One important model for disease resistance is the Prf recognition complex of tomato, which responds to different bacterial effectors. Prf incorporates a protein kinase called Pto as its recognition domain that mimics effector virulence targets, and activates resistance after interaction with specific effectors. Recent findings show that this complex is oligomeric, and reveal how this impacts mechanism. Oligomerisation brings two or more kinases into proximity, where they can phosphorylate each other after effector perception. Effector attack on one kinase activates another in trans, constituting a molecular trap for the effector. Oligomerisation of plant resistance proteins may be a general concept that broadens pathogen recognition and restricts the ability of pathogens to evolve virulence.