Mapping barley Ds insertions using wheat deletion lines reveals high insertion frequencies in gene-rich regions with high to moderate recombination rates

Gene distribution is highly uneven in the large genomes of barley and wheat; however, location, order, and gene density of gene-containing regions are very similar between the two genomes. Flanking sequences from 35 unique, single-copy, barley Ds insertion events were physically mapped using wheat nullisomic-tetrasomic, ditelosomic, and deletion lines. Of the 35 sequences, 23 (66%) detected 34 loci mapping on all 7 homoeologous wheat groups. Seven sequences were not mapped owing to lack of polymorphism and the remaining 5 (14%) were barley-specific. All 34 loci physically mapped to the previously identified gene-rich regions (GRRs) of wheat, making the contained genes candidates for targeted mutagenesis by remobilization. Transpositions occurred preferentially into GRRs with higher recombination rates. The GRRs containing 17 of the 23 Ds insertions accounted for 60%-89% of the respective arm's recombination. The remaining 6 (17%) insertions mapped to GRRs with <15% of the arm's recombination. Overall, kb/cM estimates for the Ds-containing GRRs were twofold higher than those for regions without insertions. These results suggest that all genes may be targeted by transposon-based gene cloning, although the transposition frequency for genes present in recombination-poor regions is significantly less than that present in highly recombinogenic regions.