Analysis of photoregulation in a cyanobacterium through reverse genetics

Abstract

Synechococcus sp. strain PCC 7942, a unicellular cyanobacterium which utilizes a plant-like photosynthetic apparatus, was the model organism in a search for regulators of photosynthesis genes. Cyanobacteria share with plants and algea the need to regulate expression of photosynthesis genes. This regulatory control has similarity to known cyanobacterial molecular mechanisms. These relationships were exploited in this study in an attempt to identify sequences encoding regulators of photosynthesis in cyanobacteria. Cyanobacteria have well characterized genetic tools which would allow for further dissection of the regulation if a gene were isolated. It was this desire that motivated the identification and inactivation of a response regulator gene. As determined by the genetic interruption, the cloned response regulator srrB, is not involved in the transcriptional induction of the psbAII gene encoding the photosystem 11 reaction center protein DI under high-light conditions. No phenotype is known for srrB. A publication describing an Arabidopsis thaliana, blue-light photoreceptor which is encoded by a gene that has high-similarity to a class of cyanobacterial genes encoding blue-light activated DNA repair enzymes, motivated a search for a sequence related to the blue-light photorepair gene in Synechococcus PCC 7942 that might encode a photoreceptor. The identified sequences show no similarity to either previously identified photoreceptors or photorepair enzymes. Similarly, the publication of the DNA sequence of the entire genome from the related cyanobacterium Synechocystis sp. strain 6803, which revealed a sequence encoding a protein highly similar to a known photoreceptor, prompted a search in Synechococcus PCC 7942 for the homologous sequence.