转基因小麦外源基因向近缘野生植物漂移的风险评估-以转TaDREB4小麦为例

国际上转基因作物种植面积不断增加,外源基因漂移的生态风险越来越受到人们的关注。花粉传播的方式是小麦与其近缘野生植物间发生基因漂移的主要途径。调查发现,我国小麦与近缘野生植物空间分布重叠,黄淮海麦区一些近缘野生植物与小麦花期相遇。采集这些近缘野生植物的种子并通过人工杂交获得其与转基因小麦的杂交后代,人工杂交成功率为2.18%～68.61%。但由于出苗率低(0～2.86%)或花粉败育等原因,杂交种无法自然繁殖。通过用小麦或小麦近缘野生植物亲本进行回交,结果发现,只有小亚山羊草×小麦的杂交种与转基因小麦回交成功,回交成功率为0.24%。这些杂交后代种子种植于田间后全部死亡。完全自然状态下,连续监测5年,在近缘野生植物中也没有检测到任何基因漂移事件的发生。说明转基因小麦外源基因向近缘野生植物漂移的风险极低。     

转基因栽培稻基因漂移是否会带来环境生物安全影响?

转基因通过基因漂移可以渐渗到作物的野生近缘种,由此而导致的环境风险是全球广泛关注的生物安全问题.有3个关键因素可以决定环境风险的程度:特定空间距离的转基因漂移频率,转基因在野生近缘种中的表达水平,以及转基因为野生近缘种群体带来的适合度效应.本文将根据现有研究结果,从上述3方面对转基因漂移到非转基因栽培稻、杂草稻和野生稻造成的潜在环境影响进行回顾.栽培稻品种之间的基因漂移频率很低,可以通过空间隔离或其他方法使其降低到可忽略的水平.在共同分布的环境中,栽培稻基因(包括转基因)向杂草稻和野生稻的漂移不可避免.尽管抗虫转基因(Bt或Bt/CpTI)在栽培稻和野生近缘种杂交后代中可以正常表达,但由于在低虫压环境中,抗虫转基因不会明显改变野生近缘种的适合度,抗虫转基因漂移所造成的环境影响十分有限.因此对基因漂移而言,抗虫转基因栽培稻的商品化种植应该比较安全.然而,抗除草剂转基因渐渗到杂草稻或野生稻会改变群体的适合度,可能会引起不可预测的环境后果.     

防止转基因作物释放引发“超级杂草”产生的若干对策

转基因作物释放可能导致潜在的生态风险性,其中的一个重要方面是通过花粉的传播将某些转基因（主要是抗除草剂基因）漂入野生近缘种或近缘杂草而引发难以控制的“超级杂草”的产生。本文讨论了防止“超级杂草”产生的若干对策,包括物理隔离、转基因遗传调控、雄性不育性与无融合生殖机制的利用、将转基因定位于同当地杂草不亲和的基因组和叶绿体或线粒体基因组等。     

Part．2转基因育种技术

植物转基因育种是利用遗传工程的手段，有目的地将外源基因或DNA构建导入植物基因组，通过外源基因的直接表达，或通过对内源基因表达的调控，使植物获新性状的一种品种改良技术。应用转基因育种技术能提高作物产量、改善作物营养品质、增加抗逆能力。[编者按]     

防止转基因作物释放引发“超级杂草”产生的若干对策

转基因作物释放可能导致潜在的生态风险性,其中的一个重要方面是通过花粉的传播将某些转基因(主要是抗除草剂基因)漂入野生近缘种或近缘杂草而引发难以控制的“超级杂草”的产生。本文讨论了防止“超级杂草”产生的若干对策,包括物理隔离、转基因遗传调控、雄性不育性与无融合生殖机制的利用、将转基因定位于同当地杂草不亲和的基因组和叶绿体或线粒体基因组等。     

TA29-barnase基因转化菜心

利用根癌农杆菌导入法, 以菜心带柄子叶为外植体, 对TA29-barnase基因转化菜心进行研究。获得转化植株,进行PCR、Southern blotting杂交和半定量RT-PCR检测, 表明目的基因已经整合到转化植株中, 并且目的基因在转基因植株花蕾中得到表达, 但是表达水平在不同转基因植株间存在差别; 转基因植株开花后, 均表现雄性不育, 不能产生花粉或产生没有活力的少量花粉, 自交不能结实; 用未转化植株正常花粉对雄性不育植株进行授粉, 能够正常结实; 保持系(未转化植株)与不育株杂交后代中雄性不育株与可育株的比例为1:1, 在杂交后代植株子叶期, 喷洒10 mg/L的PPT可以完全杀死可育株; 利用其他菜心品种为父本与不育株进行杂交, 获得的F1植株在生长势和产量方面表现优势, 表明开展菜心优势育种具有一定的潜力。     

