A built-in strategy for containment of transgenic plants: creation of selectively terminable transgenic rice

Construction of a Novel Female Sterility System for Hybrid Rice

The main constraints of current hybrid rice technology using male sterility (MS) are the low yield and high labor costs of hybrid rice seed (HRS) production. Therefore, there is an urgent need for innovative new hybrid rice technology. Fortunately, we discovered a unique spontaneous sporophytic female-sterile rice mutant controlled by a single recessive locus in the nucleus. Because female-sterile mutant lines cannot produce any selfed-seeds but their pollen has totally normal functions, female sterility (FS) lines may be considered ideal pollen donors to replace the female-fertile pollen donor parent lines currently used in the HRS production. In this study, a genetically engineered FS-based system was constructed to propagate a pure transgene-free FS line using a bentazon herbicide screening. Additionally, the ability of the FS + MS (FM)-line system, with mixed plantings of FS and MS lines, to produce HRS was tested. The pilot field experiment results showed that HRS of the FM-line system was more efficient compared with the conventional FS to MS strip planting control mode. Thus, this study provides new insights into genetic engineering technology and a promising strategy for the utilization of FS in hybrid rice.

How well will stacked transgenic pest/herbicide resistances delay pests from evolving resistance?

Resistance has evolved to single transgenic traits engineered into crops for arthropod and herbicide resistances, and can be expected to evolve to the more recently introduced pathogen resistances. Combining transgenes against the same target pest is being promoted as the solution to the problem. This solution will work if used pre-emptively, but where resistance has evolved to one member of a stack, resistance should easily evolve for the second gene in most cases. We propose and elaborate criteria that could be used to evaluate the value of stacked traits for pest resistance management. Stacked partners must: target the same pest species; be in a tandem construct to preclude segregation; be synchronously expressed in the same tissues; have similar tissue persistence; target pest species that are still susceptible to at least two stacked partners. Additionally, transgene products must not be degraded in the same manner, and there should be a lack of cross-resistance to stacked transgenes or to their products. With stacked herbicide resistance transgenes, both herbicides must be used and have the same persistence. If these criteria are followed, and integrated with other pest management practices, resistance may be considerably delayed. © 2016 Society of Chemical Industry.

Evolutionary and social consequences of introgression of nontransgenic herbicide resistance from rice to weedy rice in Brazil

Several studies have expressed concerns about the effects of gene flow from transgenic herbicide-resistant crops to their wild relatives, but no major problems have been observed. This review describes a case study in which what has been feared in transgenics regarding gene flow has actually changed biodiversity and people's lives. Nontransgenic imidazolinone-resistant rice (IMI-rice) cultivars increased the rice grain yield by 50% in southern Brazil. This increase was beneficial for life quality of the farmers and also improved the regional economy. However, weedy rice resistant to imidazolinone herbicides started to evolve three years after the first use of IMI-rice cultivars. Population genetic studies indicate that the herbicide-resistant weedy rice was mainly originated from gene flow from resistant cultivars and distributed by seed migration. The problems related with herbicide-resistant weedy rice increased the production costs of rice that forced farmers to sell or rent their land. Gene flow from cultivated rice to weedy rice has proven to be a large agricultural, economic, and social constraint in the use of herbicide-resistant technologies in rice. This problem must be taken into account for the development of new transgenic or nontransgenic rice technologies.

Leaf proteome analysis provides insights into the molecular mechanisms of bentazon detoxification in rice

