Tissue-specific and stress-enhancing expression of the TR promoter for mannopine synthase in transgenic medicinal plants

Transgenic tobacco (Nicotiana tabacum L.), licorice (Glycyrrhiza uralensis Fisher) and foxglove (Digitalis purpurea L.) were obtained with binary vector systems based on a disarmed Agrobacterium tumefaciens and on a virulent A. rhizogenes. The chimeric neomycin phosphotransferase II (NPT-II) gene (kan) and the beta-glucuronidase (GUS) gene (uidA) were under the control of the TR1' and 2' promoters, respectively, on a binary vector, pGSGluc1. Tissue-specific expression of the chimeric TR2' -uidA gene was studied using regenerants of N. tabacum from transformed callus and hairy roots, and also using the transformed roots of G. uralensis and B. purpurea. In all these transformed tissues, the phloem and surrounding tissues were stained with 5-bromo-4-chloro-3-indolyl-beta-D- glucuronide showing the specific expression of uidA. The enzymatic assays of NPT-II and GUS indicated that the expression of both TR1'-kan and TR2'-uidA were coordinately enhanced by wounding and by the addition of plant growth regulators. These results indicate that the gene expression by the dual TR promoters is regulated in the several plant species studied in a tissue-specific manner and enhanced by physiological stresses.