Direct evidence for requirement of phosphatidylglycerol in photosystem II of photosynthesis

Phosphatidylglycerol (PG) is considered to play an important role in the or dered assembly and structural maintenance of the photosynthetic apparatus i n thylakoid membranes. However, its function in photosynthesis remains poor ly understood. In this study we have identified a pgsA gene of Synechocysti s sp. PCC6803 that encodes a PG phosphate synthase involved in the biosynth esis of PG. A disruption of the pgsA gene allowed us to manipulate the cont ent of PG in thylakoid membranes and to investigate the function of PG in p hotosynthesis. The obtained pgsA mutant could grow only in the medium conta ining PG, and the photosynthetic activity of the pgsA mutant dramatically d ecreased with a concomitant decrease of PG content in thylakoid membranes w hen the cells grown in the presence of PG were transferred to the medium wi thout PG. This decrease of photosynthetic activity was attributed to the de crease of photosystem (PS)II activity, but not to the decrease in PSI activ ity. These findings demonstrate that PG is essential for growth of Synechoc ystis sp. PCC6803 and provide the first direct evidence that PG plays an im portant role in PSII.