Biotic stress induced by disease or insect herbivory can affect plant growth and crop yield. One strategy to abate such stresses involve the introduction of transgenes, edited genes, or native genes that convey resistance to the pathogen or insect. Mode of action of the genetics-based resistance can be quite useful for discovery, characterization, and optimization of the different genetic approaches. For this purpose, we have applied mass spectrometry-based metabolomics to augment other omics and non-omics approaches for putative mode of action determination of two plant protection traits.  Resistant and susceptible maize and sorghum plants were challenged with a pathogen or feeding insects under controlled environments. Asymptomatic leaf samples were obtained, frozen immediately in liquid nitrogen, and lyophilized. Metabolites were extracted and analyzed by both GC/MS and reversed phase LC/MS by long established sample preparation, data acquisition, and data processing protocols. Data were normalized for sample dry weight, internal standard signal, and other causes of variation emanating from both horticultural and analytical processes. Resulting data was evaluated with both univariate and multivariate statistical approaches.  Separate experiments probed the genotype-treatment interaction with either fungal pathogen or insect herbivore. In the maize fungal disease experiments, several metabolites presented as potential biomarkers for treatment and/or resistance. Metabolites associated with both induced and constitutive responses to pathogen inoculation were identified including one of very high statistical significance. In the sorghum insect herbivory experiments, the amount of a phenolic acid increased with resistance and expression of two biochemically related metabolites decreased with resistance. In both systems, putative biomarkers were consistent with other plant protection experiments.  The ability of metabolomics to indicate putative mode of action of genes responsive to stressors was exemplified by a series of experiments featuring a transgenic, drought-tolerant high-yield maize gene under multiple greenhouse/field, growth stage, watering treatment, tissue type, and genetic background.

Putative gene mode of action discovery by GC/MS and LC/MS metabolomics

2019 Fall National Meeting

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