Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 10, 2003
Publication Date: April 10, 2003
Citation: BUTCHKO, R.A., PLATTNER, R.D., PROCTOR, R. FUM13 ENCODES A SHORT-CHAIN DEHYDROGENASE/REDUCTASE REQUIRED FOR C-3 CARBONYL REDUCTION DURING FUMONISIN BIOSYNTHESIS IN GIBBERELLA MONILIFORMIS. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY. 2003. v. 51. p. 3000-3006. Interpretive Summary: Fumonisins are toxic substances produced by the corn disease fungus Gibberella moniliformis. Fumonisins are known carcinogens and can cause diseases in horses and swine. We are interested in reducing or eliminating these toxins from corn. In an effort to accomplish that goal, we are interested in understanding the biology of the fungus with regard to fumonisin production. We know that a group of genes are involved in the production of fumonisin, and in this report we concentrate on the function of one of those genes and its role in fumonisin production. One way in which we study the functions of genes is to eliminate or "knockout" the gene we are interested in. We have "knocked out" one of the genes for fumonisin production and describe the effects of this "knockout" on fumonisin production. This has allowed us to learn more about the production of fumonisin. A better understanding of the genes involved in fumonisin production may lead to novel strategies for reducing or eliminating fumonisin in corn.
Technical Abstract: Fumonisins are polyketide-derived mycotoxins produced by the filamentous fungus Gibberella moniliformis (anamorph Fusarium verticillioides). Wild-type strains of the fungus produce predominantly four B-series fumonisins, designated FB1, FB2, FB3 and FB4. Recently a cluster of fifteen putative fumonisin biosynthetic genes (FUM) was described in G. moniliformis. Here, we conducted a functional analysis of FUM13, a gene in the cluster that is predicted by amino acid sequence similarity to encode a short-chain dehydrogenase/reductase (SDR). Mass spectral analysis of metabolites from FUM13 deletion mutants revealed that they produce approximately 10% of wild-type levels of B-series fumonisins as well as two previously uncharacterized compounds. NMR analysis revealed that the new compounds are similar in structure to FB3 and FB4 but that they have a carbonyl function rather than a hydroxyl function at carbon atom 3 (C-3). These results indicate that the FUM13 protein catalyzes the reduction of the C-3 carbonyl to a hydroxyl, and are the first biochemical evidence directly linking a FUM gene to a specific reaction during fumonisin biosynthesis. The production of low levels of FB1, FB2, FB3 and FB4, which have a C-3 hydroxyl, by the FUM13 mutants suggests that G. moniliformis has an additional C-3 carbonyl reductase activity, but that this enzyme functions less efficiently than the FUM13 protein.