Glossary

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Gene Silencing

Inactivation of genes

The term gene silencing is used to describe the inactivation of a gene without changing the corresponding DNA sequence. It is not a phenomenon which occurs specifically in transgenic plants, but rather a natural mechanism used by fungi, animals and plants to regulate their genes. They can also use it to protect themselves from foreign DNA. Gene silencing is based on epigenetic (from the Greek “epi” meaning “above” or “beyond” DNA information) regulatory mechanisms and is related to RNA interference.

Genes inserted in a plant by means of genetic engineering are recognised as foreign DNA by the plant, which then targets them with its own defence mechanisms. The silencing, or switching off, of these genes can often be observed, which makes transgenic plants particularly suitable for scientific studies of epigenetic regulatory processes. Various forms of gene silencing have been discovered, including:

• The integration of multiple transgenic copies which are able to inactivate each other.
• ‘Position effects’ whereby transgenes are switched off by external factors such as light intensity and temperature, or at specific stages of development, depending on the integration site in the genome.
• When the activity of a transgene exceeds a specific threshold.