Nurse cell­-derived small RNAs define paternal epigenetic inheritance in Arabidopsis

We report here that gentic methylation in the male germline, from meiocytes to sperm, is established by siRNAs transcribed from transposons with imperfect sequence homology. These siRNAs are synthesized by meiocyte nurse cells (tapetum) via activity of the chromatin remodeler CLASSY3, which is specifically expressed in tapetal cells. Plants that produce siRNAs only in the tapetum have broadly normal DNA methylation of the entire germline. Finally, we also report that these nurse cell-derived siRNAs (niRNAs) silence germline transposons, thereby safeguarding genome integrity. Our results reveal the crucial role of tapetal niRNAs in germline methylation reprogramming, which is remarkably analogous to piRNA-mediated reprogramming in animal germlines. Overall design: Profiling of methylome and sRNAome in meiocyte and tapetum in Arabidopsis