Polycomb proteins RING1A/B promote H2A monoubiquitination to regulate female gametophyte development in Arabidopsis.

This article focuses on the role of RING1A and RING1B, two functionally redundant Polycomb Repressive Complex 1 (PRC1) catalytic subunits, in female gametophyte development in Arabidopsis thaliana. The study demonstrates that mutations in RING1A/B cause defects in the specification of the megaspore mother cell (MMC) and the functional megaspore (FM), as well as impaired mitosis of the FM, leading to female infertility due to aborted ovules. RING1A/B directly bind to and promote histone H2A monoubiquitination (H2Aub) at key genes involved in female gametophyte development, repressing their expression to ensure proper progression from MMC specification to FM mitosis. These findings reveal a critical epigenetic regulatory mechanism by which PRC1 components maintain gene expression homeostasis during female reproductive development in flowering plants.