Post-Embryonic Phase Transitions Mediated by Polycomb Repressive Complexes in Plants

Abstract

Correct timing of developmental phase transitions is critical for the survival and fitness of plants. Developmental phase transitions in plants are partially promoted by controlling relevant genes into active or repressive status. Polycomb Repressive Complex1 (PRC1) and PRC2, originally identified in Drosophila, are essential in initiating and/or maintaining genes in repressive status to mediate developmental phase transitions. Our review summarizes mechanisms in which the embryo-to-seedling transition, the juvenile-to-adult transition, and vegetative-to-reproductive transition in plants are mediated by PRC1 and PRC2, and suggests that PRC1 could act either before or after PRC2, or that they could function independently of each other. Details of the exact components of PRC1 and PRC2 in each developmental phase transitions and how they are recruited or removed will need to be addressed in the future.

Polycomb Repressive Complex 2 in Eukaryotes—An Evolutionary Perspective

“…In particular, the alternation between sporophyte and gametophyte and repression of apogamy depends on PRC2 in A. thaliana [ 277 , 278 , 279 ] as well as P. patens [ 256 ], demonstrating an evolutionarily conserved role of the complex. In accordance, developmental genes in both A. thaliana (reviewed in the work of [ 47 , 48 , 251 , 252 ]) and P. patens [ 257 ] undergo H3K27me3 remodeling during developmental phase transitions. In A. thaliana , response to salt stress and nitrate or iron deficiency is modulated by PRC2 [ 158 , 159 , 160 ], implicating PRC2 in environmental response.…”

“…The flowering dicot model plant Arabidopsis thaliana has three E(z) paralogs (CURLY LEAF (CLF), SWINGER (SWN) and MEDEA (MEA)), three Su(z)12 paralogs (EMBRYONIC FLOWER 2 (EMF2), VERNALIZATION 2 (VRN2), and FERTILIZATION INDEPENDENT SEED 2 (FIS2)), one ESC homolog (FERTILIZATION INDEPENDENT ENDOSPERM (FIE)), and five p55 homologs (MULTICOPY SUPPRESSOR OF IRA (MSI1–MSI5)), of which only MSI1 is known to be present in PRC2 ([ 102 , 130 , 131 ], reviewed in the works of [ 29 , 132 ]). SWN and CLF play significant roles during vegetative development and phase transitions ([ 133 , 134 , 135 , 136 , 137 , 138 ], reviewed in the work of [ 47 , 48 ]), while MEA is required during gametophyte development and early embryogenesis [ 131 , 139 ]. Three PRC2 complexes have been identified in Arabidopsis defined by the presence of respective Su(z)12 homologs: EMBRYONIC FLOWER (EMF), VERNALIZATION (VRN), and FERTILIZATION INDEPENDENT SEED (FIS).…”

“…Based on the currently available information, the predominating function of PRC2 in the green lineage seems to have shifted during evolution from the organization of constitutive heterochromatin ( C. reinhardtii and M. polymorpha ) to facultative repression of genes that respond to the internal and external cues ( P. patens , angiosperms). In P. patens [ 61 , 62 , 256 ] as well as in flowering plants (reviewed in the work of [ 47 , 48 , 251 , 252 ]), PRC2 is required for correct timing and execution of developmental phase transitions. In particular, the alternation between sporophyte and gametophyte and repression of apogamy depends on PRC2 in A. thaliana [ 277 , 278 , 279 ] as well as P. patens [ 256 ], demonstrating an evolutionarily conserved role of the complex.…”

“…In model species of both animals and plants, H3K27me3 is largely associated with transcriptional silencing of developmental genes ([ 37 , 38 ], reviewed in the work of [ 39 , 40 ]). PRC2 composition, its biochemical and developmental functions are well studied in animal and in flowering plant model species, and we refer to recent reviews for detailed information [ 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 ]. Here, we bring a comparative overview of PRC2 core composition and biochemical function in different eukaryotic groups, with focus on the green lineage, to highlight emerging concepts of PRC2 evolution.…”

Roles of Polycomb complexes in regulating gene expression and chromatin structure in plants

“…We first present the composition and activities of PcG complexes as a prerequisite to understanding how PRC1 and PRC2 perform their functions. Excellent reviews have recently examined the composition of the core components of these complexes and their roles in the regulation of different developmental processes ( Wang and Shen, 2018 ; Bieluszewski et al., 2021 ; Hinsch et al., 2021 ). We therefore focus our survey on the role of recently identified accessory proteins and on the new functions that have been attributed to previously known components.…”