsis and even animal cells, is localized and active in lyso-vacuolar membranes associates this cation channel species with endomembrane function.
• Tapken, D., Anschütz, U., Liu, L.-H., Huelsken, T., Seebohm, G., Becker, D., Hollmann, M. (2013) A Plant Homolog of Animal Glutamate Receptors Is an Ion Channel Gated by Multiple Hydrophobic Amino Acids, 6(279), ra47-ra47, available: http://stke.sciencemag.org/content/6/279/ra47.long.
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  @article{tapken2013plant, author = {Tapken, Daniel and Anschütz, Uta and Liu, Lai-Hua and Huelsken, Thomas and Seebohm, Guiscard and Becker, Dirk and Hollmann, Michael}, keywords = {myown}, number = 279, pages = {ra47–ra47}, title = {A Plant Homolog of Animal Glutamate Receptors Is an Ion Channel Gated by Multiple Hydrophobic Amino Acids}, volume = 6, year = 2013 }

  %0 Journal Article %1 tapken2013plant %A Tapken, Daniel %A Anschütz, Uta %A Liu, Lai-Hua %A Huelsken, Thomas %A Seebohm, Guiscard %A Becker, Dirk %A Hollmann, Michael %D 2013 %N 279 %P ra47--ra47 %T A Plant Homolog of Animal Glutamate Receptors Is an Ion Channel Gated by Multiple Hydrophobic Amino Acids %U http://stke.sciencemag.org/content/6/279/ra47.long %V 6
• Woriedh, M., Wolf, S., M{’a}rton, M.L., Hinze, A., Gahrtz, M., Becker, D., Dresselhaus, T. (2013) External application of gametophyte-specific ZmPMEI1 induces pollen tube burst in maize, Plant Reproduction, 26(3), 255–266, available: https://doi.org/10.1007/s00497-013-0221-z.
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  Regulated demethylesterification of homogalacturonan, a major component of plant cell walls, by the activity of pectin methylesterases (PMEs), plays a critical role for cell wall stability and integrity. Especially fast growing plant cells such as pollen tubes secrete large amounts of PMEs toward their apoplasmic space. PME activity itself is tightly regulated by its inhibitor named as PME inhibitor and is thought to be required especially at the very pollen tube tip. We report here the identification and functional characterization of PMEI1 from maize (ZmPMEI1). We could show that the protein acts as an inhibitor of PME but not of invertases and found that its gene is strongly expressed in both gametophytes (pollen grain and embryo sac). Promoter reporter studies showed gene activity also during pollen tube growth toward and inside the transmitting tract. All embryo sac cells except the central cell displayed strong expression. Weaker signals were visible at sporophytic cells of the micropylar region. ZmPMEI1--EGFP fusion protein is transported within granules inside the tube and accumulates at the pollen tube tip as well as at sites where pollen tubes bend and/or change growth directions. The female gametophyte putatively influences pollen tube growth behavior by exposing it to ZmPMEI1. We therefore simulated this effect by applying recombinant protein at different concentrations on growing pollen tubes. ZmPMEI1 did not arrest growth, but destabilized the cell wall inducing burst. Compared with female gametophyte secreted defensin-like ZmES4, which induces burst at the very pollen tube tip, ZmPMEI1-induced burst occurs at the subapical region. These findings indicate that ZmPMEI1 secreted by the embryo sac likely destabilizes the pollen tube wall during perception and together with other proteins such as ZmES4 leads to burst and thus sperm release.

  @article{Woriedh2013, abstract = {Regulated demethylesterification of homogalacturonan, a major component of plant cell walls, by the activity of pectin methylesterases (PMEs), plays a critical role for cell wall stability and integrity. Especially fast growing plant cells such as pollen tubes secrete large amounts of PMEs toward their apoplasmic space. PME activity itself is tightly regulated by its inhibitor named as PME inhibitor and is thought to be required especially at the very pollen tube tip. We report here the identification and functional characterization of PMEI1 from maize (ZmPMEI1). We could show that the protein acts as an inhibitor of PME but not of invertases and found that its gene is strongly expressed in both gametophytes (pollen grain and embryo sac). Promoter reporter studies showed gene activity also during pollen tube growth toward and inside the transmitting tract. All embryo sac cells except the central cell displayed strong expression. Weaker signals were visible at sporophytic cells of the micropylar region. ZmPMEI1–EGFP fusion protein is transported within granules inside the tube and accumulates at the pollen tube tip as well as at sites where pollen tubes bend and/or change growth directions. The female gametophyte putatively influences pollen tube growth behavior by exposing it to ZmPMEI1. We therefore simulated this effect by applying recombinant protein at different concentrations on growing pollen tubes. ZmPMEI1 did not arrest growth, but destabilized the cell wall inducing burst. Compared with female gametophyte secreted defensin-like ZmES4, which induces burst at the very pollen tube tip, ZmPMEI1-induced burst occurs at the subapical region. These findings indicate that ZmPMEI1 secreted by the embryo sac likely destabilizes the pollen tube wall during perception and together with other proteins such as ZmES4 leads to burst and thus sperm release.}, author = {Woriedh, Mayada and Wolf, Sebastian and M{\'a}rton, Mihaela L. and Hinze, Axel and Gahrtz, Manfred and Becker, Dirk and Dresselhaus, Thomas}, journal = {Plant Reproduction}, keywords = {myown}, number = 3, pages = {255–266}, title = {External application of gametophyte-specific ZmPMEI1 induces pollen tube burst in maize}, volume = 26, year = 2013 }

  %0 Journal Article %1 Woriedh2013 %A Woriedh, Mayada %A Wolf, Sebastian %A M{'a}rton, Mihaela L. %A Hinze, Axel %A Gahrtz, Manfred %A Becker, Dirk %A Dresselhaus, Thomas %D 2013 %J Plant Reproduction %N 3 %P 255--266 %R 10.1007/s00497-013-0221-z %T External application of gametophyte-specific ZmPMEI1 induces pollen tube burst in maize %U http://dx.doi.org/10.1007/s00497-013-0221-z %V 26 %X Regulated demethylesterification of homogalacturonan, a major component of plant cell walls, by the activity of pectin methylesterases (PMEs), plays a critical role for cell wall stability and integrity. Especially fast growing plant cells such as pollen tubes secrete large amounts of PMEs toward their apoplasmic space. PME activity itself is tightly regulated by its inhibitor named as PME inhibitor and is thought to be required especially at the very pollen tube tip. We report here the identification and functional characterization of PMEI1 from maize (ZmPMEI1). We could show that the protein acts as an inhibitor of PME but not of invertases and found that its gene is strongly expressed in both gametophytes (pollen grain and embryo sac). Promoter reporter studies showed gene activity also during pollen tube growth toward and inside the transmitting tract. All embryo sac cells except the central cell displayed strong expression. Weaker signals were visible at sporophytic cells of the micropylar region. ZmPMEI1--EGFP fusion protein is transported within granules inside the tube and accumulates at the pollen tube tip as well as at sites where pollen tubes bend and/or change growth directions. The female gametophyte putatively influences pollen tube growth behavior by exposing it to ZmPMEI1. We therefore simulated this effect by applying recombinant protein at different concentrations on growing pollen tubes. ZmPMEI1 did not arrest growth, but destabilized the cell wall inducing burst. Compared with female gametophyte secreted defensin-like ZmES4, which induces burst at the very pollen tube tip, ZmPMEI1-induced burst occurs at the subapical region. These findings indicate that ZmPMEI1 secreted by the embryo sac likely destabilizes the pollen tube wall during perception and together with other proteins such as ZmES4 leads to burst and thus sperm release.

• Schulze, W.X., Sanggaard, K.W., Kreuzer, I., Knudsen, A.D., Bemm, F., Thogersen, I.B., Brautigam, A., Thomsen, L.R., Schliesky, S., Dyrlund, T.F., Escalante-Perez, M., Becker, D., Schultz, J., Karring, H., Weber, A., Hojrup, P., Hedrich, R., Enghild, J.J. (2012) The Protein Composition of the Digestive Fluid from the Venus Flytrap Sheds Light on Prey Digestion Mechanisms, Molecular {&} Cellular Proteomics, 11(11), 1306–1319, available: https://doi.org/10.1074/mcp.m112.021006.
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  @article{Schulze_2012, author = {Schulze, W. X. and Sanggaard, K. W. and Kreuzer, I. and Knudsen, A. D. and Bemm, F. and Thogersen, I. B. and Brautigam, A. and Thomsen, L. R. and Schliesky, S. and Dyrlund, T. F. and Escalante-Perez, M. and Becker, D. and Schultz, J. and Karring, H. and Weber, A. and Hojrup, P. and Hedrich, R. and Enghild, J. J.}, journal = {Molecular {\&} Cellular Proteomics}, keywords = {myown}, month = {aug}, number = 11, pages = {1306–1319}, publisher = {American Society for Biochemistry {\&} Molecular Biology ({ASBMB})}, title = {The Protein Composition of the Digestive Fluid from the Venus Flytrap Sheds Light on Prey Digestion Mechanisms}, volume = 11, year = 2012 }

  %0 Journal Article %1 Schulze_2012 %A Schulze, W. X. %A Sanggaard, K. W. %A Kreuzer, I. %A Knudsen, A. D. %A Bemm, F. %A Thogersen, I. B. %A Brautigam, A. %A Thomsen, L. R. %A Schliesky, S. %A Dyrlund, T. F. %A Escalante-Perez, M. %A Becker, D. %A Schultz, J. %A Karring, H. %A Weber, A. %A Hojrup, P. %A Hedrich, R. %A Enghild, J. J. %D 2012 %I American Society for Biochemistry {&} Molecular Biology ({ASBMB}) %J Molecular {&} Cellular Proteomics %N 11 %P 1306--1319 %R 10.1074/mcp.m112.021006 %T The Protein Composition of the Digestive Fluid from the Venus Flytrap Sheds Light on Prey Digestion Mechanisms %U https://doi.org/10.1074%2Fmcp.m112.021006 %V 11
• Hedrich, R., Becker, D., Geiger, D., Marten, I., Roelfsema, M.R.G. (2012) Role of Ion Channels in Plants, in Okada, Y., ed., Patch Clamp Techniques: From Beginning to Advanced Protocols, Tokyo: Springer Japan, 295–322, available: https://doi.org/10.1007/978-4-431-53993-3_19.
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  @inbook{Hedrich2012, address = {Tokyo}, author = {Hedrich, Rainer and Becker, Dirk and Geiger, Dietmar and Marten, Irene and Roelfsema, M. Rob G.}, booktitle = {Patch Clamp Techniques: From Beginning to Advanced Protocols}, editor = {Okada, Yasunobu}, keywords = {myown}, pages = {295–322}, publisher = {Springer Japan}, title = {Role of Ion Channels in Plants}, year = 2012 }

  %0 Book Section %1 Hedrich2012 %A Hedrich, Rainer %A Becker, Dirk %A Geiger, Dietmar %A Marten, Irene %A Roelfsema, M. Rob G. %B Patch Clamp Techniques: From Beginning to Advanced Protocols %C Tokyo %D 2012 %E Okada, Yasunobu %I Springer Japan %P 295--322 %R 10.1007/978-4-431-53993-3_19 %T Role of Ion Channels in Plants %U http://dx.doi.org/10.1007/978-4-431-53993-3_19 %@ 978-4-431-53993-3
• Hashimoto, K., Eckert, C., Anschütz, U., Scholz, M., Held, K., Waadt, R., Reyer, A., Hippler, M., Becker, D., Kudla, J. (2012) Phosphorylation of Calcineurin B-like (CBL) Calcium Sensor Proteins by Their CBL-interacting Protein Kinases (CIPKs) Is Required for Full Activity of CBL-CIPK Complexes toward Their Target Proteins, Journal of Biological Chemistry, 287(11), 7956–7968, available: https://doi.org/10.1074/jbc.M111.279331.
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  Calcineurin B-like proteins (CBLs) represent a family of calcium sensor proteins that interact with a group of serine/threonine kinases designated as CBL-interacting protein kinases (CIPKs). CBL-CIPK complexes are crucially involved in relaying plant responses to many environmental signals and in regulating ion fluxes. However, the biochemical characterization of CBL-CIPK complexes has so far been hampered by low activities of recombinant CIPKs. Here, we report on an efficient wheat germ extract-based in vitro transcription/translation protocol that yields active full-length wild-type CIPK proteins. We identified a conserved serine residue within the C terminus of CBLs as being phosphorylated by their interacting CIPKs. Remarkably, our studies revealed that CIPK-dependent CBL phosphorylation is strictly dependent on CBL-CIPK interaction via the CIPK NAF domain. The phosphorylation status of CBLs does not appear to influence the stability, localization, or CIPK interaction of these calcium sensor proteins in general. However, proper phosphorylation of CBL1 is absolutely required for the in vivo activation of the AKT1 K+ channel by CBL1-CIPK23 and CBL9-CIPK23 complexes in oocytes. Moreover, we show that by combining CBL1, CIPK23, and AKT1, we can faithfully reconstitute CBL-dependent enhancement of phosphorylation of target proteins by CIPKs in vitro. In addition, we report that phosphorylation of CBL1 by CIPK23 is also required for the CBL1-dependent enhancement of CIPK23 activity toward its substrate. Together, these data identify a novel general regulatory mechanism of CBL-CIPK complexes in that CBL phosphorylation at their flexible C terminus likely provokes conformational changes that enhance specificity and activity of CBL-CIPK complexes toward their target proteins.

  @article{Hashimoto09032012, abstract = {Calcineurin B-like proteins (CBLs) represent a family of calcium sensor proteins that interact with a group of serine/threonine kinases designated as CBL-interacting protein kinases (CIPKs). CBL-CIPK complexes are crucially involved in relaying plant responses to many environmental signals and in regulating ion fluxes. However, the biochemical characterization of CBL-CIPK complexes has so far been hampered by low activities of recombinant CIPKs. Here, we report on an efficient wheat germ extract-based in vitro transcription/translation protocol that yields active full-length wild-type CIPK proteins. We identified a conserved serine residue within the C terminus of CBLs as being phosphorylated by their interacting CIPKs. Remarkably, our studies revealed that CIPK-dependent CBL phosphorylation is strictly dependent on CBL-CIPK interaction via the CIPK NAF domain. The phosphorylation status of CBLs does not appear to influence the stability, localization, or CIPK interaction of these calcium sensor proteins in general. However, proper phosphorylation of CBL1 is absolutely required for the in vivo activation of the AKT1 K+ channel by CBL1-CIPK23 and CBL9-CIPK23 complexes in oocytes. Moreover, we show that by combining CBL1, CIPK23, and AKT1, we can faithfully reconstitute CBL-dependent enhancement of phosphorylation of target proteins by CIPKs in vitro. In addition, we report that phosphorylation of CBL1 by CIPK23 is also required for the CBL1-dependent enhancement of CIPK23 activity toward its substrate. Together, these data identify a novel general regulatory mechanism of CBL-CIPK complexes in that CBL phosphorylation at their flexible C terminus likely provokes conformational changes that enhance specificity and activity of CBL-CIPK complexes toward their target proteins.}, author = {Hashimoto, Kenji and Eckert, Christian and Anschütz, Uta and Scholz, Martin and Held, Katrin and Waadt, Rainer and Reyer, Antonella and Hippler, Michael and Becker, Dirk and Kudla, Jörg}, journal = {Journal of Biological Chemistry}, keywords = {myown}, number = 11, pages = {7956-7968}, title = {Phosphorylation of Calcineurin B-like (CBL) Calcium Sensor Proteins by Their CBL-interacting Protein Kinases (CIPKs) Is Required for Full Activity of CBL-CIPK Complexes toward Their Target Proteins}, volume = 287, year = 2012 }

  %0 Journal Article %1 Hashimoto09032012 %A Hashimoto, Kenji %A Eckert, Christian %A Anschütz, Uta %A Scholz, Martin %A Held, Katrin %A Waadt, Rainer %A Reyer, Antonella %A Hippler, Michael %A Becker, Dirk %A Kudla, Jörg %D 2012 %J Journal of Biological Chemistry %N 11 %P 7956-7968 %R 10.1074/jbc.M111.279331 %T Phosphorylation of Calcineurin B-like (CBL) Calcium Sensor Proteins by Their CBL-interacting Protein Kinases (CIPKs) Is Required for Full Activity of CBL-CIPK Complexes toward Their Target Proteins %U http://www.jbc.org/content/287/11/7956.abstract %V 287 %X Calcineurin B-like proteins (CBLs) represent a family of calcium sensor proteins that interact with a group of serine/threonine kinases designated as CBL-interacting protein kinases (CIPKs). CBL-CIPK complexes are crucially involved in relaying plant responses to many environmental signals and in regulating ion fluxes. However, the biochemical characterization of CBL-CIPK complexes has so far been hampered by low activities of recombinant CIPKs. Here, we report on an efficient wheat germ extract-based in vitro transcription/translation protocol that yields active full-length wild-type CIPK proteins. We identified a conserved serine residue within the C terminus of CBLs as being phosphorylated by their interacting CIPKs. Remarkably, our studies revealed that CIPK-dependent CBL phosphorylation is strictly dependent on CBL-CIPK interaction via the CIPK NAF domain. The phosphorylation status of CBLs does not appear to influence the stability, localization, or CIPK interaction of these calcium sensor proteins in general. However, proper phosphorylation of CBL1 is absolutely required for the in vivo activation of the AKT1 K+ channel by CBL1-CIPK23 and CBL9-CIPK23 complexes in oocytes. Moreover, we show that by combining CBL1, CIPK23, and AKT1, we can faithfully reconstitute CBL-dependent enhancement of phosphorylation of target proteins by CIPKs in vitro. In addition, we report that phosphorylation of CBL1 by CIPK23 is also required for the CBL1-dependent enhancement of CIPK23 activity toward its substrate. Together, these data identify a novel general regulatory mechanism of CBL-CIPK complexes in that CBL phosphorylation at their flexible C terminus likely provokes conformational changes that enhance specificity and activity of CBL-CIPK complexes toward their target proteins.

• Dadacz-Narloch, B., Beyhl, D., Larisch, C., Lopez-Sanjurjo, E.J., Reski, R., Kuchitsu, K., Muller, T.D., Becker, D., Schonknecht, G., Hedrich, R. (2011) A Novel Calcium Binding Site in the Slow Vacuolar Cation Channel {TPC}1 Senses Luminal Calcium Levels, The Plant Cell, 23(7), 2696–2707, available: https://doi.org/10.1105/tpc.111.086751.
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  @article{Dadacz_Narloch_2011, author = {Dadacz-Narloch, B. and Beyhl, D. and Larisch, C. and Lopez-Sanjurjo, E. J. and Reski, R. and Kuchitsu, K. and Muller, T. D. and Becker, D. and Schonknecht, G. and Hedrich, R.}, journal = {The Plant Cell}, keywords = {myown}, month = {jul}, number = 7, pages = {2696–2707}, publisher = {American Society of Plant Biologists ({ASPB})}, title = {A Novel Calcium Binding Site in the Slow Vacuolar Cation Channel {TPC}1 Senses Luminal Calcium Levels}, volume = 23, year = 2011 }

  %0 Journal Article %1 Dadacz_Narloch_2011 %A Dadacz-Narloch, B. %A Beyhl, D. %A Larisch, C. %A Lopez-Sanjurjo, E. J. %A Reski, R. %A Kuchitsu, K. %A Muller, T. D. %A Becker, D. %A Schonknecht, G. %A Hedrich, R. %D 2011 %I American Society of Plant Biologists ({ASPB}) %J The Plant Cell %N 7 %P 2696--2707 %R 10.1105/tpc.111.086751 %T A Novel Calcium Binding Site in the Slow Vacuolar Cation Channel {TPC}1 Senses Luminal Calcium Levels %U https://doi.org/10.1105%2Ftpc.111.086751 %V 23

• Krol, E., Mentzel, T., Chinchilla, D., Boller, T., Felix, G., Kemmerling, B., Postel, S., Arents, M., Jeworutzki, E., Al-Rasheid, K.A., Becker, D., Hedrich, R. (2010) Perception of the Arabidopsis danger signal peptide 1 involves the pattern recognition receptor AtPEPR1 and its close homologue AtPEPR2, J Biol Chem, 285(18), 13471–13479, available: https://doi.org/10.1074/jbc.M109.097394.
  • [ Abstract ]
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  Plasma membrane-borne pattern recognition receptors, which recognize microbe-associated molecular patterns and endogenous damage-associated molecular patterns, provide the first line of defense in innate immunity. In plants, leucine-rich repeat receptor kinases fulfill this role, as exemplified by FLS2 and EFR, the receptors for the microbe-associated molecular patterns flagellin and elongation factor Tu. Here we examined the perception of the damage-associated molecular pattern peptide 1 (AtPep1), an endogenous peptide of Arabidopsis identified earlier and shown to be perceived by the leucine-rich repeat protein kinase PEPR1. Using seedling growth inhibition, elicitation of an oxidative burst and induction of ethylene biosynthesis, we show that wild type plants and the pepr1 and pepr2 mutants, affected in PEPR1 and in its homologue PEPR2, are sensitive to AtPep1, but that the double mutant pepr1/pepr2 is completely insensitive. As a central body of our study, we provide electrophysiological evidence that at the level of the plasma membrane, AtPep1 triggers a receptor-dependent transient depolarization through activation of plasma membrane anion channels, and that this effect is absent in the double mutant pepr1/pepr2. The double mutant also fails to respond to AtPep2 and AtPep3, two distant homologues of AtPep1 on the basis of homology screening, implying that the PEPR1 and PEPR2 are responsible for their perception too. Our findings provide a basic framework to study the biological role of AtPep1-related danger signals and their cognate receptors.

  @article{Krol:2010:J-Biol-Chem:20200150, abstract = {Plasma membrane-borne pattern recognition receptors, which recognize microbe-associated molecular patterns and endogenous damage-associated molecular patterns, provide the first line of defense in innate immunity. In plants, leucine-rich repeat receptor kinases fulfill this role, as exemplified by FLS2 and EFR, the receptors for the microbe-associated molecular patterns flagellin and elongation factor Tu. Here we examined the perception of the damage-associated molecular pattern peptide 1 (AtPep1), an endogenous peptide of Arabidopsis identified earlier and shown to be perceived by the leucine-rich repeat protein kinase PEPR1. Using seedling growth inhibition, elicitation of an oxidative burst and induction of ethylene biosynthesis, we show that wild type plants and the pepr1 and pepr2 mutants, affected in PEPR1 and in its homologue PEPR2, are sensitive to AtPep1, but that the double mutant pepr1/pepr2 is completely insensitive. As a central body of our study, we provide electrophysiological evidence that at the level of the plasma membrane, AtPep1 triggers a receptor-dependent transient depolarization through activation of plasma membrane anion channels, and that this effect is absent in the double mutant pepr1/pepr2. The double mutant also fails to respond to AtPep2 and AtPep3, two distant homologues of AtPep1 on the basis of homology screening, implying that the PEPR1 and PEPR2 are responsible for their perception too. Our findings provide a basic framework to study the biological role of AtPep1-related danger signals and their cognate receptors.}, author = {Krol, E and Mentzel, T and Chinchilla, D and Boller, T and Felix, G and Kemmerling, B and Postel, S and Arents, M and Jeworutzki, E and Al-Rasheid, K A and Becker, D and Hedrich, R}, journal = {J Biol Chem}, keywords = {myown}, month = {apr}, number = 18, pages = {13471-13479}, title = {Perception of the Arabidopsis danger signal peptide 1 involves the pattern recognition receptor AtPEPR1 and its close homologue AtPEPR2}, volume = 285, year = 2010 }

  %0 Journal Article %1 Krol:2010:J-Biol-Chem:20200150 %A Krol, E %A Mentzel, T %A Chinchilla, D %A Boller, T %A Felix, G %A Kemmerling, B %A Postel, S %A Arents, M %A Jeworutzki, E %A Al-Rasheid, K A %A Becker, D %A Hedrich, R %D 2010 %J J Biol Chem %N 18 %P 13471-13479 %R 10.1074/jbc.M109.097394 %T Perception of the Arabidopsis danger signal peptide 1 involves the pattern recognition receptor AtPEPR1 and its close homologue AtPEPR2 %U https://www.ncbi.nlm.nih.gov/pubmed/20200150 %V 285 %X Plasma membrane-borne pattern recognition receptors, which recognize microbe-associated molecular patterns and endogenous damage-associated molecular patterns, provide the first line of defense in innate immunity. In plants, leucine-rich repeat receptor kinases fulfill this role, as exemplified by FLS2 and EFR, the receptors for the microbe-associated molecular patterns flagellin and elongation factor Tu. Here we examined the perception of the damage-associated molecular pattern peptide 1 (AtPep1), an endogenous peptide of Arabidopsis identified earlier and shown to be perceived by the leucine-rich repeat protein kinase PEPR1. Using seedling growth inhibition, elicitation of an oxidative burst and induction of ethylene biosynthesis, we show that wild type plants and the pepr1 and pepr2 mutants, affected in PEPR1 and in its homologue PEPR2, are sensitive to AtPep1, but that the double mutant pepr1/pepr2 is completely insensitive. As a central body of our study, we provide electrophysiological evidence that at the level of the plasma membrane, AtPep1 triggers a receptor-dependent transient depolarization through activation of plasma membrane anion channels, and that this effect is absent in the double mutant pepr1/pepr2. The double mutant also fails to respond to AtPep2 and AtPep3, two distant homologues of AtPep1 on the basis of homology screening, implying that the PEPR1 and PEPR2 are responsible for their perception too. Our findings provide a basic framework to study the biological role of AtPep1-related danger signals and their cognate receptors.
• Jeworutzki, E., Roelfsema, M.R., Ansch{"u}tz, U., Krol, E., Elzenga, J.T., Felix, G., Boller, T., Hedrich, R., Becker, D. (2010) Early signaling through the Arabidopsis pattern recognition receptors FLS2 and EFR involves Ca-associated opening of plasma membrane anion channels, Plant J, 62(3), 367–378, available: https://doi.org/10.1111/j.1365-313X.2010.04155.x.
  • [ Abstract ]
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  The perception of microbes by plants involves highly conserved molecular signatures that are absent from the host and that are collectively referred to as microbe-associated molecular patterns (MAMPs). The Arabidopsis pattern recognition receptors FLAGELLIN-SENSING 2 (FLS2) and EF-Tu receptor (EFR) represent genetically well studied paradigms that mediate defense against bacterial pathogens. Stimulation of these receptors through their cognate ligands, bacterial flagellin or bacterial elongation factor Tu, leads to a defense response and ultimately to increased resistance. However, little is known about the early signaling pathway of these receptors. Here, we characterize this early response in situ, using an electrophysiological approach. In line with a release of negatively charged molecules, voltage recordings of microelectrode-impaled mesophyll cells and root hairs of Col-0 Arabidopsis plants revealed rapid, dose-dependent membrane potential depolarizations in response to either flg22 or elf18. Using ion-selective microelectrodes, pronounced anion currents were recorded upon application of flg22 and elf18, indicating that the signaling cascades initiated by each of the two receptors converge on the same plasma membrane ion channels. Combined calcium imaging and electrophysiological measurements revealed that the depolarization was superimposed by an increase in cytosolic calcium that was indispensable for depolarization. NADPH oxidase mutants were still depolarized upon elicitor stimulation, suggesting a reactive oxygen species-independent membrane potential response. Furthermore, electrical signaling in response to either flg22 or elf 18 critically depends on the activity of the FLS2-associated receptor-like kinase BAK1, suggesting that activation of FLS2 and EFR lead to BAK1-dependent, calcium-associated plasma membrane anion channel opening as an initial step in the pathogen defense pathway.

