Identification of the bile salt binding site on IpaD from Shigella flexneri and the influence of ligand binding on IpaD structure

Type III secretion (TTS) is an essential virulence factor for Shigella flexneri, the causative agent of shigellosis. The Shigella TTS apparatus (TTSA) is an elegant nanomachine that is composed of a basal body, an external needle to deliver effectors into human cells, and a needle tip complex that controls secretion activation. IpaD is at the tip of the nascent TTSA needle where it controls the first step of TTS activation. The bile salt deoxycholate (DOC) binds to IpaD to induce recruitment of the translocator protein IpaB into the maturing tip complex. We recently used spectroscopic analyses to show that IpaD undergoes a structural rearrangement that accompanies binding to DOC. Here, we report a crystal structure of IpaD with DOC bound and test the importance of the residues that make up the DOC binding pocket on IpaD function. IpaD binds DOC at the interface between helices α3 and α7, with concomitant movement in the orientation of helix α7 relative to its position in unbound IpaD. When the IpaD residues involved in DOC binding are mutated, some are found to lead to altered invasion and secretion phenotypes. These findings suggest that adoption of a DOC bound structural state for IpaD primes the Shigella TTSA for contact with host cells. The data presented here and in the studies leading up to this work provide the foundation for developing a model of the first step in Shigella TTS activation.     

基于分子生物学方法的外来入侵物种入侵历史重构

生物入侵是一个世界性的问题。全球每年因生物入侵造成的损失超过1万亿美元。探究入侵物种在入侵地的入侵历史对了解生物入侵的生物生态学机制、制定阻截及防除措施有重要意义。分子标记方法的兴起和大规模应用打开了入侵生物入侵历史研究的新天地。采用分子标记的方法可鉴定入侵物种的种类、追溯其来源地、回溯其扩散路径、分析扩散模式及探究物种入侵过程中对入侵种群本身的变化及其对生态系统所造成的各种影响。分子标记的应用使得多个入侵物种的入侵历史得以重现。由于分子标记方法重构的入侵历史受采样范围、采用的分子标记的种类及数量等因素的影响,该方法呈现入侵历史是否是真实发生的入侵过程还存在争议。     

Unravelling the global invasion routes of a worldwide invader,the red swamp crayfish (Procambarus clarkii)

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Nodule development on the tropical legume Sesbania virgata under flooded and non‐flooded conditions

The interaction between the Brazilian pioneer legume Sesbania virgata and its microsymbiont Azorhizobium doebereinerae leads to the formation of nitrogen‐fixing nodules on roots that grow either in well‐aerated soils or in wetlands. We studied the initiation and development of nodules under these alternative conditions. To this end, light and fluorescence microscopy were used to follow the bacterial colonisation and invasion into the host and, by means of transmission electron microscopy, we could observe the intracellular entry. Under hydroponic conditions, intercellular invasion took place at lateral root bases and mature nodules were round and determinate. However, on roots grown in vermiculite that allows aerated growth, bacteria also entered via root hair invasion and nodules were both of the determinate and indeterminate type. Such versatility in entry and developmental plasticity, as previously described in Sesbania rostrata, enables efficient nodulation in both dry and wet environments and are an important adaptive feature of this group of semi‐tropical plants that grow in temporarily flooded habitats.     

Complementarity of statistical treatments to reconstruct worldwide routes of invasion: the case of the Asian ladybird Harmonia axyridis

Inferences about introduction histories of invasive species remain challenging because of the stochastic demographic processes involved. Approximate Bayesian computation (ABC) can help to overcome these problems, but such method requires a prior understanding of population structure over the study area, necessitating the use of alternative methods and an intense sampling design. In this study, we made inferences about the worldwide invasion history of the ladybird Harmonia axyridis by various population genetics statistical methods, using a large set of sampling sites distributed over most of the species’ native and invaded areas. We evaluated the complementarity of the statistical methods and the consequences of using different sets of site samples for ABC inferences. We found that the H. axyridis invasion has involved two bridgehead invasive populations in North America, which have served as the source populations for at least six independent introductions into other continents. We also identified several situations of genetic admixture between differentiated sources. Our results highlight the importance of coupling ABC methods with more traditional statistical approaches. We found that the choice of site samples could affect the conclusions of ABC analyses comparing possible scenarios. Approaches involving independent ABC analyses on several sample sets constitute a sensible solution, complementary to standard quality controls based on the analysis of pseudo‐observed data sets, to minimize erroneous conclusions. This study provides biologists without expertise in this area with detailed methodological and conceptual guidelines for making inferences about invasion routes when dealing with a large number of sampling sites and complex population genetic structures.     

