Abstract
The 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 sp. PCC 7120, using an Anabaena oligonucleotide microarray. Among them, the nrrA gene, which encodes a response regulator of the OmpR family, 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. In the nrrA deletion mutant, heterocyst development was delayed and the induction of hetR, a master gene in regulation of heterocyst development, was suppressed up to 24 h nitrogen deprivation. It is concluded that nrrA influences heterocyst development.
