Spreading of DNA Methylation in Soybean : Impact on Genes and Genome Evolution

DNA methylation is an important mechanism of epigenetic regulation and inheritance in plants. While CG body methylation of genes is generally associated with high expression levels, the methylation of transposable elements (TEs) in the three contexts (CG, CHG and CHH where H=A, T or C) via RNA-directed DNA methylation (RdDM) machinery result in repression at the transactional level. Several reports have shown that DNA methylation can spread from TEs to neighboring genes, however less is known about the extent of such phenomena in large genomes such as soybean and its potential impact on genome evolution. To address this question a good TE annotation is required. For this purpose, we developed a new TE de novo annotation approach based on 24nt small RNAs mapping. Using this annotation, we evaluated the extent of spreading of DNA methylation form TEs to genes at the whole genome-scale and discuss its potential impact on soybean genome evolution.