Submitted to: Applied and Environmental Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/21/2011
Publication Date: 7/11/2011
Citation: Cardoza, R.E., Malmierca, M.G., Hermosa, M.R., Alexander, N., Mccormick, S.P., Proctor, R., Tijerino, A.M., Rumbero, A., Monte, E., Gutierrez, S. 2011. Identification of loci and functional characterization of trichothecene biosynthesis genes in the filamentous fungus of the genus Trichoderma. Applied and Environmental Microbiology. 77(14):4867-4877. Interpretive Summary: Trichothecenes are toxins that are harmful to the health of humans and livestock because of their ability to block protein synthesis. The toxins are produced by some fungi that infect crop plants and can contaminate food and feed prepared from infected grain. In this study, we identified three genes in the fungus Trichoderma that are required by it to produce the trichothecenes harzianum A and trichodermin. In Trichoderma, two of the genes are located near one another on a chromosome, while the third is located elsewhere on the same or a different chromosome. This arrangement of genes in Trichoderma differs from the previously reported arrangement of the same genes in Fusarium, a fungus that produces different trichothecenes. In addition, although two of the genes have similar DNA sequences in Trichoderma and Fusarium, they have different functions during trichothecene production in the two fungi. These results improve our understanding of the genetic basis for trichothecene toxin production in crop plants and provide targets that should be useful for preventing trichothecene contamination of food and feed. Thus, our findings have the potential to reduce the risk of trichothecene toxins to human and animal health.
Technical Abstract: Trichothecenes are mycotoxins produced by Trichoderma, Fusarium and at least four other genera in the fungal order Hypocreales. Fusarium has a trichothecene biosynthetic gene (TRI) cluster that encodes transport and regulatory proteins as well as most enzymes required for formation of the mycotoxins. However, little is known about trichothecene biosynthesis in the other genera. Here, we identified and characterized TRI gene orthologues (tri) in Trichoderma arundinaceum and Trichoderma brevicompactum. Our results indicate that both Trichoderma species have a tri cluster that consists of orthologues of seven genes present in the Fusarium TRI cluster. Organization of genes in the cluster is the same in the two Trichoderma species but differs from the organization in Fusarium. Sequence and functional analysis revealed that the gene (tri5) responsible for the first committed step in trichothecene biosynthesis is located outside the cluster in both Trichoderma species, rather than inside the cluster as it is in Fusarium. Heterologous expression analysis revealed that two T. arundinaceum cluster genes (tri4 and tri11) differ in function from their Fusarium orthologues. The Tatri4-encoded enzyme catalyzes only three of the four oxygenation reactions catalyzed by the orthologous enzyme in Fusarium. The Tatri11-encoded enzyme catalyzes a completely different reaction (trichothecene C-4 hydroxylation) than the Fusarium orthologue (trichothecene C-15 hydroxylation). The results of this study indicate that although some characteristics of the tri/TRI cluster have been conserved during evolution of Trichoderma and Fusarium, the cluster has undergone marked changes, including gene loss and/or gain, gene rearrangement, and divergence of gene function.