Active DNA Demethylation Regulates Plant Gamete and Zygote Genome Reprogramming

Fertilization constitutes a critical step in the plant life cycle during which the gamete genomes undergo reprogramming in preparation for embryogenesis. However, it is unclear whether and how DNA methylation that epigenetically regulates gene expression is reprogramed during fertilization. Here, we characterized DNA methylation patterns and investigated the function of DNA glycosylases in rice eggs, sperms and unicellular zygotes. We found that DNA methylation is extensively reprogramed at non-CG sites in euchromatin regions upon fertilization, which intensifies during early embryogenesis. Genetic and genomic analysis revealed that rice DNA glycosylase genes DNG702, DNG701 and DNG704 demethylate at distinct and complementary loci in egg, sperm, and zygote genomes and are required for zygotic gene expression and development. The results indicate that active demethylation takes place in the gametes and the zygote to reprogram DNA methylation and zygotic genome activation in plant. BS-seq and RNA-seq of gametes and unicellular zygote of wild type, dng702, dng701/4 knock out mutant