Location: Cereal Disease Lab
2020 Annual Report
Objectives
Objective 1: Discover specific factors involved in pathogenicity, sporulation and toxin synthesis for the FHB pathogen and related fungi by applying genomic and functional approaches.
Sub-objective 1.A. Functionally characterize cellular processes and structures that determine plant pathogenesis.
Sub-objective 1.B. Identify genes uniquely or differentially expressed during development that defines pathogen structure and function.
Objective 2: Relate fungal genotypes to mycotoxin production in fungal strains in field production environments to aid in developing enhanced methods of control.
Sub-objective 2.A. Monitor genetic changes in critical pathogen populations by pathogen surveys.
Sub-objective 2.B. Characterize populations of Fusarium from native North American grasses that may be sources of novel pathogen genotypes and/or host resistance.
Objective 3: Optimize metagenomic and functional approaches to define the phytobiome of healthy and diseased plants naturally infested with the FHB fungus.
Sub-objective 3.A. Characterize phytobiome and soil carbon composition.
Sub-objective 3.B. Determine the relative abundance of competitive phenotypes and impacts on plant productivity.
Objective 4: Identify novel sources of plant disease resistance to FHB and mycotoxins produced by FHB fungi to improve breeding for resistance.
Sub-objective 4.A. Characterize the epigenetic changes of FHB resistant durum cultivars produced by altering the DNA methylation pattern.
Sub-objective 4.B. Characterize durum lines missing a portion of chromosome 2A region that may contain the FHB suppressor locus.
Objective 5: Introgress new genes of scab resistance into barley and wheat germplasm.
Approach
Improved management strategies are needed to maintain adequate plant disease control. Specific approaches include: 1) Genetic information obtained from the fungal pathogen, Fusarium, will be used to identify genes factors responsible for fungal pathogenesis, possibly leading to novel approaches to control FHB disease and reduce toxin levels in grain; 2) FHB 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) Novel sources of FHB resistance and mycotoxin tolerance will be developed for plants.
Progress Report
In the third full year of the project, ARS scientists at Saint Paul, Minnesota have made substantial progress in the following objectives:
Sub-objective 1.A. Functionally characterize cellular processes and structures that determine plant pathogenesis: Deletion mutants were created of Fusarium (FHB) Tri14 gene and introduced into several genetic backgrounds that allow for fluorescent examination of fungal cells. Additionally, samples of toxin-induced fungi were submitted for proteomic study.
Sub-objective 1.B. Identify genes uniquely or differentially expressed during development that defines pathogen structure and function: RNAseq experiments were completed of Fusarium graminearum during toxin synthesis. Data has been analyzed and being prepared for publication.
Objective 2. Relate fungal genotypes to mycotoxin production in fungal strains in field production environments to aid in developing enhanced methods of control: Surveys for the FHB pathogen found in wheat and native grass species are in progress for the 2019 field season.
Objective 3. Optimize metagenomic and functional approaches to define the phytobiome of healthy and diseased plants naturally infested with the FHB fungus: Currently characterizing interactions of Fusarium and soil microbes for potential antagonistic interactions and tolerance of Fusarium to inhibitory chemicals.
Sub-objective 4.A. Complete phenotypic screen of populations. Bioinformatics analysis of transcriptome from modified resistant durum lines is complete and a number of differentially expressed genes (elevated and suppressed >5 fold; log2 value) were identified for further characterization.
Sub-objective 4.B. Phenotypic characterization of deletion lines. Populations have been created that showed greatly improved resistance to Fusarium head blight in initial testing.
Accomplishments
1. Halting fungal "toxin factories" may make small grains safer. Harmful byproducts of fungi, called mycotoxins, threaten food safety and cause losses in wheat and barley yield and grain quality. Little is known about structures within fungal cells that make high-level production of mycotoxins possible. ARS researchers located in Saint Paul, Minnesota, have discovered that the fungal products vomitoxin and culmorin that contaminate wheat and barley grain, are produced within specialized portions of fungal cells called toxisomes. The formation of toxisomes converts normal fungal cells into virtual "toxin factories". Moreover, treatments that prevent toxisome formation greatly reduce the ability of the fungus to produce mycotoxins. Such treatments may supplement fungicide applications and be important for developing novel strategies for preventing the contamination of grain with vomitoxin and other mycotoxins.
2. Genes identified in resistant durum wheat are involved in plant defense. The plant disease Fusarium head blight (FHB) is an important constraint to profitable production of durum wheat in the upper Midwest. Currently planted durum cultivars lack consistently high levels of resistance to the disease. To identify new genes for disease resistance, ARS researchers located in Saint Paul, Minnesota studied differences in the genes expressed by disease susceptible lines and a newly developed M4 line that has moderately high FHB resistance. During infection, the resistant M4 line activated many categories of genes associated with an active plant disease defense response. This new native source of FHB resistance in durum wheat will be a great boon to the effort in breeding for resistant cultivars.
Review Publications
Chen, Y., Kistler, H.C., Ma, Z. 2020. Fusarium graminearum trichothecene mycotoxins: biosynthesis, regulation, and management. Annual Review of Phytopathology. 57:15-39. https://doi.org/10.1146/annurev-phyto-082718-100318.
Essarioui, A., LeBlanc, N.R., Otto-Hanson, L., Schlatter, D.C., Kistler, H.C., Kinkel, L.L. 2020. Inhibitory and nutrient use phenotypes among coexisting Fusarium and Streptomyces populations suggest local coevolutionary interactions in soil. Environmental Microbiology. 22(3):976-985. https://doi.org/10.1111/1462-2920.14782.
O'Mara, S.P., Broz, K.L., Boenisch, M.J., Zhong, Z., Dong, Y., Kistler, H.C. 2020. The Fusarium graminearum t-SNARE Sso2 is involved in growth, defense, and DON accumulation and virulence. Molecular Plant-Microbe Interactions. 33(7):888-901. https://doi.org/10.1094/MPMI-01-20-0012-R.
Zhang, Y., Yang, H., Turra, D., Zhou, S., Ayhan, D.H., Delulio, G.A., Guo, L., Broz, K.L., Wiederhold, N., Coleman, J.J., O Donnell, K., Youngster, I., McAdam, A.J., Savinov, S., Shea, T., Young, S., Zeng, Q., Rep, M., Pearlman, E., Schwartz, D.C., Di Pietro, A., Kistler, H.C., Ma, L. 2020. The genome of opportunistic fungal pathogen Fusarium oxysporum carries a unique set of lineage-specific chromosomes. Communications Biology. 3:50. https://doi.org/10.1038/s42003-020-0770-2.
