Fugitive genes

In the world of genetic engineering one often talks about ‘transgenic organisms’. These are organisms that have been modified by the insertion of an alien gene into their genome. Now it turns out that there are naturally occurring transgenic plants. One such instance was found by Dr Lena Ghatnekar from the research team for evolutionary genetics at Lund University in Sweden. Her findings have just been published in the prestigious Proceedings of the Royal Society in London.

Sheep’s fescue (Festuca ovina) is a common grass that the research team at Lund University in Sweden has studied for a long time. One of its genes codes for an enzyme called PGIC. Lena Ghatnekar discovered that the enzyme did not look the same in all sheep’s fescue plants. It turned out that certain plants had extra genes for the production of PGIC and that these genes existed at a different site in the genome than the normal PGIC genes. At first the scientists believed that it was a matter of copied genes – gene duplications – but it soon proved to be a question of fugitive genes. Lena Ghatnekar explains:

”There are always minor differences from one plant to another when it comes to complex proteins like the enzyme PGIC. Maybe a difference of up to a few percent. But in this case the difference was six percent, and that is too much for an ordinary gene duplication.”

The alien has now been identified. The gene that produces the deviant PGIC comes from another grass, namely a meadow grass (Poa). This is surprising, since the fescues and the meadow grasses are not particularly closely related.

”We don’t know how the alien gene got into sheep’s fescue. When we have located precisely where in the genome the gene is situated, it will be possible for us to make a guess. But apparently the introgression led to a variant with high fitness, making the alien gene spread to later generations. Today, there are populations of sheep’s fescue where ten per cent of the plants carry the extra gene” says the head of the research team, Professor Bengt O. Bengtsson, adding:

”This is a truly unique event. Poa and Festuca are so remote from each other that a plant breeder would never dream of trying to cross them. Perhaps the gene was inserted into Festuca via a virus that can infect both grass species. In that case it is a sort of spontaneous genetic transformation; today’s genetic engineers make use of viruses to transfer genes. Another possibility is that something very special happened during fertilization. To be sure, grasses have a ‘defence system’ that normally prevents foreign pollen from growing on their pistils, but maybe in some way a fragment of a Poa pollen hitched a ride with a regular Festuca pollen.”