The Fusarium virguliforme Toxin FvTox1 Causes Foliar Sudden Death Syndrome-Like Symptoms in Soybean

Abstract

Fusarium virguliforme causes sudden death syndrome (SDS) in soybean. The pathogen has never been isolated from diseased foliar tissues; therefore, one or more toxins have been considered to cause foliar SDS development. Cell-free F. virguliforme culture filtrates containing a toxin causes foliar SDS in soybean. A low-molecular-weight protein of approximately 13.5 kDa (FvTox1), purified from F. virguliforme culture filtrates, produces foliar SDS-like symptoms in cut soybean seedlings. Anti-FvTox1 monoclonal antibodies raised against the purified FvTox1 were used in isolating the FvTox1 gene. In the presence of light, recombinant FvTox1 protein expressed in an insect cell line resulted in chlorosis and necrosis in soybean leaf disks that are typical foliar SDS symptoms. SDS-susceptible but not the SDS-resistant soybean lines were sensitive to the baculovirus-expressed toxin. The requirement of light for foliar SDS-like symptom development indicates that FvTox1 induces foliar SDS in soybean, most likely through production of free radicals by interrupting photosynthesis.

Analyses of the Xylem Sap Proteomes Identified Candidate Fusarium virguliforme Proteinacious Toxins

“…FvTox1 is a 13.5 kDa acidic protein. This toxin can rapidly cause foliar SDS-like symptoms in leaf discs of soybean lines, highly susceptible to F. virguliforme [13]. Expression of a single chain variable fragment (scFv) antibody against FvTox1 enhanced foliar SDS resistance in transgenic soybean plants supporting the role of FvTox1 in foliar SDS development [16].…”

“…Fusarium virguliforme is a soil-borne fungus that belongs to the class Sordariomycetes and is known to produce one or more phytotoxins in culture media [10], [11], [12], [13]. Though the pathogen only infects soybean roots, the disease symptoms are seen on both roots and foliar tissues.…”

“…However, the gene encoding this putative toxin has never been isolated. Recently, FvTox1 toxin was purified from the culture filtrates and the gene, FvTox1 , encoding this toxin has been isolated [13]. The FvTox1 protein, expressed in an insect line, was shown to cause foliar SDS-like symptoms in soybean leaf discs, only in the presence of light [13].…”

Effect of fungicide seed treatments onFusarium virguliformeinfection of soybean and development of sudden death syndrome

“…The pathogen infects roots, resulting in root rot and reductions in root mass (Rupe et al 1993;Roy et al 1997;Ortiz-Ribbing & Eastburn 2004;Navi & Yang 2008;Hartman et al 2015). The most-recognized symptoms of SDS include interveinal chlorotic and necrotic lesions, which develop on leaves during soybean reproductive stages, and are due to fungal phytotoxins translocated through the xylem (Baker 1994;Jin et al 1996;Li et al 1999;Navi & Yang 2008;Brar et al 2011;Abeysekara & Bhattacharyya 2014). Severe SDS can result in flower and pod abortion, decreased seed size, defoliation and premature death, which contribute to reductions in yields (Roy et al 1997;Rupe & Hartman 1999;Luo et al 2000).…”

Fusarium Mycotoxins and Their Role in Plant–Pathogen Interactions

“…Excluding the case of a protein toxin (from the soybean pathogen Fusarium virguliforme [18]), we are not aware of cases of host-selective secondary metabolites of Fusarium. The analysis of the interaction between F. graminearum and wheat has revealed only quantitative differences in resistance.…”