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Blue indicates foreign gene expression in pieces
of wheat leaves. The genes were transmitted to the plants by the
wheat streak mosaic virus vector.
(K9173-1)
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Wheat streak mosaic virus (WSMV) is
little more than a genetic snippet of ribonucleic acid. But for the Northern
Great Plains, outbreaks of this rogue RNA molecule in winter wheat can mean big
losses.
Now, Agricultural Research Service and
University of Nebraska researchers are seeking to unravel the virus' biology
and use that knowledge to fight it.
ARS plant pathologist Drake C. Stenger says wheat curl mites carrying WSMV can
transmit it to wheat plants through feeding. Once inside, invading viruses
force their host's cells to obey genetic instructions for assembling new viral
copies. When WSMV infects winter wheat in the fall, the result can be
catastrophic. A 1995 outbreak, for example, cost Montana's wheat industry
nearly $35 million in losses.
But now the virus is actually doing some good for a change—at least in the
laboratory.
Stenger's team has decoded WSMV's entire genome, revealing all 9,384 chemical
letters, or nucleotides, comprising its RNA alphabet.
This feat has enabled them to harness the virus as a vector, or a molecular
"taxi," for delivering foreign genes into the tissues of grown wheat
plants.
"We've taken advantage of the virus's natural talent for expressing its
own genetic material in plants," explains Stenger, at ARS' Wheat, Sorghum,
and Forage Research Unit, Lincoln, Nebraska.
"We've turned the virus into a powerful genetic tool," adds colleague
ARS plant pathologist Roy C. French. "The virus is most useful in
discovering and identifying what particular genes might do, and it offers a way
of getting those genes into wheat more quickly than by conventional
transformation."
For now, the scientists are outfitting the virus with two new genes for
bacterial enzymes. Both genes are easily detected in plants by use of a
chemical test or a blue stain. Either method offers visible evidence the virus
is expressing its borrowed genes as it replicates and spreads among cells. This
knowledge may reveal new ways of engineering wheat plants so that they block
crucial proteins the virus needs in order to multiply.
The team's approach, reported in The Plant Journal, vol. 23, pp. 547-555
(August 2000), should be faster than introducing new genes by inserting them
first into a callus. A callus is a mass of plant cells from which whole plants
can be regrown. Now, instead of waiting 6 to 9 months to begin evaluating such
plants, scientists can do so in 4 to 5 days by inoculating whole plants with
the gene-bearing virus.
Says French, "Many labs are identifying gene sequences for wheat, rice,
and other cereals. Often, we have little or no idea what these genes do. With
our virus gene vector, however, we can insert genes for known proteins and
quickly see how they behave in the plant."
Eventually, commercial wheat breeders will be able to adapt the approach to
provide growers with new varieties modified for better disease resistance or
other improved traits.—By
Jan Suszkiw,
Agricultural Research Service Information Staff.
This research is part of Plant Diseases, an ARS National Program (#303)
described on the World Wide Web at http://www.nps.ars.usda.gov.
Drake C. Stenger and
Roy C. French are in the
Wheat, Sorghum, and Forage
Research Unit, 334 Keim Hall, University of Nebraska, Lincoln, NE 68583;
phone (402) 472-2710 [Stenger], (402) 472-3166 [French], fax (402) 472-4020.
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