A small-molecule clock modulator quantitatively manipulates photoperiodic flowering

Photoperiodism, a seasonal response mechanism that relies on day-length measurement by the circadian clock, is a major regulator of flowering time (Imaizumi 2025). The external coincidence model proposes that the alignment between the internal circadian phase and external light signals triggers photoperiodic responses (Pittendrigh and Minis 1964). It has been challenging to establish robust models for the quantitative relationship between clock and flowering time, due to a lack of tools to modulate the clock quantitatively. Here, using a circadian period-lengthening small molecule, we demonstrated the quantitative modulation of the critical day-length for flowering in monocots.