T-DNA转移研究进展

植物遗传转化技术近年在农作物性状改良、植物生物反应器利用以及基因功能鉴定等方面得到了广泛的应用.T-DNA转移是植物细胞农杆菌介导遗传转化整合和表达外源基因的基础.农杆菌Ti质粒vir基因编码蛋白、农杆菌一些染色体基因编码蛋白及植物细胞一些基因编码蛋白或因子均参与T-DNA转移.转移过程包括农杆菌对植物细胞的识别、附着,细菌对植物信号物质的感受,细菌vir基因的诱导表达,T复合体的形成,跨膜运输,进核运输和整合等一序列过程.植物细胞因子与农杆菌T-DNA转移相关蛋白的相互作用最近被认为在T-DNA转移过程中起重要作用.     

影响农杆菌介导遗传转化的植物因子研究进展

农杆菌介导法是植物遗传转化中最常用的一种方法.越来越多的研究表明,植物遗传因子是决定农杆菌遗传转化效率的重要因素,它们至少影响了转化过程的如下5个方面:1)受伤植物释放的酚类物质和糖分子等介导农杆菌的趋化运动和毒性基因vir的诱导表达;2)农杆菌吸附到植物表面;3)T-DNA和毒性蛋白通过由VirB和virD4蛋白组成的Ⅳ型分泌系统从细菌转移到植物细胞质;4)T-复合体利用细胞质ACTIN骨架和输入蛋白进行核定位和核输入;5)T-DNA利用植物的修复装置整合进宿主基因组.就以上5个方面涉及的植物因子研究进展予以综述.     

根癌农杆菌介导的大豆遗传转化

农杆菌介导法是大豆遗传转化的重要方法之一 ,许多实验室应用该方法得到了转基因大豆 ,但目前使用该方法进行转化的效率还比较低 ,尚需深入研究。农杆菌菌株、大豆基因型、组织培养条件、T-DNA的转移效率和转化后的筛选模式都会影响大豆转化的效率。概述了近年来根癌农杆菌介导的大豆遗传转化的一些重要成果 ,以及转化过程中大豆的易感性与农杆菌的转化能力、乙酰丁香酮促进vir基因活化、转化的受体系统和巯基混合物减轻受体材料的褐化、提高T DNA的转移效率等几个重要因素的研究进展 ,并介绍了转化中常用的几个筛选标记基因 (nptⅡ、hpt、bar基因和突变的ahas基因 )及通过共转化法去除标记基因的方法 ,同时对今后研究的重点进行了讨论.     

农杆菌介导法在橡胶树遗传转化中的应用与展望

综述农杆菌介导法在巴西橡胶树遗传转化中的应用进展,分析影响农杆菌转化的关键因素,如植物基因型与外植体、菌株与载体类型、菌液浓度与侵染时间、vir诱导物、筛选剂与抑菌剂、培养基的组成和附加成分等,并对提高巴西橡胶树转化效率的策略进行探讨。     

农杆菌介导的粘帚菌遗传转化北大核心CSCD

【目的】建立分离自西藏林芝的能够产生一系列具有抗肿瘤活性的二酮哌嗪类化合物(epipolythiodioxopiperazine,ETP)的一株冬虫夏草定殖真菌——粘帚菌(Gliocladium sp.)6.102的遗传转化体系。【方法】利用农杆菌介导的方式建立了粘帚菌的遗传转化体系;用正交试验研究了影响转化效率的因素,包括共培养所用农杆菌与真菌孢子的比例、共培养的时间、pH值和乙酰丁香酮的浓度。【结果】成功建立了农杆菌介导的粘帚菌的遗传转化体系,得到了转化的最佳条件,其转化效率为50-100个转化子/106真菌孢子。通过农杆菌介导的方式分别将潮霉素B磷酸转移酶基因(hph)和绿色荧光蛋白基因(egfp)转入粘帚菌中,实现了表达并且可以稳定存在。【结论】首次建立了农杆菌介导的粘帚菌遗传转化体系,为研究ETP化合物的生物合成及其调控机制奠定了基础。     

根癌农杆菌对苜蓿的转化及其特性

通过胭脂碱型根癌农杆菌C58和T37菌株通过共培养和离体感染苜蓿下胚轴和子叶,研究表明,外 植体的生理状态对转化的促进作用明显优于酚类化合物As和复合酚类化合物处理。与感受态外植体相比, 当外植体处于非感受态时,即使通过酚类化合物活化农杆菌vir基因,其致瘤率也明显降低。可溶性蛋白质 含量和游离氨基酸含分析表明,T37和C58转化细胞系可溶性蛋白含量相近,但T37转化细胞系游离氨基酸 含量比C58转化细胞系高得多,这与T37和C58转化细胞系生长特性有关。T37菌株的这种特性对于改良 苜蓿品质具有非常重要的现实意义。     

