PICKLE-mediated nucleosome condensing drives H3K27me3 spreading for the inheritance of Polycomb memory during differentiation [ChIP-Seq]

The Polycomb repressive complex 2 (PRC2) is an essential epigenetic regulator that deposits repressive H3K27me3 for transcriptional gene silencing in eukaryotes. The PRC2-mediated gene silencing process occurs in two steps: the initial H3K27me3 deposition at the nucleation region, and the subsequent spreading of H3K27me3 over the entire gene. Lack of H3K27me3 spreading gives rise to a metastable state that could lead to loss of silencing. H3K27me3 spreading is thus a key step critical for the establishment of stable long-term Polycomb silencing in both animals and plants.Here, we uncover that Arabidopsis thaliana PICKLE (PKL), a member of the conserved Chromodomain Helicase DNA-binding (CHD) family of chromatin remodeling ATPase13, is dispensable for the nucleation but especially required for the efficient spreading of H3K27me3 at thousands of Polycomb target genes. PKL localizes to the spreading regions in a non-DNA-sequence-specific manner through its SANT-SILDE domain. PKL then upregulates the chromatin density by its CHROMODOMAIN and ATPase domain , enabling the H3K27me3 methyltransferase CURLY LEAF (CLF) to deposit H3K27me3 on nucleosomes in the spreading regions to facilitate the H3K27me3 spreading. Overall design: Examination of H3K27me3 enrichment and PKL occupancy and in 14-day-old WT and differet mutants