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Decreased Cry1Ac activation by midgut proteases associated with Cry1Ac resistance in Helicoverpa zea
- Source :
- Pest management science. 75(4)
- Publication Year :
- 2018
-
Abstract
- BACKGROUND Field-evolved resistance of Helicoverpa zea to Bacillus thuringiensis (Bt) toxin Cry1Ac was first reported more than a decade ago, yet the underlying mechanisms remain elusive. Towards understanding the mechanisms of resistance to Cry1Ac, we analyzed a susceptible (LAB-S) and two resistant (GA and GA-R) strains of H. zea. The GA strain was derived from Georgia and exposed to Bt toxins only in the field. The GA-R strain was derived from the GA strain and selected for increased resistance to Cry1Ac in the laboratory. RESULTS Resistance to MVPII, a liquid formulation containing a hybrid protoxin similar to Cry1Ac, was 110-fold for GA-R and 7.8-fold for GA relative to LAB-S. In midgut brush border membrane vesicles, activity of alkaline phosphatase and aminopeptidase N did not vary significantly among strains. The activity of total proteases, trypsin-like proteases and chymotrypsin-like proteases was significantly lower for GA-R and GA than LAB-S, but did not differ between GA-R and GA. When H. zea midgut cells were exposed to Cry1Ac protoxin that had been digested with midgut extracts, toxicity was significantly lower for extracts from GA-R and GA relative to extracts from LAB-S, but did not differ between GA-R and GA. Transcriptional analysis showed that none of the five protease genes examined was associated with the decline in Cry1Ac activation in GA-R and GA relative to LAB-S. CONCLUSION The results suggest that decreased Cry1Ac activation is a contributing field-selected mechanism of resistance that helps explain the reduced susceptibility of the GA-R and GA strains. Relative to the LAB-S strain, the two Cry1Ac-resistant strains had lower total protease, trypsin and chymotrypsin activities, a lower Cry1Ac activation rate, and Cry1Ac protoxin incubated with their midgut extracts was less toxic to H. zea midgut cells. © 2018 Society of Chemical Industry.
- Subjects :
- 0106 biological sciences
Proteases
Insecticides
medicine.medical_treatment
Bacillus thuringiensis
Moths
01 natural sciences
Insecticide Resistance
Hemolysin Proteins
Bacterial Proteins
medicine
Animals
chemistry.chemical_classification
Protease
biology
Bacillus thuringiensis Toxins
fungi
Midgut
General Medicine
biology.organism_classification
Trypsin
Molecular biology
Endotoxins
Gastrointestinal Tract
010602 entomology
Enzyme
chemistry
Cry1Ac
Insect Science
Larva
Insect Proteins
Helicoverpa zea
Agronomy and Crop Science
010606 plant biology & botany
medicine.drug
Peptide Hydrolases
Subjects
Details
- ISSN :
- 15264998
- Volume :
- 75
- Issue :
- 4
- Database :
- OpenAIRE
- Journal :
- Pest management science
- Accession number :
- edsair.doi.dedup.....c5e8b88c6715f5db8e12e7149f73ad36