Transcription factor that promotes photomorphogenesis in the light and positively regulates fruit pigmentation and fruit nutritional quality. Probably acts downstream of the light receptor network and directly affects transcription of light-induced genes. Interacts with COP1. Ubiquitinated by COP1. Ubiquitination takes place in darkness and leads to its subsequent degradation, thereby preventing to activate photomorphogenesis signals (By similarity). When it is down-regulated, plants exhibit defects in light responses, including inhibited seedling photomorphogenesis, loss of thylakoid organization, and reduced carotenoid accumulation. Belongs to the bZIP family.