BRI1 and BAK1 activated by the sequential transphosphorylation between the kinase domains of the kinases, and the kinase domain of the activated BRI1 in turn phosphorylates the plasma membrane-anchored cytoplasmic kinase, BRASSINOSTEROID-SIGNALING KINASE1 (BSK1). OsBSK1 is inferred from Arabidopsis BSK1 from orthology
