Host factors used by positive-strand RNA plant viruses for genome replication

Replication of positive-strand RNA [(+)RNA] viruses proceeds through well-orchestrated actions of both viral and host factors. Remarkable features of eukaryotic (+)RNA virus replication include hijacking of host factors by viral components and remodeling of intracellular membranes to establish the viral replication factory, where viral RNA is synthesized. Here we review recent progress in our understanding of how (+)RNA plant viruses use host factors to create favorable environments for viral RNA replication.     

Post-translational modifications in effectors and plant proteins involved in host–pathogen conflicts

Molecular interplay between two species is largely driven by protein–protein interactions and protein modifications that set the pace of co-evolution in these species. During host–pathogen interactions, proteins involved in virulence and defence impart tempospatial dynamic post-translational modifications (PTMs) to gain advantage for the causative species. Pathogens mainly cause disease in plant hosts by secreting elicitors (peptides and small molecules) or proteins in the inter- and intracellular space of host cells. These pathogen proteins have evolved a wide array of sophisticated mechanisms to manipulate host responses, including resistance. Through a set of diverse events ranging from PTMs to post-translational oligomerization, these proteins are able to enhance virulence and suppress the otherwise elaborate plant immune system. Similarly, PTMs adapted by host proteins often lead to the activation of a robust defence response. Insights into the PTMs of pathogen and host proteins are therefore germane to the understanding of the co-evolutionary arms race. This review summarizes the characterization of PTMs in pathogen effectors and their target host proteins. Based on this, a metaphorical view of host–pathogen conflicts is proposed, where PTMs act as molecular pivots in a 3D combinatorial game model – a novel abstraction of the arms race, where these molecular pivots restore the balance of competition between the two organisms.     

Effect of temperature on RNA silencing of a negative‐stranded RNA plant virus: Citrus psorosis virus

Citrus psorosis virus (CPsV), genus Ophiovirus, causes a bark scaling disease of citrus. CPsV virions are kinked filaments with three negative‐stranded RNA molecules (vRNA) and a 48 kDa coat protein. The effect of temperature on symptom expression, virus accumulation and RNA silencing was examined in sweet orange seedlings (Citrus sinensis) graft‐inoculated with three different CPsV isolates and grown in a glasshouse at 26/18°C or 32/26°C (day/night). Most plants kept in the cooler glasshouse showed a shock reaction in the first flush with shoot necrosis, and then moderate to intense chlorotic flecking and spotting in young leaves, whereas plants incubated at 32/26°C did not exhibit shoot necrosis, and young leaf symptoms were milder. Virus titre estimated by ELISA and by northern and dot blot hybridization paralleled symptom intensity, with significantly higher virus accumulation in plants incubated at 26/18°C. The amount of CPsV‐derived small RNAs (CPsV‐sRNAs) slightly increased at 32/26°C, with the ratio of CPsV‐sRNA/vRNA being higher at 32/26°C than at 26/18°C. These results suggest that (i) CPsV infection induces RNA silencing in citrus plants, (ii) symptom intensity is associated with virus accumulation, and (iii) temperature increase enhances the RNA silencing response of citrus plants and decreases virus accumulation.     

Identification and molecular dissection of broad-spectrum recessive plant virus resistance genes

Journal of General Plant Pathology -     

灰飞虱传播的一种小麦病毒病鉴定

 在实验室中利用灰飞虱接种小麦时出现一种新的病毒病症状,鉴定表明其病原为大麦黄条点花叶病毒(Barley yellow striate mosaic virus, BYSMV)。采用生物学测定、电镜观察、RT-PCR检测和序列分析的方法,明确了该病毒的粒体特性、危害症状及田间发生情况。接种试验表明该病毒通过灰飞虱传播,接种7~10 d后小麦新生叶片出现黄色斑点、斑驳,继而发展成黄色条纹,叶片对生且细而窄,重病株新叶扭曲,叶鞘不能伸长,病株矮化。对小麦病叶超薄切片电镜观察,发现细胞质中存在大量弹状病毒粒子,病毒粒体大小为（315~353）nm×（46~57） nm。利用特异性引物从病株总RNA中扩增出 565 bp基因片段,序列同源性分析显示与大麦黄条点花叶病毒(Barley yellow striate mosaic virus, BYSMV) Zanjan-1分离物聚合酶（L）基因对应序列的一致性为97 %,与北方禾谷花叶病毒(Northern cereal mosaic virus, NCMV) L基因对应序列的一致性为78 %~79 %。对采自河北邯郸、石家庄、保定、唐山的31株样品进行RT-PCR检测,25株检测到BYSMV,7株检测到水稻黑条矮缩病毒(Rice black streaked dwarf virus,RBSDV),其中5株为2种病毒复合侵染,结果表明BYSMV的田间分布较广。系统发育分析表明BYSMV-Lab/TS/ZX/QY 4个分离物与本研究的BYSMV亲缘关系密切。BYSMV是我国小麦上新发现的一种弹状病毒,并已形成危害,暂定名为小麦黄条纹矮缩病,应加强流行动态监测。     

RNA silencing against viruses: molecular arms race between Cucumber mosaic virus and its host

Plants have developed RNA silencing as an antiviral defense mechanism. To escape from the plant host’s defenses, viruses have countered their host’s antiviral silencing by producing RNA silencing suppressor proteins (RSSs). Although the mode of action of the majority of viral RSSs has been found to be through double-stranded RNA-binding, viruses have different strategies to counteract the host’s antiviral silencing pathways. The 2b protein of Cucumber mosaic virus, which is one of the most extensively studied viral RSSs, is reviewed here to provide insights on the molecular arms race between viruses and their host plants.     

