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.
| Original language | English (US) |
|---|---|
| Journal | Pest Management Science |
| DOIs | |
| State | Accepted/In press - Jan 1 2018 |
Fingerprint
Keywords
- Bacillus thuringiensis
- bollworm
- Bt crops
- cotton
- Cry1Ac protoxin
- genetically engineered
- Helicoverpa zea
ASJC Scopus subject areas
- Agronomy and Crop Science
- Insect Science
Cite this
Decreased Cry1Ac activation by midgut proteases associated with Cry1Ac resistance in Helicoverpa zea. / Zhang, Min; Wei, Jizhen; Ni, Xinzhi; Zhang, Jie; Jurat-Fuentes, Juan L.; Fabrick, Jeffrey A.; Carriere, Yves; Tabashnik, Bruce E; Li, Xianchun.
In: Pest Management Science, 01.01.2018.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Decreased Cry1Ac activation by midgut proteases associated with Cry1Ac resistance in Helicoverpa zea
AU - Zhang, Min
AU - Wei, Jizhen
AU - Ni, Xinzhi
AU - Zhang, Jie
AU - Jurat-Fuentes, Juan L.
AU - Fabrick, Jeffrey A.
AU - Carriere, Yves
AU - Tabashnik, Bruce E
AU - Li, Xianchun
PY - 2018/1/1
Y1 - 2018/1/1
N2 - 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.
AB - 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.
KW - Bacillus thuringiensis
KW - bollworm
KW - Bt crops
KW - cotton
KW - Cry1Ac protoxin
KW - genetically engineered
KW - Helicoverpa zea
UR - http://www.scopus.com/inward/record.url?scp=85055880887&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85055880887&partnerID=8YFLogxK
U2 - 10.1002/ps.5224
DO - 10.1002/ps.5224
M3 - Article
C2 - 30264537
AN - SCOPUS:85055880887
JO - Pest Management Science
JF - Pest Management Science
SN - 1526-498X
ER -