Agrobacterium, the genetic engineer

Abstract

Agrobacteria are common soil and rhizosphere bacteria. Most strains are saprophytes, but strains harboring a tumor inducing plasmid (Ti plasmid) are pathogenic and can induce tumors on plants, called crown galls. The disease may lead to growth retardation and eventually the death of the host plant and thus can cause severe damage in horticulture. Crown galls form a favorable niche for Agrobacterium as they produce specific chemicals called opines which the bacteria can use for growth. Nowadays, Agrobacterium tumefaciens is best known as a natural genetic engineer, which is based on the molecular mechanism which it employs to induce crown gall. This involves the transfer of an oncogenic segment of the Ti plasmid (the T-DNA) to plant cells and its stable maintenance as part of one of the plant chromosomes. Expression of genes on the T-DNA is responsible for the formation of a tumor.