Many disease resistance genes have been introgressed into wheat from its wild relatives. However, reduced recombination within the introgressed segments hinders cloning of the introgressed genes. Pm13 originated from Aegilops longissima, confers a broad-spectrum resistance to 108 wheat powdery mildew (Blumeria graminis f. sp. tritici) isolates collected from China and the European countries.

We cloned Pm13 using a method combining physical mapping with radiation-induced chromosomal aberrations and transcriptome sequencing analysis of ethyl methanesulfonate (EMS)-induced loss-of-function mutants. Pm13 encodes a kinase fusion protein, designated MLKL-K, with an N-terminal domain of mixed lineage kinase domain-like protein (MLKL_NTD domain) and a C-terminal serine/threonine kinase domain bridged by a brace.

The resistance function of Pm13 was validated by transient and stable transgenic complementation assays.

Transient over-expression analyses in Nicotiana benthamiana leaves and wheat protoplasts revealed that the truncated fragment containing brace plus kinase domain of MLKL-K was capable of inducing cell death, which is dependent on a functional kinase domain and the three α-helices in the brace region close to the N-terminus of the kinase domain.

Collectively, our results reveal that powdery mildew broad-spectrum resistance gene Pm13 encodes a novel kinase fusion gene, and shed light into the mechanism underlying broad-spectrum resistance.