Involved in disease resistance signaling (PubMed:20413097, PubMed:23951354, PubMed:26355215). Contributes to pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) signaling and defense responses downstream of FLS2 (PubMed:20413097). Acts as a BIK1 decoy and enables Xanthomonas campestris AvrAC/XopAC detection; X.campestris effector AvrAC/XopAC-mediated uridylylation promotes the formation of a complex with RKS1 and RPP13L4/ZAR1 which, in turn, activates effector-triggered immunity (ETI) against X.campestris (PubMed:23951354, PubMed:26355215, PubMed:30948526). Promotes, when uridylylated by AvrAC/XopAC, the release of ADP from the inactive RKS1-ZAR1 complex, thus activating the resistosome (PubMed:30948526). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with FLS2 (PubMed:20413097). Interacts with the Xanthomonas campestris effector XopAC/AvrAC; the recognition of X.campestris effector XopAC/AvrAC requires the presence of RKS1 and RPP13L4/ZAR1 (PubMed:23951354, PubMed:26355215). Component of a stable high-order oligomeric complex made of RKS1 and RPP13L4/ZAR1 which recruits X.campestris effector XopAC/AvrAC-mediated uridylylated PBL2 in the presence of ATP to form a wheel-like pentameric resistosome; this complex triggers immunity toward X.campestris in vascular tissues (PubMed:26355215, PubMed:30948527, PubMed:30948526). Binds to RKS1 when uridylylated (PubMed:30948526). Predominantly localized at the plasma membrane. Strongly expressed in leaves, moderately in roots, and barely in flowers, mostly in pedicels. Negatively regulated by AGAMOUS (AG) in floral organ primordia (PubMed:9150601). Induced by flagellin (flg22) (PubMed:20413097). Uridylylated at Ser-253 and Thr-254 by Xanthomonas campestris effector AvrAC/XopAC; this uridylylation is necessary for specific recruitment to RKS1 and to trigger immunity. No visible phenotype under normal growth conditions (PubMed:20413097). Increased sensitivity to the pathogenic biotrophic bacteria Xanthomonas campestris pv. campestris (Xcc) in vascular tissues (PubMed:26355215). Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.