Dual-role effector Bgt5481 from Blumeria graminis f. sp. tritici induces plant immunity and contributes to virulence

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a destructive fungal disease posing a serious threat to global wheat production. The function of effectors in Bgt remains mostly undiscovered. Here, we identified an effector, Bgt5481, from Bgt that triggers cell death in multiple plants. Bgt5481 homologs are widely distributed across fungi. Bgt5481-triggered cell death occurred independently of NbBAK1, NbSOBIR1, NbSGT1, and NbCERK1. Purified Bgt5481 protein activated the reactive oxygen species (ROS) burst and upregulation of defense-related genes in the non-host Nicotiana benthamiana but not in wheat. Additionally, silencing Bgt5481 expression by a virus-mediated host-induced gene silencing system significantly attenuated the pathogenicity of Bgt, while transient overexpression of Bgt5481ΔSP by a 4-component barley stripe mosaic virus (BSMV)-based system suppressed the immune response in wheat to Bgt. Overall, our data show that the Bgt5481 effector from Bgt can function as a pathogen-associated molecular pattern (PAMP) to induce the plant immune response in a non-host but contributes to Bgt virulence in wheat.