Identification of a Toxic Protein, FvTox6, Produced by Fusarium virguliforme that Causes Foliar Symptoms Typical of Soybean Sudden Death Syndrome
H. X. CHANG (1), L. L. Domier (2), O. Radwan (3), C. Yendrek (4), M. Hudson (3), G. L. Hartman (5). (1) Univ of Illinois, Urbana, IL, U.S.A.; (2) USDA–Agricultural Research Service, University of Illinois, Urbna, IL, U.S.A.; (3) University of Illinois, Urbana, IL, U.S.A.; (4) Institute for Genomic Biology, Urbana, IL, U.S.A.; (5) USDA–Agricultural Resea
Soybean sudden death syndrome (SDS) is caused by<i> Fusarium virguliforme</i>, a soilborne pathogen that rarely infects above ground parts of soybean but induces severe foliar symptoms including intervienal chlorosis and necrosis, leaf marginal curling, and defoliation. These foliar symptoms are well known for its sudden appearance that generally exhibits around flowering to maturity stages. Translocation of toxins that produced by <i>F. virguliforme </i>has been regarded as the cause of foliar symptoms; however, none of the toxins found to date is able to reproduce complete SDS foliar symptoms typical to the symptoms observed in the field. We hypothesized that multiple toxins together induce the complicated foliar symptoms. In this study, we tried to identify additional toxins produced by <i>F. virguliforme </i>through transcriptomic analysis under a toxin-producing condition, and to test their contribution individually on causing SDS foliar symptoms. Two secondary metabolites and 11 toxic proteins were identified, but in contrast to our hypothesis, one toxic protein FvTox6 individually was sufficient to complete SDS foliar symptoms through viral expression system. Instead, neither application of secondary metabolites nor overexpression of other toxic proteins induced foliar symptoms similar to SDS. Our study identified FvTox6 as a major toxin for inducing SDS foliar symptoms.
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