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The Science Behind the Recent GE Corn

April 19, 2002

from Third World Network Information Service on Biosafety

Doc. TWN/Biosafety/2002/C

Attachment 1

Astonishing Denial of Transgenic Pollution

By Dr. Mae-Wan Ho (Institute of Science in Society-UK)

A paper published in Nature last November provoked a furore of responses
from the pro-biotech community. The journal succumbed to pressure by issuing
a retraction: "In light of .. discussions and the diverse advice received,
Nature has concluded that the evidence available is not sufficient to
justify the publication of the original paper." But, as the authors wish to
stand by the evidence and conclusions, Nature thought it best to publish the
criticisms, the authors' response and new data, and to let readers "judge
the science for themselves."

The criticisms appear to hinge on the experimental techniques used by
Berkeley scientists David Quist and Ignacio Chapela to support their claim
that transgenic DNA has polluted the Mexican landraces. First, polymerase
chain reaction (PCR) enabled them to identify the cauliflower mosaic virus
(CaMV) 35S promoter in the landraces. This piece of DNA is incorporated in
virtually every commercial transgenic crop. Then, inverse PCR (iPCR) was
used to look for unknown DNA sequences joined to the CaMV promoter, which
would give information on the structure of the transgenic DNA and its
precise location in the genome. PCR is a standard technique, widely employed
for amplifying and identifying specific sequences present in trace amounts.
Inverse PCR, on the other hand, is a much newer technique, and not yet
widely used.

The critics do not take issue with the identification of the CaMV 35S
promoter, thereby implicitly acknowledging the presence of transgenic DNA in
the landraces. In other words, they are not disputing that transgenic
pollution has occurred.

Rather, their criticisms centre on the iPCR technique for identifying
unknown DNA sequences linked to the CaMV promoter, which they regard as
"suspect" and "artifactual".

Quist and Chapela have found a diversity of sequences linked to the
promoter, thus giving the impression that the transgenic constructs were
"fragmenting and promiscuously scattering throughout genomes", which "would
be unprecedented", according to the first critique. It also denies that
transgene fragments can move around the genome after integration, and does
not bother to tell us that there have been no experiments done previously to
address the issue.

The first critique comes from microbiologist Mathew Metz, former colleague
of Quist and Chapela, now in University of Washington, Seattle, and Johannes
Futterer, from Institute of Plant Science, ETH, Switzerland. The second
critique comes from six colleagues of the authors in Berkeley. In a
controversial bid to take over Berkeley's bioscience department a few years
ago, Ignacio Chapela attracted attention as a major opponent of the
take-over. There is no doubt that the attack on Chapela is at least partly
motivated by politics, a charge levelled against Chapela's work by his
critics from Berkeley. But fortunately, politics is irrelevant in
considering what the experimental results are telling us.

PCR and iPCR both depend on short stretches of DNA, called primers, which
pair up (or hybridise) with parts of the longer sequence to be amplified.
This then enables the DNA copying enzyme to make the rest of the sequence.
Unfortunately, the primers often have sequence similarity to other DNA, and
so they could hybridise to the wrong places, leading to wrong sequences in
the plant genome being amplified. The primers used do have similarities
(homologies) to known plant gene sequences, and hence false priming and
misidentification of sequences could have given the impression that the CaMV
35S promoter is scattered throughout the genome.

In their reply, Quist and Chapela acknowledge that some, though not all of
the iPCR results could represent false priming and misidentified sequences,
and point out that such problems are inherent to the technique. However,
that does not alter their main conclusions.

They provide new data based on a dot-blot technique. A measured amount of
DNA is transferred to a filter (in a dot), dried, and then probed with
transgenic DNA; in this case, the CaMV 35S promoter.

The new data clearly show the presence of CaMV 35S promoter in four landrace
samples at levels less than 5% and greater than 1%, while a historic maize
sample and a maize sample from Peru both stained negative. In other words,
transgenic pollution had indeed occurred as reported in their previous
paper.

The real disagreement is to what extent the transgenic constructs had
fragmented on entering the genome of the landraces or thereafter. The
existing evidence on transgenic instability, documented in some papers cited
by Quist and Chapela, does not rule out the possibility of "fragmenting and
promiscuous scattering" of transgenic constructs, which could have
introgressed into landraces via horizontal gene transfer as well as by
cross-pollination. The significance of Quist and Chapela's work is that it
is the first of its kind in attempting to address this possibility.

Once again, the scientific establishment serving the corporate agenda has
been caught out taking the absence of evidence as evidence of absence. The
agenda is to keep the public confused while transgenic pollution continues
unabated.

Above all, corporate scientists want to avoid having to prove transgenic
lines are stable by the appropriate 'event-specific' molecular data that the
new European Directive requires (See "Europe's new rules could sink all
GMOs", ISIS News 11/12, October 2001
http://www.i-sis.org.uk/isisnews/i-sisnews11-3.php). This involves
documenting that the transgenic insert has maintained the same structure and
location in the plant genome in successive generations. No such
'event-specific' molecular analysis has ever been done for any transgenic
line. Significantly, Monsanto's Roundup Ready GM soya failed the test when
recently analysed. Regulators should insist on this molecular data, and the
data should not be hidden away from the public under "commercial
confidentiality". Otherwise, regulators should be held liable for any
damages caused as a result.

The only decent thing for the scientific establishment to do now is to give
plenty of support to Quist and Chapela and others to extend their research.
The aim is to rule out the possibility that transgenic constructs could be
fragmenting and scattering, throughout the genome as well as throughout the
ecosystem, by horizontal gene transfer and recombination. Meanwhile, no more
transgenic crops should be released, especially those with the CaMV 35S
promoter, until they could be proved stable by event-specific analyses (see
"Who's afraid of horizontal gene transfer?" ISIS report, 4 March, 2002
http://www.i-sis.org.uk/hgt.php).

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