Identification of a conserved ph1b-mediated 5DS–5BS crossing over site in soft-kernel durum wheat (Triticum turgidum subsp. durum) lines

Authors: IBBA, MARIA ITRIA - Washington State University; ZHANG, M - North Dakota State University; CAI, X - North Dakota State University; Morris, Craig

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2019
Publication Date: 11/15/2019
Citation: Ibba, M., Zhang, M., Cai, X., Morris, C.F. 2019. Identification of a conserved ph1b-mediated 5DS–5BS crossing over site in soft-kernel durum wheat (Triticum turgidum subsp. durum) lines. Euphytica. 215:200 (2019). https://doi.org/10.1007/s10681-019-2518-y.
DOI: https://doi.org/10.1007/s10681-019-2518-y

Interpretive Summary: Wheat is a leading cereal and is responsible for a large share of the nutrition and calories for humans globally. As a largely self-pollinating, inbreeding genus, wheat improvement is highly dependent on homologous recombination; consequently, a better understanding of CO formation could enhance the effectiveness of wheat breeding and advance our understanding of wheat genetics. The present study provides greater resolution of the recombination breakpoint interval of the 5DS-5BS translocation present in Langdon 1-674 and its derived soft-kernel durum lines as an example of ph1b-mediated chiasmata formation and crossing over and examines the translocation breakpoint of additional independent homoeologous recombination events among sister lines arising from the original cross. In addition, it further investigates the genomic arrangement and kernel structural morphology of soft-textured durum lines with varying SKCS HI values in order to identify possible chromosome rearrangements or endosperm characteristics as the basis of the observed phenotypic variation. In the present study, 19 genotypes were analyzed including the hard texture durum varieties Svevo, Alzada, Havasu, Kyle, Strongfield, Creso, and Langdon, and 12 soft textured durum wheat lines derived from four different soft-textured Langdon 5DS–5BS translocation lines. Analysis of four independent 5DS-5BS soft durum translocation lines identified a conserved recombination site located within a predicted gene and limited to a 39 bp conserved region. A KASP marker was developed to accurately and rapidly identify the 5DS-5BS translocation associated with the soft kernel trait. Finally, soft durum lines with varying kernel hardness values were analyzed through GISH and SEM revealing that neither additional D-genome translocations nor obvious endosperm morphology differences are likely responsible for the observed variation in kernel texture. To the best of our knowledge, this is the first study in wheat to describe a translocation breakpoint at the DNA sequence level. Results of this study improve the overall understanding of CO formation in wheat, but also shed greater light on the morphology of soft durum endosperm and on factors affecting variation in kernel hardness observed in this “novel” durum wheat type.

Technical Abstract: Genetic recombination is the major mechanism and basis of genetic diversity and crop improvement. Recombination typically occurs between homologous chromosomes. In wheat, however, it can also occur between homoeologous chromosomes if a functional Ph1 (Pairing homeologous-1) locus is absent (ph1b). Recently, the genes for soft kernel trait on the distal 5DS chromosome of common wheat were transferred into chromosome 5BS of durum wheat through ph1b-mediated recombination. Several independend 5DS-5BS recombination lines carrying the 5DS translocation were obtained. However, the specific size of the translocation and region where the translocation breakpoint occurred was not determined for any of the lines. In the present study, four independent 5DS-5BS recombination lines were investigated and the translocation breakpoints were fine-mapped and sequenced. All the analyzed lines lost a 5BS fragment of ~20,742,245 bp and gained a 5DS fragment of ~28,163,252 bp. The recombination breakpoint in each line was located within a predicted gene in a conserved 39 bp region, suggesting the presence of a recombination hotspot. The information obtained was then used to develop a KASP marker diagnostic for the 5DS-5BS translocation. Finally, a subset of the soft durum wheat lines exhibiting varying degrees of kernel hardness was analyzed through genomic in situ hybridization (GISH) and scanning electron microscopy (SEM). From both the GISH and SEM analyses no major differences were detected among the lines, indicating that factors other than ph1b-mediated recombination or endosperm morphology were responsible for the variation in kernel hardness.