At early night, wild-type (A) and 5X (B) TOC1 are equally present and recruit transcriptional repressors NF-YB/C and HDA15 with PRR5 (not shown) to inhibit expression of PHGs. As night progresses, PIF3 levels rise, and the advanced phase of 5X, more rapid degradation and poorer PIF3 interaction result in lesser presence of 5X at target promoters, relative to wild-type TOC1, leading to attenuated inhibition of PHGs and enhanced hypocotyl growth. At late night, low TOC1 and PRR5 levels reduce NF-YB/C and HDA15 recruitment, resulting in PIF3 release to activate downstream PHGs that leads to maximal pre-dawn hypocotyl growth. 