Abstract
Aegilops tauschii, the diploid wild progenitor of the D subgenome of bread wheat, is a reservoir of genetic diversity for improving bread wheat performance and environmental resilience. Here we sequenced 242 Ae. tauschii accessions and compared them to the wheat D subgenome to characterize genomic diversity. We found that a rare lineage of Ae. tauschii geographically restricted to present-day Georgia contributed to the wheat D subgenome in the independent hybridizations that gave rise to modern bread wheat. Through k-mer-based association mapping, we identified discrete genomic regions with candidate genes for disease and pest resistance and demonstrated their functional transfer into wheat by transgenesis and wide crossing, including the generation of a library of hexaploids incorporating diverse Ae. tauschii genomes. Exploiting the genomic diversity of the Ae. tauschii ancestral diploid genome permits rapid trait discovery and functional genetic validation in a hexaploid background amenable to breeding.
Highlights
The success of bread wheat (Triticum aestivum) as a major worldwide crop is underpinned by its adaptability to diverse environments, high grain yield and nutritional content[1]
Ae. tauschii is generally categorized into two lineages, lineage 1 (L1) and lineage 2 (L2)[15,16], with L2 considered the major contributor to the wheat D subgenome[8]
We generated a phylogeny based on the presence/absence of these k-mers and found it to be consistent with earlier phylogenies generated using molecular markers in that Ae. tauschii L1 and L2 formed two major clades, whereas the wheat D subgenome formed a discrete and narrow clade most closely related to L2 (Fig. 1b)[8,15,16]
Summary
The success of bread wheat (Triticum aestivum) as a major worldwide crop is underpinned by its adaptability to diverse environments, high grain yield and nutritional content[1]. Maximizing the genetic potential of wheat requires a deep understanding of the structure and function of its genome, including its relationship with its wild progenitor species. This genomic innovation created a plant more widely adapted to a broad range of environments and with end-use qualities not found in its progenitors[1]. Direct hybridization between hexaploid wheat and Ae. tauschii is possible. This approach usually requires embryo rescue but has the advantage that it does not disrupt desirable allele combinations in the bread wheat A and B subgenomes[10,11]. We discovered that an uncharacterized Ae. tauschii lineage contributed to the initial gene flow into domesticated wheat, broadening our understanding of the evolution of bread wheat. To facilitate the discovery of useful genetic variation from Ae. tauschii, we established a k-mer-based association mapping pipeline and demonstrated the mobilization of the untapped diversity from Ae. tauschii into wheat through the use of synthetic wheats and genetic transformation for biotic stress resistance genes
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