Functions in association with RUP1 as repressor of UV-B-induced photomorphogenesis mediated by UVR8 and HY5. Plays a crucial negative feedback regulatory role downstream of UVR8-COP1 to inhibit UVR8 function, balance UV-B-specific responses and ensure normal plant growth. Is involved in the regulation of photoperiodic flowering and vegetative development. May act as negative regulator of photoperiodic flowering by suppressing flowering through the action of CONSTANS (CO) and FLOWERING LOCUS T (FT). Interacts with UVR8. Circadian-regulation. Expression increases during the dark phase with a peak at the beginning of the light phase and then decreases to reach the lowest expression at the end of the light phase. Induced by UV-B. Small stunted leaves and early flowering under short days conditions. Truncated N-terminus.