Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2008
Publication Date: 2/23/2008
Citation: Proctor, R., Busman, M., Seo, J., Lee, Y., Plattner, R.D. 2008. A fumonisin biosynthetic gene cluster in Fusarium oxysporum strain O-1890 and the genetic basis of B versus C fumonisin production. Fungal Genetics and Biology. 45:1016-1026. Available: www.elsevier.com/locate/yfgbi. Interpretive Summary: Fumonisins are chemical compounds that sometimes contaminate corn kernels. The compounds are produced by some species of the fungus Fusarium, including species that cause disease on corn. Fumonisins are of concern because consumption of fumonisin-contaminated corn is correlated with cancer of the esophagus and with neural tube defects in some human populations. In addition, fumonisins can induce several fatal animal diseases, including cancer. The results of the current study indicate that the cluster of genes responsible for fumonisin production in the species Fusarium oxysporum and F. verticillioides are highly similar. However, the results also indicate that the cluster is at different locations of the chromosomes of the two species. In addition, the results demonstrate that one of the cluster genes, FUM8, controls whether Fusarium produces B or C fumonisins, which differ from one another in their chemical structures. B fumonisins have a carbon atom and two hydrogen atoms that are absent in C fumonisins. This basic study provides insight into a critical control point in the production of a group of natural cancer-causing compounds that can contaminate a major crop. It is anticipated that such knowledge will lead to the identification of targets that can be used to reduce or eliminate fumonisin contamination in corn.
Technical Abstract: Fumonisins are carcinogenic mycotoxins produced by some species of the filamentous fungus Fusarium. Most species, including F. verticillioides, produce predominantly B fumonisins (FBs), but F. oxysporum strain O-1890 produces predominantly C fumonisins (FCs), which differ from FBs by the absence of a terminal methyl function. In this study, we determined the nucleotide sequence of the fumonisin biosynthetic gene (FUM) cluster in strain O-1890. The order and orientation of genes in the cluster were the same as in the previously described cluster in F. verticillioides. Coding regions of F. oxysporum FUM genes were 88-92% identical to those of F. verticillioides. In contrast, regions flanking ends of the cluster did not share significant identity in the two species. A previous study indicated that the FUM cluster gene FUM8 in F. verticillioides encodes an alpha-oxoamine synthase, and that fum8 mutants of the fungus cannot produce fumonisins. In the current study, transformation of a fum8 mutant with a wild-type FUM8 from F. verticillioides restored FB production. Transformation with FUM8 from F. oxysporum also restored production, but the fumonisins produced were predominantly FCs. These data indicate that different orthologues of FUM8 determine whether Fusarium produces predominantly FBs or FCs.