Transcriptome Assembly and Characterization of Chemoreceptors for Corn Rootworms

Authors

Bailee Egan, University of Nebraska-LincolnFollow

First Advisor

Etsuko N. Moriyama

Date of this Version

Summer 7-6-2022

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Biological Sciences, Under the Supervision of Professor Etsuko N. Moriyama. Lincoln, Nebraska: May, 2022

Copyright © 2022 Bailee Egan

Abstract

The western corn rootworm (Diabrotica virgifera virgifera LeConte) is the most important insect pest of corn in the United States Corn Belt, costing the agricultural industry over two billion dollars per year. As current management practices have been losing their effectiveness, new targets for corn rootworm control need to be explored. In this thesis, we focused on identifying rootworm chemoreceptors, which can be considered for potential targets for management. Transcriptomes from seven life stages were assembled for the western corn rootworm as well as two other related corn rootworm species, the northern corn rootworm (D. barberi) and the southern corn rootworm (D. undecimpunctata howardii). The three gustatory receptor genes (Gr1, Gr2, and Gr3) encoding the carbon dioxide receptors were identified from the three corn rootworm species. Unexpectedly, a duplication of Gr2 was identified. Many other candidate chemoreceptors, including a total of 200 gustatory receptors, 315 odorant receptors, and 80 ionotropic receptors, were also identified from the three rootworm species. Phylogenetic analysis among the chemoreceptors identified from corn rootworms and other insects (including both coleopteran and non-coleopteran species) revealed many coleopteran, especially rootworm-specific, expansions of some chemoreceptors. Gene expression analysus showed some of these chemoreceptors that have elevated expression in the neonate stage, indicating that these genes may have roles in host-seeking behavior of rootworm larvae. Potential ligand specificity of some rootworm chemoreceptors was also inferred based on the similarity to other insect chemoreceptors whose functions are known. Finally, using co-evolution analysis, protein structures of rootworm carbon dioxide receptors were predicted. The chemoreceptors identified in this study can serve as a valuable resource for developing new corn rootworm management strategies.

Advisor: Etsuko N. Moriyama