Differential methylation of genes and repeats in land plants.

The hypomethylated fraction of plant genomes is usually enriched in genes and can be selectively cloned using methylation filtration (MF). Therefore, MF has been used as a gene enrichment technology in sorghum and maize, where gene enrichment was proportional to genome size. Here we apply MF to a broad variety of plant species spanning a wide range of genome sizes. Differential methylation of genic and non-genic sequences was observed in all species tested, from non-vascular to vascular plants, but in some cases, such as wheat and pine, a lower than expected level of enrichment was observed. Remarkably, hexaploid wheat and pine show a dramatically large number of gene-like sequences relative to other plants. In hexaploid wheat, this apparent excess of genes may reflect an abundance of methylated pseudogenes, which may thus be more prevalent in recent polyploids.