Molecular changes of Arabidopsis thaliana plastoglobules facilitate thylakoid membrane remodeling under high light stress.

Plants require rapid responses to adapt to environmental stresses. This includes dramatic changes in the size and number of plastoglobule lipid droplets within chloroplasts. Although the morphological changes of plastoglobules are well-documented, little is known about the corresponding molecular changes. To address this gap, we have compared the quantitative proteome, oligomeric state, prenyl-lipid content, and kinase activities of A. thaliana plastoglobules under unstressed and 5-day light-stressed conditions. Our results show a specific recruitment of proteins related to leaf senescence and jasmonic acid biosynthesis under light stress and identify nearly half of the plastoglobule proteins in high native molecular weight masses. Additionally, a specific increase in plastoglobule carotenoid abundance under the light stress was consistent with enhanced thylakoid disassembly and leaf senescence, supporting a specific role for plastoglobules in senescence and thylakoid remodeling as an intermediate storage site for photosynthetic pigments. In-vitro kinase assays of isolated plastoglobules demonstrated kinase activity towards multiple target proteins, which was more pronounced in the plastoglobules of unstressed than light stressed leaf tissue and which was diminished in plastoglobules of the abc1k1/abc1k3 double mutant. These results strongly suggest that plastoglobule-localized ABC1 kinases hold endogenous kinase activity, as these were the only known or putative kinases identified in the isolated plastoglobules by deep bottom-up proteomics. Collectively, our study reveals targeted changes to the protein and prenyl-lipid composition of plastoglobules under light stress that present strategies by which plastoglobules appear to facilitate stress adaptation within chloroplasts.