Molecular properties of epimutation hotspots

Mistakes in the maintenance of CG methylation is a source of heritable epimutations in plants. Multigenerational surveys indicate that the rate of these stochastic events varies substantially across the genome, with some regions harboring localized “epimutation hotspots”. Using Arabidopsis as a model, we show that epimutation hotspots are indexed by a specific set of chromatin states (CS) that map to sub-regions of gene body methylation genes. Although these regions comprise only ~12% of all CGs in the genome, they account for ~63% of all epimutation events per unit time. Molecular profiling revealed that these regions contain unique sequence features, harbor steady-state intermediate methylation levels, and act as putative targets of antagonistic DNA methylation pathways. We further demonstrate that experimentally-induced shifts in steady-state methylation in these hotspot regions are sufficient to significantly alter local epimutation intensities. Our work thus lays foundation for dissecting the molecular mechanisms of epimutation hotspots in plants. Overall design: We created two mutant lineages of MA_cmt3, and MA_suvh4/5/6 mutation accumluation lines from Col-0 that were propagated by single seed descent growth for the indicated number of generations (G#).