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United States Department of Agriculture

Agricultural Research Service

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Location: Cereal Disease Lab

2013 Annual Report

1a. Objectives (from AD-416):
The long-term objective of this project is to reduce crop loss and mycotoxin contamination due to Fusarium head blight (FHB), the most serious disease for the U.S. wheat and barley industry. Characterization of the fungal genes critical for disease development will be emphasized, along with changes in FHB pathogen populations over time in the U.S. and understanding the makeup of fungal communities associated with diseased and healthy spring wheat. Over the next 5 years we will focus on the following objectives: Objective 1. Develop genomic sequence information for the Fusarium head blight pathogen and related fungi to identify factors involved in pathogenicity, sporulation, and toxin synthesis. Sub-objective 1.A. Obtain whole genome sequence data from strains of Fusarium graminearum and F. oxysporum that differ in toxin profiles, virulence and host specificity. Sub-objective 1.B. Identify genes uniquely or differentially expressed during spore development that define spore characteristics and function. Sub-objective 1.C. Determine the function of genes differentially expressed in spores or associated with pathogenicity and toxin production. Objective 2. Develop early warning systems tools, including molecular markers, for detection of known and novel mycotoxins in small grains. Sub-objective 2.A. Monitor genetic changes in critical pathogen populations by pathogen surveys. Sub-objective 2.B. Identify genomic characteristics of distinct populations or chemotypes of F. graminearum by resequencing representative strains. Objective 3. Develop a metagenomic approach to define fungal communities in healthy and diseased fields naturally infested with the FHB fungus. Sub-objective 3.A. Use metagenomics to characterize rhizosphere and endophytic fungal community composition and diversity among plants grown in experimental communities. Sub-objective 3.B. Determine the relative abundance of competitive phenotypes and impacts on plant productivity.

1b. Approach (from AD-416):
Improved management strategies are needed to maintain adequate plant disease control. Specific approaches include: 1) Genomic sequence information obtained from the fungal pathogen, Fusarium, will be used to identify genes related to fungal pathogenesis, possibly leading to novel approaches to control Fusarium head blight disease and reduce toxin levels in grain; 2) Fusarium head blight levels, strain diversity, and the nature of associated fungal communities, will be monitored by population genetic and metagenomic approaches improving the ability to forecast the economic impact and the design of effective management strategies.

3. Progress Report:
In the first full year of the project, demonstrable progress was made toward project goals. Whole genome, gene expression (transcriptome) data were obtained for Fusarium species under four separate experimental conditions and data were made available online. Several novel genes controlling pathogenicity and vomitoxin production were discovered in the wheat scab fungus, revealing new information on how these pathogens cause disease. A toxin with a novel chemical structure was discovered in contemporary populations of the FHB pathogen. The ability of current control measures and plant resistance to account for the novel toxin are currently being tested. The overall impact of the research is that this information will be helpful to plant improvement specialists who are working to develop plants resistant to scab pathogens and for developing novel strategies for its control.

4. Accomplishments
1. A fungus with a toxic character. Certain fungi cause diseases of wheat and barley crops and may infest the grain with harmful metabolites. The fungus Fusarium graminearum contaminates these grains with a compound known as vomitoxin, whose presence in the human diet is a food safety concern. Our previous studies have shown that the fungus is remarkably adapted for producing vomitoxin by precisely regulating the genes for its synthesis in order to promote its accumulation in plants. Researchers at the Cereal Disease Laboratory in Saint Paul, Minnesota, have now found that by labeling proteins for toxin synthesis with fluorescent proteins, that these proteins are directed to subcellular toxin factories; small vesicles called toxisomes that appear to serve as the staging area for the toxin biosynthetic assembly line. When cell conditions are changed in order to promote toxin biosynthesis, another pathway supplying precursor molecules for toxin synthesis may be shifted within the cell to toxisomes, streamlining the path to toxin synthesis. By making toxin in a confined vesicle within the cell, the fungus may protect itself from the inhibitory effects of its own toxin and may allow for an efficient way to deliver it to the plant. This study establishes that toxin synthesis requires a complex developmental event which ultimately determines the outcome of plant infection and plant health. This information will be helpful to plant improvement specialists who are working to develop plants resistant to these toxins or for developing novel strategies for amelioration of the effects of these toxins.

Review Publications
Menke, J., Weber, J., Broz, K.L., Kistler, H.C. 2013. Cellular development associated with induced secondary metabolism in the filamentous fungus Fusarium graminearum. PLoS Pathogens. 8(5):e63077.

Aoki, T., Ward, T.J., Kistler, H.C., O'Donnell, K. 2012. Systematics, phylogeny and trichothecene mycotoxin potential of Fusarium head blight cereal pathogens. Mycotoxins. 62(2):91-102.

Kistler, H.C., Rep, M., Ma, L. 2013. Structural dynamics of Fusarium genomes. In: Fusarium: genomics, molecular and cellular biology. Brown, D.W. and Proctor, R.H., Editors. Norwich, United Kingdom. Caister Academic Press. p. 46-60.

Kistler, H.C., Menke, J., Dong, Y. 2012. Fusarium graminearum Tri12p influences virulence to wheat and trichothecene accumulation. Molecular Plant-Microbe Interactions. 25:1408-1418.

Jonkers, W., Rodriguez Estrada, A.E., Breakspear, A., May, G., Kistler, H.C. 2012. The metabolome and transcriptome of the interaction between Ustilago maydis and Fusarium verticillioides in vitro. Applied and Environmental Microbiology. 78(10):3656-3667.

Ma, L., Kistler, H.C., Rep, M. 2013. Evolution of Plant Pathogenicity in Fusarium Species. Book Chapter. p. 485-500.

Last Modified: 05/22/2017
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