Xylose Selection System Used For Cucumber Transformation

With transgenic plant commercialization, the bio-safety of transgenic plants, especially the antibiotic genes as the selection marker are more and more concerned by public. People are worrying about these antibiotic genes, since these anti-genes may harm not only to environment but also to our health.The nptII, hpt, and bar genes are widely used in plant transformation, however, they may cause some harmful effects, since transformed cells are able to survive in the medium with antibiotic and herbicide. These marker genes contain some bio-safety issues. Therefore, positive selection system is important to genetic engineering.The xylose selection system is a safe way for selection, and the xylose isomerase gene XylA is a positive selective marker. In my experiment, we set up a procedure of agrobacterium-mediated cucumber transformation by xylose selection. We get the transgenic cucumber with GUS gene in this sysytem. The plant expression vector pX390-scFv was constructed in this study. In this procedure, cucumber cotoledon were used for explant, which was inoculated with Agrobacterium tumefaciens LBA4404 containing the binary vector. Selection medium contained 1 mg/ml 2ip and 1 mg/ml 2,4-D, 15g/L xylose and 15g/L sucrose, which changed to 0.3mg/ml 2ip when callus grew. We obtained positive transgenic plants detected by PCR and GUS staining.