Binding assays for brassinosteroid receptors.

BRI1, a leucine-rich repeat (CRR)-receptor kinase protein, belongs to the plant hormone brassinosteroid (BR) receptor complex in Arabidopsis thaliana (Arabidopsis). The experiments described in this chapter to carry out BR-binding assays in Arabidopsis plants are largely based on previously published procedures by Wang et al. (1) and Caño-Delgado et al. (2), which demonstrated that BRI1 and BRI1-like proteins BRL1 and BRL3, are components of the BR-receptor complexes in vivo. Furthermore, binding assays using a photo-affinity labelled castasterone have demonstrated that BRs are perceived directly by a subdomain of the extracellular domain of BRI1 defined by the 94 amino acids of the ID-LRR22 (3).