As part of the epigenome, DNA methylation is an additional layer
throughwhich the language of the genome is interpreted. However, context
is important and meanings can change with subtle variations in patterns
of the epigenome.DNAmethylation is not a simple on-off switch. In
plants, DNA can bemethylated at three sequence contexts: CG, CHG, and
CHH. These are established and maintained by distinct molecularmechanisms,
and in the cases ofmCHG andmCHH, processes that are unique to
plants. The effect of methylation on gene expression is highly dependent
upon the type of methylation as well as the pattern of that methylation
within or outside of the gene.