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1
Eiras, M. "VIROIDES, PEQUENOS RNAS PATOGÊNICOS CAPAZES DE REPLICAÇÃO AUTÔNOMA: MODELOS MOLECULARES PARA O ESTUDO DE INTERAÇÕES PATÓGENO-HOSPEDEIRO E EVOLUÇÃO." Arquivos do Instituto Biológico 77, no. 4 (December 2010): 751–58. http://dx.doi.org/10.1590/1808-1657v77p7512010.
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RESUMO Os viroides, apesar de serem constituídos por um pequeno RNA de fita simples, fortemente estruturado, circular, que não codifica proteínas, são capazes de se replicar de maneira autônoma em plantas superiores e causar doença interagindo diretamente com fatores do hospedeiro. Nesta revisão, serão apresentados e discutidos alguns dos mais recentes trabalhos envolvendo a interação de viroides com fatores do hospedeiro, incluindo aspectos relacionados à replicação, movimento e patogênese, além de suas características evolutivas. Nos últimos anos, alguns grupos de pesquisa têm se aventurado na busca por fatores do hospedeiro e mecanismos moleculares relacionados ao ciclo infeccioso dos viroides, tentando desvendar como esses pequenos RNAs interagem com o hospedeiro induzindo sintomas. Os viroides não codificam proteínas supressoras de silenciamento e, portanto, devem garantir sua existência utilizando estratégias baseadas em sua estrutura secundária, na compartimentalização em organelas, associação com fatores do hospedeiro e eficiência na replicação. A complexidade do ciclo infeccioso desses minúsculos RNAs indica que muitas interações desses patógenos com fatores do hospedeiro ainda devem ser identificadas.
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Moskalev, A. V., V. B. Sboychakov, A. V. Apchel, and N. V. Tsygan. "Вiological effects of viroids." Bulletin of the Russian Military Medical Academy 20, no. 2 (December 15, 2018): 209–14. http://dx.doi.org/10.17816/brmma12333.
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Possible potential microbial agents of a human which represent by ring highly complementary one-chained ribonucleic acid with an absent of protein coating, as for viruses containing a ribonucleic acid, are characterized. Pathogenic effects of viroids in comparison with viruses and defective viruses are considered. Intimate viroid’s mechanisms on a host cell are described. So viroids do not code any proteins, their action on a plant should be consequence of direct interaction of viroid’s ribonucleic acid and host cell’s contents. However the molecular mechanism by which viroids causes plants’ diseases still remains not completely determined. It is considered, that the first targets of viroid are the nucleic acids and proteins of the host cell. Genomes of some viroids contain areas complementary to some cellular RNA. In connection with it supposed, that disease begins because of inhibition of functions of these cellular ribonucleic acids or their cutting directed viroids by a ribonucleic acid. Pathogenicity of viroids can be also a result of mimicry at a molecular level. Because of features of structure or sequence nucleotides the viroid’s ribonucleic acid can replace by itself some cellular ribonucleic acids. In viroid’s pathogenesis also can be involved and an interference of ribonucleic acids. All this allows to assume, that viroids can become the reason of infectious diseases of the human.
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Ito, Takao, Hiroyuki Ieki, Katsumi Ozaki, Toru Iwanami, Kenji Nakahara, Tatsuji Hataya, Tsutae Ito, Masahiro Isaka, and Takeshi Kano. "Multiple Citrus Viroids in Citrus from Japan and Their Ability to Produce Exocortis-Like Symptoms in Citron." Phytopathology® 92, no. 5 (May 2002): 542–47. http://dx.doi.org/10.1094/phyto.2002.92.5.542.
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Sequential polyacrylamide gel electrophoresis analyses showed many viroid-like RNAs in samples collected from citrus trees in Japan. Reverse transcription polymerase chain reaction and sequencing analyses of the amplified fragments verified that they were derived from variants of six citrus viroids, Citrus exocortis viroid (CEVd), Citrus bent leaf viroid (CBLVd) including CVd-I-LSS (a distinct variant of CBLVd), Hop stunt viroid, Citrus viroid III, Citrus viroid IV, and Citrus viroid OS. The samples induced symptoms with variable severity in Arizona 861-S1 ‘Etrog’ citrons (Citrus medica L.) likely due to the varying accumulation patterns produced by the different viroids. Some of the symptoms caused by the samples harboring the citrus viroids other than CEVd were as severe as those caused by CEVd. Some source citrus trees showing the severe bark scaling characteristic of exocortis disease in trifoliate orange (Poncirus trifoliata (L.) Raf.) rootstocks contained only citrus viroids other than CEVd in complex. This indicates that certain exocortis-like diseases in Japan were caused by some combination of citrus viroids not including CEVd.
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Kunta, Madhurababu, J. V. da Graça, and Mani Skaria. "Molecular Detection and Prevalence of Citrus Viroids in Texas." HortScience 42, no. 3 (June 2007): 600–604. http://dx.doi.org/10.21273/hortsci.42.3.600.
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Viroids are graft- or mechanically transmissible agents, disseminated through budding. Biological indexing of commercially important citrus cultivars grown in the Lower Rio Grande Valley of Texas showed that many are infected with citrus viroids. Most of these trees carried more than one viroid. In most cases, the infected trees are asymptomatic carriers because sour orange, the predominant rootstock used in Texas, does not show symptoms of viroid infection. Detection of viroids through biological indexing on sensitive indicator plants followed by sequential polyacrylamide gel electrophoresis (sPAGE) is the gold standard but is time-consuming and requires plants to be kept at optimum conditions. A conditional use of reverse transcriptase–polymerase chain reaction (RT-PCR) provides an efficient and alternative detection of viroids for use in the Texas virus-free citrus budwood certification program. RT-PCR could be useful in Texas to help expedite the evaluation for the presence of viroids before conducting the final biologic indexing. Using RT-PCR, we could detect, clone, and sequence full-length viroids of Citrus exocortis viroid (CEVd), Hop stunt viroid (HSVd) (both cachexia and noncachexia variants), Citrus viroid-III (Citrus dwarfing viroid), and Citrus viroid-IV (Citrus bark cracking viroid) from a collection of viroid-inoculated grapefruit plants. The source plants were previously shown to be viroid-infected by biological indexing on Etrog citron plants. Based on our results, RT-PCR can be a conditional substitute for biological indexing of mother trees in foundation blocks and shoot tip-grafted trees in the virus-free budwood program. A positive RT-PCR result has a serendipitous value because those trees can be discarded from the pool before expensive biological indexing.
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Barbosa, C. J., J. A. Pina, J. Pérez-Panadés, L. Bernad, P. Serra, L. Navarro, and N. Duran-Vila. "Mechanical Transmission of Citrus Viroids." Plant Disease 89, no. 7 (July 2005): 749–54. http://dx.doi.org/10.1094/pd-89-0749.
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Preliminary transmission assays conducted under greenhouse conditions demonstrated that Citrus exocortis viroid (CEVd), Citrus bent leaf viroid (CBLVd), Hop stunt viroid (HSVd), Citrus viroid III (CVd-III), and Citrus viroid IV (CVd-IV) can be mechanically transmitted from citron to citron (Citrus medica) by a single slash with a knife blade. The impact of mechanical transmission of viroids by pruning and harvesting operations was also demonstrated in experimental and commercial field plots. Transmission efficiency under field conditions ranged from 4% in ‘Nules’ clementine to 10% in ‘Navelina’ sweet orange and 21% in ‘Verna’ lemon. Transmission efficiency varied only slightly with viroid and donor hosts. The impact of viroid transmission on tree height, canopy volume, and crop harvest was minimal. When the donor host was coinfected with several viroids, the viroids were not necessarily cotransmitted. Considerations regarding viroid transmission in other climates are discussed. Measures to control viroid spread in nurseries should be mandatory in certification programs.
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Wei, Shuang, Ruiling Bian, Ida Bagus Andika, Erbo Niu, Qian Liu, Hideki Kondo, Liu Yang, et al. "Symptomatic plant viroid infections in phytopathogenic fungi." Proceedings of the National Academy of Sciences 116, no. 26 (June 10, 2019): 13042–50. http://dx.doi.org/10.1073/pnas.1900762116.
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Viroids are pathogenic agents that have a small, circular noncoding RNA genome. They have been found only in plant species; therefore, their infectivity and pathogenicity in other organisms remain largely unexplored. In this study, we investigate whether plant viroids can replicate and induce symptoms in filamentous fungi. Seven plant viroids representing viroid groups that replicate in either the nucleus or chloroplast of plant cells were inoculated to three plant pathogenic fungi,Cryphonectria parasitica,Valsa mali, andFusarium graminearum. By transfection of fungal spheroplasts with viroid RNA transcripts, each of the three, hop stunt viroid (HSVd), iresine 1 viroid, and avocado sunblotch viroid, can stably replicate in at least one of those fungi. The viroids are horizontally transmitted through hyphal anastomosis and vertically through conidia. HSVd infection severely debilitates the growth ofV. malibut not that of the other two fungi, while inF. graminearumandC. parasitica, with deletion of dicer-like genes, the primary components of the RNA-silencing pathway, HSVd accumulation increases. We further demonstrate that HSVd can be bidirectionally transferred betweenF. graminearumand plants during infection. The viroids also efficiently infect fungi and induce disease symptoms when the viroid RNAs are exogenously applied to the fungal mycelia. These findings enhance our understanding of viroid replication, host range, and pathogenicity, and of their potential spread to other organisms in nature.
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Venkataraman, Srividhya, Uzma Badar, Erum Shoeb, Ghyda Hashim, Mounir AbouHaidar, and Kathleen Hefferon. "An Inside Look into Biological Miniatures: Molecular Mechanisms of Viroids." International Journal of Molecular Sciences 22, no. 6 (March 10, 2021): 2795. http://dx.doi.org/10.3390/ijms22062795.
