Helicoverpa armigera ATP-binding cassette transporter ABCA2 is a functional receptor of Bacillus thuringiensis Cry2Ab toxin

Authors: GAN, CHUNXIA - Nanjing Agricultural University; ZHANG, ZHENG - Nanjing Agricultural University; JIN, ZENG - Nanjing Agricultural University; WANG, FALONG - Nanjing Agricultural University; Fabrick, Jeffrey; WU,, YIDONG - Nanjing Agricultural University

Submitted to: Pesticide Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2023
Publication Date: 12/1/2023
Citation: Gan, C., Zhang, Z., Jin, Z., Wang, F., Fabrick, J.A., Wu,, Y. 2023. Helicoverpa armigera ATP-binding cassette transporter ABCA2 is a functional receptor of Bacillus thuringiensis Cry2Ab toxin. Pesticide Biochemistry and Physiology. 197. Article 105658. https://doi.org/10.1016/j.pestbp.2023.105658.
DOI: https://doi.org/10.1016/j.pestbp.2023.105658

Interpretive Summary: Genetically engineered crops producing insecticidal proteins from Bacillus thuringiensis (Bt) are important globally for the management of key insect pests, including the cotton bollworm, Helicoverpa armigera. However, pest resistance to Bt crops diminishes their efficacy and reduces the many benefits of this technology. Previous studies have shown that resistance to the Cry2Ab Bt toxin and to Bt crops producing Cry2Ab is associated with mutations in a midgut ATP-binding cassette transporter gene called ABCA2. Furthermore, gene-editing knockout of this gene confirmed that ABCA2 plays an important functional role in Cry2Ab intoxication. However, the precise role of ABCA2 in the mode of action of Cry2Ab has yet to be reported. Here, an ARS scientist at Maricopa, AZ and collaborators from Nanjing Agricultural University, China, used two in vitro expression systems to study the functional roles of the H. armigera ABCA2 (HaABCA2) protein in Cry2Ab intoxication. Cry2Ab was found to bind to cultured insect cells and frog oocytes expressing the HaABCA2, with both showing increased susceptibility to Cry2Ab. In contrast, insect cells expressing mutant HaABCA2 proteins missing any of the extracellular loop regions 1, 3, 4, and 6 as well as the intracellular loop containing nucleotide-binding domain 1 lost susceptibility to Cry2Ab, indicating each of these regions are important for receptor function. Together with previously published data, the results support that HaABCA2 is an important receptor for Cry2Ab where it functions to promote intoxication in H. armigera. These results not only improve the basic understanding of how Cry2Ab used in transgenic crops kill H. armigera, but also provide initial predictive information about regions of HaABCA2 important for intoxication, which could be used to guide the proactive monitoring of resistance to Cry2Ab Bt cotton.

Technical Abstract: Crystalline (Cry) proteins from the bacterium Bacillus thuringiensis (Bt) are widely used in transgenic crops to control important insect pests. Bt crops have many benefits compared with traditional broad-spectrum insecticides, including improved pest control with reduced negative impacts on off-target organisms and fewer environmental consequences. Transgenic corn and cotton producing Cry2Ab Bt toxin are used globally to control several major lepidopteran pests, including the cotton bollworm, Helicoverpa armigera. Resistance to the Cry2Ab toxin and to Bt crops producing Cry2Ab is associated with mutations in the midgut ATP-binding cassette transporter ABCA2 gene in several lepidopterans. Gene-editing knockout has further shown that ABCA2 plays an important functional role in Cry2Ab intoxication. However, the precise role of ABCA2 in the mode of action of Cry2Ab has yet to be reported. Here, we used two in vitro expression systems to study the roles of the H. armigera ABCA2 (HaABCA2) protein in Cry2Ab intoxication. Cry2Ab bound to cultured Sf9 insect cells producing HaABCA2, resulting in specific and dose-dependent susceptibility to Cry2Ab. In contrast, Sf9 cells expressing recombinant mutant proteins missing at least one of the extracellular loop regions 1, 3, 4, and 6 or the intracellular loop containing nucleotide-binding domain 1 lost susceptibility to Cry2Ab, indicating these regions are important for receptor function. Consistent with these results, Xenopus laevis oocytes expressing recombinant HaABCA2 showed strong ion membrane flux in the presence of Cry2Ab, suggesting that HaABCA2 is involved in promoting pore formation during Cry2Ab intoxication. Together with previously published data, our results support HaABCA2 being an important receptor of Cry2Ab where it functions to promote intoxication in H. armigera.