Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 12, 2002
Publication Date: N/A
Interpretive Summary: The fungus Fusarium graminearum causes Fusarium Head Blight (in wheat) and corn ear rot and can produce trichothecenes. Trichothecenes may cause disease in humans and animals and enhance fungal disease on crops. Human and animal exposure to trichothecenes occurs through food and feed prepared from corn and cereal crops contaminated with the toxins. Serious losses of crops occur worldwide due to lower yields and to lower value associated with trichothecene contamination. We are studying the genes involved in the synthesis of trichothecenes in order to identify strategies for reducing or eliminating fungal infection and trichothecene contamination in wheat and corn. In this study, we describe two new trichothecene genes from different species of Fusarium; F. sporotrichioides and F. graminearum. We correlate differences in gene structure with differences in the type of trichothecenes the two species produce. We also provide a genetic explanation for the chemotype difference between F. graminearum that produce deoxynivalenol (DON) and F. graminearum that produce nivalenol (NIV). This work could significantly impact our understanding of Fusarium evolutionary relationships as well as our understanding of the mechanism of trichothecene synthesis.
Technical Abstract: Species of the genus Fusarium produce a great diversity of agriculturally important trichothecene toxins that differ from each other in their pattern of oxygenation and esterification. T-2 toxin, produced by Fusarium sporotrichioides, and nivalenol (NIV), produced by some strains of F. graminearum, contain an oxygen at the C-4 position. Deoxynivalenol (DON), produced by other strains of F. graminearum, lacks a C-4 oxygen. Sequence and Northern analyses of the F. sporotrichioides genomic region upstream of the previously described core trichothecene gene cluster have extended the cluster by two genes: TRI13 and TRI14. TRI13 shares significant similarity with the cytochrome P-450 class of enzymes, but TRI14 does not share similarity with any previously characterized proteins. Gene disruption and fermentation studies of F. sporotrichioides indicate that TRI13 is required for the addition of the C-4 oxygen to T-2 toxin, but that TRI14 is not required for trichothecene biosynthesis. PCR and sequence analyses indicate that the TRI13 homologue is functional in NIV-producing strains of F. graminearum but nonfunctional in DON-producing strains of the fungus. These genetic observations are consistent with chemical observations that biosynthesis of T-2 toxin and NIV requires a C-4 hydroxylase while biosynthesis of DON does not.