Abstract
Sll1252 was identified as a novel protein in photosystem II (PS II) complexes from Synechocystis sp. PCC 6803. To address the function of Sll1252, the corresponding gene, sll1252, was deleted in Synechocystis 6803. The growth rate and cell morphology of the mutant were not affected in normal growth medium. The growth and oxygen-evolving activity of the mutant cells was highly suppressed compared with those of wild-type cells in the Cl- and/or Ca2+-depleted medium. PS II recovery from photoinhibition was suppressed in the mutant. Despite the defects in PS II, in the light, the acceptor side of PS II was more reduced and the donor side of PS I was more oxidized compared with wild-type cells, suggesting that functional impairments also occurred in cytochrome b6/f complexes. Furthermore, the amount of IsiA protein increased in the mutant, especially in the Cl--depleted medium, indicating that the mutant cells perceive environmental stress to be greater than it is. Overall, the Sll1252 protein appears to be closely related to redox-sensing of the plastoquinone pool to balance the photosynthetic electron flow and the ability to cope with global environmental stresses.
