title: Victorin triggers programmed cell death and the defense response via interaction with a cell surface mediator.
abstract: The host-selective toxin victorin is produced by Cochliobolus victoriae, the causal agent of victoria blight of oats. Victorin has been shown to bind to the P protein of the glycine decarboxylase complex (GDC) in mitochondria, and induce defense-related responses such as phytoalexin synthesis, extracellular alkalization and programmed cell death. However, evidence demonstrating that the GDC plays a critical role in the onset of cell death is still lacking, and the role of defense-like responses in the pathogenicity has yet to be elucidated. Here, cytofluorimetric analyses, using the fluorescein (VicFluor) or bovine serum albumin-fluorescein derivative of victorin (VicBSA), demonstrated that victorin-induced cell death occurs before these conjugates traverse the plasma membrane. As with native victorin, VicBSA clearly elicits apoptosis-like cell death, production of phytoalexin, extracellular alkalization, and generation of nitric oxide and reactive oxygen intermediates. These results suggest that the initial recognition of victorin takes place on the cell surface, not in mitochondria, and leads to the activation of a battery of victorin-induced responses. Pharmacological studies showed that extracellular alkalization is the essential regulator for both victorin- and VicBSA-induced cellular responses. We propose a model where victorin may kill the host cell by activating an HR-like response, independent of the binding to the GDC, through ion fluxes across the plasma membrane.
authors.affiliation: Graduate School of Natural Science and Technology, Kobe University, Japan.
authors.forename: Yasuomi
authors.initials: Y
authors.lastname: Tada
authors.forename: Koh
authors.initials: K
authors.lastname: Kusaka
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Betsuyaku
authors.forename: Takeshi
authors.initials: T
authors.lastname: Shinogi
authors.forename: Masaru
authors.initials: M
authors.lastname: Sakamoto
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Ohura
authors.forename: Shingo
authors.initials: S
authors.lastname: Hata
authors.forename: Tomoyo
authors.initials: T
authors.lastname: Mori
authors.forename: Yukio
authors.initials: Y
authors.lastname: Tosa
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Mayama
mesh_terms: D017209:Apoptosis / Q000502:physiology*; D018554:Avena / Q000166:cytology / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000502:physiology; D005656:Fungal Proteins / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D009183:Mycotoxins / Q000502:physiology*; D018515:Plant Leaves / Q000166:cytology / Q000502:physiology
chemical_list: D005656:Fungal Proteins; D009183:Mycotoxins; C094015:Victorin protein, Cochliobolus victoriae; D002118:Calcium