Two E3 ligases antagonistically regulate the UV-B response in Arabidopsis

Significance Plant seedlings encounter increasing levels of UV-B irradiation during their emergence from soil as they undergo a light-induced developmental process termed photomorphogenesis. However, less is known about the molecular mechanisms underlying plant responses to this invisible part of the light spectrum. Here, we reveal that the UV-B light signal is interpreted coordinately by two sets of E3 ligases and a transcription factor in Arabidopsis . The UV-B–inducible E3 CUL4-DDB1–RUP1/RUP2 complex targets the master transcription factor HY5 for proteolysis. COP1 directly interacts with and degrades RUP1/RUP2 to stabilize HY5, ultimately promoting photomorphogenesis under UV-B light. These findings uncover the mechanism of plant responses to UV-B irradiation, and are critical to develop methods to improve plant growth and light energy utilization.