Removal of PSII-U in a Strain of Synechocystsis sp. PCC 6803 Lacking the PSII-O Protein Prevents Photosynthesis

Abstract

The oxygen-evolving complex (OEC) of cyanobacterial photosystem II (PSII) possesses three extrinsic proteins referred to as PSII-O, PSII-U and PSII-V which are encoded by psbO, psbU and psbV, respectively (1). Deletion or interruption of psbO does not prevent photoautotrophic growth although an enhanced sensitivity to photoinactivation is observed (2–4). In Synechocystis sp. PCC 6803 the deletion of psbV also resulted in a photoautotrophic phenotype that was susceptible to photoinactivation, however, the double mutant, lacking both psbO and psbV, was found to be an obligate photoheterotroph (5,6). In contrast, the double deletion mutant ΔpsbU/ΔpsbV exhibited a phenotype similar to that observed for the ApsbV strain which is consistent with the report that PSII-U cannot bind to PSII when PSII-V is absent in Synechococcus vulcanus (1,7). It has been suggested that PSII-U and PSII-V stabilize the OEC during heat stress in Synechococcus sp. PCC 7002 (8,9) and a role for PSII-V in protecting the Mn-cluster of the OEC from endogenous reductants has also been proposed (6,10). In this report we have examined a mutant in Synechocystis sp. PCC 6803 that lacks both PSII-O and PSII-U.