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In vivo recruitment analysis and a mutant strain without any group 2 σ factors reveal roles of different σ factors in cyanobacteria

ABSTRACT: In eubacteria, replacement of one σ factor in the RNA polymerase (RNAP) holoenzyme by another one changes the transcription pattern. Cyanobacteria are eubacteria characterized by oxygenic photosynthesis and they typically encode numerous group 2 σ factors that closely resemble the essential primary σ factor. A mutant strain of the model cyanobacterium Synechocystis sp. PCC 6803 without functional group 2 σ factors (named as ΔsigBCDE) could not acclimate to heat, high salt, or bright light stress but in standard conditions ΔsigBCDE grew only 9% slower than the control strain. One-fifth of the genes in ΔsigBCDE were differently expressed compared to the control strain in standard growth conditions and several physiological changes in photosynthesis, and pigment and lipid compositions were detected. To directly analyze the σ factor content of RNAP holoenzyme in vivo, a His-tag was added to the γ subunit of RNAP in Synechocystis and RNAPs were collected. The results revealed that all group 2 σ factors were recruited by RNAP in standard conditions, but recruitment of SigB and SigC increased in heat stress, SigD in bright light, SigE in darkness and SigB, SigC and SigE in high salt, explaining the poor acclimation of ΔsigBCDE to these stress conditions.

ORGANISM(S): Synechocystis sp. PCC 6803

PROVIDER: GSE69981 | GEO | 2015/09/15

SECONDARY ACCESSION(S): PRJNA287323

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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In vivo recruitment analysis and a mutant strain without any group 2 σ factors reveal roles of different σ factors in cyanobacteria

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