Catalyzes the reduction of methionine sulfoxide (MetSO) to methionine in proteins. Specifically reduces the MetSO R-enantiomer. Plays a protective role against oxidative stress by restoring activity to proteins that have been inactivated by methionine oxidation. May play an essential function in association with MSRB1 in maintaining vegetative growth during environmental constraints, through the preservation of photosynthetic antennae. MSRB1 and MSRB2 account for most of the leaf peptide MSR capacity. [thioredoxin]-disulfide + H2O + L-methionyl-[protein] = [thioredoxin]-dithiol + L-methionyl-(R)-S-oxide-[protein] Binds 1 zinc ion per subunit. kcat is 0.028 sec(-1) with dabsyl-MetSO as substrate. Expressed in stems, young leaves, floral buds and flowers. Expressed at low levels in roots, mature leaves and siliques (at protein level). By photooxidative stress. Reduced by thioredoxins f, m, x and y through a dithiol-disulfide exchange involving both redox-active Cys of the two partners. Belongs to the MsrB Met sulfoxide reductase family.