Abstract
In this study, we examined the role of DGDG in photosystem (PS) II using a disruptant of dgdA gene (slr1508) of Synechocystis sp. PCC6803 that is defective in DGDG synthesis. Despite the lack of DGDG, the mutant cells grew photoautotrophically as rapidly as that of the wild-type cells, indicating that DGDG is not essential for photosynthesis in Synechocystis. However, the oxygen-evolving activity of PSII was decreased in the mutant. Analyses of PSII complex purified from the mutant cells indicated that the extrinsic proteins PsbU, PsbV, and PsbO were substantially dissociated from PSII complex. In addition, we found that heat susceptibility but not dark-induced inactivation of oxygen evolution was notably increased in the mutant cells in comparison to the wild-type cells, suggesting that PsbU subunit is dissociated from PSII complex even in vivo. These results demonstrate that DGDG plays important roles in PSII through the binding of extrinsic proteins.
