Arabidopsis HIGH PLOIDY2 sumoylates and stabilizes FLC through E3 ligase activity

Abstract

Flowering Locus C (FLC), which is known as a floral repressor, plays an important role in flowering. A large number of studies have been carried out to elucidate the mechanisms of FLC gene expression and its protein function. However, FLC-regulatory mechanism is not clearly identified at post-translational stage yet. Here, we showed that Arabidopsis HIGH PLOIDTY2 (HPY2) functions as a real E3 SUMO ligase for FLC. In vitro and vivo pull-down analyses showed that FLC physically interacts with HPY2. In vitro sumoylation assays showed that FLC sumoylation is stimulated by AtSIZ1 in a dependent manner of SUMO-activating enzyme E1 and conjugating enzyme E2, indicating that AtHPY2 is an E3 SUMO ligase for FLC. In transgenic plants, inducible HPY2 overexpression led to an increase in the concentration of FLC, indicating that HPY2 stabilizes FLC through direct sumoylation. The flowering time of hpy2-2 mutants was delayed compared to wild-type plants under long and short day conditions and its loss effect in flowering is bigger under short day condition than long day condition. In addition, FLC transcript level was also down-regulated in hpy2-2 mutants. The data indicate that HPY2 regulates FLC function and stability at both transcription and post-translation steps through its E3 SUMO ligase activity.