随着基因工程技术日益完善,转基因作物的种类和耕种面积迅速增长,但其潜在的问题也日益突出和明显.文章对转基因作物的研究和应用概况以及安全性进行了简要综述.

insect resistance, based on Bacillus thuringiensis (Bt) endotoxins. is the second most widely used trait (after herbicide resistance) in commercial-genetically modified (GM) crops. Other modifications for insect resistance. such as proteinase inhibitors and lectins, are also being used in many experimental crops. The extensive testing on nontarget plant-feeding insects and beneficial species that has accompanied the long-term and wide-scale use of Bt plants has not detected significant adverse effects. GM plants expressing other insect-resistant proteins that have a broader spectrum of activity have been tested on only a limited number of nontarget species. Little is known about the persistence of transgene-derived proteins in soil. with the exception of Bt endotoxins, which can persist in soil for several months. Bt plants appear to have little impact on soil biota such as earthworms, collembolans. and general soil microflora. Further research is required on the effects of GM plants on soil processes such as decomposition. Assessment of nontarget impacts is an essential part of the riskassessment process for insect-resistant GM plants.

针对当前社会上对植物转基因技术存在的偏见,通过对植物转基因技术的基本原理、方法和国内外应用状况的系统介绍,以及对当代社会和农业发展概况和存在问题的详细论述,探讨了转基因植物及其产品的安全性、世界各国对转基因技术和转基因植物的态度以及植物转基因技术与当代社会发展的关系,由此认为植物转基因技术对消除人类饥饿与贫困、构建和谐社会、促进当代社会可持续发展有重要意义,并对植物转基因技术的发展前景进行了展望。

For the past 50 years the importance of barley in Icelandic agriculture has increased, not least as a result of environmental change and new cultivars. Following this the impact of pathogens is expected to increase as well as the importance of knowing which pathogens affect barley in Iceland. Presented here is the first analysis of the diversity of barley fungal pathogens in Iceland. Samples... [Show full abstract]

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22年以来,生物技术/转基因作物的商业化带来了巨大的经济效益、健康改善和社会效益。有关生物技术作物的收益和潜力的精确信息使农民和消费者在知情的情况下分别做出了种植和消费选择,使政策制定者和监管者能够专门制定有关生物技术/转基因作物商业化和应用的生物安全性指南,使科学交流人员和媒体能够更有效地宣传这一技术的效益和潜力。国际农业生物技术应用服务组织(ISAAA)自1996年以来一直出版《全球生物技术/转基因作物商业化发展态势》年度报告,通过广泛的全球网络(生物技术信息中心和其它合作伙伴)来收集信息以便提供有关转基因产品的最新报告,本文是这一系列的第22期,记载了以下最新信息:2017年转基因作物应用和分布的全球数据,自1996年(商业化的第一年)以来的累计数据、国家状况、转基因作物的批准动态,以及转基因作物种植国家和全球的未来技术展望。

转基因作物进行第一次大规模商业化种植始于1996年,至 2007年,12年来,全球转基因作物的种植面积增加了66倍,达到1.143亿hm2,比2006年增加了12%.同时,随着智利和波兰的加入,种植转 基因作物的国家由最初6个增加到23个,其中,发展中国家(12)在数量上首次超过发达国家(11).种植转基因作物的农户比2006年又增加了200万 户,总种植户达到1 200万.全球转基因作物市场价值累计约425亿美元.2007年,全球转基因作物市场价值达到69亿美元,占农作物总价值的16%,占种子市场价值的 20%.专家预测,2008年全球转基因作物市场价值大约可达到75亿美元.

The rapid development of biotechnology, particularly the transgenic technology, has brought us with tremendous opportunities to solve the world's starvation problems that have been caused by the continued expanding of the global population. However, the application of transgenic biotechnology and the environmental release of transgenic organisms have evoked a series of extraordinary debates on biosafety issues related to the prosperity and the future of transgenic technology. The public and scientific communities are desperately interested in knowing whether the transgenic products would pose negative influences on plants and animals, human life and health, as well as on genetic resources and environment. These concerns have become universal hot topics over the last decade. Among the most debated biosafety issues caused potentially by transgenic products, transgene escape to the environment and its consequent ecological risks become one of the appealing focal points. In this review, a series of biosafety issues concerned by public, including the possibility of transgene escape and its various paths, as well as the potential ecological risks caused by such escape were discussed, and various approaches for controlling for transgene escape and the factors to consider when designing safety isolation distance between transgenic varieties and other concerned plants were also examined. The objective of this review is to allow readers to understand the potential biosafety problems caused by environmental release of transgenic crops and by the escape of foreign transgenes in particular, and to use the effective tools to control and avoid transgene escape.

转基因作物的商品化生产和大规模环境释放在带来巨大利益的同时，也引起了全球对其生物安全问题的广泛关注和争议，其中转基因通过花粉介导的基因漂移逃逸到非转基因作物及其野生近缘种，进而导致的潜在环境和生态风险就是备受争议的生物安全问题之一。转基因植物的环境生物安全涉及两方面关键问题：如何科学评价转基因植物商品化种植以后带来的环境和生态影响；如何利用环境生物安全的研究成果来制定科学有效的风险监测和管理措施。对转基因逃逸及其潜在生态风险的科学评价应包括三个重要环节：（1）检测转基因的逃逸的频率；（2）检测转基因逃逸后的表达和遗传规律；（3）确定逃逸后的转基因对野生近缘种群体适合度的影响及其进化潜力,本文将围绕对转基因逃逸及其潜在环境风险的科学评价，以转基因水稻为案例来对转基因逃逸带来生态影响的研究好评价的进展进行简要介绍，并对目前依据风险评价研究成果制定的各种管理策略进行了讨论。只有提高对转基因生物环境安全研究和评价的水平，并制定有效的风险监测和管理措施，才能为我国转基因技术的发展和转基因产品的商品化应用保驾护航。

概述了作物基因漂移的研究意义及其对整个生态环境的影响,认识到作物基因漂移对野生近缘种资源的保护和利用、作物的适应性进化和多样化的进程等方面具有的深层次意义;结合现代分子生物技术,建立合理的检控系统模型,进而深入研究转基因作物的释放环境的关系,能更好地指导转基因作物的田间试验工作。

Horizontal gene transfers among bacteria, such as natural transformation or conjugation, may have played an important role in bacterial evolution. They are thought to have been involved in promoting genome plasticity which permitted bacteria to adapt very efficiently to any change in their environment and to colonize a wide range of ecosystems. Evidence that some genes were transferred from eukaryotes, and in particular, from plants to bacteria, was obtained from nucleotide and protein sequence analyses. However, numerous factors, including some which are endogenous to the bacterial cells, tend to limit the extent of transfer, particularly among phylogenetically distant organisms. The goal of this paper is to give an overview of the potentials and limits of natural interkingdom gene transfers, with particular focus on prokaryote-originating sequences which fit the nuclear genome of transgenic plants.

Plant evolutionary biologists' view of gene flow and hybridization has undergone a revolution. Twenty-five years ago, both were considered rare and largely inconsequential. Now gene flow and hybridization are known to be idiosyncratic, varying with the specific populations involved. Gene flow typically occurs at evolutionarily significant rates and at significant distances. Spontaneous hybridization occasionally has important applied consequences, such as stimulating the evolution of more aggressive invasives and increasing the extinction risk for rare species. The same problems have occurred for spontaneous hybridization between crops and their wild relatives. These new data have implications for transgenic crops: (i) for most crops, gene flow can act to introduce engineered genes into wild populations; (ii) depending on the specific engineered gene(s) and populations involved, gene flow may have the same negative impacts as those observed for traditionally improved crops; (iii) gene flow's idiosyncratic nature may frustrate management and monitoring attempts; and (iv) intercrop transgene flow, although rarely discussed, is equally worthy of study.

