question: What is the role of  chromomethylases in plants?
answer: Chromomethylases (CMTs), which constitute a plant-specific DNA (cytosine-5)-methyltransferase family, are involved primarily in the maintenance of symmetrical CpNpG (N = A, T, C, or G) methylation and they also play a role in de novo methylation. CMTs are characterized by the presence of a chromatin-associated domain (chromodomain) inserted within the catalytic protein motifs I and IV. CMTs have likely evolved because of  the high levels of CpNpG methylation present in plant genomes relative to animal genomes. The targeting of CMT methylation is accomplished by short interfering RNA (siRNA) pathways and histone methylation (H3K9, H3K27). It has been shown that transposons are in vivo targets of CMT-dependent methylation, suggesting that CMTs play a role in the plant genome surveillance. In Arabidopsis, CMTs play a key role in egg cell reprogramming and normal embryogenesis during the first few divisions of the zygote by mediating transposon and euchromatin epigenetic gene silencing. In tomatoes, CMTs are preferentially expressed in the pericarp during fruit development which suggests involvement of CMTs in the locus-specific control of methylation in the pericarp during fruit growth.