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Gene expression changes in group 2 sigma factor mutant, ΔsigCDE, in standard growth conditions and after high-light treatment

ABSTRACT: 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 σ factors (SigB, SigC, SigD, SigE). A ∆sigCDE strain containing the stress responsive SigB as an only functional group 2 σ factor appears twice as resistant to photoinhibition of photosystem II (PSII) as the control strain. Microarray analyzes of the ∆sigCDE 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 ∆sigCDE, 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 ∆sigCDE was grown in high CO2 where carotenoid and Flv4-Sll0218-Flv2 contents were low. Additionally, photoinhibition resistance of the ∆rpoZ 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 ∆sigCDE might offer some additional protection. Comparison of photoinhibition kinetics in control, ∆sigCDE and ∆rpoZ strains showed that protection by the flavodiiron operon was most efficient during the first minutes of high-light illumination.

ORGANISM(S): Synechocystis sp. PCC 6803

PROVIDER: GSE50060 | GEO | 2013/09/20

SECONDARY ACCESSION(S): PRJNA215900

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:To obtain insight in the genome-wide response of heterologous carotenoid production in Saccharomyces cerevisiae, we have analyzed the transcriptome of S. cerevisiae strains overexpressing carotenogenic genes from the yeast Xanthophyllomyces dendrorhous. For this purpose, two strains producing different levels of carotenoids were grown in carbon-limited continuous cultures and genome-wide expression was analyzed. The strain producing low carotenoid levels did not exhibit a clear genome-wide transcriptional response, suggesting that low carotenoid levels do not result in cellular stress. Transcriptome analysis of a strain producing high carotenoid levels resulted in specific induction of genes involved in pleiotropic drug resistance (PDR). These genes encode ATP-binding cassette (ABC) type transporters and major facilitator transporters which are involved in secretion of toxic compounds out of cells. Our results suggest that production of high amounts of carotenoids in S. cerevisiae lead to toxicity and that these cells are prone to secrete carotenoids out of the cell. Indeed, secretion of ï¢-carotene into sunflower oil was observed upon addition of this hydrophobic solvent to the growth medium. Finally, it was observed that deletion of the ABC transporter pdr10, one of the induced PDR transporters, highly decreased the transformation efficiency of an episomal vector containing carotenogenic genes. The few colored transformants that were obtained had decreased growth rates and lower carotenoid production levels compared to control strains transformed with the same carotenogenic genes. These results indicate that Pdr10 might be specifically involved in carotenoid tolerance in S. cerevisiae strains. Experiment Overall Design: The genome wide transcriptional response of S. cerevisiae cells that heterologously produce carotenoids might provide information concerning the impact of carotenoid production on yeast physiology and might identify bottlenecks relevant for the production of these compounds. DNA microarray experiments have been proven to be a powerful tool to study the genome wide transcriptional response of S. cerevisiae to changes of the physiological state and the environment (for example 3,. Genomics approaches on cells producing heterologous metabolites to study their impact on yeast physiology have not been reported yet for S. cerevisiae. Additionally, most transcriptome studies with S. cerevisiae have been performed with cells grown in shake flasks cultures. The main drawback of shake flask cultivation is that the environment is continuously changing, which may be of high influence on carotenoid production, and interpretation of transcriptome data . Chemostat cultivation offers advantages for studies with DNA microarrays because it enables cultivation of microorganisms under tightly defined environmental conditions. An interlaboratory comparison of transcriptome data obtained in chemostat cultures has indeed demonstrated that the accuracy and reproducibility of this approach are superior to those obtained in previous studies with shake-flask cultures .

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Gene expression changes in group 2 sigma factor mutant, ΔsigCDE, in standard growth conditions and after high-light treatment

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