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Group 2 Sigma Factors Are Central Regulators of Oxidative Stress Acclimation in Cyanobacteria

ABSTRACT: The model cyanobacterium Synechocystis sp. PCC encodes nine different σ factors. SigA is the essential primary σ factor that is mainly responsible for expression of housekeeping genes during normal growth. Group 2 σ factors are non-essential in standard conditions, and actually all single, double, triple and quadruple inactivation strains of group 2 factors grow well in standard growth conditions. The roles of group 2 σ factors in oxidative stress acclimation were studied using the ΔsigBCDE strain of Synechocystis sp. PCC 6803 which is devoid of all group 2 σ factors, and triple inactivation strains, each containing one group 2 σ factor. The ΔsigBCD strain contains only SigE, ΔsigBCE only SigD, ΔsigBDE only SigC and ΔsigCDE only SigB. The expression of genes encoding known players of oxidative stress tolerance in the triple and quadruple mutants were compared in standard growth conditions using DNA microarray analysis.

ORGANISM(S): Synechocystis sp. PCC 6803

PROVIDER: GSE117478 | GEO | 2018/11/12

REPOSITORIES: GEO

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Project description:Adjustment of gene expression during acclimation to stress conditions, such as bright light, in the cyanobacterium Synechocystis sp. PCC 6803 depends on four group 2 M-OM-^C factors (SigB, SigC, SigD, SigE). A M-bM-^HM-^FsigCDE strain containing the stress responsive SigB as an only functional group 2 M-OM-^C factor appears twice as resistant to photoinhibition of photosystem II (PSII) as the control strain. Microarray analyzes of the M-bM-^HM-^FsigCDE strain indicated that 77 genes in standard conditions and 79 genes in high light were differently expressed compared to the control strain. Analysis of possible photoprotective mechanisms revealed that high carotenoid content and up-regulation of the photoprotective flavodiiron operon flv4-sll0218-flv2 protected PSII in M-bM-^HM-^FsigCDE, while up-regulation of pgr5-like, hlipB or isiA genes in the mutant strain did not offer particular protection against photoinhibition. The photoinhibition resistance was lost if M-bM-^HM-^FsigCDE was grown in high CO2 where carotenoid and Flv4-Sll0218-Flv2 contents were low. Additionally, photoinhibition resistance of the M-bM-^HM-^FrpoZ strain (lacking the omega subunit of RNA polymerase) with very high carotenoid but only low Flv4-Sll0218-Flv2 content supported the importance of carotenoids in PSII protection. Carotenoids likely protect mainly via quenching of singlet oxygen but efficient non-photochemical quenching in M-bM-^HM-^FsigCDE might offer some additional protection. Comparison of photoinhibition kinetics in control, M-bM-^HM-^FsigCDE and M-bM-^HM-^FrpoZ strains showed that protection by the flavodiiron operon was most efficient during the first minutes of high-light illumination. Cells from cyanobacteria Synechocystis sp. PCC 6803 named as control strain (CS) and group 2 sigma factor mutant M-NM-^TsigCDE (A730=1, 40 mL) were harvested directly from standard growth conditions (continuous illumination at the PPFD of 40 M-BM-5mol m-2s-1, 32M-BM-0C, ambient CO2) or after 30-min illumination a PPFD 750 M-BM-5mol m-2s-1. From three to four independent experiments were performed at each conditions.

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Group 2 Sigma Factors Are Central Regulators of Oxidative Stress Acclimation in Cyanobacteria

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