The circadian clock module LgPRR7-LgFKF1 negatively regulates flowering time in Luculia gratissima, a woody ornamental plant

Abstract

Photoperiod-dependent flowering is a critical trait in breeding for flowering time in woody ornamental plants. Circadian clocks are vital for the regulation of photoperiodic flowering in plants, but their molecular regulation pathways in woody perennials remain poorly explored. Here, we identified two circadian clock components LgPSEUDO-RESPONSE REGULATOR 7 (LgPRR7) and LgFLAVIN-BINDING KELCH REPEAT F-BOX 1 (LgFKF1) as key repressors of flowering in Luculia gratissima, a short-day woody ornamental plant with commercial potential. Levels of LgPRR7 and LgFKF1 transcripts exhibited photoperiodic responses and diurnal patterns. Ectopic overexpression of LgPRR7 or LgFKF1 in Arabidopsis thaliana accelerated flowering, whereas silencing LgPRR7 or LgFKF1 in L. gratissima accelerated flowering. Crucially, LgPRR7 directly interacts with LgFKF1, forming a self-reinforcing regulatory module LgPRR7-LgFKF1 to repress flowering in L. gratissima. Furthermore, the observed physical interactions among LgFKF1, LgCONSTANS-LIKE 12 (LgCOL12), and LgREPRESSOR OF ga1-3-LIKE 2 (LgRGL2) implied that they possibly formed a protein complex LgFKF1-LgCOL12-LgRGL2, bridging the circadian clock, photoperiod, and gibberellin signaling pathways to suppress downstream floral integrators. Intriguingly, silencing LgPRR7 and LgFKF1 extended the duration of L. gratissima flowering, a trait of horticultural significance. These results suggest the integration of multi-layered environmental and endogenous signals in the regulation of flowering time. The LgPRR7-LgFKF1 module provides novel targets for molecular improvement to manipulate flowering time and duration in L. gratissima and other economically valuable woody ornamental plants. Our results also support the mediation of flowering convergence in short-day plants through the action of circadian clock genes.