Bollgard II cotton expresses which genes?
Bollgard II represents stacked trait strategy designed to delay resistance and broaden insecticidal spectrum. First generation Bollgard expressing only Cry1Ac selected resistance alleles in Helicoverpa armigera under continuous exposure. Incorporating second toxin Cry2Ab with different binding site, recognizing distinct aminopeptidase N and ABC transporter, requires insects to carry simultaneous mutations in two receptors to survive, probability drastically lower. Both genes driven by enhanced constitutive promoters provide high dose exceeding LD99 for heterozygous susceptible larvae. Expression occurs in squares, bolls, and leaves protecting whole season. Commercial cultivation since 2003 showed reduced insecticide applications, preservation of beneficial predators, and improved yield. Stacking Cry1Ac plus Cry2Ab exemplifies gene pyramiding concept central to insect resistance management guidelines mandated by EPA for transgenic cotton deployment and maintenance of technology durability against lepidopteran pests. Molecular analysis shows Cry1Ac expression 2 to 5 micrograms per gram fresh weight in leaves, Cry2Ab slightly lower but additive. Insect bioassays with Helicoverpa zea second instar larvae fed on Bollgard II leaves cause complete mortality within 5 days compared to 50 percent mortality on single toxin line. Adoption data indicates reduced insecticide load and improved environmental impact quotient. Therefore combination Cry1Ac plus Cry2Ab exemplifies successful gene stacking delaying resistance
Ref: ISAAA Brief 43 Bollgard II; Tabashnik Nat Biotechnol 2009 pyramiding; NCBI NBK24601 Cry1Ac Cry2Ab; https://www.isaaa.org/resources/publications/briefs/43/