Genetic Modification without Genetic Engineering

Genetic engineering promises solutions to problems of agricultural importance including plant tolerance to stress caused by drought and salinity, resistance to insect and fungal pests, and weed prevention. However, consumer concerns about genetic engineering have slowed the release of biotech crops. A genetic modification technique called oligonucleotide-directed repair (ODR) can introduce subtle improvements to plants while avoiding some of those concerns.

ODR changes a single nucleotide in a gene that is already in a plant, animal, bacteria or fungus. Remember that a gene is a piece of DNA that provides instructions to the cell. If all the DNA in the cell represents the blueprint for a house, a gene represents instructions for making a portion of the house, the front door, for instance. The instructions are written using four nucleotides, shorthanded as “A”, “C”, “G” and “T”. Change one nucleotide and you can dramatically change the instructions.

ODR is a technique for changing one nucleotide in a plant, animal, bacterium or fungus. As an example, cystic fibrosis (CF) is an inherited disease. People with CF have an error of only one nucleotide in a critical gene. The single nucleotide change leads to a build up of mucus in the lungs, often leading to patient death in their 30’s. One potential application of this technology is for gene therapy in CF sufferers.

As the name suggests, ODR is based on the ability of an oligonucleotide to cause a change in DNA. An oligonucleotide is several nucleotides put together, but shorter than a gene. The oligonucleotide differs by only one nucleotide, or one letter of the DNA code, from a gene that has always been in the cell. The organism sees the oligonucleotide and changes its gene to match it. The result is identical to the original, with the exception of one change to the instructions (gene).

C. Dong and colleagues set out to prove that ODR would work in wheat. First they introduced a defective gene into the wheat plant, using traditional genetic engineering methods. Then they tried to correct the defective gene using ODR. They used an electric pulse to introduce an oligonucleotide, into the cell. ODR made the defective gene functional, proving the utility of the technique in wheat. This technology could be used to create healthier oils in food crops or generate new industrial oils for biofuels. In wheat, it could lead to production of gluten-free flour that would be a boon to individuals with Celiac Disease.

Dong, C, P Beetham, K Vincent, P Sharp. Oligonucleotide-directed gene repair in wheat using a transient plasmid gene repair assay system. Plant Cell Reports (2006) 25: 457-465.

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