Study On Expression And Influencing Factor Of BT Insecticidal Protein In Transgenic Insect-resistant Cotton

Expression of foreign gene in plants is affected by many factors, such as the insertion site, copy numbers, the external environment et al. In applications, however, the popular topic is whether the expression of foreign genes can achieve the desired results. The artificially modified foreign genes of Cry1Ab/Ac and CpTI were transferred to cotton that is the most important cash crop in China, and were commercialization and industrialization of development. In recent years, some farmers founded the phenomenon that the cotton of transferred Bt couldn't resisted the cotton bollworm, Heliothis armigera. In some districts of Shandong, insects overflow was found even in the fields of transgenic cotton. To solve these problems and clarify the nature of insect-resistant cotton, one side, we had collected the current varieties in three major production region of China and comprehensively analyzed the temporal and spatial expression of Bt insecticidal protein. The other side, we used different generation of transgenic cotton, family materials and different degree of seed purity to analysis several factors of influence expression of insecticidal protein such as environment, genetic background and mixed varieties. Lastly, the safety evaluation, initial detection and monitoring environmental release of transgenic cotton were analyzed using 102 cultured varieties (lines) of China in 2008 and 2009. The important findings were followed.1) Expression BT protein in transgenic cotton in China was specificity of temporal and spatial. The trend of BT protein in all varieties was higher at early growing development stage and lower at late stage. And the content of BT protein was significant different in different tissues and at different developmental stages, the content of expression in leaf was highest, that in bud was second, that in flower was third, that in boll was lowest. Among three cotton region, average level of BT protein didn't showed significantly difference. But the content of BT protein in the bud and boll of U.S. cotton varieties were significantly higher than that average level of transgenic varieties in China, but were lower than that of Nankang3 and CK (GK12,sGK321).2) Using different generation of transgenic materials, the content of BT protein in different tissue at different stage were change with generation number raised. But the diffence was not significant. It indicated that the generation number could be influence the content of BT content, but the degree of influence was low. At the same time, we found that the degree of influence was different with generation number under different genetic background.3) Compared two set of pedigree materials, the content of BT protein in L2000-2 and L169 origined Northwest inland region were significantly higher than that of Lu family cotton origined Yellow River Basin. So, it indicated that the genetic background was one factor to influence BT content. In addition, we analyzed many materials with different background and the result showed that environment was another factor to influence BT content and the effects of environment was be affected by genetic background.4) The experiment of mix varieties showed that cotton bollworm damage level was gradually increased, the mortality rate of H. armigera was decreased and the yield was significantly reduced with seed purity decreased. And the factors of yield reduction were result from declining in insect resistance, the number of fruit branches and boll number. In conclusion, the decline of seed purity had significant effection on insect resistance and cotton yeild.5) By modified safety assessment testing and monitoring, the BT content in improved varieties wasn't significant difference with that of local main varieties. It showed that the improved varieties had better resistance on cotton bollworm because the average corrected mortality of cotton bollworm was above 80% and the hazard level was lower than 2.In summary, the expression of BT insecticidal protein in transgenic Bt cotton had been comprehensively analyzed using 30 transgenic Bt cotton varieties in China and 1 transgenic cotton in American. These commercial varieties had high expression level of BT protein and had better resistance on cotton bollworm. So, we considered that the phenomenon of "Insect-resistant cotton is not" could only be caused by mixed species. From different generation and genealogy materials, we further proved that the environmental and genetic background had influence on expression of insecticidal protein. This study provided a theoretical basis about seed selection of high insect-resistant cotton varieties for breeders. The results of safety assessment showed that the environmental release of transgenic cotton was safety. But the further study will be done.