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Viroids are tiny single-stranded circular RNA pathogens that infect plants. Viroids do not encode any proteins, yet cause an assortment of symptoms. The following review describes viroid classification, molecular biology and spread. The review also discusses viroid pathogenesis, host interactions and detection. The review concludes with a description of future prospects in viroid research.
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SEČNIK, Andrej, Sebastjan RADIŠEK, Nataša ŠTAJNER, and Jernej JAKŠE. "Študij polarnosti verig različnih viroidov in njihovih kombinacij pri okuženih rastlinah hmelja." Acta agriculturae Slovenica 115, no. 1 (March 5, 2020): 193. http://dx.doi.org/10.14720/aas.2020.115.1.1319.
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<p>Hop plant (<em>Humulus lupulus </em>L.) is an important industrial crop, grown for harvesting hop cones however, it is a host to four different viroids as well. The nature of viroid infections is not entirely clarified. In our work, we focused on analyzing viroid accumulation and their strands polarity through RNA sequencing and reverse transcription polymerase chain reaction in real time. RNA-seq data indicate that viroids amplify until saturation further demonstrating plant's biological capacity. Negative fold changes in accumulation of individual viroids between hop samples with single and multiple infections are suggesting an antagonistic relationship amongst viroids, where citrus bark cracking viroid seems to be the least and hop stunt viroid the most sensitive to the other two. RNA-seq data also show that on average (−) viroid strand is dominating over (+), especially for the citrus bark cracking viroid. Reverse transcription polymerase chain reaction in real time results from strand polarity analysis seem to be less consistent between different combinations of infection but are showing level of conformity with RNA-seq in the case of citrus bark cracking viroid.</p>
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Thomas, Tina P., Madhurababu Kunta, John V. da Graça, Mamadou Sétamou, Mani Skaria, and Apurba Bhattacharya. "Suppression of Phytophthora Infection in Citrus Infected with Viroids." HortScience 45, no. 7 (July 2010): 1069–72. http://dx.doi.org/10.21273/hortsci.45.7.1069.
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Citrus viroid-induced resistance to Phytophthora infection in citrus was measured by the number of Phytophthora sporangia in ‘Rio Red’ grapefruit (Citrus paradisi Macf.) bait tissue infected with citrus viroids compared with non-inoculated controls. Different viroid isolates containing mixtures of viroids [Citrus exocortis viroid (CEVd), Hop stunt viroid (HSVd), Citrus viroid III (CVd-III), Citrus viroid IV (CVd-IV)] were designated by plant numbers and sources. Source 13E was associated with the lowest number of sporangia in bark, leaves, and roots used as baits, whereas CEVd E9, a known severe CEVd isolate, significantly reduced the number of sporangia in leaves and bark. Sources 1A, 2E, 3E, 4D, and 6E showed a significantly reduced number of sporangia on bark, leaves, and roots compared with healthy plants and 44A; however, their effect was not as pronounced as that of E9 and 13E. Sources 12E and 44A did not suppress sporangia production. Previous reverse transcriptase–polymerase chain reaction analysis showed that all source plants had mixed infections with several viroids, whereas 12E and 44A contained no viroids. In addition to confirming the earlier reports on the suppression of Phytophthora infection in general, our study showed significantly reduced Phytophthora sporangia development resulting from a number of viroids in mixed infection, but there did not appear to be any effect related to viroid species. To determine if concentration affected resistance to Phytophthora, phenolic acids were extracted. Extraction of phenolic acids with 80% ethanol was more efficient compared with 100% methanol and an acetonitrile–water mixture. High-performance liquid chromatography revealed no notable detection of salicylic acid in healthy and viroid-infected plants, but there was a small peak corresponding to salicylic acid in Phytophthora-infected and both viroid and Phytophthora-infected plants. Flavone was detected in all the source plants with a slight increase in Phytophthora-infected and both viroid and Phytophthora-infected plants. A peak corresponding to quercetin dehydrate was detected in Phytophthora-infected plants. Efficient use of the right viroid isolate(s) can result in suppression of Phytophthora infection of citrus.
10
Vernière, C., X. Perrier, C. Dubois, A. Dubois, L. Botella, C. Chabrier, J. M. Bové, and N. Duran Vila. "Interactions Between Citrus Viroids Affect Symptom Expression and Field Performance of Clementine Trees Grafted on Trifoliate Orange." Phytopathology® 96, no. 4 (April 2006): 356–68. http://dx.doi.org/10.1094/phyto-96-0356.
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Citrus exocortis viroid (CEVd), Citrus bent leaf viroid (CBLVd), a noncachexia variant of Hop stunt viroid (HSVd), Citrus viroid III (CVd-III), and Citrus viroid IV (CVd-IV) were co-inoculated as two-, three-, four-, and five-viroid mixtures to Clementine trees grafted on trifoliate orange to evaluate their effect on symptom expression, tree growth, and fruit yield. Most trees infected with CEVd-containing viroid mixtures developed exocortis scaling symptoms, as did CEVd alone, whereas most trees infected with HSVd- or CVd-IV-containing mixtures developed bark-cracking symptoms. Trees infected with mixtures containing both CEVd and CVd-IV revealed the existence of antagonism between these two viroids in terms of the expected bark-scaling and cracking symptoms. Synergistic interactions also were identified in trees infected with certain viroid combinations that, in spite of lacking CEVd, expressed exocortis-like scaling symptoms. Viroid interactions also affected the expected response of trees in terms of vegetative growth and fruit yield. Trees infected with viroid combinations containing CEVd or CVd-III were smaller and produced less fruit than trees infected with mixtures not containing these viroids. Viroid interactions on scion circumference and cumulative fruit yield, in terms of additivity of their effects, were statistically confirmed using a factorial analysis of variance model with two mean estimation approaches. In single-viroid infections, CEVd, CVd-III, and, to a lesser extent, CBLVd consistently and significantly reduced tree size and fruit yield. Conversely, HSVd and CVd-IV slightly increased fruit yield and reduced scion circumference. Rare and not consistent significant interactions were detected with the five-, four-, and three-viroid combinations. Antagonistic interactions between CEVd and CVd-III or CBLVd and CVd-III were revealed over the years with consistent significance. The antagonistic interaction between CEVd and CVd-IV was highly significant over the years when additional viroids were present; however, this antagonism appeared much later in the case of an exclusive interaction. HSVd and CVd-IV showed a consistent and significant synergistic interaction on yield only when both viroids were exclusively present. These results demonstrate antagonistic or synergistic relationships between citrus viroids depending on the viroid mixtures present in the host.
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Matsushita, Yosuke, Hironobu Yanagisawa, and Teruo Sano. "Vertical and Horizontal Transmission of Pospiviroids." Viruses 10, no. 12 (December 12, 2018): 706. http://dx.doi.org/10.3390/v10120706.
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Viroids are highly structured, single-stranded, non-protein-coding circular RNA pathogens. Some viroids are vertically transmitted through both viroid-infected ovule and pollen. For example, potato spindle tuber viroid, a species that belongs to Pospiviroidae family, is delivered to the embryo through the ovule or pollen during the development of reproductive tissues before embryogenesis. In addition, some of Pospiviroidae are also horizontally transmitted by pollen. Tomato planta macho viroid in pollen infects to the ovary from pollen tube during pollen tube elongation and eventually causes systemic infection, resulting in the establishment of horizontal transmission. Furthermore, fertilization is not required to accomplish the horizontal transmission. In this review, we will overview the recent research progress in vertical and horizontal transmission of viroids, mainly by focusing on histopathological studies, and also discuss the impact of seed transmission on viroid dissemination and seed health.
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Seo, Hyesu, Ying Wang, and Woong June Park. "Time-Resolved Observation of the Destination of Microinjected Potato Spindle Tuber Viroid (PSTVd) in the Abaxial Leaf Epidermal Cells of Nicotiana benthamiana." Microorganisms 8, no. 12 (December 20, 2020): 2044. http://dx.doi.org/10.3390/microorganisms8122044.
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Viroids are single-stranded noncoding RNA molecules of 250–400 nucleotides that cause plant diseases. One of the two families of viroids is Pospiviroidae, the members of which replicate in the nuclei of host cells. To replicate in plants, viroids of Pospiviroidae must enter the nucleus. However, the nuclear import of viroids remains understudied. In this work, we documented the time-dependent characteristics of the changes in microinjected fluorescently labeled potato spindle tuber viroid (PSTVd). The cytoplasmic fluorescence disappeared gradually, with only nuclear fluorescence remaining as the PSTVd injected in the cytoplasm was imported into the nucleus. Through this work, we determined that the time for half-maximal nuclear accumulation of the viroid was about 23 min. Interestingly, we found some cells where the nuclear import did not occur, despite the high level of cytosolic viroid injected. In some cells, the injected viroids disappeared within 10–20 min. The nuclear import of PSTVd is not a simple concentration-dependent process but was probably under the regulation of diverse factors that may be missing from some cells used for our observation.
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Adkar-Purushothama, Charith Raj, and Jean-Pierre Perreault. "Impact of Nucleic Acid Sequencing on Viroid Biology." International Journal of Molecular Sciences 21, no. 15 (August 1, 2020): 5532. http://dx.doi.org/10.3390/ijms21155532.
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The early 1970s marked two breakthroughs in the field of biology: (i) The development of nucleotide sequencing technology; and, (ii) the discovery of the viroids. The first DNA sequences were obtained by two-dimensional chromatography which was later replaced by sequencing using electrophoresis technique. The subsequent development of fluorescence-based sequencing method which made DNA sequencing not only easier, but many orders of magnitude faster. The knowledge of DNA sequences has become an indispensable tool for both basic and applied research. It has shed light biology of viroids, the highly structured, circular, single-stranded non-coding RNA molecules that infect numerous economically important plants. Our understanding of viroid molecular biology and biochemistry has been intimately associated with the evolution of nucleic acid sequencing technologies. With the development of the next-generation sequence method, viroid research exponentially progressed, notably in the areas of the molecular mechanisms of viroids and viroid diseases, viroid pathogenesis, viroid quasi-species, viroid adaptability, and viroid–host interactions, to name a few examples. In this review, the progress in the understanding of viroid biology in conjunction with the improvements in nucleotide sequencing technology is summarized. The future of viroid research with respect to the use of third-generation sequencing technology is also briefly envisaged.
