Tandem kinase protein (TKP) with two kinase domains is a new type of disease resistance gene family in wheat and barley. Wheat stripe rust resistance gene Yr15 (WTK1), wheat stem rust resistance gene Sr60 (WTK2), barley stem rust resistance gene Rpg1, and the candidate gene (MLOC_38442.1) of barley loose smut resistance gene Un8 were found to be the TKP members with two putative kinase domains.
Recently, a team led by Prof. LIU Zhiyong at the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, in collaboration with the team led by Prof. LI Hongjie at the Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, identified a rare gain of function mutation in a wheat tandem kinase that confers resistance to wheat powdery mildew (Blumeria graminis f. sp. tritici), one of the most widely epidemic diseases in wheat (Triticum aestivum).
Using the map-based cloning approach, the powdery mildew resistance gene Pm24 was characterized in the Chinese wheat landrace Hulutou. Pm24 encodes a TKP with the putative kinase-pseudokinase domains, designated WHEAT TANDEM KINASE 3 (WTK3). A 6-bp deletion (5880-AAAGGA-5881) in the fifth exon of the WTK3 gene was detected between the resistant landrace Holutou and the susceptible cultivar Shi 4185, leading to a lysine-glycine (K400G401) two-amino acid deletion in the encoded WTK3 protein of Holutou.
The powdery mildew resistance function of Pm24 was validated by transgenic assay, independent mutants, and allelic association analyses.
Haplotype analysis of the worldwide diversified wheat germplasms revealed that the rare 6-bp natural deletion of lysine-glycine codons, endemic to the wheat landraces of Shaanxi Province, China, in the kinase I domain of WTK3 is critical for the resistance function.
The transgenic assay of WTK3 chimeric variants revealed that only the specific two amino acid deletion, rather than any of the single or more amino acid deletions, in the kinase I domain of WTK3 is responsible for gaining the resistance function of WTK3 against B. graminis f. sp. tritici.
Pm24 was highly or moderately resistant (Infection type 0-2) to 93 genetically divergent B. graminis f. sp. tritici isolates collected from 45 counties in 12 provinces of China. The absence of Pm24 in the modern wheat cultivars and the identification of the key 6-bp deletion associated with the powdery mildew resistance provide a potential opportunity for developing disease resistant cultivars with marker-assisted selection and precise genome-editing technologies in wheat breeding programs.
The research was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences, the National Key Research and Development Program of China, the National Natural Science Foundation of China, and the Science and Technology Service Network Initiative of the Chinese Academy of Sciences.