Submitted to: Canadian Journal of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2008
Publication Date: 12/18/2008
Citation: Alexander, N.J., Mccormick, S.P., Blackburn, J.A. 2008. Effects of Xanthotoxin Treatment on Trichothecene Production in Fusarium sporotrichioides. Canadian Journal of Microbiology. 54(12):1023-1031. Interpretive Summary: Fusarium sporotrichioides, a mold that can cause plant diseases and is found in nature, produces a mycotoxin that can enter and contaminate the food supply. This mycotoxin causes toxicoses in humans and animals which result in severe monetary loss to the growers and seed industry as well as the health industry. We are interested in reducing or eliminating these toxins from grains. In an effort to accomplish that goal, we are interested in understanding the biology of the fungus and the genes involved in mycotoxin production. We have developed a method for quantifying the expression of the mycotoxin-producing genes in this organism and have found that certain genes are up-regulated when the mold is exposed to plant-defense compounds. This will help us develop methods to increase the plant response to the invasion of the mold and thereby reduce the amount of disease as well as reduce the amount of toxin present in the harvested grains.
Technical Abstract: There are four P450 oxygenases involved in the biosynthesis of T-2 toxin in Fusarium sporotrichioides. Exactly how these enzymes react to antimicrobial plant defense compounds is unknown. Xanthotoxin (8-methoxypsoralen), a phototoxic furanocoumarin, is a P450 oxygenase inhibitor. A previous study showed that addition of 1.5 mM xanthotoxin to liquid cultures of Fusarium sporotrichioides NRRL3299 caused a loss of T-2 toxin production and an accumulation of trichodiene, the hydrocarbon precursor of trichothecenes and the substrate for the P450 oxygenase encoded by Tri4. The current study confirmed that addition of lower concentrations of xanthotoxin could effectively block T-2 toxin production and cause an increased accumulation of trichodiene. Addition of xanthotoxin to liquid cultures of a trichodiene-accumulating F. sporotrichioides Tri4 mutant caused a three to ten fold increase in trichodiene accumulation, suggesting that xanthotoxin not only blocks trichothecene oxygenation reactions, but may in some way also promote the synthesis of trichodiene. Feeding studies using wild-type and mutant F. sporotrichioides strains showed that two of the four P450 oxygenases, TRI4 and TRI1, were more sensitive to xanthotoxin. The two remaining oxygenases, TRI11 and TRI13, were unaffected by 1.0 mM xanthotoxin. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) indicated that several of the genes in the toxin biosynthetic pathway were up-regulated by xanthotoxin with Tri4 showing the highest (1.4 fold) increase in expression. These results indicate that while xanthotoxin inhibits specific P450 oxygenase activity it also has a significant effect on gene expression.