Submitted to: Toxic Microorganisms Symposium Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: November 12, 2000
Publication Date: N/A
Technical Abstract: Fumonisins are a family of toxic fungal metabolites produced by Fusarium verticillioides, a fungus frequently found in corn worldwide. F. verticillioides has been associated with diseases such as stalk, root and kernel rots in corn. It is also among the most common fungi found even in symptomless corn plants and is considered by some to be an endophyte of corn. Most isolates produce primarily FB1 with lesser amounts of FB2, FB3 and FB4. Much less common are isolates that produce no FB1 but accumulate high levels of FB2 and FB4 or FB3 and FB4. Only a very few isolates have been isolated that do not produce any measurable fumonisins when grown on corn in the laboratory. Classical genetic analysis of these isolates has identified three closely linked loci that control fumonisin production. A polyketide synthase (PKS) gene, FUM5, required for fumonisin biosynthesis was identified and cloned using a PCR approach with generate PKS primers and cDNA from a fumonisin producing culture of F. vertifillioides. Transformation of a fumonisin non producing (fum1-) strain with a cosmid containing FUM5 restored fumonisin production. Disruption of FUM5 reduced fumonisin production by over 99% in F. verticillioides. Several open reading frames up and downstream from FUM5 have been identified. Four of these are expressed at the same time as FUM5. BLAST analysis suggests that these regions code for a cytochrome P450 monooxygenase/reductase, a dehydrogenase, an amino acid fatty acid transferase and a dioxygenase. The potential functions of these genes in fumonisin biosynthesis is being investigated. To identify the role, if any, fumonisins may play in interactions between the corn plant and the fungus, we have conducted a series of field studies.