Virulence on Pm4 kinase-based resistance is determined by two divergent wheat powdery mildew effectors

Abstract

The wheat resistance gene Pm4 encodes a kinase fusion protein and has gained particular attention as it confers race-specific resistance against two major wheat pathogens: powdery mildew and blast. Here, we describe the identification of AvrPm4, the mildew avirulence effector recognised by Pm4, using UV- mutagenesis, and its functional validation in wheat protoplasts. We show that AvrPm4 directly interacts with and is phosphorylated by Pm4. Using genetic association and QTL mapping, we furthermore demonstrate that evasion of Pm4 resistance by virulent mildew isolates relies on a second fungal component, SvrPm4, which suppresses AvrPm4-induced cell death. Surprisingly, SvrPm4 was previously described as AvrPm1a. We show that SvrPm4, but not its inactive variant svrPm4, is recognised by the NLR immune receptor Pm1a. These multiple roles of a single effector provide a new perspective on fungal (a)virulence proteins and their combinatorial interactions with different types of immune receptors.