Reactive Oxygen Species-Inducible ECF σ Factors of Bradyrhizobium japonicum

Abstract

Extracytoplasmic function (ECF) σ factors control the transcription of genes involved in different cellular functions, such as stress responses, metal homeostasis, virulence-related traits, and cell envelope structure. The genome of Bradyrhizobium japonicum, the nitrogen-fixing soybean endosymbiont, encodes 17 putative ECF σ factors belonging to nine different ECF σ factor families. The genes for two of them, ecfQ (bll1028) and ecfF (blr3038), are highly induced in response to the reactive oxygen species hydrogen peroxide (H2O2) and singlet oxygen (1O2). The ecfF gene is followed by the predicted anti-σ factor gene osrA (blr3039). Mutants lacking EcfQ, EcfF plus OsrA, OsrA alone, or both σ factors plus OsrA were phenotypically characterized. While the symbiotic properties of all mutants were indistinguishable from the wild type, they showed increased sensitivity to singlet oxygen under free-living conditions. Possible target genes of EcfQ and EcfF were determined by microarray analyses, and candidate genes were compared with the H2O2-responsive regulon. These experiments disclosed that the two σ factors control rather small and, for the most part, distinct sets of genes, with about half of the genes representing 13% of the members of H2O2-responsive regulon. To get more insight into transcriptional regulation of both σ factors, the 5′ ends of ecfQ and ecfF mRNA were determined. The presence of conserved sequence motifs in the promoter region of ecfQ and genes encoding EcfQ-like σ factors in related α-proteobacteria suggests regulation via a yet unknown transcription factor. By contrast, we have evidence that ecfF is autoregulated by transcription from an EcfF-dependent consensus promoter, and its product is negatively regulated via protein-protein interaction with OsrA. Conserved cysteine residues 129 and 179 of OsrA are required for normal function of OsrA. Cysteine 179 is essential for release of EcfF from an EcfF-OsrA complex upon H2O2 stress while cysteine 129 is possibly needed for EcfF-OsrA interaction.

PaperBLAST: Text-mining papers for information about homologs

“…The sixth hit (41% identity) was to CC3252 or NrsF from Caulobacter crescentus , which is proposed to be an anti-sigma factor: overexpression of NrsF prevents the induction of the SigF regulon after dichromate stress (Kohler et al 2012) . The ninth hit (33% identity) was to blr3039 or OsrA from Bradyrhizobium japonicum , which antagonizes the sigma factor EcfF and binds to it (Masloboeva et al 2012) . So we predict that PP_0995 is also an anti-sigma factor and that the SEED annotation is incorrect.…”

The Structure of Bradyrhizobium japonicum Transcription Factor FixK2 Unveils Sites of DNA Binding and Oxidation

“…Oxidation-sensitive cysteine thiols have also been described for the Desulfitobacterium dehalogenans CprK protein, but these form either intra-or intersubunit disulfide bridges upon oxidation (10). Interestingly, inhibition of a regulatory protein via one cysteine (Cys-179) has recently been described for the B. japonicum OsrA protein, which is an anti- -factor of the EcfF -factor (34). To the best of our knowledge, our investigation of FixK 2 is the first of a member of the CRP/ FNR superfamily for which a structural explanation has been found this kind of modification.…”

Regulation of H2O2 Stress-responsive Genes through a Novel Transcription Factor in the Protozoan Pathogen Entamoeba histolytica

“…In many systems, the transcriptional machinery that regulates gene expression in response to ROS is well characterized (12,13,(47)(48)(49)(50)(51)(52). In the pathogenic protist E. histolytica, increased virulence has been linked to the parasite's ability to survive exposure to ROS (21), and the transcriptional response to hydrogen peroxide stress has been characterized (2).…”