Expression of cadherin, aminopeptidase N and alkaline phosphatase genes in Cry1Ac-susceptible and Cry1Ac-resistant strains of Plutella xylostella (L.)

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.similar to xylostella to Bt. The information provided in the current study can be useful for the development of resistance management strategies.