检测烟草中烟草花叶病毒的RNA斑点杂交法

用普通烟草花叶病毒OM株3′-端约2kb的cDNA为探针,探索了用RNA斑点杂交法对烟草组织中烟草花叶病毒RNA进行检测的条件。这些条件包括用分子杂交法观察云南烟区和上海烟草上分到的烟草花叶病毒与OM株的同源性,从烟草组织中提取烟草花叶病毒的几种方法的比较,使RNA有效地固定在硝酸纤维素滤膜上的方法,烟草组织中是否有干扰RNA固定和杂交的物质,斑点杂交方法检测烟草花叶病毒的特异性、灵敏度等。     

应用RNAi技术培育抗2种病毒病的转基因烟草

分别提取烟草普通花叶病(TMV)和烟草黄瓜花叶病（CMV）的病毒RNA。经反转录和外壳蛋白阅读框PCR扩增,获得TMV和CMV外壳蛋白基因cDNA, 分别进行两种病毒已知株系cDNA序列比对获得各自的保守序列,设计干涉序列,将干涉片段扩增产物连接到pMD18-T的相邻酶切位点,制备融合序列,并将其正向和反向序列插入pUCCRNAi载体,再转化到pCAMBIA2300-35S-OCS表达载体中。利用农杆菌LBA4404侵染烟草K326,获得3份含有TMV和CMV外壳蛋白基因干涉序列的转化材料,经分子鉴定证实干涉序列已导入烟草,并采用荧光定量PCR技术对其mRNA表达差异进行分析。抗病性调查表明转化烟株对TMV和CMV抗性都显著增强。     

The organisation and interviral homologies of genes at the 3' end of tobacco rattle virus RNA1

The RNA1 of tobacco rattle virus (TRV) has been cloned as cDNA and the nucleotide sequence determined of 2 kb from the 3'-terminal region. The sequence contains three long open reading frames. One of these starts 5' of the cDNA and probably corresponds to the carboxy-terminal sequence of a 170-K protein encoded on RNA1. The deduced protein sequence from this reading frame shows homology with the putative replicases of tobacco mosaic virus (TMV) and tricornaviruses. The location of the second open reading frame, which encodes a 29-K polypeptide, was shown by Northern blot analysis to coincide with a 1.6-kb subgenomic RNA. The validity of this reading frame was confirmed by showing that the cDNA extending over this region could be transcribed and translated in vitro to produce a polypeptide of the predicted size which co-migrates in electrophoresis with a translation product of authentic viral RNA. The sequence of this 29-K polypeptide showed homology with two regions in the 30-K protein of TMV. This homology includes positions in the TMV 30-K protein where mutations have been identified which affect the transport of virus between cells. The third open reading frame encodes a potential 16-K protein and was shown by Northern blot hybridisation to be contained within the region of a 0.7-kb subgenomic RNA which is found in cellular RNA of infected cells but not virus particles. The many similarities between TRV and TMV in viral morphology, gene organisation and sequence suggest that these two viral groups may share a common viral ancestor.     

两个缺陷型TMV粒子在烟草中的互补表达

根据对ＴＭＶ高效复制和基因表达的顺式作用元件的分析,在体外重组包装了２个缺失型ＴＭＶ粒子：ＴＭＶＲＰ和ＴＭＶＣＰ。前者缺失了ＴＭＶ外壳蛋白ＣＰ基因的３′端及后序区域,后者缺失了大部分复制酶基因。把两者分别或共同电击感染烟草原生质体：１．用ＣＰ抗体进行免疫印渍检测,单独感染的原生质体内的ＣＰ在１６小时内无增加,而在共同感染的原生质体内,ＣＰ在感染２小时后就开始明显增加。２．用ＲＴ一两次ＰＣＲ法专一地检测新生负链ＲＮＡ的合成情况,在单独感染的原生质体内没有检测到,但在混合感染的原生质体内在感染１小时后就检测到ＣＰ基因特异的负链ＲＮＡ的形成,并用Ｓｏｕｔｈｅｒｎ杂交得到进一步验证。这些结果表明,复制酶缺失型ＴＭＶＣＰ内的ＣＰ基因不能表达,但可以在ＴＭＶＲＰ存在时,通过其所表达的复制酶互补作用得到复制从而有效表达．     

Biological activities of hybrid RNAs generated by 3''-end exchanges between tobacco mosaic and brome mosaic viruses.