油菜花叶病毒Wh株系的鉴定

依据病毒的寄主植物反应、血清学性质和RNA 3'末端含cp和mp基因1554 bp cDNA片段序列分析,明确一个侵染油菜的烟草花叶病毒属Tobamovirus病毒分离物是油菜花叶病毒(Oileed rape mosaic virus,ORMV)的一个株系,定名为Wh株系.ORMV-Wh侵染油菜、白菜和大白菜等十字花科的作物,初期产生典型明脉症状,对辣椒、番茄和烟草等茄科植物致病性弱;血清学与烟草花叶病毒(Tobacco mosaic virus,TMV)有明显差异.ORMV-Wh mp、cp基因和3'UTR区段大小分别为798、474和235个核苷酸,mp和cp基因有77个核苷酸重叠;与TMV序列同源性在60%以下,与侵染十字花科Tobamovirus属病毒株系序列同源性在80%以上;其中与ORMV的不同株系RMV-CAB、RMV-Sh、YoMV、YoMV-Cg和CTMV-W的同源性在90%以上.     

芜菁花叶病毒对寄主植物叶片PSⅡ功能的影响

 芜菁花叶病毒(Turnip mosaic virus,TuMV)是十字花科蔬菜作物上最重要的病原病毒之一,TuMV在青菜、榨菜、芥菜、油菜等作物上的主要发病症状为花叶和畸形,研究植物病毒致花叶症状的机理有助于建立新的病毒控制理论。     

西花蓟马寄主选择性与寄主物理性状及次生物质的关系

为明确西花蓟马对6种蔬菜寄主(甘蓝、莴苣、黄瓜、茄子、芹菜和大蒜)的选择性,及其与寄主物理性状(颜色、叶毛数和叶片厚度)和次生物质(单宁酸、黄酮和总酚)的关系,采用非自由选择法,以每雌每天所孵化的子代若虫数为选择性指标,探讨其与寄主叶毛数、叶片厚度和次生物质的关系;采用叶碟法观察西花蓟马成虫对颜色的自由选择。以每雌每天所孵化的子代若虫数为选择性指标表明,西花蓟马对6种寄主的选择性,从大到小依次为甘蓝>莴苣>黄瓜=茄子>芹菜=大蒜,而西花蓟马对叶片颜色的选择趋性为甘蓝>莴苣>芹菜>黄瓜>大蒜>茄子。相关分析表明,西花蓟马的选择性与寄主的叶毛数(R=-0.073,p=0.890)、叶片厚度(R=-0.683,p=0.135)和总酚含量(R=-0.023,p=0.966)不存在显著相关关系,与寄主的单宁酸和黄酮的含量存在显著的负相关关系,相关系数分别为-0.828(p=0.042)和-0.820(p=0.046)。单宁酸和黄酮的含量对西花蓟马的寄主选择性有很大的影响,其含量越高越不利于西花蓟马的寄主选择。     

Identification of an RNA silencing suppressor encoded by Grapevine leafroll-associated virus 3

GLRaV-3, a member of the Closteroviridae family and type member of the genus Ampelovirus, is involved in the grapevine leafroll disease. Until now no RNA silencing suppressor has been found among viruses of this genus, contrary to what happens with a large number of other viral genera. In the sister genus Closterovirus, RNA silencing suppressors are present in the 3’ end of the genome and have molecular weights close to 20 KDa. To test for RNA suppressing activity screening of p21, p19.6 and p19.7 proteins, coded for in an analogous genomic location of the GLRaV-3 was undertaken. Only p19.7 revealed suppressor activity demonstrated in diverse silencing inducing systems. This suppressor is able to overcome strong silencing inducers and shares several properties with the BYV p21-like family of suppressors of the closteroviruses. This is the first report of an RNA silencing suppressor in the genus Ampelovirus.     