TA29-barnase基因转化菜心

利用根癌农杆菌导入法, 以菜心带柄子叶为外植体, 对TA29-barnase基因转化菜心进行研究。获得转化植株,进行PCR、Southern blotting杂交和半定量RT-PCR检测, 表明目的基因已经整合到转化植株中, 并且目的基因在转基因植株花蕾中得到表达, 但是表达水平在不同转基因植株间存在差别; 转基因植株开花后, 均表现雄性不育, 不能产生花粉或产生没有活力的少量花粉, 自交不能结实; 用未转化植株正常花粉对雄性不育植株进行授粉, 能够正常结实; 保持系(未转化植株)与不育株杂交后代中雄性不育株与可育株的比例为1:1, 在杂交后代植株子叶期, 喷洒10 mg/L的PPT可以完全杀死可育株; 利用其他菜心品种为父本与不育株进行杂交, 获得的F1植株在生长势和产量方面表现优势, 表明开展菜心优势育种具有一定的潜力。     

控制转基因植物中基因逃逸的分子策略

转基因作物释放可能导致潜在的生态风险性,其中一个重要方面是通过花粉传播,将外源基因(如抗除草剂、抗虫基因)转入野生近缘种或近缘杂草而产生难以控制的“超级杂草”。本文讨论了防止外源基因逃逸的几种分子技术手段,主要包括：(1)母系遗传法(又称细胞质遗传法);(2)雄性不育法：(3)种子不育法;(4)染色体组特异性选择法等。     

争议不断的转基因作物

<正>今天,转基因作物正在逐渐而广泛地进入我们的生活。转基因作物的含义是,将人工分离(克隆)和修饰过的基因(外源性基因)导入到作物的基因组中,使导入的基因得到表达,引起作物的性状产生可遗传的修饰。     

转基因油菜的基因流及生态风险

综合评述了转基因油菜的基因流及其生态风险.油菜作为最早的转基因作物之一目前已在加拿大和澳大利亚大面积商业化应用.(常)异花授粉作物油菜的天然异交率可达30%左右,也易与其它芸苔属作物杂交,因此转基因油菜的生态风险已引起各国科学家的高度重视.转基因油菜主要通过与其野生近缘种的花粉交换和与非转基因油菜的花粉交换两种方式进行花粉的输出.基因可能逃逸到相关野生近缘种,但在大田环境下能够得到杂种的可能性很小;由于基因的漂流在油菜田块间确实存在,因此在种植转基因油菜的过程中必须考虑其间隔距离.     

Quantifying the effect of crop spatial arrangement on weed suppression using functional-structural plant modelling

Suppression of weed growth in a crop canopy can be enhanced by improving crop competitiveness. One way to achieve this is by modifying the crop planting pattern. In this study, we addressed the question to what extent a uniform planting pattern increases the ability of a crop to compete with weed plants for light compared to a random and a row planting pattern, and how this ability relates to crop and weed plant density as well as the relative time of emergence of the weed. To this end, we adopted the functional-structural plant modelling approach which allowed us to explicitly include the 3D spatial configuration of the crop-weed canopy and to simulate intra- and interspecific competition between individual plants for light. Based on results of simulated leaf area development, canopy photosynthesis and biomass growth of the crop, we conclude that differences between planting pattern were small, particularly if compared to the effects of relative time of emergence of the weed, weed density and crop density. Nevertheless, analysis of simulated weed biomass demonstrated that a uniform planting of the crop improved the weed-suppression ability of the crop canopy. Differences in weed suppressiveness between planting patterns were largest with weed emergence before crop emergence, when the suppressive effect of the crop was only marginal. With simultaneous emergence a uniform planting pattern was 8 and 15 % more competitive than a row and a random planting pattern, respectively. When weed emergence occurred after crop emergence, differences between crop planting patterns further decreased as crop canopy closure was reached early on regardless of planting pattern. We furthermore conclude that our modelling approach provides promising avenues to further explore crop-weed interactions and aid in the design of crop management strategies that aim at improving crop competitiveness with weeds.     

