Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2007
Publication Date: 10/20/2007
Citation: Leonard, J.M., Watson, C.J., Carter, A.H., Hansen, J.L., Zemetra, R.S., Santra, D.K., Garland Campbell, K.A., Riera-Lizarazu, O. 2008. Identification of a candidate gene for the wheat endopeptidase Ep-D1 locus and two other STS markers linked to the eyespot resistance gene Pch1. Journal of Theoretical and Applied Genetics. 116: 261-270. Interpretive Summary: The Pch1 gene has been an effective genetic resistance tool to reduce the incidence of strawbreaker foot rot on wheat for the past 30 years. The gene has been selected in segregating populations using its linkage to the endopeptiadase locus, Ep-D1b. This research reports development of a DNA-based marker that is more flexible and easier to integrate with other types of DNA markers in marker assisted selection programs for improvement of wheat. The use of the Xorw1, Xorw5 and Xorw6 markers will facilitate the continued use of the Pch1 gene in wheat improvement where strawbreaker foot rot is a problem. The research was a collaborative effort between scientists at Oregon State Univ., Univ. of Idaho, Washington State Univ and the USDA-ARS.
Technical Abstract: Wheat is prone to strawbreaker foot rot (eye- spot), a fungal disease caused by Oculimacula yallundae and O. acuformis. The most effective source of genetic resistance is Pch1, a gene derived from Aegilops ventri- cosa. The endopeptidase isozyme marker allele Ep-D1b, linked to Pch1, has been shown to be more effective for tracking resistance than DNA-based markers developed to date. Therefore, we sought to identify a candidate gene for Ep-D1 as a basis for a DNA-based marker. Comparative mapping suggested that the endopeptidase loci Ep-D1 (wheat), enp1 (maize), and Enp (rice) were orthologous. Since the product of the maize endopeptidase locus enp1 has been shown to exhibit biochemical properties similar to oligopeptidase B puriWed from E. coli, we reasoned that Ep-D1 may also encode an oligopeptidase B. Consistent with this hypothesis, a sequence-tagged-site (STS) marker, Xorw1, derived from an oligopeptidase B-encoding wheat expressed-sequence-tag (EST) showed complete linkage with Ep-D1 and Pch1in a population of 254 recombinant inbred lines (RILs) derived from a cross between wheat cultivars Coda and Brundage. Two other STS markers, Xorw5 and Xorw6, and three microsatellite markers (Xwmc14, Xbarc97, and Xcfd175) were also completely linked to Pch1. On the other hand, Xwmc14, Xbarc97, and Xcfd175 showed recombination in the W7984 x Opata85 RIL population suggesting that recombination near Pch1 is reduced in the Coda/Brundage population. In a panel of 44 wheat varieties with known eyespot reactions, Xorw1, Xorw5, and Xorw6 were 100% accurate in predicting the presence or absence of Pch1 whereas Xwmc14, Xbarc97, andXcfd175 were less effective. Thus, linkage mapping and a germplasm survey suggest that the STS markers identified here should be useful for indirect selection of Pch1.