Dual specificity kinase acting on both serine/threonine- and tyrosine-containing substrates. Acting as a counterplayer of BIR1, promotes the activation of plant defense and cell death (PubMed:19616764). Component of the RLP23-SOBIR1-BAK1 complex that mediates NLP-triggered immunity (PubMed:27251392). Functions as an inhibitor/regulator of abscission, probably by regulating membrane trafficking during abscission (PubMed:20081191). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] Interacts with CST (PubMed:21628627). Interacts with RLP23 (PubMed:24525519, PubMed:27251392). Component of a trimeric complex composed of RLP23, SOBIR1 and BAK1. BAK1 is recruited into a pre-formed RLP23-SOBIR1 complex in a ligand-dependent manner (PubMed:27251392). Mostly present in leaves and flowers, with increasing expression in older flowers. Expressed in floral organ abscission zones (AZs) prior to cell separation and subsequent shedding. Also present within the style of developing fruits, at the bases of cauline leaves, and in the stems of the first rosette leaves. Autophosphorylated on Ser, Thr and Tyr residues. Suppresses BIR1 (bir1-1) disruption phenotype. When associated with AGD5/NEV disruption, premature shedding of floral organs and enlarge abscission zones. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.