对根癌农杆菌vir区基因具诱导作用的水稻信号分子的分离和确定

以农杆菌vir::lacZ融合基因系统作为检测手段,确定在水稻(Oryza sati-va L.cv.IR72)幼穗分化期至抽穗扬花期的叶片抽提液中含有2种高效诱导农杆菌vir区基因表达的信号分子.这2种信号分子与乙酸丁香酮(AS)的诱导作用极为相似.经过红外光谱、紫外光谱、质谱、核磁共振、异核多量子相干相关谱,异核多键相关谱等波谱分析,确定这2种信号分子的化学结构分别为:5,7,4′-三羟基-3′,5′-二甲氧基黄酮(俗称小麦黄素),和5,4′-二羟基-3′,5′-二甲氧基-7-(β-D葡萄糖基)黄酮.研究结果证明:单子叶植物中确实含有高效诱导农杆菌vir区基因表达的信号分子,单子叶植物难以被农杆菌转化不是由于单子叶植物中缺乏诱导vir区基因表达的信号分子,而由于这类信号分子仅在单子叶植物中特定时期和特定部位中产生.     

农杆菌介导的斑玉蕈遗传转化

【目的】将农杆菌介导的转化应用于重要的工厂化栽培食用菌斑玉蕈中,建立稳定的农杆菌介导的斑玉蕈遗传转化技术。【方法】将构建的双元载体pYN6982转入农杆菌LBA4404菌株中,以斑玉蕈SIEF3133菌株打碎的双核菌丝为受体材料,利用根癌农杆菌介导的转化方法进行斑玉蕈转化试验。【结果】经潮霉素抗性筛选、PCR鉴定以及有丝分裂稳定性试验验证,表明潮霉素磷酸转移酶基因(hph)已经整合到斑玉蕈的基因组中;转基因斑玉蕈菌丝在荧光显微镜下可以观测到绿色荧光,表明增强型绿色荧光蛋白基因(egfp)已经在转基因斑玉蕈菌株中获得了表达;通过PCR检测,随机挑选的8个转基因斑玉蕈菌株中有2个可以扩增出载体转移DNA(T-DNA)边界重复序列外的卡那霉素基因(kan)序列。【结论】获得了稳定遗传和表达的斑玉蕈转基因菌株,建立了农杆菌介导的斑玉蕈遗传转化方法。农杆菌介导的斑玉蕈遗传转化中,存在载体T-DNA边界重复序列之外的DNA序列转移到转基因斑玉蕈中的现象,有待进一步研究。     

利用根癌农杆菌法获得转基因水稻植株及其后代

在100μmol／L乙酰丁香酮（AS）等vir基因诱导分子存在的情况下,用含双元载体pBYT2的根癌农杆菌菌株EHA101同水稻（OrizasativaL．）台北309悬浮培养细胞共培养3天。经过2个月的连续筛选,共从364颗同根癌农杆菌共培养的悬浮培养细胞团中得到17个具有稳定潮霉素抗性和GUS表达的愈伤组织。对从8个转化组织中得到的10株可能的R0代转基因植株及其后代进行外源基因的整合和表达分析,Southern分析表明外源基因已稳定地整合进水稻基因组中并实现了有性遗传传递。杂交结果显示在其中一个转化系的植株中有5个拷贝的T－DNA整合,而其余的转化系则只整合了1个拷贝。转基因水稻细胞及植株中GUS活性的组织化学染色观察和荧光分析表明玉米ubiquitin基因启动子在水稻细胞中能高效启动gus报告基因的表达。ndPAGE－X－Gluc法检测表明转基因水稻细胞中表达的GUS蛋白比Sigma公司的标准GUS蛋白（SigmaCo．G0786）要小,而与来自大肠杆菌HB101（pBI1121）中的GUS蛋白大小相同。结果表明,根癌农杆菌可有效且可靠地介导外源基因转化水稻。     

根癌农杆菌介导真菌遗传转化的研究及应用

根癌农杆菌介导转化法（Agrobacterium tumefaciens-mediated transformation,ATMT）具有转化效率高、遗传稳定、适用范围广等诸多优点,已成为真菌遗传转化研究中的强有力手段,在真菌基因资源开发、真菌性疾病研究和外源蛋白表达研究中发挥巨大作用。本文概述了根癌农杆菌转化法在真菌转化中的研究进展、技术优缺点、转化机制、实验方法和应用现状,着重介绍影响其转化效率的因素并对优化方法进行探讨,展望了该技术在真菌基因资源发掘、基因编辑等方面的应用前景,为今后真菌的遗传转化研究提供参考。     

Glycine betaine allows enhanced induction of the Agrobacterium tumefaciens vir genes by acetosyringone at low pH.

We established growth conditions for efficient induction of the vir genes of Agrobacterium tumefaciens by acetosyringone. Optimal induction was attained at a pH below 5.2 in an AB minimal medium-derived high-osmotic-strength medium containing glycine betaine. This natural osmoprotectant accelerated the adaptation of the bacteria to these conditions. We established the kinetics of induction for virB, virD, virE, and virG by using lacZ fusions, and we found that the virB mutant strain could not adapt to this low-pH medium unless 1 mM CaCl2 was added. This pH control of vir gene expression was shown to act at the level of expression of virG, which was the limiting factor. This improved vir induction at a low pH correlated with an increase in a set of proteins which was analyzed by two-dimensional gel electrophoresis. The fact that high inducibility corresponded to a reduced growth rate and the demonstration that a set of proteins was associated with the inducible state suggest that vir gene induction is linked to the adaptation of the cells to an unfavorable environment. Hence, vir gene expression in A. tumefaciens is probably dependent upon a machinery which is specific to an adaptive response; the implications for plant transformation are discussed.     

