Figure 5.
A model for BBX24 function in plant UV-B responses. The UV-B radiation is specifically perceived by the UV-B photoreceptor UVR8, resulting in the rapid accumulation of COP1 and its interaction with UVR8. COP1-UVR8 interaction presumably stabilizes and activates HY5 for its transcriptional activity, leading to UV-B-regulated gene expression and photomorphogenesis. This UV-B signaling cascade is feedback regulated by a few negative regulators, including BBX24, RCD1, and RUP1/RUP2. While RUP1/RUP2 negatively regulate UV-B signaling by interacting with UVR8 24, the BBX24 protein fine-tunes the UV-B responses by impinging on HY5. The BBX24-interacting protein RCD1 19 may also play a role in the BBX24 feedback regulatory module.