Homologs of ToxB, a host-selective toxin gene from Pyrenophora tritici-repentis, are present in the genome of sister-species Pyrenophora bromi and other members of the Ascomycota

• Published in: Fungal genetics and biology 2008-03, Vol.45 (3), p.363-377
• Main Authors: Andrie, Rachael M., Schoch, Conrad L., Hedges, Rebecca, Spatafora, Joseph W., Ciuffetti, Lynda M.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Ascomycetes; Ascomycota; Ascomycota - classification; Ascomycota - genetics; Blotting, Southern; Bromegrass; Bromus - microbiology; Brown leaf spot; DNA, Fungal - chemistry; DNA, Fungal - genetics; Evolution, Molecular; Fungal Proteins - genetics; genes; Genome, Fungal; gpd; Host-selective toxins; ITS; Magnaporthe grisea; MAT-2 HMG box; Molecular Sequence Data; Multi-gene phylogeny; mycotoxins; Mycotoxins - genetics; nucleotide sequences; Oryza sativa; Phylogeny; Plant Diseases - microbiology; Plant pathogen; Pleosporaceae; Pleosporales; Polymerase Chain Reaction; Ptr ToxB; Pyrenophora bromi; Pyrenophora tritici-repentis; Sequence Analysis, DNA; Sequence Homology, Amino Acid; Tan spot; ToxB gene; Triticum - microbiology; Triticum aestivum; Wheat
• ISSN: 1087-1845; 1096-0937
• DOI: 10.1016/j.fgb.2007.10.014

Pyrenophora tritici-repentis requires the production of host-selective toxins (HSTs) to cause the disease tan spot of wheat, including Ptr ToxA, Ptr ToxB, and Ptr ToxC. Pyrenophora bromi, the species most closely related to P. tritici-repentis, is the causal agent of brown leaf spot of bromegrass. Because of the relatedness of P. bromi and P. tritici-repentis, we investigated the possibility that P. bromi contains sequences homologous to ToxA and/or ToxB, the products of which may be involved in its interaction with bromegrass. Multiplex polymerase chain reaction (PCR) revealed the presence of ToxB-like sequences in P. bromi and high-fidelity PCR was used to clone several of these loci, which were subsequently confirmed to be homologous to ToxB. Additionally, Southern analysis revealed ToxB from P. bromi to have a multicopy nature similar to ToxB from P. tritici-repentis. A combination of phylogenetic and Southern analyses revealed that the distribution of ToxB extends further into the Pleosporaceae, and a search of available fungal genomes identified a distant putative homolog in Magnaporthe grisea, causal agent of rice blast. Thus, unlike most described HSTs, ToxB homologs are present across a broad range of plant pathogenic ascomycetes, suggesting that it may have arose in an early ancestor of the Ascomycota.