A Novel Trichothecene Toxin Phenotype Associated with Horizontal Gene Transfer and a Change in Gene Function in Fusarium

trichothecenes are among the mycotoxins of most concern to food and feed safety. Production of these mycotoxins and presence of the trichothecene biosynthetic gene ( ) cluster have been confirmed in only two multispecies lineages of : the - (Incarnatum) and (Sambucinum) species complexes. Here, we identified and characterized a cluster in a species that has not been formally described and is represented by sp. NRRL 66739. This fungus is reported to be a member of a third lineage: the species complex. Cultures of NRRL 66739 accumulated only two trichothecenes, 7-hydroxyisotrichodermin and 7-hydroxyisotrichodermol. Although these are not novel trichothecenes, the production profile of NRRL 66739 is novel, because in previous reports 7-hydroxyisotrichodermin and 7-hydroxyisotrichodermol were components of mixtures of 6-8 trichothecenes produced by several species in Sambucinum. Heterologous expression analysis indicated that the gene in NRRL 66739 confers trichothecene 7-hydroxylation. This contrasts the trichothecene 4-hydroxylation function of in other species. Phylogenetic analyses suggest that NRRL 66739 acquired the cluster via horizontal gene transfer from a close relative of Incarnatum and Sambucinum. These findings provide insights into evolutionary processes that have shaped the distribution of trichothecene production among species and the structural diversity of the toxins.