ARS | Publication request: Map-Based Cloning of the Fungal Toxin Sensitivity Gene Tsn1 in Wheat

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: October 8, 2008
Publication Date: January 14, 2009
Citation: Faris, J.D., Zhang, Z., Lu, H., Reddy, L., Lu, S., Simons, K.J., Fellers, J.P., Friesen, T.L. 2009. Map-Based Cloning of the Fungal Toxin Sensitivity Gene Tsn1 in Wheat. Plant and Animal Genome Conference XVII abstracts p. 305

Technical Abstract: The wheat Tsn1 gene on wheat chromosome arm 5BL confers sensitivity to the host-selective proteinaceous toxins Ptr ToxA and SnToxA produced by the pathogenic fungi Pyrenophora tritici-repentis and Stagonospora nodorum, respectively. Compatible Tsn1-ToxA interactions lead to extensive cell death and disease susceptibility. We employed a map-based strategy combined with haplotype analysis of natural populations to delineate the Tsn1 candidate region to a 120 kb segment containing five genes. Comparative sequence analysis of multiple independent EMS-induced ToxA-insensitive mutants revealed that Tsn1 is a member of the NBS-LRR class of disease “resistance” genes, but in this case it confers susceptibility. Evaluation of the level of micro-colinearity between the orthologous regions of wheat chromosomes 5A and 5B, Brachypodium, and rice indicated that the 5A region, Brachypodium, and rice share a higher level of micro-colinearity than the 5B region does due to the presence of numerous transpositions, deletions, and rearrangements present in the wheat 5B region. Tsn1 lies on a 100 kb chromosome 5B-specific insertion that is specific to ToxA-sensitive genotypes. Homoeoalleles of Tsn1 do not exist on chromosomes 5A and 5D, and recessive tsn1 alleles are rare because ToxA-insensitivity is usually conferred by the null allele on 5B. Phylogenetic analysis indicated that Tsn1 is related to other NBS-LRR proteins encoded by toxin sensitivity genes and several rust resistance genes from other grasses. The isolation of Tsn1 will allow us to decipher the molecular interactions and mechanisms associated with the wheat-P. tritici-repentis and wheat-S. nodorum pathosystems.