Bentazon is a widely used herbicide that selectively removes broad-leaf weeds by competing with plastoquinone for the binding site in the D1 protein and interrupting the PET (photosynthetic electron transfer) chain. However, monocotyledonous plants, such as rice, show strong resistance to bentazon due to CYP81A6 induction, which results in herbicide detoxification. Here, we confirmed that rice was sensitive to bentazon treatment during the initial exposure period, in which bentazon rapidly inhibited photosynthesis efficiency and electron transfer, based on results of chlorophyll fluorescence analysis. In order to gain a comprehensive, pathway-oriented, mechanistic understanding of the effects directly induced by bentazon, we employed 2D-DIGE (two-dimensional difference gel electrophoresis) to analyze the leaf proteome after 8h of bentazon treatment coupled with individual protein identification by MALDI-TOF (Matrix assisted laser desorption/ionization-time of flight) MS/MS. Proteomic analyses revealed that bentazon induced the relative upregulation or downregulation of 30 and 71 proteins (by 1.5-fold or more, p<0.05), respectively. The pathways involved include photosynthesis processes, carbohydrate metabolism, antioxidant systems, and DNA stabilization and protein folding. Protein analysis data revealed that bentazon primarily suppressed photosynthesis processes, and showed inhibitory effects on carbohydrate metabolism and ATP synthesis, whereas several stress response proteins were induced in response to bentazon. Importantly, we identified a 519kD protein containing two histidine kinase-like ATPase domains and a C3HC4 RING type zinc finger domain which may function as a transcript factor to drive expression of detoxification genes such as CYP81A6, leading to bentazon tolerance. This study identifies, for the first time, a candidate transcription factor that could up-regulate CYP81A6 expression, and provides a foundation for further research to advance our knowledge of mechanisms of bentazon resistance in rice.

Transgene flow: facts, speculations and possible countermeasures

Convincing evidence has accumulated that unintended transgene escape occurs in oilseed rape, maize, cotton and creeping bentgrass. The escaped transgenes are found in variant cultivars, in wild type plants as well as in hybrids of sexually compatible species. The fact that in some cases stacked events are present that have not been planted commercially, implies unintended recombination of transgenic traits. As the consequences of this continuous transgene escape for the ecosystem cannot be reliably predicted, I propose to use more sophisticated approaches of gene technology in future. If possible GM plants should be constructed using either site-directed mutagenesis or cisgenic strategies to avoid the problem of transgene escape. In cases where a transgenic trait is needed, efficient containment should be the standard approach. Various strategies available or in development are discussed. Such a cautious approach in developing novel types of GM crops will enhance the sustainable potential of GM crops and thus increase the public trust in green gene technology.

Expression of cytochrome P450 CYP81A6 in rice: tissue specificity, protein subcellular localization, and response to herbicide application

The cytochrome P450 gene CYP81A6 confers tolerance to bentazon and metsulfuron-methyl, two selective herbicides widely used for weed control in rice and wheat fields. Knockout mutants of CYP81A6 are highly susceptible to both herbicides. The present study aimed to characterize the CYP81A6 expression in rice. Quantitative real-time polymerase chain reaction (PCR) analyses demonstrated that foliar treatment of bentazon (500 mg/L) greatly induced expression of CYP81A6 in both wild-type (Jiazhe B) and its knockout mutant (Jiazhe mB): a 10-fold increase at 9 h before returning to basal levels at 24 h in Jiazhe B, while in the mutant the expression level rose to >20-fold at 12 h and maintained at such high level up to 24 h post exposure. In contrast, metsulfuron-methyl (500 mg/L) treatment did not affect the expression of CYP81A6 in Jiazhe B within 80 h; thereafter the expression peaked at 120 h and returned gradually to basal levels by Day 6. We suggest that a metabolite of metsulfuron-methyl, 1H-2,3-benzothiazin-4-(3H)-one-2,2-dioxide, is likely to be responsible for inducing CYP81A6 expression, rather than the metsulfuron-methyl itself. Use of a promoter-GUS reporter construct (CYP81A6Pro::GUS) demonstrated that CYP81A6 was constitutively expressed throughout the plant, with the highest expression in the upper surfaces of leaves. Subcellular localization studies in rice protoplasts showed that CYP81A6 was localized in the endoplasmic reticulum. These observations advance our understanding of CYP81A6 expression in rice, particularly its response to the two herbicides.