To what extent is the tree of life the best representation of the evolutionary history of microorganisms? Recent work has shown that, among sets of prokaryotic genomes in which most homologous genes show extremely low sequence divergence, gene content can vary enormously, implying that those genes that are variably present or absent are frequently horizontally transferred. Traditionally, successful horizontal gene transfer was assumed to provide a selective advantage to either the host or the gene itself, but could horizontally transferred genes be neutral or nearly neutral? We suggest that for many prokaryotes, the boundaries between species are fuzzy, and therefore the principles of population genetics must be broadened so that they can be applied to higher taxonomic categories.

Foraging range, an important component of bee ecology, is of considerable interest for insect-pollinated plants because it determines the potential for outcrossing among individuals. However, long-distance pollen flow is difficult to assess, especially when the plant also relies on self-pollination. Pollen movement can be estimated indirectly through population genetic data, but complementary data on pollinator flight distances is necessary to validate such estimates. By using radio-tracking of cowpea pollinator return flights, we found that carpenter bees visiting cowpea flowers can forage up to 6 km from their nest. Foraging distances were found to be shorter than the maximum flight range, especially under adverse weather conditions or poor reward levels. From complete flight records in which bees visited wild and domesticated populations, we conclude that bees can mediate gene flow and, in some instances, allow transgene (genetically engineered material) escape over several kilometers. However, most between-flower flights occur within plant patches, while very few occur between plant patches.

Modelling the risk of cross-pollination between maize crops can help to define efficient isolation methods to reduce the risk of gene flow between these crops. However, the use of such models over the pollen emission season is limited by poor estimations of pollen emission. In this study, we present a model that predicts hourly pollen emission fluxes over the pollen season and that accounts for effects of both meteorological conditions and crop variety. It consists of two sub-models that predict: (i) the seasonal pattern on a daily basis and (ii) the normalized diurnal pattern on an hourly basis. To assess the variability of pollen emission, ten field experiments were carried out in July and August over four years using three crop varieties. The model was built from (i) a parameterisation of the measured diurnal and seasonal patterns of pollen emission followed by (ii) a quantification of the relationships between parameter values and meteorological conditions. Total production of pollen was fairly constant for a given variety over years and sowing dates, while patterns of emission varied with meteorological conditions. The pollen emission season was longer when temperature was low and humidity was high. In most cases, the diurnal pattern was unimodal: the onset and the peak of emission were delayed when relative humidity was high or wind speed was low. In some cases, a second peak of emission occurred during the afternoon. This was observed more frequently when temperatures were high.

In order to study pollen-mediated gene flow in transgenic maize (Zea mays L.) in the Huang-huai-hai region of China, field trials were conducted in Jinan, Shandong Province in 2006 and 2007. The frequencies of gene flow from the donor plots, planted with transgenic maize as a pollen source, to the receptor plots, planted with non-transgenic maize, under different temporal or spatial separations were evaluated. The results showed that the frequency of pollen-mediated gene flow of the als gene from transgenic maize to non-transgenic maize decreased significantly with increasing distance. No gene flow was detected at 300 m. At a distance of 30 m, delaying the planting date of the transgenic maize by 1 week decreased the frequency of gene flow by 70%. A delay of 2 weeks decreased the gene flow frequency by more than 90%, while no gene flow was seen when the sowing date was delayed by 3 weeks. The results suggest that an appropriate isolation distance of 300 m or a temporal separation of 3 weeks could prevent gene flow from transgenic maize to non-transgenic maize in the Huang-huai-hai region.

在温室内人工创造风力和释放传粉昆虫蜜蜂的条件下，应用PCR和蛋白试纸条结合的方法检测外源<em>Cry</em>1Ac基因通过花粉漂移至非转基因棉的频率和距离。结果表明：风力处理和蜜蜂处理的基因漂移频率均显著高于空白对照。漂移至非转基因亲本棉石远321的频率显著高于陆地棉中棉所35和海岛棉吉扎1号。漂移至石远321的频率随距离远近差异显著，而漂移至中棉所35和吉扎1号的频率在不同距离上差异不显著。风力处理共检测到阳性样本72个，在检测范围内，漂移至石远321的最远距离为25.6 m，漂移至中棉所35和吉扎1号的最远距离均为19.2 m。蜜蜂处理中共检测到阳性样本75个，在检测范围内，漂移到常规棉的最远漂移距离均达到设置最远处36 m，并在此处达到峰值。本研究可为转基因棉花基因漂移生态风险性评估提供参考。

在转基因作物获准进行环境释放并实行大面积商品化推广的同时，基因漂移所引起的生态环境安全问题不容忽视。以含有双价抗虫基因（<em>Bt/CpTI</em>）的转基因棉花SGK321为花粉供体材料，以常规非转基因棉花品种石远321、中棉35、吉扎1号为花粉受体材料，在温室中人工创造定向风和非定向风条件，应用PCR与蛋白检测相结合的方法，检测外源基因发生基因漂移的效率。结果表明：随着与转基因棉花SGK321距离的增加，外源基因转移至非转基因棉花的基因漂移频率呈现波动性变化。在定向风处理中，基因漂移频率在距离转基因棉花6.4m处达到峰值33.33%，在测定范围内基因漂移最远距离为25.6m；而在非定向风处理中，基因漂移频率在距离转基因棉花12.8m处达到峰值36.67%，在测定范围内基因漂移最远距离为36m。非定向风可显著提高转移至海岛棉吉扎1号的基因漂移频率。外源基因从SGK321转移至其非转基因亲本石远321的基因漂移频率显著高于转移至陆地棉中棉35和海岛棉吉扎1号的漂移频率。为转基因棉花的生态安全性分析提供一定的理论参考价值。

With the large-scale release of genetically modified (GM) crops, there are ecological concerns on transgene movement from GM crops to non-GM counterparts and wild relatives. In this research, we conducted greenhouse experiments to measure pollen-mediated gene flow (PGF) in the absence and presence of pollinators (Bombus ignitus,Apis melliferaandPieris rapae) in one GM cotton (resistant to the insectHelicoverpa armigeraand the herbicide glyphosate) and two non-GM lines (Shiyuan321 and Hai7124) during 2012 and 2013. Our results revealed that: (1) PGF varied depending on the pollinator species, and was highest withB. ignitus(10.83%) and lowest withP. rapae(2.71%); (2) PGF withB. ignitusdepended on the distance between GM and non-GM cottons; (3) total PGF to Shiyuan321 (8.61%) was higher than to Hai7124 (4.10%). To confirm gene flow, we tested hybrids carrying transgenes for their resistance to glyphosate andH. armigera, and most hybrids showed strong resistance to the herbicide and insect. Our research confirmed that PGF depended on pollinator species, distance between plants and the receptor plant.

