BIOTECHNOLOGY:
Has GM
Corn 'Invaded' Mexico?Charles C. Mann
On Thursday, 21 February, the gene wars took a stunning new
twist, or so it seemed. Mexican newspapers reported that two teams
of government researchers had confirmed University of California
(UC), Berkeley, biologist Ignacio Chapela's explosive findings: that
transgenic corn was growing in Mexico, the heartland of maize
diversity.
Yet even as Chapela was proclaiming this news at a Mexico City
press conference, a scathing editorial in the February issue of
Transgenic Research was crisscrossing the globe by e-mail.
In it, editor Paul Christou charged that Chapela and his co-author,
UC Berkeley graduate student David Quist, had presented "no credible
evidence ... to justify any of [their] conclusions." Meanwhile,
Nature, which published the Quist-Chapela paper last November,
was weighing the publication of no fewer than four biting
critiques of the article. Adding to the muddle, Elena Alvarez-Buylla
Roces, a biologist at the National Autonomous University of Mexico
who appeared with Chapela at the press conference, insisted in a
later e-mail to Science that Mexican investigators "still
do not have definite answers towards corroborating or not
[corroborating] Chapela's results."
Welcome to the "maize scandal," which is driving the battle over
genetically modified (GM)crops to new heights of acrimony and
confusion. Widely circulating anonymous e-mails accuse Chapela and
Quist of conflicts of interest and
other misdeeds. Meanwhile, 144 civil-society groups have leapt to
the authors' defense, asserting in a joint statement on 19 February
that the biotech industry is using "intimidatory" techniques to
"silence" dissident scientists. "I've never seen anything like it,"
says Peggy Lemaux, a UC Berkeley molecular biologist who is one of
the most public critics of the Quist-Chapela paper. "There's been a
lot of fighting about transgenics, but this is something else."
Still unclear, say many scientists, is whether transgenic corn
has indeed invaded Mexico--and if so, whether it poses a threat to
one of the world's most important foodstuffs.
The furor began on 29 November, when Quist and Chapela reported that
transgenic maize genes had introgressed--skipped from one gene pool
to another--with traditional strains (landraces) of maize in remote
areas of Oaxaca. The highlands of Oaxaca, Chiapas, and adjacent
Guatemala are one of seven "centers of genetic diversity" that
spawned most of today's crops. To protect this diversity, an
invaluable resource for crop breeders, the Mexican government
declared a moratorium in 1998 on planting transgenic maize anywhere
in the nation. Now the Nature paper was claiming "a high
level of gene flow" from illegally planted transgenic maize to local
landraces--a process that Quist and Chapela argued could exert
"a major influence on the future genetics of the global food
system."
At risk?
Traditional strains of maize could be threatened by GM corn.
CREDIT: CIMMYT
Greenpeace and others opposed to biotechnology immediately called
on the Mexican government to ban transgenic U.S. maize, the presumed
source of the foreign genes. (Free-trade rules let transgenic maize
be shipped into Mexico but not grown there.) "World food security
depends on the availability of this diversity," Chapela told
Newsweek in January. "Having it contaminated is something
humanity should worry about."
Adding to the alarm, Quist and Chapela suggested that the
transgenes were unstable. The foreign genes, they wrote, often
"seemed to have become re-assorted and introduced into different
genomic backgrounds." In other words, when transgenic maize
hybridized with landrace maize, the novel genetic material broke up
into chunks that jumped around the genome. The implications were
profound: Because a gene's behavior depends on its place in the
genome, the displaced DNA could be creating utterly unpredictable
effects.
Activists' fears centered on the promoter sequence--usually CaMV
35S, which originates in the cauliflower mosaic virus--used to drive
the activity of newly inserted genes for, say, herbicide resistance.
If the promoter broke off during hybridization, it could conceivably
take over other genes, with unknown consequences. "The spread of the
promoter could prove to be worse than the spread of the genes for
herbicide and insect resistance," says Peter Rosset, co-director of
the Institute for Food and Development Policy (Food First), a
research group that advocates on behalf of small farmers. "If true,
this would be a red flag that would call into question every other
GM crop on the market."
But Lemaux and other critics aren't buying it. "They're saying
that the [hybrid and introgressed] genomes were completely unstable
all the time," she says. "I've worked with transgenic corn for 10
years, and I've never seen anything like that."