  @article{Jeworutzki:2010:Plant-J:20113440, abstract = {The perception of microbes by plants involves highly conserved molecular signatures that are absent from the host and that are collectively referred to as microbe-associated molecular patterns (MAMPs). The Arabidopsis pattern recognition receptors FLAGELLIN-SENSING 2 (FLS2) and EF-Tu receptor (EFR) represent genetically well studied paradigms that mediate defense against bacterial pathogens. Stimulation of these receptors through their cognate ligands, bacterial flagellin or bacterial elongation factor Tu, leads to a defense response and ultimately to increased resistance. However, little is known about the early signaling pathway of these receptors. Here, we characterize this early response in situ, using an electrophysiological approach. In line with a release of negatively charged molecules, voltage recordings of microelectrode-impaled mesophyll cells and root hairs of Col-0 Arabidopsis plants revealed rapid, dose-dependent membrane potential depolarizations in response to either flg22 or elf18. Using ion-selective microelectrodes, pronounced anion currents were recorded upon application of flg22 and elf18, indicating that the signaling cascades initiated by each of the two receptors converge on the same plasma membrane ion channels. Combined calcium imaging and electrophysiological measurements revealed that the depolarization was superimposed by an increase in cytosolic calcium that was indispensable for depolarization. NADPH oxidase mutants were still depolarized upon elicitor stimulation, suggesting a reactive oxygen species-independent membrane potential response. Furthermore, electrical signaling in response to either flg22 or elf 18 critically depends on the activity of the FLS2-associated receptor-like kinase BAK1, suggesting that activation of FLS2 and EFR lead to BAK1-dependent, calcium-associated plasma membrane anion channel opening as an initial step in the pathogen defense pathway.}, author = {Jeworutzki, E and Roelfsema, M R and Ansch{\"u}tz, U and Krol, E and Elzenga, J T and Felix, G and Boller, T and Hedrich, R and Becker, D}, journal = {Plant J}, keywords = {myown}, month = {may}, number = 3, pages = {367-378}, title = {Early signaling through the Arabidopsis pattern recognition receptors FLS2 and EFR involves Ca-associated opening of plasma membrane anion channels}, volume = 62, year = 2010 }

  %0 Journal Article %1 Jeworutzki:2010:Plant-J:20113440 %A Jeworutzki, E %A Roelfsema, M R %A Ansch{"u}tz, U %A Krol, E %A Elzenga, J T %A Felix, G %A Boller, T %A Hedrich, R %A Becker, D %D 2010 %J Plant J %N 3 %P 367-378 %R 10.1111/j.1365-313X.2010.04155.x %T Early signaling through the Arabidopsis pattern recognition receptors FLS2 and EFR involves Ca-associated opening of plasma membrane anion channels %U https://www.ncbi.nlm.nih.gov/pubmed/20113440 %V 62 %X The perception of microbes by plants involves highly conserved molecular signatures that are absent from the host and that are collectively referred to as microbe-associated molecular patterns (MAMPs). The Arabidopsis pattern recognition receptors FLAGELLIN-SENSING 2 (FLS2) and EF-Tu receptor (EFR) represent genetically well studied paradigms that mediate defense against bacterial pathogens. Stimulation of these receptors through their cognate ligands, bacterial flagellin or bacterial elongation factor Tu, leads to a defense response and ultimately to increased resistance. However, little is known about the early signaling pathway of these receptors. Here, we characterize this early response in situ, using an electrophysiological approach. In line with a release of negatively charged molecules, voltage recordings of microelectrode-impaled mesophyll cells and root hairs of Col-0 Arabidopsis plants revealed rapid, dose-dependent membrane potential depolarizations in response to either flg22 or elf18. Using ion-selective microelectrodes, pronounced anion currents were recorded upon application of flg22 and elf18, indicating that the signaling cascades initiated by each of the two receptors converge on the same plasma membrane ion channels. Combined calcium imaging and electrophysiological measurements revealed that the depolarization was superimposed by an increase in cytosolic calcium that was indispensable for depolarization. NADPH oxidase mutants were still depolarized upon elicitor stimulation, suggesting a reactive oxygen species-independent membrane potential response. Furthermore, electrical signaling in response to either flg22 or elf 18 critically depends on the activity of the FLS2-associated receptor-like kinase BAK1, suggesting that activation of FLS2 and EFR lead to BAK1-dependent, calcium-associated plasma membrane anion channel opening as an initial step in the pathogen defense pathway.
• Voelker, C., Gomez-Porras, J.L., Becker, D., Hamamoto, S., Uozumi, N., Gambale, F., Mueller-Roeber, B., Czempinski, K., Dreyer, I. (2010) Roles of tandem-pore K+ channels in plants – a puzzle still to be solved*, Plant Biology, 12, 56–63, available: https://doi.org/10.1111/j.1438-8677.2010.00353.x.
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  The group of voltage-independent K+ channels in Arabidopsis thaliana consists of six members, five tandem-pore channels (TPK1–TPK5) and a single Kir-like channel (KCO3). All TPK/KCO channels are located at the vacuolar membrane except for TPK4, which was shown to be a plasma membrane channel in pollen. The vacuolar channels interact with 14-3-3 proteins (also called General Regulating Factors, GRFs), indicating regulation at the level of protein–protein interactions. Here we review current knowledge about these ion channels and their genes, and highlight open questions that need to be urgently addressed in future studies to fully appreciate the physiological functions of these ion channels.

  @article{PLB:PLB353, abstract = {The group of voltage-independent K+ channels in Arabidopsis thaliana consists of six members, five tandem-pore channels (TPK1–TPK5) and a single Kir-like channel (KCO3). All TPK/KCO channels are located at the vacuolar membrane except for TPK4, which was shown to be a plasma membrane channel in pollen. The vacuolar channels interact with 14-3-3 proteins (also called General Regulating Factors, GRFs), indicating regulation at the level of protein–protein interactions. Here we review current knowledge about these ion channels and their genes, and highlight open questions that need to be urgently addressed in future studies to fully appreciate the physiological functions of these ion channels.}, author = {Voelker, C. and Gomez-Porras, J. L. and Becker, D. and Hamamoto, S. and Uozumi, N. and Gambale, F. and Mueller-Roeber, B. and Czempinski, K. and Dreyer, I.}, journal = {Plant Biology}, keywords = {myown}, pages = {56–63}, publisher = {Blackwell Publishing Ltd}, title = {Roles of tandem-pore K+ channels in plants – a puzzle still to be solved*}, volume = 12, year = 2010 }

  %0 Journal Article %1 PLB:PLB353 %A Voelker, C. %A Gomez-Porras, J. L. %A Becker, D. %A Hamamoto, S. %A Uozumi, N. %A Gambale, F. %A Mueller-Roeber, B. %A Czempinski, K. %A Dreyer, I. %D 2010 %I Blackwell Publishing Ltd %J Plant Biology %P 56--63 %R 10.1111/j.1438-8677.2010.00353.x %T Roles of tandem-pore K+ channels in plants – a puzzle still to be solved* %U http://dx.doi.org/10.1111/j.1438-8677.2010.00353.x %V 12 %X The group of voltage-independent K+ channels in Arabidopsis thaliana consists of six members, five tandem-pore channels (TPK1–TPK5) and a single Kir-like channel (KCO3). All TPK/KCO channels are located at the vacuolar membrane except for TPK4, which was shown to be a plasma membrane channel in pollen. The vacuolar channels interact with 14-3-3 proteins (also called General Regulating Factors, GRFs), indicating regulation at the level of protein–protein interactions. Here we review current knowledge about these ion channels and their genes, and highlight open questions that need to be urgently addressed in future studies to fully appreciate the physiological functions of these ion channels.
• Amien, S., Kliwer, I., Márton, M.L., Debener, T., Geiger, D., Becker, D., Dresselhaus, T. (2010) Defensin-Like ZmES4 Mediates Pollen Tube Burst in Maize via Opening of the Potassium Channel KZM1, PLOS Biology, 8(6), 1–13, available: https://doi.org/10.1371/journal.pbio.1000388.
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  Species-preferential osmotic pollen tube burst and sperm discharge in maize involve induced opening of the pollen tube-expressed potassium channel KZM1 by the egg apparatus-derived defensin-like protein ZmES4.

  @article{10.1371/journal.pbio.1000388, abstract = {Species-preferential osmotic pollen tube burst and sperm discharge in maize involve induced opening of the pollen tube-expressed potassium channel KZM1 by the egg apparatus-derived defensin-like protein ZmES4.}, author = {Amien, Suseno and Kliwer, Irina and Márton, Mihaela L. and Debener, Thomas and Geiger, Dietmar and Becker, Dirk and Dresselhaus, Thomas}, journal = {PLOS Biology}, keywords = {myown}, month = {06}, number = 6, pages = {1-13}, publisher = {Public Library of Science}, title = {Defensin-Like ZmES4 Mediates Pollen Tube Burst in Maize via Opening of the Potassium Channel KZM1}, volume = 8, year = 2010 }

  %0 Journal Article %1 10.1371/journal.pbio.1000388 %A Amien, Suseno %A Kliwer, Irina %A Márton, Mihaela L. %A Debener, Thomas %A Geiger, Dietmar %A Becker, Dirk %A Dresselhaus, Thomas %D 2010 %I Public Library of Science %J PLOS Biology %N 6 %P 1-13 %R 10.1371/journal.pbio.1000388 %T Defensin-Like ZmES4 Mediates Pollen Tube Burst in Maize via Opening of the Potassium Channel KZM1 %U http://dx.doi.org/10.1371%2Fjournal.pbio.1000388 %V 8 %X Species-preferential osmotic pollen tube burst and sperm discharge in maize involve induced opening of the pollen tube-expressed potassium channel KZM1 by the egg apparatus-derived defensin-like protein ZmES4.
• Dietrich, P., Ansch{"u}tz, U., Kugler, A., Becker, D. (2010) Physiology and biophysics of plant ligand-gated ion channels, Plant Biol (Stuttg), 12 Suppl 1, 80–93, available: https://doi.org/10.1111/j.1438-8677.2010.00362.x.
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  Small molecules and metabolites often act as intra- or extracellular messengers in signal transduction pathways. Ligand-gated ion channels provide a mean to transduce those biochemical signals at the membrane into electrical events and ion fluxes. In plants, cyclic nucleotides and glutamate represent intra- and extracellular signalling ligands, respectively. While the former have been shown to regulate voltage-dependent ion channels and are supposed to activate cyclic nucleotide gated (CNG) channels, the latter are perceived by ionotropic glutamate receptors (GLRs). This review summarises our current knowledge about CNG channels and glutamate receptors in plants and their proposed roles in plant development and adaptation to biotic and abiotic stresses.

  @article{Dietrich:2010:Plant-Biol-Stuttg:20712623, abstract = {Small molecules and metabolites often act as intra- or extracellular messengers in signal transduction pathways. Ligand-gated ion channels provide a mean to transduce those biochemical signals at the membrane into electrical events and ion fluxes. In plants, cyclic nucleotides and glutamate represent intra- and extracellular signalling ligands, respectively. While the former have been shown to regulate voltage-dependent ion channels and are supposed to activate cyclic nucleotide gated (CNG) channels, the latter are perceived by ionotropic glutamate receptors (GLRs). This review summarises our current knowledge about CNG channels and glutamate receptors in plants and their proposed roles in plant development and adaptation to biotic and abiotic stresses.}, author = {Dietrich, P and Ansch{\"u}tz, U and Kugler, A and Becker, D}, journal = {Plant Biol (Stuttg)}, keywords = {myown}, month = {sep}, pages = {80-93}, title = {Physiology and biophysics of plant ligand-gated ion channels}, volume = {12 Suppl 1}, year = 2010 }

  %0 Journal Article %1 Dietrich:2010:Plant-Biol-Stuttg:20712623 %A Dietrich, P %A Ansch{"u}tz, U %A Kugler, A %A Becker, D %D 2010 %J Plant Biol (Stuttg) %P 80-93 %R 10.1111/j.1438-8677.2010.00362.x %T Physiology and biophysics of plant ligand-gated ion channels %U https://www.ncbi.nlm.nih.gov/pubmed/?term=Becker+anschutz+dietrich %V 12 Suppl 1 %X Small molecules and metabolites often act as intra- or extracellular messengers in signal transduction pathways. Ligand-gated ion channels provide a mean to transduce those biochemical signals at the membrane into electrical events and ion fluxes. In plants, cyclic nucleotides and glutamate represent intra- and extracellular signalling ligands, respectively. While the former have been shown to regulate voltage-dependent ion channels and are supposed to activate cyclic nucleotide gated (CNG) channels, the latter are perceived by ionotropic glutamate receptors (GLRs). This review summarises our current knowledge about CNG channels and glutamate receptors in plants and their proposed roles in plant development and adaptation to biotic and abiotic stresses.

• Geiger, D., Becker, D., Vosloh, D., Gambale, F., Palme, K., Rehers, M., Anschuetz, U., Dreyer, I., Kudla, J., Hedrich, R. (2009) Heteromeric AtKC/AKT1 channels in Arabidopsis roots facilitate growth under K+-limiting conditions, J Biol Chem, 284(32), 21288–21295, available: https://doi.org/10.1074/jbc.M109.017574.
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  Plant growth and development is driven by osmotic processes. Potassium represents the major osmotically active cation in plants cells. The uptake of this inorganic osmolyte from the soil in Arabidopsis involves a root K(+) uptake module consisting of the two K(+) channel alpha-subunits, AKT1 and AtKC1. AKT1-mediated potassium absorption from K(+)-depleted soil was shown to depend on the calcium-sensing proteins CBL1/9 and their interacting kinase CIPK23. Here we show that upon activation by the CBL.CIPK complex in low external potassium homomeric AKT1 channels open at voltages positive of E(K), a condition resulting in cellular K(+) leakage. Although at submillimolar external potassium an intrinsic K(+) sensor reduces AKT1 channel cord conductance, loss of cytosolic potassium is not completely abolished under these conditions. Depending on channel activity and the actual potassium gradients, this channel-mediated K(+) loss results in impaired plant growth in the atkc1 mutant. Incorporation of the AtKC1 subunit into the channel complex, however, modulates the properties of the K(+) uptake module to prevent K(+) loss. Upon assembly of AKT1 and AtKC1, the activation threshold of the root inward rectifier voltage gate is shifted negative by approximately -70 mV. Additionally, the channel conductance gains a hypersensitive K(+) dependence. Together, these two processes appear to represent a safety strategy preventing K(+) loss through the uptake channels under physiological conditions. Similar growth retardation phenotypes of akt1 and atkc1 loss-of-function mutants in response to limiting K(+) supply further support such functional interdependence of AKT1 and AtKC1. Taken together, these findings suggest an essential role of AtKC1-like subunits for root K(+) uptake and K(+) homeostasis when plants experience conditions of K(+) limitation.

  @article{Geiger:2009:J-Biol-Chem:19509299, abstract = {Plant growth and development is driven by osmotic processes. Potassium represents the major osmotically active cation in plants cells. The uptake of this inorganic osmolyte from the soil in Arabidopsis involves a root K(+) uptake module consisting of the two K(+) channel alpha-subunits, AKT1 and AtKC1. AKT1-mediated potassium absorption from K(+)-depleted soil was shown to depend on the calcium-sensing proteins CBL1/9 and their interacting kinase CIPK23. Here we show that upon activation by the CBL.CIPK complex in low external potassium homomeric AKT1 channels open at voltages positive of E(K), a condition resulting in cellular K(+) leakage. Although at submillimolar external potassium an intrinsic K(+) sensor reduces AKT1 channel cord conductance, loss of cytosolic potassium is not completely abolished under these conditions. Depending on channel activity and the actual potassium gradients, this channel-mediated K(+) loss results in impaired plant growth in the atkc1 mutant. Incorporation of the AtKC1 subunit into the channel complex, however, modulates the properties of the K(+) uptake module to prevent K(+) loss. Upon assembly of AKT1 and AtKC1, the activation threshold of the root inward rectifier voltage gate is shifted negative by approximately -70 mV. Additionally, the channel conductance gains a hypersensitive K(+) dependence. Together, these two processes appear to represent a safety strategy preventing K(+) loss through the uptake channels under physiological conditions. Similar growth retardation phenotypes of akt1 and atkc1 loss-of-function mutants in response to limiting K(+) supply further support such functional interdependence of AKT1 and AtKC1. Taken together, these findings suggest an essential role of AtKC1-like subunits for root K(+) uptake and K(+) homeostasis when plants experience conditions of K(+) limitation.}, author = {Geiger, D and Becker, D and Vosloh, D and Gambale, F and Palme, K and Rehers, M and Anschuetz, U and Dreyer, I and Kudla, J and Hedrich, R}, journal = {J Biol Chem}, keywords = {myown}, month = {aug}, number = 32, pages = {21288-21295}, title = {Heteromeric AtKC/AKT1 channels in Arabidopsis roots facilitate growth under K+-limiting conditions}, volume = 284, year = 2009 }

  %0 Journal Article %1 Geiger:2009:J-Biol-Chem:19509299 %A Geiger, D %A Becker, D %A Vosloh, D %A Gambale, F %A Palme, K %A Rehers, M %A Anschuetz, U %A Dreyer, I %A Kudla, J %A Hedrich, R %D 2009 %J J Biol Chem %N 32 %P 21288-21295 %R 10.1074/jbc.M109.017574 %T Heteromeric AtKC/AKT1 channels in Arabidopsis roots facilitate growth under K+-limiting conditions %U https://www.ncbi.nlm.nih.gov/pubmed/19509299 %V 284 %X Plant growth and development is driven by osmotic processes. Potassium represents the major osmotically active cation in plants cells. The uptake of this inorganic osmolyte from the soil in Arabidopsis involves a root K(+) uptake module consisting of the two K(+) channel alpha-subunits, AKT1 and AtKC1. AKT1-mediated potassium absorption from K(+)-depleted soil was shown to depend on the calcium-sensing proteins CBL1/9 and their interacting kinase CIPK23. Here we show that upon activation by the CBL.CIPK complex in low external potassium homomeric AKT1 channels open at voltages positive of E(K), a condition resulting in cellular K(+) leakage. Although at submillimolar external potassium an intrinsic K(+) sensor reduces AKT1 channel cord conductance, loss of cytosolic potassium is not completely abolished under these conditions. Depending on channel activity and the actual potassium gradients, this channel-mediated K(+) loss results in impaired plant growth in the atkc1 mutant. Incorporation of the AtKC1 subunit into the channel complex, however, modulates the properties of the K(+) uptake module to prevent K(+) loss. Upon assembly of AKT1 and AtKC1, the activation threshold of the root inward rectifier voltage gate is shifted negative by approximately -70 mV. Additionally, the channel conductance gains a hypersensitive K(+) dependence. Together, these two processes appear to represent a safety strategy preventing K(+) loss through the uptake channels under physiological conditions. Similar growth retardation phenotypes of akt1 and atkc1 loss-of-function mutants in response to limiting K(+) supply further support such functional interdependence of AKT1 and AtKC1. Taken together, these findings suggest an essential role of AtKC1-like subunits for root K(+) uptake and K(+) homeostasis when plants experience conditions of K(+) limitation.
• Sano, T., Kutsuna, N., Becker, D., Hedrich, R., Hasezawa, S. (2009) Outward-rectifying K+ channel activities regulate cell elongation and cell division of tobacco BY-2 cells, Plant J, 57(1), 55–64, available: https://doi.org/10.1111/j.1365-313X.2008.03672.x.
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  Potassium ions (K+) are required for plant growth and development, including cell division and cell elongation/expansion, which are mediated by the K+ transport system. In this study, we investigated the role of K+ in cell division using tobacco BY-2 protoplast cultures. Gene expression analysis revealed induction of the Shaker-like outward K+ channel gene, NTORK1, under cell-division conditions, whereas the inward K+ channel genes NKT1 and NtKC1 were induced under both cell-elongation and cell-division conditions. Repression of NTORK1 gene expression by expression of its antisense construct repressed cell division but accelerated cell elongation even under conditions promoting cell division. A decrease in the K+ content of cells and cellular osmotic pressure in dividing cells suggested that an increase in cell osmotic pressure by K+ uptake is not required for cell division. In contrast, K+ depletion, which reduced cell-division activity, decreased cytoplasmic pH as monitored using a fluorescent pH indicator, SNARF-1. Application of K+ or the cytoplasmic alkalizing reagent (NH(4))(2)SO(4) increased cytoplasmic pH and suppressed the reduction in cell-division activity. These results suggest that the K+ taken up into cells is used to regulate cytoplasmic pH during cell division.

  @article{Sano:2009:Plant-J:18778403, abstract = {Potassium ions (K+) are required for plant growth and development, including cell division and cell elongation/expansion, which are mediated by the K+ transport system. In this study, we investigated the role of K+ in cell division using tobacco BY-2 protoplast cultures. Gene expression analysis revealed induction of the Shaker-like outward K+ channel gene, NTORK1, under cell-division conditions, whereas the inward K+ channel genes NKT1 and NtKC1 were induced under both cell-elongation and cell-division conditions. Repression of NTORK1 gene expression by expression of its antisense construct repressed cell division but accelerated cell elongation even under conditions promoting cell division. A decrease in the K+ content of cells and cellular osmotic pressure in dividing cells suggested that an increase in cell osmotic pressure by K+ uptake is not required for cell division. In contrast, K+ depletion, which reduced cell-division activity, decreased cytoplasmic pH as monitored using a fluorescent pH indicator, SNARF-1. Application of K+ or the cytoplasmic alkalizing reagent (NH(4))(2)SO(4) increased cytoplasmic pH and suppressed the reduction in cell-division activity. These results suggest that the K+ taken up into cells is used to regulate cytoplasmic pH during cell division.}, author = {Sano, T and Kutsuna, N and Becker, D and Hedrich, R and Hasezawa, S}, journal = {Plant J}, keywords = {myown}, month = {jan}, number = 1, pages = {55-64}, title = {Outward-rectifying K+ channel activities regulate cell elongation and cell division of tobacco BY-2 cells}, volume = 57, year = 2009 }

  %0 Journal Article %1 Sano:2009:Plant-J:18778403 %A Sano, T %A Kutsuna, N %A Becker, D %A Hedrich, R %A Hasezawa, S %D 2009 %J Plant J %N 1 %P 55-64 %R 10.1111/j.1365-313X.2008.03672.x %T Outward-rectifying K+ channel activities regulate cell elongation and cell division of tobacco BY-2 cells %U https://www.ncbi.nlm.nih.gov/pubmed/18778403 %V 57 %X Potassium ions (K+) are required for plant growth and development, including cell division and cell elongation/expansion, which are mediated by the K+ transport system. In this study, we investigated the role of K+ in cell division using tobacco BY-2 protoplast cultures. Gene expression analysis revealed induction of the Shaker-like outward K+ channel gene, NTORK1, under cell-division conditions, whereas the inward K+ channel genes NKT1 and NtKC1 were induced under both cell-elongation and cell-division conditions. Repression of NTORK1 gene expression by expression of its antisense construct repressed cell division but accelerated cell elongation even under conditions promoting cell division. A decrease in the K+ content of cells and cellular osmotic pressure in dividing cells suggested that an increase in cell osmotic pressure by K+ uptake is not required for cell division. In contrast, K+ depletion, which reduced cell-division activity, decreased cytoplasmic pH as monitored using a fluorescent pH indicator, SNARF-1. Application of K+ or the cytoplasmic alkalizing reagent (NH(4))(2)SO(4) increased cytoplasmic pH and suppressed the reduction in cell-division activity. These results suggest that the K+ taken up into cells is used to regulate cytoplasmic pH during cell division.

