Submitted to: Multicrop Aflatoxin and Fumonisin Elimination and Fungal Genomics Workshop-The Peanut Foundation
Publication Type: Proceedings
Publication Acceptance Date: October 7, 2005
Publication Date: October 25, 2005
Citation: Zimeri, A.M., Williams, L.D., Riley, R.T., Glenn, A.E. 2005. Toxicity responses of corn to the mycotoxin fumonisin b1 in the absence of fusarium verticillioides infection [abstract]. Multicrop Aflatoxin and 6th Annual Fumonisin Elimination and Fungal Genomics Workshop-The Peanut Foundation. p. 55. Interpretive Summary: Abstract - no summary.
Technical Abstract: Fusarium verticilliodes, the causative agent of ear rot in corn, produces the mycotoxin fumonisin B1 (FB1), which is a potent competitive inhibitor of ceramide synthase, a key enzyme necessary for sphingolipid metabolism. Consuming corn and corn products laden with FB1 causes a range of species specific diseases in animals and also has been shown to cause cancer in laboratory rodents. FB1 may also contribute to esophageal cancer and neural tube birth defects in humans. While FB1 contamination is typically greater when ear rot damage is more severe, recent reports have indicated corn hybrids can be infected with Fusarium and contaminated with FB1, yet do not always exhibit phenotypic signs of ear rot. We hypothesize that breeding programs may have inadvertently selected for endophytic fungal associations whereby F. verticillioides infects corn but does not cause severe ear rot, yet may still contaminate corn with significant levels of FB1. We have begun to address the role that FB1 may play in the overall biology of the fungal association with corn and have developed an experimental system based on observations that FB1-producing strains of F. verticillioides are pathogenic against seedlings of susceptible corn hybrids while non-producing strains cause no disease symptoms. Numerous corn lines were screened for their sensitivity or insensitivity to FB1 to evaluate which phenotype was most prevalent within corn. This study was enhanced by a new strategy for disinfesting seed both externally and internally using chlorine gas. The great advantage with this technique was that seed were not imbibed and could thus be sterilized more efficiently and stored until needed. Sterile seed of each corn line were place on agar supplemented with various concentrations of FB1 (0, 1, 10, and 100 µM). After 7-10 days, root and shoot weight (wet and dry) and length were noted. Teosinte and Tripsacum were also evaluated for their sensitivity to FB1 since teosinte is the likely progenitor of modern corn and Tripsacum is the sister taxon to Zea. Results indicated corn seedlings were in general sensitive to FB1, with teosinte and Tripsacum also being very sensitive. Only one corn line, W23, was very insensitive to FB1. In both sensitive and insensitive corn lines, low levels of FB1 (1 µM) stimulated root and shoot growth. Sensitive corn lines had severely inhibited growth of roots and greatly reduced germination rates when exposed to higher concentrations of FB1 (ÿ10 µM). W23 germinated and grew well even on 100 µM FB1. Thus, data supported FB1-sensitivity as ancestral while insensitivity of corn to FB1 toxicity may be recently derived. Though FB1 alone caused stunting of aerial tissues and reduced root mass, it was not sufficient to cause the full suite of seedling blight disease symptoms caused by a Fusarium infection. To determine if other secondary metabolites work synergistically with FB1 to cause disease, we germinated seedlings in the presence of fungal extracts with and without FB1. Solvent extracts were made of FB1-producing and non-producing strains grown on corn for 14 days. We found that seedlings exposed to extracts containing FB1 exhibited seedling blight disease as seen in plants infected with wild-type Fusarium. Seedlings exposed to extracts that did not contain FB1 grew similar to the control plants. In addition to mechanistic examinations of FB1 toxicity in sensitive and insensitive seedlings, future work also will focus on whether FB1 is absorbed and translocated throughout the plant. We will also investigate the impact of FB1 and other molecules on systemic signaling within corn seedlings.