Molecular-biological analysis of function of thylakoid lipids in photosynthesis

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Thylakoid membranes in chloroplasts of eukaryotic plants and cyanobacterial cells are the sites of the primary processes of oxygenic photosynthesis. The lipid composition of thylakoid membranes is highly conserved among eukaryotic plants and cyanobacterial strains, and is distinct from that of other membranes, which contain phospholipids as the major glycerolipids. As glycerolipids thylakoid membranes contain glycolipids, monogalactosyldiacylglycerol, digalactosyldiacylglycerol and sulfoquinovosyldiacylglycerol, and a phospholipid, phosphatidylglycerol (PG). To understand the function of glycerolipids in photosynthesis in vivo, it is important to identify the genes involved in the- biosynthesis of glyceroiipids and to manipulate the composition of glycerolipids of thylakoid membranes.In this study, we have identified a gene of Synechocystis sp. PCC6803, which encodes PG phosphate synthase required for the biosynthesis of PG that is the only phospholipid in thylakoid membranes, and inactivated the gene to create a mutant that is not able to synthesize PG. The results obtained by characterization of the mutant clearly demonstrated that PG is essential for growth of Synechocystis sp. PCC6803 and an indispensable component in the maintenance of photosystem II reaction center.