Question

The introduction of t-DNA into plants involves
A. Allowing the plant roots to stay in the water.
B. Infection of the plant by Agrobacterium tumefaciens.
C. Altering the pH of the soil then heat shocking the plants.
D. Exposing the plants to cold for a brief period.

Answer 1

Transfer DNA is the transferred DNA of the tumour-inducing plasmid of some of the species of bacteria such as an Agrobacterium tumefaciens and Agrobacterium rhizogenes. The T-DNA is transferred from the bacterium into the host plant nuclear DNA.

Complete step by step answer: The Agrobacterium tumefaciens is a plant pathogenic bacterium that carries Ti plasmid. It can transfer a particular segment of the tumour-inducing (Ti) plasmid into the nucleus of infected cells. The transferred T-DNA is then integrated into the host genome and it is transcribed with it. This ability of an Agrobacterium tumefaciens to transfer T-DNA in the host genome is used in genetic engineering to transfer the desired DNA segment, carrying the gene of the interest, into a genome of selected organisms. The part of a Ti plasmid transferred into the plant cell DNA is called the T- DNA.
Thus, the correct answer is option B.

Additional information: The T-DNA with the desired DNA spliced is inserted into the chromosomes of the host plant, where it produces a copy of itself by migrating from one chromosomal position to another at random. Such plant cells are then cultured, induced to multiply and differentiated to form plantlets. They are then transferred into the soil, these plantlets grow into mature plants carrying the foreign gene expressed throughout the new plant.

Note: The same procedure of T-DNA transfer can be used to disrupt genes via insertional mutagenesis. A reporter gene can be linked to the right end of the T-DNA and it is transformed along with the plasmid replicon and a selectable antibiotic.