[Hongyong Fu/Wolfgang Schmidt] The Arabidopsis deubiquitylase OTU5 suppresses flowering by histone modification-mediated activation of the major flowering repressors FLC, MAF4, and MAF5.

Radjacommare et al., 2023  Int J Mol Sci

Arabidopsis OTU5 is a novel flowering suppressor. OTU5 acts, in an associated protein complex (OTU5c), in parallel with SWR1c- and HUB1/2-mediated pathways to epigenetically activate FLC clade repressors and suppress flowering. OTU5 primarily activates FLC and, to a lesser extent, MAF5, MAF4, and MAF1, which in turn suppress major flowering initiators FT and SOC1 to repress flowering. OTU5 is involved in increasing the deposition of the activating histone mark H3K36me3 and in the downregulation of the suppressive histone marks H3K27me3 and H3K9me2 as well as ubH2B on specific loci, such as FLC, MAF4, and MAF5. OTU5-mediated flowering suppression is distinct from the SWR1c-mediated pathway, which activates FLC-related repressors through H2A.Z deposition. OTU5 also acts independently of the HUB1/2-mediated pathway, which modulates genome-wide ubH2B levels and activates a distinct set of FLC-related repressors through distinct activating/repressive histone marks. OTU5 is, however, partially required for FLC-mediated flowering suppression in autonomous pathway mutants and FRIGIDA-Col.

Distinct phylogeny and substrate specificities suggest that 12 Arabidopsis Ovarian Tumor domain-containing (OTU) deubiquitinases participate in conserved or plant-specific functions. The otu5-1 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 FLC and MAF4-5 are responsible for the early flowering of otu5-1. qChIP analyses revealed a reduction and increase in activating and repressive histone marks, respectively, on FLC and MAF4-5 in otu5-1. 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 FLC and MAF4-5. The OTU5-associated protein complex(es) appears to be distinct from SWR1c, as the molecular weights of OTU5 complex(es) were unaltered in arp6-1 plants. Furthermore, the otu5-1 arp6-1 double mutant exhibited synergistic phenotypes, and H2A.Z levels on FLC/MAF4-5 were reduced in arp6-1 but not otu5-1. Our results support the proposition that Arabidopsis OTU5, acting independently of SWR1c, suppresses flowering by activating FLC and MAF4-5 through histone modification. Double-mutant analyses also indicate that OTU5 acts independently of the HUB1-mediated pathway, but it is partially required for FLC-mediated flowering suppression in autonomous pathway mutants and FRIGIDA-Col.

Radjacommare et al., 2023 The Arabidopsis deubiquitylase OTU5 suppresses flowering by histone modification-mediated activation of the major flowering repressors FLC, MAF4, and MAF5Int J Mol Sci 24 (7), 6176, 2023-03-24.

Link: https://www.mdpi.com/1422-0067/24/7/6176