• Ranf, S., W{"u}nnenberg, P., Lee, J., Becker, D., Dunkel, M., Hedrich, R., Scheel, D., Dietrich, P. (2008) Loss of the vacuolar cation channel, AtTPC1, does not impair Ca2+ signals induced by abiotic and biotic stresses, Plant J, 53(2), 287–299, available: https://doi.org/10.1111/j.1365-313X.2007.03342.x.
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  The putative two-pore Ca(2+) channel TPC1 has been suggested to be involved in responses to abiotic and biotic stresses. We show that AtTPC1 co-localizes with the K(+)-selective channel AtTPK1 in the vacuolar membrane. Loss of AtTPC1 abolished Ca(2+)-activated slow vacuolar (SV) currents, which were increased in AtTPC1-over-expressing Arabidopsis compared to the wild-type. A Ca(2+)-insensitive vacuolar cation channel, as yet uncharacterized, could be resolved in tpc1-2 knockout plants. The kinetics of ABA- and CO(2)-induced stomatal closure were similar in wild-type and tpc1-2 knockout plants, excluding a role of SV channels in guard-cell signalling in response to these physiological stimuli. ABA-, K(+)-, and Ca(2+)-dependent root growth phenotypes were not changed in tpc1-2 compared to wild-type plants. Given the permeability of SV channels to mono- and divalent cations, the question arises as to whether TPC1 in vivo represents a pathway for Ca(2+) entry into the cytosol. Ca(2+) responses as measured in aequorin-expressing wild-type, tpc1-2 knockout and TPC1-over-expressing plants disprove a contribution of TPC1 to any of the stimulus-induced Ca(2+) signals tested, including abiotic stresses (cold, hyperosmotic, salt and oxidative), elevation in extracellular Ca(2+) concentration and biotic factors (elf18, flg22). In good agreement, stimulus- and Ca(2+)-dependent gene activation was not affected by alterations in TPC1 expression. Together with our finding that the loss of TPC1 did not change the activity of hyperpolarization-activated Ca(2+)-permeable channels in the plasma membrane, we conclude that TPC1, under physiological conditions, functions as a vacuolar cation channel without a major impact on cytosolic Ca(2+) homeostasis.

  @article{Ranf:2008:Plant-J:18028262, abstract = {The putative two-pore Ca(2+) channel TPC1 has been suggested to be involved in responses to abiotic and biotic stresses. We show that AtTPC1 co-localizes with the K(+)-selective channel AtTPK1 in the vacuolar membrane. Loss of AtTPC1 abolished Ca(2+)-activated slow vacuolar (SV) currents, which were increased in AtTPC1-over-expressing Arabidopsis compared to the wild-type. A Ca(2+)-insensitive vacuolar cation channel, as yet uncharacterized, could be resolved in tpc1-2 knockout plants. The kinetics of ABA- and CO(2)-induced stomatal closure were similar in wild-type and tpc1-2 knockout plants, excluding a role of SV channels in guard-cell signalling in response to these physiological stimuli. ABA-, K(+)-, and Ca(2+)-dependent root growth phenotypes were not changed in tpc1-2 compared to wild-type plants. Given the permeability of SV channels to mono- and divalent cations, the question arises as to whether TPC1 in vivo represents a pathway for Ca(2+) entry into the cytosol. Ca(2+) responses as measured in aequorin-expressing wild-type, tpc1-2 knockout and TPC1-over-expressing plants disprove a contribution of TPC1 to any of the stimulus-induced Ca(2+) signals tested, including abiotic stresses (cold, hyperosmotic, salt and oxidative), elevation in extracellular Ca(2+) concentration and biotic factors (elf18, flg22). In good agreement, stimulus- and Ca(2+)-dependent gene activation was not affected by alterations in TPC1 expression. Together with our finding that the loss of TPC1 did not change the activity of hyperpolarization-activated Ca(2+)-permeable channels in the plasma membrane, we conclude that TPC1, under physiological conditions, functions as a vacuolar cation channel without a major impact on cytosolic Ca(2+) homeostasis.}, author = {Ranf, S and W{\"u}nnenberg, P and Lee, J and Becker, D and Dunkel, M and Hedrich, R and Scheel, D and Dietrich, P}, journal = {Plant J}, keywords = {myown}, month = {jan}, number = 2, pages = {287-299}, title = {Loss of the vacuolar cation channel, AtTPC1, does not impair Ca2+ signals induced by abiotic and biotic stresses}, volume = 53, year = 2008 }

  %0 Journal Article %1 Ranf:2008:Plant-J:18028262 %A Ranf, S %A W{"u}nnenberg, P %A Lee, J %A Becker, D %A Dunkel, M %A Hedrich, R %A Scheel, D %A Dietrich, P %D 2008 %J Plant J %N 2 %P 287-299 %R 10.1111/j.1365-313X.2007.03342.x %T Loss of the vacuolar cation channel, AtTPC1, does not impair Ca2+ signals induced by abiotic and biotic stresses %U https://www.ncbi.nlm.nih.gov/pubmed/18028262 %V 53 %X The putative two-pore Ca(2+) channel TPC1 has been suggested to be involved in responses to abiotic and biotic stresses. We show that AtTPC1 co-localizes with the K(+)-selective channel AtTPK1 in the vacuolar membrane. Loss of AtTPC1 abolished Ca(2+)-activated slow vacuolar (SV) currents, which were increased in AtTPC1-over-expressing Arabidopsis compared to the wild-type. A Ca(2+)-insensitive vacuolar cation channel, as yet uncharacterized, could be resolved in tpc1-2 knockout plants. The kinetics of ABA- and CO(2)-induced stomatal closure were similar in wild-type and tpc1-2 knockout plants, excluding a role of SV channels in guard-cell signalling in response to these physiological stimuli. ABA-, K(+)-, and Ca(2+)-dependent root growth phenotypes were not changed in tpc1-2 compared to wild-type plants. Given the permeability of SV channels to mono- and divalent cations, the question arises as to whether TPC1 in vivo represents a pathway for Ca(2+) entry into the cytosol. Ca(2+) responses as measured in aequorin-expressing wild-type, tpc1-2 knockout and TPC1-over-expressing plants disprove a contribution of TPC1 to any of the stimulus-induced Ca(2+) signals tested, including abiotic stresses (cold, hyperosmotic, salt and oxidative), elevation in extracellular Ca(2+) concentration and biotic factors (elf18, flg22). In good agreement, stimulus- and Ca(2+)-dependent gene activation was not affected by alterations in TPC1 expression. Together with our finding that the loss of TPC1 did not change the activity of hyperpolarization-activated Ca(2+)-permeable channels in the plasma membrane, we conclude that TPC1, under physiological conditions, functions as a vacuolar cation channel without a major impact on cytosolic Ca(2+) homeostasis.
• Dunkel, M., Latz, A., Schumacher, K., M{"u}ller, T., Becker, D., Hedrich, R. (2008) Targeting of vacuolar membrane localized members of the TPK channel family, Mol Plant, 1(6), 938–949, available: https://doi.org/10.1093/mp/ssn064.
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  Four members of the tandem-pore potassium channel family of Arabidopsis thaliana (TPK1, 2, 3, and 5) reside in the vacuolar membrane, whereas TPK4 is a plasma membrane K(+)-channel. By constructing chimeras between TPK1 and TPK4, we attempted to identify channel domains involved in the trafficking process and found that the TPK1 cytoplasmic C-terminal domain (CT) is critical for the ER- as well as Golgi-sorting steps. Following site-directed mutagenesis, we identified a diacidic motif (DLE) required for ER-export of TPK1. However, this diacidic motif in the C-terminus is not conserved among other members of the TPK family, and TPK3 sorting is independent of its CT. Moreover, the 14-3-3 binding site of TPK1, essential for channel activation, is not involved in channel sorting.

  @article{Dunkel:2008:Mol-Plant:19825594, abstract = {Four members of the tandem-pore potassium channel family of Arabidopsis thaliana (TPK1, 2, 3, and 5) reside in the vacuolar membrane, whereas TPK4 is a plasma membrane K(+)-channel. By constructing chimeras between TPK1 and TPK4, we attempted to identify channel domains involved in the trafficking process and found that the TPK1 cytoplasmic C-terminal domain (CT) is critical for the ER- as well as Golgi-sorting steps. Following site-directed mutagenesis, we identified a diacidic motif (DLE) required for ER-export of TPK1. However, this diacidic motif in the C-terminus is not conserved among other members of the TPK family, and TPK3 sorting is independent of its CT. Moreover, the 14-3-3 binding site of TPK1, essential for channel activation, is not involved in channel sorting.}, author = {Dunkel, M and Latz, A and Schumacher, K and M{\"u}ller, T and Becker, D and Hedrich, R}, journal = {Mol Plant}, keywords = {myown}, month = {nov}, number = 6, pages = {938-949}, title = {Targeting of vacuolar membrane localized members of the TPK channel family}, volume = 1, year = 2008 }

  %0 Journal Article %1 Dunkel:2008:Mol-Plant:19825594 %A Dunkel, M %A Latz, A %A Schumacher, K %A M{"u}ller, T %A Becker, D %A Hedrich, R %D 2008 %J Mol Plant %N 6 %P 938-949 %R 10.1093/mp/ssn064 %T Targeting of vacuolar membrane localized members of the TPK channel family %U https://www.ncbi.nlm.nih.gov/pubmed/19825594 %V 1 %X Four members of the tandem-pore potassium channel family of Arabidopsis thaliana (TPK1, 2, 3, and 5) reside in the vacuolar membrane, whereas TPK4 is a plasma membrane K(+)-channel. By constructing chimeras between TPK1 and TPK4, we attempted to identify channel domains involved in the trafficking process and found that the TPK1 cytoplasmic C-terminal domain (CT) is critical for the ER- as well as Golgi-sorting steps. Following site-directed mutagenesis, we identified a diacidic motif (DLE) required for ER-export of TPK1. However, this diacidic motif in the C-terminus is not conserved among other members of the TPK family, and TPK3 sorting is independent of its CT. Moreover, the 14-3-3 binding site of TPK1, essential for channel activation, is not involved in channel sorting.

• Latz, A., Becker, D., Hekman, M., M{"u}ller, T., Beyhl, D., Marten, I., Eing, C., Fischer, A., Dunkel, M., Bertl, A., Rapp, U.R., Hedrich, R. (2007) TPK1, a Ca(2+)-regulated Arabidopsis vacuole two-pore K(+) channel is activated by 14-3-3 proteins, Plant J, 52(3), 449–459, available: https://doi.org/10.1111/j.1365-313X.2007.03255.x.
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  The vacuole represents a pivotal plant organelle for management of ion homeostasis, storage of proteins and solutes, as well as deposition of cytotoxic compounds. Ion channels, pumps and carriers in the vacuolar membrane under control of cytosolic factors provide for ionic and metabolic homeostasis between this storage organelle and the cytoplasm. Here we show that AtTPK1 (KCO1), a vacuolar membrane localized K(+) channel of the TPK family, interacts with 14-3-3 proteins (general regulating factors, GRFs). Following in planta expression TPK1 and GRF6 co-localize at the vacuolar membrane. Co-localization of wild-type TPK1, but not the TPK1-S42A mutant, indicates that phosphorylation of the 14-3-3 binding motif of TPK1 represents a prerequisite for interaction. Pull-down assays and surface plasmon resonance measurements revealed GRF6 high-affinity interaction with TPK1. Following expression of TPK1 in yeast and isolation of vacuoles, patch-clamp studies identified TPK1 as a voltage-independent and Ca(2+)-activated K(+) channel. Addition of 14-3-3 proteins strongly increased the TPK1 activity in a dose-dependent manner. However, an inverse effect of GRF6 on the activity of the slow-activating vacuolar (SV) channel was observed in mesophyll vacuoles from Arabidopsis thaliana. Thus, TPK1 seems to provide for a Ca(2+)- and 14-3-3-sensitive mechanism capable of controlling cytoplasmic potassium homeostasis in plants.

  @article{Latz:2007:Plant-J:17764516, abstract = {The vacuole represents a pivotal plant organelle for management of ion homeostasis, storage of proteins and solutes, as well as deposition of cytotoxic compounds. Ion channels, pumps and carriers in the vacuolar membrane under control of cytosolic factors provide for ionic and metabolic homeostasis between this storage organelle and the cytoplasm. Here we show that AtTPK1 (KCO1), a vacuolar membrane localized K(+) channel of the TPK family, interacts with 14-3-3 proteins (general regulating factors, GRFs). Following in planta expression TPK1 and GRF6 co-localize at the vacuolar membrane. Co-localization of wild-type TPK1, but not the TPK1-S42A mutant, indicates that phosphorylation of the 14-3-3 binding motif of TPK1 represents a prerequisite for interaction. Pull-down assays and surface plasmon resonance measurements revealed GRF6 high-affinity interaction with TPK1. Following expression of TPK1 in yeast and isolation of vacuoles, patch-clamp studies identified TPK1 as a voltage-independent and Ca(2+)-activated K(+) channel. Addition of 14-3-3 proteins strongly increased the TPK1 activity in a dose-dependent manner. However, an inverse effect of GRF6 on the activity of the slow-activating vacuolar (SV) channel was observed in mesophyll vacuoles from Arabidopsis thaliana. Thus, TPK1 seems to provide for a Ca(2+)- and 14-3-3-sensitive mechanism capable of controlling cytoplasmic potassium homeostasis in plants.}, author = {Latz, A and Becker, D and Hekman, M and M{\"u}ller, T and Beyhl, D and Marten, I and Eing, C and Fischer, A and Dunkel, M and Bertl, A and Rapp, U R and Hedrich, R}, journal = {Plant J}, keywords = {myown}, month = {nov}, number = 3, pages = {449-459}, title = {TPK1, a Ca(2+)-regulated Arabidopsis vacuole two-pore K(+) channel is activated by 14-3-3 proteins}, volume = 52, year = 2007 }

  %0 Journal Article %1 Latz:2007:Plant-J:17764516 %A Latz, A %A Becker, D %A Hekman, M %A M{"u}ller, T %A Beyhl, D %A Marten, I %A Eing, C %A Fischer, A %A Dunkel, M %A Bertl, A %A Rapp, U R %A Hedrich, R %D 2007 %J Plant J %N 3 %P 449-459 %R 10.1111/j.1365-313X.2007.03255.x %T TPK1, a Ca(2+)-regulated Arabidopsis vacuole two-pore K(+) channel is activated by 14-3-3 proteins %U https://www.ncbi.nlm.nih.gov/pubmed/17764516 %V 52 %X The vacuole represents a pivotal plant organelle for management of ion homeostasis, storage of proteins and solutes, as well as deposition of cytotoxic compounds. Ion channels, pumps and carriers in the vacuolar membrane under control of cytosolic factors provide for ionic and metabolic homeostasis between this storage organelle and the cytoplasm. Here we show that AtTPK1 (KCO1), a vacuolar membrane localized K(+) channel of the TPK family, interacts with 14-3-3 proteins (general regulating factors, GRFs). Following in planta expression TPK1 and GRF6 co-localize at the vacuolar membrane. Co-localization of wild-type TPK1, but not the TPK1-S42A mutant, indicates that phosphorylation of the 14-3-3 binding motif of TPK1 represents a prerequisite for interaction. Pull-down assays and surface plasmon resonance measurements revealed GRF6 high-affinity interaction with TPK1. Following expression of TPK1 in yeast and isolation of vacuoles, patch-clamp studies identified TPK1 as a voltage-independent and Ca(2+)-activated K(+) channel. Addition of 14-3-3 proteins strongly increased the TPK1 activity in a dose-dependent manner. However, an inverse effect of GRF6 on the activity of the slow-activating vacuolar (SV) channel was observed in mesophyll vacuoles from Arabidopsis thaliana. Thus, TPK1 seems to provide for a Ca(2+)- and 14-3-3-sensitive mechanism capable of controlling cytoplasmic potassium homeostasis in plants.
• Latz, A., Ivashikina, N., Fischer, S., Ache, P., Sano, T., Becker, D., Deeken, R., Hedrich, R. (2007) In planta AKT2 subunits constitute a pH- and Ca2+-sensitive inward rectifying K+ channel, Planta, 225(5), 1179–1191, available: https://doi.org/10.1007/s00425-006-0428-4.
  • [ Abstract ]
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  Heterologous expression of plant genes in yeast and animal cells represents a common approach to study plant ion channels. When expressed in Xenopus oocytes and COS cells the Arabidopsis Shaker-like K+ channel, AKT2 forms a weakly voltage-dependent channel, blocked by Ca2+ and protons. Channels with these characteristics, however, were not found in AKT2-expressing Arabidopsis cell types. To understand this phenomenon, we employed Agrobacterium-mediated transient transformation to functionally characterise Arabidopsis thaliana channels in Nicotiana benthamiana mesophyll cells. In this expression system we used AtTPK4 as a control for voltage-independent A. thaliana channels. Agrobacteria harbouring GFP-tagged constructs with the coding sequences of AKT2 and AtTPK4 were infiltrated into intact tobacco leaves. With quantitative RT-PCR analyses channel transcripts of AKT2 and AtTPK4 were determined in transformed leaves. These results were confirmed by Western blots with V5 epitope-tagged AKT2 and AtTPK4 proteins, showing that the channel protein was indeed synthesised. For functional analysis of these channels, mesophyll protoplasts were isolated from infiltrated leaf sections. Patch-clamp studies revealed that AKT2 channels in mesophyll protoplasts retained Ca2+ and pH sensitivity, characteristics of the heterologously expressed protein, but displayed pronounced differences in voltage-dependence and kinetics. AKT2-transformed mesophyll cells, displayed inward-rectifying, rather than voltage-independent K+ channels, initially characterised in AKT2-expressing animal cells. In contrast, AtTPK4 showed the same electrophysiological characteristics both, in oocytes and plant cells. Our data suggest that heterologous systems do not always possess all regulatory components for functional expression of plant channels. Therefore, transient expression of plant proteins in planta provides an additional research tool for rapid biophysical analysis of plant ion channels.

  @article{Latz:2007:Planta:17146665, abstract = {Heterologous expression of plant genes in yeast and animal cells represents a common approach to study plant ion channels. When expressed in Xenopus oocytes and COS cells the Arabidopsis Shaker-like K+ channel, AKT2 forms a weakly voltage-dependent channel, blocked by Ca2+ and protons. Channels with these characteristics, however, were not found in AKT2-expressing Arabidopsis cell types. To understand this phenomenon, we employed Agrobacterium-mediated transient transformation to functionally characterise Arabidopsis thaliana channels in Nicotiana benthamiana mesophyll cells. In this expression system we used AtTPK4 as a control for voltage-independent A. thaliana channels. Agrobacteria harbouring GFP-tagged constructs with the coding sequences of AKT2 and AtTPK4 were infiltrated into intact tobacco leaves. With quantitative RT-PCR analyses channel transcripts of AKT2 and AtTPK4 were determined in transformed leaves. These results were confirmed by Western blots with V5 epitope-tagged AKT2 and AtTPK4 proteins, showing that the channel protein was indeed synthesised. For functional analysis of these channels, mesophyll protoplasts were isolated from infiltrated leaf sections. Patch-clamp studies revealed that AKT2 channels in mesophyll protoplasts retained Ca2+ and pH sensitivity, characteristics of the heterologously expressed protein, but displayed pronounced differences in voltage-dependence and kinetics. AKT2-transformed mesophyll cells, displayed inward-rectifying, rather than voltage-independent K+ channels, initially characterised in AKT2-expressing animal cells. In contrast, AtTPK4 showed the same electrophysiological characteristics both, in oocytes and plant cells. Our data suggest that heterologous systems do not always possess all regulatory components for functional expression of plant channels. Therefore, transient expression of plant proteins in planta provides an additional research tool for rapid biophysical analysis of plant ion channels.}, author = {Latz, A and Ivashikina, N and Fischer, S and Ache, P and Sano, T and Becker, D and Deeken, R and Hedrich, R}, journal = {Planta}, keywords = {myown}, month = {apr}, number = 5, pages = {1179-1191}, title = {In planta AKT2 subunits constitute a pH- and Ca2+-sensitive inward rectifying K+ channel}, volume = 225, year = 2007 }

  %0 Journal Article %1 Latz:2007:Planta:17146665 %A Latz, A %A Ivashikina, N %A Fischer, S %A Ache, P %A Sano, T %A Becker, D %A Deeken, R %A Hedrich, R %D 2007 %J Planta %N 5 %P 1179-1191 %R 10.1007/s00425-006-0428-4 %T In planta AKT2 subunits constitute a pH- and Ca2+-sensitive inward rectifying K+ channel %U https://www.ncbi.nlm.nih.gov/pubmed/17146665 %V 225 %X Heterologous expression of plant genes in yeast and animal cells represents a common approach to study plant ion channels. When expressed in Xenopus oocytes and COS cells the Arabidopsis Shaker-like K+ channel, AKT2 forms a weakly voltage-dependent channel, blocked by Ca2+ and protons. Channels with these characteristics, however, were not found in AKT2-expressing Arabidopsis cell types. To understand this phenomenon, we employed Agrobacterium-mediated transient transformation to functionally characterise Arabidopsis thaliana channels in Nicotiana benthamiana mesophyll cells. In this expression system we used AtTPK4 as a control for voltage-independent A. thaliana channels. Agrobacteria harbouring GFP-tagged constructs with the coding sequences of AKT2 and AtTPK4 were infiltrated into intact tobacco leaves. With quantitative RT-PCR analyses channel transcripts of AKT2 and AtTPK4 were determined in transformed leaves. These results were confirmed by Western blots with V5 epitope-tagged AKT2 and AtTPK4 proteins, showing that the channel protein was indeed synthesised. For functional analysis of these channels, mesophyll protoplasts were isolated from infiltrated leaf sections. Patch-clamp studies revealed that AKT2 channels in mesophyll protoplasts retained Ca2+ and pH sensitivity, characteristics of the heterologously expressed protein, but displayed pronounced differences in voltage-dependence and kinetics. AKT2-transformed mesophyll cells, displayed inward-rectifying, rather than voltage-independent K+ channels, initially characterised in AKT2-expressing animal cells. In contrast, AtTPK4 showed the same electrophysiological characteristics both, in oocytes and plant cells. Our data suggest that heterologous systems do not always possess all regulatory components for functional expression of plant channels. Therefore, transient expression of plant proteins in planta provides an additional research tool for rapid biophysical analysis of plant ion channels.
• Sukhorukov, V., Endter, J., Zimmermann, D., Shirakashi, R., Fehrmann, S., Kiesel, M., Reuss, R., Becker, D., Hedrich, R., Bamberg, E., Roitsch, T., Zimmermann, U. (2007) Mechanisms of Electrically Mediated Cytosolic Ca2+ Transients in Aequorin-Transformed Tobacco Cells, Biophysical Journal, 93(9), 3324–3337, available: https://doi.org/http://dx.doi.org/10.1529/biophysj.107.110783.
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  @article{SUKHORUKOV20073324, author = {Sukhorukov, V.L. and Endter, J.M. and Zimmermann, D. and Shirakashi, R. and Fehrmann, S. and Kiesel, M. and Reuss, R. and Becker, D. and Hedrich, R. and Bamberg, E. and Roitsch, Th. and Zimmermann, U.}, journal = {Biophysical Journal}, keywords = {myown}, number = 9, pages = {3324 - 3337}, title = {Mechanisms of Electrically Mediated Cytosolic Ca2+ Transients in Aequorin-Transformed Tobacco Cells}, volume = 93, year = 2007 }

  %0 Journal Article %1 SUKHORUKOV20073324 %A Sukhorukov, V.L. %A Endter, J.M. %A Zimmermann, D. %A Shirakashi, R. %A Fehrmann, S. %A Kiesel, M. %A Reuss, R. %A Becker, D. %A Hedrich, R. %A Bamberg, E. %A Roitsch, Th. %A Zimmermann, U. %D 2007 %J Biophysical Journal %N 9 %P 3324 - 3337 %R http://dx.doi.org/10.1529/biophysj.107.110783 %T Mechanisms of Electrically Mediated Cytosolic Ca2+ Transients in Aequorin-Transformed Tobacco Cells %U http://www.sciencedirect.com/science/article/pii/S0006349507715862 %V 93
• Sano, T., Becker, D., Ivashikina, N., Wegner, L.H., Zimmermann, U., Roelfsema, M.R., Nagata, T., Hedrich, R. (2007) Plant cells must pass a K+ threshold to re-enter the cell cycle, Plant J, 50(3), 401–413, available: https://doi.org/10.1111/j.1365-313X.2007.03071.x.
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  Potassium is an inevitable component of plant life, and potassium channels play a pivotal role in plant growth and development. The role of potassium and of K(+) channels in plant cell division and cell-cycle progression, however, has not been determined so far. K(+) channel blocker studies with synchronized tobacco BY-2 cells revealed that K(+) uptake is required for proper cell-cycle progression during the transition from G(1) to S phase. Electrophysiological studies (patch-clamp and voltage-clamp techniques) showed a cell-cycle dependency of K(+) channel activities and reduced driving force for K(+) uptake in dividing cells. Among the four Shaker-like K(+) channel genes expressed in BY-2 cells, NKT1 represents an inwardly rectifying K(+) channel that mediates K(+) uptake. NKT1 is transcriptionally induced during G(1) phase, while transcripts of the outward-rectifier NTORK1 dominate S phase. Elongating BY-2 cells appeared hyperpolarized (-101 +/- 11 mV), and had elevated osmotic pressure and approximately twice the turgor pressure when compared with depolarized (-64 +/- 8 mV) dividing cells. This indicates that cells have to gain a threshold K(+) level to re-enter the cell cycle. Based on these findings, turgor regulation through modulation of K(+) channel density in plant cell division and cell-cycle progression is discussed.