Festuca campestris density and defoliation regulate abundance of the rhizomatous grass Poa pratensis in a fallow field

Invasion by the rhizomatous grass Kentucky bluegrass (Poa pratensis) is a global phenomenon, including into foothills rough fescue (Festuca campestris) grasslands of southwestern Alberta, Canada. In order to better understand the competitive relationships between these species, we conducted a fallow field study where rough fescue bunchgrass tussocks were transplanted at one of three planting densities (15, 30, or 45 cm spacing), and then subject to various treatments in a factorial design, including one‐time intensive summer defoliation and seeding of bluegrass into adjacent bare soil. Rough fescue plants exhibited marked intraspecific competition, as high planting densities increased tussock mortality, while decreasing plant tiller counts and relative inflorescence production, together with plant and tiller‐specific mass. However, high densities of the bunchgrass also reduced the cover and biomass of encroaching bluegrass, coincidental with reduced resource (soil moisture and light) availability in mid‐summer. Although summer defoliation increased rough fescue tiller counts, this disturbance reduced plant and tiller mass, and also increased Kentucky bluegrass. We conclude that while high densities of nondefoliated stands of rough fescue may increase resistance to bluegrass encroachment, a reduction in either fescue plant density or vigor via defoliation can increase the risk of bluegrass invasion within northern temperate grassland.     

分子标记技术在昆虫入侵研究中的应用

遗传变异与种群持续性及其进化潜力密切相关,而生物入侵导致种群遗传变异或遗传多样性的改变为研究自然界中各种生态和进化问题提供了理想模式。分子标记技术是调查种群遗传变异的重要工具,揭示了入侵种的入侵过程和结果,并预测未来的发生情况。本综述归纳了分子标记技术在昆虫入侵机制研究中的应用,以典型的研究个案为例,分别综述了分子标记技术在隐蔽入侵的监测应用,分子标记技术在重构入侵历史研究中的推算方式,分子标记技术在探索种群遗传变异与成功入侵机制方面取得的重要进展,并进一步介绍了高分辨率熔解曲线（high-resolution melting, HRM）分析在昆虫入侵研究中的应用前景。     

中国外来入侵物种的分布与传入路径分析

外来物种入侵已成为全球性的环境问题,本文采用文献调研,实地考察与专家咨询相结合的方式,调查了全国陆生,淡水水生生态系统中外来入侵微生物,无脊椎动物,两栖爬行类,鱼类,鸟类,哺乳类,杂草,树木和海洋生态系统中外来入侵物种的种类及分类地位,起源,引入路径和环境影响等内容。查明我国共有283种外来入侵物种,其中外来入侵微生物,水生植物,陆生植物,水生无脊椎动物,陆生无脊椎动物,两栖爬行类,鱼类,哺乳类分别为19种,18种,170种,25种,33种,3种,10种和5种,来源于美洲,欧洲,亚洲,非洲,大洋洲的外来入侵物种分别占55.1%,21.7%,9.9%.8.1%和0.6%。我国对外来物种的引进存在一定程度的盲目性;50.%的外来入侵植物是作为牧草或饲料,观赏植物,纤维植物,药用植物,蔬菜,草坪模特而引进的;25%的外来入侵动物是用于养殖,观赏,生物防治的引种,对外来物种只重引进,疏于管理,也可能导致外来物种逃逸到自然环境中,造成潜在的环境意传入的;76.3%的外来入侵动物是由于检查不严,随贸易物品或运输工具传入我国的。因此,我国既要加强检疫工作,又要对外来物种的有意引进进行严格管理,实行外来物种引进的风险评估制度。     

