Genome size and DNA methylation covary across Land Plants

Little is known about patterns of DNA methylation across the plant kingdom or about the evolutionary processes that shape them. One thought is that methylation levels reflect transposable element (TE) content, which is in turn tightly correlated with genome size. To test the hypothesis that genome size and methylation are correlated, we gathered methylome data from 14 plant species that range 250-fold in genome size and span the phylogenetic breadth of Land Plants. We document that methylation and genome size correlate positively, such that DNA methylation in ~20Gb conifer genomes is especially high. Yet, despite variation in methylation across species, we also find that the level of CG methylation is a property of individual genes and that this property has remained relatively conserved since at least the origin of ferns ~400 million years ago.