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Identification Of A Cyanobacterial CRR6Protein,Slrl097, Required For Efficient Assembly Of NDH-1Complexes In Synechocystis Sp. PCC6803

Posted on:2014-04-01Degree:MasterType:Thesis
Country:ChinaCandidate:H L DaiFull Text:PDF
GTID:2250330398999031Subject:Aquatic biology
Abstract/Summary:PDF Full Text Request
Cyanobacteria represent a remarkable group among prokaryoticmicroorganisms because of their ability to perform oxygenic photosynthesis. It iswell known that four types of photosynthetic membrane protein complexes wereidentified in the thylakoid membranes, including photosystem I (PSI), photosystemII (PSII), cytochrome b6f (Cytb6f) and ATPase. Two decades ago, the fifthphotosynthetic membrane protein complex, NADPH dehydrogenase (NDH-1), wasalso identified in the cyanobacterial thylakoid membrane. The NDH-1complex isinvolved in a variety of bio-energy reactions, including cellular respiration, CO2uptake and cyclic electron transport around PSI. The NDH-1complex ofSynechocystis sp. PCC6803presents “L-type”, similar to that of chloroplast NDHcomplex. The NDH complex of chloroplasts, however, contains many subunits thatare absent in cyanobacterial NDH-1complexes. These subunits, encoded by nucleargenes, form two NDH subcomplexes, the luminal complex and the subcomplex B,which are specific to chloroplast NDH. Recently, in higher plants, reverse geneticsstudies identified many nuclear-encoded auxiliary proteins for the stabilization andassembly of chloroplast NDH complex such as chlororespiratory reduction6(CRR6). However, homologues of most of these auxiliary proteins have not beenfound in cyanobacterial genomes. The severe alteration of the Ndh subunits andauxiliary proteins of the complexes during evolution from cyanobacteria to greenplants implies that the stability and assembly of chloroplast NDH complex and cyanobacterial NDH-1complexes might be significantly different.Despite significant progress has been made in resolving the subunit compositionsand functions of the multiple NADPH dehydrogenase (NDH-1) complexes in severalcyanobacterial species, the subunit maturation and assembly of cyanobacterial NDH-1complexes are poorly understood. Here, we isolated three NDH-1-mediated cyclicelectron transfer (NDH-CET)-defective mutants that were tagged in the same slr1097gene encoding an unknown protein by screening a transposon-tagged library ofSynechocystis6803cells grown under high light. The soluble Slr1097proteinlocalizes in stroma and is required for efficient assembly of NDH-1M complexes. Toreveal how the stromal protein Slr1097influences efficient assembly NDH-1complexes, we first analyzed the interaction of Slr1097with18subunits thatconstitute NDH-1L and NDH-1M complexes by using yeast two-hybrid system. Astrong interaction was only identified between Slr1097and NdhI. To test whetherSlr1097affected the accumulation of NdhI in stromal, we detected the expression ofNdhI,-K,-H and-M between slr1097and WT. The results suggested that deletionof Slr1097resulted in a significant decrease of mature NdhI populations in stroma,but not other Ndh subunits including NdhH,-K and-M. Furthermore, we found thatthe partial deficiency of NdhI significantly affected the efficient assembly of NDH-1complex. We therefore conclude that Slr1097is mostly involved in maturation ofNdhI. The deletion of this auxiliary protein results in the reduction of NdhI andimpeded efficient assembly of NDH-1complexes, therefor Slr1097appears to becrucial to the high light-dependent phenotype of the mutants resulted from defectiveNDH-CET.
Keywords/Search Tags:NDH-1complex, NDH-CET, Slr1097, NdhI, Assembly, cyanobacteria
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