Transgenic Plants

Transgenic plants are produced by introducing a foreign gene into a plant’s genome. These plants can be developed for a variety of reasons, including virus or pest resistance, higher yield, or therapeutic protein production.

To produce a transgenic plant, a gene of interest and its promoter are introduced into the plant protoplast, a plant cell without a cell wall, by incubating both in a medium containing polyethylene glycol.

The recombinant protoplast is cultivated on a sterile medium in the presence of growth regulators and nutrients.

The cells of the protoplast grow indefinitely, producing a mass of undifferentiated cells called a callus. Some cells of the callus, called totipotent cells, give rise to new shoots and roots, which can develop into a whole new plant.

Transgenic plants can also be created using the bacteria Agrobacterium tumefaciens, a gram-negative bacterium found in soil. This bacteria is a pathogen that normally causes disease in plants and contains a Ti -plasmid that can integrate into a plant cell genome.

The Ti plasmid has two regions of interest- T-DNA or transfer DNA region which can be inserted into the host cell genome and the virulence region to aid the transfer of T-DNA into the host cell.

This plasmid is modified by inserting a desired gene into the T-DNA region and a gene for antibiotic resistance to enable selective growth of plasmid-containing organisms. The recombinant plasmid is then inserted into the bacteria by applying an electric pulse to increase cell permeability and enable the uptake of the plasmid into the bacteria.

The Agrobacterium tumefaciens carrying recombinant plasmid is grown in a culture medium containing antibiotics.

Plant parts such as the cotyledonary nodes from a tomato plant are cut and incubated in the medium containing bacteria.

The wounded plant cells at the edge of the stem node release compounds that attract the bacteria. The bacteria infects the plant and releases the recombinant plasmid, which then transfers the foreign gene into the plant cell genome.

Only the transformed cells with recombinant DNA and antibiotic-resistant genes survive in the medium containing antibiotics.

The transformed cells now form a callus and develop into a new transgenic plant carrying a transgene.