Rice transcriptome analysis to identify possible herbicide quinclorac detoxification genes

Quinclorac is a highly selective auxin-type herbicide and is widely used in the effective control of barnyard grass in paddy rice fields, improving the world's rice yield. The herbicide mode of action of quinclorac has been proposed, and hormone interactions affecting quinclorac signaling has been identified. Because of widespread use, quinclorac may be transported outside rice fields with the drainage waters, leading to soil and water pollution and other environmental health problems. In this study, we used 57K Affymetrix rice whole-genome array to identify quinclorac signaling response genes to study the molecular mechanisms of action and detoxification of quinclorac in rice plants. Overall, 637 probe sets were identified with differential expression levels under either 6 or 24 h of quinclorac treatment. Auxin-related genes such as GH3 and OsIAAs responded to quinclorac treatment. Gene Ontology analysis showed that genes of detoxification-related family genes were significantly enriched, including cytochrome P450, GST, UGT, and ABC and drug transporter genes. Moreover, real-time RT-PCR analysis showed that top candidate genes of P450 families such as CYP81, CYP709C, and CYP72A were universally induced by different herbicides. Some Arabidopsis genes of the same P450 family were up-regulated under quinclorac treatment. We conducted rice whole-genome GeneChip analysis and the first global identification of quinclorac response genes. This work may provide potential markers for detoxification of quinclorac and biomonitors of environmental chemical pollution.

Dealing with transgene flow of crop protection traits from crops to their relatives

Genes regularly move within species, to/from crops, as well as to their con- specific progenitors, feral and weedy forms ('vertical' gene flow). Genes occasionally move to/from crops and their distantly related, hardly sexually interbreeding relatives, within a genus or among closely related genera (diagonal gene flow). Regulators have singled out transgene flow as an issue, yet non-transgenic herbicide resistance traits pose equal problems, which cannot be mitigated. The risks are quite different from genes flowing to natural (wild) ecosystems versus ruderal and agroecosystems. Transgenic herbicide resistance poses a major risk if introgressed into weedy relatives; disease and insect resistance less so. Technologies have been proposed to contain genes within crops (chloroplast transformation, male sterility) that imperfectly prevent gene flow by pollen to the wild. Containment does not prevent related weeds from pollinating crops. Repeated backcrossing with weeds as pollen parents results in gene establishment in the weeds. Transgenic mitigation relies on coupling crop protection traits in a tandem construct with traits that lower the fitness of the related weeds. Mitigation traits can be morphological (dwarfing, no seed shatter) or chemical (sensitivity to a chemical used later in a rotation). Tandem mitigation traits are genetically linked and will move together. Mitigation traits can also be spread by inserting them in multicopy transposons which disperse faster than the crop protection genes in related weeds. Thus, there are gene flow risks mainly to weeds from some crop protection traits; risks that can and should be dealt with.

A double built-in containment strategy for production of recombinant proteins in transgenic rice

Using transgenic rice as a bioreactor for mass production of pharmaceutical proteins could potentially reduce the cost of production significantly. However, a major concern over the bioreactor transgenic rice is the risk of its unintended spreading into environment and into food or feed supplies. Here we report a mitigating method to prevent unwanted transgenic rice spreading by a double built-in containment strategy, which sets a selectively termination method and a visual tag technology in the T-DNA for transformation. We created transgenic rice with an inserted T-DNA that harbors a human proinsulin gene fused with the far-red fluorescent protein gene mKate_S158A, an RNAi cassette suppressing the expression of the rice bentazon detoxification enzyme CYP81A6, and an EPSPS gene as the selection marker for transformation. Herbicide spray tests indicated that such transgenic rice plants can be killed selectively by a spray of bentazon at regular field application dosage for rice weed control. Moreover, the transgenic rice seeds were bright red in color due to the fused far-red fluorescent protein, and could be easily visualized under daylight by naked eyes. Thus, the transgenic rice plants reported in this study could be selectively killed by a commonly used herbicide during their growth stage, and their seeds may be detected visually during processing and consumption after harvest. This double built-in containment strategy may greatly enhance the confinement of the transgenic rice.

