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.
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.
Andrie
Rachael M
RM
Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, USA.
Schoch
Conrad L
CL
Hedges
Rebecca
R
Spatafora
Joseph W
JW
Ciuffetti
Lynda M
LM
D000595:Amino Acid Sequence; D001203:Ascomycota / Q000145:classification / Q000235:genetics*; D015139:Blotting, Southern; D031724:Bromus / Q000382:microbiology; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics; D019143:Evolution, Molecular; D005656:Fungal Proteins / Q000235:genetics*; D016681:Genome, Fungal; D008969:Molecular Sequence Data; D009183:Mycotoxins / Q000235:genetics*; D010802:Phylogeny; D010935:Plant Diseases / Q000382:microbiology; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014908:Triticum / Q000382:microbiology
D004271:DNA, Fungal; D005656:Fungal Proteins; D009183:Mycotoxins; C434209:ToxB protein, Pyrenophora tritici-repentis