ABSTRACT
In the previous decades, many methodologies were developed to introduce or move a wide variety of genes from one species into another. Many of these techniques have been discussed in other chapters and will not be considered further in this chapter. However in the following experiments, we will use Agrobacterium tumefaciens, a soil-inhabiting, pathogenic (disease-causing) bacterium occurring naturally in many areas of the world, as the agent/vector or shuttle that transfers gene(s) between the two species. This bacterium can be aptly described as nature’s own and the original genetic engineer since during pathogenesis (disease development) several genes located on a plasmid (a small circular piece of DNA) within the bacterium are delivered and incorporated into the genome of host plant cells. These genes cause an unusually high number of host cell divisions (hyperplasia) to occur and, as a result, a tumor or gall is formed. Hence, the common name of the disease is crown gall. We can take advantage of this natural gene delivery system. Via molecular biological techniques, genes that incite disease can be removed from the t-DNA region of the plasmid and replaced with gene(s) and promoters of our choice.
