A circadian morning complex modulates far-red light signaling in Arabidopsis

The plant circadian clock coordinates internal processes with daily and seasonal environmental changes by interacting with prevalent light cues. However, how the circadian clock feedback regulates light signals remains largely elusive. Here, we identify that the clock regulator TIME FOR COFFEE (TIC), which interacts with the core clock components CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY) to form a “Morning Complex” in the nucleus and co-repress numerous genes, particularly at dawn. Intriguingly, the MC inhibits PHYA and other phyA signaling components at dawn through binding to their promoters. Mutants lacking CCA1 and LHY show increased sensitivity to far-red light, similar to tic mutants, highlighting the cooperative role of TIC, CCA1, and LHY in regulating light-inhibited hypocotyl growth. Altogether, these findings indicate that the circadian MC is a key complex, feedback regulates light signal and mediates multiple biological processes at dawn to ensure plant fitness.