Detoxification of corn antimicrobial compounds by the endophytic fungus Fusarium verticillioides and the significance to plant -fungus interactions

• Main Author: Glenn, Anthony Elbie
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2001
• Subjects: Botany; Plant Pathology; Plant sciences
• ISBN: 049337079X; 9780493370798

Fusarium verticilloides (= F. moniliforme) is a fungus of significant economic importance because of its deleterious effects on plant and animal health and the quality of their products. Corn, the primary host for F. verticillioides, produces the preformed antimicrobial compounds DIMBOA (2,4-dihydroxy-7-methoxy 2H-1,4-benzoxazin-3-one) and its demethoxy derivative DIBOA, which are highly reactive benzoxazinoids that quickly degrade to the antimicrobials MBOA (6-methoxy-2-benzoxazolinone) and BOA (2-benzoxazolinone), respectively. F. verticillioides is highly tolerant of MBOA and BOA and can actively transform these compounds to non-toxic metabolites. Eleven of 29 Fusarium species had some level of tolerance to MBOA and BOA; the most tolerant, in decreasing order, were F. verticillioides, F. subglutinans, F. cereals, and F. graminearum. The difference in tolerance among species apparently was due to their ability to detoxify the antimicrobials. The limited number of species having tolerance suggested the potential utility of these compounds as biologically active agents for inclusion within a semi-selective isolation medium. We developed a medium that resulted in superior isolation frequencies for F. verticillioides from corn while effectively suppressing competing fungi. Since the BOA medium provided consistent, quantitative results with reduced in vitro and taxonomic effort, it should prove useful for surveys of F. verticilloides infection in field samples. Genetic analyses of F. verticillioides indicated two loci, Fdb1 and Fdb2, were involved in detoxification. Mutation at either locus caused sensitivity and no detoxification. In vitro physiological complementation assays resulted in detoxification of BOA and suggested an unknown intermediate compound was produced. Production of the intermediate involved Fdb1 , and a lesion in fdb2 preventing complete metabolism of BOA resulted in transformation of the intermediate into an unidentified metabolite. Feeding assays suggested the intermediate metabolite was 2-aminophenol. Based on genetic and physiological data, a branched detoxification pathway is proposed. Use of genetically characterized detoxifying and non-detoxifying strains indicated detoxification of the corn antimicrobials was not a virulence factor since detoxification was not necessary for development of seedling blight or for infection and endophytic colonization of seedlings. Production of the antimicrobials is not an effective resistance mechanism against F. verticillioides.