FKF1 and GIGANTEA Complex Formation Is Required for Day-Length Measurement in <i>Arabidopsis</i>

TLDR

In Arabidopsis, precise timing of CONSTANS (CO) gene expression is essential for photoperiodic flowering, and the FKF1 and GIGANTEA (GI) proteins regulate CO transcription. FKF1 requires GI to interact with the CO repressor CYCLING DOF FACTOR 1 (CDF1), thereby controlling CDF1 stability and enabling the FKF1–GI complex to form. The FKF1–GI complex assembles in a blue‑light–dependent manner on the CO promoter in the late afternoon, associates with CO chromatin, and its timing governs daytime CO expression, elucidating how light and circadian cues coordinate photoperiodic flowering.

Abstract

Precise timing of CONSTANS ( CO ) gene expression is necessary for day-length discrimination for photoperiodic flowering. The FLAVIN-BINDING, KELCH REPEAT, F-BOX 1 (FKF1), and GIGANTEA (GI) proteins regulate CO transcription in Arabidopsis . We demonstrate that FKF1 and GI proteins form a complex in a blue-light–dependent manner. The timing of this interaction regulates the timing of daytime CO expression. FKF1 function is dependent on GI, which interacts with a CO repressor, CYCLING DOF FACTOR 1 (CDF1), and controls CDF1 stability. GI, FKF1, and CDF1 proteins associate with CO chromatin. Thus, the FKF1-GI complex forms on the CO promoter in late afternoon to regulate CO expression, providing a mechanistic view of how the coincidence of light with circadian timing regulates photoperiodic flowering.