Sequences within the conserved, aminoacylatable 3' noncoding regions of brome mosaic virus (BMV) genomic RNAs 1, 2, and 3 direct initiation of negative-strand synthesis by BMV polymerase extracts and, like sequences at the structurally divergent but aminoacylatable 3' end of tobacco mosaic virus (TMV) RNA, are required in cis for RNA replication in vivo. A series of chimeric RNAs in which selected 3' segments were exchanged between the tyrosine-accepting BMV and histidine-accepting TMV RNAs were constructed and their amplification was examined in protoplasts inoculated with or without other BMV and TMV RNAs. TMV derivatives whose 3' noncoding region was replaced by sequences from BMV RNA3 were independently replication competent when the genes for the TMV 130,000-M(r) and 180,000-M(r) replication factors remained intact. TMV replicase can thus utilize the BMV-derived 3' end, though at lower efficiency than the wild-type (wt) TMV 3' end. Providing functional BMV RNA replicase by coinoculation with BMV genomic RNAs 1 and 2 did not improve the amplification of these hybrid genomic RNAs. By contrast, BMV RNA3 derivatives carrying the 3' noncoding region of TMV were not amplified when coinoculated with wt BMV RNA1 and RNA2, wt TMV RNA, or all three. Thus, BMV replicase appeared to be unable to utilize the TMV 3' end, and there was no evidence of intervirus complementation in the replication of any of the hybrid RNAs. In protoplasts coinoculated with BMV RNA1 and RNA2, the nonamplifiable RNA3 derivatives bearing TMV 3' sequences gave rise to diverse new rearranged or recombined RNA species that were amplifiable.     

外源RNA干涉基因在烟草中的转化及表达

依据RNA干涉机制,以TMV复制酶基因为靶标基因,针对TMV 5个株系复制酶基因间高度同源序列设计引物,经RT-PCR反应获得靶序列,构建靶序列反向重复结构的RNA干涉双元载体.用根癌农杆菌介导将外源基因转化至烟草品种K326基因组中,培育RNA干涉转基因烟草.人工接种病毒验证转基因烟草中外源基因在植物抗病毒能力方面的表达效果,实时荧光定量PCR分析转基因烟草抗病毒能力.结果表明,实验培育的RNA干涉转基因烟草67%对TMV呈现高度抗性;荧光定量PCR分析显示,对TMV具高度抗性的转基因烟草中病毒复制酶基因转录产物mRNA存在很大程度的降解,证实了RNA干涉技术在培育抗病毒烟草品种中的效果.     

A new multigene family inducible by tobacco mosaic virus or salicylic acid in tobacco.

A previously undescribed cDNA family was isolated from tobacco challenged with tobacco mosaic virus (TMV). A cDNA library was constructed with mRNA from upper leaves of Xanthi nc tobacco plants that had been inoculated with TMV on the lower leaves 11 days previously. The library was screened differentially with radiolabeled cDNA synthesized with mRNA from upper, uninoculated leaves of either TMV-inoculated or mock-inoculated tobacco plants. The new cDNA family, designated SAR8.2, had at least five expressed members, one or more of which were inducible by TMV inoculation and by salicylic acid treatment. The cDNAs encoded small, highly basic proteins containing N-terminal hydrophobic signal peptides and highly conserved cysteine-rich C-terminal domains. One of the SAR8.2 family members contained a direct repeat of the C-terminal domain in tandem. Hybridization of SAR8.2 cDNA to tobacco genomic DNAs indicated a gene family of 10-12 members.     

毛头鬼伞真菌具有抗烟草花叶病毒活性的y3基因的克隆及对烟草的转化

【目的】蛋白质Y3具有抗烟草花叶病毒(TMV)活性并由y3基因编码。本文的目的是从真菌毛头鬼伞(Coprinus comatus)中克隆y3基因全长并在植物体中展现其对TMV的抑制活性。【方法】我们利用试剂盒5′-Full RACE Core Set(TaKaRa)扩增了y3基因cDNA5′-端未知序列,通过RT-PCR获得了全长序列,并把该全长序列与CaMV 35 S启动子和NOS终止子一起插入多克隆位点(MCS)构建了植物表达载体pCAMBIA1301-y3,用于农杆菌介导的烟草转化。【结果】y3基因全长534碱基对,包含1个开放阅读框(ORF),编码一条含130个氨基酸残基的肽链(GenBank检索号:GQ859168;EMBL:FN546262)。其cDNA序列和由它推到的氨基酸序列均与已发表的y3基因部分片段有高度相似性(94%)。Northern杂交分析证实了y3基因在转基因烟草中得到表达。接种TMV的转基因植株表现出抗TMV的活性。【结论】我们克隆了y3基因全长并得到了转基因植株。在转基因植株中,由于y3基因的表达改善了植株的抗病毒活性。y3基因的克隆和表达无疑为该基因的进一步研究奠定了基础。     

烟草花叶病毒运动蛋白基因的cDNA克隆、序列测定及植物转化

植物病毒侵染宿主植物的一个重要过程是通过它在宿主体内的转移和传播,产生病害。植物病毒在宿主体内的转移主要有两种方式,一种是通过植物维管组织进行的系统转移,另一种是植物病毒在宿主细胞之间的转移,这种转移是通过植物细胞的胞间连丝实现的。实验表明,病毒自身编码的一种蛋白参与了这个转移过程,对烟草花叶病毒(TMV)而言,这种蛋白就是分子量为30kDa的运动蛋白。     

