Determining the role of lipid droplet-associated triacylglycerol lipases under pathogen infection

• Applicant: Professor Dr. Till Ischebeck
• Subject Area: Plant Physiology ; Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 429585330

Lipid droplets (LDs) are special organelles that consist of proteins in a phospholipid monolayer surrounding a hydrophobic core of mostly triacylglycerol (TAG). In plants, they occur not only in seeds and pollen but also in vegetative tissues, where they accumulate under stress. Only few protein families are known that associate with LDs. Of key interest have always been triacylglycerol lipases involved in the degradation of TAG especially during seed germination. One main player in this process is the TAG lipase SUGAR DEPENDENT 1, that is crucial for seedling establishment in Arabidopsis. However, there are many further lipases predicted in Arabidopsis whose function remains to be investigated. We have been working on a family of Arabidopsis TAG lipases that are associated with LDs (as confirmed by transient expression in tobacco pollen tubes and in part by stable expression under the intrinsic promoter in A. thaliana). For four of the five members we were able to show TAG-degradation activity.On the physiological level, OBL1 is important for pollen tube growth, while OBL3 appears to play a role in pathogen defense, as a mutant is more susceptible to Pseudomonas syringae pt tomato DC3000 Delta avrPto/avrPtoB infection, an effect that could be complemented by reintroducing OBL3 under its native promoter. The function of OBL3 could be to release fatty acids for the synthesis of oxylipins (oxidized fatty acids) and its downstream products, as oxylipins can act as phytoalexines, and as a homolog of OBL1 in tomato is involved in the generation of oxylipin-derived volatiles. Also, oxylipin-producing enzymes are associated with LDs.We want to further investigate the role of OBLs in pathogen defense. The obl3 mutant will be compared to the wild type and two complemented lines in respect to its susceptibility to a variety of pathogens.By an untargeted LC-MS (liquid chromatography coupled to mass spectrometry) approach, the metabolic changes during pathogen attack with Pseudomonas syringae will be recorded in the obl3 mutant and the oblQ mutant in comparison to the wild type and two complemented lines.We then want to show that the compounds synthesized downstream of the OBLs act as phytoalexines by testing them for direct effects on the growth of pathogens.We also want to demonstrate that OBL3 changes its expression pattern under infection by investigating lines expressing OBL3 coupled to the fluorophore mVenus, or GUS under the promoter of OBL3.At last, we also want to identify interaction partners of OBL3.

• DFG Programme: Research Grants