Allopolyploidization increases genetic recombination in the ancestral diploid D genome during wheat evolution

Genetic recombination produces new allelic combinations, thereby introducing variation for domestication. Allopolyploidization has increased the evolutionary potential of hexaploid common wheat by conferring the advantages of heterosis and gene redundancy, but whether a relationship exists between allopolyploidization and genetic recombination is currently unknown. To study the impact of allopolyploidization on genetic recombination in the ancestral D genome of wheat, we generated new synthetic hexaploid wheats by crossing tetraploid Triticum turgidum with multiple diploid Aegilops tauschii accessions, with subsequent chromosome doubling, to simulate the evolutionary hexaploidization process. Using the DArT-Seq approach, we determined the genotypes of two new synthetic hexaploid wheats with their parents, F2 plants in a diploid population (2x, D1D1 × D2D2) and its new synthetic hexaploid wheat-derived population (6x, AABBD1D1 × AABBD2D2). About 11% of detected SNP loci spanning the D genome of Ae. tauschii were eliminated after allohexaploidization, and the degree of segregation distortion was increased in their hexaploid offspring from the F2 generation. Based on codominant genotypes, the mean genetic interval length and recombination frequency between pairs of adjacent and linked SNPs on D genome of the hexaploid F2 population were 2.3 fold greater than those in the diploid F2 population, and the recombination frequency of Ae. tauschii was increased by their hexaploidization with T. turgidum. In conclusion, allopolyploidization increases genetic recombination of the ancestral diploid D genome of wheat, and DNA elimination and increased segregation distortion also occur after allopolyploidization. Increased genetic recombination could have produced more new allelic combinations subject to natural or artificial selection, helping wheat to spread rapidly to become a major global crop and thereby accelerating the evolution of wheat via hexaploidization.