TEACHING TOOLS IN PLANT BIOLOGYTM: LECTURE NOTES A Really Useful Pathogen, Agrobacterium tumefaciens

Bacteria of the genus Agrobacterium are very useful and unusual plant pathogens. Through a rare interkingdom DNA transfer, the bacteria move some of their genes into their host’s genome, thereby inducing the host cells to proliferate. The result is uncontrolled cell growth leading to a tumor (as induced by Agrobacterium tumefaciens and Agrobacterium vitis) or excessive production of roots (as induced byAgrobacterium rhizogenes). The proliferating plant tissues produce opines, which are compounds that few organisms other than Agrobacterium can metabolize. Agrobacterium’s ability to transfer DNA makes it extraordinarily useful because it can be modified to introduce other genes not involved in pathogenesis, such as those encoding useful traits, into plant genomes. Furthermore, it can be used as a model with which to study plant responses to pathogenic bacteria. The development of Agrobacterium as a tool to transform plants is a landmark event in the development of modern plant biology, and, as with most great advances, involved the cooperation and competition of many labs and individuals. This article provides an introduction toA. tumefaciens and its related species, focusing on their modes of pathogenicity and their usefulness as tools for plant transformation, as well as their use as a model for the study of plant–pathogen interactions.