Evidence for plant viruses in the region of Argentina Islands, Antarctica

This work focused on the assessment of plant virus occurrence among primitive and higher plants in the Antarctic region. Sampling occurred during two seasons (2004/5 and 2005/6) at the Ukrainian Antarctic Station 'Academician Vernadskiy' positioned on Argentina Islands. Collected plant samples of four moss genera (Polytrichum, Plagiatecium, Sanionia and Barbilophozia) and one higher monocot plant species, Deschampsia antarctica, were further subjected to enzyme-linked immunosorbent assay to test for the presence of common plant viruses. Surprisingly, samples of Barbilophozia and Polytrichum mosses were found to contain antigens of viruses from the genus Tobamovirus, Tobacco mosaic virus and Cucumber green mottle mosaic virus, which normally parasitize angiosperms. By contrast, samples of the monocot Deschampsia antarctica were positive for viruses typically infecting dicots: Cucumber green mottle mosaic virus, Cucumber mosaic virus and Tomato spotted wilt virus. Serological data for Deschampsia antarctica were supported in part by transmission electron microscopy observations and bioassay results. The results demonstrate comparatively high diversity of plant viruses detected in Antarctica; the results also raise questions of virus specificity and host susceptibility, as the detected viruses normally infect dicotyledonous plants. However, the means of plant virus emergence in the region remain elusive and are discussed.     

植物病毒病媒介昆虫的传毒特性和机制研究进展

植物病毒病是农作物的“癌症”, 至今缺少有效的防治方法。目前已知80%的植物病毒病依赖于媒介昆虫传播, 而媒介昆虫对植物病毒的传播是一个昆虫、 病毒、 寄主植物互作的过程, 历经获毒、 持毒和传毒等多个阶段, 昆虫体内一系列病毒受体或蛋白参与了这个过程。昆虫传播病毒的方式有口针携带式、 前肠保留式和体内循环式3类, 它们各自对应的持久性为非持久性、 半持久性和持久性, 不同昆虫获取这3类病毒的获毒时间、 在体内存留位置和传毒时间也各不相同。 这个过程受到媒介昆虫的性别及龄期、 寄主植物、 环境条件、 昆虫体内共生菌等多种因素的影响。与之相关的蛋白主要有病毒衣壳蛋白(CP)、 次要衣壳蛋白（CPm）、 GroEL蛋白、 辅助因子(HC)和下颚口针蛋白等。近年来对植物病毒基因组的研究也取得了很大的进展, 对昆虫传毒机制的研究正受到越来越广泛的关注。本文综述了近年来该领域内的相关研究进展, 包括昆虫传播植物病毒的传毒方式、 影响传毒效率的因素、 传毒机制特别是昆虫体内与病毒传播可能相关的受体等。     

Monitoring exposure to avian influenza viruses in wild mammals

• 1 Avian influenza (AI) viruses primarily circulate in wild waterfowl populations and are occasionally transmitted to domestic poultry flocks. However, the possible roles of other wildlife species, such as wild mammals, in AI virus ecology have not been adequately addressed.
• 2 Due to their habitat and behaviour, many wild mammals may be capable of transmitting pathogens among wild and domestic populations. Exposure to AI viruses has been reported in an array of wild and domestic animals. The presence of wild mammals on farms has been identified as a risk factor for at least one poultry AI outbreak in North America. These reports suggest the need for seroprevalence studies examining the exposure of wild mammals to AI viruses.
• 3 Serological tests are routinely used to assess domestic poultry, domestic swine and human exposure to influenza A viruses, but these tests have not been validated for use in wild mammals. As such, some of these protocols may require adjustments or may be inappropriate for use in serology testing of wild mammals. Herein, we review these serological techniques and evaluate their potential usefulness in AI surveillance of wild mammals. We call for care to be taken when applying serological tests outside their original area of validation, and for continued assay verification for multiple species and virus strains.

     

北京地区六种蜜蜂病毒病的流行病学研究

【目的】对蜜蜂的6种病毒:以色列急性麻痹病毒(Israeli acute paralysis virus,IAPV)、残翅病毒(Deformed wing virus,DWV)、囊状幼虫病病毒(Sacbrood virus,SBV)、急性蜜蜂麻痹病毒(Acute bee paralysis virus,ABPV)、黑蜂王台病毒(Black queen cell virus,BQCV)、慢性麻痹病毒(Chronic bee paralysis virus,CBPV)在北京地区的流行情况进行调查,以期为该地区蜜蜂病毒病的防控提供一定的理论依据。【方法】应用多重RT-PCR法确定上述6种病毒在该地区的感染情况,并通过序列分析确定特异性。【结果】在所有检测样本中均未检测到急性麻痹病病毒和慢性麻痹病病毒,感染率最高的是以色列急性麻痹病毒,其次是残翅病毒。检测的样本普遍存在混合感染。【结论】以色列急性麻痹病毒、残翅病毒、囊状幼虫病病毒、黑蜂王台病毒4种病毒可能在北京地区广泛分布。     

