Silence please

Researchers at Cambridge University have been studying the process of gene silencing in transgenic plants, and have cloned a genetic modifier that could reduce transgene instability. Dr Ian Furner will be presenting the results of the study at the Society for Experimental Biology conference on Monday 8 April.

Gene silencing is a naturally occurring process by which genes can become shut off within a plant. When transgenes are introduced into plants they can also show gene silencing. Genes which share sequence similarity are said to be homologous. When transgenes showing homology to normal cellular genes are introduced they can show a special form of silencing called homology-dependent gene silencing and this typically results in the silencing of one or both genes.

Dr Furner’s group studied the homology-dependent silencing process in the Arabidopsis plant. By introducing extra copies of the chalcone synthase gene (CHS) into the plant, they silenced the endogenous gene. Arabidopsis plants grown in bright white light are purple due to the accumulation of the purple pigment anthocyanin. Plants grown at low light levels and plants showing CHS silencing grown at high light levels are green with little anthocyanin.

The group mapped the transgene insert and showed that it resulted in silencing of the normal copy of CHS at the TT4 locus. They also observed an increase in DNA methylation at TT4 after the transgene had been crossed away. Genetic mutations which reduce DNA methylation relieve the CHS silencing and revert the plants to the purple phenotype. Detailed characterisation of one of these mutations and the corresponding gene will be presented.

Dr Furner’s findings could be useful for the improvement of genetic modification. “Gene silencing could potentially be used to silence undesirable traits and modifiers of gene silencing offer some potential to reduce transgene instability”, he said.