Identification of a New cry1I -Type Gene as a Candidate for Gene Pyramiding in Corn To Control Ostrinia Species Larvae

Pyramiding of diversecry toxin genes fromBacillus thuringiensis with different modes of action is a desirable strategy to delay the evolution of resistance in the European corn borer (Ostrinia nubilalis ). Considering the dependency of susceptibility to Cry toxins on toxin binding to receptors in the midgut of target pests, a diverse mode of action is commonly defined as recognition of unique binding sites in the target insect. In this study, we present a novelcry1Ie toxin gene (cry1Ie2 ) as a candidate for pyramiding with Cry1Ab or Cry1Fa in corn to controlOstrinia species larvae. The new toxin gene encodes an 81-kDa protein that is processed to a protease-resistant core form of approximately 55 kDa by trypsin digestion. The purified protoxin displayed high toxicity toOstrinia furnacalis andO. nubilalis larvae but low to no activity againstSpodoptera or heliothine species or the coleopteranTenebrio molitor . Results of binding assays with125 I-labeled Cry1Ab toxin and brush border membrane vesicles fromO. nubilalis larvae demonstrated that Cry1Ie2 does not recognize the Cry1Ab binding sites in that insect. Reciprocal competition binding assays with biotin-labeled Cry1Ie2 confirmed the lack of shared sites with Cry1Ab or Cry1Fa inO. nubilalis brush border membrane vesicles. These data support Cry1Ie2 as a good candidate for pyramiding with Cry1Ab or Cry1Fa in corn to increase the control ofO. nubilalis and reduce the risk of resistance evolution.