小RNA病毒致病机理的研究

很多小RNA科病毒感染宿主细胞后可通过自身的核酸序列或病毒性蛋白产物控制靶细胞的生命活动,而被感染细胞也会通过自身的调控机制对侵染的病毒进行有限的反击,这种现象被认为是宿主细胞对抗小RNA科病毒侵染的防御机制.这种侵染与抵抗的互作机制可由某些病毒蛋白对细胞产生信号干扰或细胞自身翻译合成的细胞因子对病毒的复制路径进行封堵来实现.虽然这些信号通路的上游事件是不同的,但最后的效应却很统一,即使细胞崩解或者细胞将自身按照一定程序与所侵入的病毒同归于尽.此外,一些病毒蛋白具有抑制细胞程序性自杀的功能,它们能够令感染病毒后的细胞不死亡,形成病毒与宿主细胞共存的持续性感染状态.     

Endogenous siRNAs derived from transposons and mRNAs in Drosophila somatic cells

Small interfering RNAs (siRNAs) direct RNA interference (RNAi) in eukaryotes. In flies, somatic cells produce siRNAs from exogenous double-stranded RNA (dsRNA) as a defense against viral infection. We identified endogenous siRNAs (endo-siRNAs), 21 nucleotides in length, that correspond to transposons and heterochromatic sequences in the somatic cells of Drosophila melanogaster. We also detected endo-siRNAs complementary to messenger RNAs (mRNAs); these siRNAs disproportionately mapped to the complementary regions of overlapping mRNAs predicted to form double-stranded RNA in vivo. Normal accumulation of somatic endo-siRNAs requires the siRNA-generating ribonuclease Dicer-2 and the RNAi effector protein Argonaute2 (Ago2). We propose that endo-siRNAs generated by the fly RNAi pathway silence selfish genetic elements in the soma, much as Piwi-interacting RNAs do in the germ line.     

Autophagy-dependent viral recognition by plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) detect viruses in the acidified endosomes by means of Toll-like receptors (TLRs). Yet, pDC responses to certain single-stranded RNA (ssRNA) viruses occur only after live viral infection. We present evidence here that the recognition of such viruses by TLR7 requires transport of cytosolic viral replication intermediates into the lysosome by the process of autophagy. In addition, autophagy was found to be required for the production of interferon-alpha by pDCs. These results support a key role for autophagy in mediating ssRNA virus detection and interferon-alpha secretion by pDCs and suggest that cytosolic replication intermediates of viruses serve as pathogen signatures recognized by TLR7.     

Crystal structure of the rabies virus nucleoprotein-RNA complex

Negative-strand RNA viruses condense their genome into a helical nucleoprotein-RNA complex, the nucleocapsid, which is packed into virions and serves as a template for the RNA-dependent RNA polymerase complex. The crystal structure of a recombinant rabies virus nucleoprotein-RNA complex, organized in an undecameric ring, has been determined at 3.5 angstrom resolution. Polymerization of the nucleoprotein is achieved by domain exchange between protomers, with flexible hinges allowing nucleocapsid formation. The two core domains of the nucleoprotein clamp around the RNA at their interface and shield it from the environment. RNA sequestering by nucleoproteins is likely a common mechanism used by negative-strand RNA viruses to protect their genomes from the innate immune response directed against viral RNA in human host cells at certain stages of an infectious cycle.     

RNA-dependent RNA polymerases,viruses, and RNA silencing

Most viruses have RNA genomes that are replicated and transcribed into messenger RNA by viral RNA-dependent RNA polymerases (RdRps), usually in concert with other viral and host factors. Many, if not most, eukaryotes also encode putative RdRps that have been implicated in sequence-specific, RNA-triggered gene silencing. Although the viral and cellular RdRps have no sequence homology, they share functional similarities such as copying messenger RNA templates and intercellular spread of the amplified sequences. Better understanding of viral and host RdRps will improve our ability to control viruses and to use RNA silencing and viruses as tools for research, biotechnology, and medicine.     

