Chloroplast proteomics highlights the subcellular compartmentation of lipid metabolism

Recent advances in the proteomic field have allowed high throughput experiments to be conducted on chloroplast samples and the data are available in several databases such as the Plant Protein Database (PPDB), or the SubCellular Proteomic Database (SUBA). However, the accurate localization of many proteins that were identified in different subplastidial compartments often remains hypothetical, thus making quantitative proteomics important for going a step further into the knowledge of Arabidopsis thaliana chloroplast proteins with regard to their accurate localization within the chloroplast. Spectral counting, a semi-quantitative proteomic strategy based on accurate mass and time tags (AMT), was used to build up AT_CHLORO, a comprehensive chloroplast proteome database with curated subplastidial localization. In this review, we focus on about a hundred enzymes involved in fatty acid biosynthesis, export and metabolism (desaturation and oxylipin metabolism), in the synthesis of chloroplast-specific glycerolipids either with a eukaryotic or a prokaryotic structure. Two main chloroplast compartments play a major role in lipid biosynthesis: the initial steps of fatty acid biosynthesis take place in the stroma, then the envelope membranes concentrate most of the proteins involved in chloroplast glycerolipid metabolism.