GIGANTEA Shapes the Photoperiodic Rhythms of Thermomorphogenic Growth in Arabidopsis

ABSTRACT Plants maintain their internal temperature by adjusting their morphology and architecture under environments with fluctuating temperatures, an adaptive process termed thermomorphogenesis. Notably, the rhythmic patterns of plant thermomorphogenesis are governed by daylength information. However, it remains elusive how thermomorphogenic rhythms are regulated by photoperiod. Here, we show that warm temperatures enhance the accumulation of the chaperone GIGANTEA (GI), which thermostabilizes REPRESSOR OF ga1-3 (RGA) under long days, thereby attenuating PHYTOCHROME INTERACTING FACTOR 4 (PIF4)-mediated thermomorphogenesis. In contrast, under short days, when GI accumulation is reduced, RGA is readily degraded through the gibberellic acid (GA)-mediated ubiquitination-proteasome pathway, promoting thermomorphogenic growth. These data indicate that the GI-RGA-PIF4 signaling module enables plant thermomorphogenic responses to occur in a daylength-dependent manner. We propose that the GI-mediated integration of photoperiodic and temperature information shapes thermomorphogenic rhythms, which enable plants to adapt to diel fluctuations in daylength and temperature during seasonal transitions.