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Di Serio, Francesco, Enza Maria Torchetti, José-Antonio Daròs, and Beatriz Navarro. "Reassessment of Viroid RNA Cytosine Methylation Status at the Single Nucleotide Level." Viruses 11, no. 4 (April 18, 2019): 357. http://dx.doi.org/10.3390/v11040357.
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Composed of a few hundreds of nucleotides, viroids are infectious, circular, non-protein coding RNAs able to usurp plant cellular enzymes and molecular machineries to replicate and move in their hosts. Several secondary and tertiary RNA structural motifs have been implicated in the viroid infectious cycle, but whether modified nucleotides, such as 5C-methylcytosine (m5C), also play a role has not been deeply investigated so far. Here, the possible existence of m5C in both RNA polarity strands of potato spindle tuber viroid and avocado sunblotch viroid -which are representative members of the nucleus- and chloroplast-replicating viroids, respectively- has been assessed at single nucleotide level. We show that a standard bisulfite protocol efficiently used for identifying m5C in cellular RNAs may generate false positive results in the case of the highly structured viroid RNAs. Applying a bisulfite conversion protocol specifically adapted to RNAs with high secondary structure, no m5C was identified in both polarity strands of both viroids, indicating that this specific nucleotide modification does not likely play a role in viroid biology.
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Hadidi, Ahmed. "Next-Generation Sequencing and CRISPR/Cas13 Editing in Viroid Research and Molecular Diagnostics." Viruses 11, no. 2 (January 29, 2019): 120. http://dx.doi.org/10.3390/v11020120.
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Viroid discovery as well as the economic significance of viroids and biological properties are presented. Next-generation sequencing (NGS) technologies combined with informatics have been applied to viroid research and diagnostics for almost a decade. NGS provides highly efficient, rapid, low-cost high-throughput sequencing of viroid genomes and of the 21–24 nt vd-sRNAs generated by the RNA silencing defense of the host. NGS has been utilized in various viroid studies which are presented. The discovery during the last few years that prokaryotes have heritable adaptive immunity mediated through clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated Cas proteins, have led to transformative advances in molecular biology, notably genome engineering and most recently molecular diagnostics. The potential application of the CRISPR-Cas13a system for engineering viroid interference in plants is suggested by targeting specific motifs of three economically important viroids. The CRISPR-Cas13 system has been utilized recently for the accurate detection of human RNA viruses by visual read out in 90 min or less and by paper-based assay. Multitarget RNA tests by this technology have a good potential for application as a rapid and accurate diagnostic assay for known viroids. The CRISPR/Cas system will work only for known viroids in contrast to NGS, but it should be much faster.
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Adkar-Purushothama, Charith Raj, Pavithran Sridharan Iyer, Teruo Sano, and Jean-Pierre Perreault. "sRNA Profiler: A User-Focused Interface for Small RNA Mapping and Profiling." Cells 10, no. 7 (July 13, 2021): 1771. http://dx.doi.org/10.3390/cells10071771.
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Viroids are circular, highly structured, single-stranded, non-coding RNA pathogens known to infect and cause disease in several plant species. They are known to trigger the host plant’s RNA silencing machinery. The detection of viroid-derived small RNAs (vd-sRNA) in viroid-infected host plants opened a new avenue of study in host–viroid pathogenicity. Since then, several viroid research groups have studied the vd-sRNA retrieved from different host–viroid combinations. Such studies require the segregation of 21- to 24-nucleotide long small RNAs (sRNA) from a deep-sequencing databank, followed by separating the vd-sRNA from any sRNA within this group that showed sequence similarity with either the genomic or the antigenomic strands of the viroid. Such mapped vd-sRNAs are then profiled on both the viroid’s genomic and antigenomic strands for visualization. Although several commercial interfaces are currently available for this purpose, they are all programmed for linear RNA molecules. Hence, viroid researchers must develop a computer program that accommodates the sRNAs derived from the circular viroid genome. This is a laborious process, and consequently, it often creates a bottleneck for biologists. In order to overcome this constraint, and to help the research community in general, in this study, a python-based pattern matching interface was developed so as to be able to both profile and map sRNAs on a circular genome. A “matching tolerance” feature has been included in the program, thus permitting the mapping of the sRNAs derived from the quasi-species. Additionally, the “topology” feature allows the researcher to profile sRNA derived from both linear and circular RNA molecules. The efficiency of the program was tested using previously reported deep-sequencing data obtained from two independent studies. Clearly, this novel software should be a key tool with which to both evaluate the production of sRNA and to profile them on their target RNA species, irrespective of the topology of the target RNA molecule.
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Hodgson, R. A. J., G. C. Wall, and J. W. Randles. "Specific Identification of Coconut Tinangaja Viroid for Differential Field Diagnosis of Viroids in Coconut Palm." Phytopathology® 88, no. 8 (August 1998): 774–81. http://dx.doi.org/10.1094/phyto.1998.88.8.774.
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Tinangaja is a widespread lethal disease of putative viroid etiology affecting coconut palm on the island of Guam. Determination of its distribution and mode of spread requires a simple and reliable diagnostic procedure that is specific for the associated coconut tinangaja viroid (CTiVd). A method of extracting tissue followed by analytical agarose gel electrophoresis for CTiVd detection has been developed and used to identify the viroid in leaf samples of suspect symptomatic palms growing in the field. Two-dimensional polyacrylamide gel electrophoresis showed that the viroid band contained circular molecules that are typical for viroids. Confirmation of the identity of CTiVd and detection of low levels of viroid below the threshold of detection by agarose gel electrophoresis was achieved either by diagnostic oligonucleotide-probe (DOP) hybridization assay or by reverse-transcription polymerase chain reaction (RT-PCR) with the oligonucleotide probe as one of the two PCR primers. RT-PCR was not substantially more sensitive than DOP-hybridization assay. This procedure also was applicable to coconut cadang-cadang viroid (CCCVd), and oligonucleotide probes designed to be specific for either CTiVd or CCCVd distinguished between these two viroids in coconut leaf extracts. This strategy provides a rapid and specific indexing procedure for the two characterized viroids of coconut palm and will be applicable to further studies on the viroid-like sequences previously reported in tropical monocotyledons.
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Gillings, MR, P. Broadbent, and BI Gollnow. "Viroids in Australian Citrus: Relationship to Exocortis, Cachexia and Citrus Dwarfing." Functional Plant Biology 18, no. 5 (1991): 559. http://dx.doi.org/10.1071/pp9910559.
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Viroids are the smallest infectious agents known, being unencapsidated RNAs of 240-380 bases. Citrus exocortis viroid (CEV) causes poor tree performance, especially when infected scions are grafted to trifoliate orange or citrange rootstocks. To eliminate infected budwood trees, various methods were used to detect CEV, including field inspections, bud inoculation of Etrog citron indicators (in which CEV causes severe epinasty) and hybridisation with CEV cDNA. A large number of trees with exocortis- like symptoms such as dwarfing and/or bud union abnormalities produced only mild epinasty when grafted on Etrog citron and did not hybridise to the CEV probe. Upon purification and electrophoretic analysis, the presence of viroids other than CEV was demonstrated. Screening of over 1800 trees resulted in the detection of four groups of viroids as determined by RNA homology and length in nucleotides. CEV was the only member of the first group and was the largest viroid detected, with 371 bases. CEV almost invariably occurred with other viroids of lower molecular weight. The second group, CV I, contained two viroids, of 325 and 332 bases, which were not homologous to CEV or hop stunt viroid (HSVd). Group CV II contained three viroids, of 297, 299 and 302 bases, all of which were homologous to HSVd. The CV III group contained two viroids, of 290 and 295 bases, which were not homologous to CEV or HSVd. The CV II and CV III groups were strongly associated with various field symptoms, including the disease cachexia (CV IIb), and dwarfing of trees on trifoliate orange rootstock. To confirm any causal relationship between individual viroids and field symptoms, viroids representative of each group were purified and used to inoculate Etrog citron. Tissue from these citrons was used to inoculate young field trees with viroids, singly and in combination. Parson's Special mandarin inoculated with CV IIb showed symptoms of cachexia after 2 years, confirming CV IIb as a causal agent of this disease. It will probably be 5 years before the effect of other inoculations can be assessed.
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Diener, Theodor. "Of Viroids and Prions." Viruses 10, no. 12 (November 23, 2018): 663. http://dx.doi.org/10.3390/v10120663.
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In 2017, Hadidi et al. edited a voluminous monograph entitled “Viroids and Satellites”, in which each known viroid and viroid-like satellite species was described in detail from many perspectives by more than 100 experts from 24 countries. In its 700+ pages, the book is a much needed detailed and reliable compendium of a subject, which, undoubtedly, is still little known by many potential readers. Because most users of the book may be expected to be practical plant pathologists, it appears essential that the book contain, in addition to the detailed viroid and satellite descriptions, one chapter, in which the basic molecular biology of viroids and satellites is described.
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Stuchi, Eduardo Sanches, Simone Rodrigues da Silva, Luiz Carlos Donadio, Otávio Ricardo Sempionato, and Eduardo Toller Reiff. "Field performance of "marsh seedless" grapefruit on trifoliate orange inoculated with viroids in Brazil." Scientia Agricola 64, no. 6 (December 2007): 582–88. http://dx.doi.org/10.1590/s0103-90162007000600004.
