Identification of a new trypsin from Spodoptera frugiperda involved in a defensive mechanism against the Bacillus thuringiensis Cry1Ca1 toxin

Both, insecticidal formulations based on the entomopathogenic bacterium Bacillus thuringiensis (Bt) and transgenic plants expressing Bt Cry toxins, have been threatened by the potential appearance of insect resistance in major crop pests. With the aim of identifying genes and mechanisms triggered against a Bt Cry1-class toxin in the midgut of fall armyworm Spodoptera frugiperda, the major pest of maize in Cuba, subtractive cDNA libraries of the molecular interaction insect-Bt Cry1Ca1 toxin were constructed. Among those genes specifically regulated in response to the intoxication, one coding for a new trypsin-like serin proteinase (SfT6) was identified. Gene function analysis using RNA interference showed SfT6 plays a crucial role for the Cry1Ca1 toxicity against S. frugiperda; gene expression suppression caused a reduction of the proteolytic processing of Cry1Ca1 by the larval midgut juice and a reduced susceptibility of insects in bioassays. Our study represents the first report on S. frugiperda midgut genes differentiallyexpressed in response to Cry1Ca1 intoxication. Besides, we have identified and cloned the full-length cDNA sequence of a novel serine proteinase whose regulation is linked to the natural process of insect adaptation to Bt in order to survive the pathogenic process.