Agrobacterium tumefaciens , a bacterial species found in temperate soils worldwide, is the causative agent of crown gall disease on many plants. The disease is called crown gall because it typically occurs at the crown of the plant, where the stem emerges from the soil. Small wounds at the crown, usually due to wind-induced bending, are potential entry sites for the bacterium. Once inside these wounds, the bacterium can cause disease if it is induced by compounds released from actively growing plant cells. Gall is a synonym for tumor.
Crown galls are tumorous growths due to increased stimulation of cell division and enlargement.
While there are some general features in common with cancer in animals, the specific steps involved in crown gall disease are very different from cancer. Over the past twenty years, the major mechanisms and genes involved in tumor induction by Agrobacterium have been identified by other labs and are summarized in Figure 1. This was not surprising since most researchers believed that all bacteria had this type of genetic organization. However, we now know that bacteria can have multiple chromosomes and some of those can be linear molecules, just as our chromosomes are linear. In 1993, Allardet-Servent et al.