  @article{Sano:2007:Plant-J:17425714, abstract = {Potassium is an inevitable component of plant life, and potassium channels play a pivotal role in plant growth and development. The role of potassium and of K(+) channels in plant cell division and cell-cycle progression, however, has not been determined so far. K(+) channel blocker studies with synchronized tobacco BY-2 cells revealed that K(+) uptake is required for proper cell-cycle progression during the transition from G(1) to S phase. Electrophysiological studies (patch-clamp and voltage-clamp techniques) showed a cell-cycle dependency of K(+) channel activities and reduced driving force for K(+) uptake in dividing cells. Among the four Shaker-like K(+) channel genes expressed in BY-2 cells, NKT1 represents an inwardly rectifying K(+) channel that mediates K(+) uptake. NKT1 is transcriptionally induced during G(1) phase, while transcripts of the outward-rectifier NTORK1 dominate S phase. Elongating BY-2 cells appeared hyperpolarized (-101 +/- 11 mV), and had elevated osmotic pressure and approximately twice the turgor pressure when compared with depolarized (-64 +/- 8 mV) dividing cells. This indicates that cells have to gain a threshold K(+) level to re-enter the cell cycle. Based on these findings, turgor regulation through modulation of K(+) channel density in plant cell division and cell-cycle progression is discussed.}, author = {Sano, T and Becker, D and Ivashikina, N and Wegner, L H and Zimmermann, U and Roelfsema, M R and Nagata, T and Hedrich, R}, journal = {Plant J}, keywords = {myown}, month = {may}, number = 3, pages = {401-413}, title = {Plant cells must pass a K+ threshold to re-enter the cell cycle}, volume = 50, year = 2007 }

  %0 Journal Article %1 Sano:2007:Plant-J:17425714 %A Sano, T %A Becker, D %A Ivashikina, N %A Wegner, L H %A Zimmermann, U %A Roelfsema, M R %A Nagata, T %A Hedrich, R %D 2007 %J Plant J %N 3 %P 401-413 %R 10.1111/j.1365-313X.2007.03071.x %T Plant cells must pass a K+ threshold to re-enter the cell cycle %U https://www.ncbi.nlm.nih.gov/pubmed/17425714 %V 50 %X Potassium is an inevitable component of plant life, and potassium channels play a pivotal role in plant growth and development. The role of potassium and of K(+) channels in plant cell division and cell-cycle progression, however, has not been determined so far. K(+) channel blocker studies with synchronized tobacco BY-2 cells revealed that K(+) uptake is required for proper cell-cycle progression during the transition from G(1) to S phase. Electrophysiological studies (patch-clamp and voltage-clamp techniques) showed a cell-cycle dependency of K(+) channel activities and reduced driving force for K(+) uptake in dividing cells. Among the four Shaker-like K(+) channel genes expressed in BY-2 cells, NKT1 represents an inwardly rectifying K(+) channel that mediates K(+) uptake. NKT1 is transcriptionally induced during G(1) phase, while transcripts of the outward-rectifier NTORK1 dominate S phase. Elongating BY-2 cells appeared hyperpolarized (-101 +/- 11 mV), and had elevated osmotic pressure and approximately twice the turgor pressure when compared with depolarized (-64 +/- 8 mV) dividing cells. This indicates that cells have to gain a threshold K(+) level to re-enter the cell cycle. Based on these findings, turgor regulation through modulation of K(+) channel density in plant cell division and cell-cycle progression is discussed.
• Englert, M., Latz, A., Becker, D., Gimple, O., Beier, H., Akama, K. (2007) Plant pre-tRNA splicing enzymes are targeted to multiple cellular compartments, Biochimie, 89(11), 1351–1365, available: https://doi.org/http://dx.doi.org/10.1016/j.biochi.2007.06.014.
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  @article{ENGLERT20071351, author = {Englert, Markus and Latz, Andreas and Becker, Dirk and Gimple, Olaf and Beier, Hildburg and Akama, Kazuhito}, journal = {Biochimie}, keywords = {myown}, number = 11, pages = {1351 - 1365}, title = {Plant pre-tRNA splicing enzymes are targeted to multiple cellular compartments}, volume = 89, year = 2007 }

  %0 Journal Article %1 ENGLERT20071351 %A Englert, Markus %A Latz, Andreas %A Becker, Dirk %A Gimple, Olaf %A Beier, Hildburg %A Akama, Kazuhito %D 2007 %J Biochimie %N 11 %P 1351 - 1365 %R http://dx.doi.org/10.1016/j.biochi.2007.06.014 %T Plant pre-tRNA splicing enzymes are targeted to multiple cellular compartments %U http://www.sciencedirect.com/science/article/pii/S0300908407001666 %V 89

• Yu, L., Becker, D., Levi, H., Moshelion, M., Hedrich, R., Lotan, I., Moran, A., Pick, U., Naveh, L., Libal, Y., Moran, N. (2006) Phosphorylation of SPICK2, an AKT2 channel homologue from Samanea motor cells, J Exp Bot, 57(14), 3583–3594, available: https://doi.org/10.1093/jxb/erl104.
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  SPICK2, a homologue of the weakly-inward-rectifying Shaker-like Arabidopsis K channel, AKT2, is a candidate K+-influx channel participating in light- and clock-regulated leaf movements of the legume, Samanea saman. Light and the biological clock regulate the in situ K+-influx channel activity differentially in extensor and flexor halves of the pulvinus (the S. saman leaf motor organ), and also-though differently-the transcript level of SPICK2 in the pulvinus. This disparity between the in situ channel activity versus its candidate transcript, along with the sequence analysis of SPICK2, suggest an in situ regulation of the activity of SPICK2, possibly by phosphorylation and/or by interaction with cAMP. Consistent with this (i) the activity of the voltage-dependent K+-selective fraction of the inward current in extensor and flexor cells was affected differentially in whole-cell patch-clamp assays promoting phosphorylation (using the protein phosphatase inhibitor okadaic acid); (ii) several proteins in isolated plasma membrane-enriched vesicles of the motor cells underwent phosphorylation without an added kinase in conditions similar to patch-clamp; and (iii) the SPICK2 protein was phosphorylated in vitro by the catalytic subunit of the broad-range cAMP-dependent protein kinase. All of these results are consistent with the notion that SPICK2 is the K+-influx channel, and is regulated in vivo directly by phosphorylation.

  @article{Yu:2006:J-Exp-Bot:16968880, abstract = {SPICK2, a homologue of the weakly-inward-rectifying Shaker-like Arabidopsis K channel, AKT2, is a candidate K+-influx channel participating in light- and clock-regulated leaf movements of the legume, Samanea saman. Light and the biological clock regulate the in situ K+-influx channel activity differentially in extensor and flexor halves of the pulvinus (the S. saman leaf motor organ), and also-though differently-the transcript level of SPICK2 in the pulvinus. This disparity between the in situ channel activity versus its candidate transcript, along with the sequence analysis of SPICK2, suggest an in situ regulation of the activity of SPICK2, possibly by phosphorylation and/or by interaction with cAMP. Consistent with this (i) the activity of the voltage-dependent K+-selective fraction of the inward current in extensor and flexor cells was affected differentially in whole-cell patch-clamp assays promoting phosphorylation (using the protein phosphatase inhibitor okadaic acid); (ii) several proteins in isolated plasma membrane-enriched vesicles of the motor cells underwent phosphorylation without an added kinase in conditions similar to patch-clamp; and (iii) the SPICK2 protein was phosphorylated in vitro by the catalytic subunit of the broad-range cAMP-dependent protein kinase. All of these results are consistent with the notion that SPICK2 is the K+-influx channel, and is regulated in vivo directly by phosphorylation.}, author = {Yu, L and Becker, D and Levi, H and Moshelion, M and Hedrich, R and Lotan, I and Moran, A and Pick, U and Naveh, L and Libal, Y and Moran, N}, journal = {J Exp Bot}, keywords = {myown}, number = 14, pages = {3583-3594}, title = {Phosphorylation of SPICK2, an AKT2 channel homologue from Samanea motor cells}, volume = 57, year = 2006 }

  %0 Journal Article %1 Yu:2006:J-Exp-Bot:16968880 %A Yu, L %A Becker, D %A Levi, H %A Moshelion, M %A Hedrich, R %A Lotan, I %A Moran, A %A Pick, U %A Naveh, L %A Libal, Y %A Moran, N %D 2006 %J J Exp Bot %N 14 %P 3583-3594 %R 10.1093/jxb/erl104 %T Phosphorylation of SPICK2, an AKT2 channel homologue from Samanea motor cells %U https://www.ncbi.nlm.nih.gov/pubmed/16968880 %V 57 %X SPICK2, a homologue of the weakly-inward-rectifying Shaker-like Arabidopsis K channel, AKT2, is a candidate K+-influx channel participating in light- and clock-regulated leaf movements of the legume, Samanea saman. Light and the biological clock regulate the in situ K+-influx channel activity differentially in extensor and flexor halves of the pulvinus (the S. saman leaf motor organ), and also-though differently-the transcript level of SPICK2 in the pulvinus. This disparity between the in situ channel activity versus its candidate transcript, along with the sequence analysis of SPICK2, suggest an in situ regulation of the activity of SPICK2, possibly by phosphorylation and/or by interaction with cAMP. Consistent with this (i) the activity of the voltage-dependent K+-selective fraction of the inward current in extensor and flexor cells was affected differentially in whole-cell patch-clamp assays promoting phosphorylation (using the protein phosphatase inhibitor okadaic acid); (ii) several proteins in isolated plasma membrane-enriched vesicles of the motor cells underwent phosphorylation without an added kinase in conditions similar to patch-clamp; and (iii) the SPICK2 protein was phosphorylated in vitro by the catalytic subunit of the broad-range cAMP-dependent protein kinase. All of these results are consistent with the notion that SPICK2 is the K+-influx channel, and is regulated in vivo directly by phosphorylation.
• Hedrich, R., Becker, D. (2006) Ion Channels Meet Cell Cycle Control, in Nagata, T., Matsuoka, K. and Inz{’e}, D., eds., Tobacco BY-2 Cells: From Cellular Dynamics to Omics, Berlin, Heidelberg: Springer Berlin Heidelberg, 65–78, available: https://doi.org/10.1007/3-540-32674-X_5.
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  @inbook{Hedrich2006, address = {Berlin, Heidelberg}, author = {Hedrich, R. and Becker, D.}, booktitle = {Tobacco BY-2 Cells: From Cellular Dynamics to Omics}, editor = {Nagata, Toshiyuki and Matsuoka, Ken and Inz{\'e}, Dirk}, keywords = {myown}, pages = {65–78}, publisher = {Springer Berlin Heidelberg}, title = {Ion Channels Meet Cell Cycle Control}, year = 2006 }

  %0 Book Section %1 Hedrich2006 %A Hedrich, R. %A Becker, D. %B Tobacco BY-2 Cells: From Cellular Dynamics to Omics %C Berlin, Heidelberg %D 2006 %E Nagata, Toshiyuki %E Matsuoka, Ken %E Inz{'e}, Dirk %I Springer Berlin Heidelberg %P 65--78 %R 10.1007/3-540-32674-X_5 %T Ion Channels Meet Cell Cycle Control %U http://dx.doi.org/10.1007/3-540-32674-X_5 %@ 978-3-540-32674-8

• Meyerhoff, O., M{"u}ller, K., Roelfsema, M.R., Latz, A., Lacombe, B., Hedrich, R., Dietrich, P., Becker, D. (2005) AtGLR3.4, a glutamate receptor channel-like gene is sensitive to touch and cold, Planta, 222(3), 418–427, available: https://doi.org/10.1007/s00425-005-1551-3.
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  The Arabidopsis genome encodes for 20 members of putative ligand-gated channels, termed glutamate receptors (GLR). Despite the fact that initial studies suggested a role for GLRs in various aspects of photomorphogenesis, calcium homeostasis or aluminium toxicity, their functional properties and physiological role in plants remain elusive. Here, we have focussed on AtGLR3.4, which is ubiquitously expressed in Arabidopsis including roots, vascular bundles, mesophyll cells and guard cells. AtGLR3.4 encodes a glutamate-, touch-, and cold-sensitive member of this gene family. Abiotic stress stimuli such as touch, osmotic stress or cold stimulated AtGLR3.4 expression in an abscisic acid-independent, but calcium-dependent manner. In plants expressing the Ca(2+) -reporter apoaequorin, glutamate as well as cold elicited cytosolic calcium elevations. Upon glutamate treatment of mesophyll cells, the plasma membrane depolarised by about 120 mV. Both glutamate responses were transient in nature, sensitive to glutamate receptor antagonists, and were subject to desensitisation. One hour after eliciting the first calcium signal, a 50% recovery from desensitisation was observed, reflecting the stimulus-induced fast activation of AtGLR3.4 transcription. We thus conclude that AtGLR3.4 in particular and GLRs in general could play an important role in the Ca(2+) -based, fast transmission of environmental stress.

  @article{Meyerhoff:2005:Planta:15864638, abstract = {The Arabidopsis genome encodes for 20 members of putative ligand-gated channels, termed glutamate receptors (GLR). Despite the fact that initial studies suggested a role for GLRs in various aspects of photomorphogenesis, calcium homeostasis or aluminium toxicity, their functional properties and physiological role in plants remain elusive. Here, we have focussed on AtGLR3.4, which is ubiquitously expressed in Arabidopsis including roots, vascular bundles, mesophyll cells and guard cells. AtGLR3.4 encodes a glutamate-, touch-, and cold-sensitive member of this gene family. Abiotic stress stimuli such as touch, osmotic stress or cold stimulated AtGLR3.4 expression in an abscisic acid-independent, but calcium-dependent manner. In plants expressing the Ca(2+) -reporter apoaequorin, glutamate as well as cold elicited cytosolic calcium elevations. Upon glutamate treatment of mesophyll cells, the plasma membrane depolarised by about 120 mV. Both glutamate responses were transient in nature, sensitive to glutamate receptor antagonists, and were subject to desensitisation. One hour after eliciting the first calcium signal, a 50% recovery from desensitisation was observed, reflecting the stimulus-induced fast activation of AtGLR3.4 transcription. We thus conclude that AtGLR3.4 in particular and GLRs in general could play an important role in the Ca(2+) -based, fast transmission of environmental stress.}, author = {Meyerhoff, O and M{\"u}ller, K and Roelfsema, M R and Latz, A and Lacombe, B and Hedrich, R and Dietrich, P and Becker, D}, journal = {Planta}, keywords = {myown}, month = {oct}, number = 3, pages = {418-427}, title = {AtGLR3.4, a glutamate receptor channel-like gene is sensitive to touch and cold}, volume = 222, year = 2005 }

  %0 Journal Article %1 Meyerhoff:2005:Planta:15864638 %A Meyerhoff, O %A M{"u}ller, K %A Roelfsema, M R %A Latz, A %A Lacombe, B %A Hedrich, R %A Dietrich, P %A Becker, D %D 2005 %J Planta %N 3 %P 418-427 %R 10.1007/s00425-005-1551-3 %T AtGLR3.4, a glutamate receptor channel-like gene is sensitive to touch and cold %U https://www.ncbi.nlm.nih.gov/pubmed/15864638 %V 222 %X The Arabidopsis genome encodes for 20 members of putative ligand-gated channels, termed glutamate receptors (GLR). Despite the fact that initial studies suggested a role for GLRs in various aspects of photomorphogenesis, calcium homeostasis or aluminium toxicity, their functional properties and physiological role in plants remain elusive. Here, we have focussed on AtGLR3.4, which is ubiquitously expressed in Arabidopsis including roots, vascular bundles, mesophyll cells and guard cells. AtGLR3.4 encodes a glutamate-, touch-, and cold-sensitive member of this gene family. Abiotic stress stimuli such as touch, osmotic stress or cold stimulated AtGLR3.4 expression in an abscisic acid-independent, but calcium-dependent manner. In plants expressing the Ca(2+) -reporter apoaequorin, glutamate as well as cold elicited cytosolic calcium elevations. Upon glutamate treatment of mesophyll cells, the plasma membrane depolarised by about 120 mV. Both glutamate responses were transient in nature, sensitive to glutamate receptor antagonists, and were subject to desensitisation. One hour after eliciting the first calcium signal, a 50% recovery from desensitisation was observed, reflecting the stimulus-induced fast activation of AtGLR3.4 transcription. We thus conclude that AtGLR3.4 in particular and GLRs in general could play an important role in the Ca(2+) -based, fast transmission of environmental stress.
• B{\"u}chsensch{"u}tz, K., Marten, I., Becker, D., Philippar, K., Ache, P., Hedrich, R. (2005) Differential expression of K+ channels between guard cells and subsidiary cells within the maize stomatal complex, Planta, 222(6), 968–976, available: https://doi.org/10.1007/s00425-005-0038-6.
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  Grass stomata are characterized by dumbbell-shaped guard cells forming a complex with a pair of specialized epidermal cells, the subsidiary cells. Stomatal movement is accomplished by a reversible exchange of potassium and chloride between these two cell types. To gain insight into the molecular machinery involved in K+ transport within the stomatal complex of Zea mays, we determined the spatial and temporal expression pattern of potassium channels in the maize leaf. KZM2 and ZORK were isolated and identified as new members of the plant Shaker K+ channel family. Northern blot analysis identified fully developed leaves as the predominant site of KZM2 expression. Following enzymatic digestion and separation of leaf tissue into epidermal, mesophyll, and vascular fractions, KZM2 and ZORK transcripts were localized in the epidermis. Using a collection of individually isolated guard cell or subsidiary cell protoplasts, ZORK transcripts were found in both cell types while KZM2 was exclusively expressed in the guard cell population. The previously identified K+ channel genes ZMK1 and KZM1 were expressed in subsidiary cells and guard cells, respectively, whereas ZMK2 transcripts were not detected. These data indicate that the interaction between subsidiary cells and guard cells is based on overlapping as well as differential expression of K+ channels in the two cell types of the maize stomatal complex.

  @article{Buchsenschutz:2005:Planta:16021501, abstract = {Grass stomata are characterized by dumbbell-shaped guard cells forming a complex with a pair of specialized epidermal cells, the subsidiary cells. Stomatal movement is accomplished by a reversible exchange of potassium and chloride between these two cell types. To gain insight into the molecular machinery involved in K+ transport within the stomatal complex of Zea mays, we determined the spatial and temporal expression pattern of potassium channels in the maize leaf. KZM2 and ZORK were isolated and identified as new members of the plant Shaker K+ channel family. Northern blot analysis identified fully developed leaves as the predominant site of KZM2 expression. Following enzymatic digestion and separation of leaf tissue into epidermal, mesophyll, and vascular fractions, KZM2 and ZORK transcripts were localized in the epidermis. Using a collection of individually isolated guard cell or subsidiary cell protoplasts, ZORK transcripts were found in both cell types while KZM2 was exclusively expressed in the guard cell population. The previously identified K+ channel genes ZMK1 and KZM1 were expressed in subsidiary cells and guard cells, respectively, whereas ZMK2 transcripts were not detected. These data indicate that the interaction between subsidiary cells and guard cells is based on overlapping as well as differential expression of K+ channels in the two cell types of the maize stomatal complex.}, author = {B{\"u}chsensch{\"u}tz, K and Marten, I and Becker, D and Philippar, K and Ache, P and Hedrich, R}, journal = {Planta}, keywords = {myown}, month = {dec}, number = 6, pages = {968-976}, title = {Differential expression of K+ channels between guard cells and subsidiary cells within the maize stomatal complex}, volume = 222, year = 2005 }

  %0 Journal Article %1 Buchsenschutz:2005:Planta:16021501 %A B{\"u}chsensch{"u}tz, K %A Marten, I %A Becker, D %A Philippar, K %A Ache, P %A Hedrich, R %D 2005 %J Planta %N 6 %P 968-976 %R 10.1007/s00425-005-0038-6 %T Differential expression of K+ channels between guard cells and subsidiary cells within the maize stomatal complex %U https://www.ncbi.nlm.nih.gov/pubmed/16021501 %V 222 %X Grass stomata are characterized by dumbbell-shaped guard cells forming a complex with a pair of specialized epidermal cells, the subsidiary cells. Stomatal movement is accomplished by a reversible exchange of potassium and chloride between these two cell types. To gain insight into the molecular machinery involved in K+ transport within the stomatal complex of Zea mays, we determined the spatial and temporal expression pattern of potassium channels in the maize leaf. KZM2 and ZORK were isolated and identified as new members of the plant Shaker K+ channel family. Northern blot analysis identified fully developed leaves as the predominant site of KZM2 expression. Following enzymatic digestion and separation of leaf tissue into epidermal, mesophyll, and vascular fractions, KZM2 and ZORK transcripts were localized in the epidermis. Using a collection of individually isolated guard cell or subsidiary cell protoplasts, ZORK transcripts were found in both cell types while KZM2 was exclusively expressed in the guard cell population. The previously identified K+ channel genes ZMK1 and KZM1 were expressed in subsidiary cells and guard cells, respectively, whereas ZMK2 transcripts were not detected. These data indicate that the interaction between subsidiary cells and guard cells is based on overlapping as well as differential expression of K+ channels in the two cell types of the maize stomatal complex.

• Becker, D., Geiger, D., Dunkel, M., Roller, A., Bertl, A., Latz, A., Carpaneto, A., Dietrich, P., Roelfsema, M.R.G., Voelker, C., Schmidt, D., Mueller-Roeber, B., Czempinski, K., Hedrich, R. (2004) AtTPK4, an Arabidopsis tandem-pore K+ channel, poised to control the pollen membrane voltage in a pH- and Ca2+-dependent manner, Proceedings of the National Academy of Sciences of the United States of America, 101(44), 15621–15626, available: https://doi.org/10.1073/pnas.0401502101.
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  The Arabidopsis tandem-pore K+ (TPK) channels displaying four transmembrane domains and two pore regions share structural homologies with their animal counterparts of the KCNK family. In contrast to the Shaker-like Arabidopsis channels (six transmembrane domains/one pore region), the functional properties and the biological role of plant TPK channels have not been elucidated yet. Here, we show that AtTPK4 (KCO4) localizes to the plasma membrane and is predominantly expressed in pollen. AtTPK4 (KCO4) resembles the electrical properties of a voltage-independent K+ channel after expression in Xenopus oocytes and yeast. Hyperpolarizing as well as depolarizing membrane voltages elicited instantaneous K+ currents, which were blocked by extracellular calcium and cytoplasmic protons. Functional complementation assays using a K+ transport-deficient yeast confirmed the biophysical and pharmacological properties of the AtTPK4 channel. The features of AtTPK4 point toward a role in potassium homeostasis and membrane voltage control of the growing pollen tube. Thus, AtTPK4 represents a member of plant tandem-pore-K+ channels, resembling the characteristics of its animal counterparts as well as plant-specific features with respect to modulation of channel activity by acidosis and calcium.

