Fdb1 and Fdb2, Fusarium verticillioides Loci Necessary for Detoxification of Preformed Antimicrobials from Corn

Abstract

Fusarium verticillioides is a fungus of significant economic importance because of its deleterious effects on plant and animal health and on the quality of their products. Corn (Zea mays) is the primary host for F. verticillioides, and we have investigated the impact of the plant's antimicrobial compounds (DIMBOA, DIBOA, MBOA, and BOA) on fungal virulence and systemic colonization. F. verticillioides is able to metabolize these antimicrobials, and genetic analyses 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 that an unknown intermediate compound was produced. Production of the intermediate compound involved Fdbl, and a lesion in fdb2 preventing complete metabolism of BOA resulted in transformation of the intermediate into an unidentified metabolite. Based on genetic and physiological data, a branched detoxification pathway is proposed. Use of genetically characterized detoxifying and nondetoxifying strains indicated that detoxification of the corn antimicrobials was not a major virulence factor, since detoxification was not necessary for development of severe seedling blight or for infection and endophytic colonization of seedlings. Production of the antimicrobials does not appear to be a highly effective resistance mechanism against F. verticillioides.

Interactions of Bacillus mojavensis and Fusarium verticillioides with a Benzoxazolinone (BOA) and its Transformation Product, APO

“…2c), indicating that fungal growth and activity are required for the production of transformation products from BOA. It is established that the transformation of BOA follows several steps that lead first to 2-aminophenol (AP), which is a microbial transformation product (Nair et al 1990;Gagliardo and Chilton 1992;Glenn et al 2002;Fomsgaard et al 2004), and subsequently microbial transformations or natural oxidative processes lead to the formation of 10 aminophenoxazinones (Fomsgaard et al 2004). That B. mojavensis is required for the accumulation of APO is indicated in those cultures that showed a greater intensity of pigment accumulation over cultures that did not contain both the bacteria and fungi, and absent in nutrient broth without the addition of BOA (Fig.…”

“…The ability of F. verticillioides to detoxify AP into several nontoxic products led to the tentative conclusion by Glenn et al (2002) that the benzoxazolinones allelochemicals are probably not effective resistance mechanisms against this fungus. However, interactive microbial activity was not considered relevant.…”

“…The strains of fungi used were those that either tested positive for detoxification of BOA or those with defective alleles at loci necessary for detoxification of BOA (Glenn et al 2002). The F. verticillioides strains used consisted of MRC826 (genotype FDB1/FDB2), a wild type for fumonisin production and tolerance to BOA, strain AEG73-A4-1, a tolerant benzoxazolinone phenotype (genotype Fdb1/Fdb2) derived from a cross of the wild-type F. verticillioides RRC826 with the female fertile AEG 3-1-6 sensitive genotype, and AEG73-A4-2 (genotype Fdb1/fdb2), a sensitive benzoxazolinone phenotype derived from this same cross (Glenn et al 2002).…”

“…The F. verticillioides strains used consisted of MRC826 (genotype FDB1/FDB2), a wild type for fumonisin production and tolerance to BOA, strain AEG73-A4-1, a tolerant benzoxazolinone phenotype (genotype Fdb1/Fdb2) derived from a cross of the wild-type F. verticillioides RRC826 with the female fertile AEG 3-1-6 sensitive genotype, and AEG73-A4-2 (genotype Fdb1/fdb2), a sensitive benzoxazolinone phenotype derived from this same cross (Glenn et al 2002). For long-term storage, conidia were frozen at −80°C in 15% glycerol.…”

“…Prior studies established that several species of Fusarium are tolerant to the benzoxazinoids , and that this tolerance in F. verticillioides is in fact caused by the presence of at least two genetic loci, FDB1 and FDB2. Detoxification of the benzoxazolinones requires both loci, and defect at either locus causes sensitivity to the compounds (Glenn et al 2002). A new transformation product is produced from 2-aminophenol (AP).…”