Catalyzes the reduction of methionine sulfoxide (MetSO) to methionine in proteins. Plays a protective role against oxidative stress by restoring activity to proteins that have been inactivated by methionine oxidation. MSRB family specifically reduces the MetSO R-enantiomer (By similarity). [thioredoxin]-disulfide + H2O + L-methionyl-[protein] = [thioredoxin]-dithiol + L-methionyl-(R)-S-oxide-[protein] Binds 1 zinc ion per subunit. Belongs to the MsrB Met sulfoxide reductase family. The predicted gene has been split into 2 genes: At4g04800 and At4g04810.