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Back on the Map
3/30/2007
Margy Fischer
To
get from point A to point B, you need to know how to read a road map.
Much is the same with the current research in wheat genetics.
Although
there is no fast lane, there have been recent advancements. The genetic
map of the wheat plant has been completed, and it is estimated the
sequence of the entire wheat genome will be done in another 10 years.
The
completed genetic map has allowed researchers to better locate the
genes responsible for desirable characteristics relative to molecular
markers that are then used in marker-assisted selection. This technique
complements traditional breeding.
“There
are two things you can do with the marker that you can’t do
in the field,” explains Jorge Dubcovsky, a researcher at the
University of California–Davis. “I can put multiple
resistance genes in a variety at one time, and I can breed for pathogen
resistance before a pathogen has arrived from another
country.”
Dubcovsky
is also the project leader of the Wheat-Coordinated Agricultural
Project (Wheat-CAP), which is funded by a
USDA–Cooperative State Research, Education, and Extension
Service (CSREES)-supported grant. The marker-assisted selection
approach uses markers as landmarks so that breeders can transfer a
particular section of chromosome.
“This
grant is bridging the gap between developing information about wheat
genetics and implementation into varieties,” he says.
“We are translating the genetics and trying to translate that
basic map of the genome into a product a farmer can use.”
To
make wheat resistant to pests requires inserting only one gene into the
plant. However, altering the characteristics of wheat—quality
and yield, for example—would require understanding the
hundreds of genes that affect those traits.
An
example of how Wheat-CAP research can be applied is using the markers
for genes that control bread-making quality. This can speed up the
breeding process by selecting genes with the best
bread-making qualities, rather than plants with the desired
characteristics, and then breeding them into a variety in many stages.
In
all, Wheat-CAP research has produced 23 lines of wheat plants (10 lines
of hard red spring wheat using marker-assisted selection).
Some of these lines are being released as new varieties; others that
are not agronomically competitive are being used as parental lines for
new crosses. The project has also been able to develop a line resistant
to the Hessian fly.
The
plants produced using marker-assisted selection have had genes
transferred from the same species. Because this process is in line with
traditional breeding, the plants are not considered genetically
modified organisms, and all local and international wheat markets
accept them.
It
is thought that only 3% of wheat’s genetic information is
used for making proteins. But, to identify the relevant genes, the
entire sequence of genes must be known.
The
next step for the researchers is to sequence the mapped genome and
navigate its genetic potential for biotechnology applications. With the
full sequence, scientists can then pinpoint specific genes on the
genetic map of wheat.
“Overall,
we don’t have enough genomic knowledge of the wheat
plant,” says Bikram Gill, founder of Kansas State
University’s (KSU) Wheat Genetic and Genomic Resources Center.
While
a genome sequencing project for rice has been successfully completed
and the corn genome is currently being sequenced, similar progress for
wheat is far behind.
“The
number of genes is very similar among crop plants, but the genome size
varies widely,” Gill explains. “Although
it’s the most complex genome and a very important crop, wheat
genomics lags way behind other crops.”
The
importance of researching wheat genomics, Gill says, stems from the
global impact wheat has on the world’s food supply.
“When
you talk about wheat, keep in mind it’s grown on more land
than any other crop. The crop is 6,000 years to 7,000 years old,
it’s the most nutritious crop as a source of protein and it
has the largest genome among all crops,” Gill says.
Gill
is a member of the International Wheat Genome Sequencing Consortium,
which was formed in May 2005. Due to the complexity of the wheat
genome, as well as its global impact, this group of scientists is
collaborating to finalize the sequence from across the globe. Although
slow, researchers are making progress in sequencing the wheat genome.
Once
the sequencing is done, researchers will know the genes responsible for
expressions. This will enable wheat plants to be
transgenic—engineered instead of bred for characteristics.
In
one project funded by USDA and the Department of Energy, KSU
researchers were able to identify 200 genes in the wheat plant that
work to build cell walls. Once it is known how these genes affect the
cell wall structure, scientists should be able to more efficiently
extract cellulose. The next step could be a wheat crop that can serve
as a more efficient feedstock for cellulosic ethanol production.
The
wheat plant also has unique genes, such as those that make gluten.
Knowing more about how the plant produces gluten could lead to new
wheat products available for people who express gluten
allergies.
Even
though each of these projects focus on different pieces of the wheat
genomic puzzle, the vast majority of their funding relies on public
support. Currently, most of the funding for the genome sequencing
project is coming from the National Science Foundation and
USDA–CSREES.
“We
did a survey, and 78% of the varieties of wheat, which is a
self-pollinating species, are public varieties,”
Dubcovsky says. “It’s inevitable we’ll
have transgenic wheat in the future, but it’s unknown when
and who will be the first to release it.”
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