Ti plasmid-specified chemotaxis of Agrobacterium tumefaciens C58C1 toward vir-inducing phenolic compounds and soluble factors from monocotyledonous and dicotyledonous plants.

Twelve phenolic compounds with related structures were analyzed for their ability to act as chemoattractants for Agrobacterium tumefaciens C58C1 and as inducers of the Ti plasmid virulence operons. The results divided the phenolic compounds into three groups: compounds that act as strong vir inducers and are chemoattractants for A. tumefaciens C58C1 harboring the nopaline Ti plasmid pDUB1003 delta 31, but not the isogenic cured strain; compounds that are at best weak vir inducers and are weak chemoattractants for Ti plasmid-harboring and cured A. tumefaciens C58C1; and compounds that are vir noninducers and are also nonattractants. A strong correlation between vir-inducing ability and Ti plasmid requirement for chemotaxis is thus established. In addition, chemical structure rules for vir induction and chemotaxis are outlined. Positive chemotaxis toward root and shoot homogenates from monocotyledonous and dicotyledonous plants was observed. At low extract concentrations, chemotaxis was enhanced by the presence of Ti plasmid. The chemoattractants do not derive from intact cell walls. Lack of attraction is not responsible for the apparent block to monocot transformation by A. tumefaciens.     

Dual control of Agrobacterium tumefaciens Ti plasmid virulence genes.

The virulence genes of nopaline (pTiC58) and octopine (pTiA6NC) Ti plasmids are similarly affected by the Agrobacterium tumefaciens ros mutation. Of six vir region complementation groups (virA, virB, virG, virC, virD, and virE) examined by using fusions to reporter genes, the promoters of only two (virC and virD) responded to the ros mutation. For each promoter that was affected by ros, the level of expression of its associated genes was substantially elevated in the mutant. This increase was not influenced by Ti plasmid-encoded factors, and the mutation did not interfere with the induction of pTiC58 vir genes by phenolic compounds via the VirA/VirG regulatory control mechanism. The effects of the ros mutation and acetosyringone were cumulative for all vir promoters examined. The pleiotropic characteristics of the ros mutant include the complete absence of the major acidic capsular polysaccharide.     

Sugar-mediated induction of Agrobacterium tumefaciens virulence genes: structural specificity and activities of monosaccharides.

The virulence genes of Agrobacterium tumefaciens are induced by specific plant phenolic metabolites and sugars (G. A. Cangelosi, R. G. Ankenbauer, and E. W. Nester, Proc. Natl. Acad. Sci. USA, in press). In this report, monosaccharides, derivatives, and analogs which induce the vir regulon have been identified and the structural requirements for monosaccharide-mediated induction have been determined. Pyranose sugars with equatorial hydroxyls at C-1, C-2, and C-3 displayed strong vir gene-inducing activity; the C-4 hydroxyl could be epimeric and a wide variety of substitutions at C-5 were permissible. The acidic monosaccharide derivatives D-galacturonic acid and D-glucuronic acid were the strongest inducers among the monosaccharides tested. Eight of the 11 inducing compounds are known plant metabolites, and 7 are monomers of major plant cell wall polysaccharides. A role for monosaccharides and plant phenolic compounds as wound-specific plant metabolites which signal the ChvE/VirA/VirG regulatory system is proposed.     

Intersubunit complementation of sugar signal transduction in VirA heterodimers and posttranslational regulation of VirA activity in Agrobacterium tumefaciens

The VirA/VirG two-component regulatory system of Agrobacterium tumefaciens regulates expression of the virulence (vir) genes that control the infection process leading to crown gall tumor disease on susceptible plants. VirA, a membrane-bound homodimer, initiates vir gene induction by communicating the presence of molecular signals found at the site of a plant wound through phosphorylation of VirG. Inducing signals include phenols, monosaccharides, and acidic pH. While sugars are not essential for gene induction, their presence greatly increases vir gene expression when levels of the essential phenolic signal are low. Reception of the sugar signal depends on a direct interaction between ChvE, a sugar-binding protein, and VirA. Here we show that the sugar signal received in the periplasmic region of one subunit within a VirA heterodimer can enhance the kinase function of the second subunit. However, sugar enhancement of vir gene expression was vector dependent. virA alleles expressed from pSa-derived vectors inhibited signal transduction by endogenous VirA. Inhibition was conditional, depending on the induction medium and the virA allele tested. Moreover, constitutive expression of virG overcame the inhibitory effect of some but not all virA alleles, suggesting that there may be more than one inhibitory mechanism.