Introduction and Expression of a Thaumatin-like Protein from Rice in American Ginseng Following Agrobacterium-mediated Transformation

Agrobacterium-mediated transformation of American ginseng (Panax quinquefolius L.) with strain LBA 4404 containing a rice thaumatin-like protein gene is described. The selectable markers used were phosphinothricin acetyltransferase and hygromycin phosphotransferase genes. Epicotyl explants from seedlings were precultured for 5-7 days on Murashige and Skoog medium with ${\alpha}$-naphthaleneacetic acid and 2,4 dichlorophenoxyacetic acid at 10 ${\mu}$M and 9 ${\mu}$M, respectively (ND medium), prior to Agrobacterium infection. The explants were immersed in a bacterial suspension for 20 min. A post-infection co-culture period of 3-4 days was provided on ND medium. Selection for transformed calli was conducted on ND medium with 20 mg/L phosphinothricin followed by 100 mg/L hygromycin over an 8-month period. it transformation frequency of 24.8% was achieved at the callusing phase. The presence of the transgenes in calli was confirmed by Southern hybridization and polymerase chain reaction analysis. The expression of the thaumatin-like protein gene in ginseng calli was demonstrated by Western blot analysis. Somatic embryos were produced from both transgenic calli and suspension cultures, and plantlets were recovered that expressed the transgenic thaumatin-like protein gene.