Wheat Pm4 resistance to powdery mildew is controlled by alternative splice variants encoding chimeric proteins

Crop breeding for resistance to pathogens largely relies on genes encoding receptors that confer race-specific immunity. Here, we report the identification of the wheat Pm4 race-specific resistance gene to powdery mildew. Pm4 encodes a putative chimeric protein of a serine/threonine kinase and multiple C2 domains and transmembrane regions, a unique domain architecture among known resistance proteins. Pm4 undergoes constitutive alternative splicing, generating two isoforms with different protein domain topologies that are both essential for resistance function. Both isoforms interact and localize to the endoplasmatic reticulum when co-expressed. Pm4 reveals additional diversity of immune receptor architecture to be explored for breeding and suggests an endoplasmatic reticulum-based molecular mechanism of Pm4-mediated race-specific resistance. The wheat Pm4 gene conferring race-specific powdery mildew resistance is identified to encode a chimeric kinase-MCTP protein. Its two alternative splice variants interact to form an ER-associated complex and are both essential for resistance function.