Research Accomplishment Reports 2010

Mycotoxins: Biosecurity and Food Safety

L.J. Vaillancourt
Department of Plant Pathology

 

Non-Technical Summary

Mycotoxins are metabolites of fungi that can adversely affect animal and human health. Mycotoxins can be produced in grain during storage or processing, but are most frequently associated with fungal infection that occur before harvest.

Environmental factors that determine fungal infection and mycotoxin production are complex. Generally, a basal level of mycotoxins is present in US grain; however, in some years, environmental conditions lead to localized or widespread outbreaks of mycotoxin contamination. However, there is no organized monitoring system for tracking the incidence and severity of mycotoxin contamination at either the national or regional levels. Although breeding and transgenic technologies have shown promise for reducing the risk of mycotoxin contamination of grain, to date no commercial variety of any major US crop is available with either genetic or transgenic resistance to mycotoxin contamination.

This project will address the needs of the stakeholders as follows. First, the research will advance detection technologies that can be used by private companies which provide mycotoxin analysis services to food industries. This will include development of new techniques and validation of their current methodology. Second, the research will generate new protocols for monitoring mycotoxins in agricultural products that will be incorporated by biosecurity agencies. Third, US and international government policy makers (USFDA, JECFA, IARC) will use our research information in their risk assessments for mycotoxins. The outcome of risk assessment has been government recommendations on maximum mycotoxin levels for agriculture products, which affects national and international use of products. Finally, we anticipate that our research information will have a major impact on the decision making by providing mode of toxicity data, survey data, and data aimed at understanding how food components affect mycotoxin biosynthesis.

2010 Project Description

Fusarium graminearum is a common fungal pathogen of corn, wheat, and barley. Production of mycotoxins including zearalenone, and trichothecenes, particularly deoxynivalenol (DON = vomitoxin) by F. graminearum in grains is a major problem. Sexual fertility in this homothallic organism is regulated by a complex mating type locus containing two different MAT genes, MAT1-1-1 and MAT1-2-1. The products of these MAT genes are transcription factors that regulate a cascade of other genes, many of which have unknown functions.

We are working to understand the precise roles of the individual MAT genes in pathogenicity to corn and wheat and toxin production, by producing and analyzing MAT1-1-1 and MAT1-2-1 knockout mutants. Preliminary data suggest that MAT1-1-1 knockouts are less aggressive than the wild type, and other MAT knockout strains.

A majority of North American isolates of F. graminearum are members of a single genetic lineage, known as group 7. Although they are phylogenetically indistinguishable, isolates within the group are known to vary significantly in aggressiveness and mycotoxin production. Studies are underway in our laboratory to try to understand the genetic basis for this phenotypic variation and also to map and characterize relevant QTLs. Complete genome sequences are available for two lineage 7 strains. These strains were crossed and random progeny were characterized for various pathogenicity-related traits including aggressiveness to susceptible and resistant wheat, sexual and asexual fecundity, and quality and quantity of mycotoxin production.

The progeny of the cross varied widely in these traits, and some were significantly more aggressive and toxigenic than the parents, suggesting the possibility that more aggressive strains could arise in the field from crosses of less aggressive parents. It would be very useful to have markers that would allow these traits to be monitored and to detect potentially more damaging recombinants, it would help to predict and monitor epidemics, If QTLs can be identified these can be used to develop markers. Understanding the molecular basis for this diversity would also be of significant benefit for breeding efforts since it would allow development of more representative groups of strains for selection and screening.

Finally, novel genes identified by QTL mapping may lead to identification of targets for new antifungal therapies. Other studies in the lab focused on understanding the role of enzymes in colonization of and survival in corn stalks, in which the pathogen commonly overwinters. We produced several mutant strains that produced altered levels of hemicellulase enzymes, and found that these were severely compromised in pathogenicity. We also developed a real-time PCR protocol for monitoring fungal biomass in corn stalks.

2010 Impact

Mycotoxins are fungal metabolites that can adversely affect animal and human health. Mycotoxins can be produced in grain during storage or processing, but are most frequently associated with fungal infection that occurs before harvest. Generally, a basal level of mycotoxins is always present in US grain; however, in some years, environmental conditions lead to localized or widespread outbreaks of mycotoxin contamination. Without an aggressive research program to prevent, treat, and contain outbreaks of mycotoxins in grain, US grain producers will suffer the consequences of reduced marketability of their products.

The natural occurrence of mycotoxins in grain is an important security concern for the grain industry and end-users of grain; mycotoxins have been used as agents of terrorism, e.g. aflatoxin in Iraq. Stakeholders need cost-effective methods to predict, monitor, and minimize mycotoxin production in the field, and to detoxify mycotoxins and prevent further deterioration in contaminated grain.

The scientists involved in this multistate, multidisciplinary research proposal work individually on mycotoxin issues related to their respective disciplines and areas of expertise. The production of mycotoxins by mycotoxigenic fungi represents a basic aspect of agricultural science. Improving our understanding of how mycotoxin biosynthesis is regulated will not only lead to novel treatment strategies, but may also advance our understanding of fungal pathogenesis in general.