Heterocyst Development and Pattern Formation

Aldea, M. Ramona; Kumar, K. Praveen; Golden, James W.

doi:10.1128/9781555815578.ch6

Chemical Communication Among Bacteria 2014

DOI: 10.1128/9781555815578.ch6

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Heterocyst Development and Pattern Formation

M. Ramona Aldea

K. Praveen Kumar

James W. Golden

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Cited by 4 publications

(2 citation statements)

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“…A crucial component of this program is a temporal sequence of activation events that leads to expression of the many structural and regulatory heterocyst-specific genes (1,15,18). Two regulators have key roles in heterocyst differentiation: the global transcription factor NtcA and the differentiation-specific factor HetR, both of which are required for initiation of heterocyst differentiation (5,16,39).…”

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“…Some cyanobacteria are able to undergo complex developmental processes to adapt to changes in their environment (25). The differentiation of cells, called heterocysts, that are specialized in the fixation of atmospheric nitrogen that takes place in some filamentous cyanobacteria in response to N deficiency merits special attention (1,15,40). In Anabaena and Nostoc strains, heterocysts differentiate at semiregular intervals along the filament, forming a truly multicellular bacterium with different cell types specialized in different nutritional tasks that exchange nutrients and regulators and contribute to the growth of the filament as the organismic unit (15).…”

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Transcription Activation by NtcA in the Absence of Consensus NtcA-Binding Sites in an Anabaena Heterocyst Differentiation Gene Promoter

et al. 2012

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Heterocyst differentiation is orchestrated by the N control transcriptional regulator NtcA and the differentiation-specific factor HetR. In Anabaena sp. strain PCC 7120, the devBCA operon is expressed from two different promoters activated upon N stepdown. The distal devB promoter (transcription start point [TSP] located at position −704) represents a canonical class II NtcA-activated promoter, including a consensus NtcA-binding site centered 39.5 nucleotides upstream from the TSP. Transcription activation from a second TSP (−454) requires NtcA and is impaired in hetR mutants. In a wild-type background, three different DNA fragments, including both or each individual promoter, directed gfp expression localized mainly to proheterocysts and heterocysts. Expression was undetectable in an ntcA background and, for the fragment including the proximal promoter alone, also in a hetR background. In spite of the absence of consensus NtcA-binding sequences between the two TSPs, NtcA was shown to interact with this DNA region, and NtcA and its effector, 2-oxoglutarate, were necessary and sufficient for in vitro transcription from the −454 TSP. No HetR binding to the DNA or in vitro transcription from the proximal devB TSP promoted by HetR alone were detected. However, a moderate positive effect of HetR on NtcA binding to the DNA between the two devB TSPs was observed. The proximal devB promoter appears to represent a suboptimal NtcA-activated promoter for which HetR may act as a coactivator, with the physiological effect of restricting gene activation to conditions of prevalence of high NtcA and HetR levels, such as those taking place during heterocyst differentiation.

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Transcription Activation by NtcA in the Absence of Consensus NtcA-Binding Sites in an Anabaena Heterocyst Differentiation Gene Promoter

et al. 2012

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NtcA-Regulated Heterocyst Differentiation Genes hetC and devB from Anabaena sp. Strain PCC 7120 Exhibit a Similar Tandem Promoter Arrangement

2009

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Transcription of the hetC gene, whose product is required for heterocyst differentiation, takes place from a long promoter region that includes the previously described HetR-independent, NtcA-activated promoter producing transcripts with a 5 end corresponding to position ؊571 with respect to the translational start site of hetC. Northern blot analysis indicated that the accumulation of hetC transcripts depends on HetR, and a second transcriptional start site located at position ؊293 that leads to NtcA-dependent, HetR-dependent inducible transcription of hetC was identified. Upon nitrogen stepdown, expression of a P hetC ::gfp fusion was transiently induced in specific cells that were differentiating into heterocysts, both when the whole promoter region (containing transcription start points ؊571 and ؊293) or a short version (containing only the transcription start point ؊293) was used. Expression of hetC from the ؊293 position was delayed in a strain bearing a deleted promoter region lacking sequences upstream from position ؊570. Such a strain was still able to differentiate functional heterocysts and to grow diazotrophically, although diazotrophic growth was impaired under certain conditions. Similarly, a second, NtcA-dependent, HetR-dependent transcriptional start site was identified at position ؊454 in the promoter region upstream from the devBCA operon encoding an ABC transport system involved in heterocyst maturation, in which an NtcA-dependent promoter producing transcripts starting at position ؊704 had been previously noted. Thus, the hetC and devBCA promoter regions exhibit similar tandem promoter arrangements.

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Specific Role of the Cyanobacterial PipX Factor in the Heterocysts of Anabaena sp. Strain PCC 7120

et al. 2011

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The PipX factor is a regulatory protein that seems to occur only in cyanobacteria. In the filamentous, heterocyst-forming Anabaena sp. strain PCC 7120, open reading frame (ORF) asr0485, identified as the pipX gene, is expressed mainly under conditions of combined-nitrogen deprivation dependent on the global N regulator NtcA and the heterocyst-specific regulator HetR. Primer extension and 5 rapid amplification of cDNA ends (RACE) analyses detected three transcription start points corresponding to a canonical NtcAactivated promoter (to which direct binding of NtcA was observed), an NtcA-and HetR-dependent promoter, and a consensus-type promoter, the last with putative ؊35 and ؊10 determinants. Activation of pipX took place in cells differentiating into heterocysts at intermediate to late stages of the process. Accordingly, disruption of pipX led to impaired diazotrophic growth, reduced nitrogenase activity, and impaired activation of the nitrogenase structural genes. The nitrogenase activity of the mutant was low under oxic conditions, likely resulting from inefficient protection against oxygen. In line with this, the activation of the coxB2A2C2 and coxB3A3C3 operons, encoding heterocyst-specific terminal respiratory oxidases responsible for internal oxygen removal, was deficient in the pipX mutant. Therefore, the Anabaena PipX factor shows a spatiotemporal specificity contributing to normal heterocyst function, including full activation of the nitrogenase structural genes and genes of the nitrogenase-protective features of the heterocyst.

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Heterocyst Development and Pattern Formation

Cited by 4 publications

References 111 publications

Transcription Activation by NtcA in the Absence of Consensus NtcA-Binding Sites in an Anabaena Heterocyst Differentiation Gene Promoter

Transcription Activation by NtcA in the Absence of Consensus NtcA-Binding Sites in an Anabaena Heterocyst Differentiation Gene Promoter

NtcA-Regulated Heterocyst Differentiation Genes hetC and devB from Anabaena sp. Strain PCC 7120 Exhibit a Similar Tandem Promoter Arrangement

Specific Role of the Cyanobacterial PipX Factor in the Heterocysts of Anabaena sp. Strain PCC 7120

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