Innate antiviral responses by means of TLR7-mediated recognition of single-stranded RNA

Interferons (IFNs) are critical for protection from viral infection, but the pathways linking virus recognition to IFN induction remain poorly understood. Plasmacytoid dendritic cells produce vast amounts of IFN-alpha in response to the wild-type influenza virus. Here, we show that this requires endosomal recognition of influenza genomic RNA and signaling by means of Toll-like receptor 7 (TLR7) and MyD88. Single-stranded RNA (ssRNA) molecules of nonviral origin also induce TLR7-dependent production of inflammatory cytokines. These results identify ssRNA as a ligand for TLR7 and suggest that cells of the innate immune system sense endosomal ssRNA to detect infection by RNA viruses.     

Visualization and functional analysis of RNA-dependent RNA polymerase lattices

Positive-strand RNA viruses such as poliovirus replicate their genomes on intracellular membranes of their eukaryotic hosts. Electron microscopy has revealed that purified poliovirus RNA-dependent RNA polymerase forms planar and tubular oligomeric arrays. The structural integrity of these arrays correlates with cooperative RNA binding and RNA elongation and is sensitive to mutations that disrupt intermolecular contacts predicted by the polymerase structure. Membranous vesicles isolated from poliovirus-infected cells contain structures consistent with the presence of two-dimensional polymerase arrays on their surfaces during infection. Therefore, host cytoplasmic membranes may function as physical foundations for two-dimensional polymerase arrays, conferring the advantages of surface catalysis to viral RNA replication.     

HLA and NK cell inhibitory receptor genes in resolving hepatitis C virus infection

Natural killer (NK) cells provide a central defense against viral infection by using inhibitory and activation receptors for major histocompatibility complex class I molecules as a means of controlling their activity. We show that genes encoding the inhibitory NK cell receptor KIR2DL3 and its human leukocyte antigen C group 1 (HLA-C1) ligand directly influence resolution of hepatitis C virus (HCV) infection. This effect was observed in Caucasians and African Americans with expected low infectious doses of HCV but not in those with high-dose exposure, in whom the innate immune response is likely overwhelmed. The data strongly suggest that inhibitory NK cell interactions are important in determining antiviral immunity and that diminished inhibitory responses confer protection against HCV.     

Induction and suppression of RNA silencing by an animal virus

RNA silencing is a sequence-specific RNA degradation mechanism that is operational in plants and animals. Here, we show that flock house virus (FHV) is both an initiator and a target of RNA silencing in Drosophila host cells and that FHV infection requires suppression of RNA silencing by an FHV-encoded protein, B2. These findings establish RNA silencing as an adaptive antiviral defense in animal cells. B2 also inhibits RNA silencing in transgenic plants, providing evidence for a conserved RNA silencing pathway in the plant and animal kingdoms.     

Hierarchical action and inhibition of plant Dicer-like proteins in antiviral defense

The mechanisms underlying induction and suppression of RNA silencing in the ongoing plant-virus arms race are poorly understood. We show here that virus-derived small RNAs produced by Arabidopsis Dicer-like 4 (DCL4) program an effector complex conferring antiviral immunity. Inhibition of DCL4 by a viral-encoded suppressor revealed the subordinate antiviral activity of DCL2. Accordingly, inactivating both DCL2 and DCL4 was necessary and sufficient to restore systemic infection of a suppressor-deficient virus. The effects of DCL2 were overcome by increasing viral dosage in inoculated leaves, but this could not surmount additional, non-cell autonomous effects of DCL4 specifically preventing viral unloading from the vasculature. These findings define a molecular framework for studying antiviral silencing and defense in plants.     

