Fig. 1.

The UVR8 photocycle. UV-B photon absorption by the UVR8 homodimer via a tryptophan-based mechanism results in UVR8 monomerization. The UVR8 monomer interacts directly with COP1 to initiate UV-B signaling, which results in changes in gene expression (including the induction of RUP1 and RUP2 expression) and ultimately regulates UV-B-induced photomorphogenesis and stress acclimation. Re-dimerization of UVR8 through the action of RUP1 and RUP2 disrupts the UVR8-COP1 interaction and regenerates the UVR8 homodimer again ready for UV-B perception. Image reprinted from [46]: thearabidopsisbook.org Copyright American Society of Plant Biologists