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Some viroids reduce citrus tree growth and may be used for tree size control aiming the establishment of orchards with close tree spacing that may provide higher productivity than conventional ones. To study the effects of citrus viroids inoculation on vegetative growth, yield and fruit quality of 'Marsh Seedless' grapefruit (Citrus paradisi Macf.) grafted on trifoliate orange [Poncirus trifoliata (L.) Raf.], an experiment was set up in January 1991, in Bebedouro, São Paulo State, Brazil. The experimental design was randomized blocks with four treatments with two plants per plot: viroid isolates Citrus Exocortis Viroid (CEVd) + Hop stunt viroid (HSVd - CVd-II, a non cachexia variant) + Citrus III viroid (CVd-III) and Hop stunt viroid (HSVd - CVd-II, a non cachexia variant) + Citrus III viroid (CVd-III) and controls: two healthy buds (control), and no grafting (absolute control). Inoculation was done in the field, six months after planting by bud grafting. Both isolates reduced tree growth (trunk diameter, plant height, canopy diameter and volume). Trees not inoculated yielded better (average of eleven harvests) than inoculated ones but the productivity was the same after 150 months. Fruit quality was affected by viroids inoculation but not in a restrictive way. The use of such severe dwarfing isolates for high density plantings of grapefruit on trifoliate orange rootstock is not recommended.
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Cottilli, Patrick, Borja Belda-Palazón, Charith Raj Adkar-Purushothama, Jean-Pierre Perreault, Enrico Schleiff, Ismael Rodrigo, Alejandro Ferrando, and Purificación Lisón. "Citrus exocortis viroid causes ribosomal stress in tomato plants." Nucleic Acids Research 47, no. 16 (August 8, 2019): 8649–61. http://dx.doi.org/10.1093/nar/gkz679.
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Abstract Viroids are naked RNAs that do not code for any known protein and yet are able to infect plants causing severe diseases. Because of their RNA nature, many studies have focused on the involvement of viroids in RNA-mediated gene silencing as being their pathogenesis mechanism. Here, the alterations caused by the Citrus exocortis viroid (CEVd) on the tomato translation machinery were studied as a new aspect of viroid pathogenesis. The presence of viroids in the ribosomal fractions of infected tomato plants was detected. More precisely, CEVd and its derived viroid small RNAs were found to co-sediment with tomato ribosomes in vivo, and to provoke changes in the global polysome profiles, particularly in the 40S ribosomal subunit accumulation. Additionally, the viroid caused alterations in ribosome biogenesis in the infected tomato plants, affecting the 18S rRNA maturation process. A higher expression level of the ribosomal stress mediator NAC082 was also detected in the CEVd-infected tomato leaves. Both the alterations in the rRNA processing and the induction of NAC082 correlate with the degree of viroid symptomatology. Taken together, these results suggest that CEVd is responsible for defective ribosome biogenesis in tomato, thereby interfering with the translation machinery and, therefore, causing ribosomal stress.
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Najar, A., and N. Duran-Vila. "Viroid Prevalence in Tunisian Citrus." Plant Disease 88, no. 11 (November 2004): 1286. http://dx.doi.org/10.1094/pdis.2004.88.11.1286b.
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The citrus industry in Tunisia is based mainly on the production of local cultivars of sweet orange (Citrus sinensis), common mandarin (C. reticulata), clementine (C. clementina), and lemon (C. limon). Sour orange (C. aurantium) is the only rootstock presently being used in the major growing area located at Cap Bon where 80% of citrus is being produced. The presence of tristeza disease in the Mediterranean basin is a threat to the Tunisian citrus industry, and new rootstocks giving tristeza tolerant rootstock/scion combinations are urgently needed as an alternative to sour orange. Since some promising rootstocks are known to be sensitive to viroids (1), a survey was conducted to determine if the cultivars grown presently in Tunisia were infected with viroids. Following a preliminary report (2), an extensive survey was conducted from 1995-2001 that included 174 symptomless sources being grown at Cap Bon: 26 Maltaise demi-sanguine, 9 Maltaise sanguine, 20 Maltaise blonde, 4 orange doublefine, 16 Washington navel, 12 Valencia late, 29 common mandarin, 42 Cassar clementine, 5 Lunari lemon, and 11 Eureka lemon. These sources were graft-inoculated into Etrog citron that subsequently developed symptoms characteristic of viroid infection. Sequential polyacrylamide gel electrophoresis analysis and molecular hybridization using viroid-specific probes (1) revealed that all sources were infected with at least two viroids. Citrus exocortis viroid (CEVd), Hop stunt viroid (HSVd), and Citrus viroid III (CVd-III) were widespread and accounted for 68.4, 67.8, and 81.0% of the sources tested, respectively. Citrus bent leaf viroid (CBLVd) and Citrus viroid IV (CVd-IV) were only found in 32.7 and 2.3% of the sources. The most frequent viroid combinations were CEVd+HSVd+CVd-III (17.8%) and CEVd+CVd-III (17,2%), whereas HSVd+CVd-IV and CEVd+CBLVd+CVd-III+CVd-IV were found in a single source (0.6%). References: (1) N. Duran-Vila and J. S. Semancik. Pages 178–194 in: Viroids. CSIRO Publishing, Australia, 2003. (2) A. Najar et al. Pages 398–400 in: Proc. 15th Conf. Int. Org. Citrus Virol, 2002.
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Singh, R. P., A. D. Dilworth, V. K. Baranwal, and K. N. Gupta. "Detection of Citrus exocortis viroid, Iresine viroid, and Tomato chlorotic dwarf viroid in New Ornamental Host Plants in India." Plant Disease 90, no. 11 (November 2006): 1457. http://dx.doi.org/10.1094/pd-90-1457a.
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Columnea latent viroid, originating from ornamental plants, is known to be harmful to crop plants (2). Despite the potential threat to crop plants, the importance of ornamental plants in viroid evolution is not fully appreciated. Availability of a Pospiviroid genus-specific primer pair (1) to detect the most prevalent viroids in ornamental plants and a simplified nucleic acid preparation protocol (3) for use in reverse-transcription polymerase chain reaction (RT-PCR) have facilitated surveys of ornamental plants for pospiviroids. Using the above protocol in India, leaf and shoot samples were collected randomly from roadside beds consisting of ground covers or creepers/trailing plants at the IARI campus, New Delhi. These were extracted in 50 mM NaOH + 2.5 mM EDTA solution, centrifuged to sediment the coarse debris from sap, and 10 μl of the supernatant was spotted on a nitrocellulose membrane. Individual spots were eluted with distilled sterile water (30 μl) and the eluates were used for RT-PCR detection of viroids (3). Amplified fragments or subsequently cloned plasmids were also purified using NaOH-EDTA membrane protocol. Cloning and sequencing of amplicons (195 to 224 bp) revealed a very high sequence identity with specific viroids from the viroid sequence database (NCBI). Among the 19 plant samples assayed, only three plant species were infected by viroids, although none of them exhibited any symptoms. The three plant species included: (i) moss verbena, Glandularia puchella (Verbenaceae, native to Argentina and Chile, now established in several regions of the world), infected with a viroid (Accession No. DQ846884) having 99% sequence identity to Citrus exocortis viroid (CEVd) (Accession No. S67446); (ii) trailing verbena, Verbena × hybrida (Verbenaceae, ornamental plant), doubly infected with a viroid (Accession No. DQ846885) having 95% sequence identity to CEVd (Accession No. DQ094297) and infected with another viroid (Accession No. DQ846883) having 98% sequence identity to Tomato chlorotic dwarf viroid (TCDVd) (Accession No. AF162131); and (iii) red joyweed, Alternanthera sessilis (Amaranthaceae, a perennial weed herb) infected with a viroid (Accession No. DQ846886) having 96% sequence identity to Iresine viroid (IrVd) (Accession No. DQ094293). CEVd and TCDVd were mechanically transferred to tomato seedlings causing reduced growth of plants, smaller leaves, and bunchy-top appearance of plants, symptoms similar to those typically observed with other isolates of these viroids. As expected from previous studies, IrVd was not transmitted to tomato plants. Natural infection of verbena with CEVd has been detected in North America (2) but this was a novel observation in India. Additional novel observations include: A. sessilis as a new host for IrVd; and TCDVd is the first crop viroid to be isolated from a naturally infected ornamental plant. The significance of these viroid findings in ground cover and widely grown ornamental plants may lie in their potential role in spreading the viroids to citrus plants in citrus-growing countries such as India. References: (1) H. Bostan et al. J. Virol. Methods 116:189, 2004, (2) R. P. Singh and J. A. Teixeira da Silva. Floriculture, Ornamental Plant Biotechnol. 3:531, 2006. (3) R. P. Singh et al. J. Virol. Methods 132:204, 2006.
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Sänger, Heinz L. "VIROIDS AND VIROID DISEASES." Acta Horticulturae, no. 234 (December 1988): 79–88. http://dx.doi.org/10.17660/actahortic.1988.234.9.
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Eiras, Marcelo, Maria Luisa P. N. Targon, Thor V. M. Fajardo, Ricardo Flores, and Elliot W. Kitajima. "Citrus exocortis viroid and Hop Stunt viroid Doubly infecting grapevines in Brazil." Fitopatologia Brasileira 31, no. 5 (October 2006): 440–46. http://dx.doi.org/10.1590/s0100-41582006000500002.
