转Bt基因水稻对土壤微生态系统的潜在影响

随着转基因作物商品化应用的增多,对其进行生态风险性评价尤为重要.国内外对转基因作物中外源基因向野生亲缘物种漂移的可能性、昆虫对抗虫转基因作物的耐受性以及转基因作物对生物多样性的潜在影响等问题进行了广泛的研究.文中从Bt杀虫结晶蛋白在土壤中的残留特性、Bt杀虫晶体蛋白对土壤微生物可培养类群和土壤酶活性的影响等方面对转Bt基因抗虫水稻的潜在生态风险性进行了简要综述,以期为同类研究提供有益的信息.     

转转基因植物对根际土壤生态系统的影响

随着全世界转基因植物种植的普及,转基因植物对生态环境的影响也受到人们的广泛关注。本文针对转基因植物对土壤生态系统带来的潜在风险做了较全面的探讨,概述了转基因植物在土壤中的残留、外源基因的水平转移及其表达产物对土壤生物、土壤理化性质的影响,为今后更安全利用转基因植物提供借鉴。     

转基因植物外源基因逃逸的途径

随着转基因植物商品化进程的加快,对其进行生态风险性评价也日益引起许多学者和科学家的重视。人们对转基因逃逸到其它亲缘物种中能否产生超级杂草、昆虫是否会产生耐受性及转基因植物对生物多样性的影响等问题进行了广泛的研究。本文对转基因植物中外源基因逃逸的几种主要途径作了综述,并对研究方法与手段进行了简要讨论,希望能为有关决策和科研部门提供一些思路。     

植物遗传转化表达载体研究进展

植物遗传转化表达载体是植物转基因研究中非常重要的一个环节,外源基因在转基因植物中的高效表达是转基因研究成功的关键。综述了植物遗传转化表达载体近年来的研究进展情况,着重介绍了在转基因植物中实现外源基因高效表达的多种途径和策略,旨在提高转基因植物中外源基因的表达水平和生物安全性,并展望了今后植物转基因研究及商业化发展方向。     

转基因植物外源基因逃逸的途径

随着转基因植物商品化进程的加快,对其进行生态风险性评价也日益引起许多学者和科学家的重视,人们对转基因逃逸到其它亲缘物种中能否产生超级杂草,昆虫是否会产生耐受性及转基因植物对生物多样性的影响等问题进行了广泛的研究,本文对转基因植物外中源基因逃逸的几种主要途径作了综述,并对研究方法与手段进行了简要讨论,希望能为有关决策和科研部门提供一些思路。     

转基因植物中T-DNA整合的分子特征及表达

植物中不同转基因方法转化外源基因的T-DNA整合特征既具有共性,又具有特性,使得转基因的遗传在各独立转化体间呈现多样性,另外多种遗传因子和限制因素使受体植物中外源基因的表达存在下降,甚至出现基因沉默等复杂现象。本文主要对农杆菌介导及裸露DNA直接转化转基因植物中T-DNA的分子特征和转基因表达的影响因子进行了介绍和概述。转化体中转基因的遗传稳定性和表达主要取决于转基因在植物基因组中的整合位置、拷贝数及组成结构。因而,通过对具有表达水平各异的转化体进行深入的遗传分析和分子生物学研究以及转化体之间进行的比较研究,将对转基因技术自身的完善、定点整合以及更有效的利用转基因技术都具有十分重要的意义。     

转Bt基因植物中外源基因时空动态表达的研究现状

在转Bt基因植株中 ,外源基因的时空动态表达对于害虫的防治和转基因安全评价管理具有重要意义。利用生物测定法和酶联免疫吸附测定法 (ELISA) ,对植物不同组织在同一发育阶段、同一组织在不同的发育阶段以及不同转基因植株的外源基因的时空动态表达进行研究。本文综述了转基因植物中外源基因时空动态表达的研究进展和现状。     

外源基因在转基因植物中的表达与稳定性

外源基因能否在转基因植物中稳定表达对转基因植物的应用前景有重要的影响。影响外源基因稳定表达的因素有多种,其中包括遗传和环境因素。在某些转基因植物中,外源基因表达是受发育调控,本文主要讨论了转基因沉默及发育时期和环境条件对源基因的表达及稳定性的影响,并进一步探讨了对策。     

转基因植物对农业生物多样性的影响

论述了近年来转基因植物对农业生态系统生物多样性影响的研究进展．主要在遗传多样性、物种多样性和生态系统多样性3个层次上予以评述．包括转基因植物对作物遗传多样性的影响;转基因植物的外源基因向杂草和近缘野生种转移;转基因抗虫植物对目标害虫的影响。抗除草剂转基因植物对作物和杂草的影响,抗病毒转基因植物对病毒的影响;转基因植物对非目标生物的影响,对土壤生态系统的影响等．     

