Figure 8.

A proposed working model for PRRs-PIF4/5 transcriptional module-mediated photoperiodic hypocotyl growth. PRRs, as core circadian clock components, can directly and sequentially bind the promoters of PIF4 and PIF5 to repress their transcription in an independent manner with the Evening Complex. Diurnal rhythms of PIF4/5 protein abundance are determined by the coordination of light signaling-mediated protein stability and circadian clock-regulated transcriptional expression. Hence, TOC1 and other PRRs represent a primary molecular node between the circadian clock and photoperiod to control photoperiodic hypocotyl growth.