Transgenic Plants

A foreign gene and its promoter are introduced into a plant protoplast—a plant cell without a cell wall—using polyethylene glycol in a medium. The recombinant protoplast is then cultured on sterile medium with growth regulators and nutrients, allowing cells to divide and form a callus. Totipotent cells within the callus develop into shoots and roots, eventually forming a complete transgenic plant.

Agrobacterium tumefaciens is a soil bacterium containing a Ti plasmid that naturally integrates into plant genomes. Scientists modify this plasmid by inserting a desired gene into the T-DNA region and adding an antibiotic resistance gene. When the recombinant bacteria infects wounded plant cells, it transfers the foreign gene into the plant genome, creating transformed cells that develop into transgenic plants.

The T-DNA region of the Ti plasmid is the segment that integrates into the host plant cell genome and carries the desired foreign gene. The virulence region facilitates the transfer of T-DNA into the plant cell. Together, these regions enable Agrobacterium to successfully deliver and incorporate recombinant DNA into the plant's genetic material.

Electroporation uses high voltage pulses delivered to a protoplast suspension to temporarily increase cell membrane permeability. This allows foreign DNA to enter the cell and integrate into the plant genome. The method is effective for introducing genes into protoplasts and is one of several physical methods used in plant genetic engineering.

Transgenic plants are developed for pest and virus resistance, improved yield, and enhanced nutritional content. Golden rice, for example, produces β-carotene—a vitamin A precursor—to address nutritional deficiencies. Bt cotton produces crystal protein that kills harmful insects. These modifications demonstrate how synthetic biology artificially synthesizing designing organisms improves crop performance and human health.

An antibiotic resistance gene is inserted into the recombinant plasmid alongside the desired foreign gene. When the transformed plant cells are cultured in medium containing antibiotics, only cells that have successfully incorporated the plasmid survive. Non-transformed cells lack the resistance gene and die, allowing researchers to isolate and propagate only the transgenic cells.

A callus is a mass of undifferentiated cells that forms when recombinant protoplasts are cultured on sterile medium with growth regulators and nutrients. Within the callus, totipotent cells—cells capable of developing into any plant tissue—differentiate to form shoots and roots. This regenerative capacity allows the callus to develop into a complete, functional transgenic plant.