Molecular-biological analysis of function of thylakoid lipids in photosynthesis

真核植物和蓝藻细胞叶绿体中的类囊体膜是氧合光合作用初级过程的场所。类囊体膜的脂质组成在真核植物和蓝藻中是高度保守的，不同于以磷脂为主要甘油脂的其他膜。作为甘油脂类，类囊体膜含有糖脂、单半乳糖二酰甘油、双半乳糖二酰甘油和磺基喹诺酮二甘油，以及磷脂，磷脂酰甘油(PG)。为了了解甘油脂在体内光合作用中的作用，鉴定参与甘油脂生物合成的基因和调控类囊体膜甘油脂的组成是非常重要的。PCC6803编码PG生物合成所需的PG磷酸合成酶，PG是类囊体膜上唯一的磷脂，并使该基因失活，创建了一个不能合成PG的突变体。对突变体的鉴定结果表明，PG对聚球藻的生长是必需的。PCC6803是光系统II反应中心维护不可缺少的组成部分。

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.