DNA methylation systems and targets in plants.

Plants contain three distinct DNA methyltransferase types that are responsible for the establishment and maintenance of cytosine methylation patterns at heterochromatic and euchromatic target regions. RNA transcripts play an important role in recruiting DNA methylation systems to specific loci, where methylation patterns are controlled by distinct epigenetic pathways that often work co-operatively and in competition with demethylation functions. DNA methylation patterns are faithfully propagated by maintenance systems that involve re-enforcing feedback effects between DNA methylation and histone marks. Our detailed knowledge about the composition of DNA methylation patterns is contrasted by a poorer understanding of the variability of DNA methylation and its contribution to gene regulation, genome evolution and adaptation to environmental changes.