生物入侵机制研究进展

本文从外来种本身的生物学特性,外来种与新栖息地土著种之间的相互作用,群落生物多样性对入侵种的抵抗能力,新栖息地生态环境变化对入侵种的影响等方面综述了近年来有关生物入侵机制的研究进展,并探讨了研究方法的发展和亟待解决的问题,大量的研究表明生物入侵机制是极为多样的,可能没有一般的,通用的机制,阐明生物入侵的机制,对推动生态学理论的发展和控制有害外来种有重要意义。     

Antisense Tiam1 Down-Regulates the Invasiveness of 95D Cells in Vitro

Invasion and metastasis are the main death causes oftumor patients, and aberrant expression of some genescontributes to tumor cell invasion and metastasis [1]. Tiam1was firstly identified as a gene amplified by insertedretrovirus which can confer metastat…     

Relative abundance of invasive plants more effectively explains the response of wetland communities to different invasion degrees than phylogenetic evenness

入侵植物的相对多度比群落系统发育均匀度更能解释湿地群落对不同入侵程度的响应 本地植物群落普遍受到入侵植物不同程度的入侵。然而,入侵植物相对多度与群落系统发育均匀度对不同入侵程度下湿地植物群落响应入侵的相对贡献尚不明确。此外,这种贡献是否随淹水等环境 条件的变化而变化也不清楚。为了探讨这些问题,我们选择空心莲子草(Alternanthera philoxeroides)作为入侵植物,通过改变植物群落物种组成,构建了4个不同的入侵程度,并且设置了水淹和无水淹两种处理。 改变群落入侵程度的同时改变了空心莲子草的相对多度和群落的系统发育均匀度。研究结果表明,不同的入侵程度显著影响了空心莲子草和一些本地物种的单株生物量。变异分割结果表明,无论淹水情况结果如何,空心莲子草相对多度对植物群落指标变异的贡献都大于系统发育均匀度。斯皮尔曼等级相关检验结果表明,空心莲子草的相对多度与空心莲子草和部分本地物种的单株生物量显著负相关;群落系统发育均匀度仅与少数本地种性状显著正相关。其相关强度和显著性均受特定的物种和水淹环境的影响。总之,这些研究结果表明：无论淹水情况如何,入侵植物(空心莲子草)的相对多度都比群落的系统发育均匀度更能有效地解释湿地植物群落对不同入侵程度的响应。     

外来种入侵的不确定性动态模拟

外来种的入侵性和生境的可入侵性是研究生物入侵机制的两个关键因素。总结多数学者的研究成果,认为外来种的拓殖率(迁移率或繁殖率)、死亡率及在新生境中的竞争力是衡量外来种能否入侵成功的内在实质。从全新的角度出发,将引入的外来种看作是对原有生态系统的一种干扰,并在此基础上结合Tilman的多物种共存模型提出了外来种干扰模型。模拟发现外来种在入侵时具有明显的不确定性。拓殖率小的外来种在新的生态系统中由于不能适应环境无法成功定殖,被排斥在系统之外;相反,拓殖率足够大的话,外来种由于自身优势具有很强的入侵性,在几年或几十年的时间内就会成功地在新的环境中建立种群并拓殖入侵,影响了当地物种的生存及原有生态系统的稳定。研究还发现,物种入侵也存在一定的不确定性,入侵不一定会一直持续下去,或许在百年或几百年的时间内入侵种会突然灭绝,原生态系统又恢复到原来的水平。     

Biotic resistance limits the invasiveness of the western flower thrips,Frankliniella occidentalis (Thysanoptera: Thripidae), in Florida

The spread of the western flower thrips, Frankliniella occidentalis (Pergande), has resulted in the world‐wide destabilization of established integrated pest management programs for many crops. It is hypothesized that frequent exposure to insecticides in intensive agriculture selected for resistant populations, which allowed invasive populations in the eastern USA to overcome biotic resistance from the native community of species. Research conducted in Florida to understand the role of biotic factors in limiting the abundance of the western flower thrips is reviewed. Orius spp. (Hemiptera: Anthocoridae) are effective predators that suppress populations of thrips on crop and non‐crop hosts in southern and northern Florida. Orius are more effective predators of the western flower thrips than the native flower thrips, F. tritici (Fitch) and F. bispinosa (Morgan). The native species are competitors of the western flower thrips. Excessive fertilization and the use of broad‐spectrum insecticides in crop fields further enhances populations of the western flower thrips. Interactions with native species clearly limit the abundance of western flower thrips in Florida, but populations are abundant in fertilized crop fields where application of insecticides excludes predators and competitor species.     

