NrrA, a nitrogen‐responsive response regulator facilitates heterocyst development in the cyanobacterium Anabaena sp. strain PCC 7120

Abstract

SummaryThe heterocyst is a specialized cell for nitrogen fixation in the filamentous cyanobacteria, and its development is triggered by limitation of combined nitrogen in the medium. During heterocyst development, patterns of gene expression change dramatically. We identified seven genes encoding transcriptional regulators that were upregulated by nitrogen deprivation in Anabaena PCC 7120, using an Anabaena oligonucleotide microarray. Among them, the nrrA gene, which encodes a response regulator of the OmpR family with a DNA-binding domain, has shown the most prominent induction after nitrogen deprivation. Expression of nrrA increased all through the filaments within 3 h of nitrogen deprivation and became higher in proheterocysts than in vegetative cells after 12 h. Sequence analysis of the promoter region of nrrA indicated that the induction of nrrA depended on NtcA, which is the global nitrogen regulator in cyanobacteria. In the nrrA deletion mutant, heterocyst development was delayed and the induction of hetR , which is the master gene in regulation of heterocyst development, was diminished up to 24 h nitrogen deprivation. It is concluded that nrrA facilitates heterocyst development.

The pknH gene restrictively expressed in heterocysts is required for diazotrophic growth in the cyanobacterium Anabaena sp. strain PCC 7120

“…Anabaena sp. strain PCC 7120 and its derivatives were grown in the BG-11 medium (containing NaNO 3 as nitrogen source), as described previously (Ehira & Ohmori, 2006a). Liquid cultures were bubbled with air containing 1.0 % (v/v) CO 2 .…”

“…In the previous study, changes in whole-gene expression of Anabaena PCC 7120 by nitrogen deprivation were investigated using a DNA microarray (Ehira & Ohmori, 2006a). The results showed induction of alr1336, encoding a putative Ser/Thr kinase, by nitrogen deprivation.…”

“…To determine the correlation between pknH expression and heterocyst development, the transcript level of pknH in the nrrA disruptant DR4312S (Ehira & Ohmori, 2006a) and the hetR disruptant DRhetRS was determined (Fig. 1).…”

“…strain PCC 7120 (hereafter Anabaena PCC 7120), approximately 10 % of chromosomal genes are upregulated with spatiotemporal regulation in the process of heterocyst development (Ehira et al, 2003;Ehira & Ohmori, 2006a). Although little is known of the regulation of gene expression during heterocyst development, the regulatory network of the early stages of heterocyst development is known in outline.…”

“…Some of these genes are involved in heterocyst development, mostly in heterocyst maturation and function. The pknE gene, encoding a Ser/Thr protein kinase, is upregulated by nitrogen deprivation (Ehira & Ohmori, 2006a). A pknE inactivation mutant shows a defect in diazotrophic growth (Zhang et al, 1998), and overexpression of pknE blocks heterocyst differentiation (Saha & Golden, 2011).…”