McDonald*, Bruce A.; Holtgrewe Stukenbrock, Eva.  Horizontal transfer of ToxA between the wheat pathogens Phaeosphaeria nodorum and Pyrenophora tritici repentis.  In: International Meeting on "Population and Evolutionary Biology of Fungal Symbionts", Ascona, Switzerland, 2007. AB-52. Click here to download the presentation on pdf format.

The host-specific ToxA toxin produced by the wheat pathogens Pyrenophora tritici-repentis and Phaeosphaeria nodorum interacts with the product of the dominant plant gene Tsn1 to induce necrosis.  We presented evidence that the ToxA gene was acquired by P. tritici-repentis from P. nodorum through a recent horizontal gene transfer event.  PCR and sequence analysis indicated that the level of ToxA variation in P. nodorum (SnToxA) was significantly higher than in P. tritici-repentis (PtrToxA). 732 isolates of P. nodorum originating from eight geographical regions were PCR-screened to infer the pattern of SnToxA deletions. The frequency of deletions differed significantly among populations, ranging from 0% (Australia) to 98% (China). Sequence analysis of the SnToxA gene in 123 P. nodorum isolates revealed 13 distinct haplotypes. The majority of SnToxA mutations were non-synonymous resulting in changes at the protein level. Evidence for positive diversifying selection supports the hypothesis that evolution of the ToxA locus is driven by the distribution of different Tsn1 alleles in the corresponding host populations.

Keywords:  pathogenicity, virulence, gene for gene models

*Institution: ETH Zuerich, Institute of Integrative Biology, Plant Pathology Group
Email: bruce.mcdonald@agrl.ethz.ch