FUNCTIONAL CHARACTERIZATION OF A PROTEIN IN THE CROSSTALK BETWEEN LIPID METABOLISM AND AUTOPHAGY IN ARABIDOPSIS
Résumé
Autophagy is an intracellular degradation process conserved among eukaryotes and critical for plant stress response. During autophagy, cytosolic material is engulfed by a growing membrane structure which ultimately closes to form a double-membrane vesicle named autophagosome. Autophagosomes are essential for autophagy by targeting cargo and then deliver it to the lytic vacuole for degradation and subsequent recycling. Nevertheless, how autophagosomes are formed remain obscure, especially in plants. By regulating the structure, identity and activities of biological membrane, lipids are potential fundamental contributors of autophagosome formation; yet their function and dynamics during autophagy stays elusive. Upstream of this project, gene co-expression analyses identified a phospholipase A2 (PLA2) as a putative component of the autophagy machinery. Phospholipases A2 catalyze phospholipids hydrolysis and generate conical lysophospholipids that promote the formation of positive curvature in biological membranes. The current project aims at exploring the implication of this lipid-remodeling enzyme in autophagy. First, we showed that the expression profile of PLA2, as ATG genes, is upregulated in conditions where autophagy is induced (aging and nutrient starvation). At steady state, we found that PLA2 localizes in the cytosol as well as in puncta scattered throughout the cytosol. Co-localization analyses with various autophagy markers showed that PLA2 labels early and late autophagy structures. Upon nutrient starvation conditions, PLA2 massively relocalizes from the cytosol to the vacuolar lumen and we found that this is dependent on active autophagy. To further characterize the role of PLA2 and its interaction with the autophagy machinery we generated transgenic lines of PLA2 that we are currently analyzing using a transdisciplinary approach to assess the impact of this protein on autophagy flux and autophagy ultrastructure, lipid metabolism as well as plant acclimation to environmental stresses.
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