Proteome Response of Tribolium castaneum Larvae to Bacillus thuringiensis Toxin Producing Strains

Abstract

Susceptibility of Tribolium castaneum (Tc) larvae was determined against spore-crystal mixtures of five coleopteran specific and one lepidopteran specific Bacillus thuringiensis Cry toxin producing strains and those containing the structurally unrelated Cry3Ba and Cry23Aa/Cry37Aa proteins were found toxic (LC50 values 13.53 and 6.30 µg spore-crystal mixture/µL flour disc, respectively). Using iTRAQ combined with LC-MS/MS allowed the discovery of seven novel differentially expressed proteins in early response of Tc larvae to the two active spore-crystal mixtures. Proteins showing a statistically significant change in treated larvae compared to non-intoxicated larvae fell into two major categories; up-regulated proteins were involved in host defense (odorant binding protein C12, apolipophorin-III and chemosensory protein 18) and down-regulated proteins were linked to metabolic pathways affecting larval metabolism and development (pyruvate dehydrogenase Eα subunit, cuticular protein, ribosomal protein L13a and apolipoprotein LI-II). Among increased proteins, Odorant binding protein C12 showed the highest change, 4-fold increase in both toxin treatments. The protein displayed amino acid sequence and structural homology to Tenebrio molitor 12 kDa hemolymph protein b precursor, a non-olfactory odorant binding protein. Analysis of mRNA expression and mortality assays in Odorant binding protein C12 silenced larvae were consistent with a general immune defense function of non-olfactory odorant binding proteins. Regarding down-regulated proteins, at the transcriptional level, pyruvate dehydrogenase and cuticular genes were decreased in Tc larvae exposed to the Cry3Ba producing strain compared to the Cry23Aa/Cry37Aa producing strain, which may contribute to the developmental arrest that we observed with larvae fed the Cry3Ba producing strain. Results demonstrated a distinct host transcriptional regulation depending upon the Cry toxin treatment. Knowledge on how insects respond to Bt intoxication will allow designing more effective management strategies for pest control.

The Red Flour Beetle as a Model for Bacterial Oral Infections

“…Btt produces the Cry3Aa toxin, which when applied in its purified form (without the addition of spores), caused mortality to the yellow mealworm beetle Tenebrio molitor but not to T. castaneum [27]. A recent study [41] reported a very low mortality in T. castaneum when exposed to spore-crystal mixtures of Cry3Aa producing strain. The different mortality observed in this study might come from a different bacterial chromosomal background or from differences in spore concentrations that were provided in the diet.…”

Investigation of Cry3Bb1 resistance and intoxication in western corn rootworm by RNA sequencing

“…It should be noted that this difference was evident only after 8 hr of plant feeding, suggesting that food intake could play a role in this difference. The immune protein apolipophorin‐III was previously reported to be upregulated in response to Cry3Ba exposure in Tribolium castaneum (Herbst) (Contreras, Rausell, & Real, ,b). However, no apolipophorin was differentially expressed in the present RNA‐seq results.…”

Infection routes matter in population-specific responses of the red flour beetle to the entomopathogen Bacillus thuringiensis

“…Generally, CSPs and OBPs are involved in olfaction and chemical communication in insects, but the functions of members of these large families of genes might be diverse [8, 45]. Elevated levels of CSP gene transcripts were previously reported after oral exposure to B. thuringiensis or its toxins in Tenebrio molitor [46] and T. castaneum [16], and a role of OBP-C12 in T. castaneum defense against B. thuringiensis was also demonstrated [16]. The beetle populations differed in the specific sets and the expression dynamics of these genes, some of which were also differentially expressed upon pricking infection.…”