To search for transgenic DNA, Quist and Chapela took sample ears of
maize from two locations in Oaxaca in October and November 2000 and
tested them using the polymerase chain reaction. PCR amplification
detects particular snippets of DNA by multiplying them to observable
levels. Unfortunately, notes molecular biologist Marilyn Warburton
of the Mexico-based International Maize and Wheat Improvement Center
(CIMMYT), PCR is so sensitive that minute traces of laboratory
contaminants can create false-positive results. "If you get a
positive result, you have to check it repeatedly," Warburton says.
"And even then you need to confirm it by another method to be
completely sure you're not fooling yourself." Chapela and
Quist did not report performing such
additional tests.
Motivated by these sorts of concerns, at least four groups of
researchers--from the University of Washington, the University of
Georgia, and two from Quist and Chapela's home base of UC
Berkeley--sent sharply critical letters to Nature in
December. Three referees reviewed the letters and recommended
publication of one or more, accompanied by a rebuttal from
Quist and Chapela. "The PCR and iPCR
[inverse PCR, a variant] data presented is simply not sufficient
data to warrant ANY of the conclusions of the authors," including
both the presence of transgenic DNA in Mexican maize and its
instability, declared the first reviewer. "Nature should
demand that the authors retract their manuscript if they cannot
demonstrate well-controlled DNA blot analyses [a common confirmatory
test] documenting transgene integration events."
"Nature is coming under pressure to use secondary
technical criticisms to discredit our main findings," responds
Quist. Regarding doubts about the
instability he reported, he believes that "the critique is coming
from expectations" created by lab experiments "that aren't
necessarily reflected in what you see when you go out in nature." To
respond to criticisms, "we're discussing with Nature the
possibility of publishing [in a reply] some new information that
substantiates our findings."
(Science obtained three of the letters, the initial
Quist-Chapela response, and some of
the anonymous referee reports from sources other than their authors,
who are blocked by Nature from discussing their critiques
before publication. Nature editor Philip Campbell says the
journal acts "as promptly as possible" on criticisms, publishing
them when "appropriate.")
Surprisingly, even Quist and Chapela's most strident
critics agree with one of their central points: Illicit transgenic
maize may well be growing in Mexico. In May 2001 Chapela shared his
initial results with the National Institute of Ecology (INE, the
research arm of the Mexican Ministry of the Environment and Natural
Resources) and the interagency National Biodiversity Council
(CONABIO). Concerned, INE and CONABIO took maize samples from 20
random locations in Oaxaca and two in the adjacent state of Puebla.
The samples were divided into two groups and independently analyzed
by researchers at the National Autonomous University of Mexico and
the Center for Investigation and Advanced Studies (CINVESTAV) at the
National Polytechnic Institute. At a 23 January meeting in Mexico
City, CINVESTAV official Elleli Huerta presented preliminary PCR
findings indicating that transgenic promoters, mostly CaMV 35S, were
present in about 12% of the plants. In some areas, up to 35.8% of
the grain contained foreign sequences, INE scientific adviser Sol
Ortiz Garcia told Science last week.
According to Ortiz, both the INE lab and the National Autonomous
University of Mexico labs are still "double-checking" the findings.
The possible corroboration, Alvarez-Buylla Roces says, is "only
based on PCR tests and [is] preliminary." Indeed, says Timothy
Reeves, director-general of CIMMYT, which is working with the
Mexican government, the two Mexican teams are now responding to the
criticism of PCR methodology by revamping their analyses to include
bigger samples and more reliable tests.
Meanwhile, CIMMYT, which develops improved crops for Third World
farmers, has been searching its vast storehouse of maize varieties
for transgenic "contamination." By 22 February, the lab had found
none, and the organization has adopted measures that it believes
will prevent GMmaize from entering its gene bank, preserving at
least some of Mexico's maize diversity. But given the amount of
transgenic maize in the United States, Reeves believes it is "very
likely" that some will eventually end up growing in Mexico. For now,
however, "transgenic maize in Mexico is still hypothetical."
Volume 295, Number 5560, Issue of 1 Mar 2002,
pp. 1617-1619.
Copyright © 2002 by The American Association for the
Advancement of Science. All rights reserved.
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