Molecular characterization of Spodoptera frugiperda-Bacillus thuringiensis Cry1Ca toxin interaction

The use of Bacillus thuringiensis Cry delta-endotoxins as bioinsecticides is threatened by the possibility of pest resistance. Determining transcriptional profiles of midgut cells early in Cry toxin poisoning is crucial for understanding the biochemical and molecular aspects of insect detoxification and for sustained use of such toxins. In this study, transcriptional responses of midgut cells from Spodoptera frugiperda third-instar larvae following treatment with Cry1Ca were investigated. Suppression subtractive hybridization (SSH) on insect midguts dissected at different time intervals during the first 24h of exposure to a sublethal concentration of Cry1Ca was used to isolate and identify S. frugiperda gut genes that change in expression on intoxication. After differential screening by membrane-based hybridization, 86 cDNA fragments were selected, sequenced, and analyzed in databases using BLASTN/BLASTX. The cDNA collection comprised a repertoire of genes mainly associated with metabolism, defence and oxidative stress. The expression of a subset of these genes was further investigated. Northern blot analysis confirmed the differential expression patterns between intoxicated and control larvae. The transcript accumulation rate at six different times taken after the initiation of the intoxication point was also examined. Differential expression of most genes examined was detected within 15 min after toxin challenge, where defence and oxidative stress-related genes were transcriptionally enhanced and metabolic-related genes were repressed.