PARENT SESSION
Posters P6B Photosynthetic acclimation: Mechanisms and gene expression. Abstracts (531-578)

RNA helicase, CrhR of Synechocystis sp. PCC 6803 is required for repair of photo-damaged Photosystem II under cold stress. Jogadhenu Prakash^*,, Yu Kanesaki, Iwane Suzuki, Suleyman Allakhverdiev, Norio Murata,

ABSTRACT- RNA helicases are enzymes that unwind base paired RNAs. They are present in a wide variety of organisms ranging from bacteria to eukaryotes. The cyanobacterium Synechocystis sp. PCC 6803 contains only one gene crhR for RNA helicase, which is induced under cold stress conditions. In the present study, we investigated the role of CrhR in this organism by targeted mutagenesis of the crhR gene with the spectinomycin resistance gene cassette. The mutant of crhR exhibited a phenotype of slow growth at low temperature, such as 24^oC. We observed that the repair of photosystem II photo damage at the low temperature was much slower in the crhR mutant cells than in wild-type cells. Further, DNA microarray and Northern blotting analyses indicated that the crhR mutation decreased the transcript levels, at low temperature, of the groESL1 operon that encodes the 10-kDa chaperonin and the 60-kDa chaperonin 1 and the groEL2 gene that encodes 60-kDa chaparonin 2 indicating that the cold-inducible expression of groESL genes is regulated by CrhR. We propose that the molecular chaperonins, GroESLs, might be involved in proper folding and assembly of newly synthesized D1 protein, during PSII repair process. In crhR mutant cells, the decreased transcript levels of groESL genes could be the reason for the reduced recovery of PSII activity after photo-inhibition at low temperature. Thus, we conclude that RNA helicase regulates the expression of groESL-related genes under cold stress, which is in turn required for efficient folding and assembly of D1 protein to photo-damaged PSII. Acknowledgment: This work was supported by a Grant-in-Aid from the Japan Society for the Promotion of Science (Grant No. 1402503)

KEY WORDS: synechocystis, gene expression, photosystem II