FUM13 Encodes a Short Chain Dehydrogenase/Reductase Required for C-3 Carbonyl Reduction during Fumonisin Biosynthesis in Gibberella moniliformis

Authors

Robert A. E. Butchko, USDA-ARSFollow
Ronald D. Plattner, USDA-ARS
Robert H. Proctor, USDA-ARSFollow

Date of this Version

2003

Citation

J. Agric. Food Chem. 2003, 51, pp. 3000-3006.

Comments

U.S. government work.

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 15 putative fumonisin biosynthetic genes (FUM) was described in G. moniliformis. We have now 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 spectrometric 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 group 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.