THE first genetically modified wine could soon be on its way to the
supermarket shelves. American scientists have added a silkworm gene to a
commercial grape variety, not to change the taste but to protect the vines from
Pierce鈥檚 disease. The bacterial infection, which spread to California from
south-eastern US in 1995, costs the region鈥檚 wine growers millions of dollars
each year.
Pierce鈥檚 disease attacks the vine鈥檚 xylem鈥攊ts vascular system鈥攁nd
kills it. At the moment, you can鈥檛 treat infected vines, and years of selective
breeding have failed to produce a resistant variety. GM vines with the silkworm
gene produce a protein called cecropin that fights the disease.
鈥淚f this works, it really is a major breakthrough,鈥� says Alexander Purcell, a
plant scientist at the University of California, Davis, who has been looking for
ways to tackle the new epidemic.
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Dennis Gray from the University of Florida in Gainesville inserted the
cecropin gene into embryonic Thompson seedless grapes using a virus common in
plant bacteria. Cecropin sticks to cell membranes and punctures them, killing
the cell. The Pierce鈥檚 bacterium is more vulnerable to this kind of attack than
human or plant cells.
Until now, scientists had been unable to make plants express extra genes in
their xylem, because it is made of dead cells. But Gray and Ralph Scorza of the
US Department of Agriculture switched the gene on by using a piece of DNA called
a promoter complex that is involved in xylem formation. The technique has
recently been patented.
The gene is expressed at low levels throughout the plant, including in the
grape. Gray is now working on Chardonnay grapes and hopes to keep the protein
out of the human food chain by selecting a variety where expression is limited
to the xylem, but he warns that this may not be possible.
This could raise safety concerns because a related protein called melittin,
which is present in bee stings, can cause anaphylactic shock in some people.
However, cecropin doesn鈥檛 bind to mammalian cells as tightly as melittin, so no
one yet knows whether cecropin will cause problems.
Purcell says he would like to know how much of the protein ends up in the
wine before it goes on sale. 鈥淩egardless of what scientists think, there鈥檚 going
to be reluctance for consumers to accept this,鈥� he says, 鈥減articularly in a
high-price bottle of wine.鈥