Maintains chromatin CpG methylation that plays a role in genomic imprinting, regulation of embryogenesis and seed viability. Required for proper patterns of CG DNA methylation in dividing cells. Required for MEA promoter methylation in seeds. a 2'-deoxycytidine in DNA + S-adenosyl-L-methionine = a 5-methyl-2'-deoxycytidine in DNA + H(+) + S-adenosyl-L-homocysteine Expressed in flowers, embryos and endosperm. Late-flowering phenotype caused by ectopic expression of FWA gene. Asymmetric zygote division and abnormal embryos. Displays genome hypomethylation, strong reduction of CpG methylation in centromeric repeats, reduction of heterochromatin and chromocenter size and gametes with fully demethylated and hemidemethylated DNA. Belongs to the class I-like SAM-binding methyltransferase superfamily. C5-methyltransferase family.