Crown Gall

Genetic engineering of plants was perfected by a bacterium named Agrobacterium tumefaciens, also called A. radiobacter, long before humans invented bioengineering. The disease is called crown gall as it most often is found in the crown of plants. It also infects roots if there are wounds present. The bacterium infects a huge range of dicotyledonous plants (trees, shrubs etc.).  It does not infect monocotyledonous plants such as grasses and grains. A few examples of susceptible fruit trees and ornamentals are pear, apple, cherry, peach, berries, grape, rose and lilac.

The bacterium has a chromosome as do other bacteria but also has a small separate DNA molecule that replicates independently.  It is circular and double stranded, known as a plasmid. The genes that cause galls are on the plasmid and therefore the plasmid is called the TI plasmid (tumor-inducing).  A small part of the plasmid is integrated into the host plant chromosome during the infection process. At the same time the inserted genes code for the production of chemicals termed opines which are modified amino acids. This process is said to hijack the biochemical machinery of the plant cells causing them to produce a source of food that only the bacterium can use.

More detailed information is readily available on the Internet by googling “crown gall disease”. There also would be information how this bacterium can be used to insert foreign DNA into any number of plants. An example of this is sweet potatoes having been made more tasty thanks to a gene introduced by the Agrobacterium.  The gene helps the plants to make hormones that change this root vegetable to a tuber-like organ that our ancestors farmed some 8,000 years ago.

Please see the many images of crown gall diseased plants on this website. There also is a narrative providing information on the bacterium’s ecology and various control methods.