Production Methods

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Transgenic Methods

1) Agrobacterium tumefaciens Mediated Gene Transfer

Agrobacterium tumefaciens Is a plant pathogen found in the soil that causes Crown Gall Disease, a disease which results in tumorous growths in the roots of the infected plant (Shelburne 2002). This pathogen transmits a tumor inducing (Ti) plasmid from a section of its T-DNA into the infected plant (Shelburne 2002). Once the Ti plasmid is introduced into the plant cell, the plasmid incorporates itself into the genome and is transcribed (Shelburne 2002). Researchers can therefore insert a desired genetic code in place of the Ti plasmid to cause the transcription in results in the production of a new protein (Shelburne 2002). An advantage of Agrobacterium Gene Transfer is that the desired gene is actually incorporated into the genome of the plant which leads to better gene expression and the ability to insert larger DNA strands into the plant cell (Shelburne 2002). This method for the creation of genetically modified organisms is one of the most commonly used methods due to its effectiveness and ease of alteration (Shelburne 2002). Agrobacterium Gene Transfer shows a lot of potential for the creation of medicinal foods.

Check here for more information on Agrobacterium tumefaciens Mediated Gene Transfer or Expression Plasmids.

2) Particle Bombardment (Gene Gun)

Particle Bombardment uses a pressurized air gun to shoot tiny gold or tungsten balls into the plant tissue you are trying to genetically modify (Watson 2002). These tiny balls are covered with the genetic material that codes for the creation of the desired protein (Watson 2002). As these cells rip into the plant cell, the DNA on these balls is left within the newly breached cell (Watson 2002). Using recombinant DNA, the newly introduced DNA is then replicated throughout the cell (Watson 2002). This method is effective in producing the desired genetically modified organism which due to this method could be a medicinal food.

Check here for more information on Particle Bombardment (Gene Gun).

3) Electroporation

Electroporation is a method which uses an electric shock stimulus to open pores in a plant tissue (Toran 2002). By opening these pores in the cell wall, DNA is able to enter into the plant cell (Toran 2002). The DNA in the cell is able to incorporate itself into the genome which is subsequently transcribed (Toran 2002). This method has been used effectively in the creation of genetically modified organisms and shows promise for the creation of medicinal foods.

Check here for more information on Electroporation.

Non-Transgenic Methods

1) Recombinant Virus Infection

This method is similar in methodology to the Agrobacterium Gene Transfer, whereas the only difference is that the inserted genetically modified material is not inserted into the plant genome. Instead the recombinant virus in the plant cell causes the expression of the genetically induced protein. This method is very common and viruses like the Tobacco Mosaic Virus have already been used in the creation of medicinal foods (Giddings, G. et al 2000).

2) Increased Gene Expression via Promoter Modulation

Some plant cells already make the protein desired; however, the plant does not make enough of it to be effective. So, through genetic manipulation scientists can amplify the gene expression through the modulation of promoters. Through this alteration, the plant cell will now over-express the gene resulting in more of that protein.

This webpage was created by David Shelburne ’04 & Paul Toran ’03 as an assignment for an

undergraduate course—Bio 361: Genetically Modified Organisms—at Davidson College.

Send comments, questions, and suggestions to: dashelburne@davidson.edu and/or patoran@davidson.edu