Direct binding of a fungal effector by the wheat RWT4 tandem kinase activates defense

Plants have intricate innate immune receptors that detect pathogens. Research has intensely focused on two receptor classes recognizing external and internal threats. Recent research has identified a new class of disease resistance proteins called tandem kinase proteins (TKPs). We investigated RWT4, a wheat TKP that confers resistance to the devastating fungal pathogen Magnaporthe oryzae . We established a rice protoplast system, revealing RWT4 specifically recognizes the AvrPWT4 effector, leading to the transcription of defense genes and inducing cell death. RWT4 possesses both kinase and pseudokinase domains, with its kinase activity essential for defense. RWT4 directly interacts with and transphosphorylates AvrPWT4. Biolayer interferometry revealed both RWT4 domains bind the effector. AlphaFold multimer modeling identified critical regions of RWT4 for effector interaction and recognition. These findings demonstrate that TKPs can directly bind a recognized effector and may act as primary immune receptors, circumventing traditional immune pathways.