Assessing the Role of Karaca Dağ Wild Emmer in Wheat Domestication and Wheat Improvement

Download or read book Assessing the Role of Karaca Dağ Wild Emmer in Wheat Domestication and Wheat Improvement written by Chad Michael Jorgensen and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Wild emmer (Triticum turgidum ssp. dicoccoides) is the progenitor of all domesticated wheat grown today, both tetraploid and hexaploid. The understanding of wild emmer's origin, the evolution of its genome, the structure and evolution of its genetic diversity, and the ways it contributed to the evolution of domesticated wheat is essential for advancing the basic and applied biology of wheat. It has been hypothesized that emmer was domesticated in the Karaca Dağ region in southeastern Turkey, yet, no analysis of domestication genes has been reported in this population. To fill this knowledge gap, accession PI 428082 from the Karaca Dağ region was crossed to durum 'Langdon' (LDN) to construct a genetic mapping population and genetic linkage maps, and map loci controlling domestication traits. First, using single nucleotide polymorphism (SNP) markers, the relationship of this accession to other accessions of wild emmer in the Karaca Dağ region and domesticated wheat was determined. PI 428082 was embedded in the Karaca Dağ wild emmer branch in the phylogenetic tree, indicating that it is representative of the Karaca Dağ wild emmer population. Recombinant inbred lines (RILs) from the cross LDN x PI 428082 were developed, a genetic map comprising 2,650 unique SNP markers and spanning 1727.93 cM was constructed and compared to the genome sequence of Aegilops tauschii, a wild relative of the wheat D genome, to investigate chromosomal rearrangements and evolution of wild emmer genome. A major structural change observed in the PI 428082 genome was a reciprocal translocation between chromosomes 3B and 6B, in addition to the already known 4A-5A-7B translocations and 4A pericentric and paracentric inversions. In addition to these rearrangements, the most common type of chromosome rearrangement was an intrachromosomal translocation. The genetic map was inconsistent with the current model of the evolution of chromosome 4A. The origin of 4A rearrangements was shown to be contemporary with the speciation of wild emmer. The study of diversity in chromosome 4A in the Karaca Dağ wild emmer uncovered a selective sweep in this chromosome that was absent from hexaploid wheat. The absence of diversity from a large portion of chromosome 4A of wild emmer population that is proposed to be the ancestor of all domesticated wheat calls into question the ancestral nature of this wild emmer population. To further characterize the relationship of PI 428082 to domesticated wheat, the LDN x PI 428082 RIL population was grown in the field for three years and measured a suite of domestication-related traits. Domestication-related QTLs were discovered and mapped. To compare them with domestication QTLs on homoeologous chromosomes and QTLs published by others, the 64 QTLs discovered here and 60 domestication QTLs discovered by others were aligned on the Ae. tauschii genome sequence. This allowed for the more precise determination of the locations of some of the QTLs and the identification of candidate genes among genes isolated in other grass genomes. Virtually all QTLs described by others in wild emmer QTL studies segregated in the LDN x PI 428082 RIL population, suggesting the presence of wild alleles at most of the domestication loci in PI 428082. This is consistent with PI 428082 and other wild emmer in the Karaca Dağ region being a wild population, and argues against the possibility that the population was derived from hybridization with domesticated wheat. Segregation for wild traits, such as brittle rachis and glume tenacity, in the RIL population made it unsuitable for the analysis of agronomic traits. Therefore, reciprocal inbred backcross lines (IBLs) from the cross LDN x PI 428082 were developed. By merging two IBL populations derived from backcrosses to the wild and domesticated parents, the creation of a genotyping matrix suitable for genetic mapping was possible. The LDN x PI 428082 map consisted of 1,830 unique markers and spanned 2,057 cM of the tetraploid genome. It was consistent with the map made using the RIL population, as 98% of markers that could be compared were in the same order. QTL analysis was also performed with this map and QTLs were aligned on the Aegilops tauschii genome sequence for comparison. The locations of QTL shared by the IBL and RIL maps were consistent. Hence, both marker order and QTL locations validated the approach to the IBL map construction and QTL mapping.