May be involved in the CpXpG methylation and in gene silencing. a 2'-deoxycytidine in DNA + S-adenosyl-L-methionine = a 5-methyl-2'-deoxycytidine in DNA + H(+) + S-adenosyl-L-homocysteine Expressed in flowers. Not detected in leaves, roots, seedlings and plants prior formation of flower buds. Alternative splice site used 50% of the time in cv. Columbia. Belongs to the class I-like SAM-binding methyltransferase superfamily. C5-methyltransferase family. Could be the product of a pseudogene. The protein is severely truncated in several ecotypes and the gene even harbors a complete retrotransposon in 3 ecotypes.