在转基因作物全球商业化推广的20年间,公众对基因漂移生态安全问题的关注持续升温.本试验以转基因双价棉SGK321 (CrylAc/CpTI)为花粉供体,常规棉“石远321”和“中棉35”为花粉授体,借助PCR和蛋白检测技术,研究温室中3种风速(0.54、0.92和1.27 m·s-1)条件下的CrylAc基因漂移频率.结果表明:“石远321”作为花粉受体时,基因漂移频率受风速影响,低风速下最高,高风速下最低;“中棉35”作为花粉授体时,基因漂移频率整体较低,不受风速影响;基因漂移频率与所选择的花粉受体品种有关,“石远321”(转基因棉亲本)(10.63％)作为花粉受体时基因漂移频率高于“中棉35”(2.50％);转基因棉花基因漂移频率随着转基因作物种植区与非转基因作物之间距离的增加而下降.本试验为风介导的基因漂移的生态风险评估提供一定的理论参考.

Abstract The occurrence of transgenic herbicide-resistant oilseed rape (Brassica napus) in ruderal (non-crop disturbed) areas has not been investigated previously in Canada. The primary objective of this study was to document their occurrence in two main ruderal areas (along railways and roads) in the province of Saskatchewan, where half of all oilseed rape is grown, and at the port of Vancouver, British Columbia on the west coast of Canada, where most oilseed rape destined for export is transported by rail. During the 2005 growing season, leaf samples of oilseed rape plants were collected at randomly-selected sites along railways and roads across Saskatchewan ecoregions and at Vancouver; infestation area, density, and plant height of oilseed rape were measured at each site. The presence of the glyphosate and glufosinate resistance traits was determined using test strips. The infestation area of oilseed rape, averaged across 155 sampled sites in the Saskatchewan survey, was markedly smaller in populations along railways than roads; in contrast, infestation area averaged across 54 sites in the Vancouver survey was greater for populations along railways than roads. In both surveys, mean plant density was greater for populations found along railways than roads. Two-thirds of oilseed rape plants sampled across Saskatchewan ecoregions and at Vancouver were transgenic, although the relative proportion of plants with the glyphosate or glufosinate resistance trait varied between surveys. Frequency of occurrence of transgenic plants in ruderal areas was similar to the proportion of the oilseed rape area planted with transgenic cultivars in the recent preceding years. A single transgenic B. rapa x B. napus hybrid was found along a road in Vancouver, confirming the relatively high probability of hybridization between these two Brassica species. With current control measures, transgenic oilseed rape populations may persist and spread in these ruderal areas.

Seed dispersal of feral crop plants along roadverges is likely to be influenced by numerous anthropogenic vectors in the agroecosystem. Within the context of introducing genetically modified (GM) cultivars, long-distance dispersal of feral seeds associated with the growth of GM feral populations (via a selective advantage due to transgene expression) could make these populations become invasive. Their expansion could then favour the spread of transgenes and modify the composition of roadverge plant communities. Because quantitative data on anthropogenic seed dispersal along roadverges were few, we estimated effective secondary dispersal for oilseed rape, the seeds of which are not adapted to dispersal by wind or biotic agents. A seed deposition experiment showed that secondary dispersal did not systematically occur along roadverges, was correlated with traffic intensity and was local. Low traffic intensity and anthropogenic disturbances (covering of seeds by mown grasses and burial by farming machinery) prevented dispersal on three of the experimental sites. Along a road with higher traffic, secondary dispersal occurred ( d max=21.5 m), probably induced by wind turbulence behind vehicles. The best-fitting dispersal kernel was a mixture of two components: 20% of seeds dispersing over a few metres on average and 80% remaining in the original place. Expansion rates of feral populations of GM herbicide-tolerant oilseed rape were computed using an invasion model and this kernel. They were low (1–4 m yr 611) when only ballistic and/or secondary dispersal were included but higher (4–20 m yr 611) when theoretically rare events of long-distance dispersal by verge mowers were added. This study suggests that secondary seed dispersal is unlikely to have a significant impact on the spread of GM feral oilseed rape populations in highly disturbed and dynamic habitats such as roadverges. Detecting long-distance dispersal events induced by other vectors (e.g. mowers) would require integrative approaches based on genetic and spatial data.

1. The consequences of the movement of transgenes from genetically modified (GM) crops into wild populations of plants continues to be of concern to ecologists and conservationists because of the possible threat posed to those populations in terms of their continued survival and because of the further knock-on effects that might occur to habitats in which they occur. 2. We examined five UK sea beet Beta vulgari s ssp. maritima populations from each of two major habitat types, cliff top and drift line. We assessed population genetic parameters, genetic diversity, gene flow, population differentiation and isolation by distance, to enable determination of the likelihood and consequences of spread to wild populations of genes from cultivated sugar beet group Beta vulgaris ssp. vulgaris , which could in the future be transgenic. 3. Drift line populations were more diverse than cliff top populations and also showed greater levels of gene flow. 4. Isolation by distance was identified in both habitats, but the relationship between genetic and geographical distance was detectable over longer distances for drift line populations. However, clear indications of vicariance (the subdivision of a population into distinct taxa by the appearance of a geological barrier) between cliff and drift line populations were also evident, because of the restriction of gene flow between the two habitats occurring more in one direction than the other. 5. Synthesis and applications. The likelihood of transgene spread from crop to wild populations is habitat dependent and conservation management decisions could therefore vary from one population to another, for example water courses were found to facilitate seed dispersal. This should be taken into account when estimating isolation distances for GM beet, and when predicting transgene frequencies (exposure estimates) for environmental risk assessments of GM beet.

Pollen-mediated gene flow is the major pathway for transgene escape from GM rice to its wild relatives. Transgene escape to wild gene flow and its ecological consequences. A framework for assessing potential ecological consequences caused by transgene escape from GM rice to its wild relatives is discussed based on studies of gene flow and fitness changes.

The objective of this study was to survey pedigreed canola (Brassica napus L.) seedlots for contaminating herbicide resistance traits because of complaints from farmers regarding glyphosate [N-(phosphonomethyl)glycine]-resistant canola volunteers occurring unexpectedly in their fields at densities and in patterns that suggested that pollen-mediated gene flow from neighboring fields in previous years was not the source of contamination. Twenty-seven unique, commercial certified canola see

The introduction of non-native populations can lead to the competitive exclusion (displacement) of native populations. This has been hypothesized to be further exacerbated by the potential of hybridization, which can dilute or genetically assimilate the native genotype leaving no ''pure'' natives. With relatively moderate to high rates of immigration, the loss of the native species can be rapid with or without hybridization. Using single-locus, two-allele models, I find that species replacement can occur very rapidly and the time to displacement decreases rapidly with increasing immigration and selection differential. Immigration and selection act in two different ways: increasing immigration results in displacement by overwhelming the native; whereas increasing the selection differential in favor of the invader leads to displacement via genetic assimilation. The implications of these results are the need for more empirical studies on the immigration patterns of invasive species and their potential for interbreeding with natives.

Natural hybridization threatens a substantial number of plant and animal species with extinction, but extinction risk has been difficult to evaluate in the absence of a quantitative assessment of risk factors. We investigated a number of ecological parameters likely to affect extinction risk, through an individual-based model simulating the life cycle of two hybridizing annual plant species. All parameters tested, ranging from population size to variance in pollen-tube growth rates, affected extinction risk. The sensitivity of each parameter varied dramatically across parameter sets, but, overall, the competitive ability, initial frequency, and selfing rate of the native taxon had the strongest effect on extinction. In addition, prezygotic reproductive barriers had a stronger influence on extinction rates than did postzygotic barriers. A stable hybrid zone was possible only when habitat differentiation was included in the model. When there was no habitat differentiation, either one of the parental species or the hybrids eventually displaced the other two taxa. The simulations demonstrated that hybridization is perhaps the most rapidly acting genetic threat to endangered species, with extinction often taking place in less than five generations. The simulation model was also applied to naturally hybridizing species pairs for which considerable genetic and ecological information is available. The predictions from these "worked examples" are in close agreement with observed outcomes and further suggest that an endemic cordgrass species is threatened by hybridization. These simulations provide guidance concerning the kinds of data required to evaluate extinction risk and possible conservation strategies.

