Dissection and physical mapping of wheat chromosome 7B by inducing meiotic recombination with its homoeologues in Aegilops speltoides and Thinopyrum elongatum.

We constructed a homoeologous recombination-based bin map of wheat chromosome 7B, providing a unique physical framework for further study of chromosome 7B and its homoeologues in wheat and its relatives. Homoeologous recombination leads to the dissection and diversification of the wheat genome. Advances in genome sequencing and genotyping have dramatically improved the efficacy and throughput of homoeologous recombination-based genome studies and alien introgression in wheat and its relatives. In this study, we aimed to physically dissect and map wheat chromosome 7B by inducing meiotic recombination of chromosome 7B with its homoeologues 7E in Thinopyrum elongatum and 7S in Aegilops speltoides. The special genotypes, which were double monosomic for chromosomes 7B' + 7E' or 7B' + 7S' and homozygous for the ph1b mutant, were produced to enhance 7B - 7E and 7B - 7S recombination. Chromosome-specific DNA markers were developed and used to pre-screen the large recombination populations for 7B - 7E and 7B - 7S recombinants. The DNA marker-mediated preselections were verified by fluorescent genomic in situ hybridization (GISH). In total, 29 7B - 7E and 61 7B - 7S recombinants and multiple chromosome aberrations were recovered and delineated by GISH and the wheat 90 K SNP assay. Integrated GISH and SNP analysis of the recombinants physically mapped the recombination breakpoints and partitioned wheat chromosome 7B into 44 bins with 523 SNPs assigned within. A composite bin map was constructed for chromosome 7B, showing the bin size and physical distribution of SNPs. This provides a unique physical framework for further study of chromosome 7B and its homoeologues. In addition, the 7B - 7E and 7B - 7S recombinants extend the genetic variability of wheat chromosome 7B and represent useful germplasm for wheat breeding. Thereby, this genomics-enabled chromosome engineering approach facilitates wheat genome study and enriches the gene pool of wheat improvement.