Characterization Of Site-2-Protease In The Stress Response Of Cyanobacterium Synechocystis Sp. PCC6803

Cyanobacteria are the oldest Gram-negative prokaryotes that perform oxygenicphotosynthesis. The extensive capabilities to adapt to various environmental conditions havebeen developed during their long evolution history, which make cyanobacteria valuable modelorganisms in studies of molecular mechanisms underlying the acclimation processes ofautotrophs. Many studies have demonstrated that acclimation to changing environmentalconditions require changes in gene expression over a wide range of different functions. Butmany puzzles are still remained that how these genes are regulated through signalingtransduction. So identification of transcriptional regulators and signaling transduction inresponse to environmental stress is essential to characterize the responsive mechanisms.Research during the last decades indicated that site-2-protease (S2P) mediated RegulatedIntramembrane Proteolysis (RIP) was an important signal transduction pathway of stressresponse in bacteria. Four S2P homologs in Synechocystis sp.PCC6803have been identifiedas Sll0862, Slr0643, Sll0528and Slr1821. However their function remains elusive. Hencehere in my thesis, research was performed to reveal the function of S2P in Synechocystissp.PCC6803.Firstly， genome re-sequence identified the similar and difference mutations ofSynechocystis sp. PCC6803wild-type and slr0643mutant compared with the referrencesequence, further suggested that mutations are likely to affect its phenotype. The resultsrevealed considerable evidence for recent microevolution of Synechocystis sp. PCC6803, andconfirmed that slr0643mutant was constructed sucessfully.Secondly， partially disrupted slr0643mutant could not grow at2.5mM glucosemixotrophic conditions, and the physiological data show a significant difference with thewild-type, which demonstrated the pivotal role of fully functional Slr0643in glucosemixotrophic acclimation. RNA-seq analyses figured out genes involved in mixotrophicacclimation and revealed differentially expressed genes due to slr0643disruption, whichprobably was responsible for explaning of the retarded growth of slr0643mutant underglucose mixotrophic.Thirdly，in order to explore the functions of S2P homologs in Synechocystis sp. PCC6803, real-time quantitative PCR was used to detect the time course expression profile offour S2P and ECF sigma factor under multiple stress conditions. The results clearly showedthat the expression of the sll0528gene was found to be multiple stress-stimulated, whileslr1821played a major role in cold and sorbitol tress, nevertheless, sigI was inducedsignificantly upon exposure to cold shock.