The Circadian Morning Complex Modulates ABA Signaling by Transcriptionally Repressing PYL4, PYL5 and PYL6 at Dawn

The circadian clock not only coordinates plant growth with daily environmental changes but also interacts with endogenous hormonal pathways, such as abscisic acid (ABA) signaling, to balance growth and abiotic stress responses. Although the feedback network between the circadian system and ABA pathway has been well-established, the regulatory relationship between the ABA receptor PYRABACTIN RESISTANCE 1-LIKE (PYLs) family and the clock remains largely unclear, and the understanding of how ABA signaling feeds back to modulate the clock is still limited. Here, we show that the null mutants of TIME FOR COFFEE (TIC) and CIRCADIAN CLOCK ASSOCIATED 1/ LATE ELONGATED HYPOCOTYL (CCA1/LHY), which are core components of circadian Morning Complex (MC), display hypersensitivity to ABA during seed germination. Mechanistically, the MC could directly bind to the promoters of PYL4, PYL5 and PYL6 to repress their transcription at dawn, which may contribute to the attenuation of ABA signal transduction. Furthermore, ABA could induce TIC expression, and TIC is required for transferring ABA signals into coherent circadian rhythm. Taken together, these findings suggest that the MC may function as a dawn-specific integrator, linking ABA signaling with the circadian core oscillator, hence offering new insights into how plants coordinate hormonal and temporal regulation.