Arabidopsis Root-Abundant Cytosolic Methionine Sulfoxide Reductase B Genes MsrB7 and MsrB8 are Involved in Tolerance to Oxidative Stress

Excess reactive oxygen species (ROS) accumulation under various environmental stresses can damage intracellular polysaccharides, DNA, lipids and proteins. Methionine sulfoxide reductase (MSR) participates in a protein repair system that is one of the defensive mechanisms that diminishes oxidative destruction. In Arabidopsis, cytosolic MsrB7 and MsrB8 are oxidative stress-inducible protein repair enzymes that are abundant in the root. Here methyl viologen (MV) treatment was demonstrated to increase greatly the accumulation of H₂O₂ in MsrB7-knockdown, MsrB8-knockdown and wild-type Arabidopsis, but not in transgenic plants overexpressing MsrB7 or MsrB8. The reduction in H₂O₂ level under MV treatment in these overexpressing plants coincided with increased activity of glutathione S-transferase (GST), a herbicide-detoxifying enzyme. MsrB7 and MsrB8 are suggested to play an important role in defense against oxidative stress. Transgenic plants overexpressing MsrB7 or MsrB8 were viable and survived after MV and H₂O₂ treatment. Ectopic expression of specific cytosolic MsrB genes may be useful for application in crop improvement.