Oxidised complex lipids in plants: On the occurrence and roles of esterified oxylipins

The enzymatic oxidation of lipids generates a large and diverse range of molecules called oxylipins, such as jasmonates and green leaf volatiles. While this phenomenon is mostly known to occur on free fatty acids derived from lipid hydrolysis, more and more studies now point out that complex lipids can also be directly oxidised, resulting in oxylipins said to be esterified. These esterified oxylipins form an extremely diverse family as they can originate from different lipids (e.g., galactolipids and phospholipids) and contain various acyl chains (e.g., jasmonates and colneleic acid). For instance, arabidopsides are oxidised galactolipids containing precursors of jasmonic acid as acyl chains. In this talk, we wish to discuss current knowledge on these arabidopsides with an emphasis on their involvement in plant stress responses. Although mainly studied in Arabidopsis thaliana, arabidopsides have been found in various plant species, mostly from the Brassicaceae family. They are present at low levels under physiological conditions but their concentration peaks upon stress induction. Both biotic and abiotic stresses induce arabidopside production e.g., bacterial infection and exposure to cold temperatures. We will present new data on this as we have shown most recently in our laboratory that phosphate deficiency also induces the production of arabidopsides. But what remains mostly unclear about arabidopsides is their functions in plant stress responses. We will thus discuss hypotheses and provide novel insights to explain how arabidopsides could contribute to plant stress responses. Indeed, recent work in our laboratory shows that in the context of the hypersensitive response, arabidopsides may modify the structure and properties of chloroplast membranes. Overall, we thus offer to provide a state-of-the-art overview of arabidopsides as esterified oxylipins, in addition to presenting innovative results on the implication of arabidopsides in plant stress responses.