Trichothecene 3-O-Acetyltransferase Protects Both the Producing Organism and Transformed Yeast from Related Mycotoxins

Abstract

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 Oacetyl group at the C-3 position in the biosynthetic pathway works as a resistance mechanism for Fusarium 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 in Schizosaccharomyces 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 Oacetyltransferase gene derived from antibiotic-producing organisms. The open reading frame of Tri101 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 catalyzes O-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.Trichothecenes belong to a family of sesquiterpenoid secondary metabolites produced by Fusarium species and other molds (1). Considerable variation exists in the oxygenation pattern of individual trichothecenes, but all are characterized by a 9,10 double bond and a 12,13 epoxide group. These compounds are potent inhibitors of protein synthesis in eukaryotes (2) and prevent polypeptide chain initiation or elongation by binding to 60 S ribosomal subunits (3). From pharmacological and toxicological points of view, trichothecenes are an important group of mycotoxins that cause serious problems of food pollution. They have been implicated in incidents of mycotoxicosis such as vomiting, dermatitis, and hemorrhagic septicemia in humans and livestock (4).The trichothecene biosynthetic pathway has been studied in detail by the use of blocked mutants and by precursor feeding experiments. The proposed pathway in Fusarium species (see Fig. 1) proceeds from mevalonate via farnesyl pyrophosphate, trichodiene (5), isotrichodiol (tricho-9-ene-2␣,11␣-diol) (6), isotrichotriol (tricho-9-ene-2␣,3␣,11␣-triol) (7, 8), trichotriol (tricho-10-ene-2␣,3␣,9␣-triol) (8, 9), isotrichodermol (3␣-hydroxytrichothecene...

Ancestral polymorphism and adaptive evolution in the trichothecene mycotoxin gene cluster of phytopathogenic Fusarium

“…Biochemical and genetic investigations of Fusarium sporotrichioides (an A-trichothecene producer) facilitated the identification of many of the genes involved in trichothecene biosynthesis (6). Homologous genes have since been identified in Fg complex species (B-trichothecene producers), and with the exception of a 3-O-acetyltransferase (TRI101) (7), all known trichothecene genes are localized within a gene cluster (6).…”

“…Only a hydroxyl group at C-4 in nivalenol distinguishes it from deoxynivalenol. However, these chemotype differences may have important fitness consequences, as differences in the pattern of oxygenation and acetylation can alter the bioactivity and toxicity of trichothecenes (7,9).…”

A Novel Regulatory Gene, Tri10 , Controls Trichothecene Toxin Production and Gene Expression

“…Tri101, which encodes isotrichodermol 3-o-acetyltransferase, has been identified in both F. sporotrichioides and F. graminearum and appears to reside outside of the trichothecene gene cluster (19,21). In addition to its acetyltransferase activity, the heterologous expression of Tri101 in yeast cells renders them resistant to trichothecenes (18,21). However, disruption of Tri101 does not appear to cause a loss of toxin self-protection in F. sporotrichioides (21), suggesting that other genes can provide this function.…”

Microbial toxins in plant-pathogen interactions: Biosynthesis, resistance mechanisms, and significance.

“…The coding regions of F. graminearum Tri4 (FgTri4), Tri5 (FgTri5), and Tri6 (FgTri6) could easily be amplified by PCR with primers that were originally designed for amplification of these genes from F. sporotrichioides (Kimura et al, 1998a). The biosynthetic and regulatory genes thus appeared to be highly conserved among type A and type B trichothecene producers.…”