Proteomic insights into the immune response of the Colorado potato beetle larvae challenged with Bacillus thuringiensis.

Bacillus thuringiensis (Bt) toxins constitute effective, environmentally safe biopesticides. Nevertheless, insects' tolerance to Bt is influenced by environmental factors affecting immunity. To understand larval immune response in the devastating coleopteran insect pest Colorado potato beetle (CPB), we undertook a proteomic analysis of hemolymph of non-treated control larvae and larvae consuming non-lethal doses of spore-crystal mixtures containing the coleopteran-active Cry3Aa toxin. Results revealed lower amount of proteins involved in insect growth and higher amount of immune response-related proteins in challenged insects, sustaining the larval weight loss observed. Additionally, we found a potential regulatory role of the evolutionary conserved miR-8 in the insect's immune response relying on antimicrobial peptides (AMPs) production. Upon toxin challenge, different patterns of hemolymph AMPs expression and phenoloxidase activity were observed in CPB larvae reared on different Solanaceae plants. This suggests that diet and diet-associated insect midgut microbiota might modulate this insects' tolerance to non-lethal doses of Bt.

Oxylipin mediated stress response of a miraculin-like protease inhibitor in Hexanoic acid primed eggplant plants infested by Colorado potato beetle.

Insect-plant interactions are governed by a complex equilibrium between the mechanisms through which plant recognize insect attack and orchestrate downstream signaling events that trigger plant defense responses, and the mechanisms by which insects overcome plant defenses. Due to this tight and dynamic interplay, insight into the nature of the plant defense response can be gained by analyzing changes in the insect herbivores digestive system upon plant feeding. In this work we have identified a Solanum melongena miraculin-like protease inhibitor in the midgut juice of Colorado potato larvae feeding on eggplant plants treated with the natural inducer of plant defenses hexanoic acid. We analyzed the corresponding gene expression by qRT-PCR and our results showed that this eggplant miraculin-like gene enhanced induction contributes to the hexanoic acid priming effect in this Solanaceae species. Moreover, our data evidencing that OPDA might be involved in this gene regulation highlights its potential as biomarker in eggplant plant responses to stress mediated this oxylipin signaling pathway.

Tribolium castaneum immune defense genes are differentially expressed in response to Bacillus thuringiensis toxins sharing common receptor molecules and exhibiting disparate toxicity.

In Tribolium castaneum larvae we have demonstrated by RNA interference knockdown that the Bacillus thuringiensis Cry3Ba toxin receptors Cadherin-like and Sodium solute symporter proteins are also functional receptors of the less active Cry3Aa toxin. Differences in susceptibility to B. thuringiensis infection might not only rely on toxin-receptor interaction but also on host defense mechanisms. We compared the expression of the immune related genes encoding Apolipophorin-III and two antimicrobial peptides, Defensin3 and Defensin2 after B. thuringiensis challenge. All three genes were up-regulated following Cry3Ba spore-crystal intoxication whereas only Defensins gene expression was induced upon Cry3Aa spore-crystal treatment, evidencing a possible association between host immune response and larval susceptibility to B. thuringiensis. We assessed the antimicrobial activity spectra of T. castaneum defensins peptide fragments and found that a peptide fragment of Defensin3 was effective against the human microbial pathogens, Escherichia coli, Staphylococcus aureus and Candida albicans, being S. aureus the most susceptible one.