The sll1418 gene encodes a PsbP-like protein in Synechocystis sp. PCC 6803. Expression of sll1418 was similar in BG-11 and in Cl- - or Ca2+ -limiting media, and inactivation of sll1418 did not prevent photoautotrophic growth in normal or nutrient-limiting conditions. Also the wild-type and DeltaPsbP strains exhibited similar oxygen evolution and assembly of Photosystem II (PS II) centers. Inactivation of sll1418 in the DeltaPsbO: DeltaPsbP, DeltaPsbQ:DeltaPsbP, DeltaPsbU:DeltaPsbP and DeltaPsbV:DeltaPsbP mutants did not prevent photoautotrophy or alter PS II assembly and oxygen evolution in these strains. Moreover, the absence of PsbP did not affect the ability of alkaline pH to restore photoautotrophic growth in the DeltaPsbO:DeltaPsbU strain. The PsbO, PsbU and PsbV proteins are required for thermostability of PS II and thermal acclimation in Synechocystis sp. PCC 6803 [Kimura et al. (2002) Plant Cell Physiol 43: 932-938]. However, thermostability and thermal acclimation in DeltaPsbP cells were similar to wild type. These results are consistent with the conclusion that PsbP is associated with approximately 3 of PS II centers, and may play a regulatory role in PS II [Thornton et al. (2004) Plant Cell 16: 2164-2175].

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