Vimentin affects the mobility and invasiveness of prostate cancer cells

A significant proportion of prostate cancer patients treated with curative intent go on to develop advanced disease. At a fundamental biological level, very little is known about what makes the disease aggressive and metastatic. Observational pathology reports and experimental data suggest that epithelial-mesenchymal transition is involved in prostate cancer invasiveness. Here, we investigated vimentin expression of prostate cancer cells, and explored the potential mechanism of vimentin promoting prostate cancer cells invasion. Vimentin expression was not detected in well differentiated tumors or in moderately differentiated tumors, but the majority of poorly differentiated cancers (5/11 with negative bone scan, 11/14 bone with positive scan) and bone metastases (8/8) had high vimentin expression in tumor cells. Downregulation of vimentin expression in PC-3 cells by transfection with antisense-vimentin led to a significant decrease in tumor cells motility and invasive activity. Furthermore, the expression of E-cadherin was inversely associated with expression of vimentin. Our results suggest that vimentin affects prostate cancer cells motility and invasiveness.     

近十年植物入侵生态学重要研究进展

外来植物入侵对本地生物多样性、生态安全、社会经济发展和人类健康造成了严重威胁。因此, 探究植物入侵机制及其生态效应对我国生态可持续发展具有重要意义, 也是植物入侵生态学的主要研究内容。过去10年, 生态学家开展了大量研究, 取得了丰硕成果, 为推动入侵植物防控与生物多样性保护提供了理论指导。为深入解析外来植物入侵机制, 为其防控管理提供依据, 本文从以下3个方面综述了植物入侵生态学重要进展: 首先是外来植物生物学特性、生物和非生物环境对植物入侵的调控作用; 其次是外来植物入侵对本地生态系统的影响; 最后介绍了外来植物入侵的类比研究范式——本地植物入侵, 以及多组学技术在入侵生态学研究中的应用。基于这些研究进展, 本文展望了该领域的未来发展趋势, 包括: (1)研究对象从单一物种扩展到多物种比较; (2)研究地理范围从局域尺度扩大到纬度梯度格局; (3)入侵机制从单一理论验证到综合阐释多个假说。     

危险性害虫西花蓟马的传播现状

西花蓟马自20世纪80年代以后从北美洲迅速向外传播扩散,已成为世界范围内温室蔬菜和观赏植物上的一种重要危险性害虫。本文依据国内外的有关资料,分析了该虫在全球范围内的传播情况和扩散原因,并提出在我国控制其传播的对策。     

水盾草入侵机制及防治对策

生物入侵是当今世界难题之一,成为维护生物安全和生态安全的共同挑战。水盾草作为一种流行的观赏水草,原分布于美洲中部,伴随人类商业、运输等活动迁移到世界各地,现已成功入侵了亚洲、欧洲和大洋洲等地区,也在我国长三角地区广泛分布。本文介绍了水盾草的生态习性、危害、入侵成因、防治与管理等方面,从生物学特征和生境分析其入侵机制。由于很强的繁殖扩散能力和对新环境的适应能力等特性,水盾草一旦定居,即迅速生长,争夺本地物种的生存空间和资源,对入侵区域的环境、生物、经济产生负面影响。适宜的气候条件、空生态位资源是水盾草入侵的外部环境因素。目前,多种物理、化学和生物控制方法用于管理水盾草,但治理效果不一,需要综合使用多种手段,重复干预以达到管控的目的。为防止水盾草在我国大面积泛滥,亟需开展基础研究,科学预测;针对可能入侵水域,研究提出早期发现和快速响应的综合管理措施,科学治理和管理水盾草。