PWO1 interacts with PcG proteins and histones to regulate Arabidopsis flowering and development

AbstractPolycomb-group (PcG) proteins mediate epigenetic gene regulation by setting H3K27me3 via Polycomb Repressive Complex 2 (PRC2). In plants, it is largely unclear how PcG proteins are recruited to their target genes.Here, we identified the PWWP-DOMAIN INTERACTOR OF POLYCOMBS1 (PWO1) protein which interacts with all threeArabidopsisPRC2 histone methyltransferases and is required for keeping full H3 occupancy at several Arabidopsis genes. PWO1 localizes and recruits CLF to nuclear speckles in tobacco nuclei, suggesting a role in spatial organization of PcG regulation.PWO1belongs to a gene family with three members acting redundantly:pwo1 pwo2 pwo3triple mutants are seedling lethal and show shoot and root meristem arrest, whilepwo1single mutants are early flowering. Interestingly, PWO1’s PWWP domain confers binding to histones, which is reduced by a point mutation in a highly conserved residue of this domain and blocked by phosphorylation of H3S28. PWO1 carrying this mutation is not able to fully complement thepwo1 pwo2 pwo3triple mutant, indicating the requirement of this domain for PWO1in vivoactivity. Thus, the PWO family may present a novel class of histone readers which are involved in recruiting PcG proteins to subnuclear domains and in promoting Arabidopsis development.