Evaluation of in vitro and in vivo effects of semipurified proteinase inhibitors from Theobroma seeds on midgut protease activity of Lepidopteran pest insects

TcTI, a Kunitz-type trypsin inhibitor from cocoa associated with defense against pathogens

Protease inhibitors (PIs) are important biotechnological tools of interest in agriculture. Usually they are the first proteins to be activated in plant-induced resistance against pathogens. Therefore, the aim of this study was to characterize a Theobroma cacao trypsin inhibitor called TcTI. The ORF has 740 bp encoding a protein with 219 amino acids, molecular weight of approximately 23 kDa. rTcTI was expressed in the soluble fraction of Escherichia coli strain Rosetta [DE3]. The purified His-Tag rTcTI showed inhibitory activity against commercial porcine trypsin. The kinetic model demonstrated that rTcTI is a competitive inhibitor, with a Ki value of 4.08 × 10-7 mol L-1. The thermostability analysis of rTcTI showed that 100% inhibitory activity was retained up to 60 °C and that at 70-80 °C, inhibitory activity remained above 50%. Circular dichroism analysis indicated that the protein is rich in loop structures and β-conformations. Furthermore, in vivo assays against Helicoverpa armigera larvae were also performed with rTcTI in 0.1 mg mL-1 spray solutions on leaf surfaces, which reduced larval growth by 70% compared to the control treatment. Trials with cocoa plants infected with Mp showed a greater accumulation of TcTI in resistant varieties of T. cacao, so this regulation may be associated with different isoforms of TcTI. This inhibitor has biochemical characteristics suitable for biotechnological applications as well as in resistance studies of T. cacao and other crops.

Higher Activities of Defense-Associated Enzymes may Contribute to Greater Resistance of Manchurian Ash to Emerald Ash Borer Than A closely Related and Susceptible Congener

Emerald ash borer (EAB) is an invasive beetle native to Asia that infests and kills ash (Fraxinus spp.) in North America. Previous experiments indicated that larvae feeding on co-evolved, resistant Manchurian ash (F. mandshurica) have increased antioxidant and quinone-protective enzyme activities compared to larvae feeding on susceptible North American species. Here, we examined mechanisms of host-generated oxidative and quinone-based stress and other putative defenses in Manchurian ash and the closely related and chemically similar, but susceptible, black ash (F. nigra), with and without exogenous application of methyl jasmonate (MeJA) to induce resistance mechanisms. Peroxidase activities were 4.6-13.3 times higher in Manchurian than black ash, although both species appeared to express the same three peroxidase isozymes. Additionally, peroxidase-mediated protein cross-linking activity was stronger in Manchurian ash. Polyphenol oxidase, β-glucosidase, chitinase, and lipoxygenase activities also were greater in Manchurian ash, but only lipoxygenase activity increased with MeJA application. Phloem H₂O₂ levels were similar and were increased by MeJA application in both species. Lastly, trypsin inhibitor activity was detected in methanol and water extracts that were not allowed to oxidize, indicating the presence of phenolic-based trypsin inhibitors. However, no proteinaceous trypsin inhibitor activity was detected in either species. In response to MeJA application, Manchurian ash had higher trypsin inhibitor activity than black ash using the unoxidized water extracts, but no treatment effects were detected using methanol extracts. Based on these results we hypothesize that peroxidases, lignin polymerization, and quinone generation contribute to the greater resistance to EAB displayed by Manchurian ash.

Comparative analysis of expression profiling of the trypsin and chymotrypsin genes from Lepidoptera species with different levels of sensitivity to soybean peptidase inhibitors

Peptidase inhibitors (PIs) are essential proteins involved in plant resistance to herbivorous insects, yet many insect species are able to escape the negative effects of these molecules. We compared the effects of acute and chronic ingestion of soybean peptidase inhibitors (SPIs) on Spodoptera frugiperda and Diatraea saccharalis, two Lepidoptera species with different sensitivities to SPI ingestion. We analyzed the trypsin and chymotrypsin gene expression profiles in both species. Acute exposure of S. frugiperda to the inhibitors activated seven genes (SfChy5, SfChy9, SfChy19, SfChy22, SfTry6, SfTry8, and SfTry10), whereas chronic exposure activated 16 genes (SfChy2, SfChy4, SfChy5, SfChy8, SfChy9, SfChy11, SfChy12, SfChy15, SfChy17, SfChy21, SfChy22, SfTry6, SfTry8, SfTry9, SfTry10, and SfTry12). By contrast, the challenge of D. saccharalis with SPIs did not differentially induce the expression of trypsin- or chymotrypsin-encoding genes, with the exception of DsChy7. Bayesian phylogenetic analysis of S. frugiperda trypsin protein sequences revealed two gene clades: one composed of genes responsive to the SPIs and a second composed of the unresponsive genes. D. saccharalis trypsin proteins were clustered nearest to the S. frugiperda unresponsive genes. Overall, our findings support a hypothesized mechanism of resistance of Noctuidae moths to SPIs, involving gene number expansion of trypsin and chymotrypsin families and regulation of gene expression, which could also explain the variable susceptibility between S. frugiperda and D. saccharalis to these plant inhibitors.