An approach for high-resolution genetic mapping of distant wild relatives of bread wheat: example of fine mapping of Lr57 and Yr40 genes.

The article reports a powerful but simple approach for high-resolution mapping and eventual map-based cloning of agronomically important genes from distant relatives of wheat, using the already existing germplasm resources. Wild relatives of wheat are a rich reservoir of genetic diversity for its improvement. The effective utilization of distant wild relatives in isolation of agronomically important genes is hindered by the lack of recombination between the homoeologous chromosomes. In this study, we propose a simple yet powerful approach that can be applied for high-resolution mapping of a targeted gene from wheat's distant gene pool members. A wheat-Aegilops geniculata translocation line TA5602 with a small terminal segment from chromosome 5 M of Ae. geniculata translocated to 5D of wheat contains genes Lr57 and Yr40 for leaf rust and stripe rust resistance, respectively. To map these genes, TA5602 was crossed with a susceptible Ae. geniculata 5 M addition line. Chromosome pairing between the 5 M chromosomes of susceptible and resistant parents resulted in the development of a high-resolution mapping panel for the targeted genes. Next-generation-sequencing data from flow-sorted 5 M chromosome of Ae. geniculata allowed us to generate 5 M-specific markers. These markers were used to delineate Lr57 and Yr40 genes each to distinct ~ 1.5 Mb physical intervals flanked by gene markers on 5 M. The method presented here will allow researchers worldwide to utilize existing germplasm resources in genebanks and seed repositories toward routinely performing map-based cloning of important genes from tertiary gene pools of wheat.