A novel rice cytochrome P450 gene, CYP72A31, confers tolerance to acetolactate synthase-inhibiting herbicides in rice and Arabidopsis

Target-site and non-target-site herbicide tolerance are caused by the prevention of herbicide binding to the target enzyme and the reduction to a nonlethal dose of herbicide reaching the target enzyme, respectively. There is little information on the molecular mechanisms involved in non-target-site herbicide tolerance, although it poses the greater threat in the evolution of herbicide-resistant weeds and could potentially be useful for the production of herbicide-tolerant crops because it is often involved in tolerance to multiherbicides. Bispyribac sodium (BS) is an herbicide that inhibits the activity of acetolactate synthase. Rice (Oryza sativa) of the indica variety show BS tolerance, while japonica rice varieties are BS sensitive. Map-based cloning and complementation tests revealed that a novel cytochrome P450 monooxygenase, CYP72A31, is involved in BS tolerance. Interestingly, BS tolerance was correlated with CYP72A31 messenger RNA levels in transgenic plants of rice and Arabidopsis (Arabidopsis thaliana). Moreover, Arabidopsis overexpressing CYP72A31 showed tolerance to bensulfuron-methyl (BSM), which belongs to a different class of acetolactate synthase-inhibiting herbicides, suggesting that CYP72A31 can metabolize BS and BSM to a compound with reduced phytotoxicity. On the other hand, we showed that the cytochrome P450 monooxygenase CYP81A6, which has been reported to confer BSM tolerance, is barely involved, if at all, in BS tolerance, suggesting that the CYP72A31 enzyme has different herbicide specificities compared with CYP81A6. Thus, the CYP72A31 gene is a potentially useful genetic resource in the fields of weed control, herbicide development, and molecular breeding in a broad range of crop species.

Use of multicopy transposons bearing unfitness genes in weed control: four example scenarios

We speculate that multicopy transposons, carrying both fitness and unfitness genes, can provide new positive and negative selection options to intractable weed problems. Multicopy transposons rapidly disseminate through populations, appearing in approximately 100% of progeny, unlike nuclear transgenes, which appear in a proportion of segregating populations. Different unfitness transgenes and modes of propagation will be appropriate for different cases: (1) outcrossing Amaranthus spp. (that evolved resistances to major herbicides); (2) Lolium spp., important pasture grasses, yet herbicide-resistant weeds in crops; (3) rice (Oryza sativa), often infested with feral weedy rice, which interbreeds with the crop; and (4) self-compatible sorghum (Sorghum bicolor), which readily crosses with conspecific shattercane and with allotetraploid johnsongrass (Sorghum halepense). The speculated outcome of these scenarios is to generate weed populations that contain the unfitness gene and thus are easily controllable. Unfitness genes can be under chemically or environmentally inducible promoters, activated after gene dissemination, or under constitutive promoters where the gene function is utilized only at special times (e.g. sensitivity to an herbicide). The transposons can be vectored to the weeds by introgression from the crop (in rice, sorghum, and Lolium spp.) or from planted engineered weed (Amaranthus spp.) using a gene conferring the degradation of a no longer widely used herbicide, especially in tandem with an herbicide-resistant gene that kills all nonhybrids, facilitating the rapid dissemination of the multicopy transposons in a weedy population.

Genetic use restriction technologies: a review

Genetic use restriction technologies (GURTs), developed to secure return on investments through protection of plant varieties, are among the most controversial and opposed genetic engineering biotechnologies as they are perceived as a tool to force farmers to depend on multinational corporations' seed monopolies. In this work, the currently proposed strategies are described and compared with some of the principal techniques implemented for preventing transgene flow and/or seed saving, with a simultaneous analysis of the future perspectives of GURTs taking into account potential benefits, possible impacts on farmers and local plant genetic resources (PGR), hypothetical negative environmental issues and ethical concerns related to intellectual property that have led to the ban of this technology.