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Viroids, non-protein-coding small (246-401 nt) circular single-stranded RNAs with autonomous replication, are currently classified into two families. Within the family Pospiviroidae, Citrus exocortis viroid (CEVd) belongs to the genus Pospiviroid while Hop stunt viroid (HSVd) is the single member of the genus Hostuviroid. These pathogens are distributed worldwide and infect a large number of hosts. In Brazil, isolates of CEVd and HSVd have been detected in both citrus and grapevine. To characterize and study the genetic variability of these viroids, total RNA from leaves of grapevine Vitis vinifera 'Cabernet Sauvignon' and V. labrusca 'Niagara Rosada' from Bento Gonçalves, RS, was used as a template for RT-PCR amplification with specific primers for the five viroids described infecting grapevines [HSVd, CEVd, Grapevine yellow speckle viroid 1 (GYSVd-1), Grapevine yellow speckle viroid 2 (GYSVd-2) and Australian grapevine viroid (AGVd)]. Leaf samples of Citrus medica infected with CEVd from São Paulo were also analyzed. The resulting products were separated by agarose gel electrophoresis and DNA fragments of the expected size were eluted, cloned and sequenced. The grapevine samples analyzed were doubly infected by CEVd and HSVd. A phylogenetic analysis showed that the Brazilian grapevine HSVd variants clustered with other grapevine HSVd variants, forming a specific group separated from citrus variants, whereas the Brazilian CEVd variants clustered with other citrus and grapevine variants.
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Flores, Ricardo, Beatriz Navarro, Sonia Delgado, Pedro Serra, and Francesco Di Serio. "Viroid pathogenesis: a critical appraisal of the role of RNA silencing in triggering the initial molecular lesion." FEMS Microbiology Reviews 44, no. 3 (May 1, 2020): 386–98. http://dx.doi.org/10.1093/femsre/fuaa011.
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ABSTRACT The initial molecular lesions through which viroids, satellite RNAs and viruses trigger signal cascades resulting in plant diseases are hotly debated. Since viroids are circular non-protein-coding RNAs of ∼250–430 nucleotides, they appear very convenient to address this issue. Viroids are targeted by their host RNA silencing defense, generating viroid-derived small RNAs (vd-sRNAs) that are presumed to direct Argonaute (AGO) proteins to inactivate messenger RNAs, thus initiating disease. Here, we review the existing evidence. Viroid-induced symptoms reveal a distinction. Those attributed to vd-sRNAs from potato spindle tuber viroid and members of the family Pospiviroidae (replicating in the nucleus) are late, non-specific and systemic. In contrast, those attributed to vd-sRNAs from peach latent mosaic viroid (PLMVd) and other members of the family Avsunviroidae (replicating in plastids) are early, specific and local. Remarkably, leaf sectors expressing different PLMVd-induced chloroses accumulate viroid variants with specific pathogenic determinants. Some vd-sRNAs containing such determinant guide AGO1-mediated cleavage of mRNAs that code for proteins regulating chloroplast biogenesis/development. Therefore, the initial lesions and the expected phenotypes are connected by short signal cascades, hence supporting a cause-effect relationship. Intriguingly, one virus satellite RNA initiates disease through a similar mechanism, whereas in the Pospiviroidae and in plant viruses the situation remains uncertain.
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Seo, Hyesu, Kyunghee Kim, and Woong June Park. "Effect of VIRP1 Protein on Nuclear Import of Citrus Exocortis Viroid (CEVd)." Biomolecules 11, no. 1 (January 13, 2021): 95. http://dx.doi.org/10.3390/biom11010095.
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Before replicating, Pospiviroidae viroids must move into the plant nucleus. However, the mechanisms of viroid nuclear import are not entirely understood. To study the nuclear import of viroids, we established a nuclear import assay system using onion cell strips and observed the import of Alexa Fluor-594-labeled citrus exocortis viroid (CEVd). To identify the plant factors involved in the nuclear import of viroids, we cloned the Viroid RNA-binding Protein 1 (VIRP1) gene from a tomato cultivar, Seokwang, and heterologously expressed and purified the VIRP1 protein. The newly prepared VIRP1 protein had alterations of amino acid residues at two points (H52R, A277G) compared with a reference VIRP1 protein (AJ249595). VIRP1 specifically bound to CEVd and promoted its nuclear import. However, it is still uncertain whether VIRP1 is the only factor required for the nuclear import of CEVd because CEVd entered the plant nuclei without VIRP1 in our assay system. The cause of the observed nuclear accumulation of CEVd in the absence of VIRP1 needs to be further clarified.
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Singh, Rudra P., Xianzhou Nie, and Mathuresh Singh. "Tomato chlorotic dwarf viroid: an evolutionary link in the origin of pospiviroids." Journal of General Virology 80, no. 11 (November 1, 1999): 2823–28. http://dx.doi.org/10.1099/0022-1317-80-11-2823.
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Over 40 isolates of potato spindle tuber viroid (PSTVd) have been reported from potato, other Solanum species and greenhouse tomato. These isolates have sequence similarities in the range 95–99%. A viroid which caused chlorotic leaves and severe dwarfing of plants in greenhouse tomato crops was detected. The viroid was found to hybridize readily with PSTVd probes. It migrated faster than PSTVd in return-polyacrylamide gel electrophoresis and was not amplified in RT–PCR by a primer pair based on the lower strand of the central conserved region of PSTVd. Nucleotide sequencing of the viroid indicated that it is a circular RNA of 360 nt, with less than 90% sequence similarities with PSTVd isolates. The Variable domain (V) has less than 60% and the Terminal Right domain less than 90% sequence similarity, while the remainder of the molecule has greater than 97% similarity with PSTVd. Because of its less-than 90% sequence similarities, unique V domain, lack of seed-transmission and lack of cross-protection by PSTVd, the viroid from tomato is proposed to be a distinct viroid species (tomato chlorotic dwarf viroid; TCDVd) which also differs from two viroids infecting tomato in nature. TCDVd may be an evolutionary link in the development of crop viroids, with Mexican papita viroid as the ancestral viroid.
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Wang, X. F., C. Y. Zhou, K. Z. Tang, and Z. A. Li. "Occurrence of Four Citrus Viroids in Chongqing, China." Plant Disease 92, no. 6 (June 2008): 978. http://dx.doi.org/10.1094/pdis-92-6-0978b.
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Chongqing Municipality, located in the superior citrus belt of the upper-middle Yangtze River, is one of the most important citrus-producing areas in China. A survey was performed to evaluate the occurrence and distribution of citrus viroids in this area, where Poncirus trifoliata is the main rootstock. From 2002 to 2006, 72 samples of sweet oranges (Citrus sinensis), lemons (C. jambhiri), mandarins (C. reticulata), and mandarin hybrids, which showed stunting, bark scaling, and cracking symptoms on the rootstock, were collected and graft inoculated into Arizona 861-S1 Etrog citron (C. medica) on rough lemon rootstock and maintained in a greenhouse at 28 to 32°C. Fifty-one of the seventy-two samples were cultivars imported from abroad, and the remaining samples were all local cultivars. Sixty samples induced symptoms typical of citrus viroids on the Etrog indicator plants. To identify the causal agent(s), a one-step reverse transcription (RT)-PCR protocol, using five primer pairs (1) targeting the complete genome sequences, was used to detect Citrus exocortis viroid (CEVd), Citrus bent leaf viroid (CBLVd), Hop stunt viroid (HSVd), Citrus viroid III (CVd-III), and Citrus viroid IV (CVd-IV) (2). All 72 samples were infected by citrus viroids. Sixty-five and thirty-five of the seventy-two samples were positive for HSVd and CVd-III, respectively. CEVd and CBLVd were found, respectively, in 20 and 11 of 72 samples, whereas CVd-IV was not detected. Of 72 samples, 12 without typical symptoms on Etrog citrons were infected by HSVd and CBLVd. Nearly all (70 of 72) infected citrus plants harbored more than one viroid species, and two plants were both infected by CEVd, CBLVd, HSVd, and CVd-III. RT-PCR products were purified and ligated into pGEM T-Easy Vector (Promega, Madison, WI) and three clones for each of the four viroid species were sequenced and deposited in GenBank: CEVd (Accession Nos. EU382202, U382203, and EU382204); CBLVd (Accession Nos. EU382211, EU382212, and EU382213); HSVd (Accession Nos. EU382208, EU382209, and EU382210); and CVd-III (Accession Nos. EU382205, EU382206, and EU382207). BLAST analysis showed that these nucleotide sequences had greater than 94% nucleotide identity to the most similar genome sequences in GenBank. Sweet orange was more frequently infected by viroids than the other citrus cultivars. To our knowledge, this is the first report of CBLVd, HSVd, and CVd-III in Chongqing and the first report of CBLVd in China. The high incidence of citrus viroids in Chongqing necessitates rapid development of a system of propagation and testing to reduce the incidence of viroids and the associated loss of citrus production. References: (1) L. Bernard and N. Duran-Vila. Mol. Cell. Probes 20:105, 2006. (2) K. Z. Tang et al. Acta Hortic. Sin. 32:408, 2005.
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Matoušek, J. "Viroids: sequence variability and evolution of pathogenic RNA." Plant Protection Science 38, SI 1 - 6th Conf EFPP 2002 (January 1, 2002): 173–76. http://dx.doi.org/10.17221/10348-pps.
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Viroids as the smallest pathogenic circular single-stranded pathogenic RNAs form populations of quasi-species, which<br />has been recently identified by thermodynamic methods like TGGE pre-selection and heteroduplex analysis. It was found<br />that replication under thermal stress led to enormously high level of viroid mutagenesis. Mostly multiple mutants having<br />non-random distribution of base changes were found. A specific “hot spots” were identified in the regions, where<br />a characteristic “pathogenicity domains” are localised in different viroids of the pospiviroidae family. Specific viroid<br />microevolution was observed upon artificial inoculation of non-host plant species. Our results suggest that viroid propagation<br />under physiological stress can be assumed as important factor, which is among others, responsible for an appearance<br />of viroid quasi-species in the nature. Evolution and new viroid patotypes could accumulate due to environmental stress<br />including various pollutants may be a potential danger for cultured plants.
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Góra-Sochacka, Anna. "Viroids: unusual small pathogenic RNAs." Acta Biochimica Polonica 51, no. 3 (September 30, 2004): 587–607. http://dx.doi.org/10.18388/abp.2004_3546.
