H3K27me2 and H3K27me3 ChIP-seq in wheat evolution

Bread wheat is a widely cultivated allohexaploid arise via two recent polyploidization events. Growing evidence suggests histone modifications are involved in response to genomic shock and adaption to adverse environments during formation of polyploid plants. However, the roles of histone modifications in wheat evolution remain elusive. We analyzed profiles of H3K27me2 and H3K27me3 during polyploidization and hybridization of wheat using hexaploid bread and its tetraploid and diploid relatives. H3K27me2 levels positively correlated with the ploidy levels and the increased H3K27me2 may contributed to repress massively amplified transposons to maintain genome stability during wheat evolution. H3K27me2 is involved in silencing euchromatic TEs and the distribution of H3K27me2 is mutually exclusive with another repressive mark H3K9me2. Regions of H3K27me2 canyons were highly related with formation of DNA double-strand breaks in genomes of wheat, maize and Arabidopsis, revealing a novel histone modification contributing to recombination regulation. Our results provided comprehensive view of H3K27me2 and H3K27me3 distribution during wheat evolution and proposed potential roles of H3K27me2 on genome stability and genetic recombination, which may contribute to accelerate crop breeding.