Involved in de novo DNA methylation. Required for CpG and non-CpG methylation. Required for normal establishment and maintenance of RNA-directed DNA methylation (RdDM) mediated by small interfering RNAs (siRNAs). Regulates proper plant development in both vegetative and reproductive stages through DNA methylation. a 2'-deoxycytidine in DNA + S-adenosyl-L-methionine = a 5-methyl-2'-deoxycytidine in DNA + H(+) + S-adenosyl-L-homocysteine Interacts (via UBA domains) with EIF4A. Pleiotropic developmental defects such as growth defects, semi-dwarfed phenotype, reductions in tiller number, delayed heading or no heading, abnormal panicle and spikelet morphology, and complete sterility. May be due to a competing donor splice site. Belongs to the class I-like SAM-binding methyltransferase superfamily. DRM-methyltransferase family.