Two ABC transporters are differentially involved in the toxicity of two Bacillus thuringiensis Cry1 toxins to the invasive crop-pest Spodoptera frugiperda (J. E. Smith)

Background: The fall armyworm Spodoptera frugiperda is a major agricultural pest that has invaded the East Hemisphere since 2016, generating a serious threat to food security worldwide including Africa and Asia. The Cry toxins produced by Bacillus thuringiensis (Bt) have been shown to be effective against this insect pest. In different insect ABC transporters (ABCC2 or ABCC3) have been shown to be involved as receptors of some Cry1 toxins. Here we analyzed the role of SfABCC2 and SfABCC3 in the toxicity of Cry1Fa and Cry1Ab toxins in this insect pest.

Results: Two S. frugiperda SfABCC2 and SfABCC3 knockout strains, coding for potential functional Bt receptors, were created using CRISPR/Cas9 genome editing system. Both knockout strains showed resistance to both Cry1Fa and Cry1Ab toxins compared with the susceptible strain. SfABCC2 knockout strain showed higher resistance to both Cry toxins than SfABCC3 knockout strain, suggesting a major role of SfABCC2 in the mode of action of these Cry toxins. In addition, expression of SfABCC2 and SfABCC3 genes in Trichoplusia ni Hi5 cells also increased the susceptibility to Cry1Ab and Cry1Fa toxins, in agreement with the genome editing results. The double knockout of SfABCC2 and SfABCC3 strain was not viable in contrast to other lepidopteran species. Furthermore, we report here that SfABCC2 or SfABCC3 knockout strains increased their susceptibility to abamectin and spinosad insecticides.

Conclusion: We provide functional evidence that in S. frugiperda these two ABCC transporters serve as receptors of Bt Cry1Fa and Cry1Ab toxins. © 2020 Society of Chemical Industry.