High-temperature-induced FKF1 accumulation promotes flowering through the dispersion of GI and degradation of SVP

Abstract

Floral transition is influenced by photoperiod and ambient temperature, which are integrated to modulate development via a molecular mechanism that remains to be elucidated. Here we demonstrate that the F-box protein FLAVIN-BINDING, KELCH REPEAT, F-BOX 1 (FKF1) and its interacting partner GIGANTEA (GI), central regulators of photoperiodic flowering, target SHORT VEGETATIVE PHASE (SVP) for 26S-proteasome-dependent degradation to regulate the temperature-responsive developmental transition to flowering. At low temperatures, GI is sequestered in liquid-like nuclear condensates. By contrast, FKF1 accumulates at high temperatures and releases GI from condensates to form a nuclear-dispersed FKF1–GI complex, leading to SVP degradation under short-day conditions. Temperature sensitivity is significantly reduced in fkf1-t, gi-2 and fkf1-2 gi-2 mutants. We propose that the FKF1–GI complex mediates the proteolysis of a floral repressor via reversible liquid–liquid phase separation to accelerate floral transition at high temperatures. GI forms an inactive nuclear condensate that is dispersed at high temperatures by FKF1 binding to GI’s intrinsically disordered region. The resulting FKF1–GI complex promotes SVP degradation, accelerating flowering at high ambient temperatures.