Abstract
A number of photosystem II (PSII) mutants have been shown to grow photoautotrophically in media at pH 10.0 but not pH 7.5 [Eaton-Rye JJ, Shand JA, Nicoll WS (2003) FEBS Letters 543: 148-153]. These strains contain two or three mutations, including the absence of at least one of the extrinsic proteins associated with the lumenal face of PSII. However, these strains do not all lack the same extrinsic protein and some also contain mutations in a hydrophilic loop of the chlorophyll a-binding core antenna protein CP47. In pH 10.0 media, the different strains exhibited variation in photoautotrophic growth, oxygen evolution and PSII assembly. At pH 10.0 a strain lacking the two extrinsic proteins PsbO and PsbU assembled the highest number of PSII centres compared to other pH-sensitive mutants. To investigate the mechanisms enabling growth at elevated pH, we have used microarray analyses to determine the gene expression changes associated with the pH dependent recovery of the ΔPsbO:ΔPsbU mutant. We have compared the impact of the transition from pH 10.0 to pH 7.5 on gene expression in the wild type and in the ΔPsbO:ΔPsbU strain.