Agrobacterium-mediated Plant Transformation: a Scientifically Intriguing Story with Significant Applications

The most widely used method for the introduction of new genes into plants is based on the natural DNA transfer capacity of Agrobacterium tumefaciens. Over the past decades, intensive studies on the mechanism of T-DNA transfer have resulted in a reasonably detailed insight into this process. This research revealed that the genetic transformation of plant cells by Agrobacterium evolved by adaptation of processes that existed long before the evolution of the plant–Agrobacterium association. This conclusion holds true for the two-component signal transduction system leading to induction of the virulence genes and for the mechanism responsible for T-DNA transfer to plant cells, which is very similar to that of bacterial conjugation. Integration of the T-DNA in the plant chromosomes is accomplished by the plant’s illegitimate recombination system, but with the help of agrobacterial proteins, which enhance the precision and the efficiency of the integration process. This chapter starts with an overview of the current knowledge on the molecular basis of Agrobacterium-mediated plant transformation. The main emphasis is on the role of the virulence proteins and on recent insights into the later steps of the transformation process. Then, a summary is given on the characteristics of the T-DNA inserted into the plant nuclear DNA. The chapter concludes with a critical assessment of the different approaches that have been used to exploit Agrobacterium tumefaciens, a natural “engineer”, for the production of transgenic plants.