Agronomic Practices for Improving Gentle Remediation of Trace Element-Contaminated Soils

The last few decades have seen the rise of Gentle soil Remediation Options (GRO), which notably include in situ contaminant stabilization (“inactivation”) and plant-based (generally termed “phytoremediation”) options. For trace element (TE)-contaminated sites, GRO aim to either decrease their labile pool and/or total content in the soil, thereby reducing related pollutant linkages. Much research has been dedicated to the screening and selection of TE-tolerant plant species and genotypes for application in GRO. However, the number of field trials demonstrating successful GRO remains well below the number of studies carried out at a greenhouse level. The move from greenhouse to field conditions requires incorporating agronomical knowledge into the remediation process and the ecological restoration of ecosystem services. This review summarizes agronomic practices against their demonstrated or potential positive effect on GRO performance, including plant selection, soil management practices, crop rotation, short rotation coppice, intercropping/row cropping, planting methods and plant densities, harvest and fertilization management, pest and weed control and irrigation management. Potentially negative effects of GRO, e.g., the introduction of potentially invasive species, are also discussed. Lessons learnt from long-term European field case sites are given for aiding the choice of appropriate management practices and plant species.     

Tandem constructs: preventing the rise of superweeds.

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.     

Recent progression and future perspectives in cotton genomic breeding

Upland cotton is an important global cash crop for its long seed fibers and high edible oil and protein content.Progress in cotton genomics promotes the advancement of cotton genetics,evolutionary studies,functional genetics,and breeding,and has ushered cotton research and breeding into a new era.Here,we summarize high-impact genomics studies for cotton from the last 10 years.The diploid Gossypium arboreum and allotetraploid Gossypium hirsutum are the main focus of most genetic and genomic studi...     

Artificial trans-acting small interfering RNA: a tool for plant biology study and crop improvements

Completion of whole genome sequencing in many plant species including economically important crop species not only opens up new opportunities but also imposes challenges for plant science research community. Functional validation and utilization of these enormous DNA sequences necessitate new or improved tools with high accuracy and efficiency. Of various tools, small RNA-mediated gene silencing platform plays an important and unique role in functional verification of plant genes and trait improvements. Artificial trans-acting small interfering RNA (atasiRNA) has emerged as a potent and specific gene silencing platform which overcomes major limitations of other small RNA silencing approaches including double-stranded RNA, artificial microRNA (amiRNA), and microRNA-induced gene silencing. To best utilize atasiRNA platform, it is essential to be able to test candidate atasiRNAs efficiently through either in vivo or in vitro validation approach. Very recently, a breakthrough has been made in developing a new method for in vitro screen of amiRNA candidates, named “epitope-tagged protein-based amiRNA screens”. Such a screen can be readily employed to validate atasiRNA candidates and thus accelerate the deployment of atasiRNA technology. Therefore, atasiRNA as an emerging tool shall accelerate both plant biology study and crop genetic improvements including trait stacking.     

Weed and Crop Allelopathy

Allelopathy can be defined as an important mechanism of plant interference mediated by the addition of plant-produced secondary products to the soil rhizosphere. Allelochemicals are present in all types of plants and tissues and are released into the soil rhizosphere by a variety of mechanisms, including decomposition of residues, volatilization, and root exudation. Allelochemical structures and modes of action are diverse and may offer potential for the development of future herbicides. We have focused our review on a variety of weed and crop species that establish some form of potent allelopathic interference, either with other crops or weeds, in agricultural settings, in the managed landscape, or in naturalized settings. Recent research suggests that allelopathic properties can render one species more invasive to native species and thus potentially detrimental to both agricultural and naturalized settings. In contrast, allelopathic crops offer strong potential for the development of cultivars that are more highly weed suppressive in managed settings. Both environmental and genotypic effects impact allelochemical production and release over time. A new challenge that exists for future plant scientists is to generate additional information on allelochemical mechanisms of release, selectivity and persistence, mode of action, and genetic regulation. In this manner, we can further protect plant biodiversity and enhance weed management strategies in a variety of ecosystems. Referee: Dr. Steve Weller, Purdue University, Dept. of Horticulture, West Lafayette, IN 47907     

Dynamics of Weeds in the Soil Seed Bank: A Hidden Markov Model to Estimate Life History Traits from Standing Plant Time Series

