How are antibiotic resistance genes useful for genetic engineering?
How are antibiotic resistance genes useful as markers for genetic engineering? I know the resistance genes are attached to a gene you want, and then the cells are treated with an antibiotic, and the surviving cells have taken up the genes. But I thought antibiotics wouldnt harm plant cells, so why would the plant cells which have NOT taken up the gene act any differently than those which have?
Submitted by: JuliaS
Expert response from Bill Reeves
Global Health and Safety Issues Management Lead, Bayer Crop Science
Tuesday, 08/09/2015 14:19
Before looking at how antibiotic resistance genes are used, it’s important to understand why there is a need to use them. DNA is transferred to dozens or even hundreds of plants early in product development and those plants need to be screened to identify which ones contain a functional copy of the transferred DNA. In order to accomplish this, a simple method for selecting the right plants is required. One way to do this selection is to include DNA encoding an antibiotic resistance marker (ARM) along with the DNA responsible for the trait of interest.
Plants are susceptible to some antibiotics. ARMs themselves are typically enzymes that can degrade an antibiotic, making it ineffective. The antibiotic neomycin is commonly used to select plants containing the ARM. Plants without the ARM cannot degrade neomycin and their leaves will turn brown while plants with the ARM are not damaged. In other words, the surviving healthy plants contain a functional copy of the antibiotic resistance gene and are the most promising candidates for further screening.
This idea could understandably lead to questions: Antibiotic resistance genes in my food? Techniques to remove marker genes have been used in GMO development. In one of the more recent methods, a DNA sequence containing two separate regions is inserted into the plant. One region contains the gene that provides insect protection, for example, and the other region contains the marker gene. Plants containing the entire DNA sequence can be easily identified, as described above. These plants are then crossed with another plant that does not contain any inserted DNA. The two regions of DNA segregate away from each other in the resulting offspring, and only those plants containing the gene of interest, with no marker gene, move on for further evaluation and testing. As this segregation technology has become more widespread, ARMs have become less common in commercial GM crops.
This is just the first step in creating a GM plant. Once the plants with a functional copy of the DNA are identified, they still need to be grown to maturity, tested for efficacy and safety and bred with other varieties of the same crop in order to reach commercialization.
ARM proteins undergo the same extensive safety testing as other newly expressed proteins in GM crops. In addition, multiple safety assessments of this technology have demonstrated that ARM coding sequences do not transfer from plants to animals and they do not alter the efficacy of antibiotic treatments. For more information about ARMs and how they are used, see my other post here.
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