Whole-genome gene expression profiling in the cyanobacterium Synechococcus sp. PCC 7002 : impacts of electron transfer mutations and low CO₂ stress

Photosynthesis;Biotechnology;Cyanobacteria;Gene expression;Genomics

Weir IV, GeorgeKallas, Toivo ;

University of Wisconsin

关键词: Photosynthesis;    Biotechnology;    Cyanobacteria;    Gene expression;    Genomics;   

Others  :  https://minds.wisconsin.edu/bitstream/handle/1793/76932/WeirGeorgeIV.pdf?sequence=3&isAllowed=y

瑞士|英语

来源: University of Wisconsin

【 摘 要 】

Cyanobacteria are the ancestors of plant chloroplasts and perform ~25% of globalphotosynthesis. The photosynthetic reaction center complexes (PSII and PSI) capturesolar energy to catalyze a series of electron transfer, oxidation/reduction (redox) reactionsalong the pathway: H2O!PSII!plastoquinone (PQ) pool!cytochrome (Cyt) bfcomplex!PSI!ferredoxin. These reactions generate a transmembrane proton gradientfor adenosine triphosphate (ATP) synthesis and reduce nicotine adenine dinucleotide(NADP+) to generate NAD(P)H. ATP and NAD(P)H provide the energy and electrons todrive carbon fixation, the conversion of CO2 into carbon polymers. The Cyt bf complex isimplicated in sensing the redox potential of the PQ pool and signaling adaptive changesin photosynthesis and gene expression. This thesis research tested the hypothesis that theCyt bf complex mediates redox-dependent signaling of gene expression and sought toidentify the gene targets of this regulation. Specifically, mutants defective in Cyt bf lowandhigh-potential electron transfer chains were used to investigate the role of thesepathways in redox signaling during optimal photosynthesis and low CO2 stress. Customhigh-density oligonucleotide microarrays (NimbleGen®) and commercial (DNAStar®),as well as open-source bioinformatics programs (Bioconductor R) were used toinvestigate whole-genome gene expression responses and identify transcription start sitesof 94 key photosynthesis genes in the cyanobacterium Synechococcus sp. PCC 7002.These microarray studies identified ~250 genes (~13% of the genome) differentiallyupregulated genes. Transcription start site mapping revealed that 87 of 94 genes had upstreamtranscriptional activity. 52 of 94 genes had transcripts beginning within ~100-300base pairs of their known start codons. 34 of 94 genes showed continuous transcriptionwith neighboring genes, indicating operon structures. Specifically, this work identified anoperon of carbon assimilation genes (rbcR–ndhF3–ndhD3–cupA–A0175) upregulatedunder low CO2 as in the cyanobacterium Synechocystis sp. PCC 6803. In contrast to thewild type, Cyt bf low- and high-potential chain mutants (PetB-R214H and PetC1-!2G,respectively) upregulated a bicarbonate Na+/H+ antiporter (bicA) operon under low CO2,suggesting the induction of an additional carbon acquisition response in these mutants.Uniquely, the Cyt bf low-potential chain mutant upregulated a petF gene for ferredoxin,the electron acceptor for PSI. The Cyt bf high-potential chain mutant upregulated ndhDfor a subunit of the NAD(P)H dehydrogenase (NDH-1) complex. Both PSI and NDH-1are important for adjusting the redox balance of electron transfer and photosynthesis.These altered gene expression patterns in the Cyt bf low- and high potential chainmutants provide evidence that the distribution of electron flow in the Cyt bf complexplays a central role in regulating redox potential and photosynthesis. This researchcontributes to understanding redox regulation of gene expression in cyanobacteria andto strategies for bioproduct-biofuels production.