Wild-type Agrobacterium rhizogenes-mediated gene transfer in plants: Agrobacterium virulence and selection of transformants

Abstract

Agrobacterium rhizogenes ATCC 15834 wild type strain was transformed with the binary vector pBI121 using the heat shock method. The transformed Agrobacterium was then tested for virulence through tobacco leaf explant transformation. Compared to the non-transformed Agrobacterium, the transformed Agrobacterium showed reduced virulence, producing significantly lower number of hairy roots in tobacco leaf explants. Although the transformed Agrobacterium showed reduced virulence, it was able to transfer the T-DNA of the binary vector into the plant genome, resulting in stable GUS expression in the generated hairy roots. This indicated that in addition to the transfer DNA (T-DNA) from its root inducing (Ri) plasmid, the transformed Agrobacterium is also capable of transferring the binary vector T-DNA and allowing the integration of a foreign gene. Results also showed that hairy root generation efficiency of the transformed Agrobacterium varied with the concentration of the selection agent (kanamycin). Hairy root generation efficiency (hairy roots·explant-1) progressively increased with decreasing concentrations of kanamycin; and the efficiency was highest in the absence of kanamycin. Generated hairy roots showed very strong to tiny GUS expression even those that grew under the highest concentration of the kanamycin (50 mg·L-1). This indicated that co-transformation and efficient transgene expression does not always occur.