Food Safety Evaluation Why Antibiotic Resistance Genes?

The techniques used for transferring a new gene into a plant are rather inefficient. Very few cells actually take up the gene of interest; when conditions are favourable, only some five cells in a thousand are genetically modified. Most often this ratio is lower. In order to find the cells that have been successfully transformed, some kind of marker is needed.

To do this, the gene that will give the plant its new trait (gene of interest) is coupled with a marker gene. Plant cells are then transformed with both genes simultaneously. The vast majority of these marker genes work by giving genetically modified cells the ability to break down a poisonous substance.

Successfully transformed cells growing up to GM plants. Non-transformed cells stop growing in the presence of the antibiotic.

Plant cells expressing an antibiotic resistance marker gene (ABR gene) are thus not harmed by that antibiotic. Treating the cells after the gene transfer with an antibiotic allows only the successfully transformed cells to survive. These cells also possess the gene of interest. Genetically modified plants containing the gene of interest are then regenerated from these individual, successfully transformed cells. Although the marker gene serves no purpose after this procedure, it remains part of the genetically modified plant. Removing a marker gene from an existing transgenic plant is virtually impossible. Some techniques exist to remove marker genes, but they cannot be implemented retroactively.

Bacterial marker

Before a plant cell can be genetically modified, it is necessary to have many copies of the gene of interest. These copies are produced in laboratories by transgenicbacteria. Just like in plant cells, a marker gene is needed to select for bacteria that carry the gene of interest. This is done with a second marker gene that enables the bacteria possessing the gene of interest to survive in the presence of antibiotics.

Oftentimes this marker gene does not make its way into the plant, but if a procedure is used that indeed transfers the bacterial marker, the gene no longer serves a purpose. Some GM plants possess a bacterial marker for ampicillin resistance.

See also on GMO-Compass:

• Position of EFSA on antibiotic resistance markers: Limited use