Submitted to: The Plant Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 6, 2010
Publication Date: December 18, 2010
Citation: Abeysekara, N.S., Friesen, T.L., Liu, Z., Mcclean, P.E., Faris, J.D. 2010. Marker Development and Saturation Mapping of the Tan Spot Ptr ToxB Sensitivity locus Tsc2 in Hexaploid Wheat. The Plant Genome. 3:179-189. Interpretive Summary: The fungus that causes the disease tan spot in wheat produces a host-selective toxin known as Ptr ToxB that contributes to the development of disease in wheat lines that carry the gene Tsc2. Therefore, the elimination of the Tsc2 gene from wheat lines results in a greater level of tan spot resistance. Here, research was conducted to identify and/or develop molecular markers closely associated with Tsc2 that can be used by wheat breeders and geneticists to rapidly and efficiently screen wheat lines for the presence or absence of Tsc2. By using previously developed molecular markers and by developing new markers through comparative analysis of wheat with the related grasses rice and Brachypodium, a genetic map of the chromosome carrying Tsc2 was constructed. One DNA marker, which was completely associated with Tsc2, was refined to make it user-friendly and amenable to high-throughput analysis. This marker was used to evaluate wheat lines known to carry Tsc2 and lines known to lack Tsc2, and the results indicated that the marker is diagnostic for the presence or absence of Tsc2. Therefore, this marker will be useful for wheat breeders to rapidly and efficiently identify lines lacking Tsc2, which will lead to the development of lines with improved tan spot resistance.
Technical Abstract: Ptr ToxB is a host-selective toxin produced by the tan spot fungus that induces chlorosis in wheat lines harboring the Tsc2 gene, which was previously located to chromosome arm 2BS in tetraploid wheat. In this study, molecular mapping in a recombinant inbred (RI) population derived from a cross between the Ptr ToxB-sensitive cultivar Katepwa and the Ptr ToxB-insensitive landrace Salamouni (SK population) confirmed the location of Tsc2 on 2BS in hexaploid wheat. Analysis of an F2 population derived from the same parents for reaction to Ptr ToxB indicated that a single dominant gene governs sensitivity. Thirteen microsatellite markers were used to construct a basic map of the Tsc2 region in the SK population, and 14 additional markers developed from bin-mapped expressed sequence tags (ESTs) and from ESTs identified based on colinearity with rice and Brachypodium were mapped to the Tsc2 region. Tsc2 was delineated to a 3.3 cM interval, and the marker XBE444541 co-segregated with Tsc2. Spore inoculations and composite interval-regression mapping demonstrated that a compatible Tsc2-Ptr ToxB interaction accounted for 54% of the variation in disease. Analysis of Ptr ToxB-sensitive and -insensitive genotypes with XBE444541 suggests that it is diagnostic for Tsc2 and should be useful for marker-assisted selection.