Mapping genetic modifiers of epimutation rates identifies VIM2/4 as dosage-sensitive negative regulators of CG methylation maintenance [RNAseq_VIM2/4]

At CG sites, such epimutations can be inherited across generations in plants and constitute a major source of CG methylation (mCG) diversity. However, why the fidelity of mCG inheritance varies among genotypes, and how this variation relates to steady-state mCG levels, remain poorly understood.

Here we tracked DNA methylation over ten generations in ~400 mutation-accumulation lines derived from ~70 Arabidopsis thaliana Ler × Cvi recombinant inbred founders. By treating methylation gain and loss rates as quantitative molecular traits, we mapped a major-effect locus to a Cvi-derived deletion between VIM2 and VIM4, two components of the MET1-dependent mCG maintenance pathway. Lines carrying this deletion showed elevated VIM2/4 expression, a rapid shift of genome-wide mCG toward a lower steady state, and reduced fidelity of methylation inheritance across generations.