Submitted to: Canadian Journal of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2006
Publication Date: 7/4/2006
Citation: McCormick, S.P., Alexander, N.J., Proctor, R.H. 2006. Fusarium Tri4 encodes a multifunctional oxygenase required for trichothecene biosynthesis. Canadian Journal of Micribiology. 52:636-642. Interpretive Summary: The mold Fusarium is a common contaminant of grain and other livestock feeds. Several species of Fusarium produce trichothecene toxins such as T-2 toxin and vomitoxin which cause adverse effects on human and animal health. We have found a group of about 15 genes that control the production of the toxins. In this report we focus on the a gene Tri4 that begins the process of producing toxic compounds by adding oxygens to a hydrocarbon substrate. When this gene is knocked out, the fungus cannot make the toxins. We transferred this gene into a related species, Fusarium verticillioides, in order to figure out how many steps it controlled. Our studies showed that four steps are controlled by this one gene. This is the first report of a multifunctional gene in trichothecene biosynthesis. This research benefits other scientists and growers by providing a defined target for methods of controlling or eliminating vomitoxin from wheat crops.
Technical Abstract: Fusarium graminearum and F. sporotrichioides produce the trichothecene mycotoxins 15-acetyldeoxynivalenol and T-2 toxin, respectively. In both species, disruption of the P450 monooxygenase-encoding gene Tri4 blocks production of the mycotoxins and leads to the accumulation of the trichothecene precursor trichodiene. To further characterize its function, the F. graminearum Tri4 (FgTri4) was heterologously expressed in the trichothecene-nonproducing species F. verticillioides. Transgenic F. verticillioides carrying the FgTri4 converted exogenous trichodiene to the trichothecene biosynthetic intermediates isotrichodermin and trichothecene. Conversion of trichodiene to isotrichodermin requires seven biochemical steps. As shown previously, the fifth and sixth steps can occur non-enzymatically. Precursor feeding studies done in the current study indicate that wild-type F. verticillioides has the enzymatic activity necessary to carry out the seventh step, the C-3-acetylation of isotrichodermol to form isotrichodermin. Together, the results of this study indicate that the Tri4 protein catalyzes the remaining four steps and is therefore a multifunctional monooxygenase required for trichothecene biosynthesis.