Expression and purification of recombinant human serum albumin from selectively terminable transgenic rice

Human serum albumin (HSA) is widely utilized for medical purposes and biochemical research. Transgenic rice has proved to be an attractive bioreactor for mass production of recombinant HSA (rHSA). However, transgene spread is a major environmental and food safety concern for transgenic rice expressing proteins of medical value. This study aimed to develop a selectively terminable transgenic rice line expressing HSA in rice seeds, and a simple process for recovery and purification of rHSA for economical manufacture. An HSA expression cassette was inserted into a T-DNA vector encoding an RNA interference (RNAi) cassette suppressing the CYP81A6 gene. This gene detoxifies the herbicide bentazon and is linked to the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) cassette which confers glyphosate tolerance. ANX Sepharose Fast Flow (ANX FF) anion exchange chromatography coupled with Butyl Sepharose High Performance (Butyl HP) hydrophobic interaction chromatography was used to purify rHSA. A transgenic rice line, HSA-84, was obtained with stable expression of rHSA of up to 0.72% of the total dry weight of the dehusked rice seeds. This line also demonstrated high sensitivity to bentazon, and thus could be killed selectively by a spray of bentazon. A two-step chromatography purification scheme was established to purify the rHSA from rice seeds to a purity of 99% with a recovery of 62.4%. Results from mass spectrometry and N-terminus sequencing suggested that the purified rHSA was identical to natural plasma-derived HSA. This study provides an alternative strategy for large-scale production of HSA with a built-in transgene safety control mechanism.

A built-in strategy to mitigate transgene spreading from genetically modified corn

Transgene spreading is a major concern in cultivating genetically modified (GM) corn. Cross-pollination may cause the spread of transgenes from GM cornfields to conventional fields. Occasionally, seed lot contamination, volunteers, mixing during sowing, harvest, and trade can also lead to transgene escape. Obviously, new biological confinement technologies are highly desired to mitigate transgene spreading in addition to physical separation and isolation methods. In this study, we report the development of a built-in containment method to mitigate transgene spreading in corn. In this method, an RNAi cassette for suppressing the expression of the nicosulfuron detoxifying enzyme CYP81A9 and an expression cassette for the glyphosate tolerant 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene G10 were constructed and transformed into corn via Agrobacterium-mediated transformation. The GM corn plants that were generated were found to be sensitive to nicosulfuron but resistant to glyphosate, which is exactly the opposite of conventional corn. Field tests demonstrated that GM corn plants with silenced CYP81A9 could be killed by applying nicosulfuron at 40 g/ha, which is the recommended dose for weed control in cornfields. This study suggests that this built-in containment method for controlling the spread of corn transgenes is effective and easy to implement.

The benefits of herbicide-resistant crops

Since 1996, genetically modified herbicide-resistant crops, primarily glyphosate-resistant soybean, corn, cotton and canola, have helped to revolutionize weed management and have become an important tool in crop production practices. Glyphosate-resistant crops have enabled the implementation of weed management practices that have improved yield and profitability while better protecting the environment. Growers have recognized their benefits and have made glyphosate-resistant crops the most rapidly adopted technology in the history of agriculture. Weed management systems with glyphosate-resistant crops have often relied on glyphosate alone, have been easy to use and have been effective, economical and more environmentally friendly than the systems they have replaced. Glyphosate has worked extremely well in controlling weeds in glyphosate-resistant crops for more than a decade, but some key weeds have evolved resistance, and using glyphosate alone has proved unsustainable. Now, growers need to renew their weed management practices and use glyphosate with other cultural, mechanical and herbicide options in integrated systems. New multiple-herbicide-resistant crops with resistance to glyphosate and other herbicides will expand the utility of existing herbicide technologies and will be an important component of future weed management systems that help to sustain the current benefits of high-efficiency and high-production agriculture.