Much has been written about the role of interspecific competition, disease, herbivory, and the loss of key mutualisms in the extinction of rare plant species. Interspecific hybridization rarely is considered among the biotic interactions that promote extinction. We show how hybridization may contribute to the demise of rare plant species through demographic swamping and genetic assimilation by an abundant congener. We contend that the growth of the hybrid subpopulation is the key to rare species assimilation, and we show how the production of hybrid seed, the fitness of hybrids, and pest pressure affect hybrid proliferation. We also discuss how habitat disturbance, unspecialized pollinators, and weak crossing barriers promote hybridization, and how the negative consequences of hybridization are unlikely to be compensated for by immigration from conspecific populations. We also illustrate stages in the demise of species in island floras. We suggest that hybridization is an increasing threat to rare species because ecological barriers are being disrupted by human activities.

Transgene outflow from genetically modified (GM) rice to its wild relatives may cause undesirable ecological consequences. Understanding the level of transgene expression in wild rice following gene flow is important for assessing such consequences, providing that transgene escape from GM rice cannot be prevented. To determine the expression of a transgene in common wild rice (), we analyzed the content of Cry1Ac protein in three GM rice lines containing a transgene, their Fhybrids with common wild rice and Fprogeny at different growth stages, using the sandwich enzyme-linked immunosorbent assay. The average content of Cry1Ac protein in leaf samples of the wild rice lines ranged between 0.016 and 0.069% during the entire growth period, whereas that in stems varied between 0.12 and 0.39%. A great variation in Cry1Ac protein content was detected among individuals of Fhybrids and Fprogeny, with some wild individuals showing higher level of toxin than the cultivated GM rice. The results suggest that the transgene can express normally in the interspecific hybrids between insect-resistant GM rice and common wild rice, and may have similar effects on the target insects as in GM rice.

Kentucky bluegrass (Poa pratensis L.), one of the most commonly grown turfgrasses in temperate regions, is being developed for possible commercial release with transgenic traits. The use of this technology raises risk assessment questions because P. pratensis is perennial, often apomictic, competitive in many habitats, and hybridizes with other Poa To further understand the potential environmental impact of a transgenic P. pratensis, we measured intra- and interspecific pollen-mediated gene flow in field conditions from P. pratensis to other Poa We used a wagon-wheel design with a glyphosate (N-phosphono methyl-glycine) resistant P. pratensis as a pollen donor and a pollen receptor plot at 0 m and plots at 13 and 53 m along six equally spaced vectors. Each receptor plot included accessions from 25 Poa species. Seedlings from the receptor plants were screened for resistance to glyphosate and potential hybrids verified by PCR and genomic fingerprinting. Hybrids were found with P. arachnifera Torrey, P. interior Rydb., P. pratensis P. secunda J. Presl, and three other P. pratensis entries, but did not occur with P. annua L., P. palustris L., P. trivialis L., or P. compressa L., among other species. Overall hybrid frequency was 0.048% and hybrid frequency at the 0-m distance was 0.53%. While apomixis in receptor plants and pollen competition likely reduced the number of hybrids, gene flow did occur but at low frequency and over short distances.

Abstract Top of page Abstract I. Introduction II. How do transgenes escape? – Hybridization, gene flow, and introgression III. Assessing selection on transgenes – costs and benefits IV. The effects of transgenes – case studies V. Can we prevent transgene escape? VI. Conclusions and future directions Acknowledgements References Contents Summary429 I. Introduction429 II. How do transgenes escape? – Hybridization, gene flow, and introgression432 III. Assessing selection on transgenes – costs and benefits434 IV. The effects of transgenes – case studies435 V. Can we prevent transgene escape?437 VI. Conclusions and future directions440 Acknowledgements440 References440 Summary Genetically modified (GM) plants are rapidly becoming a common feature of modern agriculture. This transition to engineered crops has been driven by a variety of potential benefits, both economic and ecological. The increase in the use of GM crops has, however, been accompanied by growing concerns regarding their potential impact on the environment. Here, we focus on the escape of transgenes from cultivation via crop×wild hybridization. We begin by reviewing the literature on natural hybridization, with particular reference to gene flow between crop plants and their wild relatives. We further show that natural selection, and not the overall rate of gene flow, is the most important factor governing the spread of favorable alleles. Hence, much of this review focuses on the likely effects of transgenes once they escape. Finally, we consider strategies for transgene containment.

The public concern about pollen-mediated gene flow (PGF) from genetically modified (GM) crops to non-GM crops heats up in recent years over China. In the current study, we conducted greenhouse and field experiments to measure PGF with various physical isolation measures, including 90, 80, 60 and 40 holes/cm2separation nets andSorghum bicolor,Zea maysandLycopersicon esculentumseparation crops between GM cotton and non-GM line (Shiyuan321) by seed DNA test during 2013 to 2015, and pollen grain dyeing was also conducted to assess the pollen flow in greenhouse during 2013. Our results revealed that (1) PGF varied depending on the physical isolation measures. PGF was the lowest with 90 holes/cm2separation net andS.bicolorseparation crop, and the highest with 40 holes/cm2separation net and no isolation measure. (2) Similar to PGF results, 90 holes/cm2separation net andS.bicolorseparation crop could minimize the pollen dispersal. (3) PGF declined exponentially with increasing distance between GM cotton and Shiyuan321. Because of the production mode of farm household (limited cultivated area) in China, our study is particularly important, which is not only benefit for constraining PGF, but also has potential application value in practical production and the scientific researches.

Characterizing the spatial patterns of gene flow from transgenic crops is challenging, making it difficult to design containment strategies for markets that regulate the adventitious presence of transgenes. Insecticidal Bacillus thuringiensis (Bt) cotton is planted on millions of hectares annually and is a potential source of transgene flow. Here we monitored 15 non-Bt cotton (Gossypium hirsutum, L.) seed production fields (some transgenic for herbicide resistance, some not) for gene flow of the Bt cotton cry1Ac transgene. We investigated seed-mediated gene flow, which yields adventitious Bt cotton plants, and pollen-mediated gene flow, which generates outcrossed seeds. A spatially-explicit statistical analysis was used to quantify the effects of nearby Bt and non-Bt cotton fields at various spatial scales, along with the effects of pollinator abundance and adventitious Bt plants in fields, on pollen-mediated gene flow. Adventitious Bt cotton plants, resulting from seed bags and planting error, comprised over 15% of plants sampled from the edges of three seed production fields. In contrast, pollen-mediated gene flow affected less than 1% of the seed sampled from field edges. Variation in outcrossing was better explained by the area of Bt cotton fields within 750 m of the seed production fields than by the area of Bt cotton within larger or smaller spatial scales. Variation in outcrossing was also positively associated with the abundance of honey bees. A comparison of statistical methods showed that our spatially-explicit analysis was more powerful for understanding the effects of surrounding fields than customary models based on distance. Given the low rates of pollen-mediated gene flow observed in this study, we conclude that careful planting and screening of seeds could be more important than field spacing for limiting gene flow.

