Science in Society Archive

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 the I-SIS website:

GM Rice in Japan
GM Rice in India


GM Rice Release in China?

Reduced production and transportation bottlenecks have persuaded China to think of growing GM rice, but Joe Cummins says it is unwise for serious safety reasons.

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.

Article first published 30/11/04



References

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  7. Wu W, Ye Q and Min H. Effect of straws from Bt-transgenic rice on selected biological activities in water-flooded soil. European Journal of Soil Biology 2004, 40, 15-22.
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  11. Cummins J. Bt toxins in genetically modified crops: Regulation by deceit. Science in Society 2004, 22, 32-33.
  12. Kleter GA and Peijnenburg AdACM. Screening of transgenic proteins expressed in transgenic food crops for the presence of short amino acid sequences identical to potential, IgE-binding linear epitopes of allergens. BMC Structural Biology 2002, 2(8) http://www.biomedcentral.com/1472-6807/2/8.
  13. Sun X, Wu A and Tang K. Transgenic rice lines with enhanced resistance to the small brown planthopper. Crop Protection 2002, 21, 511–14.
  14. Ewen S. and Pusztai A. Effect of diets containing genetically modified potatoes expressing Galanthus nivalis lectin on rat small intestine. Lancet 1999, 354, 1353-4.
  15. Tang K, Sun X, Hu Q, Wu A, Lin C, Lin H, Twyman R, Christou P and Feng T. Transgenic rice plants expressing the ferredoxin-like protein (AP1) from sweet pepper show enhanced resistance to Xanthomonas oryzae pv. Oryzae. Plant Science 2001, 160, 1035-42.
  16. Zhai W, Chen C, Zhu X, Chen X, Zhang D, Li X and Zhu L. Analysis of T-DNA- Xa21 loci and bacterial blight resistance effects of the transgene Xa21 in transgenic rice. Theor. Appl. Genet. 2004, 109, 534–42.
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  19. Cummins J. Trichosanthin transgenic rice enhances resistance to fungus; Is it safe for humans? Health Risks 2002, http://www.biotech-info.net/trichosanthin.html
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  21. See Ho MW. Living with the Fluid Genome, ISIS and TWN, London and Penang, 2003, for a review on the risks of horizontal gene transfer in general, and the CaMV 35S promoter in particular.

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