The PHYB-FOF2-VOZ2 module functions to fine-tune flowering in response to changes in light quality by modulating FLC expression in Arabidopsis

Proper timing for plants to flower under different environmental conditions is critical for their propagation. Light quality is a pivotal environmental cue that plays a critical role in regulating flowering. Plants tend to flower late under light with high red (R)/far-red (FR) light ratio, whereas flower early under light with a low R/FR light ratio. However, how plants fine-tune flowering in response to changes in light quality is not well understood. Here, we demonstrate that the F-box Protein F-box of Flowering 2 (FOF2), an autonomous pathway-related regulator, physically interacts with VASCULAR PLANT ONE-ZINC FINGER 1 and 2 (VOZ1 and VOZ2), which are the direct downstream factors of R/FR light receptor phytochrome B (PHYB). Furthermore, we show that PHYB physically interacts with FOF2 and mediates FR light and end-of-day far-red light (EOD-FR) stabilization of the FOF2 protein and enhances FOF2 binding to VOZ2, leading to VOZ2 protein degradation by SCFFOF2 E3 ligase. In contrast, PHYB mediates R light and end-of-day red light (EOD-R) degradation of FOF2 protein. Genetic interaction studies demonstrate that FOF2 functions downstream of PHYB to promote FLC expression and inhibit flowering under both high R/FR light and simulated shade conditions, which partially depend on VOZ proteins. Taken together, our findings suggest a novel mechanism whereby plants fine-tune flowering time through PHYB-FOF2-VOZ2 module that modulates FLC expression in response to changes in light quality.