Why use expression plasmids with plant transformation?
One property of plants that facilitates genetic modification with expression plasmids is that the growing cells of a dissected or excised plant will regenerate in culture to form callus tissue. Therefore, with the addition of plant growth hormones, development from the callus will occur, resulting in a new, whole, fertile plant. Introducing new genes to the callus enables the new genes to be contained in all the newly developing cells (Darnell 1990). Which plasmid is used? (illustration) The bacteria Agrobacterium tumefaciens is a naturally occurring pathogen found in soil. A. tumefaciens has the unique ability to transfer its DNA into a plants genome. A. tumefaciens infection, normally occurring at the site of a wound in the plant, causes the formation of crown gall tumors (Hall 1 Sept 2002). A large (200 kb) circular DNA plasmid is responsible for the production of the tumor and the transforming abilities. This tumor inducing (Ti) plasmid transfers and inserts a region of the plasmid
