March 29, 1997

Article at New Scientist

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NEWS | Killer gene makes the pips squeak

Wilson da Silva, Sydney

THE writing may be on the wall for oranges with pips. Biologists in Australia and Japan have genetically engineered tobacco plants so that they destroy their own seeds. They say the same technique should work in citrus crops.

Anna Koltunow of the Division of Horticulture of the CSIRO, Australia’s national research agency, in Adelaide, and Fumio Takaiwa of Japan’s National Institute of Agrobiological Resources in Tsukuba, linked a gene that kills cells with a “promoter” DNA sequence that switches on a gene active during seed formation. The gene chimera delivers a deathblow to developing seeds.

“It looks promising from the results we’ve got in tobacco,” Koltunow told New Scientist. “All of the seeds in the plant stop developing. All that is left is a small, soft seed trace.”

The researchers call their gene SDLS-2. The cell-killing component is found in a wide range of plants, and kills unwanted cells during plant development. Koltunow and Takaiwa have been trying to link the gene to promoters that would make it destroy seeds since 1992. 

The first version killed seeds, but did not obliterate them. Another problem was ensuring that the promoter did not switch on the gene too early, which in citrus crops could prevent fruit forming, or cause it to fall off the tree before it is full grown.

Koltunow and Takaiwa are now inserting SDLS-2 into citrus plants, and are positive about the chances of success. The trees take up to five years to flower for the first time. But in the meantime, the researchers hope to get some early indications from tests on the short-lived weed Arabidopsis thaliana, the seeds of which develop in much the same way as citrus seeds.