Predicting the population dynamics of annual plants is a challenge due to their hidden seed banks in the field. However, such predictions are highly valuable for determining management strategies, specifically in agricultural landscapes. In agroecosystems, most weed seeds survive during unfavourable seasons and persist for several years in the seed bank. This causes difficulties in making accurate predictions of weed population dynamics and life history traits (LHT). Consequently, it is very difficult to identify management strategies that limit both weed populations and species diversity. In this article, we present a method of assessing weed population dynamics from both standing plant time series data and an unknown seed bank. We use a Hidden Markov Model (HMM) to obtain estimates of over 3,080 botanical records for three major LHT: seed survival in the soil, plant establishment (including post-emergence mortality), and seed production of 18 common weed species. Maximum likelihood and Bayesian approaches were complementarily used to estimate LHT values. The results showed that the LHT provided by the HMM enabled fairly accurate estimates of weed populations in different crops. There was a positive correlation between estimated germination rates and an index of the specialisation to the crop type (IndVal). The relationships between estimated LHTs and that between the estimated LHTs and the ecological characteristics of weeds provided insights into weed strategies. For example, a common strategy to cope with agricultural practices in several weeds was to produce less seeds and increase germination rates. This knowledge, especially of LHT for each type of crop, should provide valuable information for developing sustainable weed management strategies.     

Functional molecular markers for crop improvement

A tremendous decline in cultivable land and resources and a huge increase in food demand calls for immediate attention to crop improvement. Though molecular plant breeding serves as a viable solution and is considered as “foundation for twenty-first century crop improvement”, a major stumbling block for crop improvement is the availability of a limited functional gene pool for cereal crops. Advancement in the next generation sequencing (NGS) technologies integrated with tools like metabolomics, proteomics and association mapping studies have facilitated the identification of candidate genes, their allelic variants and opened new avenues to accelerate crop improvement through development and use of functional molecular markers (FMMs). The FMMs are developed from the sequence polymorphisms present within functional gene(s) which are associated with phenotypic trait variations. Since FMMs obviate the problems associated with random DNA markers, these are considered as “the holy grail” of plant breeders who employ targeted marker assisted selections (MAS) for crop improvement. This review article attempts to consider the current resources and novel methods such as metabolomics, proteomics and association studies for the identification of candidate genes and their validation through virus-induced gene silencing (VIGS) for the development of FMMs. A number of examples where the FMMs have been developed and used for the improvement of cereal crops for agronomic, food quality, disease resistance and abiotic stress tolerance traits have been considered.     

Effect of fertilization patterns on the assemblage of weed communities in an upland winter wheat field

Aims Understanding the response of farmland weed community assembly to fertilization is important for designing better nutrient management strategies in integrated farmland ecological systems. Many studies have focused on weed characteristics, mainly crop–weed competition responses to fertilization or weed communities alone. However, weed community assembly in association with crop growth is poorly understood in the agroecosystems, but is important for the determination of integrated weed management. Biodiversity promotes ecosystem productivity in the grassland, but whether it applies to the agroecosystems is unclear. Based on an 11-year field experiment, the cumulative effects of different fertilization patterns on the floristic composition and species diversity of farmland weed communities along with wheat growth in a winter wheat–soybean rotation were investigated.Methods The field trial included five fertilization patterns with different combinations of N, P and K fertilizers. Species composition and diversity of weed communities, aboveground plant biomass and nutrient accumulation of weeds and winter wheat, light penetration to the ground surface and wheat yield were measured at each plot in 2009 and 2010. Multivariate analysis, regression and analysis of variance were used to analyze the responses of these parameters to the different fertilization treatments.Important findings Four dominant weeds (Galium aparine L., Veronica persica Poir., Vicia sativa L. and Geranium carolinianum L.) accounted for ~90% of the total weed density in the 2 years of experimental duration. The residual weed community assembly was influenced primarily by topsoil available nutrients in the order P> N> K. Competition for nutrients and solar radiation between crops and weeds was the main indirect effect of fertilization on the changes in weed community composition and species diversity. The indices of species diversity (species richness, Shannon–Wiener, Pielou and Simpson indices) showed significant linear relationships with wheat yield. The balanced fertilization treatment was more efficient at inhibiting the potential growth of weeds because of solar radiation being intercepted by wheat. These results support the conclusion that wheat yield is favored by balanced fertilization, whereas the weed community is favored by PK fertilization in terms of density and diversity. However, the negative effects on wheat yield may be compromised by simultaneous positive effects of weed communities in the fertilization treatments, for instance, the NP and NK treatments, which are intermediate in terms of increasing wheat production and to a level maintaining a diverse community.