The probable reversibility of the MTHFR reaction in plants suggests that they can metabolize the methyl group of 5,10-methylenetetrahydrofolate to serine, sugars and starch. (6S)-5-methyl-5,6,7,8-tetrahydrofolate + NADP(+) = (6R)-5,10-methylene-5,6,7,8-tetrahydrofolate + H(+) + NADPH (6S)-5-methyl-5,6,7,8-tetrahydrofolate + NAD(+) = (6R)-5,10-methylene-5,6,7,8-tetrahydrofolate + H(+) + NADH Plant MTHFRs strongly prefer NADH over NADPH. Not inhibited by methionine or S-adenosylmethionine. One-carbon metabolism; tetrahydrofolate interconversion. Homodimer. May be due to an intron retention. Belongs to the methylenetetrahydrofolate reductase family.