Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/20/2014
Publication Date: 6/2/2014
Citation: Lu, S., Edwards, M.C. 2014. Molecular cloning and characterization of a ToxA-like gene from the maize pathogen Cochliobolus heterostrophus [abstract]. XVI International Congress on Molecular Plant-Microbe Interactions, July 6-10, 2014, Rhodes, Greece. Available: http://www.mpmi2014rhodes-hellas.gr/bookOfAbstracts/Posters/P316.pdf
Technical Abstract: ToxA, the first discovered fungal proteinaceous host-selective toxin, was originally identified from the tan spot fungus Pyrenophora tritici-repentis (Ptr). Homologues of the PtrToxA gene have not been identified from any other ascomycetes except the leaf/glume blotch fungus Stagonospora nodorum, which harbors a ToxA gene presumed to have been acquired by Ptr through horizontal gene transfer. Here we report the identification of a ToxA-like gene from the maize pathogen Cochliobolus heterostrophus (Ch). ChToxA consists of a 535-bp open reading frame interrupted by a 49-bp intron featuring ToxA-specific splicing sites (5’-ATAAGT…TAC-3’) and a conserved position relative to that of PtrToxA. RT-PCR revealed that ChToxA is expressed at very low levels in fungal cultures but up-regulated during fungal infection on corn plants. Subsequent cDNA cloning validated the 841-bp full-length mRNA transcript of ChToxA. The deduced ChToxA protein is composed of 161 amino acids (aa), including a N-terminal signal peptide. The predicted mature ChToxA (116 aa) shares 64% similarity with its counterpart PtrToxA (118 aa). Homology-based molecular modeling suggests that the 12.3 kD mature ChToxA adopts a three-dimensional structure featuring a ß-sandwich fold with two antiparallel ß-sheets as found in PtrToxA. Both ChToxA and PtrToxA have N-terminal asparagine-rich motifs recently shown to be essential for ToxA activity, but ChToxA lacks the RGD motif in the C-terminal region. Database searches identified ChToxA homologues in other plant-pathogenic fungi, including species of both Dothideomycetes and Sordariomycetes. Further studies on ChToxA and its homologues would provide new insights into the evolution of effector-mediated fungal pathogenesis in plants.