Genetic and Physical Mapping of a Gene Conditioning Sensitivity in Wheat to a Partially Purified Host-Selective Toxin Produced by Stagonospora nodorum

Abstract

A toxin, designated SnTox1, was partially purified from culture filtrates of isolate Sn2000 of Stagonospora nodorum, the causal agent of wheat leaf and glume blotch. The toxin showed selective action on several different wheat genotypes, indicating that it is a host-selective toxin (HST). The toxic activity was reduced when incubated at 50 degrees C and activity was eliminated when treated with proteinase K, suggesting that the HST is a protein. The synthetic hexaploid wheat W-7984 and hard red spring wheat Opata 85, the parents of the International Triticeae Mapping Initiative (ITMI) mapping population, were found to be sensitive and insensitive, respectively, to SnTox1. The ITMI mapping population was evaluated for toxin reaction and used to map the gene conditioning sensitivity. This gene, designated Snn1, mapped to the distal end of the short arm of chromosome 1B. The wheat cv. Chinese Spring (CS) and all CS nullisomic-tetrasomic lines were sensitive to the toxin, with the exception of N1BT1D. Insensitivity also was observed when the 1B chromosome of CS was substituted with the 1B chromosome of an insensitive accession of Triticum dicoccoides. In addition, a series of 1BS chromosome deletion lines were used to physically localize the sensitivity gene. Physical mapping indicated that Snn1 lies within a major gene-rich region on 1BS. This is the first report identifying a putative proteinaceous HST from S. nodorum and the chromosomal location of a host gene conferring sensitivity.

Evaluation and Association Mapping of Resistance to Tan Spot and Stagonospora Nodorum Blotch in Adapted Winter Wheat Germplasm

“…The culture was then spun down to collect the supernatant for infiltration. Infiltrations were performed as described by Liu et al (2004a). Briefly, approximately 20 ml of culture filtrate was infiltrated into leaf tissue by using a needleless 1-ml syringe, and the water-soaked expansion area was marked.…”

Sensitivity to three Parastagonospora nodorum necrotrophic effectors in current Australian wheat cultivars and the presence of further fungal effectors

“…The corresponding dominant sensitivity gene Snn1 has been mapped to the short arm of chromosome 1B (Liu et al 2004a). Functional analysis indicates that SnTox1 functions as a key virulence factor.…”

“…Culture filtrates of P. nodorum were produced as described by Liu et al (2004a). Briefly, 1 Â 10 6 P. nodorum spores were inoculated into a 250-mL conical flask containing 50 mL of Fries broth.…”

Dothideomycete–Plant Interactions Illuminated by Genome Sequencing and EST Analysis of the Wheat Pathogen Stagonospora nodorum

“…An RGD motif that is involved in import into susceptible plant cells is required for activity (Meinhardt et al, 2002;Manning et al, 2004;Manning and Ciuffetti, 2005). Biochemical and genetic evidence suggests that S. nodorum isolates contain several other proteinaceous toxins (Liu et al, 2004a(Liu et al, , 2004b. ToxA is a 13.2-kD protein, and current research indicates that the other toxins are also small proteins.…”

“…Well-known examples are found in Alternaria alternata, Cochliobolus heterostrophus, and Pyrenophora tritici-repentis, while species in the genera Mycosphaerella, Corynespora, and Stemphylium are also thought to produce hostspecific toxins (Agrios, 2005). Proteinaceous host-specific toxins have recently been shown to be important virulence determinants in S. nodorum (Liu et al, 2004a(Liu et al, , 2004b, including one whose gene is thought to have been interspecifically transferred to the wheat tan spot pathogen, P. tritici-repentis . Only one example of a host-specific toxin has been identified outside of the Dothideomycetes (Wolpert et al, 2002).…”