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SYMPTOMS OF BACTERIAL DISEASES

Another symptom associated with some bacterial infections is the production of GALLS (see arrow). Galls are composed of plant tissue where there is an abnormal overproduction of cells and where cells typically grow abnormally large. While some fungi can cause galls, the classic gall disease is crown gall (shown in this photo) caused by the bacterium Agrobacterium tumefaciens. This bacterium induces gall formation by injecting a portion of its own DNA into a plant cell. This DNA hijacks the cell's metabolism and gall formation results.

Agrobacterium tumefaciens has revolutionized the area of plant genetic engineering. Scientists discovered that they could insert genes of interest into that portion of the bacterium's DNA that is injected into plant cells. Once genes are inserted, scientists inoculate plants with the altered Agrobacterium tumefaciens and the bacterium goes through its normal infection process. It injects its DNA (along with the extra DNA) into the plant and the inserted genes are expressed. This technique provides a novel and relatively easy way of incorporating genes from one plant into another plant, even if the two plants are not closely related and would not normally breed with one another.