Rice War Continues
Editor’s note
The productivity of rice has been falling along with that of other food
grains. Chief among the causes of the fall in productivity are severe water
shortages due to over-irrigation and depletion of aquifers, eroded soils from
over-application of chemical fertilizers and pesticides, and rising
temperatures from global warming.
While innovative farmers have been addressing these problems with a
range of effective measures to increase yields through regenerating degraded
soils, conserving water and minimizing inputs (see many articles in
SiS23), pro-GM
scientists in the three major rice-growing countries, China, India and Japan,
have all been researching and promoting GM rice with scant regard for safety or
sustainability.
We are circulating Professor Joe Cummins’ review on GM rice in
China, and making available two others, on GM rice in India and Japan
respectively on ISIS’ website:
GM Rice in Japan
GM Rice in India
ISIS Report 30/11/04
GM Rice Release in China?
Reduced production and transportation bottlenecks have persuaded
China to think of growing GM rice, but Prof.
Joe Cummins says it is unwise for serious safety reasons.
The references for this
article are posted on ISIS members’ website.
Details here.
GM rice a solution to rice shortfall?
Remote sensing data reveal that China has about 1.27 million square
miles of cropland. Annual rice production, as a single or double crop, or
cropped with wheat or oilseed rape, accounts for about 19% of the cropland in
China [1]. Rice is far and away the most important food crop in China.
At the same time, agricultural biotechnology is growing faster in China
than in any country apart from the United States. In 2002, China announced
regulations for biosafety management of genetically modified (GM) crops and
rules for labeling GM products [2].
This year, rice prices rose about 27% in China because of reduced
production and transportation bottlenecks; and it was thought that
commercializing GM rice could solve the problem.
The government reportedly set aside one billion dollars to hasten the
commercial release of GM rice to farmers [3]. Even though there has been
extensive research on GM rice in China, it is not yet clear which GM rice
varieties will be selected for first release to farmers. Likely candidates may
be among those featured in recent scientific publications in international
journals.
Insect resistant rice
Insect resistant rice tops the list of likely candidates for commercial
release; the most widely used transgenes being the Cry toxins isolated from the
soil bacterium Bacillus thuringiensis (Bt). There are a number of Cry
toxin proteins, each specific for a range of insect pests. Individual
cry genes and their proteins are identified by a number 1, 2, 3 etc.,
followed by a letter A, B, C etc. That letter is followed by a lower case
letter a, b, c, etc. The numbers signify a cry gene on the bacterial
chromosome, while the letters signify the alleles (different forms) of the
gene; the upper and lower case letters indicate respectively greater and lesser
DNA code letters differences between the alleles, which in turn determine their
toxicities to different insect pests.
A gene fusion protein toxin made up of two different synthetic Cry
toxins - Cry1Ab fused with Cry1Ac - has been inserted into Indica rice
[4]. The fusion protein was under the control of the rice actin promoter with
its first intron and the nos gene terminator, tnos, from the soil
bacterium, Agrobacterium. The fusion toxin was active against two insect
pests of rice, leaf folder and yellow stem borer. However, the fusion toxin
does not appear to have been tested for mammalian toxicity and it has not yet
been used in any GM crop that has been released commercially.
About a third of rice lines transformed with Bt toxin Cry1Ab or Cry1Ac
suffer genetic aberrations, such as chlorophyll deficiency or stunted plants.
The variability was ascribed to ‘somaclonal’ variation [5], the
consequence of genetic instability common to the plant tissue culture technique
used in creating the GE lines. It is thought to result from the activation of
mobile genetic elements or transposons that frequently insert into and disrupt
the rice genes. Such insertion mutations are capable of creating unexpected
toxins and for that reason cannot be ignored.
Research has shown that rice leafhoppers are controlled by GM rice with
Cry1Ab toxin. The synthetic cry1Ab gene was placed under the control of
the maize ubiquitin promoter, linked in tandem with gus (encoding the
b-glucuronidase, a positive selection marker), and
the negative selection antibiotic resistance markers hpt (encoding
hygromycin resistance), and npt (encoding neomycin resistance) [6]. The
GM rice reduced leafhopper damage, but there has not been much study on the
environmental and human-health impacts.
Straw from GM rice containing Cry1Ab was found to alter important
biological properties in water-soaked soil, indicating a shift in the metabolic
activities of the soil [7]. In China, rice straw is usually incorporated along
with the plant residues into soil to enhance fertility, so the implications of
these changes are important.
There are both scientific and anecdotal evidence, reviewed in earlier
reports, suggesting that the natural Cry toxins pose serious health hazards to
human beings and animals. Bt spores containing a mixture of different Cry
toxins caused allergic reactions in farm workers [8]. Cry1Ac, in particular,
has been shown to be a potent immunogen [9, 10]. The synthetic Cry toxins
incorporated into GE crops differ from the natural toxins in many respects and
are often hybrids of two or more Cry proteins. These synthetic proteins are
completely unknown and untested for their toxicities and allergenicities
[11].