Transmission of plant viruses by fungi

The evidence for the mechanisms involved in virus transmission by fungi is reviewed in relation to the non-persistent and persistent categories usually recognised. Non-persistent transmission by Olpidium spp. has been little studied in the last 20 years, but appears to depend on adsorption of virus to the outside of the fungal zoospores. This seems to be under the genetic control of both the virus (via its coat protein) and the vector. Such viruses are not transmitted in the fungal resting spores. The route by which the virus is transferred from the vector to the host may involve uptake into the zoospore but this deserves further study. Persistent transmission by Olpidium, Polymyxa and Spongospora spp. is less well characterised. Some of the evidence used for its support is inconclusive. The viruses are probably always carried inside zoospores, and they also persist in the fungal resting spores. Transmission depends on the genome of the vector and the virus, but not exclusively on the virus coat protein.     

Host factors against plant viruses

Plant virus genome replication and movement is dependent on host resources and factors. However, plants respond to virus infection through several mechanisms, such as autophagy, ubiquitination, mRNA decay and gene silencing, that target viral components. Viral factors work in synchrony with pro-viral host factors during the infection cycle and are targeted by antiviral responses. Accordingly, establishment of virus infection is genetically determined by the availability of the pro-viral factors necessary for genome replication and movement, and by the balance between plant defence and viral suppression of defence responses. Sequential requirement of pro-viral factors and the antagonistic activity of antiviral factors suggest a two-step model to explain plant–virus interactions. At each step of the infection process, host factors with antiviral activity have been identified. Here we review our current understanding of host factors with antiviral activity against plant viruses.     

RNA viruses in the sea

Viruses are ubiquitous in the sea and appear to outnumber all other forms of marine life by at least an order of magnitude. Through selective infection, viruses influence nutrient cycling, community structure, and evolution in the ocean. Over the past 20 years we have learned a great deal about the diversity and ecology of the viruses that constitute the marine virioplankton, but until recently the emphasis has been on DNA viruses. Along with expanding knowledge about RNA viruses that infect important marine animals, recent isolations of RNA viruses that infect single-celled eukaryotes and molecular analyses of the RNA virioplankton have revealed that marine RNA viruses are novel, widespread, and genetically diverse. Discoveries in marine RNA virology are broadening our understanding of the biology, ecology, and evolution of viruses, and the epidemiology of viral diseases, but there is still much that we need to learn about the ecology and diversity of RNA viruses before we can fully appreciate their contributions to the dynamics of marine ecosystems. As a step toward making sense of how RNA viruses contribute to the extraordinary viral diversity in the sea, we summarize in this review what is currently known about RNA viruses that infect marine organisms.     

Approaches of the diagnosis of hepatitis viruses

Hepatitis virus infection occurs in close to a billion people worldwide at some point in their lifetimes. Hepatitis B and C viruses together account for infections in half a billion people and are considered the most carcinogenic of any known biological agent. The diagnostic approaches to detect hepatitis viruses are discussed.     

Susceptibility of endothelial cells derived from different blood vessels to common viruses

Summary We examined whether endothelial cells derived from different blood vessels vary in their susceptibility to viral infection. Five common viral pathogens of humans (herpes simplex 1, measles, mumps, echo 9, and coxsackie B4 viruses) were evaluated for growth in endothelial cells derived from bovine fetal pulmonary artery thoracic aorta, and vena cava. All five viruses replicated in each type of endothelial cell. There were apparent differences in the quantities of measles and mumps viruses produced in pulmonary artery endothelium compared with thoracic aorta and vena cava when endothelial cells were obtained from different animals. However when pulmonary artery endothelial cells were compared with vena cava cells from the same animal, growth of each virus was similar in the two cell types. Four of the viruses replicated in the various endothelial cells without producing appreciable changes in cell morphology. These results indicate that endothelial cells from different blood vessels are equally susceptible to the human viruses evaluated, and that viral replication can occur without major alteration in cell morphology. Endothelial cells could serve as permissive cells permitting viruses to leave the circulation and initiate infection in adjacent tissues, including subendothelial smooth muscle cells. This work was supported by Public Health Service grants HL28220, HL 29492, and HL 24914 from the National Heart, Lung and Blood Institute, Bethesda, MD.     