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Viroids are small (about 300 nucleotides), single-stranded, circular, non-encapsidated pathogenic RNA molecules. They do not code for proteins and thus depend on plant host enzymes for their replication and other functions. They induce plant diseases by direct interaction with host factors but the mechanism of pathogenicity is still unknown. They can alter the expression of selected plant genes important for growth and development. Viroids belong to two families, the Avsunviroidae and the Pospiviroidae. Viroids of the Avsunviroidae family adopt a branched or quasi rod-like secondary structure in their native state. Members of the Pospiviroidae family adopt a rod-like secondary structure. In such native structures five structural/functional domains have been identified: central (C), pathogenicity, variable and two terminal domains. The central conserved region (CCR) within the C domain characterizes viroids of the Pospiviroidae. Specific secondary structures of this region play an important role in viroid replication and processing. Viroids of the Avsunviroidae family lack a CCR but possess self-cleaving properties by forming hammerhead ribozyme structures; they accumulate and replicate in chloroplasts, whereas members of the Pospiviroidae family have a nuclear localization. Viroid replication occurs via a rolling circle mechanism using either a symmetric or asymmetric pathway in three steps, RNA transcription, processing and ligation.
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Itaya, Asuka, Yoshie Matsuda, Robert A. Gonzales, Richard S. Nelson, and Biao Ding. "Potato spindle tuber viroid Strains of Different Pathogenicity Induces and Suppresses Expression of Common and Unique Genes in Infected Tomato." Molecular Plant-Microbe Interactions® 15, no. 10 (October 2002): 990–99. http://dx.doi.org/10.1094/mpmi.2002.15.10.990.
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Viroids are the smallest plant pathogens. These RNAs do not encode proteins and are not encapsidated, and yet they can replicate autonomously, move systemically, and cause diseases in infected plants. Notably, strains of a viroid with subtle differences in nucleotide sequences can cause dramatically different symptoms in infected plants. These features make viroids unique probes to investigate the role of a pathogenic RNA genome in triggering host responses. We conducted a comprehensive analysis of the differential gene expression patterns of tomato plants at various stages of infection by a mild and severe strain of Potato spindle tuber viroid (PSTVd). We also compared tomato gene expression altered by the PSTVd strains with that altered by Tobacco mosaic virus (TMV). Our analyses revealed that the two PSTVd strains altered expression of both common and unique tomato genes. These genes encode products involved in defense/stress response, cell wall structure, chloroplast function, protein metabolism, and other diverse functions. Five genes have unknown functions. Four genes are novel. The expression of some but not all of these genes was also altered by TMV infection. Our results indicate that viroids, although structurally simple, can trigger complex host responses. Further characterization of viroid-altered gene expression in a host plant should help understand viroid pathogenicity and, potentially, the mechanisms of RNA-mediated regulation of plant gene expression.
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Rizza, S., A. Catara, X. F. Ma, and Z. Deng. "Detection of Multiple Infections of Citrus exocortis viroid, Citrus viroid III, and Hop stunt viroid Variants in Hunan Province, China." Plant Disease 91, no. 9 (September 2007): 1205. http://dx.doi.org/10.1094/pdis-91-9-1205a.
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Citrus cultivation in China has increased since the late 1970s, with China now having the largest area of citrus in culture in the world that is spread in 22 provinces and municipalities. Hunan Province has undergone a program to become one of the major citrus producers in China. Poncirus trifoliata is the main rootstock, so citrus viroids are a limiting factor for further citriculture development. In mainland China, only the presence of Citrus exocortis viroid (CEVd) has been reported from Etrog citron indexing, sPAGE (sequential polyacrylamide gel electrophoresis) analysis (2), and reverse transcription (RT)-PCR (3). Three viroid-like RNAs, a1, b1, and d, based on sPAGE patterns were detected years ago in our laboratory in budsticks received from Sichuan Province. To identify different viroids and determine their distribution, a survey has been undertaken. Field trees showing stunting, bark scaling and cracking of the rootstock, and poor yield were tested using biological indexing and PCR for the most frequent citrus viroids. Samples from six trees of a local sweet orange variety and three of a Clementine variety introduced from abroad, both grafted on P. trifoliata and showing a variable degree of bark scaling and cracking, were collected near Changsha and in the County of Xin Ning at the end of summer 2006. Small pieces of bark were inserted in stems of young E. citron budwood grafted on rough lemon and maintained in a warm greenhouse (24 to 32°C). Indexing on E. citron showed mild epinasty and leaf roll typical of citrus viroid infections. To identify specific viroids, bark was ground to a fine powder with liquid nitrogen and total RNA was extracted with TRIZOL Reagent (Invitrogen, San Diego, CA) and tested by RT-PCR to detect CEVd, Hop Stunt viroid (HSVd), and Citrus viroid III (CVd-III), as well as to identify the cachexia variants of HSVd. Four primer pairs were used to test the RNA extracts by RT-PCR (1). All samples were infected by HSVd, eight with CVd-III, and six with CEVd. The cachexia variants of HSVd were detected in four of nine samples. Mixed infections were as follows: one sample had CEVd and HSVd, eight had HSVd and CVd-III, and five were infected by the three viroids. A second sampling 3 months after inoculation gave the same amplification patterns. The results show that at least three viroids are present in citrus orchards in Hunan Province. To our knowledge, this is the first report of cachexia variants of HSVd and CVd-III in China. The common occurrence of these viroids supports the need for proper indexing of mother trees and a specific shoot tip grafting program to create healthy budwood sources to provide healthy plants. References: (1) L. Bernard and N. Duran-Vila. Mol. Cell. Probes, 20:105, 2006. (2) L. Han et al. Viroids. CSIRO Publishing, Melbourne, 283, 2003. (3). Q. Hu et al. Acta Bot. Sin. 39:613, 1997.
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Flores, Ricardo, Carmen Hernández, A. Emilio Martínez de Alba, José-Antonio Daròs, and Francesco Di Serio. "Viroids and Viroid-Host Interactions." Annual Review of Phytopathology 43, no. 1 (September 2005): 117–39. http://dx.doi.org/10.1146/annurev.phyto.43.040204.140243.
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Kalantidis, K., M. A. Denti, S. Tzortzakaki, E. Marinou, M. Tabler, and M. Tsagris. "Virp1 Is a Host Protein with a Major Role in Potato Spindle Tuber Viroid Infection in Nicotiana Plants." Journal of Virology 81, no. 23 (September 26, 2007): 12872–80. http://dx.doi.org/10.1128/jvi.00974-07.
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ABSTRACT Viroids are small, circular, single-stranded RNA molecules that, while not coding for any protein, cause several plant diseases. Viroids rely for their infectious cycle on host proteins, most of which are likely to be involved in endogenous RNA-mediated phenomena. Therefore, characterization of host factors interacting with the viroid may contribute to the elucidation of RNA-related pathways of the hosts. Potato spindle tuber viroid (PSTVd) infects several members of the Solanaceae family. In an RNA ligand screening we have previously isolated the tomato protein Virp1 by its ability to specifically interact with PSTVd positive-strand RNA. Virp1 is a bromodomain-containing protein with an atypical RNA binding domain and a nuclear localization signal. Here we investigate the role of Virp1 in the viroid infection cycle by the use of transgenic lines of Nicotiana tabacum and Nicotiana benthamiana that either overexpress the tomato Virp1 RNA or suppress the orthologous Nicotiana genes through RNA silencing. Plants of the Virp1-suppressed lines were not infected by PSTVd or Citrus exocortis viroid through mechanical inoculation, indicating a major role of Virp1 in viroid infection. On the other hand, overexpression of tomato Virp1 in N. tabacum and N. benthamiana plants did not affect PSTVd KF 440-2 infectivity or symptomatology in these species. Transfection experiments with isolated protoplasts revealed that Virp1-suppressed cells were unable to sustain viroid replication, suggesting that resistance to viroid infection in Virp1-suppressed plants is likely the result of cell-autonomous events.
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Jiang, Dong-Mei, Meng Wang, Shi-Fang Li, and Zhi-Xiang Zhang. "High-Throughput Sequencing Analysis of Small RNAs Derived from Coleus Blumei Viroids." Viruses 11, no. 7 (July 5, 2019): 619. http://dx.doi.org/10.3390/v11070619.
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Characterization of viroid-derived small RNAs (vd-sRNAs) is important to understand viroid–host interactions; however, vd-sRNAs belonging to the genus Coleviroid are yet to be identified and characterized. Herein, we used coleus plants singly infected with coleus blumei viroid (CbVd)-1, -5, or -6 and doubly infected with CbVd-1 and -5 to identify and analyze their vd-sRNAs. We found sense and antisense vd-sRNAs for CbVd-1, -5 and -6, and 22-nt vd-sRNAs were the most abundant; moreover, the 5′-terminal nucleotides (nts) of CbVd-1, -5, and -6 were biased toward U and C, and sRNAs derived from these three viroids were unevenly distributed along their genomes. We also noted that CbVd-5 and -6 share a fragment that forms the right half of the rod-like secondary structure of these viroids, which implied that they generated almost the same type of vd-sRNAs. This finding indicated that vd-sRNA biogenesis is mainly determined by the primary sequence of their substrates. More importantly, we found two complementary vd-sRNAs (22 nt) that were generated from the central conserved region (CCR) of these three viroids, suggesting an important role of CCR in vd-sRNA biogenesis. In conclusion, our results provide novel insight into the biogenesis of vd-sRNAs and the biological roles of CCR.
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Štajner, Nataša, Sebastjan Radišek, Ajay Kumar Mishra, Vishnu Sukumari Nath, Jaroslav Matoušek, and Jernej Jakše. "Evaluation of Disease Severity and Global Transcriptome Response Induced by Citrus bark cracking viroid, Hop latent viroid, and Their Co-Infection in Hop (Humulus lupulus L.)." International Journal of Molecular Sciences 20, no. 13 (June 28, 2019): 3154. http://dx.doi.org/10.3390/ijms20133154.
