3 September 1999

NEWWAYTOMODIFY CROPS

RESEARCHERS in the US say they have developed a way to genetically engineer crops without introducing foreign genes. The new method, known as chimeraplasty, is more precise and may be less controversial than current techniques.

Seed giant Pioneer Hi-Bred International recently announced that it had used the chimeraplasty technique to develop a herbicide-resistant maize based on a natural mutation found in some corn varieties.

The new process, developed by Pennsylvania-based Kimeragen Inc, can only use the genetic material that exists inside the organism. However, it offers much more precise control than other genetic manipulation technologies.

"We may one day be able to quickly reduce caffeine in coffee beans or shorten the long-chain fatty acids found in plants like soybeans – making the fat in them more heart-healthy like olive oil," says Charles Arntzen, chief executive officer of the Boyce Thompson Institute at Cornell University who used chimeraplasty on tobacco plants.

Chimeraplasty involves creating a novel molecule using a desirable sequence of DNA combined with RNA. This is the chimera or chimeraplast, which is "painted" onto microscopic gold particles and fired into plant cells.

Once bound to the target part of DNA, the chimera activates a naturally occurring gene-correcting mechanism. This changes the DNA at the target site precisely. In effect, the host organism uses its own DNA repair apparatus to alter one of its own genes.

Other GM techniques involving disabled viruses or a gene gun to randomly blast thousands of new genes into cells are clumsy by comparison. Inserting entire genes into cells is akin to supplying an entire new word-processing program to correct a single letter in just one document. By contrast chimeraplasty changes just one or two nucleotides – the letters that make a genes program.

Although the process cannot insert foreign genetic material it can be used to tweak an already genetically modified organism. It may be used to fix a transgene transformation that had not worked previously, says Chris Baszczynski, research co-ordinator at Pioneer Hi-Bred.

However, the target characteristic must be controlled by a single gene. Many desirable traits like resistance to drought or disease are often controlled by a number of genes, which may limit the usefulness of the process at this point, he says.

Kimeragen, a privately held company, has licensed the technique to Pioneer, which is due to be acquired by DuPont, and to AgrEvo. AgrEvo has said it will use the technology to help identify specific gene functions in selected crops. &#42