  @article{Becker02112004, abstract = {The Arabidopsis tandem-pore K+ (TPK) channels displaying four transmembrane domains and two pore regions share structural homologies with their animal counterparts of the KCNK family. In contrast to the Shaker-like Arabidopsis channels (six transmembrane domains/one pore region), the functional properties and the biological role of plant TPK channels have not been elucidated yet. Here, we show that AtTPK4 (KCO4) localizes to the plasma membrane and is predominantly expressed in pollen. AtTPK4 (KCO4) resembles the electrical properties of a voltage-independent K+ channel after expression in Xenopus oocytes and yeast. Hyperpolarizing as well as depolarizing membrane voltages elicited instantaneous K+ currents, which were blocked by extracellular calcium and cytoplasmic protons. Functional complementation assays using a K+ transport-deficient yeast confirmed the biophysical and pharmacological properties of the AtTPK4 channel. The features of AtTPK4 point toward a role in potassium homeostasis and membrane voltage control of the growing pollen tube. Thus, AtTPK4 represents a member of plant tandem-pore-K+ channels, resembling the characteristics of its animal counterparts as well as plant-specific features with respect to modulation of channel activity by acidosis and calcium.}, author = {Becker, D. and Geiger, D. and Dunkel, M. and Roller, A. and Bertl, A. and Latz, A. and Carpaneto, A. and Dietrich, P. and Roelfsema, M. R. G. and Voelker, C. and Schmidt, D. and Mueller-Roeber, B. and Czempinski, K. and Hedrich, R.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, keywords = {myown}, number = 44, pages = {15621-15626}, title = {AtTPK4, an Arabidopsis tandem-pore K+ channel, poised to control the pollen membrane voltage in a pH- and Ca2+-dependent manner}, volume = 101, year = 2004 }

  %0 Journal Article %1 Becker02112004 %A Becker, D. %A Geiger, D. %A Dunkel, M. %A Roller, A. %A Bertl, A. %A Latz, A. %A Carpaneto, A. %A Dietrich, P. %A Roelfsema, M. R. G. %A Voelker, C. %A Schmidt, D. %A Mueller-Roeber, B. %A Czempinski, K. %A Hedrich, R. %D 2004 %J Proceedings of the National Academy of Sciences of the United States of America %N 44 %P 15621-15626 %R 10.1073/pnas.0401502101 %T AtTPK4, an Arabidopsis tandem-pore K+ channel, poised to control the pollen membrane voltage in a pH- and Ca2+-dependent manner %U http://www.pnas.org/content/101/44/15621.abstract %V 101 %X The Arabidopsis tandem-pore K+ (TPK) channels displaying four transmembrane domains and two pore regions share structural homologies with their animal counterparts of the KCNK family. In contrast to the Shaker-like Arabidopsis channels (six transmembrane domains/one pore region), the functional properties and the biological role of plant TPK channels have not been elucidated yet. Here, we show that AtTPK4 (KCO4) localizes to the plasma membrane and is predominantly expressed in pollen. AtTPK4 (KCO4) resembles the electrical properties of a voltage-independent K+ channel after expression in Xenopus oocytes and yeast. Hyperpolarizing as well as depolarizing membrane voltages elicited instantaneous K+ currents, which were blocked by extracellular calcium and cytoplasmic protons. Functional complementation assays using a K+ transport-deficient yeast confirmed the biophysical and pharmacological properties of the AtTPK4 channel. The features of AtTPK4 point toward a role in potassium homeostasis and membrane voltage control of the growing pollen tube. Thus, AtTPK4 represents a member of plant tandem-pore-K+ channels, resembling the characteristics of its animal counterparts as well as plant-specific features with respect to modulation of channel activity by acidosis and calcium.

• Becker, D., Hoth, S., Ache, P., Wenkel, S., Roelfsema, M.R., Meyerhoff, O., Hartung, W., Hedrich, R. (2003) Regulation of the ABA-sensitive Arabidopsis potassium channel gene GORK in response to water stress, FEBS Lett, 554(1-2), 119–126, available: https://www.ncbi.nlm.nih.gov/pubmed/14596925.
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  The phytohormone abscisic acid (ABA) regulates many stress-related processes in plants. In this context ABA mediates the responsiveness of plants to environmental stresses such as drought, cold or salt. In response to water stress, ABA induces stomatal closure by activating Ca2+, K+ and anion channels in guard cells. To understand the signalling pathways that regulate these turgor control elements, we studied the transcriptional control of the K+ release channel gene GORK that is expressed in guard cells, roots and vascular tissue. GORK transcription was up-regulated upon onset of drought, salt stress and cold. The wilting hormone ABA that integrates responses to these stimuli induced GORK expression in seedlings in a time- and concentration-dependent manner and this induction was dependent on extracellular Ca2+. ABA-responsive expression of GORK was impaired in the ABA-insensitive mutants abi1-1 and abi2-1, indicating that these protein phosphatases are regulators of GORK expression. Application of ABA to suspension-cultured cells for 2 min followed by a 4 h chase was sufficient to manifest transcriptional activation of the K+ channel gene. As predicted for a process involved in drought adaptation, only 12-24 h after the release of the stress hormone, GORK mRNA slowly decreased. In contrast to other tissues, GORK expression as well as K+(out) channel activity in guard cells is ABA insensitive, allowing the plant to adjust stomatal movement and water status control separately.

  @article{Becker:2003:FEBS-Lett:14596925, abstract = {The phytohormone abscisic acid (ABA) regulates many stress-related processes in plants. In this context ABA mediates the responsiveness of plants to environmental stresses such as drought, cold or salt. In response to water stress, ABA induces stomatal closure by activating Ca2+, K+ and anion channels in guard cells. To understand the signalling pathways that regulate these turgor control elements, we studied the transcriptional control of the K+ release channel gene GORK that is expressed in guard cells, roots and vascular tissue. GORK transcription was up-regulated upon onset of drought, salt stress and cold. The wilting hormone ABA that integrates responses to these stimuli induced GORK expression in seedlings in a time- and concentration-dependent manner and this induction was dependent on extracellular Ca2+. ABA-responsive expression of GORK was impaired in the ABA-insensitive mutants abi1-1 and abi2-1, indicating that these protein phosphatases are regulators of GORK expression. Application of ABA to suspension-cultured cells for 2 min followed by a 4 h chase was sufficient to manifest transcriptional activation of the K+ channel gene. As predicted for a process involved in drought adaptation, only 12-24 h after the release of the stress hormone, GORK mRNA slowly decreased. In contrast to other tissues, GORK expression as well as K+(out) channel activity in guard cells is ABA insensitive, allowing the plant to adjust stomatal movement and water status control separately.}, author = {Becker, D and Hoth, S and Ache, P and Wenkel, S and Roelfsema, M R and Meyerhoff, O and Hartung, W and Hedrich, R}, journal = {FEBS Lett}, keywords = {myown}, month = {nov}, number = {1-2}, pages = {119-126}, title = {Regulation of the ABA-sensitive Arabidopsis potassium channel gene GORK in response to water stress}, volume = 554, year = 2003 }

  %0 Journal Article %1 Becker:2003:FEBS-Lett:14596925 %A Becker, D %A Hoth, S %A Ache, P %A Wenkel, S %A Roelfsema, M R %A Meyerhoff, O %A Hartung, W %A Hedrich, R %D 2003 %J FEBS Lett %N 1-2 %P 119-126 %T Regulation of the ABA-sensitive Arabidopsis potassium channel gene GORK in response to water stress %U https://www.ncbi.nlm.nih.gov/pubmed/14596925 %V 554 %X The phytohormone abscisic acid (ABA) regulates many stress-related processes in plants. In this context ABA mediates the responsiveness of plants to environmental stresses such as drought, cold or salt. In response to water stress, ABA induces stomatal closure by activating Ca2+, K+ and anion channels in guard cells. To understand the signalling pathways that regulate these turgor control elements, we studied the transcriptional control of the K+ release channel gene GORK that is expressed in guard cells, roots and vascular tissue. GORK transcription was up-regulated upon onset of drought, salt stress and cold. The wilting hormone ABA that integrates responses to these stimuli induced GORK expression in seedlings in a time- and concentration-dependent manner and this induction was dependent on extracellular Ca2+. ABA-responsive expression of GORK was impaired in the ABA-insensitive mutants abi1-1 and abi2-1, indicating that these protein phosphatases are regulators of GORK expression. Application of ABA to suspension-cultured cells for 2 min followed by a 4 h chase was sufficient to manifest transcriptional activation of the K+ channel gene. As predicted for a process involved in drought adaptation, only 12-24 h after the release of the stress hormone, GORK mRNA slowly decreased. In contrast to other tissues, GORK expression as well as K+(out) channel activity in guard cells is ABA insensitive, allowing the plant to adjust stomatal movement and water status control separately.
• Deeken, R., Ivashikina, N., Czirjak, T., Philippar, K., Becker, D., Ache, P., Hedrich, R. (2003) Tumour development in Arabidopsis thaliana involves the Shaker-like K+ channels AKT1 and AKT2/3, Plant J, 34(6), 778–787, available: https://www.ncbi.nlm.nih.gov/pubmed/12795698.
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  After completion of the Arabidopsis genome-sequencing programme, crown galls induced by Agrobacterium tumefaciens may become a model system to study plant tumour development. The molecular mechanisms of nutrient supply to support tumour growth and development are still unknown. In this study, we have identified a unique profile of Shaker-like potassium channels in agrobacteria-induced Arabidopsis tumours. Comparing the gene expression pattern of rapidly growing tumours with that of non-infected tissues, we found the suppression of shoot in favour of root-specific K+ channels. Among these, the upregulation of AKT1 and AtKC1 and the suppression of AKT2/3 and GORK were most pronounced. As a consequence, K+ uptake and accumulation were elevated in the tumour (163 mm) compared to control tissues (92 mm). Patch clamp studies on tumour protoplasts identified a population expressing the electrical properties of the AKT1 K+ channel. Furthermore, plants lacking a functional AKT1 or the AKT2/3 phloem K+ channel gene did not support tumour growth. This indicates that the delivery of potassium by AKT1 and the direction of assimilates, triggered by AKT2/3, are essential for tumour growth.

  @article{Deeken:2003:Plant-J:12795698, abstract = {After completion of the Arabidopsis genome-sequencing programme, crown galls induced by Agrobacterium tumefaciens may become a model system to study plant tumour development. The molecular mechanisms of nutrient supply to support tumour growth and development are still unknown. In this study, we have identified a unique profile of Shaker-like potassium channels in agrobacteria-induced Arabidopsis tumours. Comparing the gene expression pattern of rapidly growing tumours with that of non-infected tissues, we found the suppression of shoot in favour of root-specific K+ channels. Among these, the upregulation of AKT1 and AtKC1 and the suppression of AKT2/3 and GORK were most pronounced. As a consequence, K+ uptake and accumulation were elevated in the tumour (163 mm) compared to control tissues (92 mm). Patch clamp studies on tumour protoplasts identified a population expressing the electrical properties of the AKT1 K+ channel. Furthermore, plants lacking a functional AKT1 or the AKT2/3 phloem K+ channel gene did not support tumour growth. This indicates that the delivery of potassium by AKT1 and the direction of assimilates, triggered by AKT2/3, are essential for tumour growth.}, author = {Deeken, R and Ivashikina, N and Czirjak, T and Philippar, K and Becker, D and Ache, P and Hedrich, R}, journal = {Plant J}, keywords = {myown}, month = {jun}, number = 6, pages = {778-787}, title = {Tumour development in Arabidopsis thaliana involves the Shaker-like K+ channels AKT1 and AKT2/3}, volume = 34, year = 2003 }

  %0 Journal Article %1 Deeken:2003:Plant-J:12795698 %A Deeken, R %A Ivashikina, N %A Czirjak, T %A Philippar, K %A Becker, D %A Ache, P %A Hedrich, R %D 2003 %J Plant J %N 6 %P 778-787 %T Tumour development in Arabidopsis thaliana involves the Shaker-like K+ channels AKT1 and AKT2/3 %U https://www.ncbi.nlm.nih.gov/pubmed/12795698 %V 34 %X After completion of the Arabidopsis genome-sequencing programme, crown galls induced by Agrobacterium tumefaciens may become a model system to study plant tumour development. The molecular mechanisms of nutrient supply to support tumour growth and development are still unknown. In this study, we have identified a unique profile of Shaker-like potassium channels in agrobacteria-induced Arabidopsis tumours. Comparing the gene expression pattern of rapidly growing tumours with that of non-infected tissues, we found the suppression of shoot in favour of root-specific K+ channels. Among these, the upregulation of AKT1 and AtKC1 and the suppression of AKT2/3 and GORK were most pronounced. As a consequence, K+ uptake and accumulation were elevated in the tumour (163 mm) compared to control tissues (92 mm). Patch clamp studies on tumour protoplasts identified a population expressing the electrical properties of the AKT1 K+ channel. Furthermore, plants lacking a functional AKT1 or the AKT2/3 phloem K+ channel gene did not support tumour growth. This indicates that the delivery of potassium by AKT1 and the direction of assimilates, triggered by AKT2/3, are essential for tumour growth.

• Geiger, D., Becker, D., Lacombe, B., Hedrich, R. (2002) Outer pore residues control the H(+) and K(+) sensitivity of the Arabidopsis potassium channel AKT3, The Plant Cell, 14(8), 1859–1868, available: http://www.plantcell.org/content/14/8/1859.long.
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  The Arabidopsis phloem channel AKT3 is the founder of a subfamily of shaker-like plant potassium channels characterized by weak rectification, Ca(2+) block, proton inhibition, and, as shown in this study, K(+) sensitivity. In contrast to inward-rectifying, acid-activated K(+) channels of the KAT1 family, extracellular acidification decreases AKT3 currents at the macroscopic and single-channel levels. Here, we show that two distinct sites within the outer mouth of the K(+)-conducting pore provide the molecular basis for the pH sensitivity of this phloem channel. After generation of mutant channels and functional expression in Xenopus oocytes, we identified the His residue His-228, which is proximal to the K(+) selectivity filter (GYGD) and the distal Ser residue Ser-271, to be involved in proton susceptibility. Mutations of these sites, H228D and S271E, drastically reduced the H(+) and K(+) sensitivity of AKT3. Although in K(+)-free bath solutions outward K(+) currents were abolished completely in wild-type AKT3, S271E as well as the AKT3-HDSE double mutant still mediated K(+) efflux. We conclude that the pH- and K(+)-dependent properties of the AKT3 channel involve residues in the outer mouth of the pore. Both properties, H(+) and K(+) sensitivity, allow the fine-tuning of the phloem channel and thus seem to represent important elements in the control of membrane potential and sugar loading.

  @article{geiger2002outer, abstract = {The Arabidopsis phloem channel AKT3 is the founder of a subfamily of shaker-like plant potassium channels characterized by weak rectification, Ca(2+) block, proton inhibition, and, as shown in this study, K(+) sensitivity. In contrast to inward-rectifying, acid-activated K(+) channels of the KAT1 family, extracellular acidification decreases AKT3 currents at the macroscopic and single-channel levels. Here, we show that two distinct sites within the outer mouth of the K(+)-conducting pore provide the molecular basis for the pH sensitivity of this phloem channel. After generation of mutant channels and functional expression in Xenopus oocytes, we identified the His residue His-228, which is proximal to the K(+) selectivity filter (GYGD) and the distal Ser residue Ser-271, to be involved in proton susceptibility. Mutations of these sites, H228D and S271E, drastically reduced the H(+) and K(+) sensitivity of AKT3. Although in K(+)-free bath solutions outward K(+) currents were abolished completely in wild-type AKT3, S271E as well as the AKT3-HDSE double mutant still mediated K(+) efflux. We conclude that the pH- and K(+)-dependent properties of the AKT3 channel involve residues in the outer mouth of the pore. Both properties, H(+) and K(+) sensitivity, allow the fine-tuning of the phloem channel and thus seem to represent important elements in the control of membrane potential and sugar loading.}, author = {Geiger, D. and Becker, D. and Lacombe, B. and Hedrich, R.}, journal = {The Plant Cell}, keywords = {myown}, number = 8, pages = {1859-1868}, title = {Outer pore residues control the H(+) and K(+) sensitivity of the Arabidopsis potassium channel AKT3}, volume = 14, year = 2002 }

  %0 Journal Article %1 geiger2002outer %A Geiger, D. %A Becker, D. %A Lacombe, B. %A Hedrich, R. %D 2002 %J The Plant Cell %N 8 %P 1859-1868 %T Outer pore residues control the H(+) and K(+) sensitivity of the Arabidopsis potassium channel AKT3 %U http://www.plantcell.org/content/14/8/1859.long %V 14 %X The Arabidopsis phloem channel AKT3 is the founder of a subfamily of shaker-like plant potassium channels characterized by weak rectification, Ca(2+) block, proton inhibition, and, as shown in this study, K(+) sensitivity. In contrast to inward-rectifying, acid-activated K(+) channels of the KAT1 family, extracellular acidification decreases AKT3 currents at the macroscopic and single-channel levels. Here, we show that two distinct sites within the outer mouth of the K(+)-conducting pore provide the molecular basis for the pH sensitivity of this phloem channel. After generation of mutant channels and functional expression in Xenopus oocytes, we identified the His residue His-228, which is proximal to the K(+) selectivity filter (GYGD) and the distal Ser residue Ser-271, to be involved in proton susceptibility. Mutations of these sites, H228D and S271E, drastically reduced the H(+) and K(+) sensitivity of AKT3. Although in K(+)-free bath solutions outward K(+) currents were abolished completely in wild-type AKT3, S271E as well as the AKT3-HDSE double mutant still mediated K(+) efflux. We conclude that the pH- and K(+)-dependent properties of the AKT3 channel involve residues in the outer mouth of the pore. Both properties, H(+) and K(+) sensitivity, allow the fine-tuning of the phloem channel and thus seem to represent important elements in the control of membrane potential and sugar loading.
• Reintanz, B., Szyroki, A., Ivashikina, N., Ache, P., Godde, M., Becker, D., Palme, K., Hedrich, R. (2002) AtKC1, a silent Arabidopsis potassium channel α-subunit modulates root hair K+ influx, Proceedings of the National Academy of Sciences, 99(6), 4079–4084, available: https://doi.org/10.1073/pnas.052677799.
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  Ion channels in roots allow the plant to gain access to nutrients. The composition of the individual ion channels and the functional contribution of different α-subunits is largely unknown. Focusing on K+-selective ion channels, we have characterized AtKC1, a new α-subunit from the Arabidopsis shaker-like ion channel family. Promoter-β-glucuronidase (GUS) studies identified AtKC1 expression predominantly in root hairs and root endodermis. Specific antibodies recognized AtKC1 at the plasma membrane. To analyze further the abundance and the functional contribution of the different K+ channels α-subunits in root cells, we performed real-time reverse transcription–PCR and patch-clamp experiments on isolated root hair protoplasts. Studying all shaker-like ion channel α-subunits, we only found the K+ inward rectifier AtKC1 and AKT1 and the K+ outward rectifier GORK to be expressed in this cell type. Akt1 knockout plants essentially lacked inward rectifying K+ currents. In contrast, inward rectifying K+ currents were present in AtKC1 knockout plants, but fundamentally altered with respect to gating and cation sensitivity. This indicates that the AtKC1 α-subunit represents an integral component of functional root hair K+ uptake channels.

  @article{Reintanz19032002, abstract = {Ion channels in roots allow the plant to gain access to nutrients. The composition of the individual ion channels and the functional contribution of different α-subunits is largely unknown. Focusing on K+-selective ion channels, we have characterized AtKC1, a new α-subunit from the Arabidopsis shaker-like ion channel family. Promoter-β-glucuronidase (GUS) studies identified AtKC1 expression predominantly in root hairs and root endodermis. Specific antibodies recognized AtKC1 at the plasma membrane. To analyze further the abundance and the functional contribution of the different K+ channels α-subunits in root cells, we performed real-time reverse transcription–PCR and patch-clamp experiments on isolated root hair protoplasts. Studying all shaker-like ion channel α-subunits, we only found the K+ inward rectifier AtKC1 and AKT1 and the K+ outward rectifier GORK to be expressed in this cell type. Akt1 knockout plants essentially lacked inward rectifying K+ currents. In contrast, inward rectifying K+ currents were present in AtKC1 knockout plants, but fundamentally altered with respect to gating and cation sensitivity. This indicates that the AtKC1 α-subunit represents an integral component of functional root hair K+ uptake channels.}, author = {Reintanz, Birgit and Szyroki, Alexander and Ivashikina, Natalya and Ache, Peter and Godde, Matthias and Becker, Dirk and Palme, Klaus and Hedrich, Rainer}, journal = {Proceedings of the National Academy of Sciences}, keywords = {myown}, number = 6, pages = {4079-4084}, title = {AtKC1, a silent Arabidopsis potassium channel α-subunit modulates root hair K+ influx}, volume = 99, year = 2002 }

  %0 Journal Article %1 Reintanz19032002 %A Reintanz, Birgit %A Szyroki, Alexander %A Ivashikina, Natalya %A Ache, Peter %A Godde, Matthias %A Becker, Dirk %A Palme, Klaus %A Hedrich, Rainer %D 2002 %J Proceedings of the National Academy of Sciences %N 6 %P 4079-4084 %R 10.1073/pnas.052677799 %T AtKC1, a silent Arabidopsis potassium channel α-subunit modulates root hair K+ influx %U http://www.pnas.org/content/99/6/4079.abstract %V 99 %X Ion channels in roots allow the plant to gain access to nutrients. The composition of the individual ion channels and the functional contribution of different α-subunits is largely unknown. Focusing on K+-selective ion channels, we have characterized AtKC1, a new α-subunit from the Arabidopsis shaker-like ion channel family. Promoter-β-glucuronidase (GUS) studies identified AtKC1 expression predominantly in root hairs and root endodermis. Specific antibodies recognized AtKC1 at the plasma membrane. To analyze further the abundance and the functional contribution of the different K+ channels α-subunits in root cells, we performed real-time reverse transcription–PCR and patch-clamp experiments on isolated root hair protoplasts. Studying all shaker-like ion channel α-subunits, we only found the K+ inward rectifier AtKC1 and AKT1 and the K+ outward rectifier GORK to be expressed in this cell type. Akt1 knockout plants essentially lacked inward rectifying K+ currents. In contrast, inward rectifying K+ currents were present in AtKC1 knockout plants, but fundamentally altered with respect to gating and cation sensitivity. This indicates that the AtKC1 α-subunit represents an integral component of functional root hair K+ uptake channels.
• Becker, D., Stanke, R., Fendrik, I., Frommer, W.B., Vanderleyden, J., Kaiser, W.M., Hedrich, R. (2002) Expression of the NH4 +-transporter gene LEAMT1;2 is induced in tomato roots upon association with N2-fixing bacteria, Planta, 215(3), 424–429, available: https://doi.org/10.1007/s00425-002-0773-x.
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  Plants growing in close association with N2-fixing bacteria are able to overcome growth limitations in N-depleted soils. The molecular mechanism by which free-living, N2-fixing bacteria promote plant growth is still a matter of debate. By inoculating N-depleted tomato (Lycopersicon esculentum Mill.) plants with Azospirillum brasilense or Azoarcus sp. we could demonstrate the induction of the root NH4 +-transporter gene, LEAMT1;2 (L. esculentum ammonium transporter 1;2), indicating that bacterial NH4 + might be used as an N source under these conditions. Azospirillum brasilense (nif --) mutants, which lack the structural nifDK genes, failed to induce LEAMT1;2 expression. This suggests that root-associated N2-fixing bacteria do excrete NH4 + to levels that can be sensed by tomato roots and is in agreement with the induction of expression of LEAMT1;2 with as low as ≥1 {textmu}M external NH4 +. While peak expression was obtained with 2--5 {textmu}M NH4 +, a further increase in NH4 + reduced LEAMT1;2-mRNA levels in a concentration-dependent manner. The inhibition of LEAMT1;2 expression by glutamine and the glutamine synthetase blocker L-methionine sulfoximine (MSX) provided evidence for the control of LEAMT1;2 expression by cytoplasmic NH4 + concentration or the plant N status. Since micromolar concentrations of NH4 + strongly increased the LEAMT1;2-mRNA levels, the transported NH4 + ion itself could represent a key signal in the associative interaction between higher plants and N2-fixing micro-organisms.

