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[SANET-MG] gm cotton that people forgot
http://www.i-sis.org.uk/GMCTPF.phpISIS Press Release 20/01/05
GM Cotton that People Forgot
GM cotton has aroused relatively little resistance outside the Third
World for the simple reason that it is wrongly perceived to be a
non-food crop. Prof. Joe Cummins and Dr. Mae-Wan Ho report
A longer, fully referenced version is posted on ISIS members’ website.
GM cotton a triple-threat
Cotton is a triple-treat (or threat) crop because it produces fibre,
food and feed. Fibre is recovered from the flower bolls, while the seeds
are pressed to yield oil for the kitchen and cake for animal feed.
Monsanto Corporation has been a major source of genetically modified
(GM) cotton lines.
A line called Bollgard was first marketed in the United States in 1995,
followed in later years by Canada, Australia, China, Argentina, Japan,
Mexico, South Africa, India and the Philippines. In 2002, an enhanced
line called Bollgard II was approved in the United States, Canada,
Australia, Japan and the Philippines.
Bollgard II was made from Bollgard simply by inserting into the plant
cells a gene cassette containing a Bacillus thuringiensis (Bt) toxin,
Cry2Ab, different from the one in the original Bollgard, Cry1Ac. From
the transformed cells, a line containing the two different Bt toxin
genes were selected. Two toxin genes were more than twice as effective
in pest control than the original Bollgard and theoretically, far less
likely to allow insect resistant mutants to evolve.
The Bt toxin genes, unlinked, are reported to be driven by different
versions of the cauliflower mosaic virus (CaMV) 35S promoter: that of
crylAc has a duplicated enhancer, while that of cry2Ab has the enhancer
and also the leader sequence from petunia heat shock 70 gene as an extra
booster. CrylAc is accompanied by the kanamycin resistance marker gene,
nptII, while cry2Ab is accompanied by the marker gene uidA that produces
a staining reaction. CrylAc confers resistance to lepidopteran-insects
in general, and cotton bollworm, tobacco budworm, and pink bollworm, in
particular. Upon ingestion of this protein by susceptible insects,
feeding is inhibited, eventually resulting in death.
The Bt toxin genes are both synthetic versions of the natural genes in
the soil bacterium, Bacillus thuringiensis var. kurstaki, with coding
sequences modified to improve expression in plants. The synthetic genes
have not been subject to evolution and their recombinational and other
properties relevant to safety are unknown and untested.
Thus, Bolgard II has two separate transgene insertions with some regions
of DNA homology (similarity). Such regions could act as recombination
signals for somatic or meiotic recombination, leading to drastic
chromosome rearrangements. The claim to genetic stability reported in
the governmental reviews is simply the finding that the insertions
segregate according to Mendelian ratios in a few crosses and does not
consider molecular and chromosomal instability associated with inter-
and intra-chromosomal recombination at sites of DNA homology. Signs of
instability and other failures have been observed in the field (see
"Australia adopts GM cotton" and "GM cotton fiascos around the world",
Seed distribution is controlled by the licenses of the patentee, and
seed lines can, and should be screened at that point for translations,
duplications or deficiencies resulting from intra- and inter chromosomal
Furthermore, in evaluating safety to humans and the environment, the
toxin proteins are frequently isolated from liquid culture of the
bacteria to avoid having to carry out the more expensive isolation of
the toxins from cotton plants. As the toxin transgenes are synthetic
approximations of the natural genes and the toxin proteins are not
identical, the test results with bacterial proteins do not truly
represent the impact of the toxins from the transgenic cotton plants.
Some feeding studies indicated that Bollgard II cotton controlled insect
pests more effectively. One research group predicted that the need for
supplemental insecticides would be reduced or eliminated for
lepidopteran pests. Another research group indicated, however, that
insect-resistance to Bollgard II could best be controlled with an
overspray of chemical insecticide. Further studies showed that
resistance to the two Cry toxins seemed to evolve simultaneously,
raising considerable doubt over the efficacy of gene stacking in
delaying insect resistance. Studies reported by researchers from
Monsanto Corporation showed that the Cry1Ac toxin and the Cry2Ab toxin
were produced in equivalent amounts in Bollgard II, but that Cry2Ab was
the larger contributor to insect toxicity, and they suggested a
relatively simple resistance monitoring policy. It seems likely that
chemical pesticides will be needed to combat insect resistance arising
in Bollgard II after all (see "Australia adopts GM cotton", this series).
