Abstract
Polycomb Repressive Complex 2 (PRC2) is arguably the best-known plant complex of the Polycomb Group (PcG) pathway, formed by a group of proteins that epigenetically represses gene expression. PRC2-mediated deposition of H3K27me3 has amply been studied in Arabidopsis and, more recently, data from other plant model species has also been published, allowing for an increasing knowledge of PRC2 activities and target genes. How PRC2 molecular functions are regulated and how PRC2 is recruited to discrete chromatin regions are questions that have brought more attention in recent years. A mechanism to modulate PRC2-mediated activity is through its interaction with other protein partners or accessory proteins. Current evidence for PRC2 interactors has demonstrated the complexity of its protein network and how far we are from fully understanding the impact of these interactions on the activities of PRC2 core subunits and on the formation of new PRC2 versions. This review presents a list of PRC2 interactors, emphasizing their mechanistic action upon PRC2 functions and their effects on transcriptional regulation.
Highlights
Polycomb Repressive Complex 2 (PRC2) mediates the deposition of the trimethylation of the lysine 27 of the histone 3 (H3K27me3), a histone modification associated with gene repression in eukaryotes [1]
PRC2 was first identified in Drosophila consisting of four core components: Enhancer of zeste (E(z)), a histone methyltransferase unit that catalyses H3K27me3; Extra sex combs (Esc), a WD40 domain protein scaffolding the interactions within the complex; Suppressor of zeste 12 (Su(z)12), a Zinc Finger protein that is essential for binding to nucleosomes; and Nuclear remodeling factor (Nurf55, called p55), a Trp-Asp (WD) repeat protein involved in nucleosome remodelling [1,2]
A third possibility proposes the existence of a PRC1like complex containing LIKE HETEROCHROMATIN PROTEIN 1 (LHP1) that is able to interact with CURLY LEAF (CLF)-PRC2 via the MSI1 subunit, since LHP1 copurifies with MSI1 in co-IP [77]
Summary
Polycomb Repressive Complex 2 (PRC2) mediates the deposition of the trimethylation of the lysine 27 of the histone 3 (H3K27me3), a histone modification associated with gene repression in eukaryotes [1]. In Arabidopsis thaliana (Arabidopsis), there are three E(z) homologs—CURLY LEAF (CLF), SWINGER (SWN) and MEDEA (MEA); three Su(z) homologs—EMBRYONIC FLOWER 2 (EMF2), VERNALIZATION 2 (VRN2) and FERTILIZATION-INDEPENDENT SEED 2 (FIS2); a single Esc homolog—FERTILIZATION-INDEPENDENT ENDOSPERM (FIE); and there are five Arabidopsis homologs of p55 protein—MULTICOPY SUPPRESSOR OF IRA (MSI) 1–5, but MSI1 is the only one demonstrated to be part of the PRC2 complex [6,7] Based on their different subunit compositions, at least three PRC2-like complexes controlling different developmental processes have been described in Arabidopsis: the EMF, VRN and FIS complexes [3]. Similar percentages of H3K27me marked genes were observed in different plant model species (e.g., maize, oilseed rape, rice and Brachypodium distachyon) [13–16] These data further demonstrate the importance of PRC2 activity in regulating the expression of key developmental genes in crops and thereby governing the major agricultural traits, e.g., flowering. We discuss PRC2 recruitment strategies on target genes mediated by the cooperation with accessory proteins and its associated gene repression and explore the impact of PRC2 interactions especially on the modulation of PRC2 activities
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