Progress 10/01/11 to 09/30/12
Outputs OUTPUTS: Mycotoxins are toxic and carcinogenic compounds produced by fungi growing on food and feed. Mycotoxin contamination is a worldwide problem causing losses exceeding 1 billion dollars annually. The major mycotoxins on maize are aflatoxins produced by Aspergillus flavus and fumonisins produced by Fusarium verticillioides. Losses in the US to aflatoxin contamination alone results in direct losses of 200 million dollars annually. This loss is compounded by indirect losses due to contaminated by-products, such as distillers grains. Plant resistance is the most economical strategy for resistance to plant diseases. Unfortunately, 30 years of breeding efforts has not resulted in maize genotypes with adequate resistance to fumonisin or aflatoxin accumulation. A limitation to commercial plant breeding for resistance is the lack of a way to rapidly identify resistant genotypes. To better understand host pathogen interactions of mycotoxin producing fungi, we studying factors in the fungus that govern pathogenicity and mycotoxin production, and we are studying the dynamics of the disease in maize seed to identify important defenses, either physical or chemical, that can be enhanced by plant breeding. PARTICIPANTS: Greg OBrian, technician; Xioamei Shu, graduate student, Farhana Runa, graduate student TARGET AUDIENCES: Producers and utilizers of maize PROJECT MODIFICATIONS: Not relevant to this project.
Impacts A collaborative study between my lab and Massimo Reverberi's lab at the Universita` Sapienza, Roma, Italy showed a correlation between peroxisome proliferation, fatty acids b-oxidation and aflatoxin biosynthesis. Aspergillus flavus was transformed with a vector containing P33, a gene from Cymbidium ringspot virus, which causes peroxisome proliferation, and the promoter for a Cu-Zn SOD gene of A. flavus, which responses to oxidative stress. The transformant showed an upregulation of lipid metabolism and a higher content of both intracellular ROS and oxylipins. The combined presence of a higher amount of fatty acids, a hyper-oxidant cell environment and of hormone-like signals (oxylipins) enhanced the synthesis of aflatoxins. These finding provide support to earlier observations that reactive oxygen species and certain fatty acids are conducive for aflatoxin production. In other studies examining the pathogenicity of A. flavus, we found diploids to be more virulent than the parental haploids to the wax moth, Galleria mellonella. Similarly, overexpression of a homolog of NepA increased pathogenicity to G. mellonella. These studies show that insect model systems may be an effective way to evaluate pathogenicity in A. flavus.
Publications
- Reverberi M, Punelli M, Smith CA, Zjalic S, Scarpari M, Scala V, Cardinali G, Aspite N, Pinzari F, Payne G, Fabbri A, Fanelli C. (2012) How Peroxisomes Affect Aflatoxin Biosynthesis in Aspergillus Flavus. PLoS ONE 7(10): e48097. doi:10.1371/journal.pone.0048097.
|
Progress 10/01/10 to 09/30/11
Outputs OUTPUTS: Aspergillus flavus and Fusarium verticillioides are the dominant mycotoxin producing fungi on maize in North Carolina. Pathogenesis of these two fungi was compared on developing maize seeds in field studies. After an initial colonization of the seeds at the site of inoculation, mycelia of two fungi appeared next in the aleurone layer. A. flavus destroyed the cells in the process of colonization whereas cells colonized by F. verticillioides initially retained their integrity during the early stages of colonization. In situ RNA hybridization showed the plant defense related genes PRms (pathogenesis related protein, maize seeds) and UGT (UDP-glucosyltransferases) to be induced in maize seed tissues before fungal colonization. PRms was differentially expressed in the aleurone and the scutellum by A. flavus and F. verticillioides infected maize seeds. UGT was expressed only in the scutellum of A. flavus and F. verticillioides infected maize seeds. Results from these studies show that these fungi colonize specific seed tissues and trigger plant defense response in tissues before fungal colonization. In another study, genotypes from a B73 X TX303 near isogenic population were evaluated for their resistance to A. flavus and aflatoxin accumulation after wound inoculation with A. flavus. Ear rot ratings did not correlate well with aflatoxin concentrations in the kernels. Tex303 showed some resistance in North Carolina in 2011, a year very conducive to aflatoxin formation. Over a three year period, TX303 showed lower levels of aflatoxin than B73. Five lines from the population that showed lower levels of aflatoxin after three years of evaluation are being tested again in 2012. PARTICIPANTS: Greg OBrian, technician; Xioamei Shu, graduate student TARGET AUDIENCES: Producers and utilizers of maize. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts A research protocol was established to compare the colonization of maize seeds by A. flavus and F. verticillioides. An understanding of similarities and differences in their patterns of colonization and the host's response to infection may provide information on the classes of resistance genes effective for these two fungi. Two genes associated with host resistance were induced by the fungi. By changing the timing or absolute expression of these genes, or other genes identified in these studies it may be possible to confer resistance to this fungus during stressed conditions.
Publications
- Reese, B.N. Payne, G.A., Nielsen, D.M. and Woloshuk, C.P. 2011. Gene Expression profile and response to maize kernels by Aspergillus flavus. Phytopathology 101:797-804. Wu, F., Bhatnagar, D., Bui-Klimke, T., Carbone, I., Hellmich, R., Munkvold, G., Paul, P., Payne, G., Takle, E. 2011. Climate Change Impacts on Mycotoxin Risks in US Maize. World Mycotoxin Journal 4: 79-93.
|
|