水稻转基因技术的现状及在育种上的应用

近十几年来,随着分子生物学的飞速发展,人类对植物基因的结构、功能和表达有了较为清晰的了解,分子生物学对作物育种的促进作用越来越明显。与植物基因组的研究、ＲＦＬＰ和ＰＣＲ等辅助选择手段相比较,转基因技术以其把外源基因主动导入、定向改造植物的优点日益为世人所瞩目转基因技术使基因可以在植物、动物、微生物之间相互转移,克服了物种间的隔离,已成为一种新的育种手段。     

受体介导的鳞翅目昆虫对Bt毒素抗性机制进展

苏云金芽孢杆菌作为一种对人畜安全、环境友好型绿色杀虫剂在全球被广泛使用。Bt毒素与昆虫中肠上特定毒素受体结合并发挥作用,形成毒素穿孔导致昆虫死亡是其重要的杀虫机制之一,靶标害虫对Bt毒素产生抗性是制约转Bt作物长期有效种植和Bt毒素持续使用的重要因素。文中从鳞翅目昆虫中肠细胞Bt毒素重要受体的研究阐述昆虫对Bt的抗性机制,为Bt抗性机制的深入研究和对害虫的防控与治理提供了一定的理论参考。     

Using seed purity data to estimate an average pollen mediated gene flow from crops to wild relatives

Gene flow from crops to wild related species has been recently under focus in risk-assessment studies of the ecological consequences of growing transgenic crops. However, experimental studies addressing this question are usually temporally or spatially limited. Indirect population-structure approaches can provide more global estimates of gene flow, but their assumptions appear inappropriate in an agricultural context. In an attempt to help the committees providing advice on the release of transgenic crops, we present a new method to estimate the quantity of genes migrating from crops to populations of related wild plants by way of pollen dispersal. This method provides an average estimate at a landscape level. Its originality is based on the measure of the inverse gene flow, i.e. gene flow from the wild plants to the crop. Such gene flow results in an observed level of impurities from wild plants in crop seeds. This level of impurity is usually known by the seed producers and, in any case, its measure is easier than a direct screen of wild populations because crop seeds are abundant and their genetic profile is known. By assuming that wild and cultivated plants have a similar individual pollen dispersal function, we infer the level of pollen-mediated gene flow from a crop to the surrounding wild populations from this observed level of impurity. We present an example for sugar beet data. Results suggest that under conditions of seed production in France (isolation distance of 1,000 m) wild beets produce high numbers of seeds fathered by cultivated plants. Received: 5 February 2001 / Accepted: 26 March 2001     

Structure of Cry2Aa suggests an unexpected receptor binding epitope

BACKGROUND: Genetically modified (GM) crops that express insecticidal protein toxins are an integral part of modern agriculture. Proteins produced by Bacillus thuringiensis (Bt) during sporulation mediate the pathogenicity of Bt toward a spectrum of insect larvae whose breadth depends upon the Bt strain. These transmembrane channel-forming toxins are stored in Bt as crystalline inclusions called Cry proteins. These proteins are the active agents used in the majority of biorational pesticides and insect-resistant transgenic crops. Though Bt toxins are promising as a crop protection alternative and are ecologically friendlier than synthetic organic pesticides, resistance to Bt toxins by insects is recognized as a potential limitation to their application. RESULTS: We have determined the 2.2 A crystal structure of the Cry2Aa protoxin by multiple isomorphous replacement. This is the first crystal structure of a Cry toxin specific to Diptera (mosquitoes and flies) and the first structure of a Cry toxin with high activity against larvae from two insect orders, Lepidoptera (moths and butterflies) and Diptera. Cry2Aa also provides the first structure of the proregion of a Cry toxin that is cleaved to generate the membrane-active toxin in the larval gut. CONCLUSIONS: The crystal structure of Cry2Aa reported here, together with chimeric-scanning and domain-swapping mutagenesis, defines the putative receptor binding epitope on the toxin and so may allow for alteration of specificity to combat resistance or to minimize collateral effects on nontarget species. The putative receptor binding epitope of Cry2Aa identified in this study differs from that inferred from previous structural studies of other Cry toxins.     

Molecular strategies for gene containment in transgenic crops

The potential of genetically modified (GM) crops to transfer foreign genes through pollen to related plant species has been cited as an environmental concern. Until more is known concerning the environmental impact of novel genes on indigenous crops and weeds, practical and regulatory considerations will likely require the adoption of gene-containment approaches for future generations of GM crops. Most molecular approaches with potential for controlling gene flow among crops and weeds have thus far focused on maternal inheritance, male sterility, and seed sterility. Several other containment strategies may also prove useful in restricting gene flow, including apomixis (vegetative propagation and asexual seed formation), cleistogamy (self-fertilization without opening of the flower), genome incompatibility, chemical induction/deletion of transgenes, fruit-specific excision of transgenes, and transgenic mitigation (transgenes that compromise fitness in the hybrid). As yet, however, no strategy has proved broadly applicable to all crop species, and a combination of approaches may prove most effective for engineering the next generation of GM crops.     

