Special Issue "Plant Viruses"

Guest Editor
Prof. Dr. Henryk Czosnek
Institute of Plant Sciences and Genetics in Agriculture; Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel
Website: http://departments.agri.huji.ac.il/plantscience/staff-eng/czosnek.html
E-Mail: czosnek@agri.huji.ac.il
Phone: + 972 8 9489249
Fax: + 972 8 9468265
Interests: genetic engineering; molecular genetics; plant genetic engineering; biotechnology in agriculture; aspects of plant molecular biology

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• classification of plant viruses
• diseases
• symptoms
• and damages to plants
• morphology of virions and structure of genome
• detection methods
• origin
• evolution and phylogeny
• transmission and vectors
• replication and expression
• plant-virus interactions
• plant defense
• resistance genes
• silencing of viruses

Type of Paper: Article
Title: First report of Cowpea mild mottle carlavirus on Yardlong Bean (Vigna unguiculata subsp. sesquipedalis) in Venezuela
Authors: Miriam Brito¹, Thaly Fernández-Rodríguez², Mario José Garrido¹, Alexander Mejías³, Mirtha Romano³ and Edgloris Marys^3,*
Affiliations: ¹ Universidad Central de Venezuela, Facultad de Agronomía, Instituto de Botánica Agrícola. Laboratorio de Virología Vegetal y Bacterias Fitopatógenas. Apartado 4579, Maracay 2101-A, Venezuela; E-mails: britom@agr.ucv.ve (Miriam Brito); mariojgarrido@gmail.com (Mario José Garrido); ² RLP AgroScience GmbH, AlPlanta-Institute for Plant Research, Breitenweg 71, D 67435 Neustadt, Germany; E-mail: thaly.fernandez rodriguez@agroscience.rlp.de (Thaly Fernández-Rodríguez);³ Instituto Venezolano de Investigaciones Científicas (IVIC), Centro de Microbiología y Biología Celular, Laboratorio de Biotecnología y Virología Vegetal, Apartado Postal 20632, Caracas 1020-A, Venezuela; E-mails; amejias@ivic.gob.ve (Alexander Mejías); mirtha.romano@gmail.com (Mirtha Romano); eemarys@ivic.gob.ve (Edgloris Marys);*   Author to whom correspondence should be addressed; E-mail: eemarys@ivic.gob.ve (Edgloris Marys); Tel.:+58-212-5041500; Fax: +58-212-5041382
Abstract: Yardlong bean (Vigna unguiculata subsp. sesquipedalis) plants with virus-like systemic mottling and leaf distortion were observed in both experimental and commercial fields in Aragua State, Venezuela. Symptomatic leaves were shown to contain carlavirus-like particles. RT-PCR analysis with carlavirus-specific primers was positive in all tested samples. Nucleotide sequences of the obtained amplicons showed 84-74% similarity to corresponding sequences of Cowpea mild mottle virus (CPMMV) isolates deposited in the GenBank database. This is the first report of CPMMV in Venezuela and is thought to be the first report of CPMMV infecting yardlong bean.
Keywords: Vigna unguiculata, sesquipedalis, yardlong bean, Cowpea mild mottle carlavirus, CPMMV, diagnosis, RT-PCR, Venezuela

