Submitted to: Theoretical and Applied Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/6/2006
Publication Date: 2/3/2006
Citation: Lu, H., Fellers, J.P., Friesen, T.L., Faris, J.D. 2006. Genomic analysis and marker devlopment for the TSN1 locus in wheat using bin-mapped ests and flanking bac contigs. Theoretical and Applied Genetics. 112:1132-142. Interpretive Summary: Tan spot is a foliar disease of wheat caused by a fungal pathogen (Pyrenophora tritici-repentis). The fungus produces a host-selective toxin known as Ptr ToxA. Sensitivity to the toxin is controlled by a single gene in wheat designated Tsn1. The long-term objective of this work is to isolate the Tsn1 gene to gain knowledge regarding the molecular interaction between Tsn1 and Ptr ToxA so that novel strategies to obtain resistance can be devised. Here, we describe the saturation mapping of the Tsn1 genomic region with markers representing expressed genes. We also describe the initiation of a chromosome walk to Tsn1, which is the first step toward isolation of the gene. Finally, we describe the development of markers closely linked to Tsn1 suitable for marker-assisted selection of the gene using high-throughput technologies. The markers will be valuable for breeders and geneticists who wish to incorporate toxin insensitivity and tan spot resistance into adapted germplasm and cultivars.
Technical Abstract: The wheat Tsn1 gene confers sensitivity to the host-selective toxin Ptr ToxA produced by the tan spot fungus (Pyrenophora tritici-repentis). The long-term goal of this research is to isolate Tsn1 using positional cloning technology. Here, we evaluated 54 ESTs physically mapped to deletion bin 5BL 0.75-0.76, which is a gene-rich region containing Tsn1. Twenty-three EST loci were mapped as either PCR-based SSCPs or RFLP markers in a low-resolution wheat population. The genetic map corresponding to the 5BL 0.75-0.76 deletion bin spans 18.5 cM and contains 37 markers for a density of 2 markers/cM. The EST-based genetic map will be useful for tagging other genes, establishing colinearity with rice, and anchoring sequence ready BAC contigs of the 5BL 0.75-0.76 deletion bin. High-resolution mapping showed that EST-derived markers together with previously developed AFLP-derived markers delineated Tsn1 to a 0.8 cM interval. Flanking markers were used to screen the Langdon durum BAC library and contigs of 205 and 228 kb flanking Tsn1 were assembled, sequenced, and anchored to the genetic map. Recombination frequency averaged 760 kb/cM across the 228 kb contig, but no recombination was observed across the 205 kb contig resulting in an expected recombination frequency of more than 10 Mb/cM. Therefore, chromosome walking within the Tsn1 region may be difficult. However, the sequenced BACs allowed the identification of one microsatellite in each contig for which markers were developed and shown to be highly suitable for marker-assisted selection of Tsn1.