Functional validation of Capsicum frutescens aminotransferase gene involved in vanillylamine biosynthesis using Agrobacterium mediated genetic transformation studies in Nicotiana tabacum and Capsicum frutescens calli cultures

Capsaicinoid biosynthesis involves the participation of two substrates viz. vanillylamine and C(9)-C(11) fatty acid moieties. Vanillylamine which is a derivative of vanillin is synthesized through a transaminase reaction in the phenylpropanoid pathway of capsaicinoid synthesis. Here we report the functional validation of earlier reported putative aminotransferase gene for vanillylamine biosynthesis in heterologous system using Agrobacterium mediated genetic transformation studies in Nicotiana tabacum and Capsicum frutescens calli cultures. Molecular analysis tools comprising PCR and Southern blot analysis have shown the integration of the foreign gene in N. tabacum and C. frutescens calli cultures. The study shows the production of vanillylamine in transformed N. tabacum callus cultures and also the reduction of vanillylamine production when whole gene based antisense binary vector construct was used in transformation of C. frutescens callus cultures. Vanillylamine production, aminotransferase assay with Western blot analysis for crude proteins of transformants established the production of putative aminotransferase (pAMT) protein in alternate plant. The result is a clear evidence of involvement of the reported putative aminotransferase responsible for vanillylamine biosynthesis in capsaicinoid biosynthesis pathway, confirming the gene function through functional validation.

A built-in mechanism to mitigate the spread of insect-resistance and herbicide-tolerance transgenes into weedy rice populations

BACKGROUND

The major challenge of cultivating genetically modified (GM) rice (Oryza sativa) at the commercial scale is to prevent the spread of transgenes from GM cultivated rice to its coexisting weedy rice (O. sativa f. spontanea). The strategic development of GM rice with a built-in control mechanism can mitigate transgene spread in weedy rice populations.

METHODOLOGY/PRINCIPAL FINDINGS

An RNAi cassette suppressing the expression of the bentazon detoxifying enzyme CYP81A6 was constructed into the T-DNA which contained two tightly linked transgenes expressing the Bt insecticidal protein Cry1Ab and the glyphosate tolerant 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), respectively. GM rice plants developed from this T-DNA were resistant to lepidopteran pests and tolerant to glyphosate, but sensitive to bentazon. The application of bentazon of 2000 mg/L at the rate of 40 mL/m(2), which is approximately the recommended dose for the field application to control common rice weeds, killed all F(2) plants containing the transgenes generated from the Crop-weed hybrids between a GM rice line (CGH-13) and two weedy rice strains (PI-63 and PI-1401).

CONCLUSIONS/SIGNIFICANCE

Weedy rice plants containing transgenes from GM rice through gene flow can be selectively killed by the spray of bentazon when a non-GM rice variety is cultivated alternately in a few-year interval. The built-in control mechanism in combination of cropping management is likely to mitigate the spread of transgenes into weedy rice populations.

Expression of an Acidothermus cellulolyticus endoglucanase in transgenic rice seeds

The thermostable endo-1,4-β-glucanase (E1) from Acidothermus cellulolyticus, is a useful enzyme for commercial hydrolysis of cellulose into glucose. A codon-optimized synthetic gene encoding this enzyme was transformed into rice (Oryza sativa L. ssp. japonica) under the control of the rice seed storage protein Gt1 promoter. The transgenic line C19 was identified as the one with the highest endoglucanase activity among the total of 36 independent transgenic lines obtained. The cellulase activity in the C19 seeds was estimated at about 830U/g of dried seeds using CMC as substrate. The enzymes produced in the seeds had an optimum pH of 5.0 and optimum temperature of 80°C, which is similar to the enzymes produced by the native bacterium host. This study demonstrates that the transgenic rice seeds could be used as a bioreactor for production of enzymes for cellulosic biomass conversion.

