Characterization of Fusarium verticillioides genes necessary for benzoxazolinone biotransformation

Authors: Glenn, Anthony - Tony; Bacon, Charles

Submitted to: International Allelopathy Congress
Publication Type: Abstract Only
Publication Acceptance Date: 6/27/2008
Publication Date: 9/21/2008
Citation: Glenn, A.E., Bacon, C.W. 2008. Characterization of Fusarium verticillioides genes necessary for benzoxazolinone biotransformation. International Allelopathy Congress. Sept. 21-25,2008. Saratoga Springs, NY.

Interpretive Summary: Abstract - no summary required.

Technical Abstract: Maize produces the benzoxazinones DIMBOA and DIBOA, which naturally transform into the more stable benzoxazolinones MBOA and BOA, respectively. These weed-suppressive allelopathic compounds are also implicated in resistance to microbial diseases and insect feeding. Fusarium verticillioides, the most common fungal pathogen associated with maize, has the physiological capacity to detoxify MBOA and BOA. The biotransformation pathway is suggested to involve hydrolysis of BOA (encoded by the FDB1 locus) to produce 2-aminophenol (2-AP), which is subsequently acylated (encoded by the FDB2 locus) to produce N-(2-hydroxyphenyl)malonamic acid (HPMA). Fungal growth is inhibited on BOA-amended medium if either gene is mutated. An fdb2 mutant can produce low levels of an acetylated 2-AP branch metabolite, N-(2-hydroxyphenyl)acetamide (HPAA). In order to molecularly characterize genes involved in biotransformation, suppression subtractive hybridization was used to identify genes up-regulated in response to BOA. Two gene clusters were identified that functionally correspond to the FDB1 and FDB2 loci. Genes at both loci are being evaluated. At the FDB2 locus a putative N-acetyltransferase (NAT) was of particular interest due to the postulated role of the FDB2 locus. This gene was subcloned from an identified cosmid that complemented an fdb2 mutant. The subcloned gene also complemented an fdb2 mutation. Deletion of the gene eliminated the ability of F. verticillioides to metabolize BOA, and the mutants did not grow. We therefore functionally associate FDB2 as the gene encoding this putative NAT activity. The branch metabolite HPAA was produced at low concentrations in 'fdb2 mutants suggesting acetylation of the intermediate 2-aminophenol occurred independently from the putative N-acyltransferase activity of FDB2, which is proposed to involve malonylation of 2-aminophenol. Thus, we have provided further evidence for the genetics and biochemical nature of benzoxazolinone biotransformation, a metabolic process that may enhance the ecological fitness of F. verticillioides in the maize field environment.