Rice Wars
Rice, the staple food crop for more than half the world’s population, among them the poorest, is the current target of genetic modification, an activity that has greatly intensified after the rice genome was announced two years ago (see "Rice is life" series, SiS 15, Summer 2002). Since then, all major biotech giants are investing in rice research.
At the same time, a low-input cultivation system that really benefits small farmers worldwide has been spreading, but is dismissed by the scientific establishment as "unscientific". This is one among several recent innovations that increase yields and ward off disease without costly and harmful inputs, all enthusiastically and widely adopted by farmers.
A war is building up between the corporate establishment and the peoples of the world for the possession of rice. The food security of billions is at stake, as is their right to grow the varieties of rice they have created and continue to create, and in the manner they choose.
Rice, the food crop for half the world’s population is the current target of genetic modification. What are the health and environmental consequences? Prof. Joe Cummins reviews
Rice is the primary food for half the people in the world, providing more calories than any other single food. It supplies an average of 889 calories per day per person in China, as opposed to only 82 calories in the United States. Rice is a nutritious food, providing about 90 percent of calories from carbohydrates and as much as 13 percent of calories from protein [1]. Such a crop of immense global importance is a certain target for control by multinational corporations, especially since the rice genome was announced two years ago (see "Rice is life" series, SiS 15, 2002).
Only one GM rice trait – tolerance to the herbicide glufosinate - is currently available on the market [2]. The rice varieties under development include resistance to insects, microbial pests and tolerance to high salt levels. Pharmaceutical products and multiple transgenic traits are being pyramided into a single strain of rice. It is likely that the next GM rice to be approved for commercial release will contain an insect toxin gene from the bacterium, Bacillus thuringiensis (Bt), but that will be followed by a range of modifications, including insect resistance based on lectins and protease inhibitors. Because rice has a huge impact on the world’s food supply, we should at least make sure it is safe.
Two glufosinate-tolerant GM rice events, LLRICE06 and LLRICE62, have been approved for commercial production. They have been inserted into the rice varieties M202 and Bengal, consisting of the bar gene encoding the phosphoinothricin-N-acetyltransferase (PAT) enzyme - a highly altered copy of a gene from the soil bacterium S. hygroscopicus genes for herbicide tolerance – driven by the CaMV 35S promoter and the CaMV transcription terminator.
Safety testing of the bar gene and PAT enzyme was done using the bacterial gene and protein, not the synthetic gene and its product in the rice crop. Despite this obvious flaw, the United States Department of Agriculture determined that the GM rice strains were suitable for commercial release, and these are marketed by Bayer as Liberty Link rice [2]. In 2002, Aventis (later purchased by Bayer) destroyed 5 million pounds of Liberty Link rice because they feared rejection by the international market [3], but efforts are continuing to promote and disseminate the transgenic crop. Bayer is currently seeking approval for the import of LLRICE62 for food, feed and industrial uses into Europe.
Synthetic analogues of the Bt Cry toxin genes have been used extensively to construct experimental rice varieties. Indica Basmati rice was transformed by a synthetic Cry1Ab gene driven by the constitutive rice ubiquitin promoter, or a Brassica seed-specific promoter, and terminated with the CaMV 35S terminator or nos terminator. These transgenic rice plants contained up to 0.15% of their total protein as synthetic toxin. Such high levels of toxin are preferred because it discourages insect resistance, but it also means that the synthetic toxin protein makes a significant contribution to people’s diet and to the rice straw fed to animals [4].
Rice lines containing Cry1Ab and Cry1Ab/Cry1Ac fusion protein genes were reported to have no effect on the fitness of non-target insects. These transgenes were used with different promoters in different rice strains: CaMV 35S, rice actin, rice ubiquitin and a maize pith-specific promoter (specifically works in the pith of the stem, to target stem borer insects) [5]. A comparison of Indica rice bearing constitutive and pith-specific promoters and the Cry1Ab toxin showed that the pith-specific promoter provided protection from stem borer insects while reportedly producing reduced levels of Cry toxin protein in seeds [6].
Rice with Cry1Ab toxin gene driven by a maize ubiquitin promoter and resistance genes for the antibiotics hygromycin and neomycin was resistant to rice leafhopper insects [7]. However, elite Indica rice with a synthetic Cry1Ac toxin gene in the same construct, although resistant to the yellow stem borer insect, had high toxin levels in all of the plant tissues [8]. European rice cultivars were transformed with synthetic Cry1Aa or synthetic Cry1B toxin genes under a constitutive ubiquitin promoter, or synthetic Cry1B gene under a wound inducible maize promoter (responding to stresses such as insect predation). The constitutive promoter-driven toxin genes produced high toxin levels that prevented striped stem borer predation but left toxin in all the rice tissues and seeds, while the wound inducible strain produced toxin mainly at the site of insect attack [9].
Research has established that Bt toxin was introduced into soil by root exudates of transgenic rice. The toxin released into the soil affected the enzymes of soil microbes, increasing soil acid phosphatase and decreasing soil urease [10].
The benefit of insect protection from Bt rice is offset by the potential harmful effects of high levels of toxin protein in the rice grain. As rice is such an important food crop, the safety of Bt rice must be concretely established. It has been found that food irradiation improved the "quality" of GM rice modified with the Cry1Ab toxin, by selectively removing the toxin protein [11]. However, study of the radiation products and adducts created during destruction of the toxin is essential. Furthermore, it is clear that food irradiation may be used to disguise GM rice.