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Viroids are small non-capsidated, single-stranded, covalently-closed circular noncoding RNA replicons of 239–401 nucleotides that exploit host factors for their replication, and some cause disease in several economically important crop plants, while others appear to be benign. The proposed mechanisms of viroid pathogenesis include direct interaction of the genomic viroid RNA with host factors and post-transcriptional or transcriptional gene silencing via viroid-derived small RNAs (vd-sRNAs) generated by the host defensive machinery. Humulus lupulus (hop) plants are hosts to several viroids among which Hop latent viroid (HLVd) and Citrus bark cracking viroid (CBCVd) are attractive model systems for the study of viroid-host interactions due to the symptomless infection of the former and severe symptoms induced by the latter in this indicator host. To better understand their interactions with hop plant, a comparative transcriptomic analysis based on RNA sequencing (RNA-seq) was performed to reveal the transcriptional alterations induced as a result of single HLVd and CBCVd infection in hop. Additionally, the effect of HLVd on the aggressiveness of CBCVd that underlies severe stunting in hop in a mixed infection was studied by transcriptomic analysis. Our analysis revealed that CBCVd infection resulted in dynamic changes in the activity of genes as compared to single HLVd infection and their mixed infection. The differentially expressed genes that are involved in defense, phytohormone signaling, photosynthesis and chloroplasts, RNA regulation, processing and binding; protein metabolism and modification; and other mechanisms were more modulated in the CBCVd infection of hop. Nevertheless, Gene Ontology (GO) classification and pathway enrichment analysis showed that the expression of genes involved in the proteolysis mechanism is more active in a mixed infection as compared to a single one, suggesting co-infecting viroids may result in interference with host factors more prominently. Collectively, our results provide a deep transcriptome of hop and insight into complex single HLVd, CBCVd, and their coinfection in hop-plant interactions
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Martínez de Alba, A. E., R. Flores, and C. Hernández. "Two Chloroplastic Viroids Induce the Accumulation of Small RNAs Associated with Posttranscriptional Gene Silencing." Journal of Virology 76, no. 24 (December 15, 2002): 13094–96. http://dx.doi.org/10.1128/jvi.76.24.13094-13096.2002.
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ABSTRACT In plants, posttranscriptional gene silencing (PTGS) has been reported for cytoplasmic RNAs from endogenous nuclear genes, transgenes, viruses, and, recently, for a viroid with nuclear replication and accumulation. However, phenomena of this kind have not been described for mitochondrial or chloroplastic RNAs. Here we show that viroids that replicate and accumulate in the chloroplast are also targets of PTGS and this process may control viroid titer.
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Broadbent, P., and CM Dephoff. "Virus indexing in the New South Wales citrus improvement scheme." Australian Journal of Experimental Agriculture 32, no. 4 (1992): 493. http://dx.doi.org/10.1071/ea9920493.
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A virus indexing program was initiated in the 1950s to test local citrus clones with commercial potential, for the presence of citrus exocortis viroid and psorosis. As indexing techniques improved, clones have also been tested for the presence of citrus cachexia viroid and other viroids, citrus infectious variegation virus, citrus tatter leaf virus, and strain severity of citrus tristeza virus. Of 123 candidate clones tested, only 2 were infected with psorosis virus. Crinkly leaf (infectious variegation virus) was widespread in lemons but has been eliminated by nucellar embryony. The widespread incidence of citrus exocortis and other lower molecular weight viroids has been reduced by screening mother trees on Poncirus trifoliata stocks, biological indexing, and, more recently, by sequential polyacrylamide gel electrophoresis of RNA extracts. Cachexia is rarely found in Australian citrus clones.
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Di Serio, Francesco, Silvia Ambrós, Teruo Sano, Ricardo Flores, and Beatriz Navarro. "Viroid Diseases in Pome and Stone Fruit Trees and Koch’s Postulates: A Critical Assessment." Viruses 10, no. 11 (November 7, 2018): 612. http://dx.doi.org/10.3390/v10110612.
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Composed of a naked circular non-protein-coding genomic RNA, counting only a few hundred nucleotides, viroids—the smallest infectious agents known so far—are able to replicate and move systemically in herbaceous and woody host plants, which concomitantly may develop specific diseases or remain symptomless. Several viroids have been reported to naturally infect pome and stone fruit trees, showing symptoms on leaves, fruits and/or bark. However, Koch’s postulates required for establishing on firm grounds the viroid etiology of these diseases, have not been met in all instances. Here, pome and stone fruit tree diseases, conclusively proven to be caused by viroids, are reviewed, and the need to pay closer attention to fulfilling Koch’s postulates is emphasized.
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Leichtfried, Thomas, Stefanie Dobrovolny, Helga Reisenzein, Siegrid Steinkellner, and Richard A. Gottsberger. "Apple chlorotic fruit spot viroid: a putative new pathogenic viroid on apple characterized by next-generation sequencing." Archives of Virology 164, no. 12 (October 9, 2019): 3137–40. http://dx.doi.org/10.1007/s00705-019-04420-9.
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Abstract Viroid-like symptoms were observed in 2016 on apple fruits of the cultivar “Ilzer Rose” in southern Burgenland, Austria. Preliminary molecular biological investigations indicated that the symptoms were caused by a new unknown viroid. Therefore, new primers were designed, and the whole genome sequence of the viroid (354 nt) was determined by next-generation amplicon sequencing using the Illumina MiSeq® platform (San Diego, California, USA). The viroid secondary structure has a rod-like conformation and contains conserved regions (the TCR, CCR upper strand, and CCR lower strand) that are characteristic of members of the genus Apscaviroid. Based on our results and the demarcation criteria for viroids, the tentatively named “apple chlorotic fruit spot viroid” should be considered a putative new member of the genus Apscaviroid.
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Verhoeven, Jacobus Th J., Ellis T. M. Meekes, Johanna W. Roenhorst, Ricardo Flores, and Pedro Serra. "Dahlia latent viroid: a recombinant new species of the family Pospiviroidae posing intriguing questions about its origin and classification." Journal of General Virology 94, no. 4 (April 1, 2013): 711–19. http://dx.doi.org/10.1099/vir.0.048751-0.
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A viroid-like RNA has been detected in two asymptomatic dahlia accessions by return and double PAGE. It appeared smaller than Chrysanthemum stunt viroid and Potato spindle tuber viroid, the two members of the genus Pospiviroid, family Pospiviroidae, reported in this ornamental previously. RT-PCR with primers designed for amplifying all pospiviroids produced no amplicons, but RT-PCR with random primers revealed a 342 nt RNA. The sequence of this RNA was confirmed with specific primers, which additionally revealed its presence in many dahlia cultivars. The RNA was named Dahlia latent viroid (DLVd) because it replicates autonomously, but symptomlessly, in dahlia and shares maximum sequence identity with other viroids of less than 56 %. Furthermore, DLVd displays characteristic features of the family Pospiviroidae: a predicted rod-like secondary structure of minimum free energy with a central conserved region (CCR), and the ability to form the metastable structures hairpins I and II. Its CCR is identical to that of Hop stunt viroid (HSVd, genus Hostuviroid). However, DLVd: (i) has the terminal conserved region present in members of the genus Pospiviroid, but absent in HSVd, and (ii) lacks the terminal conserved hairpin present in HSVd. Phylogenetic reconstructions indicate that HSVd and Pepper chat fruit viroid (genus Pospiviroid) are the closest relatives of DLVd, but DLVd differs from these viroids in its host range, restricted to dahlia so far. Therefore, while DLVd fulfils the criteria to be a novel species of the family Pospiviroidae, its recombinant origin makes assignment to the genera Pospiviroid or Hostuviroid problematic.
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Reanwarakorn, K., and J. S. Semancik. "Correlation of Hop Stunt Viroid Variants to Cachexia and Xyloporosis Diseases of Citrus." Phytopathology® 89, no. 7 (July 1999): 568–74. http://dx.doi.org/10.1094/phyto.1999.89.7.568.
Full textAbstract:
Citrus viroid (CVd) group II is comprised of hop stunt viroid (HSVd)-related variants of 295 to 302 nucleotides. Included in this group are the cachexia-inducing agents citrus cachexia viroid (or CVd-IIb), CVd-IIc, Ca-903, and Ca-909 as well as the non-cachexia-inducing variant CVd-IIa. The cachexia indexing hosts ‘Parson's Special’ mandarin and ‘Orlando’ tangelo as well as Citrus macrophylla responded with symptoms of gumming, discoloration, and stem pitting when infected by CVd-IIb, CVd-IIc, or Ca-903. However, ‘Palestine’ sweet lime, the indicator host used to describe the xyloporosis disease, displayed a distinctly different fine-pitting reaction and no discoloration or gumming when infected by the same viroids. Cachexia-inducing variants contain a number of nucleotide changes more similar to hop-type HSVd sequences than to the citrus-type HSVd sequences, as typified by CVd-IIa. The nucleotide sequence of CVd-IIc was identical to CVd group II isolates common to trees expressing xyloporosis. Experimental evidence indicates that either CVd-IIb or CVd-IIc can cause citrus diseases known as cachexia and xyloporosis and that the two disease designations reflect the distinct responses of different indexing hosts to the same viroids.
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Hammond, Rosemarie W., and Yan Zhao. "Characterization of a Tomato Protein Kinase Gene Induced by Infection by Potato spindle tuber viroid." Molecular Plant-Microbe Interactions® 13, no. 9 (September 2000): 903–10. http://dx.doi.org/10.1094/mpmi.2000.13.9.903.
