CsABCC2 Mediate The Resistance Of Chilo Suppressalis (Walker) To Bt Toxin

The popularization and application of insect-resistant genetically modified?IRGM?crops has effectively controlled the damage to target pests.As a biological control method,it has significant benefits,including higher farmer profits,increasing crop yields and protecting ecological environment.In China,many transgenic rice lines have been transformed into Bt genes,which are highly effective against rice pests and shown robust prospects for commercial application.However,the potential risk of targeted pests developing resistance is a key consideration influencing IRGM rice regulation and sustainable use after widespread adoption.Therefore,it is necessary to delay the evolution of pest resistance and make appropriate resistance management strategies for the application of IRGM rice.Clarifying the molecular mechanism of insect resistance is the basis of implementing insect resistance management.ABCC2 is a transmembrane transporter protein in insect.Many studies have reported that ABCC2 was the midgut receptor for Bt toxin.And there are demonstrated the mutation of ABCC2 gene was closely related to the Bt resistance of Heliothis viresce and Trichoplussia ni.But the function of ABCC2 in the toxicity mechanism of Bt toxin against Chilo suppressalis has not been reported.In this study,the laboratory raised Bt susceptible strain,Cry1C and Cry1Ab resistant strains of C.suppressalis were studied and analysed.qRT-PCR was used to detect the expression level of CsABCC2 gene in susceptible and resistant strain of C.suppressalis.RNA interference knockdown the expression of CsABCC2 gene.The results demonstrated the function of ABCC2 in the mode of Bt Cry toxin action in C.suppressalis.The main results are as follows:1)Quantitative comparisons were made among CsABCC2 expressed from C.suppressalis susceptible?FZS?and laboratory selected strains resistant to Cry1C?FZ-Cry1C-R?and Cry1Ab toxins?FZ-Cry1Ab-R?.The results showed that CsABCC2 was expressed in all developmental stages but peaked in the 3rd-and 4th-instar larvae.Meanwhile,expression levels of CsABCC2 were markedly different from the 3th-instar larvae tissues The results showed the highest expression were detected in foregut and midgut,for other tissues,the expression levels of CsABCC2 were relatively low.Compared with the expression levels of CsABCC2 in Bt susceptible and resistant strains.We found that the relative expression of CsABCC2 of FZ-Cry1C-R strain were significantly lower than FZS strain in 1st-to 5th-instar larvae.And in FZ-Cry1Ab-R strain,the expression of CsABCC2 was significantly lower than FZS strain in 3rd-and 4th-instar larvae.2)In order to explore the function of ABCC2 in the toxicity mechanism of Bt toxin,RNA interference was used to silence the expression of CsABCC2 gene.Newly hatched larvae were put into petri dishes containing artificial diet smeared with dsRNAs and the expression levels of CsABCC2 were measured with RT-qPCR after 48 hrs.RT-qPCR results showed that the expression level of CsABCC2gene was significantly decreased.qPCR revealed that oral delivery of dsRNA-ABCC2 into newly hatched larvae significantly reduced CsABCC2 transcript levels by 70%relative to controls.Subsequent bioassays showed that silencing the expression of CsABCC2 gene significantly reduced larval susceptibility to Cry1C and Cry1Ab toxin at 1.0?g/g(the LC₅₀ value)and at 2.0?g/g(the LC₈₀ value).These results suggest that ABCC2 plays a key role in the toxicity of Cry1C and Cry1Ab toxin to C.suppressalis.This study demonstrated the ABCC2 protein plays an important role in toxicity mechanism of Cry toxin to C.suppressalis.A more complete understanding of Bt resistance mechanism will be helpful for designing resistance management strategies that will delay the evolution of Bt resistance to insect populations.