Abstract
Polycomb repressive complex 1 (PRC1) and PRC2 are the major complexes composed of polycomb-group (PcG) proteins in plants. PRC2 catalyzes trimethylation of lysine 27 on histone 3 to silence target genes. Like Heterochromatin Protein 1/Terminal Flower 2 (LHP1/TFL2) recognizes and binds to H3K27me3 generated by PRC2 activities and enrolls PRC1 complex to further silence the chromatin through depositing monoubiquitylation of lysine 119 on H2A. Mutations in PcG genes display diverse developmental defects during shoot apical meristem (SAM) maintenance and differentiation, seed development and germination, floral transition, and so on so forth. PcG proteins play essential roles in regulating plant development through repressing gene expression. In this review, we are focusing on recent discovery about the regulatory roles of PcG proteins in SAM maintenance, root development, embryo development to seedling phase transition, and vegetative to reproductive phase transition.
Highlights
Higher eukaryotes have evolved mechanisms to temporally and specially control gene expression
Asymmetric leaves 1 (AS1) integrates into PRC2 through physically interacting with CURLY LEAF (CLF) and Fertilization Independent Endosperm (FIE), whereas AS2 is directly associated with Embryonic Flower 2 (EMF2) and recruit PRC2 complex to BP and KNAT2 regions to modify the chromatin with H3K27me3 mark and silence shoot apical meristem (SAM)-specific homeobox domain genes in leaf tissue (Figure 1d) [88]
Embryonic Flower 1 (EMF1) binds to major seed regulated genes, such as FUSCA 3 (FUS3), Abscisic acid (ABA) Insensitive 3 (ABI3), and the downstream seed maturation genes, including LEC2, Late Embryogenesis Abundant proteins (LEAs), OLEO2, Lipid Transfer Protein 3 (LTP3), and seed storage protein genes, which are modified by H3K27me3 [130,131]
Summary
Higher eukaryotes have evolved mechanisms to temporally and specially control gene expression. Embryonic Flower 2 (EMF2), VERNALIZATION 2 (VRN2), and Fertilization Independent Seed (FIS2) are the three homologs of Su(z), which promote the activity of H3K27 methyltransferase and confer target specificity to the corresponding PRC2s [11,12,13]. Like Heterochromatin Protein 1/Terminal Flower 2 (LHP1/TFL2), performing as the reader of histone modification, recognizes and binds to H3K27me generated by PRC2 activities [32,33]. Plant-specific proteins, including Embryonic Flower 1 (EMF1), VERNALIZATION 1 (VRN1), and VP1/ABI3-Like 1/2/3 (VAL1/2/3), are involved in PRC1 function [34,35,36]. In addition to the involvement in PRC1 complex, LHP1 is associated with PRC2 through interacting with MSI1 and EMF2 to deposit H3K27me mark on the chromatin [17,39]. We are focusing on recent findings on roles of PcG proteins in SAM maintenance, root development, seed to germination phase transition, and floral transition
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