Abstract
Many plants measure changes in day-length to ensure that flowering occurs under optimum conditions. In Arabidopsis, the most prominent molecular mechanisms in the photoperiodic flowering pathway are the clock-regulated gene expression of CONSTANS (CO) and the stabilization and activation of CO protein by light. We show that the timing of the blue-light dependent formation of FLAVIN-BINDING, KELCH REPEAT AND F-BOX 1 (FKF1) and GIGANTEA (GI) protein complex is crucial for regulating the timing of CO gene expression. The expression of FKF1 and GI is clock regulated, and the peak expression of both genes coincides in long days (LD) but not in short days (SD). Hence, the timing of the FKF1-GI complex formation is regulated by the coincidence of both external and internal cues. We propose the importance of external and internal coincidence mechanisms on CO transcription regulated by the FKF1-GI complex.
