Integration and inheritance stability of foreign Bt toxin gene in the bivalent insect-resistant transgenic cotton plants

Genetic and expressional stability of Bt toxin gene is crucial for the breeding of insect-resistant transgenic cotton varieties and their commercialization. Genomic Southern blot analysis of R-3, R-4 and R-5 generations of bivalent transgenic insect-resistant cotton plants was done in order to determine the integration, the copy number and the inheritance stability of Bt toxin gene in the transgenic cotton plants. The results Indicated that there was a 4.7 kb positive band in the Southern blot when the genomic DNA of the bivalent transgenic Insect-resistant cotton plants and the positive control (the plasmid) were digested with Hind III respectively. This result proved that the Bt toxin gene had been integrated into the genome of the cotton in full length. There is only one Xho I restriction site in the Bt toxin gene. Southern blot analysis indicated that many copies of Bt toxin gene had been integrated into the genome of the cotton when the genomic DNA of transgenic plants was digested with Xho I. Among them, there were four copies (about 17.7, 8, 5.5 and 4.7 kb in size) existing in all the tested plants of R-3, R-4 and R-5 generations. The preliminary conclusion was that there were more than four copies of Bt toxin gene integrated into the genome of the cotton, among them, more than one copy can express and inherit steadily. This result provides a scientific basis for the breeding of the bivalent insect-resistant transgenic cotton plants and its commercialization.