From 1983 to 2006, the development of biotech crops is very rapid. The first transgenic plant is the tomato appearing. The number of countries planting biotech crops increased from 21 to 22. The global area of biotech crops continued to climb reaching 102 million hectares (252 million acres). This is a historical landmark in that it is the first time for more than 100 million hectares of biotech crops to be grown in any one year. In 2006, herbicide tolerance, deployed in soybean, maize, canola, cotton and alfalfa occupied 68% or 69.9 million hectares of the global biotech 102 million hectares and 13.1 million hectares (13%) to the stacked traits of Bt and herbicide tolerance. It is noteworthy that the glyphosate tolerance has been the dominant trait of the herbicide tolerance.Glyphosate was used worldwide. Glyphosate inhibits the enzyme 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase. EPSP synthase is the sixth enzyme of the shikimic acid pathway, which is essential for the biosynthesis of aromatic amino acids in algae, higher plants, bacteria, and fungi. EPSP synthase catalyzes the conversion of shikimate-3-phosphate (S3P) and phosphoenolpyruvate (PEP) to yield EPSP and inorganic phosphate(Pi). Glyphosate is a competitive inhibitor of PEP, as it occupies the binding site of PEP, mimicking an intermediate state of the ternary enzyme-substrates complex.Glyphosate-toleran soybean, maize, oilseed plants, cotton and alfalfa have been commercialized and Glyphosate-toleran wheat, sugarbeet and Creeping bentgrass have been developed. The study about glyphosate tolerante crops is lagging and hasn't obtained intellectual property rights in China. Consequently development of glyphosate-tolerant transgenic tobacco and cotton by Introducing EPSPS gene is significant.The target gene used in this study was the EPSP synthase encoding gene aroAG2M which was cloned from Pseudomonas fluorescens G2 strain and modified with dicotyledonous plant-preferred codon usage. Plant expression vector was constructed by adding a chloroplast signal peptide at the 5' end of the target gene and hooked with the chrysanthemum Rubisco small subunit promoter. Transgenic tobacco plants obtained via Agrobacterium-mediated leaf disc transformation were confirmed by PCR analysis. Leaves of transgenic and non-transgenic tobacco plants at 6-8 leaf stage were daubed with different concentrations of glyphosate. Results showed that the transgenic tobacco was tolerant to glyphosate up to 4‰concentration, while the non-transgenic plants died at the concentration of 2‰. The plasmid of plant expression vector was also used for cotton transformation by pollen tube pathway method. PCR and Southern blot analysis of transgenic cotton showed that the target gene was integrated into cotton genome. To date, three transgenic cotton plants of T1 generation have been obtained which show tolerance to the herbicide glyphosate. |