Regulatory Response to Carbon Starvation in Caulobacter crescentus

Bacteria adapt to shifts from rapid to slow growth, and have developed strategies for long-term survival during prolonged starvation and stress conditions. We report the regulatory response of C. crescentus to carbon starvation, based on combined high-throughput proteome and transcriptome analyses. Our results identify cell cycle changes in gene expression in response to carbon starvation that involve the prominent role of the FixK FNR/CAP family transcription factor and the CtrA cell cycle regulator. Notably, the SigT ECF sigma factor mediates the carbon starvation-induced degradation of CtrA, while activating a core set of general starvation-stress genes that respond to carbon starvation, osmotic stress, and exposure to heavy metals. Comparison of the response of swarmer cells and stalked cells to carbon starvation revealed four groups of genes that exhibit different expression profiles. Also, cell pole morphogenesis and initiation of chromosome replication normally occurring at the swarmer-to-stalked cell transition are uncoupled in carbon-starved cells

CYP76C2, an Arabidopsis thaliana cytochrome P450 gene expressed during hypersensitive and developmental cell death.

AbstractThe characterisation of an Arabidopsis thaliana cytochrome P450-encoding cDNA clone, B72, preferentially expressed during the hypersensitive response (HR) provoked by the bacterial pathogen Pseudomonas syringae pathovar maculicola, is reported. The B72 cDNA clone corresponded to the CYP76C2 gene, which belongs to a small multigene family comprising four genes. HR-triggering bacteria harbouring different avirulence genes induced the accumulation of transcripts of this P450 gene. CYP76C2 gene expression was moreover associated with various processes leading to cell death such as leaf senescence, ageing of cell cultures, wounding as well as with treatment with the necrotising heavy metal salt, lead nitrate

A partner-switching system controls activation of mixed-linkage β-glucan synthesis by c-di-GMP in Sinorhizobium meliloti

Sinorhizobium meliloti synthesizes a linear mixed-linkage (1 → 3)(1 → 4)-β-d-glucan (ML β-glucan, MLG) in response to high levels of cyclic diguanylate (c-di-GMP). Two proteins BgsA and BgsB are required for MLG synthesis, BgsA being the glucan synthase which is activated upon c-di-GMP binding to its C-terminal domain. Here we report that the product of bgrR (SMb20447) is a diguanylate cyclase (DGC) that provides c-di-GMP for the synthesis of MLG by BgsA. bgrR is the first gene of a hexacistronic bgrRSTUWV operon, likely encoding a partner-switching regulatory network where BgrR is the final target. Using different approaches, we have determined that the products of genes bgrU (containing a putative PP2C serine phosphatase domain) and bgrW (with predicted kinase effector domain), modulate the phosphorylation status and the activity of the STAS domain protein BgrV. We propose that unphosphorylated BgrV inhibits BgrR DGC activity, perhaps through direct protein–protein interactions as established for other partner switchers. A bgrRSTUWV operon coexists with MLG structural bgsBA genes in many rhizobial genomes but is also present in some MLG non-producers, suggesting a role of this partner-switching system in other processes besides MLG biosynthesis.This work was supported by Grants BIO2014-55075-P, BIO2017-83533-P and BIO2015-64480/R MINECO/FEDEREU. I.B. was supported by a Ministerio de Educación FPU fellowship (AP2010-0811). DPM was supported by Andalucía Talent Hub Program launched by the Andalusian Knowledge Agency, co-funded by the European Union’s Seventh Framework Program, Marie Skłodowska-Curie actions (COFUND –Grant Agreement no. 291780) and the Ministry of Economy Innovation, Science and Employment of the Junta de AndalucíaPeer Reviewe

Response of Sinorhizobium meliloti to Elevated Concentrations of Cadmium and Zinc▿ †

Whole-genome transcriptional profiling was used to identify genes in Sinorhizobium meliloti 1021 that are differentially expressed during exposure to elevated concentrations of cadmium and zinc. Mutant strains with insertions in metal-regulated genes and in genes encoding putative metal efflux pumps were analyzed for their metal sensitivities, revealing a crucial role for the SMc04128-encoded P-type ATPase in the defense of S. meliloti against cadmium and zinc stress

Role of Sphingomonas sp. Strain Fr1 PhyR-NepR-σEcfG Cascade in General Stress Response and Identification of a Negative Regulator of PhyR▿†

The general stress response in Alphaproteobacteria was recently described to depend on the alternative sigma factor σEcfG, whose activity is regulated by its anti-sigma factor NepR. The response regulator PhyR, in turn, regulates NepR activity in a partner-switching mechanism according to which phosphorylation of PhyR triggers sequestration of NepR by the sigma factor-like effector domain of PhyR. Although genes encoding predicted histidine kinases can often be found associated with phyR, little is known about their role in modulation of PhyR phosphorylation status. We demonstrate here that the PhyR-NepR-σEcfG cascade is important for multiple stress resistance and competitiveness in the phyllosphere in a naturally abundant plant epiphyte, Sphingomonas sp. strain Fr1, and provide evidence that the partner switching mechanism is conserved. We furthermore identify a gene, designated phyP, encoding a predicted histidine kinase at the phyR locus as essential. Genetic epistasis experiments suggest that PhyP acts upstream of PhyR, keeping PhyR in an unphosphorylated, inactive state in nonstress conditions, strictly depending on the predicted phosphorylatable site of PhyP, His-341. In vitro experiments show that Escherichia coli inner membrane fractions containing PhyP disrupt the PhyR-P/NepR complex. Together with the fact that PhyP lacks an obvious ATPase domain, these results are in agreement with PhyP functioning as a phosphatase of PhyR, rather than a kinase