Abstract Pollen flow from a 0.46 ha plot of genetically engineered (GE) Prunus domestica located in West Virginia, USA was evaluated from 2000-2010. Sentinel plum trees were planted at distances ranging from 132 to 854 m from the center of the GE orchard. Plots of mixed plum varieties and seedlings were located at 384, 484 and 998 m from the GE plot. Bee hives (Apis mellifera) were dispersed between the GE plum plot and the pollen flow monitoring sites. Pollen-mediated gene flow from out of the GE plum plot to non-GE plums under the study conditions was low, only occurring at all in 4 of 11 years and then in only 0.31% of the 12,116 seeds analyzed. When it occurred, gene flow, calculated as the number of GUS positive embryos/total embryos sampled, ranged from 0.215% at 132 m from the center of the GE plum plot (28 m from the nearest GE plum tree) to 0.033-0.017% at longer distances (384-998 m). Based on the percentage of GUS positive seeds per individual sampled tree the range was 0.4% to 12%. Within the GE field plot, gene flow ranged from 4.9 to 39%. Gene flow was related to distance and environmental conditions. A single year sample from a sentinel plot 132 m from the center of the GE plot accounted for 65% of the total 11-year gene flow. Spatial modeling indicated that gene flow dramatically decreased at distances over 400 m from the GE plot. Air temperature and rainfall were, respectively, positively and negatively correlated with gene flow, reflecting the effects of weather conditions on insect pollinator activity. Seed-mediated gene flow was not detected. These results support the feasibility of coexistence of GE and non-GE plum orchards.

Genetically modified (GM) insect and herbicide resistant cottons are now the mainstay of the cotton industry based in the eastern States of Australia. However, during the early years of breeding and seed increase, there was some uncertainty among regulators about containment measures needed to prevent the movement of regulated GM traits into adjacent fields of conventional cotton and possibly into the human or animal food chain. This was particularly relevant in the more tropical north of Australia that was being used as a winter nursery. Field experiments on GM cottons in eastern Australia were commonplace, but even there, regulators required confirmation that the containment practices already in place (buffer zones and isolation distances) were effective. A series of experiments in a range of environments, designed to monitor the movement of GM pollen into adjacent cotton buffers, adjacent fields, across bare ground and over long distances are reported here. Gene flow from GM plots into adjacent conventional cotton was found to be much higher in northern Australia than in eastern Australia, most likely due to higher honey bee ( Apis mellifera) numbers, often deliberately enhanced to aid the surrounding horticultural industries. Movement of pollen over bare ground to nearby crops was observed at a number of locations indicating that small isolation zones should not be used for containment of regulated GM cotton. In general, buffers of 20 m of conventional cotton surrounding GM plots proved to be highly effective unless bee numbers were artificially high. Based on insect observations and rates of pollen flow, it was concluded that pollen beetles ( Carpophilus spp.), another potential pollen vector normally highly abundant in cotton, were not associated with movement of pollen more than 1 m away from crops.

Chloroplast genetic engineering offers several unique advantages, including high-level transgene expression, multi-gene engineering in a single transformation event and transgene containment by maternal inheritance, as well as a lack of gene silencing, position and pleiotropic effects and undesirable foreign DNA. More than 40 transgenes have been stably integrated and expressed using the tobacco chloroplast genome to confer desired agronomic traits or express high levels of vaccine antigens and biopharmaceuticals. Despite such significant progress, this technology has not been extended to major crops. However, highly efficient soybean, carrot and cotton plastid transformation has recently been accomplished through somatic embryogenesis using species-specific chloroplast vectors. This review focuses on recent exciting developments in this field and offers directions for further research and development.

Chloroplast genetic engineering offers a number of unique advantages, including a high-level of transgene expression, multi-gene engineering in a single transformation event, transgene containment via maternal inheritance, lack of gene silencing, position and pleiotropic effects, and undesirable foreign DNA. Thus far, over forty transgenes have been stably integrated and expressed via the tobacco chloroplast genome to confer important agronomic traits, as well as express industrially valuable biomaterials and therapeutic proteins. The hyperexpression of recombinant proteins within plastid engineered systems offers a cost effective solution for using plants as bioreactors. Additionally, the presence of chaperones and enzymes within the chloroplast help to assemble complex multi-subunit proteins and correctly fold proteins containing disulfide bonds, thereby drastically reducing the costs of in vitro processing. Oral delivery of vaccine antigens against cholera, tetanus, anthrax, plague, and canine parvovirus are made possible because of the high expression levels and antibiotic-free selection systems available in plastid transformation systems. Plastid genetic engineering also has become a powerful tool for basic research in plastid biogenesis and function. This approach has helped to unveil a wealth of information about plastid DNA replication origins, intron maturases, translation elements and proteolysis, import of proteins and several other processes. Although many successful examples of plastid engineering have set a foundation for various future applications, this technology has not been extended to many of the major crops. Highly efficient plastid transformation has been recently accomplished via somatic embryogenesis using species-specific chloroplast vectors in soybean, carrot, and cotton. Transgenic carrots were able to withstand salt concentrations that only halophytes could tolerate; more than twice the effectiveness of other engineering attempts. Recent advances in plastid engineering provide an efficient platform for the production of therapeutic proteins, vaccines, and biomaterials using an environmentally friendly approach. This review takes an in-depth look into the state of the art in plastid engineering and offers directions for further research and development.

The first characterization of transcriptional, posttranscriptional, and translational processes of heterologous operons expressed via the tobacco (Nicotiana tabacum) chloroplast genome is reported here. Northern-blot analyses performed on chloroplast transgenic lines harboring seven different heterologous operons revealed that polycistronic mRNA was the predominant transcript produced. Despite the lack of processing of such polycistrons, large amounts of foreign protein accumulation was observed in these transgenic lines, indicating abundant translation of polycistrons. This is supported by polysome fractionation assays, which allowed detection of polycistronic RNA in lower fractions of the sucrose gradients. These results show that the chloroplast posttranscriptional machinery can indeed detect and translate multigenic sequences that are not of chloroplast origin. In contrast to native transcripts, processed and unprocessed heterologous polycistrons were stable, even in the absence of 3′ untranslated regions (UTRs). Unlike native 5′UTRs, heterologous secondary structures or 5′UTRs showed efficient translational enhancement independent of cellular control. Abundant read-through transcripts were observed in the presence of chloroplast 3′UTRs but they were efficiently processed at introns present within the native operon. Heterologous genes regulated by the psbA (the photosystem II polypeptide D1) promoter, 5′ and 3′UTRs have greater abundance of transcripts than the endogenous psbA gene because transgenes were integrated into the inverted repeat region. Addressing questions about polycistrons, and the sequences required for their processing and transcript stability, are essential in chloroplast metabolic engineering. Knowledge of such factors would enable engineering of foreign pathways independent of the chloroplast complex posttranscriptional regulatory machinery.

Glyphosate is a potent herbicide. It works by competitive inhibition of the enzyme 5-enol-pyruvyl shikimate-3-phosphate synthase (EPSPS), which catalyzes an essential step in the aromatic amino acid biosynthetic pathway. We report the genetic engineering of herbicide resistance by stable integration of the petunia EPSPS gene into the tobacco chloroplast genome using the tobacco or universal vector. Southern blot analysis confirms stable integration of the EPSPS gene into all of the chloroplast genomes (5000-10,000 copies per cell) of transgenic plants. Seeds obtained after the first self-cross of transgenic plants germinated and grew normally in the presence of the selectable marker, whereas the control seedlings were bleached. While control plants were extremely sensitive to glyphosate, transgenic plants survived sprays of high concentrations of glyphosate. Chloroplast transformation provides containment of foreign genes because plastid transgenes are not transmitted by pollen. The escape of foreign genes via pollen is a serious environmental concern in nuclear transgenic plants because of the high rates of gene flow from crops to wild weedy relatives.