The regulation of Bollgard II has been ‘fast and loose’. Bollgard II was
supposed to address the major concern of resistance management, but
research is already indicating that gene stacking is not a panacea and
that chemical pesticide overspray will be required to cope with
Round up Ready Cotton
Roundup Ready cotton, like Bollgard I and II, is also used for fibre,
food and feed. Roundup Ready (rr cotton) was first marketed in the
United States in 1995, and in later years, in Canada, Japan, Argentina,
South Africa, Australia, the Philippines and in 2004, in China.
The herbicide tolerant cotton marketed as rr cotton was originally
derived from two different transformation events of a cotton line called
Coker 312. These events, designated 1445 and 1698, differed in both gene
sequences inserted and insertion sites in the cotton genome. Currently,
event 1445 is the primary rr cotton marketed.
Event 1445 was obtained by transformation with a plasmid containing a
synthetic version of the glyphosate oxidase (gox) gene driven by a
modified figwort mosaic virus promoter and terminated by the nos
terminator tnos from Agrobacterium, plus a synthetic CP4 epsps gene
derived from Agrobacterium strain CP4 (encoding the enzyme
5-enolpyruvylshikimate-3-phosphate synthase) preceded by a chloroplast
targeting sequence from Arabidopsis, also driven by the figwort mosaic
virus promoter, and terminated by a terminator from the pea plant.
In addition, two antibiotic resistance marker genes were present: aad
from a bacterial transposon,Tn5, conferring resistance to streptomycin
and spectomycin, inserted after the epsps gene cassette; followed by
kanamycin resistance gene, also from Tn5 driven by the CaMV promoter and
terminated with the tnos.
In the marketed crop, event 1445 appeared to have lost the gox gene but
retained aad, which the company claims, is inactive in the cotton plant.
However, the rr cotton failed to gain approval from the European
Commission in 1999 on account of serious concerns over the aad
antibiotic resistance marker. The fact that it is inactive in cotton
plants is irrelevant, because it is surely active in bacteria, to which
it could be transferred.
Event 1698 is similar except that it has an additional epsps gene. The
events were described as being "stably inherited", with no molecular
Monsanto and the regulators seem to agree that direct human exposure to
the transgenes and their products will be very limited because
cottonseed oil contains very little protein and DNA. Nevertheless, farm
animals consume a great deal of seed cake.
Monsanto’s safety assessment of rr cotton dismissed the possibility that
the epsps gene and the antibiotic resistance marker genes could
participate in horizontal gene transfer with soil bacteria. However, the
bacterial marker gene for kanamycin reistance in transgenic sugar beet
was found to readily transform soil Pseudomonas, while transgenic potato
marker gene readily transformed soil Actinobacter through homologous
recombination. In both cases, the marker persisted for long periods in
the soil bacteria and such bacteria are capable of exchanging genes with
animal pathogens. It is very likely that the streptomycin resistance
marker gene will transform soil bacteria.
Monsanto’s claim, that to effectively transform bacteria the marker
genes require co-transformation with a bacterial promoter, is not
realistic; operator fusions are commonplace in bacteria, suggesting that
the marker genes can easily become activated. There are also special
mobile genetic elements called integrons containing sites with
ready-made promoters for insertion of antibiotic resistance coding
sequences so they can be expressed.
Glyphosate applications can be used to control weeds prior to flowering,
but glyphosate application after initiation of flowering in rr cotton
reduced pollen viability and seed set, resulting in reduced yield; while
glyphosate application to rr cotton combined with water stress resulted
the young cotton bolls dropping off. Use of rr cotton seems to require
irrigation technology and considerable technical savvy.
An additional concern related to using glyphosate on cotton is that the
herbicide has been shown to move from cotton fabric into and through
GM cotton not safe
Regulators seem to have taken a relaxed attitude towards many safety
issues including antibiotic resistance markers going into GM crops. The
potential toxicities of the synthetic genes, their ability to recombine
and stability have yet to be documented. Already, all the transgene
products, Cry1Ac, Cry2Ab, CP4 EPSPS, as well as the marker gene product,
UidA, show stretches of amino-acid sequence identities to known
allergens, and are hence suspected allergens; at least, until proven
otherwise by further studies.
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