text: In A. thaliana, the main feedback loop is proposed to involve a transcriptional regulation between several proteins. The three main components of this loop are TOC1 (also known as PRR1), CCA1 and LHY. Each individual component peaks in transcriptions at different times of day. PRR 9, 7 and 5 each significantly reduce the transcription levels of CCA1 and LHY. In the opposite manner, PRR 9 and 7 slightly increase the transcription levels of TOC1. The Constans (CO) is also indirectly regulated by the PRR proteins as well by setting up the molecular mechanism to dictate the photosensitive period in the afternoon. PRRs are also known to stabilize CO at certain times of day to mediate its accumulation. This results in the regulation of early flowering in shorter photoperiods, making light sensitivity and control of flowering time important functions of the PRR class.