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Gene expression under low O2 in Synechocystis sp. PCC 6803 wild type and hik31 mutant

ABSTRACT: We have investigated the response of the cyanobacterium Synechocystis sp. PCC 6803 during growth at very low O2 concentration (bubbled with 99.9% N2/0.1% CO2). Significant transcriptional changes upon low O2 incubation included up-regulation of a cluster of genes that contained psbA1 and an operon that includes a gene encoding the two-component regulatory histidine kinase, Hik31. This regulatory cluster is of particular interest, since there are virtually identical copies on both the chromosome and on plasmid pSYSX. We used a knockout mutant lacking the chromosomal copy of hik31 and studied differential transcription during the aerobic- low O2 transition in this ΔHik31 strain and the wild type. We observed two distinct responses to this transition, one Hik31 dependent, the other Hik31 independent. The Hik31 independent responses included the psbA1 induction and genes involved in chlorophyll biosynthesis. In addition, there were changes in a number of genes that may be in involved in assembling or stabilizing Photosystem II (PSII), and the hox operon and the LexA-like protein (Sll1626) were up-regulated during low O2 growth. This family of responses mostly focused on PSII and overall redox control. There was also a large set of genes that responded differently in the absence of the chromosomal Hik31. In the vast majority of these cases, Hik31 functioned as a repressor and transcription was enhanced when Hik31 was deleted. Genes in this category encoded both core and peripheral proteins for Photosystem I and PS II, the main phycobilisome proteins, chaperones, the ATP synthase cluster and virtually all of the ribosomal proteins. These findings, coupled with the fact that ΔHik31 grew better than the wild-type under low O2 conditions, suggested that Hik31 helped to regulate growth and overall cellular homeostasis. We detected changes in the transcription of other regulatory genes that may compensate for the loss of Hik31. We conclude that Hik31 regulates an important series of genes that relate to energy production and growth and that helps to determine how Synechocystis responds to changes in O2 conditions.

ORGANISM(S): Synechocystis sp. PCC 6803

PROVIDER: GSE24882 | GEO | 2010/10/28

SECONDARY ACCESSION(S): PRJNA132025

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.

Project description:Photosystem II (PSII) is the most thermally sensitive component of photosynthesis. Thermal acclimation of this complex activity is likely to be critically important to the ability of photosynthetic organisms to tolerate temperature changes in the environment. We have analysed gene expression using whole-genome microarrays and monitored alterations in physiology during acclimation of PSII to elevated growth temperature in Synechocystis sp. PCC 6803. PSII acclimation is complete within 480 minutes of exposure to elevated temperature and is associated with a highly dynamic transcriptional response. 176 genes were identified and classified into seven distinct response profile groups. Response profiles suggest the existence of an early transient phase and a sustained phase to the acclimation response. The early phase was characterised by induction of general stress response genes, including heat shock proteins, which are likely to influence PSII thermal stability. The sustained phase consisted of acclimation-specific alterations that are involved in other cellular processes. Sustained responses included genes involved in phycobillisome structure and modification, photosynthesis, respiration, lipid metabolism and motility. Approximately 60% of genes with sustained altered expression levels have no known function. The potential role of differentially expressed genes in thermotolerance and acclimation is discussed. We have characterised the acclimation physiology of selected gene ‘knockouts’ to elucidate possible gene function in the response. All mutants show lower PSII rates under normal growth conditions. Basal PSII thermotolerance was affected by mutations in clpB1, cpcC2, hspA, htpG and slr1674. Final PSII thermotolerance was affected by mutations in cpcC2, hik34, hspA and hypA1, suggesting that these gene products play roles in long-term thermal acclimation of PSII. Gene expression levels were compared during a time-course (up to 8 hours) of thermal acclimation (from 25C to 38C) of a wild-type strain grown under continuous illumination and bubbled with CO2 -enriched air. Up to four independent biological replicates were generated and analysed. Each array: replicate matched time-point vs. 0hr control.

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Gene expression under low O2 in Synechocystis sp. PCC 6803 wild type and hik31 mutant

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