[Effect of transgenic insect-resistant rice on biodiversity]

Rice is the most important food crops in maintaining food security in China. The loss of China's annual rice production caused by pests is over ten million tons. Present studies showed that the transgenic insect-resistant rice can substantially reduce the application amount of chemical pesticides. In the case of no pesticide use, the pest density in transgenic rice field is significantly lower than that in non-transgenic field, and the neutral insects and natural enemies of pests increased significantly, indicating that the ecological environment and biodiversity toward the positive direction. The gene flow frequency from transgenic rice is dramatically reduced with the distance increases, reaching less than 0.01% at the distance of 6.2 m. Application of transgenic insect-resistant rice in China has an important significance for ensuring food security, maintaining sustainable agricultural development, and protecting the ecological environment and biodiversity. This review summarized the research progress in transgenic insect-resistant rice and its effect on biodiversity. The research directions and development trends of crop pest controlling in future are discussed. These help to promote better use of transgenic insect-resistant rice.

Transgene introgression in crop relatives: molecular evidence and mitigation strategies

Incorporation of crop genes into wild and weedy relative populations (i.e. introgression) has long been of interest to ecologists and weed scientists. Potential negative outcomes that result from crop transgene introgression (e.g. extinction of native wild relative populations; invasive spread by wild or weedy hosts) have not been documented, and few examples of transgene introgression exist. However, molecular evidence of introgression from non-transgenic crops to their relatives continues to emerge, even for crops deemed low-risk candidates for transgene introgression. We posit that transgene introgression monitoring and mitigation strategies are warranted in cases in which transgenes are predicted to confer selective advantages and disadvantages to recipient hosts. The utility and consequences of such strategies are examined, and future directions provided.

Insect-resistant genetically modified rice in China: from research to commercialization

From the first insect-resistant genetically modified (IRGM) rice transformation in 1989 in China to October 2009 when the Chinese Ministry of Agriculture issued biosafety certificates for commercial production of two cry1Ab/Ac Bacillus thuringiensis (Bt) lines, China made a great leap forward from IRGM rice basic research to potential commercialization of the world's first IRGM rice. Research has been conducted on developing IRGM rice, assessing its environmental and food safety impacts, and evaluating its socioeconomic consequences. Laboratory and field tests have confirmed that these two Bt rice lines can provide effective and economic control of the lepidopteran complex on rice with less risk to the environment than present practices. Commercializing these Bt plants, while developing other GM plants that address the broader complex of insects and other pests, will need to be done within a comprehensive integrated pest management program to ensure the food security of China and the world.

A selectively terminable transgenic rice line expressing human lactoferrin

Human lactoferrin (hLF) is a multifunctional milk protein which could be utilized for promoting human health. Transgenic rice has been used as a bioreactor for mass production of recombinant hLF. However, one major concern over such transgenic rice is the risk of its unintended spreading into environment and into our food supplies. Here we report the development of selectively terminable transgenic rice expressing human lactoferrin in seeds. These transgenic rice plants could be selectively terminated by bentazon, a common herbicide used for rice weed control. The hLF expression cassette was constructed into a T-DNA containing the RNA interference cassette suppressing the expression of the rice gene CYP81A6 which detoxifies herbicide bentazon, and the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) cassette which confers to glyphosate tolerance. A transgenic line, named as G281, was identified for its high sensitivity to bentazon, high tolerance to glyphosate, and high expression of hLF. Southern analysis suggested G281 is a single copy insertion event. Field tests demonstrated that G281 plants can be completely killed by a single spray of bentazon at 1000 mg/L, which is safe to regular rice and represents only half of the dose recommended by manufacturer for rice field weed control. Therefore, any G281 contaminations in regular rice could be selectively terminated to make sure it will not enter food or feed supplies.

Gene flow, invasiveness, and ecological impact of genetically modified crops

The main environmental concerns about genetically modified (GM) crops are the potential weediness or invasiveness in the crop itself or in its wild or weedy relatives as a result of transgene movement. Here we briefly review evidence for pollen- and seed-mediated gene flow from GM crops to non-GM or other GM crops and to wild relatives. The report focuses on the effect of abiotic and biotic stress-tolerance traits on plant fitness and their potential to increase weedy or invasive tendencies. An evaluation of weediness and invasive traits that contribute to the success of agricultural weeds and invasive plants was of limited value in predicting the effect of biotic and abiotic stress-tolerance GM traits, suggesting context-specific evaluation rather than generalizations. Fitness data on herbicide, insect, and disease resistance, as well as cold-, drought-, and salinity-tolerance traits, are reviewed. We describe useful ecological models predicting the effects of gene flow and altered fitness in GM crops and wild/weedy relatives, as well as suitable mitigation measures. A better understanding of factors controlling population size, dynamics, and range limits in weedy volunteer GM crop and related host or target weed populations is necessary before the effect of biotic and abiotic stress-tolerance GM traits can be fully assessed.