Type of Paper: Article
Title: Base Composition and Translational Seclection are Insufficient to Explain Codon Usage Bias in Plant Viruses
Authors: Daniel J. Cardinale, Kate DeRosa and Siobain Duffy *
Affiliations: Department of Ecology, Evolution, and Natural Resources, School of Environmental and Biological Sciences, Rutgers, The State University of New Jersey, 14 College Farm Road, New Brunswick, NJ 08901; E-Mails: daniel.j.cardinale@gmail.com (D.C.), klderosa@eden.rutgers.edu (K.D.), duffy@aesop.rutgers.edu (S.D.); * Author to whom correspondence should be addressed; E-Mail: duffy@aesop.rutgers.edu (S.D.);Tel.: +1-848-932-6299; Fax: +1-848-932-0312.
Abstract: Viral codon usage bias may be the product of a number of synergistic or antagonistic factors, including genomic nucleotide composition, translational selection, genomic architecture, and mutational or repair biases. Most studies of viral codon bias evaluate only the relative importance of genomic base composition and translational selection, ignoring other possible factors. We analyzed the codon preferences of ssRNA (luteoviruses and potyviruses) and ssDNA plant viruses (geminiviruses) that infect translationally distinct monocot and dicot hosts. We found that neither genomic base composition nor translational selection satisfactorily explains their codon usage biases. Furthermore, we observed a strong relationship between the codon preferences of viruses in the same family or genus, regardless of host or genomic nucleotide content. Our results suggest that analyzing codon bias as either due to base composition or translational selection is a false dichotomy that obscures the role of other factors. Constraints such as genomic architecture and secondary structure can and do influence codon usage in plant viruses, and likely in viruses of other hosts.
Keywords: synonymous codon usage; translational selection; genomic content; mutational bias

Type of Paper: Review
Title: Tobacco Rattle virus -based Post Transcriptional Gene Silencing (TRV-PTGS) to discover host genes involved in the infection by the Tomato yellow leaf curl virus family and in the establishment of resistance to the virus
Authors: Czosnek , H. ¹, Eybishtz, A. ¹,  Sade, D. ¹,  Bejarano, E. ²,  Rosas-Díaz, T. ², and Lozano-Duran, R. ²
Affiliations: ¹ Institute of Plant Science and genetics in Agriculture, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel.
² Departamento de Biología Celular, Genética y Fisiología, Instituto de Hortofruticultura Subtropical y Mediterranea (UMA), Universidad de Málaga, Campus de Teatinos. 29071 Málaga, Spain.
Abstract: We have proposed to use a TRV-VIGS RNAi-based screen to uncover the genes and gene networks underlying Tomato yellow leaf curl virus (TYLCV) resistance in tomato and identify host factor involved in the viral infection. As a first approach genes preferentially expressed in resistant plants (compared to susceptible), and up-regulated upon TYLCV infection were selected to determine if silencing the genes will lead to the collapse of resistance or induce resistance in sensitive lines. To decipher the networks of resistance we have used two inbred tomato lines: one was resistant (R), the other was susceptible (S) to the virus. Sixty nine genes preferentially expressed in R tomatoes were identified by differential screening of cDNA libraries from infected and uninfected R and S tomato plants. From the twenty genes silenced so far, eight answered to this criterion: their silencing led to the total collapse of resistance. The hierarchy of the resistance signalling pathway is being deciphered by silencing one gene at a time and measuring the transcriptional activity of the others. In addition a home-designed oligonucleotide microarray representing all the genes discovered so far in tomato has been used to analyze gene cross-talk upon infection of R and S lines and upon silencing of a single gene. In a second approach we explore the potential of 2IRGFP Nicotiana benthamiana plants in combination with VIGS to identify host genes with a role in geminivirus infection. We have achieved an accurate description of the dynamics of viral replication by monitoring GFP expression in both space and time, explored the limitations of the strategy to be used in a reverse-genetics screening, and unveiled the effect of silencing selected N. benthamiana genes. Using this strategy, we have identified eighteen genes involved in several cellular processes whose silencing alters geminivirus infection: with a potential anti-viral effect, are required for a full infection. Hence, our results provide new insights into the molecular mechanisms underlying geminivirus resistance and infections, and at the same time reveal the VIGS system as a powerful tool for functional reverse genetics studies.

