Functional Analysis of SI10875 in the Regulation of PS I Activity in Synechocystis sp.PCC 6803 / 中国生物化学与分子生物学报

Phylloquinone is a unique cofactor of photosystem I (PS I ) , made up of a redox-active naphthoquinone ring attached to a partially saturated C-20 phytyl side chain.At present, the research on the biosynthesis of phylloquinone in cyanobacteria is mainly focused on the formation of naphthoquinone ring, while there was a shortage of reports in the biosynthesis of phytyl side chain.In this study, a highly homologous protein S110875 was found in Synechocystis sp.PCC 6803 by homologous sequence alignment with VTE6, a kinase involved in phylloquinone biosynthesis by converting phytyl-phosphate into phytyl- diphosphate in Arabidopsis thaliana.The resulting S110875 mutant, called As/Z0875, accumulates none phylloquinone and tocopherol, as well as low amounts of chlorophyll content (P<0.05).The mutant had retarded growth in the absence of added glucose.Chlorophyll fluorescence, P700 absorbance changes, 77 K fluorescence emission spectra and Western blot analyses showed that in As/Z0875, PS I function was impaired and accumulation of the PS I complex was reduced remarkably (P<0.01), indicating that phvlloquinone deficiency affected PS I function, thus hindering the normal growth of cyanobacteria.Our results provide the evidence that the phytol phosphorylation pathway is essential for phylloquinone biosynthesis in cyanobacteria for the first time, and a basis for further investigate the protein synthesis, assembly and stability of PS I complex in cyanobacteria.

Identification of a Pair of Toxin-antitoxin (TA) Gene in the Chromosome of Cyanobacteria Synechocystis sp. PCC6803 / 微生物学通报

Chromosomally encoded toxin–antitoxin (TA) systems are thought to result in growth arrest and eventual cell death upon exposure to environmental stress in E. coli. In the chromosome of cyanobacteria Synechocystis sp. PCC6803, the genetic organization of a 360 bp open reading frame (ORF), slr0664, and another small ORF of 256 bp, ssr1114, is similar to that of TA system. The predicted protein encoded by slr0664 is homologous to RelE, but neither homologue of ssr1114 nor ssr1114-encoding protein was found in TA system. To see whether slr0664 encodes a toxin protein, ssr1114 encodes an antitoxin, an expressing plasmid containing promoter Plac and PBAD, was constructed. In this construct, Both slr0664 and ssr1114 were controlled by Plac and PBAD, respectively. Expression of slr0664 in Escherichia coli results in the inhi-bition of bacterial growth, the expression of ssr1114 neutralize the toxicity of slr0664 expression. These re-sults show that slr0664 is toxin gene and ssr1114 is antitoxin gene, both ssr1114 and slr0664 constitute achromosomal TA system in Synechocystis sp. PCC6803.