State how Agrobacterium tumifaciens has been made a useful cloning vector to transfer DNA to plant cells.

Agrobacterium is a pathogen that affects several dicots and delivers a piece of DNA known as ‘T-DNA’ to transform normal cells to tumor cells. This potential of Agrobacterium has been used to transfer desired gene into the plant. The desired gene is inserted in the T-DNA region and the bacterium is allowed to infect the plant. In this way, the desired changes are made in the plant.