Abstract Transgenic chloroplasts offer unique advantages in plant biotechnology, including high-level foreign protein expression, absence of epigenetic effects, and gene containment due to the lack of transgene transmission through pollen. However, broad application of plastid genome engineering in biotechnology has been largely hampered by both the lack of chloroplast transformation systems for major crop plants and the usually low plastid gene expression levels in nongreen tissues such as fruits, tubers, and other storage organs. Here we describe the development of a plastid transformation system for tomato, Lycopersicon esculentum. This is the first report on the generation of fertile transplastomic plants in a food crop with an edible fruit. We show that chromoplasts in the tomato fruit express the transgene to approximately 50% of the expression levels in leaf chloroplasts. Given the generally very high foreign protein accumulation rates that can be achieved in transgenic chloroplasts (>40% of the total soluble protein), this system paves the way to efficient production of edible vaccines, pharmaceuticals, and antibodies in tomato.

Several strategies have been proposed for creating transgenic cultivars from which transgene escape to wild relatives would seem unlikely; for example, to impede escape through pollen, a transgene could be inserted into chloroplast DNA (cpDNA), which in many crops is rarely transmitted through pollen. None of these strategies would be failsafe; for example, the rate of cpDNA transmission through pollen may be low but non-zero in many crops. Here, we study how the probability distribution of escape time depends on the rates of pollen and seed flow from the crop to wild populations, the number and sizes of the wild populations, the selection coefficient for the transgene, and a leakage parameter characteristic of the strategy, for example, the rate of cpDNA transmission through pollen. We find that even with a leakage parameter as small as 10 3, the probability of escape within as few as 10 generations could be appreciable.

Plastid DNA is absent in pollen or sperm cells of Arabidopsis thaliana . Accordingly, plastids and mitochondria, in a standard genetic cross, are transmitted to the seed progeny by the maternal parent only. Our objective was to test whether paternal plastids are transmitted by pollen as an exception. The maternal parent in our cross was a nuclear male sterile ( ms1-1 / ms1-1 ), spectinomycin-sensitive L er plant. It was fertilized with pollen of a male fertile RLD-Spc1 plant carrying a plastid-encoded spectinomycin resistance mutation. Seedlings with paternal plastids were selected by spectinomycin resistance encoded in the paternal plastid DNA. Our data, in general, support maternal inheritance of plastids in A. thaliana . However, we report that paternal plastids are transmitted to the seed progeny in Arabidopsis at a low (3.9 10 5 ) frequency. This observation extends previous reports in Antirrhinum majus , Epilobium hirsutum , Nicotiana tabacum , Petunia hybrida, and the cereal crop Setaria italica to a cruciferous species suggesting that low-frequency paternal leakage of plastids via pollen may be universal in plants previously thought to exhibit strict maternal plastid inheritance. The genetic tools employed here will facilitate testing the effect of Arabidopsis nuclear mutations on plastid inheritance and allow for the design of mutant screens to identify nuclear genes controlling plastid inheritance.

Plastids (chloroplasts) are maternally inherited in most crops. Maternal inheritance excludes plastid genes and transgenes from pollen transmission. Therefore, plastid transformation is considered a superb tool for ensuring transgene containment and improving the biosafety of transgenic plants. Here, we have assessed the strictness of maternal inheritance and the extent to which plastid transformation technology confers an increase in transgene confinement. We describe an experimental system facilitating stringent selection for occasional paternal plastid transmission. In a large screen, we detected low-level paternal inheritance of transgenic plastids in tobacco. Whereas the frequency of transmission into the cotyledons of F1 seedlings was ≈1.58 × 10615 (on 100% cross-fertilization), transmission into the shoot apical meristem was significantly lower (2.86 × 10616). Our data demonstrate that plastid transformation provides an effective tool to increase the biosafety of transgenic plants. However, in cases where pollen transmission must be prevented altogether, stacking with other containment methods will be necessary to eliminate the residual outcrossing risk.

Cytoplasmic male sterility (CMS) in plants is a classical example of genomic conflict, opposing maternally-inherited cytoplasmic genes (mitochondrial genes in most cases), which induce male sterility, and nuclear genes, which restore male fertility. In natural populations, this type of sex control leads to gynodioecy, that is, the co-occurrence of female and hermaphroditic individuals within a population. According to theoretical models, two conditions may maintain male sterility in a natural population: (1) female advantage (female plants are reproductively more successful than hermaphrodites on account of their global seed production); (2) the counter-selection of nuclear fertility restorers when the corresponding male-sterility-inducing cytoplasm is lacking. In this review, we re-examine the model of nuclear-mitochondrial conflict in the light of recent experimental results from naturally occurring CMS, alloplasmic CMS (appearing after interspecific crosses resulting from the association of nuclear and cytoplasmic genomes from different species), and CMS plants obtained in the laboratory and carrying mitochondrial mutations. We raise new hypotheses and discuss experimental models that would take physiological interactions between cytoplasmic and nuclear genomes into account.

Mitochondrial function depends on the coordinate action of nuclear and mitochondrial genomes. The genetic dissection of these interactions presents special challenges in obligate aerobes, because the viability of these organisms depends on mitochondrial respiration. The plant trait cytoplasmic male sterility (CMS) is determined by the mitochondrial genome and is associated with a pollen sterility phenotype that can be suppressed or counteracted by nuclear genes known as restorer-of-fertility genes. Here, I review the nature and the origin of the genes that determine CMS, together with recent investigations that have exploited CMS to provide new insights into plant mitochondrial uclear communication. These studies have implicated mitochondrial signaling pathways, including those involved in regulating cell death and nuclear gene expression, in the elaboration of CMS. The molecular cloning of nuclear genes that restore fertility (i.e. restorer-of-fertility genes) has identified genes encoding pentatricopeptide-repeat proteins as key regulators of plant mitochondrial gene expression.

Cytoplasmic male sterility (CMS) is a maternally transmitted trait, whereby a plant is unable to produce viable pollen. Studies have revealed that this trait is a tool for enabling effi cient and reliable coexistence between genetically modified (GM) and non-GM cultivation by biocontainment of GM maize (Zea mays L.) pollen. Maize has three types of male-sterile cytoplasm (T, S, and C), the fertility of which can be restored by nuclear rf genes or by interactions with the environment. Twenty-two CMS versions of modern European maize hybrids were evaluated in 17 environments in Switzerland, France, and Bulgaria, with two or three sowing dates, in 2005 and 2006. Stable and unstable male sterility occurred in all three CMS types. T-cytoplasm hybrids were the most stable, while S-cytoplasm hybrids often showed partial restoration of fertility. C-cytoplasm was similar to T-cytoplasm with regard to maintaining male sterility. Climatic factors, especially air temperature, evapotranspiration, and water vapor, during the 10 d before anthesis as well as during anthesis, were correlated positively or negatively with the partial reversion to male fertility of CMS hybrids, indicating an interaction between genetic and climatic factors. This study illustrates that T- and C-cytoplasm in particular open up viable prospects for containing transgenic pollen, especially for Bt-maize.