Occurrence and relative incidence of viruses infecting papaya in Venezuela

A survey of the main papaya (Carica papaya L.) production fields in Venezuela during 1997, indicated that crops were heavily affected with various virus‐like symptoms. A total of 745 samples from papaya plants showing symptoms suggestive of virus infection were collected and analysed using electron microscopy and enzyme‐linked immunosorbent assay (ELISA). Papaya ringspot virus (PRSV) and Papaya mild yellowing virus (PMYV) were the most frequently found viruses, which also occurred, in mixed infections. Rhabdovirus‐like particles were found only in samples collected in Distrito Federal (D.F). Papaya mosaic virus (papMV) and Tomato spotted wild virus (TSW V) were not detected during the survey.     

A comparison of serological techniques for detecting and identifying honeybee viruses

The sensitivity and specificity of conventional Ouchterlony gel-diffusion, immuno-osmoelectrophoresis (IO), immune serum electron microscopy (ISEM), “decoration,” radioimmunoassay (RIA), and enzyme-linked immunosorbent assay (ELISA) tests for detecting black queen cell virus (BQCV), chronic bee paralysis virus (CBPV), Kashmir bee virus (KBV), and sacbrood virus (SBV) particles in extracts of diseased honeybees were compared. A “slow” ISEM method detected virus particles in extracts of individuals or groups of individuals diluted to 10^?3 and 10^?4, respectively, whereas the IO method and a “fast” ISEM method using protein A were one-tenth as sensitive, and Ouchterlony gel-diffusion tests were only one-thousandth as sensitive. Using the antibody “decoration” technique, mixtures of serologically unrelated virus particles could be resolved. RIA and ELISA were found to be one thousand times more sensitive than ISEM in detecting the particles of BQCV, CBPV, KBV, and SBV; however, nonspecific reactions occurred when using RIA with very dilute particle suspensions, and this made dilution endpoints difficult to assess, but this did not occur when using the ELISA method. There was little difference in the effectiveness of rabbit or hen antisera in the tests, except when protein A was used as it does not combine with hen antibodies.     

Overlooking the smallest matter: viruses impact biological invasions

Parasites and pathogens have recently received considerable attention for their ability to affect biological invasions, however, researchers have largely overlooked the distinct role of viruses afforded by their unique ability to rapidly mutate and adapt to new hosts. With high mutation and genomic substitution rates, RNA and single‐stranded DNA (ssDNA) viruses may be important constituents of invaded ecosystems, and could potentially behave quite differently from other pathogens. We review evidence suggesting that rapidly evolving viruses impact invasion dynamics in three key ways: (1) Rapidly evolving viruses may prevent exotic species from establishing self‐sustaining populations. (2) Viruses can cause population collapses of exotic species in the introduced range. (3) Viruses can alter the consequences of biological invasions by causing population collapses and extinctions of native species. The ubiquity and frequent host shifting of viruses make their ability to influence invasion events likely. Eludicating the viral ecology of biological invasions will lead to an improved understanding of the causes and consequences of invasions, particularly as regards establishment success and changes to community structure that cannot be explained by direct interspecific interactions among native and exotic species.     

Gene amplification and expression by RNA viruses and potential for further application to plant gene transfer

The great majority of plant viruses encapsidate messenger-sense ssRNA and have no natural DNA phase in their life cycle. Despite their RNA nature, essentially any desired change can be introduced into such genomes by using recombinant DNA techniques with suitably constructed, expressible viral cDNA clones. For some viruses such as brome mosaic virus, these methods have been used to define the sequences controlling RNA-directed genomic RNA replication and the expression of internal genes via subgenomic mRNAs. The results suggest a surprising degree of genetic flexibility, which appears to be reflected in the varied gene complements and genetic organizations of presumably related plant and animal RNA viruses sharing conserved replication genes. Foreign genes inserted in such RNA virus genomes can be amplified and expressed to a high level in transfected plant cells. In addition to the potential use of such viruses as episomal expression vectors, it should be possible to couple the viral pathways of RNA-dependent RNA synthesis to amplify and to further regulate the expression of genes transformed into plant chromosomes.     

Association of soybean root mycoflora with root modulation, root necrosis and plant fresh weight

Fungi were isolated from soybean plants in ten fields in south-west France. Correspondence analysis (COA) was used to find associations among taxa (species, genera, groups) and sampling units (i.e. one field at one sampling date). The first axis of the COA demonstrated a dominant sampling date effect; the second indicated an association among certain sampling units and specific taxa. Regression analysis of COA coordinate values indicated that fields with high relative isolation frequencies of Fusarium spp., F. oxysporum and ‘other species’ (mostly Chaetomium spp. and sterile fungi) were characterised by greater plant fresh weight and nodule number and lower ratings for root necrosis. Cylindrocarpon spp., Cephalosporium spp. and F. solanihad high relative isolation frequencies in fields with lower plant weight, lower nodule number and higher root necrosis ratings. The relative importance of fungal taxa was also related to soil type.     

