Reduced cadherin expression associated with resistance to Bt toxin Cry1Ac in pink bollworm

Authors: Fabrick, Jeffrey; Mathew, Lolita; Leroy, Dannialle; Hull, Joe; UNNITHAN, GOPALAN - University Of Arizona; YELICH, ALEX - University Of Arizona; CARRIERE, YVES - University Of Arizona; LI, XIANCHUN - University Of Arizona; TABASHNIK, BRUCE - University Of Arizona

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2019
Publication Date: 5/29/2019
Citation: Fabrick, J.A., Mathew, L.G., LeRoy, D.M., Hull, J.J., Unnithan, G.C., Yelich, A.J., Carriere, Y., Li, X., Tabashnik, B.E. 2019. Reduced cadherin expression associated with resistance to Bt toxin Cry1Ac in pink bollworm. Pest Management Science. 76(1):67-74. https://doi.org/10.1002/ps.5496.
DOI: https://doi.org/10.1002/ps.5496

Interpretive Summary: Transgenic crops engineered to produce insecticidal proteins from the bacterium Bacillus thuringiensis (Bt) provide many benefits including pest suppression, increased yields and farmer profits, reduced conventional insecticide use, decreased harm to non-target species, and enhanced biological control. However, pest resistance to Bt crops decreases such benefits. To improve strategies for monitoring, delaying, and countering pest resistance to Bt crops, better understanding of the fundamental mechanisms underlying resistance is needed. Previous work in the pink bollworm, a worldwide pest of cotton, indicates that resistance to Cry1Ac Bt toxin is caused by major qualitative changes in a midgut cadherin protein (PgCad1) that binds Cry1Ac in susceptible insects. In contrast, here we show that resistance to Cry1Ac in a lab-selected strain of pink bollworm is not associated with major qualitative changes in PgCad1, but rather involves reduced production of the PgCad1 protein. Because resistance can occur in pests via both qualitative and quantitative changes in receptor proteins demonstrates their remarkable adaptability and presents challenges for monitoring and managing resistance to Bt crops.

Technical Abstract: Better understanding of the molecular basis of resistance is needed to improve management of pest resistance to transgenic crops that produce insecticidal proteins from Bacillus thuringiensis (Bt). Here we analyzed resistance of the pink bollworm (Pectinophora gossypiella) to Bt toxin Cry1Ac, which is used widely in transgenic Bt cotton. Field-evolved practical resistance of pink bollworm to Cry1Ac is widespread in India, but not in China or the United States. Previous work with laboratory- and field-selected pink bollworm indicated that resistance to Cry1Ac is caused by qualitative changes in the amino acid sequence of a midgut cadherin protein (PgCad1) that binds Cry1Ac in susceptible larvae. Relative to a susceptible strain, the laboratory-selected APHIS-R strain had 530-fold resistance to Cry1Ac with autosomal recessive inheritance. Unlike previous results, resistance in this strain was not consistently associated with insertions or deletions in the expected amino acid sequence of PgCad1. However, this resistance was associated with 79- to 190-fold reduced transcription of the PgCad1 gene and markedly lower abundance of PgCad1 protein. The ability of pink bollworm and other major pests to evolve resistance to Bt toxins via both qualitative and quantitative changes in receptor proteins demonstrates their remarkable adaptability and presents challenges for monitoring and managing resistance to Bt crops.