  @article{Becker2002, abstract = {Plants growing in close association with N2-fixing bacteria are able to overcome growth limitations in N-depleted soils. The molecular mechanism by which free-living, N2-fixing bacteria promote plant growth is still a matter of debate. By inoculating N-depleted tomato (Lycopersicon esculentum Mill.) plants with Azospirillum brasilense or Azoarcus sp. we could demonstrate the induction of the root NH4 +-transporter gene, LEAMT1;2 (L. esculentum ammonium transporter 1;2), indicating that bacterial NH4 + might be used as an N source under these conditions. Azospirillum brasilense (nif –) mutants, which lack the structural nifDK genes, failed to induce LEAMT1;2 expression. This suggests that root-associated N2-fixing bacteria do excrete NH4 + to levels that can be sensed by tomato roots and is in agreement with the induction of expression of LEAMT1;2 with as low as ≥1 {\textmu}M external NH4 +. While peak expression was obtained with 2–5 {\textmu}M NH4 +, a further increase in NH4 + reduced LEAMT1;2-mRNA levels in a concentration-dependent manner. The inhibition of LEAMT1;2 expression by glutamine and the glutamine synthetase blocker L-methionine sulfoximine (MSX) provided evidence for the control of LEAMT1;2 expression by cytoplasmic NH4 + concentration or the plant N status. Since micromolar concentrations of NH4 + strongly increased the LEAMT1;2-mRNA levels, the transported NH4 + ion itself could represent a key signal in the associative interaction between higher plants and N2-fixing micro-organisms.}, author = {Becker, Dirk and Stanke, Ruediger and Fendrik, Istvan and Frommer, Wolf B. and Vanderleyden, Jos and Kaiser, Werner M. and Hedrich, Rainer}, journal = {Planta}, keywords = {myown}, number = 3, pages = {424–429}, title = {Expression of the NH4 +-transporter gene LEAMT1;2 is induced in tomato roots upon association with N2-fixing bacteria}, volume = 215, year = 2002 }

  %0 Journal Article %1 Becker2002 %A Becker, Dirk %A Stanke, Ruediger %A Fendrik, Istvan %A Frommer, Wolf B. %A Vanderleyden, Jos %A Kaiser, Werner M. %A Hedrich, Rainer %D 2002 %J Planta %N 3 %P 424--429 %R 10.1007/s00425-002-0773-x %T Expression of the NH4 +-transporter gene LEAMT1;2 is induced in tomato roots upon association with N2-fixing bacteria %U http://dx.doi.org/10.1007/s00425-002-0773-x %V 215 %X Plants growing in close association with N2-fixing bacteria are able to overcome growth limitations in N-depleted soils. The molecular mechanism by which free-living, N2-fixing bacteria promote plant growth is still a matter of debate. By inoculating N-depleted tomato (Lycopersicon esculentum Mill.) plants with Azospirillum brasilense or Azoarcus sp. we could demonstrate the induction of the root NH4 +-transporter gene, LEAMT1;2 (L. esculentum ammonium transporter 1;2), indicating that bacterial NH4 + might be used as an N source under these conditions. Azospirillum brasilense (nif --) mutants, which lack the structural nifDK genes, failed to induce LEAMT1;2 expression. This suggests that root-associated N2-fixing bacteria do excrete NH4 + to levels that can be sensed by tomato roots and is in agreement with the induction of expression of LEAMT1;2 with as low as ≥1 {textmu}M external NH4 +. While peak expression was obtained with 2--5 {textmu}M NH4 +, a further increase in NH4 + reduced LEAMT1;2-mRNA levels in a concentration-dependent manner. The inhibition of LEAMT1;2 expression by glutamine and the glutamine synthetase blocker L-methionine sulfoximine (MSX) provided evidence for the control of LEAMT1;2 expression by cytoplasmic NH4 + concentration or the plant N status. Since micromolar concentrations of NH4 + strongly increased the LEAMT1;2-mRNA levels, the transported NH4 + ion itself could represent a key signal in the associative interaction between higher plants and N2-fixing micro-organisms.
• Moshelion, M., Becker, D., Czempinski, K., Mueller-Roeber, B., Attali, B., Hedrich, R., Moran, N. (2002) Diurnal and Circadian Regulation of Putative Potassium Channels in a Leaf Moving Organ, {PLANT} {PHYSIOLOGY}, 128(2), 634–642, available: https://doi.org/10.1104/pp.010549.
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  @article{Moshelion_2002, author = {Moshelion, M. and Becker, D. and Czempinski, K. and Mueller-Roeber, B. and Attali, B. and Hedrich, R. and Moran, N.}, journal = {{PLANT} {PHYSIOLOGY}}, keywords = {myown}, month = {feb}, number = 2, pages = {634–642}, publisher = {American Society of Plant Biologists ({ASPB})}, title = {Diurnal and Circadian Regulation of Putative Potassium Channels in a Leaf Moving Organ}, volume = 128, year = 2002 }

  %0 Journal Article %1 Moshelion_2002 %A Moshelion, M. %A Becker, D. %A Czempinski, K. %A Mueller-Roeber, B. %A Attali, B. %A Hedrich, R. %A Moran, N. %D 2002 %I American Society of Plant Biologists ({ASPB}) %J {PLANT} {PHYSIOLOGY} %N 2 %P 634--642 %R 10.1104/pp.010549 %T Diurnal and Circadian Regulation of Putative Potassium Channels in a Leaf Moving Organ %U https://doi.org/10.1104%2Fpp.010549 %V 128
• Moshelion, M., Becker, D., Biela, A., Uehlein, N., Hedrich, R., Otto, B., Levi, H., Moran, N., Kaldenhoff, R. (2002) Plasma membrane aquaporins in the motor cells of Samanea saman: diurnal and circadian regulation, Plant Cell, 14(3), 727–739, available: https://www.ncbi.nlm.nih.gov/pubmed/11910017.
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  Leaf-moving organs, remarkable for the rhythmic volume changes of their motor cells, served as a model system in which to study the regulation of membrane water fluxes. Two plasma membrane intrinsic protein homolog genes, SsAQP1 and SsAQP2, were cloned from these organs and characterized as aquaporins in Xenopus laevis oocytes. Osmotic water permeability (P(f)) was 10 times higher in SsAQP2-expressing oocytes than in SsAQP1-expressing oocytes. SsAQP1 was found to be glycerol permeable, and SsAQP2 was inhibited by 0.5 mM HgCl(2) and by 1 mM phloretin. The aquaporin mRNA levels differed in their spatial distribution in the leaf and were regulated diurnally in phase with leaflet movements. Additionally, SsAQP2 transcription was under circadian control. The P(f) of motor cell protoplasts was regulated diurnally as well: the morning and/or evening P(f) increases were inhibited by 50 microM HgCl(2), by 2 mM cycloheximide, and by 250 microM phloretin to the noon P(f) level. Our results link SsAQP2 to the physiological function of rhythmic cell volume changes.

  @article{Moshelion:2002:Plant-Cell:11910017, abstract = {Leaf-moving organs, remarkable for the rhythmic volume changes of their motor cells, served as a model system in which to study the regulation of membrane water fluxes. Two plasma membrane intrinsic protein homolog genes, SsAQP1 and SsAQP2, were cloned from these organs and characterized as aquaporins in Xenopus laevis oocytes. Osmotic water permeability (P(f)) was 10 times higher in SsAQP2-expressing oocytes than in SsAQP1-expressing oocytes. SsAQP1 was found to be glycerol permeable, and SsAQP2 was inhibited by 0.5 mM HgCl(2) and by 1 mM phloretin. The aquaporin mRNA levels differed in their spatial distribution in the leaf and were regulated diurnally in phase with leaflet movements. Additionally, SsAQP2 transcription was under circadian control. The P(f) of motor cell protoplasts was regulated diurnally as well: the morning and/or evening P(f) increases were inhibited by 50 microM HgCl(2), by 2 mM cycloheximide, and by 250 microM phloretin to the noon P(f) level. Our results link SsAQP2 to the physiological function of rhythmic cell volume changes.}, author = {Moshelion, M and Becker, D and Biela, A and Uehlein, N and Hedrich, R and Otto, B and Levi, H and Moran, N and Kaldenhoff, R}, journal = {Plant Cell}, keywords = {myown}, month = {mar}, number = 3, pages = {727-739}, title = {Plasma membrane aquaporins in the motor cells of Samanea saman: diurnal and circadian regulation}, volume = 14, year = 2002 }

  %0 Journal Article %1 Moshelion:2002:Plant-Cell:11910017 %A Moshelion, M %A Becker, D %A Biela, A %A Uehlein, N %A Hedrich, R %A Otto, B %A Levi, H %A Moran, N %A Kaldenhoff, R %D 2002 %J Plant Cell %N 3 %P 727-739 %T Plasma membrane aquaporins in the motor cells of Samanea saman: diurnal and circadian regulation %U https://www.ncbi.nlm.nih.gov/pubmed/11910017 %V 14 %X Leaf-moving organs, remarkable for the rhythmic volume changes of their motor cells, served as a model system in which to study the regulation of membrane water fluxes. Two plasma membrane intrinsic protein homolog genes, SsAQP1 and SsAQP2, were cloned from these organs and characterized as aquaporins in Xenopus laevis oocytes. Osmotic water permeability (P(f)) was 10 times higher in SsAQP2-expressing oocytes than in SsAQP1-expressing oocytes. SsAQP1 was found to be glycerol permeable, and SsAQP2 was inhibited by 0.5 mM HgCl(2) and by 1 mM phloretin. The aquaporin mRNA levels differed in their spatial distribution in the leaf and were regulated diurnally in phase with leaflet movements. Additionally, SsAQP2 transcription was under circadian control. The P(f) of motor cell protoplasts was regulated diurnally as well: the morning and/or evening P(f) increases were inhibited by 50 microM HgCl(2), by 2 mM cycloheximide, and by 250 microM phloretin to the noon P(f) level. Our results link SsAQP2 to the physiological function of rhythmic cell volume changes.
• Becker, D., Hedrich, R. (2002) Channelling auxin action: modulation of ion transport by indole-3-acetic acid, Plant Mol Biol, 49(3-4), 349–356, available: https://www.ncbi.nlm.nih.gov/pubmed/12036259.
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  The growth hormone auxin is a key regulator of plant cell division and elongation. Since plants lack muscles, processes involved in growth and movements rely on turgor formation, and thus on the transport of solutes and water. Modern electrophysiological techniques and molecular genetics have shed new light on the regulation of plant ion transporters in response to auxin. Guard cells, hypocotyls and coleoptiles have advanced to major model systems in studying auxin action. This review will therefore focus on the molecular mechanism by which auxin modulates ion transport and cell expansion in these model cell types.

  @article{Becker:2002:Plant-Mol-Biol:12036259, abstract = {The growth hormone auxin is a key regulator of plant cell division and elongation. Since plants lack muscles, processes involved in growth and movements rely on turgor formation, and thus on the transport of solutes and water. Modern electrophysiological techniques and molecular genetics have shed new light on the regulation of plant ion transporters in response to auxin. Guard cells, hypocotyls and coleoptiles have advanced to major model systems in studying auxin action. This review will therefore focus on the molecular mechanism by which auxin modulates ion transport and cell expansion in these model cell types.}, author = {Becker, D and Hedrich, R}, journal = {Plant Mol Biol}, keywords = {myown}, month = {Jun-Jul}, number = {3-4}, pages = {349-356}, title = {Channelling auxin action: modulation of ion transport by indole-3-acetic acid}, volume = 49, year = 2002 }

  %0 Journal Article %1 Becker:2002:Plant-Mol-Biol:12036259 %A Becker, D %A Hedrich, R %D 2002 %J Plant Mol Biol %N 3-4 %P 349-356 %T Channelling auxin action: modulation of ion transport by indole-3-acetic acid %U https://www.ncbi.nlm.nih.gov/pubmed/12036259 %V 49 %X The growth hormone auxin is a key regulator of plant cell division and elongation. Since plants lack muscles, processes involved in growth and movements rely on turgor formation, and thus on the transport of solutes and water. Modern electrophysiological techniques and molecular genetics have shed new light on the regulation of plant ion transporters in response to auxin. Guard cells, hypocotyls and coleoptiles have advanced to major model systems in studying auxin action. This review will therefore focus on the molecular mechanism by which auxin modulates ion transport and cell expansion in these model cell types.

• Ache, P., Becker, D., Deeken, R., Dreyer, I., Weber, H., Fromm, J., Hedrich, R. (2001) VFK1, a Vicia faba K(+) channel involved in phloem unloading, Plant J, 27(6), 571–580, available: https://www.ncbi.nlm.nih.gov/pubmed/11576440.
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  In search of a K(+) channel involved in phloem transport we screened a Vicia faba cotyledon cDNA library taking advantage of a set of degenerated primers, flanking regions conserved among K(+) uptake channels. We cloned VFK1 (for Vicia faba K(+) channel 1) characterised by a structure known from the Shaker family of plant K(+) channels. When co-expressed with a KAT1 mutant in Xenopus oocytes, heteromers revealed the biophysical properties of a K(+) selective, proton-blocked channel. Northern blot analyses showed high levels of expression in cotyledons, flowers, stem and leaves. Using in situ PCR techniques we could localise the K(+) channel mRNA in the phloem. In the stem VFK1 expression levels were higher in the lower internodes. There channel transcripts increased in the light and thus under conditions of increased photosynthate allocation. VFK1 transcripts are elevated in sink leaves, and rise in source leaves during the experimental transition into sinks. Fructose- rather than sucrose- or glucose-feeding via the petiole induced VFK1 gene activity. We therefore monitored the fructose sensitivity of the sieve tube potential through cut aphid stylets. In response to an 1 h fructose treatment the sieve tube potential shift increased from 19 mV to 53 mV per 10-fold change in K(+) concentration. Under these conditions K(+) channels dominated the electrical properties of the plasma membrane. Based on the phloem localisation and expression patterns of VFK1 we conclude that this K(+) channel is involved in sugar unloading and K(+) retrieval.

  @article{Ache:2001:Plant-J:11576440, abstract = {In search of a K(+) channel involved in phloem transport we screened a Vicia faba cotyledon cDNA library taking advantage of a set of degenerated primers, flanking regions conserved among K(+) uptake channels. We cloned VFK1 (for Vicia faba K(+) channel 1) characterised by a structure known from the Shaker family of plant K(+) channels. When co-expressed with a KAT1 mutant in Xenopus oocytes, heteromers revealed the biophysical properties of a K(+) selective, proton-blocked channel. Northern blot analyses showed high levels of expression in cotyledons, flowers, stem and leaves. Using in situ PCR techniques we could localise the K(+) channel mRNA in the phloem. In the stem VFK1 expression levels were higher in the lower internodes. There channel transcripts increased in the light and thus under conditions of increased photosynthate allocation. VFK1 transcripts are elevated in sink leaves, and rise in source leaves during the experimental transition into sinks. Fructose- rather than sucrose- or glucose-feeding via the petiole induced VFK1 gene activity. We therefore monitored the fructose sensitivity of the sieve tube potential through cut aphid stylets. In response to an 1 h fructose treatment the sieve tube potential shift increased from 19 mV to 53 mV per 10-fold change in K(+) concentration. Under these conditions K(+) channels dominated the electrical properties of the plasma membrane. Based on the phloem localisation and expression patterns of VFK1 we conclude that this K(+) channel is involved in sugar unloading and K(+) retrieval.}, author = {Ache, P and Becker, D and Deeken, R and Dreyer, I and Weber, H and Fromm, J and Hedrich, R}, journal = {Plant J}, keywords = {myown}, month = {sep}, number = 6, pages = {571-580}, title = {VFK1, a Vicia faba K(+) channel involved in phloem unloading}, volume = 27, year = 2001 }

  %0 Journal Article %1 Ache:2001:Plant-J:11576440 %A Ache, P %A Becker, D %A Deeken, R %A Dreyer, I %A Weber, H %A Fromm, J %A Hedrich, R %D 2001 %J Plant J %N 6 %P 571-580 %T VFK1, a Vicia faba K(+) channel involved in phloem unloading %U https://www.ncbi.nlm.nih.gov/pubmed/11576440 %V 27 %X In search of a K(+) channel involved in phloem transport we screened a Vicia faba cotyledon cDNA library taking advantage of a set of degenerated primers, flanking regions conserved among K(+) uptake channels. We cloned VFK1 (for Vicia faba K(+) channel 1) characterised by a structure known from the Shaker family of plant K(+) channels. When co-expressed with a KAT1 mutant in Xenopus oocytes, heteromers revealed the biophysical properties of a K(+) selective, proton-blocked channel. Northern blot analyses showed high levels of expression in cotyledons, flowers, stem and leaves. Using in situ PCR techniques we could localise the K(+) channel mRNA in the phloem. In the stem VFK1 expression levels were higher in the lower internodes. There channel transcripts increased in the light and thus under conditions of increased photosynthate allocation. VFK1 transcripts are elevated in sink leaves, and rise in source leaves during the experimental transition into sinks. Fructose- rather than sucrose- or glucose-feeding via the petiole induced VFK1 gene activity. We therefore monitored the fructose sensitivity of the sieve tube potential through cut aphid stylets. In response to an 1 h fructose treatment the sieve tube potential shift increased from 19 mV to 53 mV per 10-fold change in K(+) concentration. Under these conditions K(+) channels dominated the electrical properties of the plasma membrane. Based on the phloem localisation and expression patterns of VFK1 we conclude that this K(+) channel is involved in sugar unloading and K(+) retrieval.
• Lacombe, B., Becker, D., Hedrich, R., DeSalle, R., Hollmann, M., Kwak, J.M., Schroeder, J.I., Le Nov{`e}re, N., Nam, H.G., Spalding, E.P., Tester, M., Turano, F.J., Chiu, J., Coruzzi, G. (2001) The identity of plant glutamate receptors, Science, 292(5521), 1486–1487, available: https://www.ncbi.nlm.nih.gov/pubmed/11379626.
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  @article{Lacombe:2001:Science:11379626, author = {Lacombe, B and Becker, D and Hedrich, R and DeSalle, R and Hollmann, M and Kwak, J M and Schroeder, J I and Le Nov{\`e}re, N and Nam, H G and Spalding, E P and Tester, M and Turano, F J and Chiu, J and Coruzzi, G}, journal = {Science}, keywords = {myown}, month = {may}, number = 5521, pages = {1486-1487}, title = {The identity of plant glutamate receptors}, volume = 292, year = 2001 }

  %0 Journal Article %1 Lacombe:2001:Science:11379626 %A Lacombe, B %A Becker, D %A Hedrich, R %A DeSalle, R %A Hollmann, M %A Kwak, J M %A Schroeder, J I %A Le Nov{`e}re, N %A Nam, H G %A Spalding, E P %A Tester, M %A Turano, F J %A Chiu, J %A Coruzzi, G %D 2001 %J Science %N 5521 %P 1486-1487 %T The identity of plant glutamate receptors %U https://www.ncbi.nlm.nih.gov/pubmed/11379626 %V 292
• Ivashikina, N., Becker, D., Ache, P., Meyerhoff, O., Felle, H.H., Hedrich, R. (2001) K(+) channel profile and electrical properties of Arabidopsis root hairs, FEBS Lett, 508(3), 463–469, available: https://www.ncbi.nlm.nih.gov/pubmed/11728473.
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  Ion channels and solute transporters in the plasma membrane of root hairs are proposed to control nutrient uptake, osmoregulation and polar growth. Here we analyzed the molecular components of potassium transport in Arabidopsis root hairs by combining K(+)-selective electrodes, reverse transcription-PCR, and patch-clamp measurements. The two inward rectifiers AKT1 and ATKC1 as well as the outward rectifier GORK dominated the root hair K(+) channel pool. Root hairs of AKT1 and ATKC1 loss-of-function plants completely lack the K(+) uptake channel or exhibited altered properties, respectively. Upon oligochitin-elicitor treatment of root hairs, transient changes in K(+) fluxes and membrane polarization were recorded in wild-type plants, while akt1-1 root hairs showed a reduced amplitude and pronounced delay in the potassium re-uptake process. This indicates that AKT1 and ATKC1 represent essential alpha-subunits of the inward rectifier. Green fluorescent protein (GFP) fluorescence following ballistic bombardment with GORK promoter-GFP constructs as well as analysis of promoter-GUS lines identified this K(+) outward rectifier as a novel ion channel expressed in root hairs. Based on the expression profile and the electrical properties of the root hair plasma membrane we conclude that AKT1-, ATKC- and GORK-mediated potassium transport is essential for osmoregulation and repolarization of the membrane potential in response to elicitors.

  @article{Ivashikina:2001:FEBS-Lett:11728473, abstract = {Ion channels and solute transporters in the plasma membrane of root hairs are proposed to control nutrient uptake, osmoregulation and polar growth. Here we analyzed the molecular components of potassium transport in Arabidopsis root hairs by combining K(+)-selective electrodes, reverse transcription-PCR, and patch-clamp measurements. The two inward rectifiers AKT1 and ATKC1 as well as the outward rectifier GORK dominated the root hair K(+) channel pool. Root hairs of AKT1 and ATKC1 loss-of-function plants completely lack the K(+) uptake channel or exhibited altered properties, respectively. Upon oligochitin-elicitor treatment of root hairs, transient changes in K(+) fluxes and membrane polarization were recorded in wild-type plants, while akt1-1 root hairs showed a reduced amplitude and pronounced delay in the potassium re-uptake process. This indicates that AKT1 and ATKC1 represent essential alpha-subunits of the inward rectifier. Green fluorescent protein (GFP) fluorescence following ballistic bombardment with GORK promoter-GFP constructs as well as analysis of promoter-GUS lines identified this K(+) outward rectifier as a novel ion channel expressed in root hairs. Based on the expression profile and the electrical properties of the root hair plasma membrane we conclude that AKT1-, ATKC- and GORK-mediated potassium transport is essential for osmoregulation and repolarization of the membrane potential in response to elicitors.}, author = {Ivashikina, N and Becker, D and Ache, P and Meyerhoff, O and Felle, H H and Hedrich, R}, journal = {FEBS Lett}, keywords = {myown}, month = {nov}, number = 3, pages = {463-469}, title = {K(+) channel profile and electrical properties of Arabidopsis root hairs}, volume = 508, year = 2001 }

  %0 Journal Article %1 Ivashikina:2001:FEBS-Lett:11728473 %A Ivashikina, N %A Becker, D %A Ache, P %A Meyerhoff, O %A Felle, H H %A Hedrich, R %D 2001 %J FEBS Lett %N 3 %P 463-469 %T K(+) channel profile and electrical properties of Arabidopsis root hairs %U https://www.ncbi.nlm.nih.gov/pubmed/11728473 %V 508 %X Ion channels and solute transporters in the plasma membrane of root hairs are proposed to control nutrient uptake, osmoregulation and polar growth. Here we analyzed the molecular components of potassium transport in Arabidopsis root hairs by combining K(+)-selective electrodes, reverse transcription-PCR, and patch-clamp measurements. The two inward rectifiers AKT1 and ATKC1 as well as the outward rectifier GORK dominated the root hair K(+) channel pool. Root hairs of AKT1 and ATKC1 loss-of-function plants completely lack the K(+) uptake channel or exhibited altered properties, respectively. Upon oligochitin-elicitor treatment of root hairs, transient changes in K(+) fluxes and membrane polarization were recorded in wild-type plants, while akt1-1 root hairs showed a reduced amplitude and pronounced delay in the potassium re-uptake process. This indicates that AKT1 and ATKC1 represent essential alpha-subunits of the inward rectifier. Green fluorescent protein (GFP) fluorescence following ballistic bombardment with GORK promoter-GFP constructs as well as analysis of promoter-GUS lines identified this K(+) outward rectifier as a novel ion channel expressed in root hairs. Based on the expression profile and the electrical properties of the root hair plasma membrane we conclude that AKT1-, ATKC- and GORK-mediated potassium transport is essential for osmoregulation and repolarization of the membrane potential in response to elicitors.
• Gaedeke, N. (2001) The Arabidopsis thaliana {ABC} transporter {AtMRP}5 controls root development and stomata movement, The {EMBO} Journal, 20(8), 1875–1887, available: https://doi.org/10.1093/emboj/20.8.1875.
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  @article{Gaedeke_2001, author = {Gaedeke, N.}, journal = {The {EMBO} Journal}, keywords = {myown}, month = {apr}, number = 8, pages = {1875–1887}, publisher = {Wiley-Blackwell}, title = {The Arabidopsis thaliana {ABC} transporter {AtMRP}5 controls root development and stomata movement}, volume = 20, year = 2001 }

  %0 Journal Article %1 Gaedeke_2001 %A Gaedeke, N. %D 2001 %I Wiley-Blackwell %J The {EMBO} Journal %N 8 %P 1875--1887 %R 10.1093/emboj/20.8.1875 %T The Arabidopsis thaliana {ABC} transporter {AtMRP}5 controls root development and stomata movement %U https://doi.org/10.1093%2Femboj%2F20.8.1875 %V 20
• Hoth, S., Geiger, D., Becker, D., Hedrich, R. (2001) The pore of plant K(+) channels is involved in voltage and pH sensing: domain-swapping between different K(+) channel alpha-subunits, Plant Cell, 13(4), 943–952, available: https://www.ncbi.nlm.nih.gov/pubmed/11283347.
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  Plant K(+) uptake channel types differ with respect to their voltage, Ca(2)+, and pH dependence. Here, we constructed recombinant chimeric channels between KST1, a member of the inward-rectifying, acid-activated KAT1 family, and AKT3, a member of the weakly voltage-dependent, proton-blocked AKT2/3 family. The homologous pore regions of AKT3 (amino acids 216 to 287) and KST1 (amino acids 217 to 289) have been exchanged to generate the two chimeric channels AKT3/(p)KST1 and KST1/(p)AKT3. In contrast to AKT3 wild-type channels, AKT3/(p)KST1 revealed a strong inward rectification reminiscent of that of KST1. Correspondingly, the substitution of the KST1 by the AKT3 pore led to less pronounced rectification properties of KST1/(p)AKT3 compared with wild-type KST1. Besides the voltage dependence, the interaction between the chimera and extracellular H(+) and Ca(2)+ resembled the properties of the inserted rather than the respective wild-type pore. Whereas AKT3/(p)KST1 was acid activated and Ca(2)+ insensitive, extracellular protons and Ca(2)+ inhibited KST1/(p)AKT3. The regulation of the chimeric channels by cytoplasmic protons followed the respective wild-type backbone of the chimeric channels, indicating that the intracellular pH sensor is located outside the P domain. We thus conclude that essential elements for external pH and Ca(2)+ regulation and for the rectification of voltage-dependent K(+) uptake channels are located within the channel pore.

