Polycomb Group Proteins RING1A and RING1B Regulate the Vegetative Phase Transition in Arabidopsis

Abstract

Polycomb group (PcG) protein-mediated gene silencing is a major regulatory mechanism in higher eukaryotes that affects gene expression at the transcriptional level. Here, we report that two conserved homologous PcG proteins, RING1A and RING1B (RING1A/B), are required for global H2A monoubiquitination (H2Aub) in <i>Arabidopsis</i>. The mutation of RING1A/B increased the expression of members of the <i>SQUAMOSA PROMOTER BINDING PROTEIN-LIKE</i> (<i>SPL</i>) gene family and caused an early vegetative phase transition. The early vegetative phase transition observed in <i>ring1a ring1b</i> double mutant plants was dependent on an <i>SPL</i> family gene, and the H2Aub status of the chromatin at <i>SPL</i> locus was dependent on RING1A/B. Moreover, mutation in RING1A/B affected the miRNA156a-mediated vegetative phase transition, and RING1A/B and the AGO7-miR390-TAS3 pathway were found to additively regulate this transition in <i>Arabidopsis</i>. Together, our results demonstrate that RING1A/B regulates the vegetative phase transition in <i>Arabidopsis</i> through the repression of <i>SPL</i> family genes.