Screening for inhibitors of chloroplast galactolipid synthesis acting in membrano and in planta.

The knowledge of the membrane lipid metabolism in photosynthetic cells is expected to benefit from the availability of inhibitors acting at the level of specific enzymes like MGD1 (E.C. 2.4.1.46) that catalyzes the synthesis of monogalactosyldiacylglycerol (MGDG) in chloroplasts. MGDG is a major lipid of photosynthetic membrane, interacting with photosystems. It is the precursor of digalactosyldiacylglycerol that serves as a phospholipid surrogate when plants are deprived of phosphate, and it is a source of polyunsaturated fatty acids for jasmonic acid syntheses. MGD1 is activated by phosphatidic acid and thus a coupling point between phospholipid and galactolipid metabolisms. Here we describe a method to screen for inhibitors of MGD1 assayed in liposomes. Selected compounds can therefore reach the core of the biological membranes in which the target sits. We then describe a secondary screen to evaluate the efficiency of developed compounds at the whole plant level. Major issues raised by the screening of inhibitors acting on membrane proteins are discussed and can be useful for similar targets.