Overexpression of Brachypodium distachyon Methionine Sulfoxide Reductase BdMSRB1.1 Gene Contributes to Salinity or Osmotic Stress Tolerance in Arabidopsis

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Methionine sulfoxide reductases (MSRs) serve an important role in maintaining the redox balance in plant cells, but the function of the Brachypodium (Brachypodium distachyon (L.) P. Beauv.) homologs have not been reported to date. Previous studies have demonstrated that Brachypodium distachyon MSRB1.1 gene belongs to the MSRB subfamily and is induced by salinity or osmotic stress. In the present study, we found that the BdMSRB1.1 protein localized to the chloroplast. In our experiments, we used transgenic Arabidopsis thaliana with constitutive expression of BdMSRB1.1 and a loss-of-function msrb1 mutant, verified by MSR enzyme activity assays and quantitative reverse transcription-PCR. When treated with NaCl, mannitol, H2O2 or abscisic acid, the phenotype of the BdMSRB1.1 overexpression line exhibited higher tolerance than that of the wild type, whereas the msrb1 mutant was more sensitive. Under conditions of salt stress, constitutive expression of BdMSRB1.1 in Arabidopsis promoted reactive oxygen species (ROS)-scavenging capacity, supported by increased activity of ROS-removal enzymes, increased transcription levels of several ROS-clearance genes, and decreased malondialdehyde content; the msrb1 mutant plants exhibited the opposite results. Furthermore, BdMSRB1.1 overexpression led to increased soluble sugar content, in accordance with the observed upregulation of the sucrose synthase and sucrose phosphate synthase genes, which are key in the soluble sugar synthesis pathway. These findings suggest that BdMSRB1.1 plays a positive role in responses to salinity and osmotic stress.