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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. 

Summary The juvenile‐to‐adult vegetative phase change in flowering plants is mediated by a decrease in miR156 levels. Downregulation ofMIR156A/MIR156C, the two major sources of miR156, is accompanied by a decrease in acetylation of histone 3 lysine 27 (H3K27ac) and an increase in trimethylation of H3K27 (H3K27me3) atMIR156A/MIR156CinArabidopsis.Here, we show that histone deacetylase 9 (HDA9) is recruited toMIR156A/MIR156Cduring the juvenile phase and associates with the CHD3 chromatin remodeler PICKLE (PKL) to erase H3K27ac atMIR156A/MIR156C.H2Aub and H3K27me3 become enriched atMIR156A/MIR156C, and the recruitment of Polycomb Repressive Complex 2 (PRC2) toMIR156A/MIR156Cis partially dependent on the activities of PKL and HDA9.Our results suggest that PKL associates with histone deacetylases to erase H3K27ac and promote PRC1 and PRC2 activities to mediate vegetative phase change and maintain plants in the adult phase after the phase transition.