Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/5/2004
Publication Date: 4/16/2004
Citation: Bojja, R.S., Cerny, R.L., Proctor, R., Du, L. 2004. Determining the biosynthetic sequence in the early steps of the fumonisin pathway by use of three gene-disruption mutants of Fusarium verticillioides. Journal of Agricultural and Food Chemistry. 52(10):2855-2860. Interpretive Summary: Ear and stalk rot, a common disease on maize, is caused by a fungus called Fusarium verticillioides. In addition to causing rot on maize ears, this fungus also produces toxic chemicals, or mycotoxins, called fumonisins. We are interested in understanding the biology and genetics of fumonisin production by F. verticillioides in order to try to reduce or eliminate these mycotoxins from maize. In this report, we determined the order of the biochemical steps that occur early in the formation of fumonisins. This approach has allowed us to more fully understand the process of fumonisin production. A better understanding of fumonisin production may lead to novel strategies for controlling mycotoxin contamination in maize.
Technical Abstract: Fumonisins are polyketide-derived mycotoxins produced by Fusarium verticillioides, a fungal pathogen of corn plants. Although a gene cluster for the biosynthesis of fumonisins has been cloned, the biosynthetic pathway is still not clear. We have used three gene-disrupted mutants, designated delta-FUM1, delta-FUM6, and delta-FUM8, to study the early steps of the pathway. Fumonisins were not produced in single-strain cultures of the delta-FUM1, delta-FUM6, and delta-FUM8 mutants. However, fumonisins were produced by delta-FUM1 or delta-FUM8 mutants when they were cocultured with the delta-FUM6 mutant. No fumonisins were produced when the delta-FUM1 and delta-FUM8 mutants were cocultured. These results suggest that the delta-FUM6 mutant produces a fumonisin intermediate that can be further metabolized by fumonisin biosynthetic enzymes in the delta-FUM1 and delta-FUM8 mutants. To isolate the potential intermediates produced by delta-FUM6, we followed a time course of cocultures of the delta-FUM1 and delta-FUM6 and the delta-FUM8 and delta-FUM6 mutants. Liquid chromatographic-mass spectrometric data suggested that metabolites having the general carbon skeleton of fumonisins with 1-4 hydroxyl groups were accumulated over a 7-day period. These results indicate that fumonisin biosynthesis starts with Fum1p-catalyzed carbon-chain assembly followed by the Fum8p-catalyzed alanine condensation. The resulting product then can be further oxidized by Fum6p and other enzymes.