|CARRIERE, YVES - University Of Arizona
|SHOWALTER, ANN - University Of Arizona
|SOLLOME, JAMES - University Of Arizona
|ELLERS-KIRK, CHRISTA - University Of Arizona
|TABASHNIK, BRUCE - University Of Arizona
Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/30/2009
Publication Date: 11/1/2009
Citation: Carriere, Y., Showalter, A.M., Fabrick, J.A., Sollome, J., Ellers-Kirk, C., Tabashnik, B.E. 2009. Cadherin Gene Expression and Effects of Bt Resistance on Sperm Transfer in Pink Bollworm. Journal of Insect Physiology. 55:1058-1064.
Interpretive Summary: Bacillus thuringiensis (Bt) toxins are expressed in transgenic Bt crops to control key insect pests. Insect cadherin-like proteins function as receptors of Bt toxins in a number of lepidopteran insects and mutations in the pink bollworm (Pectinophora gossypiella) cadherin are linked with resistance to a Bt toxin and to transgenic Bt cotton. However, the intrinsic function of insect cadherin-like protein is unknown. Here we examined cadherin expression profiles and the association between cadherin resistance and sperm transfer in pink bollworm. Cadherin is most abundant in larval gut tissue, affirming its proposed role as a Bt toxin receptor, although its presence in larval testes and fitness costs associated with reduced sperm transfer, indicate it may also have an important inherent function in sperm production.
Technical Abstract: Cadherin proteins bind Bacillus thuringiensis (Bt) toxins in lepidopteran midguts but their inherent function remains unclear. In pink bollworm, Pectinophora gossypiella, three recessive mutations in a cadherin gene (BtR) are tightly linked with resistance to Bt toxin Cry1Ac. Here we examined patterns of transcription of this gene and the association between cadherin genotype and sperm transfer in pink bollworm. Cadherin RNA was most abundant in larvae, but also occurred in adults and embryos. In fourth instar larvae, cadherin RNA was most abundant in the gut, yet its presence in the testes indicates a potential role in sperm production. Previously, we found reduced first-male paternity in pink bollworm males homozygous for cadherin mutations conferring resistance to Bt, when a resistant and susceptible male competed for access to a female. However, the number of offspring sired by resistant and susceptible males was similar without competition. Male Lepidoptera produce both fertile eupyrene sperm and anucleate, non-fertile apyrene sperm, suggesting that apyrene sperm may contribute to male reproductive success when sperm competition occurs. Accordingly, we hypothesized that cadherin-based resistance to Bt entails fitness costs that reduce apyrene sperm transfer. To test this hypothesis, we compared apyrene and eupyrene sperm transfer in males from four strains of pink bollworm. Transfer of apyrene and eupyrene sperm was lower in homozygous resistant than in susceptible males. Furthermore, homozygous resistant males weighed less than susceptible males, which could have diminished sperm transfer by resistant males directly, or via a positive association between male weight, spermatophore weight and sperm transfer. While data suggest that cadherin mutations induced a recessive fitness cost affecting apyrene sperm transfer, these mutations also generated recessive costs that affected other traits and could have lowered first-male paternity.