Functional demarcation of the Fusarium core trichothecene gene cluster.

Many Fusarium species produce toxic sesquiterpenoids known as trichothecenes, including deoxynivalenol and nivalenol by Fusarium graminearum and T-2 toxin by Fusarium sporotrichioides. These toxins are potent inhibitors of protein synthesis and are a significant agricultural problem due to their adverse affect on human, animal, and plant health. Previously, 10-12 co-regulated orthologous genes within a 26-kb region were identified in F. graminearum and F. sporotrichioides, respectively. A majority of these clustered genes have been shown to be involved in different aspects of trichothecene metabolism including 7 of 15 biosynthetic steps. Three other biosynthetic steps are carried out by genes located elsewhere in the genome. In this study, we sequenced 14-16 kb of DNA on both sides of the core clusters and identified 12 new ORFs in both Fusarium species. Although the predicted functions of some of the new ORFs are consistent with some unassigned biochemical reactions, gene expression and gene deletion studies indicate that none are required for trichothecene biosynthesis. These results provide evidence to demarcate both ends of the core trichothecene gene cluster. Index descriptors: Fungal secondary metabolite, Pathogenic fungi, Gene cluster, Fusarium, Trichothecene, DON