T-DNA

A specialised DNA fragment (transfer-DNA) found in the Ti plasmid harboured by the soil bacterium Agrobacterium tumefaciens, which is commonly used to transfer genes to plants

T-DNA is not located on the main chromosome of Agrobacterium, rather, it is part of a smaller, circular piece of DNA called the Ti-plasmid (Ti=tumour inducing). When Agrobacterium infects a plant, it naturally transfers a set of genes into the plant genome that causes the plant to produce a tumourous growth (crown gall). The gall provides a home for the bacteria.

Each end of the T-DNA sequence carries specialised genetic signals to enable the natural genetic transfer. Genetic engineering has made it possible to replace the tumour inducing genes with any gene of interest. In this way, Agrobacterium tumefaciens can be used to transfer desirable genes into plants. Today, this procedure is commonly used to transfer genes to dicotyledenous plants (not to grasses like wheat, rice, or maize).