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We have cause to be concerned about the arsenic in rice since rice and rice
flour can be a large component of a gf diet (though it doesn't need to be).
This might be one of the good applications of genetic engineering, leading
to arsenic free or lower arsenic GMO rice, if over expression can indeed be
proven to further reduce arsenic levels in the rice grains.

How Rice Overcomes Arsenic
Researchers have discovered a transporter protein in rice that sequesters
arsenic in vacuoles, preventing the toxic element from traveling into
grains.
By Kate Yandell | October 20, 2014
Rice (Oryza sativa) is a staple crop for half of the world's population, but
it can accumulate high levels of arsenic. When consumed over time, arsenic
can lead to cancer and skin lesions. But the plant has its own mechanisms
for fighting arsenic accumulation, according to a paper published today
(October 20) inPNAS. Researchers based in Korea and Japan have shown that a
rice transporter protein called OsABCC1 prevents arsenic from damaging plant
tissues by sequestering the element in vacuoles. Because of this,
potentially harmful arsenic remains in these cellular waste containers
rather than building up in rice grains.
"What they have shown in this paper is really quite impressive," said Andy
Meharg
<http://pure.qub.ac.uk/portal/en/persons/andrew-meharg(7ec0f8da-1d21-4903-9a
6f-9b1ac32afc44).html> , chair of plant and soil science at Queen's
University Belfast in the U.K. "The difference between having these ABC
transporters and not having them is very, very large."
The researchers now hope to find rice plants that express high levels of
OsABCC1 or to genetically engineer rice to overexpress the transporter. This
strategy "offers one of the simplest and most cost-effective approaches to
solving the problem of arsenic contamination of rice and rice-based
products," Mary Lou Guerinot
<http://www.dartmouth.edu/~guerinot/LAB_/Mary_Lou_Guerinot.html> , who
studies metal transport at Dartmouth College, wrote in an e-mail to The
Scientist.
Rice accumulates arsenic both because of its growing conditions and biology.
The crop is often grown in flooded rice paddy fields, where arsenic becomes
arsenite, a compound that bears a strong chemical resemblance to silicic
acid. The rice plants take up the silicic acid through transporters in their
roots. Silicon makes rice plants stiff and sharp, allowing them to remain
upright in damp conditions and to ward off pests. But while rice is getting
its needed dose of silicon, it's accidentally drinking up arsenite. Arsenic
is also found as arsenate, which mimics the key nutrient phosphate.
Arsenic toxicity is particularly problematic in areas of Southeast Asia
where people drink arsenic-contaminated water and eat rice as a staple of
their diets. Sometimes, they grow and cook their rice in the same
arsenic-rich water they drink. "The risk is related to the concentration in
rice that they have, and also the water they are drinking, and the amount of
rice that [they] eat," said Steve McGrath
<http://www.rothamsted.ac.uk/people/mcgrath> , a biogeochemist at Rothamsted
Research in Harpenden, U.K., who was not involved in the study.
Arsenic toxicity also poses a problem for rice; among other things, it can
significantly stunt plant growth.
The researchers opted to examine the role of OsABCC1 in rice because of
previous research <http://www.pnas.org/content/107/49/21187.short>  led by
coauthor Won-Yong Song of Pohang University of Science and Technology, whose
team found that related transporters sequesters arsenic in the model plant
Arabidopsis thaliana.
Song and his colleagues have now found that OsABCC1 is found in the lipid
membrane surrounding vacuoles, called the tonoplast, in rice cells. When the
researchers knocked out OsABCC1, the rice grew poorly in the presence of
arsenic compared to wild-type plants. Furthermore, while only 3.4 percent of
arsenic found in total in the rice plants ended up in rice grains in
wild-type rice, 20 percent to 24 percent made it to the rice grains in
plants when OsABCC1 was knocked out.
The next step is to determine whether increased OsABCC1 expression can
reduce arsenic levels in rice below their current levels in major cultivars.
"The key now is to find rice or make rice through GMO [genetically modified
organism] techniques that are suited to storing arsenic in the vacuoles,"
said Meharg.
Study coauthor Jian Feng Ma
<http://www.rib.okayama-u.ac.jp/plant.stress/index.html> , a professor at
the Institute of Plant Science and Resources at Okayama University in Japan,
said that his team plans to proceed on all fronts. He and his colleagues
will attempt to use a strong promoter to overexpress OsABCC1, and they will
also look at how expression levels of the transporter vary naturally between
rice cultivars. If they find a cultivar that expresses high levels of the
transporter and sequesters extra arsenic, they then may be able to breed
that cultivar with more mainstream varieties.
Finally, Ma's team continues to look for other transporters that either help
bring arsenic to the rice grain or sequester it. "Maybe there are a lot of
transporters for arsenic in different cells," he said. "If you combine all
of them, maybe you can get an arsenic-free rice."
W. Song et al., "A rice ABC transporter, OsABCC1, reduces arsenic
accumulation in the grain,"PNAS, doi:10.1073/pnas.1414968111, 2014.


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