Utilizing -omics technologies to study drought stress related to host resistance against aspergillus flavus colonization and aflatoxin production
Fountain, Jake Clayton
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Aspergillus flavus is a pathogen of several important crop species including maize and peanut. During infection, A. flavus produces mycotoxins known as aflatoxins which pose a serious threat to global food safety and security. Host resistance to infection and aflatoxin contamination has been linked to drought stress with drought tolerant hosts tending to be more resistant. However, potential causes of this phenomenon have yet to be characterized. To better understand both the host and pathogen stress interactions, field and laboratory analyses, particularly biochemical and –omics analyses including metabolomics, proteomics, and transcriptomics were used. Drought sensitive, aflatoxin contamination susceptible maize lines were found to accumulate higher levels of reactive oxygen species (ROS) in their leaf and kernel tissues compared to tolerant and resistant lines. Drought sensitive lines also exhibited more rapid and vigorous physiological responses to stress including changes in antioxidant enzyme activity, photosynthesis, and stomatal conductance. Metabolomics analysis of developing kernels under drought also showed increased accumulation of free simple sugars, oxylipins, and polyunsaturated fatty acids in drought sensitive lines which may provide resources for aflatoxin production during A. flavus infection. Examination of A. flavus responses in vitro using H2O2-derived oxidative stress as a mimic for drought stress found that these responses correlate with aflatoxin production capability with highly aflatoxigenic isolates exhibiting greater stress tolerance. Biological control isolates were also able to tolerate greater levels of stress than field isolated atoxigenic isolates suggesting this as a trait for biocontrol selection. Transcriptional and proteomic examination of isolate responses to oxidative stress suggest that isolate development, pathogenicity, and secondary metabolite production are regulated in response to oxidative stress. Secondary metabolite production, including aflatoxin, composed a large component of oxidative stress responses in A. flavus suggesting their possible roles in stress alleviation for the fungus under adverse environmental conditions. Together, these studies identified stress responsive mechanisms in both the host and pathogen which can be targeted and manipulated independently or in tandem including ROS signaling, sugar metabolism, and oxylipin signaling using biotechnologies such as genome editing. This will provide a novel avenue to search for and produce practical solutions to mitigate aflatoxin contamination.