This entry describes several enzymes, characterized from plants, that successively methylate the L-lysine-9 residue of histone H3 (H3K9) twice, ultimately generating a dimethylated form. These modifications influence the binding of chromatin-associated proteins. In general, the methylation of H3K9 leads to transcriptional repression of the affected target genes. cf. EC 22.214.171.1247, [histone H3]-lysine9 N-methyltransferase, EC 126.96.36.1996, [histone H3]-N6,N6-dimethyl-lysine9 N-methyltransferase, and EC 188.8.131.525, [histone H3]-lysine9 N-trimethyltransferase.