Transcription factor that binds specifically to a 5'-AA[AG]G-3' consensus core sequence (By similarity). Regulates a photoperiodic flowering response. Transcriptional repressor of 'CONSTANS' expression. Interacts with ADO2 (via kelch repeats) and ADO3 (via kelch repeats). Expressed in the vasculature of cotyledons and hypocotyls, leaves and roots. Circadian-regulation. Highly expressed at the beginning of the light period, then decreases, reaching a minimum between 16 and 29 hours after dawn before rising again at the end of the day. No alteration in flowering time, probably due to the redundancy with CDF1, CDF2 and CDF5.