Genetic Engineering of Plants

Yet another post on the applications of cell biology! Hopefully this post will also help you understand some of the science behind GMOs.

Be able to define a transgene.

A transgene is simply a gene that has been inserted into the genome of an organism. This can be done through recombinant DNA technology, which I touched on in an earlier post.

Know the properties of Agrobacterium tumefaciens.

Agrobacterium tumefaciens is a bacterium that infects plants, forming small galls, or tumours. It can be used to introduce transgenes into plants as they contain Ti plasmids, as I will explain next.

Be able to describe a Ti plasmid and the properties that make it useful for genetically modifying plants.

Ti plasmids, or tumour-inducing plasmids, are the plasmids inside Agrobacterium tumefaciens. (I've described plasmids before in my post about cloning.) Ti plasmids contain a section called T-DNA, which can be integrated into a plant chromosome. Within this T-DNA is the onc gene, which contains the information required for the formation of a gall. Elsewhere in the plasmid is the vir gene, which is required for the transfer of T-DNA.

Know the basic steps in regenerating a plant from transformed callus tissue.

The production of transgenic plants often involves the binary vector system, in which two plasmids are used. One of these plasmids has T-DNA but no vir gene. This plasmid has the foreign DNA inserted into the T-DNA section- a process also described in that post about cloning. The other plasmid has the vir gene but no T-DNA. Both plasmids are required for insertion of the transgene.

To insert the gene, small discs taken from leaves of a plant are incubated in a dish along with genetically engineered Agrobacterium tumefaciens. These bacteria infect the edges of the discs, as this is where wounded cells are located. Calluses then grow here. To ensure that calluses all contain the new gene, they are usually grown on some kind of selectable media- for example, if an antibiotic-resistance gene is to be transferred over, the calluses will be grown on an antibiotic-containing media. The medium also contains plant growth substances to encourage the growth of shoots. These shoots can be transferred to a root-inducing medium where they can grow to full size.

Another way in which a transgene can be inserted is through biolistic genetic engineering, which is a fancy way of saying "shooting it with a gene gun." In this method, transgene-coated particles are shot into the plant tissue, allowing DNA to become incorporated into the plant chromosome.

Be able to define sense and antisense plants.

Sense plants are genetically modified plants that either produce a new protein or produce more of a protein that they already produce. Antisense plants, on the other hand, produce less of a target protein.