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Primary Functional Characterization Of Slr0643 And Sll0862 In Synechocystis Sp. PCC6803

Posted on:2011-03-16Degree:MasterType:Thesis
Country:ChinaCandidate:L B ZhongFull Text:PDF
GTID:2120360308964353Subject:Sugar works
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The metalloprotease EGY1,first identified in Arabidopsis thaliana, has homologs in mammal, bacteria, archaea, plant (e.g. rice, cotton, phaseolus ) and many cyanobacteria, which indicates that EGY1 protease families have important and conserved function. Gene slr0643 and sll0862 are EGY1 homologs in Synechocystis sp. PCC6803. Exploring their function may lay the foundation for revealing the function and mechanism of other EGY1 familes and also facilite to illustrate the photosynthesis regulatory mechanisms in cyanobacteria.Bioinformatics revealed the proteins encoded by slr0643 and sll0862 were transmembrane proteins resident in cytoplasmic or thylakoid with targeting sequences. They contain the conserved motif HEXXH and NPDG as the other members of M50 protease. In this thesis, two mutants of Synechocystis sp. PCC6803, slr0643::km and sll0862::km, were constructed by interrupting slr0643 and sll0862 gene with kanamycin gene. The complete replacement of the wild type copies by interrupted copies were confirmed by PCR and RT-PCR. Then the physiological and biochemical properties of these two interrupted mutants were characterized. Compared with wild type, the photosynthetical system I (PSI) content in slr0643::km reduced significantly and the electron transport efficiency of PSI and PSII were reduced to 68% and 88%, which reduced the whole electron transport chain efficiency to 67%. Thus, the growth rate of slr0643::km was slower than wild type. But thylakoid membranes in slr0643::km keep their integrity. Together these data indicate that the protein encoded by slr0643 is involved in the assembly of photosynthetical system but not in biogenesis of thylakoid membranes. In addition, significant differences were observed between wild type and slr0643::km, when they were transfered from low light (20μE/m~2·s)to high light (100μE/m~2·s). This phenomenon indicted slr0643 may participate in regulating response to high light induced oxidative stress. Compared with wild type, though the chlorophyll a content remain at the same level, carotenoid change significantly in the sll0862::km mutant. HPLC results revealed myxoxanthophyll increased by one time while zeaxanthin, echinenone andβ-carotene decreased. This data indicated protein encoded by sll0862 involved in biosynthesis of carotenoid, most possibly on synthesis of myxoxanthophyll and/orβ-carotene. Results of this thesis lay foundation of revealing function and regulation mechanism of slr0643 and sll0862 gene in the future.
Keywords/Search Tags:Synechocystis sp. PCC6803, slr0643, sll0862, Photosystem assembly, Carotenoid biosynthesis
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