Identification of a novel thylakoid protein gene involved in cold acclimation in cyanobacteria

In cyanobacteria, genes involved in cold acclimation can be upregulated in response to cold stress with or without light. By inactivating 17 such genes in Synechocystis sp. PCC 6803, slr0815 (ccr2) was identified to be a novel gene required for survival at 15 degrees C. It was upregulated by cold stress in the light. Upon exposure to low temperature, a ccr2-null mutant showed greatly reduced photosynthetic and respiratory activities within 12 h relative to the wild-type. At 48 h, the photosystem (PS)II-mediated electron transport in the mutant was reduced to less than one-third of the wild-type level, and the duration of electron transfer from the OB binding site of PSII to PSI was increased to about eight times the wild-type level, whereas the PSI-mediated electron transport remained unchanged. Using an antibody against GFP, a Ccr2-GFP fusion protein was localized to the thylakoid membrane rather than the cytoplasmic and outer membranes. Homologues to Ccr2 can be found in most cyanobacteria, algae and higher plants with sequenced genomes. Ccr2 is probably representative of a group of novel thylakoid proteins involved in acclimation to cold or other stresses.