Insect resistance to Bt crops: evidence versus theory

Evolution of insect resistance threatens the continued success of transgenic crops producing Bacillus thuringiensis (Bt) toxins that kill pests. The approach used most widely to delay insect resistance to Bt crops is the refuge strategy, which requires refuges of host plants without Bt toxins near Bt crops to promote survival of susceptible pests. However, large-scale tests of the refuge strategy have been problematic. Analysis of more than a decade of global monitoring data reveals that the frequency of resistance alleles has increased substantially in some field populations of Helicoverpa zea, but not in five other major pests in Australia, China, Spain and the United States. The resistance of H. zea to Bt toxin Cry1Ac in transgenic cotton has not caused widespread crop failures, in part because other tactics augment control of this pest. The field outcomes documented with monitoring data are consistent with the theory underlying the refuge strategy, suggesting that refuges have helped to delay resistance.     

Bacillus thuringiensis: a biotechnology model

This paper is on the different biotechnological approaches that have been used to improve Bacillus thuringiensis (Bt) for the control of agricultural insect pests and have contributed to the successful use of this biological control agent; it describes how a better knowledge of the high diversity of Bt strains and toxins genes together with the development of efficient host-vector systems has made it possible to overcome a number of the problems associated with Bt based insect control measures. First we present an overview of the biology of Bt and of the mode of action of its insecticidal toxins. We then describe some of the progress that has been made in furthering our knowledge of the genetics of Bt and of its insecticidal toxin genes and in the understanding of their regulation. The paper then deals with the use of recombinant DNA technology to develop new Bt strains for more effective pest control or to introduce the genes encoding partial-endotoxins directly into plants to produce insect-resistant trangenic plants. Several examples describing how biotechnology has been used to increase the production of insecticidal proteins in Bt or their persistence in the field by protecting them against UV degradation are presented and discussed. Finally, based on our knowledge of the mechanism of transposition of the Bt transposon Tn4430, we describe the construction of a new generation of recombinant strains of Bt, from which antibiotic resistance genes and other non-Bt DNA sequences were selectively eliminated, using a new generation of site-specific recombination vectors. In the future, continuing improvement of first generation products and research into new sources of resistance is essential to ensure the long-term control of insect pests. Chimeric toxins could also be produced so as to increase toxin activity or direct resistance towards a particular type of insect. The search for new insecticidal toxins, in Bt or other microorganisms, may also provide new weapons for the fight against insect damage.     

Insect resistance to Bacillus thuringiensis: uniform or diverse

Resistance to the insecticidal proteins produced by the soil bacterium Bacillus thuringiensis (Bt) has been documented in more than a dozen species of insect. Nearly all of these cases have been produced primarily by selection in the laboratory, but one pest, the diamondback moth (Plutella xylostella), has evolved resistance in open-field populations. Insect resistance to Bt has immediate and widespread significance because of increasing reliance on Bt toxins in genetically engineered crops and conventional sprays. Furthermore, intense interest in Bt provides an opportunity to examine the extent to which evolutionary pathways to resistance vary among and within species of insect. One mode of resistance to Bt is characterized by more than 500-fold resistance to at least one Cry1A toxin, recessive inheritance, little or no cross-resistance to Cry1C, and reduced binding of at least one Cry1A toxin. Analysis of resistance to Bt in the diamondback moth and two other species of moth suggests that although this particular mode of resistance may be the most common, it is not the only means by which insects can attain resistance to Bt.     

Capturing the interaction types of two Bt toxins Cry1Ac and Cry2Ab on suppressing the cotton bollworm by using multi‐exponential equations

Transgenic crops are increasingly promoted for their practical effects on suppressing certain insect pests, but all transgenic crops are not equally successful. The insect pests can easily develop resistance against single Bacillus thuringiensis (Bt) toxin transgenic crops. Therefore, transgenic crops including two or more mixed Bt‐toxins can solve this problem by delaying the resistance development and killing the majority of targeted pests before the evolution of resistance. It is important to test the controlling effects of transgenic crops including multiple mixed toxins on a particular insect pest. Previous research has checked the cross‐resistance and interactions between Bt toxins Cry1Ac and Cry2Ab against one susceptible and four resistant strains of cotton bollworm. The results showed that independence was the main interaction type between two toxins for the susceptible strain, whereas synergism was the main interaction type for any one resistant strain. However, the optimal combinations of two toxins were not obtained. In the present study, we developed two multi‐exponential equations (namely bi‐ and tri‐exponential equations) to describe the combination effects of two Bt toxins. Importantly, the equations can provide predictions of combination effects of different continuous concentrations of two toxins. We compared these two multi‐exponential equations with the generalized linear model (GLM) in describing the combination effects, and found that the bi‐ and tri‐exponential equations are better than GLM. Moreover, the bi‐exponential equation can also provide the optimal dose combinations for two toxins.