Gene Gun
Many methods of delivering extra DNA into the nucleus of plant cells have been tried, and several have been successfully used to produce transgenic plants. The first to be discussed is the gene gun, also called particle acceleration or microprojectile bombardment. While this method was used to create several commercial events such as RoundupReady soybean, it has several limitations that make it less appealling than the use of Agrobacterium as a transformation method. We will describe the Agrobacterium method in the next section. The gene gun is a good example of a creative idea being developed into a practical technology.
Troy Weeks uses the gene gun to transform sorghum cells. (Image by T. Weeks)
The gene gun can be used on either tissue culture cells or seedlings (to make chimeric plants) of any species. As the name implies, this method works by shooting DNA into the plant cells. As seen in these figures from the animation, microscopic gold or tungsten particles are coated with hundreds of copies of the gene(s) to be introduced.
Microscopic gold particles are used as ’bullets’ to deliver DNA into callus cells. (Image by P. Hain)
In earlier versions of the gene gun, DNA coated metal was loaded into a 22-caliber cartridge and then shot into plant tissue culture cells. Current versions place the tissue culture cells in a vacuum chamber and then propel the metal particles with a high pressure gas that is released in a sudden burst much like a popped balloon.
The gold particles are coated with hundreds of copies of the gene of interest. (Image by P. Hain)
Gene gun transformation begins by growing cells in tissue culture, bombarding the cells with gene coated gold particles in the gene gun, selecting out transgenic cells on selection media, and regenerating the transgenic cells into plants. (Image by P. Hain)
*This animation has no audio.*
Once inside the nucleus of a cell, the genes dissolve off of the gold particle and can potentially insert into a chromosome. A major limitation of this method is that several copies of the transgene will often insert into a chromosomal position. These high copy insertion events can be detected as DNA that should not be expressed by the plant cell and the transgene copies are silenced. (Image by P. Hain)