Toxicometabolomic profiling of resistant and susceptible western corn rootworm larvae feeding on Bt maize seedlings

Authors: HUYNH, MAN - University Of Missouri; Hibbard, Bruce; HO, KHANH-VAN - University Of Missouri; Shelby, Kent

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2022
Publication Date: 7/8/2022
Citation: Huynh, M.P., Hibbard, B.E., Ho, K., Shelby, K. 2022. Toxicometabolomic profiling of resistant and susceptible western corn rootworm larvae feeding on Bt maize seedlings. Scientific Reports. 12. Article 11639. https://doi.org/10.1038/s41598-022-15895-z.
DOI: https://doi.org/10.1038/s41598-022-15895-z

Interpretive Summary: The western corn rootworm (WCR) is the most serious pest of maize in the U.S. Corn Belt. This highly adaptive pest has evaded nearly all management tactics developed for managing it. Transgenic corn hybrids expressing insecticidal toxins from Bacillus thuringiensis (Bt) are currently the most widely adopted control method in continuous corn, however, these toxins have faltered in some areas where the pest has adapted to survive the toxins. Unfortunately, the resistance mechanisms in WCR to Bt toxins are not fully understood. We hypothesized that exploring shifts in WCR metabolome by Bt toxins could provide insights into altered pathway activities associated with the resistance mechanism. By using an untargeted metabolomics analysis, more than 580 metabolites were identified in susceptible and resistant WCR larvae fed on corn hybrids expressing one of three available Cry3 proteins (eCry3Ab1, mCry3A, and Cry3Bb1) targeting corn rootworms or an isoline corn. Subsequently, multivariate analyses revealed clear similarities and differences in metabolic profiles of susceptible and resistant larvae reared on corn hybrids with and without the expression of Cry3 proteins. Several metabolites were significantly altered between susceptible and resistant larvae that may be involved in defense against or recovery from Bt ingestion by these larvae were further identified. Pathway analyses resulted in the identification of multiple metabolic pathways (e.g., biosynthesis of cofactors, ABC transporters, sphingolipid metabolism, amino acid metabolism) in which the metabolites expressed differently in the susceptible and resistant larvae that recovered from the intoxication of the Cry3 proteins. These results identify candidate metabolites and pathways that may be associated with the resistance mechanisms in WCR to Bt toxins.

Technical Abstract: The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, is the most serious pest of maize (Zea mays L.) in the U.S. Corn Belt and parts of Europe. Transgenic maize hybrids expressing at least one of the four currently available insecticidal toxins from Bacillus thuringiensis (Bt) Berliner, currently the most widely adopted control method in continuous maize, have faltered due to the emergence of resistance. The resistance mechanisms of WCR to Bt toxins are not fully understood. We identified metabolic profiles of susceptible and resistant WCR larvae fed on maize hybrids expressing each of three available Cry3 proteins (eCry3Ab1, mCry3A, and Cry3Bb1) targeting corn rootworms and a control non-Bt maize via an untargeted metabolomics approach. Over 580 unique metabolites found in WCR larvae were classified into different pathways (amino acids, carbohydrates, cofactors and vitamins, energy, lipid, nucleotide, peptide, and xenobiotics). By exploring shifts in WCR larval metabolome exclusively by Bt toxins, several candidate metabolites and metabolic pathways were identified in susceptible and resistant larvae that may be involved in defense against or recovery from Bt ingestion by these larvae. These findings would provide mechanistic insights into altered metabolic pathways associated with the resistance mechanisms of WCR to Bt toxins.