YieldGard™ VT™ Rootworm/RR2™ Maize

Corn rootworm-resistant maize line MON88017 was produced using recombinant-DNA techniques to express the cry3Bb1 gene encoding a Coleopteran-specific insecticidal protein from Bacillus thuringiensis (subsp. kumamotoensis) in order to control infestation with corn root worm, and the cp4 epsps gene from the soil bacterium Agrobacterium ssp. strain CP4.

PV-ZMIR39

The wild-type cry3Bb1 coding sequence was modified to encode six specific amino acid substitutions, resulting in the synthetic cry3Bb1 coding sequence present in the vector. The differences at the six positions are: 2A (insertion), H232R, S312L, N314T, E318K, Q349R.

Molecular analyses of MON 88017 confirmed that single copies of the cp4 epsps and cry3Bb1 genes are integrated at a single locus in the corn genome with all expression elements intact and no plasmid bacterial backbone present. Plasmid PV-ZMIR39 contains the left and right transfer DNA (T-DNA) border sequences that facilitate transformation.

The cry3Bb1 gene encodes the insect control protein Cry3Bb1, a delta-endotoxin. The toxin protects the plant from the Coleopteran insects western corn rootworm (Diabrotica virgifera), northern corn rootworm (D. barberi), and Mexican corn rootworm (D. virgifera zeae).  Cry proteins, of which Cry3Bb1 is only one, act by selectively binding to specific sites localized on the lining of the midgut of susceptible insect species. Following binding, pores are formed that disrupt midgut ion flow, causing gut paralysis and eventual death due to bacterial sepsis. Cry3Bb1 is lethal only when eaten by Coleopteran species, including corn root worm, and its specificity of action is directly attributable to the presence of specific binding sites in the target insects. There are no binding sites for the delta-endotoxins of B. thuringiensis on the surface of mammalian intestinal cells, therefore, livestock animals and humans are not susceptible to these proteins.

The cp4 epsps gene encodes for a form of the plant enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) that is highly tolerant to inhibition by glyphosate.