Chloroplast phosphatases LPP and LPP1 facilitate conversion of extraplastidic phospholipids to galactolipids

Galactolipids comprise the majority of chloroplast membranes in plants, and their biosynthesis requires dephosphorylation of phosphatidic acid at the chloroplast envelope membranes. In Arabidopsis (Arabidopsis thaliana), the lipid phosphate phosphatases LPP gamma, LPP epsilon 1, and LPP epsilon 2 have been previously implicated in chloroplast lipid assembly, with LPP gamma being essential, as null mutants were reported to exhibit embryo lethality. Here, we show that lpp gamma mutants are in fact viable and that LPP gamma, LPP epsilon 1, and LPP epsilon 2 do not appear to have central roles in the plastid pathway of membrane lipid biosynthesis. Redundant LPP gamma and LPP epsilon 1 activity at the outer envelope membrane is important for plant development, and the respective lpp gamma lpp epsilon 1 double mutant exhibits reduced flux through the ER pathway of galactolipid synthesis. While LPP epsilon 2 is imported and associated with interior chloroplast membranes, its role remains elusive and does not include basal nor phosphate limitation-induced biosynthesis of glycolipids. The specific physiological roles of LPP gamma, LPP epsilon 1, and LPP epsilon 2 are yet to be uncovered, as does the identity of the phosphatidic acid phosphatase required for plastid galactolipid biosynthesis. Chloroplast lipid phosphatases LPP gamma and LPP epsilon 1 have redundant activity in facilitating conversion of extraplastidic phosphatidic acid to galactolipids and are important for plant growth.