RNA interference of cadherin gene expression in Spodoptera exigua reveals its significance as a specific Bt target

Abstract

Cadherin is a calcium-dependent cell surface molecule and has been proposed to be a target molecule of Bacillus thuringiensis Cry proteins. Based on a partial cadherin gene obtained from 454 pyrosequencing transcripts of the fifth instar Spodoptera exigua midgut, a full open reading frame of cadherin gene (SeCad1) was cloned. Its predicted amino acid sequence encodes extracellular 9 cadherin repeats, a transmembrane, and intracellular domain. SeCad1 gene was expressed in all developmental stages specifically in gut tissue by RT-PCR analysis. Expression of SeCad1 gene was suppressed by both injection and feeding of its specific double-stranded RNA (dsRNASeCad1) in the fifth instar. The suppression of SeCad1 expression did not significantly influence on pupal and adult developments of S. exigua. However, the larvae treated with dsRNASeCad1 (100ng/larva) significantly reduced susceptibility to B. thuringiensis ssp. aizawai. In contrast, the dsRNASeCad1-treated larvae did not show any change in susceptibility to B. thuringiensis ssp. kurstaki. These results suggest that SeCad1 is a specific target molecule to Cry1C toxin from B. thuringiensis in S. exigua, but not to Cry1A toxin.