甜瓜黄斑病毒三亚分离物S RNA的分子特征

 甜瓜黄斑病毒（Melon yellow spot virus, MYSV）首次发生于日本,造成甜瓜和黄瓜的严重损失,Kato等系统地研究了病毒的传播方式、寄主范围、超微结构和基因组特征,认为MYSV应为番茄斑萎病毒属（Tospovirus）的1个新种［1,2］。2006年以来,台湾的西瓜［3］和黄瓜［4］上相继发现MYSV。2009年春季,古勤生在海南三亚的保护地甜瓜上发现一种新发生的病毒病,发病率30%~100%,病株出现系统性黄化坏死斑点,为MYSV侵染的典型症状,结合分子检测结果判定病原为MYSV。     

侵染四川辣椒的番茄斑萎病毒和辣椒轻斑驳病毒的小RNA测序检测及鉴定

 调查发现四川省汶川县当地辣椒的病毒病严重且症状多样,病样粗提液摩擦接种辣椒、矮牵牛和三生烟,出现辣椒系统性花叶焦枯和茎尖坏死,指示植物表现局部枯斑。对3个不同症状的病果进行sRNA深度测序鉴定,发现均含有番茄斑萎病毒(Tomato spotted wilt virus,TSWV)和辣椒轻斑驳病毒(Pepper mild mottle virus,PMMoV)。通过RT-PCR技术进行验证,结果显示所有病样的果皮和部分新鲜种子以及回接寄主的病叶均检测到TSWV和PMMoV,表明该地辣椒病毒病是由TSWV和PMMoV复合侵染引起。这是TSWV侵染四川辣椒的首次报道。分别基于TSWV N基因序列和PMMoV CP基因序列构建系统发育树,汶川分离物TSWV-WC(MK468469)与贵州分离物(KP684518)亲缘关系最近,PMMoV-WC(MK408614)与北京分离物(AY859497)亲缘关系最近。推测该地辣椒病毒病可能与品种引进有关。     

Biological and genetic characterization of carrot red leaf virus and its associated virus/RNA isolated from carrots in Hokkaido,Japan

Carrot motley dwarf (CMD) is caused by mixed infection of carrot red leaf virus (CtRLV) with either carrot mottle virus (CMoV) or carrot mottle mimic virus, and additional infection with CtRLV-associated RNA (CtRLVaRNA). Here, the author investigated the viruses or virus-like RNA isolated from carrots with reddening symptoms in Hokkaido, the northern island of Japan. Three types of infections were mainly detected: single infection with CtRLV, which was most prevalent; double infection with CtRLV and CMoV; and triple infection with CtRLV, CMoV, and CtRLVaRNA. Fields with the three agents were severely affected, with diseased plants showing mottling, whereas in fields where disease incidence was low and sporadic, CtRLV was often found alone in plants with mild symptoms. Inoculation tests using carrot plants showed that CMoV enhanced disease severity, and the RNA accumulation of CtRLV. However, in the presence of CtRLVaRNA (+ CMoV), distinct symptoms such as systemic mottling and stunting developed, while the enhancement of CtRLV accumulation was abolished. These results imply that CtRLVaRNA (+ CMoV) antagonizes CtRLV despite its dependence on CtRLV for aphid transmission, and that mixed infection with CtRLVaRNA is involved in the development of the conspicuous mottling. All agents detected in Hokkaido were very similar to European and American isolates in terms of their genomic sequences and host range. This represents the first report of CMD in Japan, and provides further information on the genetic and biological properties of CMD-associated agents, as well as the aetiology of the disease.     

侵染梨的苹果茎痘病毒基因组序列及小RNA分析

苹果茎痘病毒(Apple stem pitting virus,ASPV)是危害梨(Pyrus spp.)和苹果(Malus spp.)的重要病毒。本研究采用小RNA深度测序技术获得了ASPV基因组的部分序列,在此基础上设计引物对该病毒基因组进行RT-PCR扩增,通过序列拼接得到1个来源于玉露香(Yuluxiang)梨的ASPV分离物(YLX)长度为9 291个核苷酸(nt)(不包括基因组5'末端约30个核苷酸)的基因组序列,该序列与已报道的13个ASPV分离物的基因组核苷酸序列相似性为71.6%~80.7%,与多个来自苹果的ASPV分离物系统进化关系较近。首次分析了来源于ASPV基因组的干扰性小RNA(siRNA),发现来源于ASPV基因组链和互补链的siRNA长度均以21 nt和22 nt为主,siRNA的5'端具有一定的碱基偏好性。本研究结果为深入了解ASPV的分子特性提供了重要信息。     

昆虫视觉在寄主寻找及定位过程中的作用

昆虫与寄主植物相互作用的研究一直是生态学研究的重要问题,在过去的几十年中一直以化学生态学为主导,昆虫视觉在寄主寻找与定位过程中的功能研究很少。随着试验技术与观测手段的不断提高,尤其是昆虫视网膜电位测定技术的发展,为昆虫视觉功能研究提供了新手段和新技术。本文阐述了昆虫视觉的概念与内涵,分析了昆虫视觉的研究现状及目前对昆虫视觉功能的认识误区,总结了昆虫视觉在寄主植物寻找过程中的作用:包括昆虫视觉的光谱学响应,对寄主植物形态刺激、寄主分布及农业景观的反应,并介绍了视网膜电位技术在昆虫视觉功能研究中的应用。本文认为将来的昆虫与植物关系的研究应综合考虑视觉和嗅觉的作用,昆虫视觉功能的研究应与化学信息通讯研究同样受到重视。昆虫视觉在寄主寻找、定位过程中的作用和功能将会成为昆虫-植物关系研究中一个非常具有前景的领域。