A screening of transgenic proteins expressed in market-approved
transgenic food crops against known allergens in the public databases raised
further concerns [12]. Twenty-two out of 33 proteins screened were found to
have stretches of identities with known allergens, and therefore "warrant
further clinical testing for potential allergenicity". These include all the
Cry toxins, the CP4-EPSPS and GOX (responsible for glyphosate tolerance), many
viral coat proteins (viral resistance) and even proteins encoded by marker
genes such as GUS.
The Galanthus nivalis (snowdrop) plant lectin gene (gna)
was used to protect rice from the small brown planthopper [13]. The genetically
engineered rice contained the gna gene, driven by the phloem-specific
Rss1 promoter, accompanied by the markers hpt gusA, both driven
by the cauliflower mosaic virus (CaMV) 35S promoter. While the GM rice
controlled the sap-sucking insect [8], further studies on the safety of GNA
rice should be undertaken because GNA potatoes containing the snowdrop lectin
and the CaMV 35S promoter were found to increase proliferation of the gastric
mucosa, and the hyperplasia was attributed to the transgenic construct or
process [14].
Disease resistant rice
One of the most devastating diseases of rice in Africa and Asia is
bacterial leaf blight (BB), which is caused by the Gram-negative bacterium
Xanthomonas oryzae pv. oryzae (Xoo). The rice gene Xa21
provides resistance against some races of Xoo, although the endogenous
gene is expressed at a low level.
A ferredoxin-like protein from sweet pepper was found to confer
resistance to Xoo. Ferredoxins are iron-sulphur proteins that mediate
electron transfer in a range of metabolic reactions, and plant type ferredoxin
is located in the chloroplast membrane.
The sweet pepper ferrodoxin gene (ap1) was inserted in the rice
genome to confer resistance against BB [15]. Ap1with the chloroplast
transit peptide was driven by the CaMV promoter and transcription terminated by
tnos. The transgenic rice also contained the marker genes gusA
and hpt, both driven by the CaMV 35S promoter and terminated by
tnos.
Enhanced resistance to BB was conferred using the rice Xa21 gene.
However, the transformation included the bacterial hygromycin antibiotic
resistance marker and the gus marker along with the bacterial
beta-galactosidase (z) gene [16], not to mention the CaMV 35S promoter
and Agrobacterium nos terminator. Transferring genes from rice to rice
using genetic engineering, rather than crossing and selection, was justified by
the researchers, as they considered the conventional crosses needed to separate
Xa21 from flanking genes that were undesirable too time-consuming. Yet,
molecular marker-assisted selection has actually been used to introduce the
Xa21 gene into rice cultivars using conventional breeding and selection
[17]. The marker-assisted variant of conventional breeding and selection
provides the advantage of conferring BB resistance, while avoiding the
insertion of antibiotic markers and other potentially problematic genes into
rice.
Rice blast is one of the most important diseases of rice worldwide; and
is caused by a fungus, Pyricularia oryzae (Pyricularia grisea),
which can attack the aerial parts of the rice plant at any stage of growth.
Trichosanthin, a protein isolated from the medicinal Chinese cucumber,
Trichosanthes kirilowii, was found to control the rice blast fungus. The
gene for trichosanthin was introduced into rice, driven by the CaMV promoter
and terminated by tnos. Rice with the trichosanthin gene resisted the
blast disease [18]. However, trichosanthin has long been used to produce
abortion in humans and is immunosuppressive and can induce renal toxicity [19].
The immunosuppressive ability of trichosanthin has been used to treat HIV/AIDS
and cancer. It is clear that exposure of the general public to GM trichosanthin
rice is unwise.
A conventionally-selected rice resistant to blast disease has been
pyramided (pyramiding is conventional crossing and selection) with transgenic
rice carrying the Xa23 gene, to induce tolerance to both the fungal and
the bacterial diseases [20]. Xa23 comes from rice, but it has regulatory
genes from other organisms associated with it, so it is a transgene. The full
health and environmental implications of pyramiding genes have yet to be
considered. At the very least, the toxicity of each transgenic toxin,
and the combinations of toxins brought about by crossing must be
considered and assessed for risks.
Safety concerns still to be addressed
Scientific research on transgenic crops in China has focused on the
control of important pests and diseases. However, the remedies appear to have
had little scrutiny regarding human health and environmental (including the
implications of gene flow to wild and weedy relatives of rice) impacts.
In the case of Bt rice straw on wet soil there is evidence of a clear
impact that bears fuller study. Concerns about the impacts of insect resistant
rice on non-target organisms and of the development of insect resistance have
been raised for other Bt crops, and these must be considered in relation to GM
rice as well.
The Bt cry genes used in insect resistant rice are synthetic
approximations of the real bacterial gene, altered for high-level production in
rice plants. It is thus crucial that the real toxin from Bt rice, not the
bacterial surrogate, is tested for health and environmental impacts.
The use of antibiotic resistance marker genes in GM crops is an
acknowledged risk factor, with European legislation mandating a phasing out of
such marker genes. This is because of the serious concern of potential gene
transfer to pathogenic bacteria, which could compromise the treatment of
diseases. Most of the GM rice lines reviewed here have used antibiotic
resistance marker genes, and this factor must be adequately considered in the
risk assessment.
In addition, the potential of the CaMV 35S promoter to cause genetic
instability, genome rearrangements, and secondary gene transfer into genomes of
animals including humans [21], should also be given sufficient
consideration.
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