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. 2015 Feb 16;5(1):587-603.
doi: 10.3390/life5010587.

Regulation of Genes Involved in Heterocyst Differentiation in the Cyanobacterium Anabaena Sp. Strain PCC 7120 by a Group 2 Sigma Factor SigC

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Regulation of Genes Involved in Heterocyst Differentiation in the Cyanobacterium Anabaena Sp. Strain PCC 7120 by a Group 2 Sigma Factor SigC

Shigeki Ehira et al. Life (Basel). .
Free PMC article

Abstract

The filamentous cyanobacterium Anabaena sp. strain PCC 7120 differentiates specialized cells for nitrogen fixation called heterocysts upon limitation of combined nitrogen in the medium. During heterocyst differentiation, expression of approximately 500 genes is upregulated with spatiotemporal regulation. In the present study, we investigated the functions of sigma factors of RNA polymerase in the regulation of heterocyst differentiation. The transcript levels of sigC, sigE, and sigG were increased during heterocyst differentiation, while expression of sigJ was downregulated. We carried out DNA microarray analysis to identify genes regulated by SigC, SigE, and SigG. It was indicated that SigC regulated the expression of genes involved in heterocyst differentiation and functions. Moreover, genes regulated by SigC partially overlapped with those regulated by SigE, and deficiency of SigC was likely to be compensated by SigE.

Figures

Figure 1
Figure 1
Changes in the transcript levels of genes encoding sigma factors after nitrogen deprivation. (A) The relative transcript levels of sigma factor genes before (white bars) and 3 h (light gray bars), 8 h (gray bars), and 24 h (dark gray bars) after nitrogen deprivation were determined by quantitative reverse transcription PCR. The transcript levels at 0 h were set to 1 for each gene. The t-test was used to compare 0 h and each time point, and data that represent a significant difference (p < 0.01 or 0.05) are marked with black or white circles; (B) the transcript levels of sigC, sigE, and sigG were determined in the wild-type (WT) strain (white bars) and the hetR disruptant (gray bars). The transcript levels at 0 h in the WT strain were set to 1. The t-test was used to compare the WT strain and the hetR disruptant, and data that represent a significant difference (p < 0.01) are marked with black circles.
Figure 2
Figure 2
Heterocyst development after nitrogen deprivation in the sigC disruptant. Micrographs were taken before and 24 h after nitrogen deprivation. The polysaccharide layer of heterocysts was stained with Alcian blue.
Figure 3
Figure 3
Changes in the transcript levels of genes downregulated by sigC disruption during heterocyst differentiation. The transcript levels of fbp, talB, coxB3, coxA2, hepA, hepB, all4160, and ntcA were determined in the wild-type (WT) strain (white bars) and the sigC disruptant (gray bars). The transcript levels at 0 h in the WT strain were set to 1. The t-test was used to compare the WT strain and the sigC disruptant, and data that represent a significant difference (p < 0.01 or 0.05) are marked with black or white circles.

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