Figure 8: Schematic model for the COP1-PIF-HEC module regulating light signaling.
PIF1, COP1, SPA1 and HEC2 directly interact with each other to form a complex. During photomorphogenesis, HECs are a group of positive regulators that are targeted by COP1 Ubiquitin E3 ligase for degradation in the dark. PIF1 promotes COP1-mediated ubiquitylation and subsequent degradation of HEC2 through the 26S proteasome pathway. HECs also antagonize PIF activity to promote plant photomorphogenesis.