Gene transfer methods

With indirect gene transfers, the gene to be transferred is incorporated into a biological vector, such as Agrobacterium tumefaciens, which is used in plant breeding. The bacterium prompts host plants to produce the desired amino acids by specifically introducing genetic information and it is this natural characteristic which permits the targeted transfer of foreign genes to plants today.

Bacterial genes are removed from the Ti plasmid and replaced by foreign genes. By coupling the foreign gene to be transferred with a selection marker, cells which have successfully been genetically modified can be selected at an early stage of plant cell culture.

These man-made vehicles for the transfer of foreign genes across species barriers are known as vectors. Particularly dicotyledons, such as oilseed rape, potatoes, sugar beet and vegetables, can be genetically modified with the aid of Agrobacteria.

Gen transfer in red genetic engineering

Red genetic engineering also uses numerous vectors to transport genes into the cell nucleus. This is normally done with the aid of viruses: like Trojan Horses, they have been transferring their genetic material into cells for millions of years in order to reproduce. In addition to viruses, specific genes can also be introduced into cells directly by electric shock. Another method is to pack the DNA in fat globules (liposomes) which then fuse with the cell membrane and transfer the gene into the cell.

Direct gene transfer, on the other hand, refers to techniques by which a gene is incorporated into a cell directly. Such methods are used in plant breeding particularly for monocotyledons, such as cereals.

next page »

Gene transfer methods

• 1.
  Liposome fusion: Foreign DNA is introduced into protoplasts by artificial membrane vesicles which fuse with the protoplasts' cell membrane.
• 2.
  Microinjection: A very fine syringe pierces the cell wall to clear the way into the nucleus for the foreign genes.
• 3.
  Electroporation: The thin cell membrane is torn apart in places by the force of the electronic discharges. DNA molecules suspended in the surrounding liquid enter the cell before the membrane re-closes of its own accord.
• 4.
  Particle nuclei: Propelled by an explosive shock wave, DNA coated projectiles measuring only a thousandth of a millimetre penetrate through the wall of a plant cell. The projectiles of gold or tungsten also unload their freight in the cell nucleus at an acceptable "hit" rate.
• 5.
  Agrobacteria transfer: The microbe Agrobacterium tumefaciens causes plant cells to multiply rapidly by smuggling "cancer genes" through a lesion in the cell wall. In the laboratory, the micro-organism has been converted into a gene shuttle so that it now transports the required genetic information instead of cancer.

« previous page