Cryptochrome 2 competes with COP1 substrates to repress COP1 ubiquitin ligase activity during Arabidopsis photomorphogenesis

Significance Plants adapt their growth and development to ambient light conditions by modulating the activity of the COP1/SPA ubiquitin ligase. In Arabidopsis , photoactivated cryptochromes interact directly with COP1/SPA to suppress the activity of COP1 in blue light. The molecular mechanisms of CRY-mediated inhibition of COP1 are not fully understood. Here we show that CRY2 inhibits COP1 by displacing degradation substrates from COP1. This mechanism requires a valine-proline (VP) motif present in the C-terminal domain of CRY2. These amino acids are also present in interactors of Arabidopsis and human COP1 and have been previously shown to directly bind the WD repeat of Arabidopsis and human COP1. Thus, the evolution of the plant-specific, VP-containing C-terminal domain of CRY2 might have allowed for light control of COP1 activity.