Oxylipins are derived by oxidation of polyunsaturated fatty acids. Several oxylipins regulate growth and development as well as responses of plants to environmental stress factors. Particularly the function of jasmonic acid has been intensively investigated and its role in the defense of herbivores and necrotrophic pathogens was shown. Comparatively little is known on the role of oxylipins besides jasmonates. We are investigating the biological activity of a variety of oxylipins on the level of gene expression, metabolite production and plant physiology. One focus of our research is to elucidate the signal transduction mechanisms of oxylipins from perception to regulation of gene expression. To address this, mutants of the model plant Arabidopsis thaliana with defects in the synthesis or signaling of oxylipins are used. Furthermore, the investigation of these mutants will help to understand the function of different oxylipins in plants.
The function of jasmonic acid in plant development and stress responses is well established and several factors of the signal transduction chain have been identified. Little is known on the function and signaling of reactive electrophile oxylipins which comprises oxylipins containing an α,β-unsaturated carbonyl structure such as 12-oxo phytodienoic acid and phytoprostanes. To elucidate the signaling mechanisms, mutants with altered responses to RES-oxylipins have been isolated using a luciferase reporter line. To understand the function of RES-oxylipins, these mutants are being characterized with regard to the tolerance to abiotic stresses such as drought and salt and to resistance to bacterial and fungal pathogens. The identification of the mutations causal for the mutant phenotypes will reveal new signal transduction factors and also enables to elucidate the function of these compounds in plants.
The accumulation and function of oxylipin signals in plant leaves has been investigated in detail and it was shown that jasmonates are important signaling molecules involved in regulating development and stress responses. Less is known on the accumulation and function of these compounds in roots. We could show that roots produce jasmonates independent of leaves. Lipoxygenase 6 –which catalyses the first oxygenation step- is responsible for production of jasmonates in roots in response to wounding, drought and sorbitol stress. Mutants defective in this enzyme are more sensitive to drought stress and detritivor feeding. Currently we are investigating which oxylipins besides jasmonates are produced via the lipoxygenase 6 pathway using targeted and untargeted lipidomics with knock out and overexpressing lines. In addition, we are interested in the localization of oxylipin biosynthetic enzymes in roots and whether increased stress sensitivity is based on root to shoot signalling.
Storage of seeds is accompanied by loss of germination and oxidation of cellular components such as proteins and lipids. This aging process of seeds depends on the plant species and the storage conditions. We are studying oxidation of storage and membrane lipids in seeds of Arabidopsis thaliana and tomato, which have been naturally aged or have been subjected to accelerated aging by higher temperatures and high humidity. Oxidation can be enzymatically catalyzed or can be triggered in non-enzymatic processes by reactive oxygen species, which increase during seed aging. For enzymatic lipid oxidation lipoxygenases are responsible for the first oxygenation step of polyunsaturated fatty acids such as linoleic acid and linolenic acid. Mutants with defects in these enzymes are being used to elucidate the relevance of these enzymes for lipid oxidation during seed aging and for loss of germination.