On the grapevine 18 May 2001
The first genetically modified wine could soon appear, thanks to the silkworm
The first genetically modified wine could soon appear, after scientists succeeded in introducing a silkworm gene. It is the first useful gene placed in a commercial variety of vine, by Dennis Gray and colleagues at the University of Florida.
The gene produces a protein to fight Pierce's Disease. This is caused by a bacterium which infects a vine's vascular system, or xylem, and kills it. Since spreading from the southeastern US to California in 1995, it has cost the state's plantation owners hundreds of millions of dollars.
There is no existing way to treat infected vines and years of conventional breeding have never produced a resistant variety.
"If this works, it really is a major breakthrough," says Alexander Purcell, a plant scientist who has been looking for ways to tackle the new epidemic at the University of California, Davis.
The Florida team used a virus common in plant bacteria to insert a gene derived from silkworms into embryonic grapes. In the past scientists could not work out how to get genes expressed in the xylem, which is made of dead cells.
But Gray and Ralph Scorza of the US Department of Agriculture switched the gene on by using a promoter complex that is involved in xylem formation, for which they have just been awarded a patent.
The silkworm gene creates a protein called cecropin that is attracted to cell membranes and eventually punches a hole killing the cell. The Pierce's bacterium is more sensitive to this mechanism than human or plant cells.
In many of the modified plants the gene is expressed at low levels throughout the plant, including in the grape. Gray hopes to select a variety where expression is limited to the xylem to keep the peptide out of the human food chain, but says this may not be possible.
Safety concerns will be raised because a related protein called melittin is present in bee venom and can cause anaphylactic shock in some humans. However melattin is known to bind more tightly to mammalian cells than cecropin.
Purcell says he would like to know what the levels of the peptides are in the wine before seeing it reach the market. "Regardless of what scientists think there's going to be reluctance for consumers to accept this, particularly in a high price bottle of wine."
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Eugenie Samuel, Boston
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