UV-B radiations is part of the light spectrum that reaches the earth and has potentially dangerous effects for biomolecules. UV-B photons are perceived by the UVR8 photoreceptor, which is in the homodimer form in its inactive ground state. UV-B induces a conformational change of UVR8, associated with its conversion into monomer, which interacts with COP1. The interaction between COP1 and UVR8 inhibits the COP1-SPA E3 ubiquitin ligase activity which allows the stabilization of the transcription factor HY5 and promote a transcriptional reprogramming inducing the UV-B response. The transcription of the two genes RUP1 and RUP2 is induced early by HY5. These genes encode two proteins that contain WD40 domain repeats. Several roles have been associated to RUP2 in the literature: induction of UVR8 redimerization, part of an E3 ubiquitin ligase in association with the DDB1-CUL4 complex or repression of flowering under short day conditions with UV-B. But its molecular action is still poorly understood and in particular which domains interact with its partners. This study investigates the function of three RUP2 domains in the interaction with UVR8, DDB1 and CO: the N-terminal domain containing a helix-loop-helix structure, the DxR motifs and three specific amino acids potentially binding to the VP domain of proteins.