FUM gene expression and variation in fumonisin production of clonal isolates of Fusarium verticillioides MRC 826

Authors: LILLY, MARISKA - Cape Peninsula University Of Technology; RHEEDER, JOHN - Cape Peninsula University Of Technology; Proctor, Robert; GELDERBLOM, WENTZEL - Stellenbosch University

Submitted to: World Mycotoxin Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2020
Publication Date: 2/12/2021
Citation: Lilly, M., Rheeder, J.P., Proctor, R.H., Gelderblom, W.C.A. 2021. FUM gene expression and variation in fumonisin production of clonal isolates of Fusarium verticillioides MRC 826. World Mycotoxin Journal. 14(2):121-137. https://doi.org/10.3920/WMJ2020.2626.
DOI: https://doi.org/10.3920/WMJ2020.2626

Interpretive Summary: Fumonisins are fungal toxins that pose health risks to humans and livestock because of their toxicity and frequent occurrence in corn. Fumonisins cause multiple fatal animal diseases, including cancer in rodents, and they are associated with several human diseases, including esophageal cancer. The fungus Fusarium verticillioides is the predominant cause of fumonisin contamination in corn, and there is a worldwide effort to develop strategies that reduce the contamination caused by this fungus. As part of the effort, we investigated the genetic basis for low levels of fumonisins produced by some isolates of F. verticillioides. We found that the reduced production resulted from decreased activity of the genes directly responsible for synthesis of fumonisins (i.e., fumonisin biosynthetic genes), but that the decreased activity was not due to changes in DNA sequence of the genes. Instead, the decreased activity was due to a change(s) in DNA sequence of other genes and/or by chemical modifications of DNA that does not change the sequence (i.e., epigenetic modifications). These findings provide insight into the genetic control of fumonisin production in F. verticillioides and have potential to aid identification of genetic targets that can be used to reduce fumonisin contamination. Thus, the findings have potential to improve the safety of human food and animal feed that is derived from corn.

Technical Abstract: B-series fumonisins (FBs) are a family of carcinogenic mycotoxins that commonly occur in maize. The mycotoxins cause multiple diseases in animals and are epidemiologically associated with several human diseases in some populations for which maize is a dietary staple. FBs are produced by multiple species of the fungi Aspergillus, Fusarium and Tolypocladium, but the maize pathogen Fusarium verticillioides is considered the primary cause of FB contamination in maize. The F. verticillioides strain MRC 826 was reported to produce high levels of FBs. However, in the current study, analyses of 18 isolates derived from strain MRC 826 revealed that some produced high levels of FB (high-production isolates), some produced intermediate levels, while others produced relatively low FB levels (low-production isolates). Further, FB production and growth in maize patty culture exhibited a negative correlation (r = -0.333; P<0.008). Microsatellite analysis indicated that all MRC 826-derived isolates examined were clonal. DNA sequence analysis of two high- and two low-production isolates indicated that the sequences of the fumonisin biosynthetic gene (FUM) cluster in the four isolates were identical. However, expression analysis of selected FUM genes at 7, 14, 21 and 28 days of incubation were, in general, higher in high-production isolates than in low-production isolates. Together the results indicated that variation in FB production in MRC 826-derived isolates is likely due to differences in FUM gene expression among isolates, but that the differences in gene expression most likely result from sequence differences at loci other than the FUM cluster or from epigenetic differences in and/or outside the cluster. Clarification of the genetic/epigenetic basis for quantitative differences in fumonisin production among strains and isolates of F. verticillioides has potential to reveal targets for reducing FB contamination in maize.