OxyRdependent 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 Medicago sativa, Sinorhizobium meliloti cells are exposed to H2O2 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). S. meliloti cells likely also experience oxidative stress, from both internal and external sources, during life in the soil. Here, we present microarray transcription data for S. meliloti wild-type cells compared to a mutant deficient in the key oxidative regulatory protein OxyR, each in response to H2O2 treatment. Several alternative sigma factor genes are upregulated in the response to H2O2; the stress sigma gene rpoE2 shows OxyR-dependent induction by H2O2, while rpoH1 expression is induced by H2O2 irrespective of the oxyR genotype. The activity of the RpoE2 sigma factor in turn causes increased expression of two more sigma factor genes, rpoE5 and rpoH2. Strains with deletions of rpoH1 showed improved survival in H2O2 as well as increased levels of oxyR and total catalase expression. These results imply that ΔrpoH1 strains are primed to deal with oxidative stress. This work presents a global view of S. meliloti gene expression changes, and of regulation of those changes, in response to H2O2.