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A novel signaling cascade regulates growth of the cyanobacterium Synechocystis sp. PCC 6803 according to CO2

ABSTRACT: Gene expression changes were followed in cultures of the cyanobacterium Synechocystis sp. PCC 6803 substrain GT-T cultivated at ambient air or supplemented with 3% CO2. The acclimation to different CO2 concentrations is crucial for photoautotrophic organisms living in aquatic environments such as cyanobacteria. Samples were taken before and 1 h and 24 h after transfer to the3 % CO2 environment. The analyzed strains were wild type, a deletion mutant of gene ssl2982/rpoZ (ΔrpoZ) and two suppressor strains (R1, ΔrpoZ-S1 and R2, ΔrpoZ-S2). In cyanobacteria, elevated CO2 is known to down-regulate carbon concentrating mechanisms and accelerate photosynthesis and growth, but mechanism(s) of carbon signalling remains only poorly understood. Here we reveal a novel signalling cascade connecting the amount of CO2 and growth in the model cyanobacterium Synechocystis sp. PCC 6803. Deletion of the small ω subunit of the RNA polymerase (RNAP) in the ΔrpoZ strain prevents normal high-CO2-induced up-regulation of numerous photosynthetic genes, and low expression of peptidoglycan synthesis genes induced lysis of dividing ΔrpoZ cells in high CO2. Spontaneously raised secondary mutations in the ssr1600 gene rescued the high-CO2-sensitive phenotype of the ΔrpoZ strain. Biochemical analyses showed that the ssr1600 gene encodes an anti-σ factor antagonist of group 2 σ factor SigC, and 3D structural modelling suggest that Slr1861 functions as an anti-SigC factor. In ΔrpoZ, excess formation of RNAP-SigC lead to high CO2 sensitive phenotype, whereas the drastically reduced Ssr1600 content in the suppressor mutants reduce the formation of the RNAP-SigC holoenzyme to the similar level as in the control strain, allowing almost normal transcriptome and growth of suppressor lines in high CO2. We propose that the SigC σ factor, the anti-SigC factor Slr1861 and the anti-SigC antagonist Ssr1600 forms a growth regulating signalling cascade in cyanobacteria.

ORGANISM(S): Synechocystis sp. PCC 6803

PROVIDER: GSE233434 | GEO | 2025/05/01

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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A novel signaling cascade regulates growth of the cyanobacterium Synechocystis sp. PCC 6803 according to CO2

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