A strategy to provide long-term control of weedy rice while mitigating herbicide resistance transgene flow, and its potential use for other crops with related weeds

Transgenic herbicide-resistant rice is needed to control weeds that have evolved herbicide resistance, as well as for the weedy (feral, red) rice problem, which has been exacerbated by shifting to direct seeding throughout the world-firstly in Europe and the Americas, and now in Asia, as well as in parts of Africa. Transplanting had been the major method of weedy rice control. Experience with imidazolinone-resistant rice shows that gene flow to weedy rice is rapid, negating the utility of the technology. Transgenic technologies are available that can contain herbicide resistance within the crop (cleistogamy, male sterility, targeting to chloroplast genome, etc.), but such technologies are leaky. Mitigation technologies tandemly couple (genetically link) the gene of choice (herbicide resistance) with mitigation genes that are neutral or good for the crop, but render hybrids with weedy rice and their offspring unfit to compete. Mitigation genes confer traits such as non-shattering, dwarfism, no secondary dormancy and herbicide sensitivity. It is proposed to use glyphosate and glufosinate resistances separately as genes of choice, and glufosinate, glyphosate and bentazone susceptibilities as mitigating genes, with a six-season rotation where each stage kills transgenic crop volunteers and transgenic crop x weed hybrids from the previous season.

Plants as bioreactors: Recent developments and emerging opportunities

In recent years, the use of plants as bioreactors has emerged as an exciting area of research and significant advances have created new opportunities. The driving forces behind the rapid growth of plant bioreactors include low production cost, product safety and easy scale up. As the yield and concentration of a product is crucial for commercial viability, several strategies have been developed to boost up protein expression in transgenic plants. Augmenting tissue-specific transcription, elevating transcript stability, tissue-specific targeting, translation optimization and sub-cellular accumulation are some of the strategies employed. Various kinds of products that are currently being produced in plants include vaccine antigens, medical diagnostics proteins, industrial and pharmaceutical proteins, nutritional supplements like minerals, vitamins, carbohydrates and biopolymers. A large number of plant-derived recombinant proteins have reached advanced clinical trials. A few of these products have already been introduced in the market.

Intein-mediated protein assembly in transgenic wheat: production of active barnase and acetolactate synthase from split genes

Engineering traits by the assembly of non-functional gene products is a promising tool for modern plant biotechnology. In this article, we describe the establishment of male sterility and herbicide resistance in wheat (Triticum aestivum) by complementing inactive precursor protein fragments through a split intein system. N- and C-terminal fragments of a barnase gene from Bacillus amyloliquifaciens were fused to intein sequences from the Synechocystis sp. gene DnaB and delivered into the wheat genome via biolistic particle bombardment. Both barnase fragments were expressed under the control of a tapetum-specific promoter. High efficiency of the split barnase system was achieved by introducing GGGGS linkers between the fusion domains of the assembled protein. Depending on the vector version that was transformed, up to 51% of primary transformed plants produced sterile pollen. In the F(1) progeny, the male-sterile phenotype segregated with both barnase gene fragments. Expression of the cytotoxic barnase in the tapetum did not apparently affect the vegetative phenotype and remained stable under increased temperatures. In addition, the reconstitution of sulphonylurea resistance was achieved by DnaE intein-mediated assembly of a mutated acetolactate synthase (ALS) protein from rice. The impacts of the technical advances revealed in this study on the concepts for trait control, transgene containment and hybrid breeding are discussed.