ESTERIFICATION OF TRICARBALLYLIC ACID SIDE CHAINS TO THE FUMONISIN BACKBONE REQUIRES THE ACTIVITY OF FOUR FUM GENES

Authors: Butchko, Robert; PLATTNER, RONALD - RETIRED, USDA/ARS, PEORIA; Proctor, Robert

Submitted to: Aflatoxin Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 10/15/2003
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: The fungus Fusarium verticillioides can cause stalk and ear rot of maize. F. verticillioides can also contaminate maize with the polyketide derived mycotoxins called fumonisins. A number of animal diseases have been associated with ingestion of maize contaminated with fumonisins. Equine leukoencephalomalacia and porcine pulmonary edema have been correlated with fumonisin as well as cancer in laboratory animals. In an effort to reduce or eliminate fumonisins from food products, we are interested in understanding the molecular genetics required for the production of fumonisins by F. verticillioides. Recently, a gene cluster comprised of 15-coregulated transcripts was described in F. verticillioides. Predicted amino acid sequences of the genes in the cluster reveal activities that could be required for fumonisin production. To determine the role in fumonisin production, if any, of each of the 15 FUM genes, we have disrupted or deleted each of them individually and have assessed the resulting mutants for fumonisin production. Deletion of a number of genes has led to the characterization of fumonisin pathway intermediates. For example, FUM3 which encodes a dioxygenase is required for the hydroxylation of carbon 5 of the fumonisin backbone. Similarly, FUM13 which encodes a short chain dehydrogenase/reductase is required for the reduction of a keto group to a hydroxyl group on carbon 3 of the fumonisin backbone. Here we describe the affects of individual deletions in FUM7, FUM10, FUM11 and FUM14 of the FUM gene cluster. Deletions in FUM10 and FUM14 result in the accumulation of hydrolyzed forms of fumonisin B3 and fumonisin B4. These hydrolyzed forms of fumonisin lack the tricarboxylic acid molecules usually attached to carbons 14 and 15 of the fumonisin backbone. Deletion of FUM11 results in the accumulation of half-hydrolyzed forms of fumonisin B3 and fumonisin B4. Deletion of FUM7 resulted in the accumulation of a fumonisin-like molecule with a molecular weight of 718. This compound is consistent with a molecule with additional carbon-carbon double bonds in the tricarboxylic acid portion of the molecule. Taken together, these results indicate that these four genes are all involved in the addition of the tricarballylic acid molecules. Deletion analysis has allowed us to more fully understand the biosynthetic pathway leading to fumonisin production. We have been able to identify stable intermediates in the biosynthetic pathway and in conjunction with the individual deletion mutants we have been able to more precisely order the biosynthetic pathway and assign particular roles to specific FUM cluster genes.