Localization of Ptr ToxA Produced by Pyrenophora tritici-repentis Reveals Protein Import into Wheat Mesophyll Cells

Plant Cell. 2005 Nov;17(11):3203-12. doi: 10.1105/tpc.105.035063. Epub 2005 Sep 30.

Abstract

The plant pathogenic fungus Pyrenophora tritici-repentis secretes host-selective toxins (HSTs) that function as pathogenicity factors. Unlike most HSTs that are products of enzymatic pathways, at least two toxins produced by P. tritici-repentis are proteins and, thus, products of single genes. Sensitivity to these toxins in the host is conferred by a single gene for each toxin. To study the site of action of Ptr ToxA (ToxA), toxin-sensitive and -insensitive wheat (Triticum aestivum) cultivars were treated with ToxA followed by proteinase K. ToxA was resistant to protease, but only in sensitive leaves, suggesting that ToxA is either protected from the protease by association with a receptor or internalized. Immunolocalization and green fluorescent protein tagged ToxA localization demonstrate that ToxA is internalized in sensitive wheat cultivars only. Once internalized, ToxA localizes to cytoplasmic compartments and to chloroplasts. Intracellular expression of ToxA by biolistic bombardment into both toxin-sensitive and -insensitive cells results in cell death, suggesting that the ToxA internal site of action is present in both cell types. However, because ToxA is internalized only in sensitive cultivars, toxin sensitivity, and therefore the ToxA sensitivity gene, are most likely related to protein import. The results of this study show that the ToxA protein is capable of crossing the plant plasma membrane from the apoplastic space to the interior of the plant cell in the absence of a pathogen.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Cell Membrane / drug effects
  • Cell Membrane / metabolism
  • Chloroplasts / drug effects
  • Chloroplasts / metabolism
  • Endocytosis / drug effects
  • Endocytosis / physiology
  • Endopeptidase K / metabolism
  • Endopeptidase K / pharmacology
  • Fungal Proteins / metabolism*
  • Fungal Proteins / pharmacokinetics
  • Fungi / metabolism*
  • Genetic Predisposition to Disease / genetics
  • Green Fluorescent Proteins
  • Immunity, Innate / genetics
  • Mycoses / microbiology*
  • Mycotoxins / metabolism*
  • Mycotoxins / pharmacokinetics
  • Plant Diseases / microbiology*
  • Plant Epidermis / drug effects
  • Plant Epidermis / metabolism
  • Plant Epidermis / microbiology
  • Protein Transport / drug effects
  • Protein Transport / physiology
  • Triticum / genetics
  • Triticum / metabolism
  • Triticum / microbiology*

Substances

  • Fungal Proteins
  • Mycotoxins
  • TOXA protein, Pyrenophora tritici-repentis
  • Green Fluorescent Proteins
  • Endopeptidase K