  @article{Hoth:2001:Plant-Cell:11283347, abstract = {Plant K(+) uptake channel types differ with respect to their voltage, Ca(2)+, and pH dependence. Here, we constructed recombinant chimeric channels between KST1, a member of the inward-rectifying, acid-activated KAT1 family, and AKT3, a member of the weakly voltage-dependent, proton-blocked AKT2/3 family. The homologous pore regions of AKT3 (amino acids 216 to 287) and KST1 (amino acids 217 to 289) have been exchanged to generate the two chimeric channels AKT3/(p)KST1 and KST1/(p)AKT3. In contrast to AKT3 wild-type channels, AKT3/(p)KST1 revealed a strong inward rectification reminiscent of that of KST1. Correspondingly, the substitution of the KST1 by the AKT3 pore led to less pronounced rectification properties of KST1/(p)AKT3 compared with wild-type KST1. Besides the voltage dependence, the interaction between the chimera and extracellular H(+) and Ca(2)+ resembled the properties of the inserted rather than the respective wild-type pore. Whereas AKT3/(p)KST1 was acid activated and Ca(2)+ insensitive, extracellular protons and Ca(2)+ inhibited KST1/(p)AKT3. The regulation of the chimeric channels by cytoplasmic protons followed the respective wild-type backbone of the chimeric channels, indicating that the intracellular pH sensor is located outside the P domain. We thus conclude that essential elements for external pH and Ca(2)+ regulation and for the rectification of voltage-dependent K(+) uptake channels are located within the channel pore.}, author = {Hoth, S and Geiger, D and Becker, D and Hedrich, R}, journal = {Plant Cell}, keywords = {myown}, month = {apr}, number = 4, pages = {943-952}, title = {The pore of plant K(+) channels is involved in voltage and pH sensing: domain-swapping between different K(+) channel alpha-subunits}, volume = 13, year = 2001 }

  %0 Journal Article %1 Hoth:2001:Plant-Cell:11283347 %A Hoth, S %A Geiger, D %A Becker, D %A Hedrich, R %D 2001 %J Plant Cell %N 4 %P 943-952 %T The pore of plant K(+) channels is involved in voltage and pH sensing: domain-swapping between different K(+) channel alpha-subunits %U https://www.ncbi.nlm.nih.gov/pubmed/11283347 %V 13 %X Plant K(+) uptake channel types differ with respect to their voltage, Ca(2)+, and pH dependence. Here, we constructed recombinant chimeric channels between KST1, a member of the inward-rectifying, acid-activated KAT1 family, and AKT3, a member of the weakly voltage-dependent, proton-blocked AKT2/3 family. The homologous pore regions of AKT3 (amino acids 216 to 287) and KST1 (amino acids 217 to 289) have been exchanged to generate the two chimeric channels AKT3/(p)KST1 and KST1/(p)AKT3. In contrast to AKT3 wild-type channels, AKT3/(p)KST1 revealed a strong inward rectification reminiscent of that of KST1. Correspondingly, the substitution of the KST1 by the AKT3 pore led to less pronounced rectification properties of KST1/(p)AKT3 compared with wild-type KST1. Besides the voltage dependence, the interaction between the chimera and extracellular H(+) and Ca(2)+ resembled the properties of the inserted rather than the respective wild-type pore. Whereas AKT3/(p)KST1 was acid activated and Ca(2)+ insensitive, extracellular protons and Ca(2)+ inhibited KST1/(p)AKT3. The regulation of the chimeric channels by cytoplasmic protons followed the respective wild-type backbone of the chimeric channels, indicating that the intracellular pH sensor is located outside the P domain. We thus conclude that essential elements for external pH and Ca(2)+ regulation and for the rectification of voltage-dependent K(+) uptake channels are located within the channel pore.

• Schreiber, L., Skrabs, M., Hartmann, K., Becker, D., Cassagne, C., Lessire, R. (2000) Biochemical and molecular characterization of corn (Zea mays L.) root elongases, Biochem Soc Trans, 28(6), 647–649, available: https://www.ncbi.nlm.nih.gov/pubmed/?term=Schreiber+skrabs+becker.
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  Root surfaces are protected against the soil environment by the deposition of lignin and suberin. In order to obtain more insight into the regulation of root suberin biosynthesis, elongases from primary roots of corn (Zea mays L.) seedlings were characterized. Elongase activities (acyl-CoA and ATP-dependent) were located in the microsomal fraction of the root cells. C(20), C(22) and C(24) fatty acids were detected as primary products of elongases. Preferred substrates of the acyl-CoA elongases were C(18:0)-CoA and C(20:0)-CoA. Applying a molecular approach, using PCR and degenerate primers derived from the sequences of known leaf and seed 3-ketoacyl-CoA synthases (KCSs), catalysing the first step of very-long-chain fatty acid synthesis, the cDNA of a putative root KCS was obtained showing high homology to known leaf and seed KCSs at the DNA and amino acid levels. Thus, our approach provides the first direct evidence for the presence and the activity of root elongases in Z. mays. Ongoing research is focusing on the molecular analysis and the regulation of KCS expression in roots in reaction to different environmental stimuli.

  @article{Schreiber:2000:Biochem-Soc-Trans:11171156, abstract = {Root surfaces are protected against the soil environment by the deposition of lignin and suberin. In order to obtain more insight into the regulation of root suberin biosynthesis, elongases from primary roots of corn (Zea mays L.) seedlings were characterized. Elongase activities (acyl-CoA and ATP-dependent) were located in the microsomal fraction of the root cells. C(20), C(22) and C(24) fatty acids were detected as primary products of elongases. Preferred substrates of the acyl-CoA elongases were C(18:0)-CoA and C(20:0)-CoA. Applying a molecular approach, using PCR and degenerate primers derived from the sequences of known leaf and seed 3-ketoacyl-CoA synthases (KCSs), catalysing the first step of very-long-chain fatty acid synthesis, the cDNA of a putative root KCS was obtained showing high homology to known leaf and seed KCSs at the DNA and amino acid levels. Thus, our approach provides the first direct evidence for the presence and the activity of root elongases in Z. mays. Ongoing research is focusing on the molecular analysis and the regulation of KCS expression in roots in reaction to different environmental stimuli.}, author = {Schreiber, L and Skrabs, M and Hartmann, K and Becker, D and Cassagne, C and Lessire, R}, journal = {Biochem Soc Trans}, keywords = {myown}, month = {dec}, number = 6, pages = {647-649}, title = {Biochemical and molecular characterization of corn (Zea mays L.) root elongases}, volume = 28, year = 2000 }

  %0 Journal Article %1 Schreiber:2000:Biochem-Soc-Trans:11171156 %A Schreiber, L %A Skrabs, M %A Hartmann, K %A Becker, D %A Cassagne, C %A Lessire, R %D 2000 %J Biochem Soc Trans %N 6 %P 647-649 %T Biochemical and molecular characterization of corn (Zea mays L.) root elongases %U https://www.ncbi.nlm.nih.gov/pubmed/?term=Schreiber+skrabs+becker %V 28 %X Root surfaces are protected against the soil environment by the deposition of lignin and suberin. In order to obtain more insight into the regulation of root suberin biosynthesis, elongases from primary roots of corn (Zea mays L.) seedlings were characterized. Elongase activities (acyl-CoA and ATP-dependent) were located in the microsomal fraction of the root cells. C(20), C(22) and C(24) fatty acids were detected as primary products of elongases. Preferred substrates of the acyl-CoA elongases were C(18:0)-CoA and C(20:0)-CoA. Applying a molecular approach, using PCR and degenerate primers derived from the sequences of known leaf and seed 3-ketoacyl-CoA synthases (KCSs), catalysing the first step of very-long-chain fatty acid synthesis, the cDNA of a putative root KCS was obtained showing high homology to known leaf and seed KCSs at the DNA and amino acid levels. Thus, our approach provides the first direct evidence for the presence and the activity of root elongases in Z. mays. Ongoing research is focusing on the molecular analysis and the regulation of KCS expression in roots in reaction to different environmental stimuli.
• Philippar, K., Becker, D., Hedrich, E., Edwards, L., Ljung, S., Sandberg, G. (2000) . . . response: living with gravity, Trends Plant Sci, 5(3), 86–87, available: https://www.ncbi.nlm.nih.gov/pubmed/10707070.
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  @article{Philippar:2000:Trends-Plant-Sci:10707070, author = {Philippar, K and Becker, D and Hedrich, E and Edwards, L and Ljung, S and Sandberg, G}, journal = {Trends Plant Sci}, keywords = {myown}, month = {mar}, number = 3, pages = {86-87}, title = {. . . response: living with gravity}, volume = 5, year = 2000 }

  %0 Journal Article %1 Philippar:2000:Trends-Plant-Sci:10707070 %A Philippar, K %A Becker, D %A Hedrich, E %A Edwards, L %A Ljung, S %A Sandberg, G %D 2000 %J Trends Plant Sci %N 3 %P 86-87 %T . . . response: living with gravity %U https://www.ncbi.nlm.nih.gov/pubmed/10707070 %V 5
• Ache, P., Becker, D., Ivashikina, N., Dietrich, P., Roelfsema, M.R., Hedrich, R. (2000) GORK, a delayed outward rectifier expressed in guard cells of Arabidopsis thaliana, is a K(+)-selective, K(+)-sensing ion channel, FEBS Lett, 486(2), 93–98, available: https://www.ncbi.nlm.nih.gov/pubmed/11113445.
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  Here we report on the molecular identification, guard cell expression and functional characterization of AtGORK, an Arabidopsis thaliana guard cell outward rectifying K(+) channel. GORK represents a new member of the plant Shaker K(+) channel superfamily. When heterologously expressed in Xenopus oocytes the gene product of GORK mediated depolarization-activated K(+) currents. In agreement with the delayed outward rectifier in intact guard cells and protoplasts thereof, GORK is activated in a voltage- and potassium-dependent manner. Furthermore, the single channel conductance and regulation of GORK in response to pH changes resembles the biophysical properties of the guard cell delayed outward rectifier. Thus GORK very likely represents the molecular entity for depolarization-induced potassium release from guard cells.

  @article{Ache:2000:FEBS-Lett:11113445, abstract = {Here we report on the molecular identification, guard cell expression and functional characterization of AtGORK, an Arabidopsis thaliana guard cell outward rectifying K(+) channel. GORK represents a new member of the plant Shaker K(+) channel superfamily. When heterologously expressed in Xenopus oocytes the gene product of GORK mediated depolarization-activated K(+) currents. In agreement with the delayed outward rectifier in intact guard cells and protoplasts thereof, GORK is activated in a voltage- and potassium-dependent manner. Furthermore, the single channel conductance and regulation of GORK in response to pH changes resembles the biophysical properties of the guard cell delayed outward rectifier. Thus GORK very likely represents the molecular entity for depolarization-induced potassium release from guard cells.}, author = {Ache, P and Becker, D and Ivashikina, N and Dietrich, P and Roelfsema, M R and Hedrich, R}, journal = {FEBS Lett}, keywords = {myown}, month = {dec}, number = 2, pages = {93-98}, title = {GORK, a delayed outward rectifier expressed in guard cells of Arabidopsis thaliana, is a K(+)-selective, K(+)-sensing ion channel}, volume = 486, year = 2000 }

  %0 Journal Article %1 Ache:2000:FEBS-Lett:11113445 %A Ache, P %A Becker, D %A Ivashikina, N %A Dietrich, P %A Roelfsema, M R %A Hedrich, R %D 2000 %J FEBS Lett %N 2 %P 93-98 %T GORK, a delayed outward rectifier expressed in guard cells of Arabidopsis thaliana, is a K(+)-selective, K(+)-sensing ion channel %U https://www.ncbi.nlm.nih.gov/pubmed/11113445 %V 486 %X Here we report on the molecular identification, guard cell expression and functional characterization of AtGORK, an Arabidopsis thaliana guard cell outward rectifying K(+) channel. GORK represents a new member of the plant Shaker K(+) channel superfamily. When heterologously expressed in Xenopus oocytes the gene product of GORK mediated depolarization-activated K(+) currents. In agreement with the delayed outward rectifier in intact guard cells and protoplasts thereof, GORK is activated in a voltage- and potassium-dependent manner. Furthermore, the single channel conductance and regulation of GORK in response to pH changes resembles the biophysical properties of the guard cell delayed outward rectifier. Thus GORK very likely represents the molecular entity for depolarization-induced potassium release from guard cells.

• Br{"u}ggemann, L., Dietrich, P., Becker, D., Dreyer, I., Palme, K., Hedrich, R. (1999) Channel-mediated high-affinity K+ uptake into guard cells from Arabidopsis, Proc Natl Acad Sci U S A, 96(6), 3298–3302, available: https://www.ncbi.nlm.nih.gov/pubmed/10077678.
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  Potassium uptake by higher plants is the result of high- or low-affinity transport accomplished by different sets of transporters. Although K+ channels were thought to mediate low-affinity uptake only, the molecular mechanism of the high-affinity, proton-dependent K+ uptake system is still scant. Taking advantage of the high-current resolution of the patch-clamp technique when applied to the small Arabidopsis thaliana guard cells densely packed with voltage-dependent K+ channels, we could directly record channels working in the concentration range of high-affinity K+ uptake systems. Here we show that the K+ channel KAT1 expressed in Arabidopsis guard cells and yeast is capable of mediating potassium uptake from media containing as little as 10 microM of external K+. Upon reduction of the external K+ content to the micromolar level the voltage dependence of the channel remained unaffected, indicating that this channel type represents a voltage sensor rather than a K+-sensing valve. This behavior results in K+ release through K+ uptake channels whenever the Nernst potential is negative to the activation threshold of the channel. In contrast to the H+-coupled K+ symport shown to account for high-affinity K+ uptake in roots, pH-dependent K+ uptake into guard cells is a result of a shift in the voltage dependence of the K+ channel. We conclude that plant K+ channels activated by acid pH may play an essential role in K+ uptake even from dilute solutions.

  @article{Bruggemann:1999:Proc-Natl-Acad-Sci-U-S-A:10077678, abstract = {Potassium uptake by higher plants is the result of high- or low-affinity transport accomplished by different sets of transporters. Although K+ channels were thought to mediate low-affinity uptake only, the molecular mechanism of the high-affinity, proton-dependent K+ uptake system is still scant. Taking advantage of the high-current resolution of the patch-clamp technique when applied to the small Arabidopsis thaliana guard cells densely packed with voltage-dependent K+ channels, we could directly record channels working in the concentration range of high-affinity K+ uptake systems. Here we show that the K+ channel KAT1 expressed in Arabidopsis guard cells and yeast is capable of mediating potassium uptake from media containing as little as 10 microM of external K+. Upon reduction of the external K+ content to the micromolar level the voltage dependence of the channel remained unaffected, indicating that this channel type represents a voltage sensor rather than a K+-sensing valve. This behavior results in K+ release through K+ uptake channels whenever the Nernst potential is negative to the activation threshold of the channel. In contrast to the H+-coupled K+ symport shown to account for high-affinity K+ uptake in roots, pH-dependent K+ uptake into guard cells is a result of a shift in the voltage dependence of the K+ channel. We conclude that plant K+ channels activated by acid pH may play an essential role in K+ uptake even from dilute solutions.}, author = {Br{\"u}ggemann, L and Dietrich, P and Becker, D and Dreyer, I and Palme, K and Hedrich, R}, journal = {Proc Natl Acad Sci U S A}, keywords = {myown}, month = {mar}, number = 6, pages = {3298-3302}, title = {Channel-mediated high-affinity K+ uptake into guard cells from Arabidopsis}, volume = 96, year = 1999 }

  %0 Journal Article %1 Bruggemann:1999:Proc-Natl-Acad-Sci-U-S-A:10077678 %A Br{"u}ggemann, L %A Dietrich, P %A Becker, D %A Dreyer, I %A Palme, K %A Hedrich, R %D 1999 %J Proc Natl Acad Sci U S A %N 6 %P 3298-3302 %T Channel-mediated high-affinity K+ uptake into guard cells from Arabidopsis %U https://www.ncbi.nlm.nih.gov/pubmed/10077678 %V 96 %X Potassium uptake by higher plants is the result of high- or low-affinity transport accomplished by different sets of transporters. Although K+ channels were thought to mediate low-affinity uptake only, the molecular mechanism of the high-affinity, proton-dependent K+ uptake system is still scant. Taking advantage of the high-current resolution of the patch-clamp technique when applied to the small Arabidopsis thaliana guard cells densely packed with voltage-dependent K+ channels, we could directly record channels working in the concentration range of high-affinity K+ uptake systems. Here we show that the K+ channel KAT1 expressed in Arabidopsis guard cells and yeast is capable of mediating potassium uptake from media containing as little as 10 microM of external K+. Upon reduction of the external K+ content to the micromolar level the voltage dependence of the channel remained unaffected, indicating that this channel type represents a voltage sensor rather than a K+-sensing valve. This behavior results in K+ release through K+ uptake channels whenever the Nernst potential is negative to the activation threshold of the channel. In contrast to the H+-coupled K+ symport shown to account for high-affinity K+ uptake in roots, pH-dependent K+ uptake into guard cells is a result of a shift in the voltage dependence of the K+ channel. We conclude that plant K+ channels activated by acid pH may play an essential role in K+ uptake even from dilute solutions.
• Philippar, K., Fuchs, I., Lüthen, H., Hoth, S., Bauer, C.S., Haga, K., Thiel, G., Ljung, K., Sandberg, G., Böttger, M., Becker, D., Hedrich, R. (1999) Auxin-induced K+ channel expression represents an essential step in coleoptile growth and gravitropism, Proceedings of the National Academy of Sciences, 96(21), 12186–12191, available: https://doi.org/10.1073/pnas.96.21.12186.
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  Auxin-induced growth of coleoptiles depends on the presence of potassium and is suppressed by K+ channel blockers. To evaluate the role of K+ channels in auxin-mediated growth, we isolated and functionally expressed ZMK1 and ZMK2 (Zea mays K+ channel 1 and 2), two potassium channels from maize coleoptiles. In growth experiments, the time course of auxin-induced expression of ZMK1 coincided with the kinetics of coleoptile elongation. Upon gravistimulation of maize seedlings, ZMK1 expression followed the gravitropic-induced auxin redistribution. K+ channel expression increased even before a bending of the coleoptile was observed. The transcript level of ZMK2, expressed in vascular tissue, was not affected by auxin. In patch-clamp studies on coleoptile protoplasts, auxin increased K+ channel density while leaving channel properties unaffected. Thus, we conclude that coleoptile growth depends on the transcriptional up-regulation of ZMK1, an inwardly rectifying K+ channel expressed in the nonvascular tissue of this organ.

  @article{Philippar12101999, abstract = {Auxin-induced growth of coleoptiles depends on the presence of potassium and is suppressed by K+ channel blockers. To evaluate the role of K+ channels in auxin-mediated growth, we isolated and functionally expressed ZMK1 and ZMK2 (Zea mays K+ channel 1 and 2), two potassium channels from maize coleoptiles. In growth experiments, the time course of auxin-induced expression of ZMK1 coincided with the kinetics of coleoptile elongation. Upon gravistimulation of maize seedlings, ZMK1 expression followed the gravitropic-induced auxin redistribution. K+ channel expression increased even before a bending of the coleoptile was observed. The transcript level of ZMK2, expressed in vascular tissue, was not affected by auxin. In patch-clamp studies on coleoptile protoplasts, auxin increased K+ channel density while leaving channel properties unaffected. Thus, we conclude that coleoptile growth depends on the transcriptional up-regulation of ZMK1, an inwardly rectifying K+ channel expressed in the nonvascular tissue of this organ.}, author = {Philippar, Katrin and Fuchs, Ines and Lüthen, Hartwig and Hoth, Stefan and Bauer, Claudia S. and Haga, Ken and Thiel, Gerhard and Ljung, Karin and Sandberg, Göran and Böttger, Michael and Becker, Dirk and Hedrich, Rainer}, journal = {Proceedings of the National Academy of Sciences}, keywords = {myown}, number = 21, pages = {12186-12191}, title = {Auxin-induced K+ channel expression represents an essential step in coleoptile growth and gravitropism}, volume = 96, year = 1999 }

  %0 Journal Article %1 Philippar12101999 %A Philippar, Katrin %A Fuchs, Ines %A Lüthen, Hartwig %A Hoth, Stefan %A Bauer, Claudia S. %A Haga, Ken %A Thiel, Gerhard %A Ljung, Karin %A Sandberg, Göran %A Böttger, Michael %A Becker, Dirk %A Hedrich, Rainer %D 1999 %J Proceedings of the National Academy of Sciences %N 21 %P 12186-12191 %R 10.1073/pnas.96.21.12186 %T Auxin-induced K+ channel expression represents an essential step in coleoptile growth and gravitropism %U http://www.pnas.org/content/96/21/12186.abstract %V 96 %X Auxin-induced growth of coleoptiles depends on the presence of potassium and is suppressed by K+ channel blockers. To evaluate the role of K+ channels in auxin-mediated growth, we isolated and functionally expressed ZMK1 and ZMK2 (Zea mays K+ channel 1 and 2), two potassium channels from maize coleoptiles. In growth experiments, the time course of auxin-induced expression of ZMK1 coincided with the kinetics of coleoptile elongation. Upon gravistimulation of maize seedlings, ZMK1 expression followed the gravitropic-induced auxin redistribution. K+ channel expression increased even before a bending of the coleoptile was observed. The transcript level of ZMK2, expressed in vascular tissue, was not affected by auxin. In patch-clamp studies on coleoptile protoplasts, auxin increased K+ channel density while leaving channel properties unaffected. Thus, we conclude that coleoptile growth depends on the transcriptional up-regulation of ZMK1, an inwardly rectifying K+ channel expressed in the nonvascular tissue of this organ.

• Dreyer, I., Becker, D., Bregante, M., Gambale, F., Lehnen, M., Palme, K., Hedrich, R. (1998) Single mutations strongly alter the K+-selective pore of the K(in) channel KAT1, FEBS Lett, 430(3), 370–376, available: https://www.ncbi.nlm.nih.gov/pubmed/9688573.
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  Voltage-dependent potassium uptake channels represent the major pathway for K+ accumulation underlying guard cell swelling and stomatal opening. The core structure of these Shaker-like channels is represented by six transmembrane domains and an amphiphilic pore-forming region between the fifth and sixth domain. To explore the effect of point mutations within the stretch of amino acids lining the K+ conducting pore of KAT1, an Arabidopsis thaliana guard cell K(in) channel, we selected residues deep inside and in the periphery of the pore. The mutations on positions 256 and 267 strongly altered the interaction of the permeation pathway with external Ca2+ ions. Point mutations on position 256 in KAT1 affected the affinity towards Ca2+, the voltage dependence as well as kinetics of the Ca2+ blocking reaction. Among these T256S showed a Ca2+ phenotype reminiscent of an inactivation-like process, a phenomenon unknown for K(in) channels so far. Mutating histidine 267 to alanine, a substitution strongly affecting C-type inactivation in Shaker, this apparent inactivation could be linked to a very slow calcium block. The mutation H267A did not affect gating but hastened the Ca2+ block/unblock kinetics and increased the Ca2+ affinity of KAT1. From the analysis of the presented data we conclude that even moderate point mutations in the pore of KAT1 seem to affect the pore geometry rather than channel gating.

  @article{Dreyer:1998:FEBS-Lett:9688573, abstract = {Voltage-dependent potassium uptake channels represent the major pathway for K+ accumulation underlying guard cell swelling and stomatal opening. The core structure of these Shaker-like channels is represented by six transmembrane domains and an amphiphilic pore-forming region between the fifth and sixth domain. To explore the effect of point mutations within the stretch of amino acids lining the K+ conducting pore of KAT1, an Arabidopsis thaliana guard cell K(in) channel, we selected residues deep inside and in the periphery of the pore. The mutations on positions 256 and 267 strongly altered the interaction of the permeation pathway with external Ca2+ ions. Point mutations on position 256 in KAT1 affected the affinity towards Ca2+, the voltage dependence as well as kinetics of the Ca2+ blocking reaction. Among these T256S showed a Ca2+ phenotype reminiscent of an inactivation-like process, a phenomenon unknown for K(in) channels so far. Mutating histidine 267 to alanine, a substitution strongly affecting C-type inactivation in Shaker, this apparent inactivation could be linked to a very slow calcium block. The mutation H267A did not affect gating but hastened the Ca2+ block/unblock kinetics and increased the Ca2+ affinity of KAT1. From the analysis of the presented data we conclude that even moderate point mutations in the pore of KAT1 seem to affect the pore geometry rather than channel gating.}, author = {Dreyer, I and Becker, D and Bregante, M and Gambale, F and Lehnen, M and Palme, K and Hedrich, R}, journal = {FEBS Lett}, keywords = {myown}, month = {jul}, number = 3, pages = {370-376}, title = {Single mutations strongly alter the K+-selective pore of the K(in) channel KAT1}, volume = 430, year = 1998 }

  %0 Journal Article %1 Dreyer:1998:FEBS-Lett:9688573 %A Dreyer, I %A Becker, D %A Bregante, M %A Gambale, F %A Lehnen, M %A Palme, K %A Hedrich, R %D 1998 %J FEBS Lett %N 3 %P 370-376 %T Single mutations strongly alter the K+-selective pore of the K(in) channel KAT1 %U https://www.ncbi.nlm.nih.gov/pubmed/9688573 %V 430 %X Voltage-dependent potassium uptake channels represent the major pathway for K+ accumulation underlying guard cell swelling and stomatal opening. The core structure of these Shaker-like channels is represented by six transmembrane domains and an amphiphilic pore-forming region between the fifth and sixth domain. To explore the effect of point mutations within the stretch of amino acids lining the K+ conducting pore of KAT1, an Arabidopsis thaliana guard cell K(in) channel, we selected residues deep inside and in the periphery of the pore. The mutations on positions 256 and 267 strongly altered the interaction of the permeation pathway with external Ca2+ ions. Point mutations on position 256 in KAT1 affected the affinity towards Ca2+, the voltage dependence as well as kinetics of the Ca2+ blocking reaction. Among these T256S showed a Ca2+ phenotype reminiscent of an inactivation-like process, a phenomenon unknown for K(in) channels so far. Mutating histidine 267 to alanine, a substitution strongly affecting C-type inactivation in Shaker, this apparent inactivation could be linked to a very slow calcium block. The mutation H267A did not affect gating but hastened the Ca2+ block/unblock kinetics and increased the Ca2+ affinity of KAT1. From the analysis of the presented data we conclude that even moderate point mutations in the pore of KAT1 seem to affect the pore geometry rather than channel gating.

