Project description: Bacillus thuringiensis Cry toxin is used for insect pest management. When susceptible insect larvae ingest the Bt toxin it shows various physiological and cellular changes. We have employed Agilent One Color matrix based microarray to check the mid-gut gene expression upon Cry toxin exposure in Achaea janata (Castor semilooper). Microarray analysis shows significant variation in gene expression upon Cry toxin exposure.
Project description:Insecticidal effects of Bacillus thuringiensis Cry toxins in hemocoel of larvae have not been properly evaluated. In the present study, hemocoelic injection of four representative Cry toxins i.e., Cry1Aa, Cry1Ab, Cry1Ac, and DOR5 to an economically important lepidopteran insect pest Achaea janata, induced larval mortality, reduced larval growth rate and gave rise to smaller pupae, all in a dose-dependent manner. We observed extensive degeneration as well as the disintegration of larval tissues, most notably, fat body, and the possible involvement of lysosomal enzymes in tissue histolysis. The resultant "hypoproteinemia" and most relevantly, the drastic reduction of 80-85 kDa hexamerin proteins levels of hemolymph could be attributed to the pathological state of the fat body induced by Cry toxin injection. Formation of non-viable larval-pupal intermediates and emergence of defective adults also indicate toxicity effects of Cry toxins during metamorphosis. Thus, findings from our study suggest Cry toxins in larval hemocoel are also toxic to A. janata larval survival and subsequent development.
Project description:Larvae of most lepidopteran insect species are known to be voracious feeders and important agricultural pests throughout the world. Achaea janata larvae cause serious damage to Ricinus communis (Castor) in India resulting in significant economic losses. Microbial insecticides based on crystalline (Cry) toxins of Bacillus thuringiensis (Bt) have been effective against the pest. Excessive and indiscriminate use of Bt-based biopesticides could be counter-productive and allow susceptible larvae to eventually develop resistance. Further, lack of adequate genome and transcriptome information for the pest limit our ability to determine the molecular mechanisms of altered physiological responses in Bt-exposed susceptible and tolerant insect strains. In order to facilitate biological, biochemical and molecular research of the pest species that would enable more efficient biocontrol, we report the midgut de novo transcriptome assembly and clustering of susceptible Cry toxin-exposed and Cry toxin tolerant Achaea janata larvae with appropriate age-matched and starvation controls.
Project description:Insect midgut membrane-anchored aminopeptidases N (APNs) are Zn(++) dependent metalloproteases. Their primary role in dietary protein digestion and also as receptors in Cry toxin-induced pathogenesis is well documented. APN expression in few non-gut hemocoelic tissues of lepidopteran insects has also been reported but their functions are widely unknown. In the present study, we observed specific in vitro interaction of Cry1Aa toxin with a 113 kDa AjAPN1 membrane protein of larval fat body, Malpighian tubule and salivary gland of Achaea janata. Analyses of 3D molecular structure of AjAPN1, the predominantly expressed APN isoform in these non-gut hemocoelic tissues of A. janata showed high structural similarity to the Cry1Aa toxin binding midgut APN of Bombyx mori, especially in the toxin binding region. Structural similarity was further substantiated by in vitro binding of Cry1Aa toxin. RNA interference (RNAi) resulted in significant down-regulation of AjAPN1 transcript and protein expression in fat body and Malpighian tubule but not in salivary gland. Consequently, reduced AjAPN1 expression resulted in larval mortality, larval growth arrest, development of lethal larval-pupal intermediates, development of smaller pupae and emergence of viable defective adults. In vitro Cry1Aa toxin binding analysis of non-gut hemocoelic tissues of AjAPN1 knockdown larvae showed reduced interaction of Cry1Aa toxin with the 113 kDa AjAPN1 protein, correlating well with the significant silencing of AjAPN1 expression. Thus, our observations suggest AjAPN1 expression in non-gut hemocoelic tissues to play important physiological role(s) during post-embryonic development of A. janata. Though specific interaction of Cry1Aa toxin with AjAPN1 of non-gut hemocoelic tissues of A. janata was demonstrated, evidences to prove its functional role as a Cry1Aa toxin receptor will require more in-depth investigation.
Project description:The lack of homogeneity in field application of Bacillus thuringiensis formulation often results in ingestion of sub-lethal doses of the biopesticide by a fraction of pest population and there by promotes the toxin tolerance and resistance in long term. Gut regeneration seems to be one of the possible mechanism by which this is accomplished. However, the existing information is primarily derived from in vitro studies using mid-gut cell cultures. Present study illustrates cellular and molecular changes in mid-gut epithelium of a Bt-susceptible polyphagous insect pest castor semilooper, Achaea janata in response to a Cry toxin formulation. The present report showed that prolonged exposure to sub-lethal doses of Cry toxin formulation has deleterious effect on larval growth and development. Histological analysis of mid-gut tissue exhibits epithelial cell degeneration, which is due to necrotic form of cell death followed by regeneration through enhanced proliferation of mid-gut stem cells. Cell death is demonstrated by confocal microscopy, flow-cytometry, and DNA fragmentation analysis. Cell proliferation in control vs. toxin-exposed larvae is evaluated by bromodeoxyuridine (BrdU) labeling and toluidine blue staining. Intriguingly, in situ mRNA analysis detected the presence of arylphorin transcripts in larval mid-gut epithelial cells. Quantitative PCR analysis further demonstrates altered expression of arylphorin gene in toxin-exposed larvae when compared with the control. The coincidence of enhanced mid-gut cell proliferation coincides with the elevated arylphorin expression upon Cry intoxication suggests that it might play a role in the regeneration of mid-gut epithelial cells.