Dynamics of DNA methylation and its impact on plant embryogenesis

Flowering plants exhibit unique DNA methylation dynamics during development. Particular attention can be focused on seed development and the embryo, which represents the starting point of the sporophytic life cycle. A build-up of CHH methylation is now recognized as highly characteristic of embryo development. This process is thought to occur in order to silence potentially harmful transposable element expression, though roles in promoting seed dormancy and dessication tolerance have also been revealed. Recent studies show that increased CHH methylation in embryos inhabits both novel loci, unmethylated elsewhere in the plant, as well as shared loci, exhibiting more dense methylation. The role of DNA methylation in cis-regulatory gene regulation in plants is less well established compared to mammals, and here we discuss both transposable element regulation and the potential role of DNA methylation in dynamic gene expression. •Noncanonical SUVH2/9 proteins are suggested to confer H3K9me2 and CHH methylation in early embryos.•Methylation-null Arabidopsis exhibits developmental and epigenetic defects.•CHH methylation occurs at both novel embryo-specific and shared loci.•Small RNAs in endosperm are potentially involved in early embryo TE silencing.