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Cadherin proteins, aminopeptidase N (APN) and alkaline phosphatase (ALP) bind to Bacillus thuringiensis (Bt) toxins in the lepidopteran midgut, but the inherent function of these receptors remains unclear. To clarify whether these three potential receptors contribute to the resistance of lepidopteran insects to the Bt toxin, the transcription patterns of these genes in Cry1Ac-susceptible Plutella xylostella strains and strains highly resistant to Cry1Ac were examined using real-time quantitative polymerase chain reactions. Both gene expressions of cadherin and APNs were most abundant in the midgut of fourth larval instars but were also found in pupae. The transcription levels of cadherin, APN2 and ALP genes in the midgut were more abundant in the susceptible strain than in the resistant strain and also clearly differed between the two strains. Moreover, the transcription levels of cadherin increased as the insect developed from the second to the fourth larval instars and then decreased in pupae. mRNA of the APN2 gene was more abundant than that of the APN1, APN3 and APN4 genes in the susceptible strain. The results suggested that these differences were attributable to the adaptation of the resistant strain to the Bt toxin and demonstrated a possible link between the gene expression of cadherin, ALP and APN2 and the resistance of P. xylostella to Bt. The information provided in the current study can be useful for the development of resistance management strategies. [ABSTRACT FROM AUTHOR]

Two laboratory diamondback moth (DBM) strains were used to study the effects of injecting cadherin gene double-stranded RNA (dsRNA) on the growth and development of Plutella xylostella (L.). Specifically, the susceptible strain named DBM.1Ac-S and the low resistant strain DBM.1Ac-R selected with Cry1Ac toxin were studied. The third larvae of the two strains were injected dsRNA of cadherin gene and their corresponding controls, DBM.1Ac-RH and DBM.1Ac-SH, were both injected diethypyrocarbonate (DEPC)-treated water respectively. The basic biological properties such as death rate, hatching ratio, fecundity, weight of pupa and eclosion rate of the strains mentioned above were likewise studied. Meanwhile, the length and width of the egg and pupa were also measured. The results showed that the cadherin gene dsRNA injection resulted in a significant increase of the death rate and sex ratio. On the other hand, hatching ratio, fecundity, weight of pupa, eclosion rate and adult longevity for male and female of treatments decreased compared to their corresponding controls. As such, there was no significant difference on the length of egg and pupa in between treatments and the corresponding controls. However, their width increased inversely with their corresponding controls. Hence, the results suggest that cadherin gene dsRNA injection retarded the larval growth and development of P. xylostella. Also, these results can help reveal the function of cadherin gene through the RNA interference technique. [ABSTRACT FROM AUTHOR]