Co-electroporation of rice protoplasts with RNAs of cucumber mosaic and tobacco mosaic viruses

Cucumber mosaic virus (CMV) RNA was used to study electroporation conditions suitable for protoplasts from rice suspension cultures. Rice protoplasts required a stronger and shorter electric pulse than tobacco protoplasts for introduction of viral RNA. Under optimized conditions, CMV infection was established in 65 % of electroporated protoplasts. In contrast, electroporation with tobacco mosaic virus (TMV) RNA did not result in infection of rice protoplasts. However, when TMV RNA was electroporated into rice protoplasts together with CMV RNA, TMV production was demonstrated in 15 % of protoplasts. Differential staining with fluorescent antibodies against the two viruses showed that the protoplasts producing TMV were without exception also infected by CMV. The results show that CMV replicates in rice protoplasts by itself, whereas TMV does so only with the aid of CMV.Abbreviations CMV cucumber mosaiv virus - PBS phosphate buffered saline - TMV tobacco mosaic virus.     

Cross protection in transgenic tobacco plants expressing a mild strain of tobacco mosaic virus

Summary Cross protection of plant viruses is a phenomenon in which plants infected with one strain of a virus are protected from the effects of superinfection by other related strains. Recently, we have succeeded in the introduction and expression of a cDNA copy of the tobacco mosaic virus (TMV) genomic RNA in transgenic tobacco plants. Using this system, we introduced a cDNA copy of a mild strain of TMV into tobacco plants. The transgenic plants did not develop any severe symptoms upon inoculation with a virulent TMV strain, indicating that these transgenic plants were cross protected against TMV infection. The system described here can be a useful model system to study the mechanism(s) of cross protection.     

The tobacco mosaic virus assembly origin RNA. Functional characteristics defined by directed mutagenesis

The in vitro reassembly of tobacco mosaic virus (TMV) begins with the specific recognition by the viral coat protein disk aggregate of an internal TMV RNA sequence, known as the assembly origin (Oa). This RNA sequence contains a putative stem-loop structure (loop 1), believed to be the target for disk binding in assembly initiation, which has the characteristic sequence AAGAAGUCG exposed as a single strand at its apex. We show that a 75-base RNA sequence encompassing loop 1 is sufficient to direct the encapsidation by TMV coat protein disks of a heterologous RNA fragment. This RNA sequence and structure, which is sufficient to elicit TMV assembly in vitro, was explored by site-directed mutagenesis. Structure analysis of the RNA identified mutations that appear to effect assembly via a perturbation in RNA structure, rather than by a direct effect on coat protein binding. The binding of the loop 1 apex RNA sequence to coat protein disks was shown to be due primarily to its regularly repeated G residues. Sequences such as (UUG)3 and (GUG)3 are equally effective at initiating assembly, indicating that the other bases are less functionally constrained. However, substitution of the sequences (CCG)3, (CUG)3 or (UCG)3 reduced the assembly initiation rate, indicating that C residues are unfavourable for assembly. Two additional RNA sequences within the 75-base Oa sequence, both of the form (NNG)3, may play subsidiary roles in disk binding. RNA structure plays an important part in permitting selective protein-RNA recognition, since altering the RNA folding close to the apex of the loop 1 stem reduces the rate of disk binding, as does shortening the stem itself. Whereas the RNA sequence making up the hairpin does not in general affect the specificity of the protein-RNA interaction, it is required to present the apex signal sequence in a special conformation. Mechanisms for this are discussed.     

Isolation from tobacco mosaic virus-infected tobacco of a solubilized template-specific RNA-dependent RNA polymerase containing a 126K/183K protein heterodimer

The complete nucleotide sequence was determined for the putative RNA polymerase (183K protein) gene of tobacco mosaic virus (TMV) OM strain, which differed from the related strain, vulgare, by 51 positions in its nucleotide sequence and 6 residues in its amino acid sequence. Three segments of this 183K protein, each containing the sequence motif of methyltransferase (M), helicase (H), or RNA-dependent RNA polymerase (P), were expressed in Escherichia coli as fusion proteins with hexahistidine tags, and domain-specific antibodies were raised against purified His-tagged M and P polypeptides. By immunoaffinity purification, a template-specific RNA-dependent RNA polymerase containing a heterodimer of the full-length 183K and 126K (an amino-terminal-proximal portion of the 183K protein) viral proteins was isolated. We propose that the TMV RNA polymerase for minus-strand RNA synthesis is composed of one molecule each of the 183- and 126-kDa proteins, possibly together with two or more host proteins.