Process of Developing Genetically Modified (GM) Crops

Genetic modification refers to techniques used to manipulate the genetic composition of an organism by adding specific useful genes. A gene is a sequence of DNA that contains information that determines a particular characteristic/trait. All organisms have DNA (genes). Genes are located in chromosomes. Genes are units of inheritance that are passed from one generation to the next and provide instructions for development and function of the organism. Crops that are developed through genetic modification are referred to as genetically modified (GM) crops, transgenic crops or genetically engineered (GE) crops.

The main steps involved in the development of GM crops are:

  1. Isolation of the gene(s) of interest: Existing knowledge about the structure, function or location on chromosomes is used to identify the gene(s) that is responsible for the desired trait in an organism, for example, drought tolerance or insect resistance.
    The developer provides regulators detailed information about the characteristics of the gene of interest and other functional sequences such as promoters. This includes functions of the gene and its products in the donor organism and intended function in the recipient organism to help regulators in determining potential adverse effects before experiments are done.
  2. Insertion of the gene(s) into a transfer vector and plant transformation:

    The most commonly used gene transfer tool for plants is a circular molecule of DNA (plasmid) from the naturally occurring soil bacterium, Agrobacterium tumefaciens. The gene(s) of interest is inserted into the plasmid using recombinant DNA (rDNA) techniques. For additional information see Plasmids link.

    The modified A. tumefaciens cells containing the plasmid with the new gene are mixed with plant cells or cut pieces of plants such as leaves or stems (explants). Some of the cells take up a piece of the plasmid known as the T-DNA (transferred-DNA). The A. tumefaciens inserts the desired genes into one of the plant’s chromosomes to form GM (or transgenic) cells. The other most commonly used method to transfer DNA is particle bombardment (gene gun) where small particles coated with DNA molecules are bombarded into the cell. For additional information see Plant Transformation using Agrobacterium tumefaciens and Plant Transformation using Particle Bombardment links.

  3. Selection and regeneration of the modified plant cells into whole plants:

    After transformation, only a small fraction of the plant cells take up the gene of interest and most often, selectable marker genes that confer antibiotic or herbicide resistance are used to favor growth of the transformed cells relative to the non-transformed cells. For this method, genes responsible for resistance are inserted into the vector and transferred along with the gene(s) conferring desired traits to the plant cells. When the cells are exposed to the antibiotic or herbicide, only the transformed cells containing and expressing the selectable marker gene will survive. The transformed cells are then regenerated into whole plants using tissue culture methods.

    Information about the marker genes and whether they will be present or absent in the developed GM plant is provided to the regulators.

    Note: Detailed information about the genes of interest, promoters, marker genes, vectors and transformation methods (step 1, 2 and 3) must be presented to the regulators by the developer before the experiments are done .

  4. Verification of transformation and characterization of the inserted DNA fragment.

    Verification of plant transformation involves demonstrating that the gene has been inserted and is inherited normally. Tests are done to determine the number of copies inserted, whether the copies are intact, and whether the insertion does not interfere with other genes to cause unintended effects. Testing of gene expression (i.e., production of messenger RNA and/or protein, evaluation of the trait of interest) is done to make sure that the gene is functional.

    Methods and results used to determine: if gene was inserted, number of copies inserted, if the copies are intact, if insertion does not interfere with normal plant function, and gene expression are well presented to the regulators by the developer.

  5. Testing of plant performance

    After transformation, only a small fraction of the plant cells take up the gene of interest and most often, selectable marker genes that confer antibiotic or herbicide resistance are used to favor growth of the transformed cells relative to the non-transformed cells. For this method, genes responsible for resistance are inserted into the vector and transferred along with the gene(s) conferring desired traits to the plant cells. When the cells are exposed to the antibiotic or herbicide, only the transformed cells containing and expressing the selectable marker gene will survive. The transformed cells are then regenerated into whole plants using tissue culture methods.

    Information about the marker genes and whether they will be present or absent in the developed GM plant is provided to the regulators.

    Note: Detailed information about the genes of interest, promoters, marker genes, vectors and transformation methods (step 1, 2 and 3) must be presented to the regulators by the developer before the experiments are done.

  6. Safety assessment.

    Food and environmental safety assessment are carried out in conjunction with testing of plant performance. Descriptions of safety testing are described in the Food Safety Assessment and Environmental Safety Assessment links.

Further Reading

Figure 1: Regeneration of transgenic banana using tissue culture method

Somatic embryos are embryos that originate in tissue culture in response to plant hormones added to the growth medium. Source: National Agricultural Biotechnology Centre, Uganda

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