Inhibition of BRI1 by the synthetic microProtein miP-BRI1. A, Model of BRI1 activation and miP-BRI1 regulation. The BRI1 homodimer is inactivated by BKI1. BL binding activates BRI1 and causes dissociation of BKI1 and association of BAK1. The synthetic microProtein miP-BRI1 prevents BRI1 activation during BL binding. B, Image of representative Col-0, bri1-5, det2, and two 35S::miP-BRI1 lines treated with mock (−BL) or 100 nm BL (+BL). C, RT-qPCR showing expression of endogenous BRI1 and transgene miP-BRI1 in 35S::miP-BRI1 lines compared with Col-0. Experimental replicates were statistically tested using a Student’s t test (**P < 0.01). D, Altered CPD expression in Col-0, det2, bri1-5, and the two 35S::miP-BRI1 lines in response to 100 nm exogenous BL.