Functional characterization of powdery mildew resistance gene MlIW172, a new Pm60 allele and its allelic variation in wild emmer wheat

Wild emmer wheat (Triticum dicoccoides, WEW) is an immediate progenitor of both the cultivated tetraploid and hexaploid wheats and it harbors rich genetic diversity against powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt). A powdery mildew resistance gene MlIW172 originated from WEW accession IW172 (G-797-M) is fine mapped in a 0.048 centimorgan (cM) genetic interval on 7AL, corresponding to a genomic region spanning 233 kb, 1 Mb and 800 kb in Chinese Spring, WEW Zavitan, and T. urartu G1812, respectively. MlIW172 encodes a typical NLR protein NLRIW172 and physically locates in an NBS-LRR gene cluster. NLRIW172 is subsequently identified as a new allele of Pm60, and its function is validated by EMS mutagenesis and transgenic complementation. Haplotype analysis of the Pm60 alleles reveals diversifications in sequence variation in the locus and presence and absence variations (PAV) in WEW populations. Four common single nucleotide variations (SNV) are detected between the Pm60 alleles from WEW and T. urartu, indicative of speciation divergence between the two different wheat progenitors. The newly identified Pm60 alleles and haplotypes in WEW are anticipated to be valuable for breeding powdery mildew resistance wheat cultivars via marker-assisted selection.