1.The formal and monosomic genetic analysis of stripe rust (Puccinia striiformis) resistance in wheat. Macer, RCF. In: In J. Mackey (ed.) Proc. of 2nd Int. Wheat Genet. Symp. Lund, Sweden 1963. Hereditas Suppl., 1966, 2:127-142.
2. Genetic control of yellow rust resistance in T. spelta album. Law CNIn: Plant Breeding Institute, Cambridge, Annual Report 1975, 1976, 108-109.
3. Resistance in spelt wheat to yellow rust I. Formal analysis and variation for gliadin patterns. Kema GHJ. In: Euphytica, 1992, 63:207-217.
4. Resistance gene analog polymorphism markers co-segregating with the Yr5 gene for resistance to wheat stripe rust have homology with plant disease resistance genes. Yan GP, Chen XM , Line RF, Wellings CR . In: Theoretical and Applied Genetics, 2003, 106:636-643.
The Yr5 gene confers resistance to all races of the stripe rust pathogen (Puccinia striiformis f. sp. tritici) of wheat in the United States. To develop molecular markers for Yr5, a BC7:F3 population was developed by backcrossing the Yr5 donor 'Triticum spelta album' (TSA) with the recurrent parent 'Avocet Susceptible' (AVS). Seedlings of the Yr5 near-isogenic lines (AVS/6*Yr5), AVS, TSA, and the BC7:F3 lines were tested with North American races of P. striiformis f. sp. tritici under controlled greenhouse conditions. The single gene was confirmed by a 1:2:1 segregation ratio for homozygous-resistant, heterozygous and homozygous-susceptible BC7:F3 lines. Genomic DNA was extracted from the parents (the Yr5 near-isogenic line and AVS) and 202 BC7:F3 lines. The resistance gene-analog polymorphism (RGAP) technique was used to identify molecular markers. The parents and the homozygous-resistant and homozygous-susceptible BC7:F3 bulks were used to identify putative RGAP markers for Yr5. Association of the markers with Yr5 was determined using segregation analysis with DNA from the individual BC7:F3 lines. Of 16 RGAP markers confirmed by segregation analysis with 109 BC7:F3 lines, and nine of the markers confirmed with an additional 93 BC7:F3 lines, three markers co-segregated with the resistance allele and three markers co-segregated with the susceptibility allele at the Yr5 locus. The other four markers were tightly linked to the locus. Analysis of a set of Chinese Spring nulli-tetrasomic lines with three markers that co-segregated with, or were linked to, the susceptibility allele confirmed that the Yr5 locus is on chromosome 2B. Of five RGAP markers that were cloned and sequenced, markers Xwgp-17 and Xwgp-18 that co-segregated with the Yr5 locus were co-dominant and had 98% homology with each other in both DNA and translated amino-acid sequences. The two markers had 97% homology with a resistance gene-like sequence from Aegilops ventricosa and had significant homology with many known plant resistance genes, resistance gene analogs and expressed sequence tags (ESTs) from wheat and other plant species. The markers Xwgp-17 and Xwgp-18 also had significant homology with the NB-ARC domain that is in several genes for plant resistance to diseases, nematode cell death and human apoptotic signaling. These markers should be useful to clone Yr5 and combine Yr5 with other genes for durable and superior resistance for the control of stripe rust.
5. Isolation of a superfamily of candidate disease resistance genes in soybean based on a conserved nucleotide-binding site.. Yu YG, Buss GR, Maroof MA. In: Proc Natl Acad Sci USA, 1996, 93:11751-11756.
The tobacco N and Arabidopsis RPS2 genes, among several recently cloned disease-resistance genes, share a highly conserved structure, a nucleotide-binding site (NBS). Using degenerate oligonucleotide primers for the NBS region of N and RPS2, we have amplified and cloned the NBS sequences from soybean. Each of these PCR-derived NBS clones detected low- or moderate-copy soybean DNA sequences and belongs to 1 of 11 different classes. Sequence analysis showed that all PCR clones encode three motifs (P-loop, kinase-2, and kinase-3a) of NBS nearly identical to those in N and RPS2. The intervening region between P-loop and kinase-3a of the 11 classes has high (26% average) amino acid sequence similarity to the N gene although not as high (19% average) to RPS2. These 11 classes represent a superfamily of NBS-containing soybean genes that are homologous to N and RPS2. Each class or subfamily was assessed for its positional association with known soybean disease-resistance genes through near-isogenic line assays, followed by linkage analysis in F2 populations using restriction fragment length polymorphisms. Five of the 11 subfamilies have thus far been mapped to the vicinity of known soybean genes for resistance to potyviruses (Rsv1 and Rpv), Phytophthora root rot (Rps1, Rps2, and Rps3), and powdery mildew (rmd). The conserved N- or RPS2-homologous NBS sequences and their positional associations with mapped soybean-resistance genes suggest that a number of the soybean disease-resistance genes may belong to this superfamily. The candidate subfamilies of NBS-containing genes identified by genetic mapping should greatly facilitate the molecular cloning of disease-resistance genes.
6. Development of Sequence Tagged Site and Cleaved Amplified Polymorphic Sequence Markers for Wheat Stripe Rust Resistance Gene Yr5. Chen XM, Soria MA, Yan GP, Sun J, Dubcovsky J. In: Crop Science, 2003, In press.
The Yr5 gene confers resistance to all races of the wheat stripe rust pathogen (Puccinia striiformis f. sp. tritici) identified so far in the United States. Co-segregating resistance gene analog polymorphism (RGAP) markers for Yr5 are available but their use requires skills in polyacrylamide gel electrophoresis and may not be polymorphic across various varieties. To develop better markers to be used in marker-assisted selection for the Yr5 resistance, sequence tagged site (STS) primers were designed based upon the sequences of RGAP markers Xwgp-18 (AY167598) from the spring wheat (Triticum aestivum L.) ‘Avocet Susceptible’ (AVS) and Xwgp-17 (AY167597) from the Yr5 near isogenic line (NIL) in the AVS background carrying the Yr5 gene from T. spelta album (TSA). Three sets of STS markers (2 co-dominant and one dominant) were developed to amplify a region including a polymorphic 6-bp insertion/deletion (indel). The co-segregation of the STS markers with Yr5 was confirmed with 114 BC7:F3 lines developed from the cross between AVS and TSA. The STS markers worked well in five out of 17 non-Yr5 wheat varieties, but the remaining varieties had a similar size of fragment to the Yr5 marker. Because the co-dominant STS markers were based on a 6-bp indel, they could not be separated by agarose gel electrophoresis. Cleaved amplified polymorphic sequence (CAPS) markers were then developed based on a Dpn II restriction site that is present in all non-Yr5 varieties and absent in the Yr5 NIL. The CAPS markers for the Yr5 NIL and non-Yr5 varieties can be separated using agrose gel electrophoresis. The co-dominant STS markers are easier to score than the original RGAP markers. The CAPS markers are not only easier to score, but also can be used in crosses of an Yr5 donor with a much wider range of wheat germplasms. These markers should be valuable tools to accelerate the introgression of Yr5 into commercial cultivars and to combine Yr5 with other genes for durable resistance to stripe rust.