A number of projects have studied the use of snowdrop lectin, Galanthus nivalis agglutinin (GNA) alone or in conjunction with other genes to control rice pests. Lectins are proteins that interact with human blood cells (agglutinin) and also act as anti-predator chemicals in plants or microbes. A GNA gene was driven by a phloem specific promoter accompanied by a hygromycin antibiotic resistance gene and was used to transform japonica rice strains. The modified rice controlled sap-sucking insects that spread rice viruses [12]. However, Ewen and Pusztai [13] showed that potatoes modified with GNA affected different parts of the rat digestive system. Similar research on the in vivo effects of rice genetically engineered with GNA has not been reported.
Rice plants containing both the GNA gene and the unlinked Cry1Ac gene were reported to be resistant to the major rice insect pests, striped stem borer and brown leaf hopper (rice with only Cry1Ac resisted striped stem borer while rice with GNA resisted brown leaf hopper) [14]. Rice transformed with a single vector containing Cry1Ab driven by the maize ubiquitin promoter, along with GNA driven by sucrose synthetase promoter and the bar gene for herbicide tolerance driven by the CaMV promoter was intended to be resistant to yellow stem borer and three sap sucking insects, along with the herbicide glufosinate. This huge package of genes was integrated at a single chromosomal site [15]. No account has been taken of the interaction of the various toxins in the human food supply and in the environment.
Basmati rice was co-transformed with three plasmids carrying four genes including GNA, synthetic Cry1Ac, synthetic Cry2A and resistance to the antibiotic hygromycin. The promoters used in these constructions included maize ubiquitin and CaMV 35S while the transcription terminators were nos [16]. As in the previous construction, care must be taken to evaluate the toxicity of the toxin products and their interaction in the human diet and in the environment.
Elite Chinese rice cultivars were transformed with a gene for bacterial blight and a GNA gene, along with a hygromycin antibiotic resistance gene in constructions employing promoters, including rice sucrose synthetase promoter, maize ubiquitin promoter and the CaMV promoter. Transcription was terminated using the nos terminator in every case. The transformed rice was resistant to sap sucking insects and to bacterial blight [17].
Insect and bacterial disease resistant lines have been pyramided (pyramiding is combining transgenes by genetic crosses). A strain with a fused Cry1Ab/Cry1Ac gene was combined with a gene derived from a wild rice for resistance to bacterial blight, in a male sterile restorer line of rice. The pyramided line was resistant to bacterial blight and to stem borer insects [18]. In the pyramided lines, regulators must consider and evaluate the toxicity of each transgenic toxin and the combination of toxins brought about by crossing.
Resistance to the rice stem borer was produced using a synthetic trypsin inhibitor that interferes with insect food digestion. The synthetic gene was roughly based on a winged bean chymotrypsin inhibitor. The genetic construction included the CaMV promoter and was enhanced with an omega sequence from tobacco mosaic virus and the first intron of a gene for phaseolin [19]. A synthetic copy of a gene product that interferes with digestion surely requires extensive safety testing!
Increasing the transcription level of a rice sodium antiporter (a pump that moves sodium ion into a vacuole) gene, called OsNHX1, is reported to improve the salt tolerance of rice [20], with the potential of opening large tracks of land to rice cultivation. Over expression of barley aquaporin gene in rice led to increased carbon dioxide conductance and assimilation [21]. Such modifications are potentially able to enhance biomass production in rice.
Rice has also been the target of genetic modifications that nutritionally enrich food crops. ‘Golden Rice’ genetically engineered to produce pro-vitamin A has been discussed extensively elsewhere [22]. Although much touted as a cure for vitamin A deficiency in developing countries, it has yet to be commercialized and its effectiveness in addressing vitamin A deficiency has been called into question.
Production of pharmaceutical proteins in rice crops poses potent threats to the food supply. Recent efforts to test and produce rice modified to produce the human gene products lactoferrin and lysozyme have been temporarily thwarted [23]. However, rice producing human growth hormone has been developed despite the likelihood that the GM rice could cause cancer in those consuming it [24]. Rice is not a suitable cross for producing pharmaceutical products because of the high likelihood that the products will pollute the food supply.
The genetic modifications being used or promoted for rice pose a significant threat to the environment if they contaminate conventional rice fields or spread transgenes to weedy relatives such as red rice. Pollen mediated gene flow was substantial from Mediterranean GM rice bearing a gene for herbicide tolerance to conventional rice and to the weed, red rice [25]. Gene flow from herbicide tolerant to cultivated rice was also substantial in another study of Mediterranean rice [26]. Rice pollen was spread from a test plot up to 110 meters from the boundary of the test plot [27]. It is very clear that transgenic rice will pollute any nearby conventional rice.
GM rice may soon be approved for commercial production in a number of countries. Safety testing of the currently described products has not yet been published. GM rice cannot be presumed to be substantially equivalent to conventional rice, but that may not hamper approval in the United States of many such constructions. For the most part, GM rice is formed from synthetic genes that should require much fuller safety testing than has been done in the past.
In North America, regulators have allowed substitution of genes and proteins produced in bacterial surrogates for the actual genes and proteins produced in crop plants in toxicity tests of human and environmental safety. The use of the bacterial surrogates is allowed, to save corporations the cost of preparing genes and proteins from the crop plants, even though the genes and proteins tested differ significantly from the genes and proteins produced in the crop plants [28]. The public should insist that the actual genes and proteins produced in the crops be tested.
The world’s leading food crop should be treated with more care than has been done with maize, soy and canola.
Article first published 09/07/04
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