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ARS Home » Southeast Area » Tifton, Georgia » Crop Genetics and Breeding Research » Research » Publications at this Location » Publication #326385
Title: Decreased Cry1Ac activation by midgut proteases associated with Cry1Ac resistance in Helicoverpa zea

Author
item ZHANG, MIN - University Of Arizona
item WEI, JIZHEN - University Of Arizona
item Ni, Xinzhi
item ZHANG, JIE - Chinese Academy Of Sciences
item JURAT-FUENTES, JUAN - University Of Tennessee
item Fabrick, Jeffrey
item CARRIERE, YVES - University Of Arizona
item TABASHNIK, BRUCE - University Of Arizona
item LI, XIANCHUN - University Of Arizona

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2018
Publication Date: 4/1/2019
Citation: Zhang, M., Wei, J., Ni, X., Zhang, J., Jurat-Fuentes, J.L., Fabrick, J.A., Carriere, Y., Tabashnik, B.E., Li, X. 2019. Decreased Cry1Ac activation by midgut proteases associated with Cry1Ac resistance in Helicoverpa zea. Pest Management Science. 75(4):1099-1106. https://doi.org/10.1002/ps.5224.
DOI: https://doi.org/10.1002/ps.5224

Interpretive Summary: Reduced activation of a bacterial protoxin Cry1Ac by midgut enzymes that digest proteins (i.e., total proteases, trypsin, or chymotrypsin) was evaluated as a potential mechanism of bacterial toxin resistance in two strains (namely GA and GA-R, respectively) of the corn earworm. Whereas the GA strain had field-evolved Cry1Ac resistance, GA-R strain was derived from the GA strain that was further exposed to the toxin, and acquired additional resistance to the toxin in the laboratory. These two strains of the corn earworm did not differ significantly in activity of three types of midgut enzymes, activation of the bacterial protoxin, mortality of corn earworm midgut cells caused by Cry1Ac protoxin activated by the midgut extracts. When the GA and GA-R strains were compared to a susceptible laboratory strain (LAB-S), both GA and GA-R strains had significantly lower activity of the three enzymes and lower mortality of corn earworm midgut cells caused by Cry1Ac protoxin activated by midgut extracts. Activation of Cry1Ac protoxin to the 62 kDa toxin band but not to the 67 kDa toxin band by midgut extracts was significantly lower in GA and GA-R than LAB-S. None of the five protease genes further examined showed lower transcription in GA or GA-R when compared to the susceptible LAB-S strain. Combining with previous results indicating Cry1Ac resistance in the corn earworm did not differ between the protoxin and the activated toxin, the findings from the current study imply that reduced activation of the protoxin may not be a major mechanism of Cry1Ac resistance in the corn earworm strains examined.

Technical Abstract: We evaluated reduced activation of Cry1Ac protoxin as a potential mechanism of resistance in two strains of Helicoverpa zea (GA and GA-R). Whereas GA had field-evolved resistance, GA-R was derived from GA and selected for additional resistance to Cry1Ac in the laboratory. These two strains did not differ significantly in activity of total proteases, trypsin, or chymotrypsin; activation of Cry1Ac protoxin; or mortality of H. zea midgut cells caused by Cry1Ac protoxin activated by midgut extracts. Relative to an unrelated susceptible laboratory strain (LAB-S), both GA and GA-R had significantly lower activity of total proteases, trypsin, and chymotrypsin; and lower mortality of H. zea midgut cells caused by Cry1Ac protoxin activated by midgut extracts. Activation of Cry1Ac protoxin to the 62 kDa toxin band but not to the 67 kDa toxin band by midgut extracts was significantly lower in GA and GA-R than LAB-S. None of the five protease genes examined had lower transcription in GA and GA-R relative to LAB-S. Together with previously reported data indicating resistance was not higher to Cry1Ac protoxin than activated toxin, the results imply that reduced activation of Cry1Ac protoxin is not a major mechanism of resistance in the strains examined in the current study.