• Hoth, S., Dreyer, I., Dietrich, P., Becker, D., M{\"u}ller-R{"o}ber, B., Hedrich, R. (1997) Molecular basis of plant-specific acid activation of K+ uptake channels, Proc Natl Acad Sci U S A, 94(9), 4806–4810, available: https://www.ncbi.nlm.nih.gov/pubmed/9114073.
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  During stomatal opening potassium uptake into guard cells and K+ channel activation is tightly coupled to proton extrusion. The pH sensor of the K+ uptake channel in these motor cells has, however, not yet been identified. Electrophysiological investigations on the voltage-gated, inward rectifying K+ channel in guard cell protoplasts from Solanum tuberosum (KST1), and the kst1 gene product expressed in Xenopus oocytes revealed that pH dependence is an intrinsic property of the channel protein. Whereas extracellular acidification resulted in a shift of the voltage-dependence toward less negative voltages, the single-channel conductance was pH-insensitive. Mutational analysis allowed us to relate this acid activation to both extracellular histidines in KST1. One histidine is located within the linker between the transmembrane helices S3 and S4 (H160), and the other within the putative pore-forming region P between S5 and S6 (H271). When both histidines were substituted by alanines the double mutant completely lost its pH sensitivity. Among the single mutants, replacement of the pore histidine, which is highly conserved in plant K+ channels, increased or even inverted the pH sensitivity of KST1. From our molecular and biophysical analyses we conclude that both extracellular sites are part of the pH sensor in plant K+ uptake channels.

  @article{Hoth:1997:Proc-Natl-Acad-Sci-U-S-A:9114073, abstract = {During stomatal opening potassium uptake into guard cells and K+ channel activation is tightly coupled to proton extrusion. The pH sensor of the K+ uptake channel in these motor cells has, however, not yet been identified. Electrophysiological investigations on the voltage-gated, inward rectifying K+ channel in guard cell protoplasts from Solanum tuberosum (KST1), and the kst1 gene product expressed in Xenopus oocytes revealed that pH dependence is an intrinsic property of the channel protein. Whereas extracellular acidification resulted in a shift of the voltage-dependence toward less negative voltages, the single-channel conductance was pH-insensitive. Mutational analysis allowed us to relate this acid activation to both extracellular histidines in KST1. One histidine is located within the linker between the transmembrane helices S3 and S4 (H160), and the other within the putative pore-forming region P between S5 and S6 (H271). When both histidines were substituted by alanines the double mutant completely lost its pH sensitivity. Among the single mutants, replacement of the pore histidine, which is highly conserved in plant K+ channels, increased or even inverted the pH sensitivity of KST1. From our molecular and biophysical analyses we conclude that both extracellular sites are part of the pH sensor in plant K+ uptake channels.}, author = {Hoth, S and Dreyer, I and Dietrich, P and Becker, D and M{\"u}ller-R{\"o}ber, B and Hedrich, R}, journal = {Proc Natl Acad Sci U S A}, keywords = {myown}, month = {apr}, number = 9, pages = {4806-4810}, title = {Molecular basis of plant-specific acid activation of K+ uptake channels}, volume = 94, year = 1997 }

  %0 Journal Article %1 Hoth:1997:Proc-Natl-Acad-Sci-U-S-A:9114073 %A Hoth, S %A Dreyer, I %A Dietrich, P %A Becker, D %A M{\"u}ller-R{"o}ber, B %A Hedrich, R %D 1997 %J Proc Natl Acad Sci U S A %N 9 %P 4806-4810 %T Molecular basis of plant-specific acid activation of K+ uptake channels %U https://www.ncbi.nlm.nih.gov/pubmed/9114073 %V 94 %X During stomatal opening potassium uptake into guard cells and K+ channel activation is tightly coupled to proton extrusion. The pH sensor of the K+ uptake channel in these motor cells has, however, not yet been identified. Electrophysiological investigations on the voltage-gated, inward rectifying K+ channel in guard cell protoplasts from Solanum tuberosum (KST1), and the kst1 gene product expressed in Xenopus oocytes revealed that pH dependence is an intrinsic property of the channel protein. Whereas extracellular acidification resulted in a shift of the voltage-dependence toward less negative voltages, the single-channel conductance was pH-insensitive. Mutational analysis allowed us to relate this acid activation to both extracellular histidines in KST1. One histidine is located within the linker between the transmembrane helices S3 and S4 (H160), and the other within the putative pore-forming region P between S5 and S6 (H271). When both histidines were substituted by alanines the double mutant completely lost its pH sensitivity. Among the single mutants, replacement of the pore histidine, which is highly conserved in plant K+ channels, increased or even inverted the pH sensitivity of KST1. From our molecular and biophysical analyses we conclude that both extracellular sites are part of the pH sensor in plant K+ uptake channels.

• Becker, D., Dreyer, I., Hoth, S., Reid, J.D., Busch, H., Lehnen, M., Palme, K., Hedrich, R. (1996) Changes in voltage activation, Cs+ sensitivity, and ion permeability in H5 mutants of the plant K+ channel KAT1, Proc Natl Acad Sci U S A, 93(15), 8123–8128, available: https://www.ncbi.nlm.nih.gov/pubmed/8755614.
  • [ Abstract ]
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  KAT1 is a voltage-dependent inward rectifying K+ channel cloned from the higher plant Arabidopsis thaliana [Anderson, J. A., Huprikar, S. S., Kochian, L. V., Lucas, W. J. & Gaber, R. F. (1992) Proc. Natl. Acad. Sci. USA 89, 3736-3740]. It is related to the Shaker superfamily of K+ channels characterized by six transmembrane spanning domains (S1-S6) and a putative pore-forming region between S5 and S6 (H5). The 115 region between Pro-247 and Pro-271 in KAT1 contains 14 additional amino acids when compared with Shaker [Aldrich, R. W. (1993) Nature (London) 362, 107-108]. We studied various point mutations introduced into H5 to determine whether voltage-dependent plant and animal K+ channels share similar pore structures. Through heterologous expression in Xenopus oocytes and voltage-clamp analysis combined with phenotypic analysis involving a potassium transport-defective Saccharomyces cerevisiae strain, we investigated the selectivity filter of the mutants and their susceptibility toward inhibition by cesium and calcium ions. With respect to electrophysiological properties, KAT1 mutants segregated into three groups: (i) wild-type-like channels, (ii) channels modified in selectivity and Cs+ or Ca2+ sensitivity, and (iii) a group that was additionally affected in its voltage dependence. Despite the additional 14 amino acids in H5, this motif in KAT1 is also involved in the formation of the ion-conducting pore because amino acid substitutions at Leu-251, Thr-256, Thr-259, and Thr-260 resulted in functional channels with modified ionic selectivity and inhibition. Creation of Ca2+ sensitivity and an increased susceptibility to Cs+ block through mutations within the narrow pore might indicate that both blockers move deeply into the channel. Furthermore, mutations close to the rim of the pore affecting the half-activation potential (U1/2) indicate that amino acids within the pore either interact with the voltage sensor or ion permeation feeds back on gating.

  @article{Becker:1996:Proc-Natl-Acad-Sci-U-S-A:8755614, abstract = {KAT1 is a voltage-dependent inward rectifying K+ channel cloned from the higher plant Arabidopsis thaliana [Anderson, J. A., Huprikar, S. S., Kochian, L. V., Lucas, W. J. \& Gaber, R. F. (1992) Proc. Natl. Acad. Sci. USA 89, 3736-3740]. It is related to the Shaker superfamily of K+ channels characterized by six transmembrane spanning domains (S1-S6) and a putative pore-forming region between S5 and S6 (H5). The 115 region between Pro-247 and Pro-271 in KAT1 contains 14 additional amino acids when compared with Shaker [Aldrich, R. W. (1993) Nature (London) 362, 107-108]. We studied various point mutations introduced into H5 to determine whether voltage-dependent plant and animal K+ channels share similar pore structures. Through heterologous expression in Xenopus oocytes and voltage-clamp analysis combined with phenotypic analysis involving a potassium transport-defective Saccharomyces cerevisiae strain, we investigated the selectivity filter of the mutants and their susceptibility toward inhibition by cesium and calcium ions. With respect to electrophysiological properties, KAT1 mutants segregated into three groups: (i) wild-type-like channels, (ii) channels modified in selectivity and Cs+ or Ca2+ sensitivity, and (iii) a group that was additionally affected in its voltage dependence. Despite the additional 14 amino acids in H5, this motif in KAT1 is also involved in the formation of the ion-conducting pore because amino acid substitutions at Leu-251, Thr-256, Thr-259, and Thr-260 resulted in functional channels with modified ionic selectivity and inhibition. Creation of Ca2+ sensitivity and an increased susceptibility to Cs+ block through mutations within the narrow pore might indicate that both blockers move deeply into the channel. Furthermore, mutations close to the rim of the pore affecting the half-activation potential (U1/2) indicate that amino acids within the pore either interact with the voltage sensor or ion permeation feeds back on gating.}, author = {Becker, D and Dreyer, I and Hoth, S and Reid, J D and Busch, H and Lehnen, M and Palme, K and Hedrich, R}, journal = {Proc Natl Acad Sci U S A}, keywords = {myown}, month = {jul}, number = 15, pages = {8123-8128}, title = {Changes in voltage activation, Cs+ sensitivity, and ion permeability in H5 mutants of the plant K+ channel KAT1}, volume = 93, year = 1996 }

  %0 Journal Article %1 Becker:1996:Proc-Natl-Acad-Sci-U-S-A:8755614 %A Becker, D %A Dreyer, I %A Hoth, S %A Reid, J D %A Busch, H %A Lehnen, M %A Palme, K %A Hedrich, R %D 1996 %J Proc Natl Acad Sci U S A %N 15 %P 8123-8128 %T Changes in voltage activation, Cs+ sensitivity, and ion permeability in H5 mutants of the plant K+ channel KAT1 %U https://www.ncbi.nlm.nih.gov/pubmed/8755614 %V 93 %X KAT1 is a voltage-dependent inward rectifying K+ channel cloned from the higher plant Arabidopsis thaliana [Anderson, J. A., Huprikar, S. S., Kochian, L. V., Lucas, W. J. & Gaber, R. F. (1992) Proc. Natl. Acad. Sci. USA 89, 3736-3740]. It is related to the Shaker superfamily of K+ channels characterized by six transmembrane spanning domains (S1-S6) and a putative pore-forming region between S5 and S6 (H5). The 115 region between Pro-247 and Pro-271 in KAT1 contains 14 additional amino acids when compared with Shaker [Aldrich, R. W. (1993) Nature (London) 362, 107-108]. We studied various point mutations introduced into H5 to determine whether voltage-dependent plant and animal K+ channels share similar pore structures. Through heterologous expression in Xenopus oocytes and voltage-clamp analysis combined with phenotypic analysis involving a potassium transport-defective Saccharomyces cerevisiae strain, we investigated the selectivity filter of the mutants and their susceptibility toward inhibition by cesium and calcium ions. With respect to electrophysiological properties, KAT1 mutants segregated into three groups: (i) wild-type-like channels, (ii) channels modified in selectivity and Cs+ or Ca2+ sensitivity, and (iii) a group that was additionally affected in its voltage dependence. Despite the additional 14 amino acids in H5, this motif in KAT1 is also involved in the formation of the ion-conducting pore because amino acid substitutions at Leu-251, Thr-256, Thr-259, and Thr-260 resulted in functional channels with modified ionic selectivity and inhibition. Creation of Ca2+ sensitivity and an increased susceptibility to Cs+ block through mutations within the narrow pore might indicate that both blockers move deeply into the channel. Furthermore, mutations close to the rim of the pore affecting the half-activation potential (U1/2) indicate that amino acids within the pore either interact with the voltage sensor or ion permeation feeds back on gating.

• Müller-Röber, B., Ellenberg, J., Provart, N., Willmitzer, L., Busch, H., Becker, D., Dietrich, P., Hoth, S., Hedrich, S. (1995) Cloning and electrophysiological analysis of KST1, an inward rectifying K+ channel expressed in potato guard cell, EMBO Journal, 14(11), 2409–16, available: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC398354/.
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  @article{noauthororeditor, author = {Müller-Röber, B and Ellenberg, J and Provart, N and Willmitzer, L and Busch, H and Becker, D and Dietrich, P and Hoth, S and Hedrich, S}, journal = {EMBO Journal}, keywords = {myown}, number = 11, pages = {2409-16}, title = {Cloning and electrophysiological analysis of KST1, an inward rectifying K+ channel expressed in potato guard cell}, volume = 14, year = 1995 }

  %0 Journal Article %1 noauthororeditor %A Müller-Röber, B %A Ellenberg, J %A Provart, N %A Willmitzer, L %A Busch, H %A Becker, D %A Dietrich, P %A Hoth, S %A Hedrich, S %D 1995 %J EMBO Journal %N 11 %P 2409-16 %T Cloning and electrophysiological analysis of KST1, an inward rectifying K+ channel expressed in potato guard cell %U https://www.ncbi.nlm.nih.gov/pmc/articles/PMC398354/ %V 14
• Hedrich, R., Moran, O., Conti, F., Busch, H., Becker, D., Gambale, F., Dreyer, I., K{"u}ch, A., Neuwinger, K., Palme, K. (1995) Inward rectifier potassium channels in plants differ from their animal counterparts in response to voltage and channel modulators, Eur Biophys J, 24(2), 107–115, available: https://www.ncbi.nlm.nih.gov/pubmed/8582318.
  • [ Abstract ]
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  We have investigated the electrophysiological basis of potassium inward rectification of the KAT1 gene product from Arabidopsis thaliana expressed in Xenopus oocytes and of functionally related K+ channels in the plasma membrane of guard and root cells from Vicia faba and Zea mays. The whole-cell currents passed by these channels activate, following steps to membrane potentials more negative than -100 mV, with half activation times of tens of milliseconds. This voltage dependence was unaffected by the removal of cytoplasmic magnesium. Consequently, unlike inward rectifier channels of animals, inward rectification of plant potassium channels is an intrinsic property of the channel protein itself. We also found that the activation kinetics of KAT1 were modulated by external pH. Decreasing the pH in the range 8.5 to 4.5 hastened activation and shifted the steady state activation curve by 19 mV per pH unit. This indicates that the activity of these K+ channels and the activity of the plasma membrane H(+)-ATPase may not only be coordinated by membrane potential but also by pH. The instantaneous current-voltage relationship, on the other hand, did not depend on pH, indicating that H+ do not block the channel. In addition to sensitivity towards protons, the channels showed a high affinity voltage dependent block in the presence of cesium, but were less sensitive to barium. Recordings from membrane patches of KAT1 injected oocytes in symmetric, Mg(2+)-free, 100 mM-K+, solutions allowed measurements of the current-voltage relation of single open KAT1 channels with a unitary conductance of 5 pS. We conclude that the inward rectification of the currents mediated by the KAT1 gene product, or the related endogenous channels of plant cells, results from voltage-modulated structural changes within the channel proteins. The voltage-sensing or the gating-structures appear to interact with a titratable acidic residue exposed to the extracellular medium.

  @article{Hedrich:1995:Eur-Biophys-J:8582318, abstract = {We have investigated the electrophysiological basis of potassium inward rectification of the KAT1 gene product from Arabidopsis thaliana expressed in Xenopus oocytes and of functionally related K+ channels in the plasma membrane of guard and root cells from Vicia faba and Zea mays. The whole-cell currents passed by these channels activate, following steps to membrane potentials more negative than -100 mV, with half activation times of tens of milliseconds. This voltage dependence was unaffected by the removal of cytoplasmic magnesium. Consequently, unlike inward rectifier channels of animals, inward rectification of plant potassium channels is an intrinsic property of the channel protein itself. We also found that the activation kinetics of KAT1 were modulated by external pH. Decreasing the pH in the range 8.5 to 4.5 hastened activation and shifted the steady state activation curve by 19 mV per pH unit. This indicates that the activity of these K+ channels and the activity of the plasma membrane H(+)-ATPase may not only be coordinated by membrane potential but also by pH. The instantaneous current-voltage relationship, on the other hand, did not depend on pH, indicating that H+ do not block the channel. In addition to sensitivity towards protons, the channels showed a high affinity voltage dependent block in the presence of cesium, but were less sensitive to barium. Recordings from membrane patches of KAT1 injected oocytes in symmetric, Mg(2+)-free, 100 mM-K+, solutions allowed measurements of the current-voltage relation of single open KAT1 channels with a unitary conductance of 5 pS. We conclude that the inward rectification of the currents mediated by the KAT1 gene product, or the related endogenous channels of plant cells, results from voltage-modulated structural changes within the channel proteins. The voltage-sensing or the gating-structures appear to interact with a titratable acidic residue exposed to the extracellular medium.}, author = {Hedrich, R and Moran, O and Conti, F and Busch, H and Becker, D and Gambale, F and Dreyer, I and K{\"u}ch, A and Neuwinger, K and Palme, K}, journal = {Eur Biophys J}, keywords = {myown}, number = 2, pages = {107-115}, title = {Inward rectifier potassium channels in plants differ from their animal counterparts in response to voltage and channel modulators}, volume = 24, year = 1995 }

  %0 Journal Article %1 Hedrich:1995:Eur-Biophys-J:8582318 %A Hedrich, R %A Moran, O %A Conti, F %A Busch, H %A Becker, D %A Gambale, F %A Dreyer, I %A K{"u}ch, A %A Neuwinger, K %A Palme, K %D 1995 %J Eur Biophys J %N 2 %P 107-115 %T Inward rectifier potassium channels in plants differ from their animal counterparts in response to voltage and channel modulators %U https://www.ncbi.nlm.nih.gov/pubmed/8582318 %V 24 %X We have investigated the electrophysiological basis of potassium inward rectification of the KAT1 gene product from Arabidopsis thaliana expressed in Xenopus oocytes and of functionally related K+ channels in the plasma membrane of guard and root cells from Vicia faba and Zea mays. The whole-cell currents passed by these channels activate, following steps to membrane potentials more negative than -100 mV, with half activation times of tens of milliseconds. This voltage dependence was unaffected by the removal of cytoplasmic magnesium. Consequently, unlike inward rectifier channels of animals, inward rectification of plant potassium channels is an intrinsic property of the channel protein itself. We also found that the activation kinetics of KAT1 were modulated by external pH. Decreasing the pH in the range 8.5 to 4.5 hastened activation and shifted the steady state activation curve by 19 mV per pH unit. This indicates that the activity of these K+ channels and the activity of the plasma membrane H(+)-ATPase may not only be coordinated by membrane potential but also by pH. The instantaneous current-voltage relationship, on the other hand, did not depend on pH, indicating that H+ do not block the channel. In addition to sensitivity towards protons, the channels showed a high affinity voltage dependent block in the presence of cesium, but were less sensitive to barium. Recordings from membrane patches of KAT1 injected oocytes in symmetric, Mg(2+)-free, 100 mM-K+, solutions allowed measurements of the current-voltage relation of single open KAT1 channels with a unitary conductance of 5 pS. We conclude that the inward rectification of the currents mediated by the KAT1 gene product, or the related endogenous channels of plant cells, results from voltage-modulated structural changes within the channel proteins. The voltage-sensing or the gating-structures appear to interact with a titratable acidic residue exposed to the extracellular medium.

• Hedrich, R., Becker, D. (1994) Green circuits--the potential of plant specific ion channels, Plant Mol Biol, 26(5), 1637–1650, available: https://www.ncbi.nlm.nih.gov/pubmed/7532027.
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  @article{Hedrich:1994:Plant-Mol-Biol:7532027, author = {Hedrich, R and Becker, D}, journal = {Plant Mol Biol}, keywords = {myown}, month = {dec}, number = 5, pages = {1637-1650}, title = {Green circuits–the potential of plant specific ion channels}, volume = 26, year = 1994 }

  %0 Journal Article %1 Hedrich:1994:Plant-Mol-Biol:7532027 %A Hedrich, R %A Becker, D %D 1994 %J Plant Mol Biol %N 5 %P 1637-1650 %T Green circuits--the potential of plant specific ion channels %U https://www.ncbi.nlm.nih.gov/pubmed/7532027 %V 26

• Becker, D., Zeilinger, C., Lohse, G., Depta, H., Hedrich, R. (1993) Identification and biochemical characterization of the plasma-membrane H+-ATPase in guard cells of Vicia faba L., Planta, 190(1), 44–50, available: https://doi.org/10.1007/BF00195673.
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  The plasma-membrane H+-pump in guard cells generates the driving force for the rapid ion fluxes required for stomatal opening. Since our electrophysio-logical studies revealed a two fold higher pump-current density in guard cells than in mesophyll cells of Vicia faba L. we elucidated the biochemical properties of this proton-translocating ATPase in plasma-membrane vesicles isolated from both cell types. The capability of the H+ ---ATPase to create an H+ gradient is maintained in plasma-membrane vesicles derived from purified guard cells via blender maceration, high-pressure homogenization and polymer separation. The H+-pumping activity of these vesicles coincides with the presence of two polypeptides of approx. 100 and 92 kDa which are recognized by a monoclonal antibody raised against the plasma-membrane H+-ATPase from Zea mays L. coleoptiles. Comparison of H+-pumping activities of isolated membranes revealed an approximately two fold higher activity in guard cells than in mesophyll cells with respect to the total membrane protein content. Furthermore, we demonstrated by western blotting that the difference in pump activities resulted from a higher abundance of the electroenzyme per unit membrane protein in guard-cell plasma membranes. We suggest that the high H+-pump capacity is necessary to enable guard cells to respond to sudden changes in the environment by a change in stomatal aperture.

  @article{Becker1993, abstract = {The plasma-membrane H+-pump in guard cells generates the driving force for the rapid ion fluxes required for stomatal opening. Since our electrophysio-logical studies revealed a two fold higher pump-current density in guard cells than in mesophyll cells of Vicia faba L. we elucidated the biochemical properties of this proton-translocating ATPase in plasma-membrane vesicles isolated from both cell types. The capability of the H+ —ATPase to create an H+ gradient is maintained in plasma-membrane vesicles derived from purified guard cells via blender maceration, high-pressure homogenization and polymer separation. The H+-pumping activity of these vesicles coincides with the presence of two polypeptides of approx. 100 and 92 kDa which are recognized by a monoclonal antibody raised against the plasma-membrane H+-ATPase from Zea mays L. coleoptiles. Comparison of H+-pumping activities of isolated membranes revealed an approximately two fold higher activity in guard cells than in mesophyll cells with respect to the total membrane protein content. Furthermore, we demonstrated by western blotting that the difference in pump activities resulted from a higher abundance of the electroenzyme per unit membrane protein in guard-cell plasma membranes. We suggest that the high H+-pump capacity is necessary to enable guard cells to respond to sudden changes in the environment by a change in stomatal aperture.}, author = {Becker, Dirk and Zeilinger, Carsten and Lohse, Gabi and Depta, Hans and Hedrich, Rainer}, journal = {Planta}, keywords = {myown}, number = 1, pages = {44–50}, title = {Identification and biochemical characterization of the plasma-membrane H+-ATPase in guard cells of Vicia faba L.}, volume = 190, year = 1993 }

  %0 Journal Article %1 Becker1993 %A Becker, Dirk %A Zeilinger, Carsten %A Lohse, Gabi %A Depta, Hans %A Hedrich, Rainer %D 1993 %J Planta %N 1 %P 44--50 %R 10.1007/BF00195673 %T Identification and biochemical characterization of the plasma-membrane H+-ATPase in guard cells of Vicia faba L. %U http://dx.doi.org/10.1007/BF00195673 %V 190 %X The plasma-membrane H+-pump in guard cells generates the driving force for the rapid ion fluxes required for stomatal opening. Since our electrophysio-logical studies revealed a two fold higher pump-current density in guard cells than in mesophyll cells of Vicia faba L. we elucidated the biochemical properties of this proton-translocating ATPase in plasma-membrane vesicles isolated from both cell types. The capability of the H+ ---ATPase to create an H+ gradient is maintained in plasma-membrane vesicles derived from purified guard cells via blender maceration, high-pressure homogenization and polymer separation. The H+-pumping activity of these vesicles coincides with the presence of two polypeptides of approx. 100 and 92 kDa which are recognized by a monoclonal antibody raised against the plasma-membrane H+-ATPase from Zea mays L. coleoptiles. Comparison of H+-pumping activities of isolated membranes revealed an approximately two fold higher activity in guard cells than in mesophyll cells with respect to the total membrane protein content. Furthermore, we demonstrated by western blotting that the difference in pump activities resulted from a higher abundance of the electroenzyme per unit membrane protein in guard-cell plasma membranes. We suggest that the high H+-pump capacity is necessary to enable guard cells to respond to sudden changes in the environment by a change in stomatal aperture.