Type of Paper: Review
Title: Antiviral Defense Roles of Plant Latex
Authors: David S. Buss *, Silas P. Rodrigues and Patricia M. B. Fernandes
Affiliation: Universidade Federal do Espirito Santo, Av. Marechal Campos, 1468 Vitória, ES, Brazil, 29040-090;  E-Mails: dsbuss@gmail.com, pmbfernandes@gmail.com; * Author to whom correspondence should be addressed; E-Mail: dsbuss@gmail.com; Tel. 55.27. 3335-7348; Fax. 55.27.2122-7275
Abstract: At least 20,000 plant species produce latex, a capacity that appears to have evolved independently on a number of occasions. Latex is stored under pressure in specialized tissues called laticifers and is exuded on wounding, leading to the assumption that it has a role in securing the plant after mechanical injury. In addition, a defensive effect against insect herbivores and fungal infection has been well established. Latex also appears to be protective against viruses, and laticifers a hostile environment for virus colonization. Only one example of successful colonization has been reported, Papaya meleira virus (PMeV), although there are indications that other species may be capable of establishment. In this review, we summarize studies that support the idea of laticifers/latex as a plant defense system against viruses. The latex components involved in this natural protective role represent a promising natural source of new anti-viral molecules in medicine.
Keywords: latex; laticifer; virus; plant

Type of Paper: Review
Title: The Role of Bacterial Chaperones in the Circulative Transmission of Plant Viruses by Insect Vectors
Author: Murad Ghanim
Affiliation: Department of Entomology, The Volcani Center, Bet Dagan, 50250, Israel
Tentative Abstract: Persistent circulative transmission of plant viruses involves complex interactions between the virus and its insect vector. Several studies have shown that insect vector proteins could be involved in the passage and the transmission of the virus. Interestingly, among those are proteins which are expressed by bacterial endosymbionts that reside in the insect vector. Thus far, that transmission of two plant viruses that belong to different virus genera was shown to be facilitated by a protein called GroEL. This protein is a bacterial chaperone and was shown to be implicated in the transmission of Potato leafroll virus (PLRV) by the green peach aphid Myzus persicae, and the transmission of Tomato yellow leaf curl virus (TYLCV) by the sweetpotato whitefly Bemisia tabaci. These tri-trophic levels of interactions and their possible role on an evolutionary scale for benefitting the organisms involved will be reviewed.

Type of Paper: Article
Title: The Use of two Green Fluorescent Protein-Expressing Bipartite Begomoviruses and their Pseudorecombinants to Investigate Cell-to-Cell and long-distance Movement in Different Hosts and to Develop a Begomovirus gene-silencing Vector
Authors: Robert L. Gilbertson et al.
Affiliation: College of Biological Sciences (CBS), University of California, Davis, One Shields Avenue, Davis, CA 95616, USA; E-Mail: rlgilbertson@ucdavis.edu
Abstract: The bipartite begomoviruses (genus Begomovirus, family Geminiviridae), Bean dwarf mosaic virus (BDMV) and Tomato mottle virus (ToMoV), are closely related based on phylogenic analyses and their capacity to form highly infectious pseudorecombinants (PRs). Interestingly, the PRs formed between these viruses are asymmetric, with the ToMoV DNA-A (TA) and BDMV DNA-B (BB) PR highly infectious, and the reciprocal combination of BDMV DNA-A (BA) and ToMoV DNA-B (TB) poorly infectious. The TA and BA components were tagged with the (GFP) gene to generate TAG and BAG, respectively, and used to investigate the cell-to-cell and long distance movement of the parental viruses and their pseudorecombinants in Nicotiana benthamiana, common bean (Phaseolus vulgaris), and tomato (Lycopersicon esculentum) plants.  Following particle bombardment inoculation, all four viruses induced systemic symptoms in N. benthamiana and GFP expression was detected in inoculated and systemically infected leaves.  BDMV-GFP induced systemic symptoms and expressed GFP in common bean, the host to which BDMV is well-adapted, but BDMV-GFP was not infectious in tomato. In contrast, ToMoV-GFP induced mild or no symptoms and did not express GFP in tomato, the host to which ToMoV is well-adapted, and ToMoV-GFP was poorly infectious in common bean and expressed GFP only in inoculated hypocotyl tissues.  The PR TAG+BB induced severe symptoms and expressed GFP in common bean, whereas it induced a symptomless systemic infection in a small number of tomato plants, but did not express GFP.  In contrast, the BAG+TB PR induced a symptomless systemic infection with no GFP expression in a small number of tomato plants, and failed to systemically infect common bean. Taken together, these results are consistent with a key role of the DNA-B encoded proteins in host adaptation, and a role for the CP in systemic infection and symptom development, especially in hosts to which viruses are not well-adapted. In the case of ToMoV, the CP also was required for typical symptom development in tomato, which may reveal a more recent adaptation of ToMoV to tomato or a host-specific requirement of CP.  Thus, our results support the notion that host adaptation of bipartite begomoviruses involves factors from both DNA components. Finally, the TA component was used to generate a gene silencing vector (TA vector) in which the CP gene was deleted and a multiple cloning site inserted. Using particle bombardment inoculation, the TA vector carrying the GFP gene triggered systemic silencing of GFP expression in transgenic plants, and a co-bombardment assay was successfully developed to test for viral suppressors of gene silencing.

