Functional analysis of the PsbX protein by deletion of the corresponding gene in Synechocystis sp PCC 6803

The psbX gene (sml0002) coding for a 4.1 kDa protein in Photosystem II of p lants and cyanobacteria was deleted in both wild type and in a Photosystem I-less mutant of the cyanobacterium Synechocystis sp. PCC 6803. Polymerase chain reaction and sequencing analysis showed that the mutants had complete ly segregated. Deletion of the PsbX protein does not seem to influence grow th rate, electron transport or water oxidation ability. Whereas a high ligh t induction of the psbX mRNA could be observed in wild type, deletion of th e gene did not lead to high light sensibility. Light saturation measurement s and 77K fluorescence measurements indicated a minor disconnection of the antenna in the deletion mutant. Furthermore, fluorescence induction measure ments as well as immuno-staining of the D1 protein showed that the amount o f Photosystem II complexes in the mutants was reduced by 30%. Therefore, Ps bX does not seem to be necessary for the Photosystem II electron transport, but directly or indirectly involved in the regulation of the amount of fun ctionally active Photosystem II centres in Synechocystis sp. PCC 6803.