TaXA21-A1 on chromosome 5AL is associated with resistance to multiple pests in wheat.

KEY MESSAGE: The wheat ortholog of the rice gene OsXA21 against bacterial leaf blight showed resistance to multiple pests in bread wheat but different interacting proteins. ABSTRACT: A quantitative trait locus QYr.osu-5A on the long arm of chromosome 5A in bread wheat (Triticum aestivum L., 2n = 6x = 42; AABBDD) was previously reported to confer consistent resistance in adult plants to predominant stripe rust races, but the gene causing the quantitative trait locus (QTL) is not known. Single-nucleotide polymorphism (SNP) markers were used to saturate the QTL region. Comparative and syntenic regions between wheat and rice (Oryza sativa) were applied to identify candidate genes for QYr.osu-5A. TaXA21-A1, which is referred to as a wheat ortholog of OsXA21-like gene on chromosome 9 in rice, was mapped under the peak of the QYr.osu-5A. TaXA21-A1 not only explained the phenotypic variation in reaction to different stripe rust races but also showed significant effects on resistance to powdery mildew and Hessian fly biotype BP. The natural allelic variation resulted in the alternations of four amino acids in deduced TaXA21-A1 proteins. The interacting proteins of TaXA21-A1 were different from those identified by OsXA21 on rice chromosome 11 against bacterial leaf blight. TaXA21-A1 confers unique resistance against multiple pests in wheat but might not have common protein interactors or thus overlapping functions with OsXA21 in rice. XA21 function has diverged during evolution of cereal crops. The molecular marker developed for TaXA21-A1 would accelerate its application of the candidate gene at the QYr.osu-5A locus in wheat breeding programs.

Identification of a candidate gene for the wheat endopeptidase Ep-D1 locus and two other STS markers linked to the eyespot resistance gene Pch1.

Wheat is prone to strawbreaker foot rot (eyespot), a fungal disease caused by Oculimacula yallundae and O. acuformis. The most effective source of genetic resistance is Pch1, a gene derived from Aegilops ventricosa. 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 purified 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 Pch1 in 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, and Xcfd175 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.