Analysis of defense mechanism against Agrobacterium-reinfection in plants regenerated from hairy roots.

点击翻译按钮获取中文摘要

Agrobacterium rhizogenes 15834 and Agrobacterium tumefaciens LBA4404 harboring pBI121 infected tobacco BY-2 cells, forming hairy root cells and kanamycin-resistant (Km^R) cells, respectively. However, no Km^R-transformant of hairy root cells was obtained by introducing the neomycin phosphotransferase II (NPT II) gene on the T-DNA of pBI121 into the hairy root cells, although the hairy root cells of Km^R clones were obtained by introducing Ri T-DNA into Km^R clones. The similar results were obtained using the wild-type tobacco plant, the plants regenerated from hairy root clones and Km^R transgenic plants of Nicotiana plumbaginifolia.These transformation experiments suggest that transgenic plants which have been already transformed by Ri T-DNA cannot undergo a second Agrobacterium-mediated T-DNA transformation. Plants carrying Ri T-DNA,which is integrated into the host chromosome analogously with lambda phage DNA,are possibly immune to further infection with Agrobacteria.Both characteristics of the kanamycin resistance and the phytohormone-independent growth were stably maintained in the hairy root clones derived from the Km^R transgenic plants after culturing in the medium without kanamycin for 8 months. These results show that two types of T-DNA coexist and the genes on the T-DNAs are normally expressed in the plant genome.When NPT II gene was directly introduced into the tobacco protoplasts by electroporation, Km^R cells were obtained from BY-2 cells but not from the hairy root cells. The process of infection with Agrobacteria can be separated into the four stages ; (1) Attachment to the plant cells, (2) T-DNA transfer to the plant cells, (3)T-DNA integration into the plant genome, and (4) Gene expression from the integrated T-DNA.These results show that the "immune" response in the plant cells carrying Ri T-DNA may be occurred in the stage of T-DNA integration into the plant genome.