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United States Department of Agriculture

Agricultural Research Service

Research Project: CHARACTERIZATION OF HOST-PATHOGEN INTERACTIONS IN BARLEY AND WHEAT Title: Quantitative variation in effector activity of ToxA isoforms from Stagonospora nodorum and Pyrenophora tritici-repentis

Authors
item Tan, K -
item Ferguson-Hunt, M -
item Rybak, K -
item Waters, D -
item Stanley, W -
item Bond, C -
item Stukenbrock, Eva -
item Friesen, Timothy
item Faris, Justin
item Mcdonald, Bruce -
item Oliver, Richard -

Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 12, 2011
Publication Date: January 8, 2012
Repository URL: http://handle.nal.usda.gov/10113/58112
Citation: Tan, K.C., Ferguson-Hunt, M., Rybak, K., Waters, O.D.C., Stanley, W.A., Bond, C.S., Stukenbrock, E.H., Friesen, T.L., Faris, J.D., McDonald, B.A., Oliver, R.P. 2012. Quantitative variation in effector activity of ToxA isoforms from Stagonospora nodorum and Pyrenophora tritici-repentis. Molecular Plant-Microbe Interactions. 25:515-522.

Interpretive Summary: Both Stagonospora nodorum (causal agent of Stagonospora nodorum blotch of wheat) and Pyrenophora tritici-repentis (causal agent of tan spot of wheat) produces the proteinaceous necrotrophic effector (host selective toxin) ToxA. In this study, all eight mature forms of the ToxA protein known to exist in nature were purified and compared. All forms were structurally intact and had indistinguishable structural features. The different forms of ToxA were infiltrated into wheat lines that carry the corresponding sensitivity gene Tsn1. It was observed that different wheat lines carrying identical Tsn1 alleles varied in sensitivity to ToxA. All ToxA isoforms induced necrosis when introduced into any Tsn1 wheat line, but we observed quantitative variation in effector activity, with the least active version found in isolates of P. tritici-repentis. As ToxA concentrations were increased, pathogen sporulation was also shown to increase. Additionally, the ToxA forms that induced the most rapid necrosis also induced the most sporulation, indicating that pathogen fitness is affected by differences in ToxA activity and therefore that the variation at the ToxA gene results from selection that favors increased toxin activity.

Technical Abstract: ToxA is a proteinaceous necrotrophic effector produced by Stagonospora nodorum and Pyrenophora tritici-repentis. In this study, all eight mature isoforms of the ToxA protein were purified and compared. Circular dichroism spectra indicated that all isoforms were structurally intact and had indistinguishable secondary structural features. ToxA isoforms were infiltrated into wheat lines that carry the sensitivity gene Tsn1. It was observed that different wheat lines carrying identical Tsn1 alleles varied in sensitivity to ToxA. All ToxA isoforms induced necrosis when introduced into any Tsn1 wheat line, but we observed quantitative variation in effector activity, with the least active version found in isolates of P. tritici-repentis. Pathogen sporulation increased with higher doses of ToxA. The isoforms that induced the most rapid necrosis also induced the most sporulation, indicating that pathogen fitness is affected by differences in ToxA activity. We show that differences in toxin activity encoded by a single gene can contribute to the quantitative inheritance of necrotrophic virulence. Our findings support the hypothesis that the variation at ToxA results from selection that favors increased toxin activity.

Last Modified: 10/21/2014
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