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[EN] Plant viruses cannot exploit any of the membrane fusion-based routes of entry described for animal viruses. In addition, one of the distinctive structures of plant cells, the cell wall, acts as the first barrier against the invasion of pathogens. To overcome the rigidity of the cell wall, plant viruses normally take advantage of the way of life of different biological vectors. Alternatively, the physical damage caused by environmental stresses can facilitate virus entry. Once inside the cell and taking advantage of the characteristic symplastic continuity of plant cells, viruses need to remodel and/or modify the restricted pore size of the plasmodesmata (channels that connect plant cells). In a successful interaction for the virus, it can reach the vascular tissue to systematically invade the plant. The connections between the different cell types in this path are not designed to allow the passage of molecules with the complexity of viruses. During this process, viruses face different cell barriers that must be overcome to reach the distal parts of the plant. In this review, we highlight the current knowledge about how plant RNA viruses enter plant cells, move between them to reach vascular cells and overcome the different physical and cellular barriers that the phloem imposes. Finally, we update the current research on cellular organelles as key regulator checkpoints in the long-distance movement of plant viruses., This work was funded by grant BIO2017-88321-R from the Spanish Ministerio de Ciencia, Innovacion y Universidades and the Prometeo Program GV2015/010 from the Generalitat Valenciana.

Capítulo 8., Studies on viroid–host interactions have become essential to understand different aspects of the structure–function relationships in the RNA world. Work on viroid RNA has led to seminal discoveries in RNA biology. Over the last two decades, significant progress has been made as to how viroid RNA traffics within and among cells, and how these noncoding RNAs reach vascular tissue to systemically invade plants. The viroid RNA structure consists of different loops and bulges, flanked by double-stranded segments, which give rise to potential RNA motifs that can serve as guiding signals for their intra- and intercellular movement. In this chapter we update knowledge on viroid RNA movement and emphasize its potential as an ideal model to study RNA trafficking., Work in the laboratories of G. Gomez and V. Pallas was supported by grants AGL2013-47886-R (GG) and BIO2014-54362-R (VP) from the Spanish Granting Agency (Direccion General Investigacion Cientifica) and PROMETEO program 2015/010 (Gen. Valenciana).

Since 1971 when the first viroid, potato spindle tuber viroid, was identified, there have been many reports of viroids in horticultural, agricultural, and ornamental crops. Due to their long-range spread by vegetative propagules and seeds from infected plants, viroids have been identified practically all over the world, and almost all of them have been reported in Europe on various hosts.

The International Committee on Virus Taxonomy (ICTV) is the organization responsible for establishing the rules to classify viroids into species, genera, and families, and ultimately to endorse viroid taxonomy. The ICTV recently called for more stringent rules to create new virus and viroid species, which must be based on at least two independent criteria. This chapter discusses the resulting implications and presents an updated viroid classification scheme that takes into account the identification of new viroids by next-generation sequencing and bioinformatics tools, which ICTV may finally accept as new species.

Despite the importance of phloem as an integrative pathway for resource distribution, signaling and plant virus transport little is known about the modifications induced by these pathogens in phloem sap proteome. Only one previous study has actually examined the phloem sap proteome during viral infection using conventional two-dimensional electrophoresis. Since the major limitation of this technique has been its low sensitivity, the authors only identified five phloem proteins with altered abundance. To circumvent this issue we use two-dimensional difference in-gel electrophoresis (2D DIGE) technique, which combined with DeCyder Differential Analysis Software allows a more accurate and sensitive quantitative analysis than with conventional 2D PAGE. We identified 19 different proteins which accumulation in phloem sap was altered during a compatible plant virus infection including redox and hypersensitivity response-related proteins. Therefore, this work would help to understand the basic processes that occur in phloem during plant-virus interaction. (C) 2015 Elsevier B.V. All rights reserved., This work was funded by grant BIO2014-54862-R from the Spanish Direccion General de Investigacion Cientifica y Tecnica (DGICYT) and the Prometeo Program GV2011/003 from the Generalitat Valenciana. J.A.N. and M.S. are the recipients of a postdoctoral contract and a PhD fellowship from the Ministerio de Educacion y Ciencia of Spain. We thank L. Corachan for her technical assistance.

[EN] Tospovirus is the only genus containing virus species which infect plants in the Bunyaviridae family. The aims of this study were to understand the in vivo membrane association of the movement protein (NSm) of the tospovirus species Bean necrotic mosaic virus, Chrysanthemum stem necrosis virus, Tomato chlorotic spot virus and Tomato spotted wilt virus and the homologous and heterologous interactions among NSm and nucleocapsid protein (N). The results obtained by bimolecular fluorescence complementation (BiFC) assay and chemical treatments after membrane fractionation revealed that the four NSm proteins are associated with the biological membranes with the N- and C-termini oriented to the cytoplasm. BiFC analysis for protein protein interactions showed: i) dimer formation for all NSm and N proteins; ii) interaction between NSm and the cognate N and iii) heterologous interactions between the NSm and N proteins. The implications of these interactions in the life cycle of tospoviruses are discussed. (C) 2015 Elsevier Inc. All rights reserved., We thank L. Corachan for her excellent technical assistance. This work was supported by Grant BIO2011-25018 from the Spanish granting agency DGICYT, joint Grant 564633/2010-0 CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico) and CAPES (Conselho de Aperfeicoamento de Pessoal de Nivel Superior) and Grant 2009/00102-2 from FAP-DF (Fundacao de Apoio a Pesquisa do Distrito Federal).