Toxicogenomics of Diabrotica virgifera virgifera leconte in response to eCry3.1Ab-expressing transgenic maize

In modern agricultural systems, insect pests are constantly facing stresses from natural factors and pest management. Strong selection pressure results in evolution of insect resistance to control substances such as chemical insecticides and biological toxins, e.g. Bacillus thuringiensis (Bt) toxins. As one of the most severe insect pests for maize in the U.S. Corn Belt, the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, is in a constant arms race with control strategies. Since 2003, transgenic maize expressing Cry3 toxins have been broadly adopted for rootworm control. WCR has reported resistance to Bt maize in lab-selected colonies and in the field. But the genetics of resistance, and the mode of action of Cry3 toxins to WCR are still not clear. We used eCry3.1Ab-expressing maize and its resistant WCR colony as a model to study Bt resistance. Comprehensive toxicogenomics approaches, including RNA-seq and PacBio Iso-seq, were employed to detect regulation of gene expression regulation, alternative splicing, and genomic variation in eCry3.1Ab-resistance WCR. We also compared the gene expressional response of resistant and susceptible WCR when they were intoxicated with eCry3.1Ab. From these studies we were able to identify genes with functions associated with Bt resistance due to their specific expressional profile, splicing pattern or genomic variation in resistant colonies. We also evaluated differences in responses of resistant and susceptible colonies when being intoxicated by eCry3.1Ab. The preliminary results of genomic variation also reflect the bottleneck of selection process and reveal that a variant allele on a potential Bt receptor increased in the resistant colony. This knowledge will assist our understanding of the unique mode of action of eCry3.1Ab, and develop molecular markers for resistance monitoring in the field.