Abstract
The wild emmer wheat (Triticum turgidum ssp. dicoccoides; WEW) yellow (stripe) rust resistance genes Yr15, YrG303, and YrH52 were discovered in natural populations from different geographic locations. They all localize to chromosome 1B but were thought to be non-allelic based on differences in resistance response. We recently cloned Yr15 as a Wheat Tandem Kinase 1 (WTK1) and show here that these three resistance loci co-segregate in fine-mapping populations and share an identical full-length genomic sequence of functional Wtk1. Independent ethyl methanesulfonate (EMS)-mutagenized susceptible yrG303 and yrH52 lines carried single nucleotide mutations in Wtk1 that disrupted function. A comparison of the mutations for yr15, yrG303, and yrH52 mutants showed that while key conserved residues were intact, other conserved regions in critical kinase subdomains were frequently affected. Thus, we concluded that Yr15-, YrG303-, and YrH52-mediated resistances to yellow rust are encoded by a single locus, Wtk1. Introgression of Wtk1 into multiple genetic backgrounds resulted in variable phenotypic responses, confirming that Wtk1-mediated resistance is part of a complex immune response network. WEW natural populations subjected to natural selection and adaptation have potential to serve as a good source for evolutionary studies of different traits and multifaceted gene networks.
Highlights
Wheat has been the basic staple food for the major civilizations and durum wheat [T. turgidum ssp. durum (Desf.) Husnot] proof Europe,West Asia, and North Africa for at least 10 000 years vide 20% of the calories and proteins for human consumption, (Nevo et al, 2002).Today, common wheat (Triticum aestivum L.) as well as vitamins, dietary fibers, and phytochemicals (Shewry2562 | Klymiuk et al.and Hey, 2015)
functional Wheat Tandem Kinase 1 (WTK1) allele (Wtk1) provides resistance at both seedling and adult stages, YrG303 exhibited a resistance response in three independent tetraploid recombinant lines only at the adult stage under field inoculation (Fig. 2).Taking into account that controlled conditions in the dew chamber used for seeding inoculation are more favorable for Puccinia striiformis f. sp. tritici (Pst) development than field conditions used for adult stage inoculation, our results suggest that the environment plays an important role in the resistance response of these genes
Differences in phenotypic responses of Wild emmer wheat (WEW) donor lines and introgression lines of Yr15, YrG303, and YrH52 are probably related to differences due to genetic backgrounds rather than to the presence of different alleles
Summary
Wheat has been the basic staple food for the major civilizations and durum wheat [T. turgidum ssp. durum (Desf.) Husnot] proof Europe,West Asia, and North Africa for at least 10 000 years vide 20% of the calories and proteins for human consumption, (Nevo et al, 2002).Today, common wheat (Triticum aestivum L.) as well as vitamins, dietary fibers, and phytochemicals (Shewry2562 | Klymiuk et al.and Hey, 2015). Wheat annual yield reaches >>750 Mt (Food and Agriculture Organization Corporate Statistical Database, FAOSTAT); losses due to biotic (pathogens) and abiotic (unfavorable growth conditions) stresses prevent the maximum yield potential from being achieved. Tritici (Pst), an obligate pathogen that threatens wheat production around the globe (Chen, 2005).Yield losses due to yellow rust have ranged from 10% to 70% in susceptible varieties, and a total yield loss (100%) can occur under severe epidemics (Chen, 2005). Resistant wheat variety breeding is a continuous process to withstand yellow rust epidemics globally, using all possible sources of Pst resistance, in order to widen and diversify the existing R-gene pool (Roelfes et al, 1992)
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