Catalyzes the reduction of methionine sulfoxide (MetSO) to methionine in proteins. Involved in abiotic and salt stress responses. Plays a protective role against oxidative stress by restoring activity to proteins that have been inactivated by methionine oxidation. MSRA family specifically reduces the MetSO S-enantiomer. [thioredoxin]-disulfide + H2O + L-methionyl-[protein] = [thioredoxin]-dithiol + L-methionyl-(S)-S-oxide-[protein] [thioredoxin]-disulfide + H2O + L-methionine = [thioredoxin]-dithiol + L-methionine (S)-S-oxide Expressed in roots, stems, leaves and flowers. By salt, mannitol, cold, high temperatures and methyl viologen. Belongs to the MsrA Met sulfoxide reductase family.