Location: Toxicology and Mycotoxin Research
Title: A fungal metallo-beta-lactamase necessary for biotransformation of maize phytoprotectant compounds Authors
Submitted to: Fungal Genetics Reports
Publication Type: Abstract Only
Publication Acceptance Date: December 12, 2012
Publication Date: March 12, 2013
Citation: Glenn, A.E., Davis, C.B., Snook, M.E., Gold, S.E. 2013. A fungal metallo-beta-lactamase necessary for biotransformation of maize phytoprotectant compounds [abstract]. Fungal Genetics Reports. 60(Suppl):540. Interpretive Summary: Abstract - no summary required.
Technical Abstract: Xenobiotic compounds such as phytochemicals, microbial metabolites, and agrochemicals can impact the diversity and frequency of fungal species occurring in agricultural environments. Resistance to xenobiotics may allow plant pathogenic fungi to dominate the overall fungal community, with potential negative impacts on crop yield and value. The mycotoxigenic Fusarium verticillioides is such a fungus commonly associated with maize worldwide, often contaminating maize kernels with the fumonisin mycotoxins. The dominance of F. verticillioides as an endophyte may be due in part to its ability to metabolize phytoprotectants produced by maize. The benzoxazinoids and benzoxazolinones are broad spectrum allelopathic, antimicrobial, and anti-herbivory compounds from maize, yet F. verticillioides can rapidly biotransform these phytochemicals into non-toxic metabolites. We have identified the genes responsible for the biotransformation process. Two gene clusters were identified that correspond to the previously characterized FDB1 and FDB2 loci, with both loci being necessary for metabolic tolerance to 2-benzoxazolinone (BOA), one of the maize phytoprotectants. Analysis of the nine ORFs (FVEG_08287 to FVEG_08295) at the FDB1 locus indicated that one of the genes (FVEG_08291) encodes a protein having a metallo-beta-lactamase domain, and deletion of the gene in wild-type strain M3125 resulted in the fungus being unable to grow on BOA-amended agar due to an inability to metabolize the compound. Deletion mutants were complemented to wild-type phenotype by transformation with the native allele. Other ORFs were not found to be essential when deleted in M3125. Microarray analysis indicated the metallo-beta-lactamase (FVEG_08291) had a 13-fold induction in response to BOA (2-hr incubation), with other genes in the cluster ranging from 3-fold (FVEG_08287) to 42-fold induction (FVEG_08292). Beta-lactamases are well-known for conferring bacterial resistance to lactam-type antibiotics, but to our knowledge this is the first report of fungal enzymes of this type metabolizing lactam-like xenobiotics. We are investigating other beta-lactamase encoding genes in F. verticillioides (see poster by Gold et al.) to further evaluate their possible role in tolerance to both exogenous as well as endogenous metabolites having lactam-type moieties.