Insights into epigenome evolution from animal and plant methylomes

Abstract

Evolutionary studies of DNA methylation offer insights into the mechanisms governing the variation of genomic DNA methylation across different species. Comparisons of gross levels of DNA methylation between distantly related species indicate that the size of the genome and the level of genomic DNA methylation are positively correlated. In plant genomes, this can be reliably explained by the genomic contents of repetitive sequences. In animal genomes, the role of repetitivfe sequences on genoimc DNAmethylation is less clear. On a shorter timescale, population-level comparisons demonstrate that genetic variation can explain the observed variabilityofDNAmethylation tosomedegree. The amount ofDNAmethylation variationthat hasbeenattributedtogenetic variationin the human population studies so far is substantially lower than that from Arabidopsis population studies, but this disparity might reflect the differences in the computational and experimental techniques used. The effect of genetic variation on DNAmethylation has been directly examined inmammalian systems, revealing several causative factors that govern DNA methylation. On the other hand, studies from Arabidopsis have furthered our understanding of spontaneous mutations of DNA methylation, termed "epimutations." Arabidopsis has an extremely high rate of spontaneous epimutations, which may play a major role in shaping the global DNA methylation landscape in this genome. Key missing information includes the frequencies of spontaneous epimutations in other lineages, in particular animal genomes, and howpopulation-level variation ofDNAmethylation leads to species-level differences.