Sunflower pollen flow over long distance was evaluated. Plants from three CMS lines were cultivated at distances 10 m, 1.0 km and 1.5 km from the male fertile line used as pollen donor. The assessment of the seed set of the CMS plants showed a decrease in the pollination with the distance from the pollen donor plants. The microsatellite analysis of bulk samples from the collected seeds demonstrated pollen dispersal from the pollen donor plants over all three tested distances. Further analysis of individual seeds suggested that a small portion of the collected seeds may have resulted from selfpollination of studied CMS lines and crosspollination between them. The observed restoration of fertility in the CMS lines was most probably caused by the excessive rainfall and lower average temperatures during the period of the flowering of the CMS lines. The stability of a wider range of CMS lines carrying cytoplasms from H. petiolaris, H. argophylis, H. rigidus and H. praoxes species were evaluated within three years (2006 2008) in two different locations in Bulgaria. Sixteen CMS lines, studied in 2006, were sterile in tested environmental conditions. Six of the CMS lines were further assessed in the period 2007 2008 after two periods of sowing and parallel cultivation in greenhouse. The investigated CMS lines differed in regard to the stability of cytoplasmic male sterility. Four of them were fully sterile across all nine different environmental conditions in the period 2006 2008. Two CMS lines showed unstable sterility that varied under the different environmental conditions. The restoration of fertility in these CMS lines was partial and affected only few individual plants. Taken together these data suggest that the climatic condition (temperature, humidity and daily light intensity) may affect the stability of sterility of the sunflower CMS lines depending of their genotype. The results from the present study indicated that long distance pollen dispersal is a major factor limiting the cultivation of transgenic sunflower plants. The prevention of transgenic pollen spread through cultivation of transgenic CMS plants has to be well evaluated in direction to the stability of the used CMS lines for each specific location, multiple periods of cultivation and various climatic conditions.

The current practice of manual emasculation of tomato 0004owers for hybrid seed production is labour-intensive and contributes signi0003cantly to the high cost of seed. Here we report on a photoperiod-sensitive, single gene male-sterile mutant (7B-1) in tomato which is 100% male sterile in long days (LD, minimum of 12.h daylength) in summer 0003eld conditions, but produces many male-fertile 0004owers in short days (SD, 8.h). In LD, 7B-1 0004owers contain stamens that are pale, short and in the anthers microspore mother cells are differentiated but meiosis does not occur, i.e. microspores and pollen grains are not formed. Unlike the wild type 0004owers, the style and stigma of 7B-1 0004owers are well exposed and this allows for ready access for pollination without emasculation. In SD, mutant 0004owers possess normal-looking orange-yellow anthers that enclose the stigma and produce normal viable pollen, which when used for pollination of 7B-1 0004owers yield good fruit- and seed-set. The 7B-1 seed in turn generate a 100% population of male-sterile plants all of which can be used as female parents for hybrid seed production. The female fertility is not affected in 7B-1 0004owers in both LD and SD conditions. The 7B-1 mutant has been grown in various 0003eld locations including, Saskatoon, California, Florida and in Chile, and at all locations it has shown stable male sterility. The 7B-1 mutant is a simple, natural and costeffective system that has a strong potential for use in commercial-scale production of tomato hybrid seed.

A major challenge for future genetically modified (GM) crops is to prevent undesired gene flow of transgenes to plant material intended for another use. Recombinase-mediated auto excision of transgenes directed by a tightly controlled microspore-specific promoter allows efficient removal of either the selectable marker gene or of all introduced transgenes during microsporogenesis. This way, transgene removal becomes an integral part of the biology of pollen maturation, not requiring any external stimulus such as chemical induction by spraying. We here show the feasibility of engineering transgenic plants to produce pollen devoid of any transgene. Highly efficient excision of transgenes from tobacco pollen was achieved with a potential failure rate of at most two out of 16,800 seeds (0.024%). No evidence for either premature activation or absence of activation of the recombinase system was observed under stress conditions in the laboratory. This approach can prevent adventitious presence of transgenes in non-GM crops or related wild species by gene flow. Such biological containment may help the deployment and management of coexistence practices to support consumer choice and will promote clean molecular farming for the production of high-value compounds in plants.

A major limitation of crop biotechnology and breeding is the lack of efficient molecular technologies for precise engineering of target genomic loci. While transformation procedures have become routine for a growing number of plant species, the random introduction of complex transgenenic DNA into the plant genome by current methods generates unpredictable effects on both transgene and homologous native gene expression. The risk of transgene transfer into related plant species and consumers is another concern associated with the conventional transformation technologies. Various approaches to avoid or eliminate undesirable transgenes, most notably selectable marker genes used in plant transformation, have recently been developed. These approaches include contransformation with two independent T-DNAs or plasmid DNAs followed by their subsequent segregation, transposon-mediated DNA elimination, and most recently, attempts to replace bacterial T-DNA borders and selectable marker genes with functional equivalents of plant origin. The use of site-specific recombination to remove undesired DNA from the plant genome and concomitantly, via excision-mediated DNA rearrangement, switch-activate by choice transgenes of agro-nomical, food or feed quality traits provides a versatile "transgene maintenance and control" strategy that can significantly contribute to the transfer of transgenic laboratory developments into farming practice. This review focuses on recent reports demonstrating the elimination of undesirable transgenes (essentially selectable marker and recombinase genes) from the plant genome and concomitant activation of a silent transgene (e.g., a reporter gene) mediated by different site-specific recombinases driven by constitutive or chemically, environmentally or developmentally regulated promoters. These reports indicate major progress in excision strategies which extends application of the technology from annual, sexually propagated plants towards perennial, woody and vegetatively propagated plants. Current trends and future prospects for optimization of excision-activation machinery and its practical implementation for the generation of transgenic plants and plant products free of undesired genes are discussed.

There is strong evidence indicating that gene flow from transgenic B. napus into weedy wild relatives is inevitable following commercial release. Research should now focus on the transmission, stability, and impact of transgene expression after the initial hybridization event. The present study investigated the transfer of a phosphinothricin-tolerance transgene by inter-specific hybridization between B. rapa and two transgenic B. napus lines. The expression of the transgene was monitored in the F 1 hybrids and in subsequent backcross generations. The transgene was transmitted relatively easily into the F 1 hybrids and retained activity. Large differences in the transmission frequency of the transgene were noted between offspring of the two transgenic lines during backcrossing. The most plausible explanation of these results is that the line showing least transmission during backcrossing contains a transgene integrated into a C-genome chromosome. Approximately 10% of offspring retained the tolerant trait in the BC 3 and BC 4 generations. The implications of these findings for the stable introgression of transgenes carried on one of the chromosomes of the C-genome from B. napus and into B. rapa are briefly discussed.

ABSTRACT Flowers which show cleistogamy (CL) remain closed during pollen shedding, and thus are predominantly self-pollinated. CL in barley is controlled either by the single, multi-allelic gene cly1 located on the long arm of chromosome 2H, or by two closely linked, epistatic genes (cly1 and Cly2). Here, we have taken advantage of the co-linearity which exists between chromosome 2H of barley and rice chromosome 4 to generate de novo markers targeted to the CL region, and these have been used to construct a localized high resolution genetic map. While synteny is largely conserved in this region, the critical 18 cM barley segment appears to be inverted with respect to the equivalent 1.6 Mb physical stretch of the rice genome. The cly1 locus was located in a 0.76 cM region of barley genetic map, and rice orthologue of cly1 (if there is one) is one of the 11 genes predicted to lie within 90 kb interval of rice genome.