翻译起始因子4E及其异构体与植物病毒感染的联系

近年来,对植物隐性基因抗病毒感染的研究取得了一些新的进展。从植物抗病毒与感病,eIF4E及其异构体对植物抗病毒感染作用的影响及机制,以及在此理论基础上设计抗病毒的新策略作一阐述。     

Virus-directed protein synthesis in different animal and human cells

The relative proportions of viral gene products (viral proteins) that are synthesized in different types of animal cells infected with the same RNA virus inoculum were compared. The relative rates of synthesis of the various virus proteins late in infection were remarkably constant regardless of cell type infected. This was true in cell lines that produced only small amounts of virus and virus proteins, as well as in those that gave large yields of viruses and virus proteins.     

Wolbachia and virus protection in insects

Wolbachia pipientis bacteria are common endosymbionts of insects that are best known for their ability to increase their prevalence in populations by manipulating host reproductive systems. However, there are examples of Wolbachia that exist in nature that seem to induce no reproductive parasitism trait and yet are able to invade populations. We demonstrate a fitness benefit for Wolbachia-infected insects that may explain this paradox. Drosophila melanogaster flies infected with Wolbachia are less susceptible to mortality induced by a range of RNA viruses. The antiviral protection associated with Wolbachia infection might be exploited in future strategies to reduce transmission of pathogens by insects.     

Identification of Viruses Infecting Peppers in Guangdong by Small RNA Deep Sequencing

【Objective】 The viral disease is one of the major diseases of pepper production in Guangdong Province. The disease incidence is generally 5%-30% in the field, which can up to 100% in serious field. The objective of this study is to identify virus species infecting pepper in Guangdong Province, and to provide a theoretical basis for the prevention and control of pepper virus disease. 【Method】 From 2013 to 2016, a total of 125 susceptible pepper plant samples were collected from 8 major pepper growing areas of Guangzhou, Foshan, Huizhou, Jiangmen, Meizhou, Zhanjiang, Maoming and Shaoguan in Guangdong Province. Total RNA was extracted respectively from the leaves of 125 pepper samples. The 7 mixed samples collected from Maoming, Meizhou and Shaoguan were analyzed by small RNA deep sequencing. According to the results of small RNA deep sequencing analysis, two pairs of specific primers of each virus were designed to RT-PCR. The first pair of specific primers was designed according to the sequences of spliced gene fragments from small RNA deep sequencing. The second pair of specific primers was designed according to the conserved region sequences of viral genome in the GenBank database with the highest homology to sequences of spliced gene fragments from small RNA deep sequencing. Using disease samples RNA involved in small RNA deep sequencing as a template, the RT-PCR amplification was carried out with the two pairs of primers. Based on RT-PCR amplification results, the better pair of specific primers of each virus was selected. Furthermore, all 125 samples collected from Guangdong Province were subjected to detect viruses with the better pair of specific primers by RT-PCR. 【Result】 Fourteen viruses were identified in 125 samples collected from major pepper growing areas in 8 cities of Guangdong Province. According to the order of detection rate from high to low, they were Pepper mild mottle virus (PMMoV) (44.0%), Bell pepper endornavirus (BPEV) (32.8%), Tobacco mild green mosaic virus (TMGMV) (31.2%), Chilli veinal mottle virus (ChiVMV) (29.6%), Pepper vein yellow virus 1 (PeVYV-1) (26.4%), Pepper veinal mottle virus (PVMV) (25.6%), Cucumber mosaic virus (CMV) (18.4%), Chilli ringspot virus (ChiRSV) (16.8%), Pepper vein yellow virus 6 (PeVYV-6) (16.8%), Potato virus Y (PVY) (15.2%), Capsicum chlorosis virus (CaCV) (14.4%), Broad bean wilt virus 2 (BBWV-2) (9.6%), Pepper cryptic virus 1 (PCV1) (8.8%), Tobacco mosaic virus (TMV) (4.0%). The detection rates of PMMoV, BPEV, TMGMV, ChiVMV, PeVYV-1 and PVMV were over 25%. PMMoV, ChiVMV and PVMV were widely distributed in Guangdong Province. PMMoV (except Maoming), ChiVMV (except Shaoguan) were detected in pepper producing areas of other 7 cities. PVMV was detected in pepper producing areas of 8 cities. According to detection rate and distribution range, it was concluded that PMMoV, ChiVMV and PVMV were the dominant viruses infecting pepper in Guangdong Province. The mixed infection phenomenon was common on peppers in Guangdong Province. The detection rate of mixed infection was up to 88.0% in 125 samples. Among them, the mixed detection rates of 2 kinds, 3 kinds, 4 kinds, 5 kinds, 6 kinds, 7 kinds and 8 kinds of viruses were 28.0%, 25.6%, 12.0%, 9.6%, 6.4%, 1.6%, 2.4%, respectively. So, 2 kinds and 3 kinds of viruses mixed infection were the main infection forms on peppers in Guangdong Province. 【Conclusion】 There are 14 kinds of viruses endangering pepper plants in Guangdong Province, among which PMMoV, ChiVMV and PVMV are the dominant viruses. The phenomenon of mixed infection is common. The main infection forms on peppers are 2 kinds and 3 kinds of viruses mixed infection in Guangdong Province.     

