Abstract
Transgenic cotton plants expressing a novel cry2AX1 gene consisting of sequences from the cry2Aa and cry2Ac genes, driven by the CaMV35S or the EnCaMV35S promoters, were generated through Agrobacterium-mediated transformation. Among 40 independent PCR-positive events, 14 produced Cry2AX1 protein at detectable levels. Cry2AX1 levels in T-0 plants ranged from 0.012 to 1.068 mu g/g fresh leaf tissue. Insect bioassays on Cry2AX1-expressing T-0 transgenic lines showed 27.0 to 88.8% mortality of Helicoverpa armigera. Southern hybridization analysis revealed single locus integration of the cry2AX1 gene in two T-0 plants which caused 87.5 and 88.8% mortality in H. armigera. The presence and expression of the cry2AX1 gene were confirmed in T-1 progeny using PCR and quantitative ELISA. The highest expression level of Cry2AX1 protein recorded in the T-1 generation was 0.766 mu g/g fresh leaf tissue, far less than the expression of Cry2Ab protein (23 mu g/g leaf tissue) reported in the commercialized Bt cotton, Bollgard II. In spite of the low Cry2AX1 level, the mortality against H. armigera ranged between 33.3 and 85.7% in the T-1 generation. These results indicate that this novel cry2AX1 gene produced a potent insecticidal protein that was effective against H. armigera in transgenic cotton plants at very low concentrations.