FVE coordinates with COP1 to modulate flowering time at low ambient temperature

Plants delay flowering in response to low ambient temperatures. The WD40 domain-containing protein FVE regulates histone acetylation and flowering time, but how it responds to low ambient temperatures to modulate flowering time is largely unknown. Here, we report that FVE regulates flowering time in Arabidopsis (Arabidopsis thaliana) at low ambient temperature through SHORT VEGETATIVE PHASE (SVP). Loss of FVE function resulted in late flowering at both 16 and 22°C. The flowering time of fve plants at 16°C was similar to that at 22°C. We demonstrated that FVE and SVP form a protein complex by interacting with the β isoform of FLOWERING LOCUS M (FLM-β). FVE removes histone H3 lysine 9 acetylation (H3K9ac) marks at the FLOWERING LOCUS T (FT) locus. FVE occupancy at FT requires SVP. The svp-32 fve-21 double mutant flowered at the same time as the svp-32 single mutant and at similar times at 16 and 22°C. FVE also interacted with CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) in vitro and in vivo. We determined that COP1 promotes the ubiquitination and degradation of FVE. Loss of COP1 function resulted in increased FVE occupancy and decreased H3K9ac levels at FT. These findings reveal that FVE is regulated by COP1 and forms a protein complex with SVP and FLM-β to modulate flowering time at low ambient temperatures.