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

Apr 12, 2026Plant & cell physiology

The Morning Biological Clock Controls ABA Hormone Signals by Turning Off Key Receptor Genes at Dawn

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Abstract

Null mutants of TIME FOR COFFEE (TIC) and CIRCADIAN CLOCK ASSOCIATED 1/ LATE ELONGATED HYPOCOTYL (CCA1/LHY) display hypersensitivity to abscisic acid (ABA) during seed germination.

The circadian clock interacts with hormonal pathways, balancing plant growth and stress responses.
The regulatory relationship between ABA receptors (PYLs) and the circadian clock is largely unclear.
The circadian Morning Complex (MC) directly binds to and represses the transcription of PYL4, PYL5, and PYL6 at dawn.
ABA induces the expression of TIC, which is necessary for integrating ABA signals into the circadian rhythm.
The findings suggest that the MC may serve as a dawn-specific integrator of ABA signaling and circadian regulation.

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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.

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

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