GM tree gives non-GM fruit

7 November 2001

Walnuts grown from genetically modified plants could soon be hitting the supermarket shelves. The GM roots will beat off costly bacterial infections but the nuts themselves will be GM-free. The hybrid plants, the first of their kind, should appease both farmers and consumers wary of GM food.

Fruit tree and vine growers are plagued by Agrobacterium, a bug which causes cancerous growths called galls in the roots. The bug gets into the roots via a wound and transfers tumour-causing genes, which invade the plant’s DNA and the gall starts to form.

Now Abhaya Dandekar and a team at the University of California, Davis, say they can prevent the tumour genes being expressed by triggering a plant defence mechanism.

They have made GM varieties of thale cress and tomato that have versions of the tumour-causing genes in their DNA. When expressed as mRNA, an intermediate stage between a gene and a protein, the molecule’s structure forces it to fold back on itself.


Because plant cells don’t normally have double-stranded mRNA, they “silence” the genetic material by chopping it up. This prompts the plant cells to recognise the similar tumour gene mRNA as alien and chop it up.

A standard cultivation technique could be used to ensure that walnut trees modified in the same way will not produce GM fruit. Usually, the chosen fruiting variety is grafted onto a root stock that copes well with local conditions. In this case, non-GM plants would be grafted onto modified roots without the two sets of genes mixing.

Journal reference: Proceedings of the National Academy of Sciences (vol 98, p 13,437)