Trichothecenes are a large family of sesquiterpenoid secondary metabolites of Fusarium species (e.g., F. graminearum) and other molds. They are major mycotoxins that can cause serious problems when...

Trichothecene mycotoxins such as deoxynivalenol, 4,15-diacetoxyscirpenol, and T-2 toxin, are potent protein synthesis inhibitors for eukaryotic organisms. The 3-O-acetyl derivatives of these toxins were shown to reduce their in vitro activity significantly as assessed by assays using a rabbit reticulocyte translation system. The results suggested that the introduction of an O-acetyl group at the C-3 position in the biosynthetic pathway works as a resistance mechanism forFusarium species that produce t-type trichothecenes (trichothecenes synthesized via the precursor trichotriol). A gene responsible for the 3-O-acetylation reaction,Tri101, has been successfully cloned from a Fusarium graminearum cDNA library that was designed to be expressed inSchizosaccharomyces pombe. Fission yeast transformants were selected for their ability to grow in the presence of T-2 toxin, and this strategy allowed isolation of 25 resistant clones, all of which contained a cDNA for Tri101. This is the first drug-inactivating O-acetyltransferase gene derived from antibiotic-producing organisms. The open reading frame ofTri101 codes for a polypeptide of 451 amino acid residues, which shows no similarity to any other proteins reported so far. TRI101 from recombinant Escherichia coli catalyzesO-acetylation of the trichothecene ring specifically at the C-3 position in an acetyl-CoA-dependent manner. By using the Tri101 cDNA as a probe, two least overlapping cosmid clones that cover a region of 70 kilobase pairs have been isolated from the genome of F. graminearum. Other trichothecene biosynthetic genes, Tri4, Tri5, and Tri6, were not clustered in the region covered by these cosmid clones. These new cosmid clones are considered to be located in other parts of the large biosynthetic gene cluster and might be useful for the study of trichothecene biosynthesis.

Zearalenone (ZEN) is converted into a far less oestrogenic product by incubation with Clonostachys rosea IFO 7063. An alkaline hydrolase responsible for the detoxification was purified to homogeneity from the fungus by a combination of salt precipitation and column chromatography methods. The purified enzyme was homodimeric with a subunit molecular mass of 30kDa and contained an intra-subunit disulphide bridge. On the basis of the internal peptide sequences of the purified protein, we cloned the entire coding region of the gene (designated as zhd101) by PCR techniques. The ZEN degradation activity was detected in heterologous hosts (Schizosaccharomyces pombe and Escherichia coli) carrying the cloned gene. Zhd101 could be a promising genetic resource for in planta detoxification of the mycotoxin in important crops.