The overwhelming majority of cotton harvested in the U.S. and worldwide is upland cotton, or Gossypium hirsutum, with more than 6.5 million acres planted in 2012 in Texas alone, according to the USDA. A higher-end cotton called Gossypium barbadense
is more desirable because of greater fiber length and strength but is
late-maturing, low-yielding and more difficult to grow because it
requires dry climates with significant irrigation and is less resistant
to pathogens and pests.
“For a long time cotton breeders have
been trying to develop upland cotton with the fiber qualities of
barbadense cotton,” Pepper said. “Globally, everybody’s trying to do it.
Economically, it’s a huge deal, because every millimeter you add to
fiber length adds that much to the price of cotton when the farmer sells
it.”
The researchers’ method increased the length of the fiber
by at least 5 millimeters, or 17 percent, compared to the control plants
in their experiment.
Pepper, a plant biologist at Texas A&M
since 1995, acknowledges that the cotton plants developed in the project
technically are genetically modified organisms (GMOs), a controversial
subject. But he makes a key distinction: A major criticism of GMOs,
Pepper notes, focuses on cases where genes from other species — even
bacterial ones — have been added to an organism to achieve a desired
trait. For instance, the agricultural giant Monsanto adds a gene to
cotton that makes it resistant to Roundup® and then sells both the seeds
and the weed killer to farmers.
“What we’re doing is a little
different,” Pepper said. “We’re not actually adding in a gene from
another species. Rather, we’re knocking down the effect of one of the
genes that’s already in the plant.”
Like human and animal eyes,
plants also have photoreceptors that pick up information about the
environment. Pepper’s interest is in a type of photoreceptor called a
phytochrome, which is mainly responsive to different wavelengths of red
light. The phytochromes regulate many plant traits, including the length
of leaves and stems and flowering time. The researchers found
literature from the 1990s that suggested the amount of red light also
influenced fiber length in cotton plants.
Using a genetic cross
between a long-fiber plant and a short-fiber plant, then zeroed in on a
region of the genome that sat directly on top of one the phytochrome
genes. They then used a technique called RNA interference to “knock
down” or interfere with expression of that gene, Pepper said.
“This
was pure basic science, seeking to understand the biological function
of a gene,” Pepper said. “And sure enough, the phytochrome ‘knock-down’
plants had all these phenotypic changes associated with it, and one of
them was longer fiber.”
The discovery was especially important to
Ibrokhim Abdurakhmonov, the lead author of the study who received his
master’s degree in plant breeding from Texas A&M in 2001 and is now a
professor in his native Uzbekistan. The landlocked agricultural nation
that borders Afghanistan historically has relied heavily on cotton to
strengthen its rapidly diversifying economy. Once used by the former
Soviet Union as a base for its cotton production, Uzbekistan currently
accounts for around 10 percent of world cotton fiber exports.
“Sustainability
and biosecurity of cotton production is pivotal for the Uzbekistan
economy because agriculture accounts for 24-to-28 percent of the
country’s gross domestic product,” said Abdurakhmonov, who also serves
as director of the Center of Genomics and Bioinformatics at the Academy
of Sciences of Uzbekistan, which is located in the capital, Tashkent,
and part of the Ministry of Agriculture and Water Resources.
“The
increased value of longer and stronger lint, at 10 cents per pound,
would be at least $100 per acre more income from the lint for each new
cultivar using this technology. New markets for longer, finer, stronger
and more uniform cotton lint fiber, as well as early maturity and
increased yield potential could further increase estimated economic
value. Our anticipation of possible improvement of resistance to abiotic
stresses via phytochrome RNA interference further adds to its
commercial potential.”
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