Sequencing and analyzing cadherin and alkaline phosphatase genes in Cry1Ab-susceptible and -resistant strains of the sugarcane borer

Cadherins (CADs) and alkaline phosphatases (ALPs) have been identified as Bacillus thuringiensis (Bt) endotoxins binding proteins in some lepidopterous midguts. cDNAs of one CAD and three ALPs were sequenced from Cry1Ab-susceptible (Cry1Ab-SS) and -resistant (Cry1Ab-RR) larvae of the sugarcane borer, Diatraea saccharalis, using reverse transcriptase polymerase chain reaction (RT-PCR) and 5’ rapid amplification of cDNA end (5’ RACE). cDNA sequences of the CAD and three ALP genes were identical between the Cry1Ab-SS and -RR strains. Expression levels of the CAD and three ALP genes between the two strains were analyzed by quantitative RT-PCR. The gene expression of the CAD from Cry1Ab-RR larvae was significantly lower than that of the Cry1Ab-SS strain. There were no significant differences in expressions of the three ALPs and the total ALP activities between the two strains. RNA interference (RNAi) was employed by oral droplet feeding for knocking down the CAD gene in the Cry1Ab-SS larvae. The knock-down of the CAD in vivo by RNAi resulted in a decrease in Cry1Ab susceptibility. The results suggest that Cry1Ab resistance in this sugarcane borer strain might be associated with reduction in expression of the CAD in the midgut.