Figure 10.

Schematic Representation of the Roles Played by ADS2 in MGDG and PG Biosynthesis in Arabidopsis Leaves.

The glycerol backbones with the typical carbon length of FAs in the sn-1 and sn-2 positions are indicated to illustrate the main molecular species derived from each pathway. The head groups are always at the glycerol sn-3 position. The MGD1-DGD1 pathway represents the plastid pathway and contributes to the bulk of galactolipid synthesis at the inner envelope membranes of chloroplasts. These galactolipids are assumed to transport and integrate into the thylakoid. The alternative MGD2/3-DGD2 pathway (extraplastidic pathway) synthesizes galactolipid at the outer envelope membranes using precursor derived from the ER pathway, and these galactolipids are assumed to be transported out and integrated into extraplastidic membrane through unresolved mechanisms. ER-derived PG was assumed to integrate into multiple subcellular membranes. Reactions that are blocked in ads2 mutants are indicated. The arrow illustrates how the ads2 mutation affects carbon flux into different pathways of lipid biosynthesis. The upward-pointing arrow represents higher lipid content, and the downward-pointing arrow represents lower lipid content in ads2 mutant plants compared with the wild type. Dashed arrows represent reactions that have not been experimentally confirmed yet. DAG, diacylglycerol; CDP, cytidine-5′-diphosphate.