RNA viruses as vectors for the expression of heterologous proteins

RNA viruses comprise a wide variety of infectious agents, some of which are the cause of disease in humans, animals, and plants. Recombinant DNA technology is now making it feasible to modify these genomes and engineer them to express heterologous proteins. Several different schemes are being employed that depend on the genome organization of the virus and on the strategy of replication of the particular virus. Several different examples are illustrated and potential uses as well as possible problems are discussed. In the future reverse genetics may convert some of these viruses from agents of disease to agents of cure.     

Perspectives on intracellular perception of plant viruses

The intracellular nucleotide-binding domain leucine-rich repeat (NLR) class of immune receptors plays an important role in plant viral defence. Plant NLRs recognize viruses through direct or indirect association of viral proteins, triggering a downstream defence response to prevent viral proliferation and movement within the plant. This review focuses on current knowledge of intracellular perception of viral pathogens, activation of NLRs and the downstream signalling components involved in plant viral defence.     

A general method to quantify quasi-equivalence in icosahedral viruses

A quantitative, atom-based, method is described for comparing protein subunit interfaces in icosahedral virus capsids with quasi-equivalent surface lattices. An integrated, normalized value (between 0 and 1) based on equivalent residue contacts (Q-score) is computed for every pair of subunit interactions and scores that are significantly above zero readily identify interfaces that are quasi-equivalent to each other. The method was applied to all quasi-equivalent capsid structures (T=3, 4, 7 and 13) in the Protein Data Bank and the Q-scores were interpreted in terms of their structural underpinnings. The analysis allowed classification of T=3 structures into three groups with architectures that resemble different polyhedra with icosahedral symmetry. The preference of subunits to form dimers in the T=4 human Hepatitis B virus capsid (HBV) was clearly reflected in high Q-scores of quasi-equivalent dimers. Interesting differences between the classical T=7 capsid and polyoma-like capsids were also identified. Application of the method to the outer-shell of the T=13 Blue tongue virus core (BTVC) highlighted the modest distortion between the interfaces of the general trimers and the strict trimers of VP7 subunits. Furthermore, the method identified the quasi 2-fold symmetry in the inner capsids of the BTV and reovirus cores. The results show that the Q-scores of various quasi-symmetries represent a "fingerprint" for a particular virus capsid architecture allowing particle classification into groups based on their underlying structural and geometric features.     

Biotechnology of virus eradication and plant vaccination in phytobiome context

A plant’s associated biota plays an integral role in its metabolism, nutrient uptake, stress tolerance, pathogen resistance and other physiological processes. Although a virome is an integral part of the phytobiome, a major contradiction exists between the holobiont approach and the practical need to eradicate pathogens from agricultural crops. In this review, we discuss grapevine virus control, but the issue is also relevant for numerous other crops, including potato, cassava, citrus, cacao and other species. Grapevine diseases, especially viral infections, cause main crop losses. Methods have been developed to eliminate viruses and other microorganisms from plant material, but elimination of viruses from plant material does not guarantee protection from future reinfection. Elimination of viral particles in plant material could create genetic drift, leading in turn to an increase in the occurrence of pathogenic strains of viruses. A possible solution may be a combination of virus elimination and plant propagation in tissue culture with in vitro vaccination. In this context, possible strategies to control viral infections include application of plant resistance inducers, cross protection and vaccination using siRNA, dsRNA and viral replicons during plant ‘cleaning’ and in vitro propagation. The experience and knowledge accumulated in human immunization can help plant scientists to develop and employ new methods of protection, leading to more sustainable and healthier crop production.     

Incidence and Distribution of Grapevine Leafroll-associated viruses in Tunisian Vineyards

Surveys were carried out in Tunisian table grape vineyards for assessing the occurrence and distribution of grapevine leafroll-associated viruses (GLRaVs). Leafroll symptoms were commonly observed in most of the surveyed vineyards. Samples were randomly collected from 712 individual vines for laboratory testing. Enzyme-linked immunosorbent assay (ELISA) tests showed that 81.5% of the vines were infected by one (35.7%) or more (45.8%) viruses. GLRaV-3 was the most widespread virus (76.3%), followed by GLRaV-5 (38.5 %), GLRaV-6 (13.2%), GLRaV-1 (9.1%), GLRaV-2 (6.3%), and GLRaV-7 (0.9%). GLRaV-3 and GLRaV–5, two mealybug-transmissible Ampeloviruses, were present in mixture in 35.9% of samples. The highest infection rate was found in Cape Bon region (81.7 %), where cv. Italia had an infection rate of 79.5%. Superior seedless, the main cultivar in Sidi Bouzid, had 75% infection. GLRaV-6 and -7 were detected for the first time in Tunisia.