Cleistogamy, the production of open (chasmogamous, CH) and closed (cleistogamous, CL) floral forms by one species, is present in [(L.) Merr.]. cultivars that originated from high latitudes generally have a strong tendency to produce CL flowers. The first objective of this study was to determine varietal differences in cleistogamy. The second objective was to observe morphological differences between CH and CL flowers. A total of 32 and 31 cultivars (maturity groups 00 to II) were grown in fields at Tsukuba and Sapporo, Japan, respectively, in 2005. Flowers that were fertilized up to 5 d after anthesis were classified into either CH or CL. Frequency of CL flowers ranged from 0.0 to 100.0% in Tsukuba and 6.7 to 100.0% in Sapporo. Cultivars from Russia and Hokkaido generally had a high frequency of CL flowers, whereas those from the Tohoku region had a lower frequency. Average of mean temperatures for 1 wk before anthesis was negatively correlated with frequency of CL flowers. chamber experiments were conducted using CL cv. Severnaya 4 and a CH cv. Toyosuzu under constant temperatures of 25 C to eliminate temperature effects. Frequency of CL flowers in Severnaya 4 and Toyosuzu was 33.7 and 92.8%, respectively, suggesting involvement of genetic factors. At the same developmental stage, CL flowers had shorter sepal, petal, and stamen than CH flowers. There was no distinct morphological change in floral organs between CH and CL flowers except for length of the organs.

1. Most dimorphic angiosperm species produce chasmogamous flowers adapted for allogamy and cleistogamous flowers adapted for autogamy. Plant size is an important internal environmental factor and several studies have suggested an adaptive strategy whereby cleistogamous flowering ensures a basic seed output while larger plants can spare resources to make additional investment in the more expensive but presumably more fit outcrossed seed produced by chasmogamous flowering. This study tests the effect of plant size on the percentage of chasmogamy in a species, Mimulus nasutus, where both the cleistogamous and chasmogamous flowers are autogamous and so seed from chasmogamous flowers has no genetic advantage. 2. We measured change in expression of cleistogamy/chasmogamy in glasshouse-grown plants of different sizes and architecture. Size was manipulated by varying the length of time for which the plants were grown under short days. Architecture was manipulated by removing stems. 3. We found that increased size led to an increase in the percentage of chasmogamy in M. nasutus. This is unexpected given the lack of genetic advantage of outcrossing and suggests that this effect can occur as a direct result of increased resource availability without the necessity of selection for progeny fitness. 4. An increase in plant size was also found to lead to an increase in resource sinks (developing flowers and seed capsules on other parts of the plant). As increased plant size can therefore produce both increased total resources and increased number of resource sinks, the net resources available to a developing flower will be a balance of these two effects. Resource re-allocation is shown to occur between flowers on a stem, between stems and between flowers and seed set. In each case, this results in a net decrease in resources to new flowers and so results in there being only sufficient resources for cleistogamous flowering. 5. We discuss the difficulties of using species with varying growth forms to test the hypothesis that expression of allogamous chasmogamy increases with plant size because of the genetic advantage of outcrossing.

With the rapid advancement of transgenic biotechnology, large numbers of transgenic crops have been produced and released for commercial cultivation (James, 2001), raising considerable biosafety concerns all over the world. One of the major issues is the potential ecological risk resulting from transgenes escaping into and persist- ing in the environment. The extensive on-going debate on this issue (Arriola, 1997; Wolfenbarger and Phifer, 2000; Crawley et al., 2001; Prakash, 2001; Dale et al., 2002) poses challenging questions regarding the research direc- tions that need to be taken to ensure that biotechnology outputs are responsibly deployed worldwide. Unless these biosafety issues are satisfactorily addressed, large-scale commercial release of the transgenic crops developed and further advancement of transgenic bio- technology are likely to be hampered. For an in-depth review of crop-to-wild gene flow, see Jenczewski et al. (2002) in this number of EBR. Here the more specific issue of the effectiveness of preventing gene flow from occurring will be discussed.

Transgenic crops may interbreed with nearby weeds, increasing their competitiveness, and may themselves become a 'volunteer' weed in the following crop. The desired transgene can be coupled in tandem with genes that would render hybrid offspring or volunteer weeds less able to compete with crops, weeds and wild species. Genes that prevent seed shatter or secondary dormancy, or that dwarf the recipient could all be useful for mitigation and may have value to the crop. Many such genes have been isolated in the past few years.

Some transgenic crops can introgress genes into other varieties of the crop, to related weeds or themselves remain as 'volunteer' weeds, potentially enhancing the invasiveness or weediness of the resulting offspring. The presently suggested mechanisms for transgene containment allow low frequency of gene release (leakage), requiring the mitigation of continued spread. Transgenic mitigation (TM), where a desired primary gene is tandemly coupled with mitigating genes that are positive or neutral to the crop but deleterious to hybrids and their progeny, was tested as a mechanism to mitigate transgene introgression. Dwarfism, which typically increases crop yield while decreasing the ability to compete, was used as a mitigator. A construct of a dominant ahas R (acetohydroxy acid synthase) gene conferring herbicide resistance in tandem with the semidominant mitigator dwarfing gai (gibberellic acid-insensitive) gene was transformed into tobacco ( Nicotiana tabacum ). The integration and the phenotypic stability of the tandemly linked ahas R and gai genomic inserts in later generations were confirmed by polymerase chain reaction. The hemizygous semidwarf imazapyr-resistant TM T 1 (= BC 1 ) transgenic plants were weak competitors when cocultivated with wild type segregants under greenhouse conditions and without using the herbicide. The competition was most intense at close spacings typical of weed offspring. Most dwarf plants interspersed with wild type died at 1-cm, > 70% at 2.5-cm and 45% at 5-cm spacing, and the dwarf survivors formed no flowers. At 10-cm spacing, where few TM plants died, only those TM plants growing at the periphery of the large cultivation containers formed flowers, after the wild type plants terminated growth. The highest reproductive TM fitness relative to the wild type was 17%. The results demonstrate the suppression of crop eed hybrids when competing with wild type weeds, or such crops as volunteer weeds, in seasons when the selector (herbicide) is not used. The linked unfitness would be continuously manifested in future generations, keeping the transgene at a low frequency.

主粮转基因技术产业化选择的前提和基础是粮食供求短缺程度。基于一般均衡的经济学框架分析我国粮食供求关系的变化趋势可得出以下结论：（1）人均食品消费量、动物性食品消费占比与收入水平间呈倒U关系;（2）在结论（1）和人口总量增长的作用下,我国粮食需求压力集中在今后16年,2030年后自然缓解;（3）我国的耕地保护政策和制度创新能够保证粮食供给,满足未来粮食需求的增长;（4）净进口将因主粮转基因技术产业化而上升;（5）我国没有推进主粮转基因技术产业化的紧迫性和必要性。建议在今后16年,我国应守住耕地红线、转变农业生产方式和提高粮食利用效率、节约粮食消费,实现粮食供求关系平稳过渡。

近年来,转基因技术在作物育种中应用已取得显著成效,并产生巨大的商业价值。综述了转基因技术在作物改良方面的显著成绩,分析了这一领域的研究现状和新进展,展望了转基因技术研究和应用的未来,以期为推进我国农业生物技术发展与转基因作物商业化提供指导。

基因组编辑技术为农作物遗传改良提供了革命性的遗传操作工具,欧美等国对技术的安全管理采取不同的思路.本文基于对基因组编辑技术发展脉络的全面梳理,深入剖析欧美等国对基因组编辑生物的安全管理策略及核心思路,识别基因组编辑技术与转基因生物安全管理政策的异同,为中国基因编辑组技术安全管理政策的制定提供思路借鉴.