Type of Paper: Article
Title: Biological and Molecular Characterization of the Polish Zucchini Yellow Mosaic Virus Isolates
Authors: Beata Hasiów-Jaroszewska^*, Natalia Rymelska, Natasza Borodynko and Henryk Pospieszny
Affiliation: Department of Virology and Bacteriology, Institute of Plant Protection, National Research Institute, u. Wegorka 20, PL-60-318, Poland
* Corresponding author, E-mail: beatahasiow@tlen.pl
Abstract: The diversity of Zucchini yellow mosaic virus (ZYMV) was analyzed by the biological and genetic characterization of isolates collected from cucumber and zucchini plants in various regions of Poland. The isolates differed in their host range and symptoms induced by them on a series of plant species. In addition, the analysis of the genetic diversity of the coat protein (CP) revealed high level of nucleotide variability among the isolates. Comparison of the coat protein sequences of 70 isolates from different geographical regions worldwide revealed that the Polish isolates belong to different groups and they do not form a monophyletic cluster with European isolates. Interestingly, among the central European ZYMV isolates lower variability has been observed previously. The analysis of selection pressure using CP revealed two codons under positive selection. The recombination events between isolates analyzed were also identified. Our results indicate that specific isolates can spread rapidly to geographically adjacent areas but may not be directly related to isolates found in other neighboring countries.

Type of Paper: Article
Title: Deletions within the 3′ NTR of Alfalfa mosaic virus Subgenomic RNA4 do not Affect Replication of Chimeric Tobacco mosaic virus but Significantly Reduce its Encapsidation, Long-distance Movement and Virus Yield
Authors: Gourgopal Roy, Oleg Fedorkin, Masaaki Fujiki, Marina Skarjinskaia, Elisabeth Knapp, Shailaja Rabindran and Vidadi Yusibov
Affiliation: Fraunhofer USA Center for Molecular Biotechnology, 9 Innovation Way, Suite 200, Newark, DE 19711, USA. *Author to whom correspondence should be addressed. E-mail: vyusibov@fraunhofer-cmb.org. Tel: 1 302 369 3766. Fax: 1 302 369 8955.
Abstract: Alfalfa mosaic virus (AlMV) RNAs 1 and 2 with deletions in their 3′ non-translated regions (NTRs) have been previously shown to be encapsidated into virions by coat protein (CP) expressed from RNA3 (Vlot et al, 2001), indicating that the 3′ NTRs of RNAs 1 and 2 are not required for virion assembly. Here, we constructed various mutants by deleting sequences within the 3′ NTR of AlMV subgenomic (sg) RNA4 (same as of sgRNA3) and examined the effect of these deletions on replication and translation of chimeric Tobacco mosaic virus (TMV) expressing AlMV sgRNA4 from the TMV CP sg promoter (Av/A4 [Spitsin et al, 1999]) in tobacco protoplasts and Nicotiana benthamiana plants. While the Av/A4 mutants were as competent as the wild-type Av/A4 in RNA replication in protoplasts, their encapsidation, long-distance movement and virus yield varied significantly in N. benthamiana. These data suggest that the 3′ NTR of AlMV sgRNA4 contains potential elements necessary for virus encapsidation.
Keywords: Alfalfa mosaic virus; Tobacco mosaic virus; origin of assembly; subgenomic RNA; virus encapsidation