Location: Corn Insects and Crop Genetics ResearchTitle: Down-regulation of aminopeptidase N and ABC transporter subfamily G transcripts in Cry1Ab and Cry1Ac resistant Asian corn borer, Ostrina furnacalis (Lepidoptera: Crambidae) Author
Submitted to: International Journal of Biological Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2017
Publication Date: 7/6/2017
Citation: Zhang, T., Coates, B.S., Wang, Y., Wang, Y., Bai, S., Wang, Z., He, K. 2017. Down-regulation of aminopeptidase N and ABC transporter subfamily G transcripts in Cry1Ab and Cry1Ac resistant Asian corn borer, Ostrina furnacalis (Lepidoptera: Crambidae). International Journal of Biological Sciences. 13(7):835-851. doi:10.7150/ijbs.18868. Interpretive Summary: Pest insects that feed on crop plants have evolved resistance to transgenic insecticidal crystaliine (Cry) toxins derived from Bacillus thuringiensis (Bt), which is a threat to sustainable agricultural production in the United States and worldwide. Collaborative research between an ARS researcher in Ames, IA and international colleagues used high-throughput DNA sequencing technologies to develop a catalog of gene expressed in the midgut tissue of corn borer larvae, which is the tissue wherein Bt demonstrates toxicity in susceptible insects. Compared to susceptible corn borer, the expression of a suite of genes showed significant changes within the midgut of Cry1Ab and Cry1Ac resistant corn borer. These genes included reduced expression of a set of genes previously known to be important receptors required for Bt toxicity in susceptible insects. This study for the first time demonstrated that corn borer resistant to the Bt toxins show significant differences in the levels of known Bt toxin receptors, which may be involved in the mode of resistance evolution in the group of insect species. These results are important to university and government researchers, as well as corporate stakeholders who are interested in understanding the modes by which insect evolution resistance to transgenic Bt toxins and enhancing product durability.
Technical Abstract: Bacillus thuringiensis (Bt) crystalline protein (Cry) toxins cause mortality by a mechanism involving pore formation or signal transduction following toxin binding to receptors along the midgut lumen of susceptible insects, but this mechanism and mutations therein that lead to resistance remain poorly understood. The Asian corn borer, Ostrinia furnacalis (Lepidoptera: Crambidae), is a highly destructive pest of cultivated maize throughout East Asia. In the current study, quantitative comparisons were made among midgut expressed transcripts from O. furnacalis susceptible (ACB-BtS) and laboratory selected strains resistant to Cry1Ab (ACB-AbR) and Cry1Ac toxins (ACB-AcR) when feeding on non-Bt diet. From a combined de novo transcriptome assembly of 83,370 transcripts, ORFs of = 100 amino acids were predicted and annotated for 28,940 unique isoforms derived from 12,288 transcripts. Transcriptome-wide expression estimated from RNA-seq read depths predicted significant down-regulation of transcripts for previously known Bt resistance genes, aminopeptidase N1 (apn1) and apn3, as well as a putative ATP binding cassette transporter group G (ABCG) gene in both ACB-AbR and -AcR (log2[fold-change] = 1.36; P < 0.0001). The transcripts that were most highly differentially regulated in both ACB-AbR and -AcR compared to ACB-BtS (log2[fold-change] = 2.0; P < 0.0001) included up- and down-regulation of serine proteases, storage proteins and cytochrome P450 monooxygenases, as well as up-regulation of genes with predicted transport function. Commonality among constitutively differentially expressed transcripts between independently selected Cry1Ab and Cry1Ac resistant lines suggest that changes in toxin binding receptors as well as background selection for modifications in cell transport, cell component recycling, and stress response may be involved in certain Bt resistance mechanisms.