基于小RNA深度测序技术鉴定侵染广东辣椒的病毒种类

【目的】病毒病是广东省辣椒生产上主要病害之一,田间病株率一般为5%—30%,严重时可达100%。本研究旨在探明危害广东辣椒的病毒种类,为辣椒病毒病的防控提供理论依据。【方法】2013—2016年,从广东省广州、佛山、惠州、江门、梅州、湛江、茂名和韶关8市辣椒主要种植区采集疑似病毒病辣椒样品125份,分别提取每份辣椒病样总RNA,对从茂名、梅州、韶关3市采集的病样按地点和症状混合成7份混合病样进行小RNA深度测序分析,根据小RNA深度测序分析结果,对每种病毒分别根据小RNA深度测序拼接的基因片段序列和GenBank数据库中与该拼接序列同源性最高的病毒基因组序列保守区设计2对特异性引物,以小RNA深度测序的病样RNA为模板进行RT-PCR扩增,根据扩增效果对引物进行筛选,进一步应用筛选出的引物,对采集于广东省的125份辣椒病样分别进行RT-PCR检测,根据检测结果明确危害广东辣椒的病毒种类。【结果】从采集于广东省8市的辣椒主要种植区的125份病样中检测到14种病毒,按照检出率从高到低依次为辣椒轻斑驳病毒（Pepper mild mottle virus,PMMoV）(44.0%）、甜椒内源RNA病毒（Bell pepper endornavirus,BPEV）（32.8%）、烟草轻型绿花叶病毒（Tobacco mild green mosaic virus,TMGMV）（31.2%）、辣椒脉斑驳病毒（Chilli veinal mottle virus,ChiVMV）（29.6%）、辣椒黄脉病毒1（Pepper vein yellow virus 1,PeVYV-1）（26.4%）、甜椒斑驳病毒（Pepper veinal mottle virus,PVMV）（25.6%）、黄瓜花叶病毒（Cucumber mosaic virus,CMV）（18.4%）、辣椒环斑病毒（Chilli ringspot virus,ChiRSV）（16.8%）、辣椒黄脉病毒6（Pepper vein yellow virus 6,PeVYV-6）（16.8%）、马铃薯 Y 病毒（Potato virus Y,PVY）（15.2%）、辣椒褪绿病毒（Capsicum chlorosis virus,CaCV）（14.4%）、蚕豆萎蔫病毒2号（Broad bean wilt virus 2,BBWV-2）（9.6%）、辣椒隐症病毒1（Pepper cryptic virus 1,PCV1）（8.8%）、烟草花叶病毒（Tobacco mosaic virus,TMV）（4.0%）。其中,PMMoV、BPEV、TMGMV、ChiVMV、PeVYV-1和PVMV 6种病毒的检出率在25%以上,但PMMoV、ChiVMV和PVMV分布广泛,PMMoV除了茂名外,ChiVMV除了韶关外,其他7市辣椒产区均有分布;PVMV广泛分布于8市辣椒产区,根据检出率和分布范围,得出PMMoV、ChiVMV和PVMV是危害广东辣椒的优势病毒。同时发现,广东辣椒上多种病毒复合侵染现象普遍,在本研究125份病样中病毒复合侵染率达到88.0%,其中2种、3种、4种、5种、6种、7种和8种病毒复合侵染检出率分别为28.0%、25.6%、12.0%、9.6%、6.4%、1.6%和2.4%,由此可知,2种和3种病毒复合侵染是主要侵染形式。【结论】危害广东辣椒的病毒有14种,其中PMMoV、ChiVMV和PVMV为优势病毒,且复合侵染普遍,2种和3种病毒复合侵染是主要侵染形式。     

