Abstract
PSII complexes in Synechocystis sp. PCC 6803 co-exist with several uncharacterized proteins, including Sll1252, which has a N-terminal extension and an S4-like domain and is conserved in all the known photosynthetic organisms. We inserted a kanamycin-resistant gene into an upstream site of S4 domain of the sll1252 gene. Although cultures of the mutant were sustainable at 5 μmole photons m-2 s-1, they were severely photodamaged at 70 μmole photons m-2 s-1. Activity of PSII and rate of respiration in the mutant were similar to those in wild-type cells. However, activity of net photosynthesis, from H2O to MV, was drastically dropped in the mutant. Profiles of transcriptome in the mutant cells were resembled those in cells treated with DBMIB and PQ-pool in the mutant was more reduced than that in wild-type cells. These results indicate decrease in the rate of electron transfer from PQH2to Cytb6/f.
Each suppressor mutant had an transposon insertion between kanamycine-resistant gene and S4 domain, suggested that imbalance of the expression level of the S4 domain and the N-terminal portion of Sll1252 might cause the severe phenotypes.
