A microscopic genetic engineer

A firefly gene inserted into this tobacco with A. tumefaciens causes the plant to glow. You’ll never lose your cigarettes again.
A firefly gene inserted into this tobacco with A. tumefaciens causes the plant to glow. You’ll never lose your cigarettes again.
Courtesy Biocrawler

Viruses, bacteria, fungi, and insects can all cause the abnormal growths on plants that we call galls. The crown gall, like the one in the object of the month display, is caused by a kind of bacterium called Agrobacterium tumefaciens. The bacteria live in soil, and cement themselves to cells after infecting a plant. Once anchored to its host, A. tumefaciens inserts a special portion of DNA into the plant cell.

The bacteria's DNA reprograms the plant’s cells so that they form into a swollen gall and begin to produce special amino acids for the bacteria to eat.

Even though the bacteria is a disease-causing parasite—plants receive no benefit from the infection—its natural genetic engineering abilities have been tremendously useful to scientists. By replacing the genes that cause the formation of a gall with genes selected and cloned by researchers, specific traits can be inserted into plants by infecting them with A. tumefaciens. Special genes from fireflies, for instance, have been inserted into cells using the crown gall bacterium to produce glowing plants—a strange trait, but useful for research.