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鈥檚 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.
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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鈥檚 structure forces it to fold back on itself.
Because plant cells don鈥檛 normally have double-stranded mRNA, they 鈥渟ilence鈥� 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)