应用分析双链RNA技术诊断苹果潜隐性病毒病

本文报导一种以分析病毒双链RNA为依据,检测苹果潜隐性病毒的新方法。这种方法能快速、准确地从苹果组织中分离和分析病毒的双链RNA(ds RNA),因此能直接、有效地从病毒侵染的组织诊断苹果潜隐性病毒。双链RNA是从自然侵染的苹果叶片或花瓣用酚萃取,经CF-11纤维素层析纯化,再用6％聚丙烯酰胺凝胶电泳和溴乙锭或银盐染色分析ds RNA电泳图谱。经脱毒的苹果树叶片,未发现有病毒的ds RNA存在。文中还报导了使用这一技术诊断苹果潜隐性病毒的有关技术条件。     

植物病毒编码RNA沉默抑制子的研究进展

RNA沉默是真核生物用来抵抗病毒入侵的一种普遍而又古老的防御机制，而病毒在进化过程中也相应地产生了一些与之抗衡的功能，其中编码沉默抑制子就是对抗RNA沉默的有效策略。它们分别能够在不同阶段，以不同的方式干扰来自于寄主的RNA沉默，从而有效地建立侵染。本文主要针对目前已经发现的由植物病毒编码RNA沉默抑制子的作用特征、鉴定方法以及作用副效应进行综述，并讨论了RNA沉默抑制子的研究及应用前景。     

CRISPR/Cas13b系统对猪流行性腹泻病毒增殖的抑制作用

【目的】猪流行性腹泻是由猪流行性腹泻病毒(Porcine epidemic diarrhea virus,PEDV)引起的一种对养猪业造成巨大损失的高致死率的传染性疫病。CRISPR/Cas13b系统精准切割和编辑RNA的功能提供了一种靶向抑制RNA病毒的策略。本研究尝试利用CRISPR/Cas13b的RNA干扰功能对PEDV的基因组RNA进行切割,以探索一种新型的PEDV病毒抑制策略。【方法】设计了4对靶向PEDV基因组不同区域的CRISPR RNA(crRNA)位点,构建了CRISPR/Cas13b打靶载体,以打靶载体转染Vero细胞,并利用PEDV感染转染细胞,检测PEDV在CRISPR/Cas13b转染细胞内的增殖情况。【结果】CRISPR/Cas13b系统对PEDV在Vero细胞的增殖具有明显的抑制作用。打靶载体U6-crRNA3和U6-crRNA4转染组相较于正常细胞组,病毒免疫荧光试验中荧光团明显减少;定量PCR结果显示,打靶载体转染组在细胞水平抑制50%以上病毒增殖量。【结论】本研究构建的CRISPR/Cas13b系统能有效抑制PEDV增殖,为开发有效的RNA病毒防控手段、建立抗病动物模型提供了新的研究策略。