THE CONSTRUCTION OF A BAC CONTIG FOR CHROMOSOME WALKING AT THE TSN1 LOCUS IN WHEAT

¹ Department of Plant Sciences, North Dakota State University, Fargo, ND 58105, USA

² USDA-ARS Plant Science and Entomology Research Unit, Kansas State University, Manhattan, KS 66506, USA

³ USDA-ARS Cereal Crops Research Unit, Red River Valley Agricultural Research Center, Fargo, ND 58105, USA

⁴ Department of Biochemistry, North Dakota State University, Fargo, ND 58105, USA

Tsn1 conditions sensitivity to a host-selective proteinaceous toxin (Ptr ToxA) produced by the pathogenic fungus Pyrenophora tritici-repentis (Died.) Drechs, and plays an important role in pathogen-host recognition. A large F2 population consisting of 5,450 gametes was produced to develop a high-resolution map for positional cloning of the gene. High-resolution mapping delineated the Tsn1 gene to a 0.55 cM interval flanked by AFLP-derived markers Xfcg17 and Xfcg9 at 0.15 and 0.41 cM from the gene, respectively. More tightly linked markers were developed using chromosome walking in conjunction with complete sequencing of BACs identified in the Langdon durum BAC library. Although the Tsn1 gene lies within a recombination hot spot along the chromosome, our results indicate that recombination frequencies vary significantly within the BAC contig. From the regions that have been sequenced, we identified more than ten genes, most of which are genes that encode cell wall associated receptors or kinases. It is possible that the product of the Tsn1 gene is also a cell wall associated protein that interacts with the toxin to manifest necrosis because plants having tsn1 or the null allele (deletion lines) are insensitive to Ptr ToxA. The cloning and characterization of Tsn1 will be helpful in better understanding the host-pathogen interaction.