Ithaca, New Yrok
August 6, 2009
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This
image shows the tremendous genetic diversity in maize,
as seen by the wide range of kernel and ear traits.
{Photo credit: Carlos Harjes) |
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Two new large-scale studies by
researchers at Cornell
University and the U.S. Department of Agriculture (USDA),
published in this week's Science (Aug. 7) journal, report major
discoveries in maize genetics that could revolutionize maize
breeding and may help researchers better predict complex traits
in humans.
In a study using more than 1 million maize plants to identify
the genes involved in flowering time, the researchers found that
the trait is influenced by the combined effects of more than 40
genes.
Flowering time influences whether a plant can adapt to new
environments and is the main hindrance to exchanging crops
internationally.
The study is relevant to humans, because such traits as height,
for example, are likely to also involve many genes.
"We looked as hard as we could for big genes and big effects,
but they don't exist," said Ed Buckler, the lead author of the
maize flowering time paper, a USDA-Agricultural Research Station
(ARS) research geneticist in Cornell's Institute for Genomic
Diversity and an adjunct professor in plant breeding and
genetics.
"Instead, there are lots of smaller genes around the genome that
contribute to flowering time," Buckler added. "What we see in
maize is probably what is going on in humans as well."
Buckler and Stephen Kresovich, Cornell's vice provost for life
sciences and a professor of plant breeding and plant biology,
were lead co-authors of both papers, along with USDA-ARS
research geneticists James Holland at North Carolina State
University and Michael McMullen at the University of Missouri.
Researchers from many other institutions also contributed to
both studies.
While some genes are known to interact with other genes with
unexpected results, the researchers noted that the effects of
the genes they studied all added together to influence
maize-flowering time, which can vary by months in the 5,000
maize varieties that were crossed in the study.
Using a computer model based on the additive effects of these
genes, the researchers predicted with 93 percent accuracy when a
maize plant would flower. The research offers promise for
designing new maize varieties with computers and then predicting
their flowering time in the field, Buckler said.
In human genetics, researchers can only explain 4 percent or 5
percent of variation, but the researchers believe the new maize
model may help geneticists better predict the effects of genetic
variations in humans.
In the second large-scale study by the same group, also in this
week's Science, the researchers uncovered for the first time an
important pattern in gene recombination (the ability to shuffle
genetic variation), where large parts of the genome fail to
recombine near the center of a hybrid corn's chromosome. Known
as the centromere, this area looks like a knot between two
strands of yarn tied together near the middle.
Over the last 100 years, breeders have created vigorous and
diverse hybrids that have increased U.S. yields eightfold. But
after crossing 25 diverse lines of maize and producing 136,000
recombinations since 2001, the researchers uncovered a
consistent pattern that genes near the centromeres are often in
arrangements that produce less vigorous plants. The researchers
believe this pattern may contribute to the survival and vigor of
hybrids, but that it has also prevented breeders from arriving
at optimal genetic combinations.
"Now, combining gene variants near the centromere will be a
future direction for plant breeders," said Buckler. "Breeding
schemes designed to exploit this knowledge could accelerate
plant breeding worldwide."
For this study, the researchers created 5,000 different
varieties of maize, each capturing a wide range of trait
variation. The seeds are available to the public.
The studies were funded by the National Science Foundation and
the USDA-ARS. |
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