OxyR-Dependent Transcription Response of Sinorhizobium meliloti to Oxidative Stress

Abstract

Reactive oxygen species such as peroxides play an important role in plant development, cell wall maturation, and defense responses. During nodulation with the host plant , cells are exposed to HO in infection threads and developing nodules (R. Santos, D. Hérouart, S. Sigaud, D. Touati, and A. Puppo, Mol Plant Microbe Interact 14:86-89, 2001, https://doi.org/10.1094/MPMI.2001.14.1.86). cells likely also experience oxidative stress, from both internal and external sources, during life in the soil. Here, we present microarray transcription data for wild-type cells compared to a mutant deficient in the key oxidative regulatory protein OxyR, each in response to HO treatment. Several alternative sigma factor genes are upregulated in the response to HO; the stress sigma gene shows OxyR-dependent induction by HO, while expression is induced by HO irrespective of the genotype. The activity of the RpoE2 sigma factor in turn causes increased expression of two more sigma factor genes, and Strains with deletions of showed improved survival in HO as well as increased levels of and total catalase expression. These results imply that Δ strains are primed to deal with oxidative stress. This work presents a global view of gene expression changes, and of regulation of those changes, in response to HO Like all aerobic organisms, the symbiotic nitrogen-fixing bacterium experiences oxidative stress throughout its complex life cycle. This report describes the global transcriptional changes that makes in response to HO and the roles of the OxyR transcriptional regulator and the RpoH1 sigma factor in regulating those changes. By understanding the complex regulatory response of to oxidative stress, we may further understand the role that reactive oxygen species play as both stressors and potential signals during symbiosis.

Characterization of the Sinorhizobium meliloti HslUV and ClpXP Protease Systems in Free-Living and Symbiotic States

“…We then showed that hslUV transcription was induced by low temperature and high NaCl stress and to lesser extent by treatment with H 2 O 2 . A recent mRNA microarray experiment following H 2 O 2 treatment showed signal log ratios of 2.1 and 1.8 for hslU and hslV, respectively, which is in rough agreement with our findings (32). Furthermore, we showed that clpXP1 expression was repressed by treatment with low concentrations of the aminoglycoside antibiotic neomycin, which was expected to increase the frequency of amino acid misincorporation and thereby alter protein stability (33).…”

A high-throughput system to identify inhibitors of Candidatus Liberibacter asiaticus transcription regulators

“…RpoH. Sme RpoH1 and RpoH2 alternative sigma factors mediate response to various stressors, including heat, acid, hydrogen peroxide, stationary phase growth, and envelope disrupting agents (30)(31)(32)(33). CLas RpoH is most similar to Sme RpoH1 (72% identity), which is required for an effective nitrogen-fixing symbiosis (32,34).…”

Polyamines produced by Sinorhizobium meliloti Rm8530 contribute to symbiotically relevant phenotypes ex planta and to nodulation efficiency on alfalfa

“…In Escherichia coli, PAs also combat oxidative stress by preventing DNA damage and increasing the expression of the genes for catalase (katG) and its transcriptional activator oxyR [3,44]. OxyR is well conserved in proteobacteria such as S. meliloti, where it regulates the expression of the catalase gene katA, the product of which is essential for counteracting oxidative stress [45,46]. Catalase activity assays of extracts of cells exposed to H 2 O 2 shock (2 mM) revealed no differences between the Rm8530 odc2 mutant and the wild-type (data not shown).…”