Reprogramming the epigenome in Arabidopsis pollen

Abstract

Epigenetic reprogramming in Arabidopsis thaliana occurs in developing pollen. The male gametophyte is derived from haploid microspores via two postmeiotic cell divisions to give rise to the gametes (sperm cells, SC) and the vegetative cell (VC). The purificationof individual cell types during pollen development coupled with genome-wide DNA methylation analysis and small RNA sequencing has revealed a dynamic regulation of the epigenome during gametogenesis. Interestingly, imprinted loci and previously identified variable epialleles are hypermethylated in the germline; however, their stability after fertilizationappears to require targeted demethylation in the neighboring vegetative cell nucleus, possibly by releasing mobile small RNAs that reinforce transcriptional gene silencing and DNA methylation in the gametes. These results have led to a new model for the establishmentand transgenerational maintenance of epigenetic marks in flowering plants. © 2012 Cold Spring Harbor Laboratory Press; all rights reserved.