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. Prevents cellular oxidative damage in long nights. 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 Activated during dark in short day conditions. In short day conditions, reduced growth and increased oxidative stress late in the dark period. Belongs to the MsrA Met sulfoxide reductase family.