Ahy5-Col3-Col13regulatory Chain For Controlling Hypocotyl Elongation Inarabidopsis

CONSTANS-LIKE (COL) family members are commonly implicated in light signal transduction during early photomorphogenesis. However, some of their functions remain unclear. Here, we propose a role forCOL13in hypocotyl elongation inArabidopsis thaliana. We found thatCOL13RNA accumulates at high levels in hypocotyls and that a disruption in theCOL13function via a T-DNA insertion or RNAi led to the formation of longer hypocotyls ofArabidopsisseedlings under red light. On the contrary, overexpression ofCOL13resulted in the formation of shorter hypocotyls. Using various genetic, genomic, and biochemical assays, we proved that another COL protein, COL3, directly binds to the promoter ofCOL13, and the promoter region ofCOL3was targeted by the transcription factor LONG HYPOCOTYL 5 (HY5), to form an HY5-COL3-COL13 regulatory chain for regulating hypocotyl elongation under red light. Additionally, further study demonstrated that COL13 interacts with COL3, and COL13 promotes the interaction between COL3 and CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1), suggesting a possible COP1-dependent COL3-COL13 feedback pathway. Our results provide new information regarding the gene network in mediating hypocotyl elongation.