Full textAbstract:
Viroids—covalently closed, circular RNA molecules in the size range of 250 to 450 nucleotides—are the smallest known infectious agents and cause a number of diseases of crop plants. Viroids do not encode proteins and replicate within the nucleus without a helper virus. In many cases, viroid infection results in symptoms of stunting, epinasty, and vein clearing. In our study of the molecular basis of the response of tomato cv. Rutgers to infection by Potato spindle tuber viroid (PSTVd), we have identified a specific protein kinase gene, pkv, that is transcriptionally activated in plants infected with either the intermediate or severe strain of PSTVd, at a lower level in plants inoculated with a mild strain, and not detectable in mock-inoculated plants. A full-length copy of the gene encoding the 55-kDa PKV (protein kinase viroid)-induced protein has been isolated and sequence analysis revealed significant homologies to cyclic nucleotide-dependent protein kinases. Although the sequence motifs in the catalytic domain suggest that it is a serine/threonine protein kinase, the recombinant PKV protein autophosphorylates in vitro on serine and tyrosine residues, suggesting that it is a putative member of the class of dual-specificity protein kinases.
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Matoušek, J., L. Orctová, J. Ptáček, J. Patzak, P. Dědič, G. Steger, and D. Riesner. "Experimental Transmission of Pospiviroid Populations to Weed Species Characteristic of Potato and Hop Fields." Journal of Virology 81, no. 21 (August 22, 2007): 11891–99. http://dx.doi.org/10.1128/jvi.01165-07.
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ABSTRACT Weed plants characteristic for potato and hop fields have not been considered in the past as potential hosts that could transmit and lead to spreading of potato spindle tuber (PSTVd) and hop stunt (HSVd) viroids, respectively. To gain insight into this problem, we biolistically inoculated these weed plants with viroid populations either as RNA or as cDNA. New potential viroid host species, collected in central Europe, were discovered. From 12 weed species characteristic for potato fields, high viroid levels, detectable by molecular hybridization, were maintained after both RNA and DNA transfers in Chamomilla reculita and Anthemis arvensis. Low viroid levels, detectable by reverse transcription-PCR (RT-PCR) only, were maintained after plant inoculations with cDNA in Veronica argensis and Amaranthus retroflexus. In these two species PSTVd concentrations were 105 and 103 times, respectively, lower than in tomato as estimated by real-time PCR. From 14 weeds characteristic for hop fields, high HSVd levels were detected in Galinsoga ciliata after both RNA and DNA transfers. HSVd was found, however, not to be transmissible by seeds of this weed species. Traces of HSVd were detectable by RT-PCR in HSVd-cDNA-inoculated Amaranthus retroflexus. Characteristic monomeric (+)-circular and linear viroid RNAs were present in extracts from weed species propagating viroids to high levels, indicating regular replication, processing, and circularization of viroid RNA in these weed species. Sequence analyses of PSTVd progenies propagated in C. reculita and A. arvensis showed a wide spectrum of variants related to various strains, from mild to lethal variants; the sequence variants isolated from A. retroflexus and V. argensis exhibited similarity or identity to the superlethal AS1 viroid variant. All HSVd clones from G. ciliata corresponded to a HSVdg variant, which is strongly pathogenic for European hops.
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LEMMETTY, A., J. LAAMANEN, and M. SOUKAINEN. "Emerging virus and viroid pathogen species identified for the first time in horticultural plants in Finland in 1997-2010." Agricultural and Food Science 20, no. 1 (December 4, 2008): 29. http://dx.doi.org/10.2137/145960611795163060.
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Expansion and intensification of global trade in horticultural plants has increased the risk of spread of new alien pathogen species in the EU. Alien species of pathogenic viruses and viroids in horticultural plants have been introduced into Finland in infected plant material (plants, seedlings, cuttings, tubers, seeds). By 1997, about 30 virus species of horticultural plants had been detected in Finland. We aimed at compiling emerging new virus and viroid records during 1997-2010. Eight new viruses belonging to tospo-, potex-, poty-, tymo-, ilar- and allexiviruses were detected in horticultural plants: four occurred in greenhouse crops, two in vegetables and two in garden ornamentals outdoors. Five new findings of viroids were made in ornamental and vegetable greenhouse crops during 2008-2009. More rapid and accurate diagnostic methods have contributed to identifying new alien pathogens. Global trade seems to be the main reason for the introduction of the newest virus and viroid pathogens into Finland.;
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Mitrofanova, Irina Vjacheslavovna, Alexsandr Vladimirovich Zakubanskiy, and Olga Vladimirovna Mitrofanova. "Viruses infecting main ornamental plants: an overview." Ornamental Horticulture 24, no. 2 (June 1, 2018): 95–102. http://dx.doi.org/10.14295/oh.v24i2.1199.
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Ornamental plants are cultivated for decorative and utility purposes in urban landscapes throughout the world. They are much valued for their aesthetic properties and constitute an important part of the global horticulture industry. Plant viruses and viroids of various taxonomic groups have a significant negative impact on ornamentals provoking a wide range of symptoms, reducing both decorative value and quality of propagated material and causing large economic damage. A significant growth of the ornamental plants market in recent years promotes the spread of viral diseases. Therefore, systematization of data on virus and viroid phytopathogens diversity in these cultures is an urgent research task. Among the most popular ornamentals are chrysanthemum, rose, clematis, canna, and lavender. More than fifty viruses and viroids from 17 different families (including two viroid families) have been identified in these crops to date. In the presented review, we described the variety of these pathogens and their effect on the above-mentioned ornamentals
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Elleuch, A., M. Marrakchi, D. Lévesque, N. Bessais, PerreaultJP, and H. Fakhfakh. "Molecular variability of Citrus exocortis viroid in a single naturally infected citrus tree." Plant Protection Science 39, No. 4 (November 25, 2011): 139–45. http://dx.doi.org/10.17221/3833-pps.
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We report the nucleotide sequence of Citrus exocortis viroid (CEVd) from a single natural infected citrus tree of the clementinier variety (Citrus clementina) in Tunisia. The sequence variability of this viroid from its natural host without using an alternative passage by an indicator host or an artificial inoculation was found to occur at 14 positions, giving a variability of 3.8%. This work confirms that naturally – occurring viroids belonging to the Pospiviroid genera contain a mixture of sequence variants. In addition, this study confirms the worldwide distribution of this viroid.
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Vernière, C., X. Perrier, C. Dubois, A. Dubois, L. Botella, C. Chabrier, J. M. Bové, and N. Duran Vila. "Citrus Viroids: Symptom Expression and Effect on Vegetative Growth and Yield of Clementine Trees Grafted on Trifoliate Orange." Plant Disease 88, no. 11 (November 2004): 1189–97. http://dx.doi.org/10.1094/pdis.2004.88.11.1189.
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Citrus are natural hosts of five viroid species: Citrus exocortis viroid (CEVd), Citrus bent leaf viroid (CBLVd), Hop stunt viroid (HSVd), Citrus viroid III (CVd-III), and Citrus viroid IV (CVd-IV). CEVd and specific sequence variants of HSVd are the causal agents of the wellknown diseases of citrus, exocortis and cachexia. Other viroids have been found to induce different degrees of stunting. Since commercial citrus trees are commonly infected with mixtures of these viroids, only limited information is available on their effect in species other than Etrog citron. A field assay was conducted to establish the effect of each viroid on Commune clementine trees grafted on Pomeroy trifoliate orange. Infected trees were periodically monitored over a 12-year period (1990 to 2002) for symptom expression, growth, and fruit yield. Only CEVd caused bark scaling on the trifoliate orange rootstock and marked dwarfing, both characteristic of exocortis disease as initially described. In addition, very conspicuous bumps were observed in the wood of the rootstock after removing the bark. Only those HSVd variants, previously characterized as pathogenic in several cachexia-sensitive species, induced pits and gum deposits characteristic of this disease in the clementine scion. Bark cracking symptoms on the trifoliate orange rootstock were also observed. They were associated with CVd-IV, HSVd, or CEVd infection, but in the latter, they were only clearly observed in trees that showed mild scaling. Other abnormalities (deep pits, crests, and gummy pits) were not associated with viroid infection. No specific symptoms resulted from infection with CBLVd and CVd-III. HSVd, CVd-IV, and CBLVd had little or no effect in growth and yield, whereas CEVd and CVd-III caused a significant reduction of growth and yield, which became more pronounced over time with CEVd infection. Yield reduction was associated mainly with loss of production of large fruits. In general, there was a good correlation between reduction in vegetative growth and yield.
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Gómez, Gustavo, and Vicente Pallás. "A Long-Distance Translocatable Phloem Protein from Cucumber Forms a Ribonucleoprotein Complex In Vivo with Hop Stunt Viroid RNA." Journal of Virology 78, no. 18 (September 15, 2004): 10104–10. http://dx.doi.org/10.1128/jvi.78.18.10104-10110.2004.
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ABSTRACT Viroids are highly structured plant pathogenic RNAs that do not code for any protein, and thus, their long-distance movement within the plant must be mediated by direct interaction with cellular factors, the nature of which is presently unknown. In addition to this type of RNAs, recent evidence indicates that endogenous RNAs move through the phloem acting as macromolecular signals involved in plant defense and development. The form in which these RNA molecules are transported to distal parts of the plant is unclear. Viroids can be a good model system to try to identify translocatable proteins that could assist the vascular movement of RNA molecules. Here, we demonstrate by use of immunoprecipitation experiments, that the phloem protein 2 from cucumber (CsPP2) is able to interact in vivo with a viroid RNA. Intergeneric graft assays revealed that both the CsPP2 and the Hop stunt viroid RNA were translocated to the scion. The translocated viroid is symptomatic in the nonhost scion, indicating that the translocated RNA is functional. The CsPP2 gene was cloned and sequenced. The analysis of its primary structure revealed the existence of a potential double-spaced-RNA-binding motif, previously identified in a set of proteins that bind to highly structured RNAs, which could explain its RNA-binding properties. The possible involvement of this phloem protein in assisting the long-distance movement of the viroid RNA within the plant is discussed.