The Arabidopsis Deubiquitylase OTU5 Suppresses Flowering by Histone Modification-Mediated Activation of the Major Flowering Repressors , , and .

Distinct phylogeny and substrate specificities suggest that 12 Arabidopsis Ovarian Tumor domain-containing (OTU) deubiquitinases participate in conserved or plant-specific functions. The null mutant displayed a pleiotropic phenotype, including early flowering, mimicking that of mutants harboring defects in subunits (e.g., ARP6) of the SWR1 complex (SWR1c) involved in histone H2A.Z deposition. Transcriptome and RT-qPCR analyses suggest that downregulated and are responsible for the early flowering of . qChIP analyses revealed a reduction and increase in activating and repressive histone marks, respectively, on and in . Subcellular fractionation, GFP-fusion expression, and MNase treatment of chromatin showed that OTU5 is nucleus-enriched and chromatin-associated. Moreover, OTU5 was found to be associated with and . The OTU5-associated protein complex(es) appears to be distinct from SWR1c, as the molecular weights of OTU5 complex(es) were unaltered in plants. Furthermore, the double mutant exhibited synergistic phenotypes, and H2A.Z levels on were reduced in but not . Our results support the proposition that Arabidopsis OTU5, acting independently of SWR1c, suppresses flowering by activating and through histone modification. Double-mutant analyses also indicate that acts independently of the HUB1-mediated pathway, but it is partially required for -mediated flowering suppression in autonomous pathway mutants and -Col.