Manhattan, Kansas
November 24, 2008
Russian wheat aphids are insects
that are as small as one-sixteenth of an inch, but are capable
of much larger damage. The tiny insects have been feeding on
wheat plants in the United States since 1986, and their plant
destruction has been costing Kansas wheat producers.
Michael Smith and other researchers at
Kansas State University have
been studying wheat plants that are resistant to the aphids as a
way to find a low-risk method of pest management and increase
crop yields.
Smith, a K-State professor of entomology, is focusing on
identifying a gene that controls a single property in the wheat
plant that could deter aphid feeding. The researchers think that
when an aphid threatens a resistant wheat plant, the plant
responds by expressing genes that make some kind of defensive
compound.
"Our goal is to find a gene or genes that are responsible for
the resistance -- something like a product of a signal that
tells the plant to make a toxin or to make a bitter taste,"
Smith said.
He said there is a two-fold benefit to this low-risk method of
pest management. The wheat yield would increase because the pest
damage would be reduced, and plant resistance would reduce or
eliminate the need for insecticide, which affects the producer's
cost and might affect the environment.
"Anytime you use a pesticide, you do run some risk of runoff,
which can affect wildlife and drinking water," Smith said. "We
have very, very few problems with runoff in Kansas, but that's
the whole idea of getting away from the use of insecticides."
When aphids feed on susceptible wheat plants, the insects
destroy the plants' capability to make nutrients to produce
grains. This is visible on the plant when its leaves yellow and
roll into narrow tubes.
Smith's research involves using gene expression experiments. The
ongoing project started two-and-half years ago, but Smith said
the experimental research only took about a week or two. The
quick process involved extracting RNA from infested and
non-infested wheat plant tissues, making DNA from the RNA, and
placing it on a microarray chip.
By damaging the wheat plant, genes are expressed that are not
normally active. K-State researchers looked for a difference of
genes in the resistant and susceptible wheat plants.
"We did the experiment with plants that had been fed on for 24
hours," Smith said. "We have since found that some of the genes
are turned on as soon as one hour within feeding. For a long
time, entomologists and other biological scientists haven't been
able to see this kind of rapid response."
The postexperimental part is more extensive.
"It's the process of taking all the data you get and making
sense of it, because a microarray chip has 55,000 different
little bits of wheat DNA on it, so you can get a lot of
information," Smith said. "You have to go out there and search
yourself. Most of the two-and-a-half years have been searching
the information databases and trying to make sense of this
story."
The researchers narrowed the results down to four genes that are
unique to the aphid-resistant plant. The final step of the
project involves using virus-induced gene silencing that could
identify which of these possible genes control resistance.
"Once we know what that gene for resistance is, we can
selectively add the resistance gene into a normally high
yielding but aphid-susceptible plant, and that's our ultimate
goal," Smith said.
Smith presented the ongoing project in 2004 in Australia at the
International Congress of Entomology and also at the 2007
national meeting of the Entomological Society of America.
Smith said the four possible genes were identified in the last
six months, and he hopes to have the gene-silencing results in
the next two to three months.
"Wheat is the largest major plant genome known," he said. "It's
very repetitive, and you have to sort through lots of stuff. But
we're willing to do that because it's the major crop in Kansas,
and we work for the people of Kansas, and in our case, we also
work for the wheat and barley producers."
Some of the funding for the research project was provided by
grants from the Kansas Crop Improvement Association, the U.S.
Agency for International Development, and the Kansas
Agricultural Experiment Station.
Others involved in the project from K-State include Xuming Liu,
research assistant professor of entomology; Ming-Shun Chen,
adjunct associate professor of entomology; Sharon Starkey,
laboratory technician in entomology; and JianFa Bai, assistant
professor in the K-State Veterinary Diagnostic Lab. Also
involved in the research are Xiang Liu, research associate of
biology at North Carolina State University, and L. J. Wang,
assistant professor of genomics and bioinformatics at Clemson
University. |
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