Fig. 2.

CONSTANS (CO) oscillatory transcription is dependent on multiple factors throughout the day: CO gene expression changes throughout the day. In inductive long-day conditions for flowering in Arabidopsis, the peak of CO expression is constrained to the afternoon before dusk. In the morning, CDF family transcription factors bind to the CO promoter to repress transcription. Beginning in the afternoon, FKF1 and GI form a protein complex that ubiquitinates CDFs through an F-box protein function on FKF1 and targets them for proteasomal degradation, freeing the CO promoter from repression. FBH transcriptional activators are then recruited to the CO genomic locus, resulting in increased transcription of CO before dusk. Constraining CO mRNA expression to the late afternoon, and stabilization of resultant CO protein results in FT expression at dusk and promotes flowering in long days.