DNA binding properties of the HrmR protein of Nostoc punctiforme responsible for transcriptional regulation of genes involved in the differentiation of hormogonia

Abstract

SummaryNostoc punctiforme is an example of a filamentous cyanobacterium that is capable of differentiating nongrowing cells that constitute gliding filaments termed hormogonia. These gliding filaments serve in short distance dispersal and as infective units in establishing a symbiosis with plants, such as the bryophyte Anthoceros punctatus . Mutants of N . punctiforme exist which show elevated levels of initial infection of A . punctatus as a consequence of repeated cycles of hormogonium differentiation. Such mutations occur within the hrmA and hrmU genes. Further characterization of the hrm locus revealed several genes with an organizational and predicted protein sequence similarity to genes of heterotrophic bacteria that are involved in hexuronic acid metabolism. Genes in the N. punctiforme locus are transcribed in response to the presence of a plant extract containing hormogonium-repressing factors. A predicted transcriptional repressor encoded in the locus, HrmR , was shown herein to be a specific DNA binding protein that regulates the transcription of its own gene and that of hrmE , a nearby gene. The ability of HrmR to bind DNA was abolished upon addition of either galacturonate or lysate from specifically induced N . punctiforme cells, implying that the in vivo HrmR binding activity is modulated via an internal compound, most likely a sugar molecule.

Regulation of Fructose Transport and Its Effect on Fructose Toxicity in Anabaena spp

“…The striking similarity in these regions suggests that hrmE and frtA have similar modes of regulation, which is supported by the similarity of FrtR and HrmR. There are two HrmR binding sites in the promoter region of hrmR, and HrmR binds to this region; thus, it is autoregulatory (8). Since frtA and frtR in A. variabilis are divergent genes (Fig.…”

“…The hrmE gene in N. punctiforme is regulated by HrmR, a homolog of FrtR (8). Although there is no similarity between HrmE in N. punctiforme and FrtA in A. variabilis, there is striking similarity in the regulatory regions of these genes.…”

“…strain PCC 7120 and N. spumigena. The homolog of FrtR in N. punctiforme (73% identical) is HrmR (Npun02008536), a repressor of its own gene, hrmR, and of hrmE (Npun02008530), which are genes involved in the differentiation of hormogonia in N. punctiforme (8). There is no homolog of hrmE in A. variabilis or in the genomes of any other sequenced cyanobacteria.…”

Improving the coverage of the cyanobacterial phylum using diversity-driven genome sequencing

“…This is consistent with previous studies (11) that noted the presence of essential genes for heterocyst development in nonheterocystous cyanobacteria. Similarly, this could explain why several genes previously proposed to underlie other morphological attributes (e.g., hormogonium or akinete formation) (12,13) are also found spread across the phylum, suggesting they have lineage-specific functions (SI Appendix, Dataset S2). Overall, comparison of the functional categories of Clusters of Orthologous Groups (COG) from the five morphological subsections shows that, in general, more complex morphologies are enriched in genes found in signal transduction and transcription-related functional categories (SI Appendix, Fig.…”

Nostopeptolide plays a governing role during cellular differentiation of the symbiotic cyanobacterium Nostoc punctiforme

“…Different plant partners were shown to strictly downregulate the factor in symbiosis, thereby unveiling a complex cross-talk network between plants and Nostoc. the differentiation response of N. punctiforme to plant signals and the infection process itself (11)(12)(13). Notably, a large part of the 9-Mbp genome of N. punctiforme ATCC 29133 is devoted to the synthesis of a multitude of secondary metabolites of the nonribosomal peptide (NRPS) and polyketide (PKS) classes (14).…”