Plant viruses
Viral Species Diversity of Plants
Genomic Approaches to Discovery of Viral Species Diversity of Non-cultivated Plants
from Ulrich Melcher and Veenita Grover writing in Recent Advances in Plant Virology
Outbreaks of newly emerging and re-emerging animal and plant viruses pose a constant threat to public health and food security and emphasize the need to develop efficient methods for viral detection and identification. Ongoing studies for discovery of viral species in non-cultivated plants utilize genomic approaches for systematic unbiased searches for viruses related to known viruses. Genomic approaches use various combinations of methods for sampling the environment, enriching samples for content of viral genomes, amplifying nucleic acids, and detecting virus-related sequences among the amplified nucleic acids. These methods include particularly array hybridization to macroarrays and microarrays, and various megasequencing approaches. In all cases, relatives of known viruses are discovered. However, the identification of a novel plant virus completely unrelated to known ones remains a challenge. Despite a growing list of viruses infecting wild plants, virus infections in wild plant communities are often underestimated relative to cultivated systems, since viruses in wild plants are generally considered not to harm the host. Viruses may not be explicitly damaging wild plants, but their biodiversity and abundance suggest an important role of these viruses in ecosystems. These roles should not be under-rated just because they are under-researched.
Further reading: Recent Advances in Plant Virology | Virology Publications
from Ulrich Melcher and Veenita Grover writing in Recent Advances in Plant Virology
Outbreaks of newly emerging and re-emerging animal and plant viruses pose a constant threat to public health and food security and emphasize the need to develop efficient methods for viral detection and identification. Ongoing studies for discovery of viral species in non-cultivated plants utilize genomic approaches for systematic unbiased searches for viruses related to known viruses. Genomic approaches use various combinations of methods for sampling the environment, enriching samples for content of viral genomes, amplifying nucleic acids, and detecting virus-related sequences among the amplified nucleic acids. These methods include particularly array hybridization to macroarrays and microarrays, and various megasequencing approaches. In all cases, relatives of known viruses are discovered. However, the identification of a novel plant virus completely unrelated to known ones remains a challenge. Despite a growing list of viruses infecting wild plants, virus infections in wild plant communities are often underestimated relative to cultivated systems, since viruses in wild plants are generally considered not to harm the host. Viruses may not be explicitly damaging wild plants, but their biodiversity and abundance suggest an important role of these viruses in ecosystems. These roles should not be under-rated just because they are under-researched.
Further reading: Recent Advances in Plant Virology | Virology Publications
Begomovirus
Category: Pathogens | Plant Science
Emergence of Begomovirus Diseases
from Enrique Moriones, Jesus Navas-Castillo and Juan-Antonio Díaz-Pendón writing in Recent Advances in Plant Virology
Begomoviruses (genus Begomovirus, family Geminiviridae) rank among the top of the most important plant viruses causing disease of severe consequences in economically and socially relevant crops. From the early 1990s, a rapid emergence and geographic expansion of begomoviruses has occurred worldwide. As a result, these viruses have become the most destructive group of plant viruses in tropical and subtropical regions of the world. Their emergence is associated with the emergence of populations of the insect vector, the whitefly Bemisia tabaci, probably due to increased plant trading between distantly separated geographical regions and changes in agricultural practices. Human activity seems to have been a major factor promoting emergence of begomoviruses. Other factors also drive emergence.
Further reading: Recent Advances in Plant Virology | Virology Publications
from Enrique Moriones, Jesus Navas-Castillo and Juan-Antonio Díaz-Pendón writing in Recent Advances in Plant Virology
Begomoviruses (genus Begomovirus, family Geminiviridae) rank among the top of the most important plant viruses causing disease of severe consequences in economically and socially relevant crops. From the early 1990s, a rapid emergence and geographic expansion of begomoviruses has occurred worldwide. As a result, these viruses have become the most destructive group of plant viruses in tropical and subtropical regions of the world. Their emergence is associated with the emergence of populations of the insect vector, the whitefly Bemisia tabaci, probably due to increased plant trading between distantly separated geographical regions and changes in agricultural practices. Human activity seems to have been a major factor promoting emergence of begomoviruses. Other factors also drive emergence.
Further reading: Recent Advances in Plant Virology | Virology Publications
Plant Infection by Viruses
Population Dynamics and Genetics of Plant Infection by Viruses
from Fernando García-Arenal and Aurora Fraile writing in Recent Advances in Plant Virology
During the last thirty years, progress in understanding the mechanistic aspects of virus-plant interactions has been remarkable, notably in aspects such as genome replication, movement within the infected host or pathogenesis and resistance. Progress in understanding the population dynamics and genetics of plant infection by viruses has not been as great. However, understanding the kinetics of plant colonisation and the genetic structure of the within-host virus population is necessary for addressing many issues of plant-virus interaction and of virus evolution. The quantitative aspects of plant infection and colonisation by viruses were mostly addressed during the early period of plant virology, when many detailed studies were published that often incorporated mathematical modelling. These issues have not been thoroughly re-examined using molecular techniques. Recent work has focussed on the description of the genetic structure of the virus population at the organ and the plant level. Data suggest that in spite of huge fecundity, the effective numbers of the within-host virus population may be small due to severe population bottlenecks at each stage of plant infection and colonisation, which results in a spatially structured population.
Further reading: Recent Advances in Plant Virology | Virology Publications
from Fernando García-Arenal and Aurora Fraile writing in Recent Advances in Plant Virology
During the last thirty years, progress in understanding the mechanistic aspects of virus-plant interactions has been remarkable, notably in aspects such as genome replication, movement within the infected host or pathogenesis and resistance. Progress in understanding the population dynamics and genetics of plant infection by viruses has not been as great. However, understanding the kinetics of plant colonisation and the genetic structure of the within-host virus population is necessary for addressing many issues of plant-virus interaction and of virus evolution. The quantitative aspects of plant infection and colonisation by viruses were mostly addressed during the early period of plant virology, when many detailed studies were published that often incorporated mathematical modelling. These issues have not been thoroughly re-examined using molecular techniques. Recent work has focussed on the description of the genetic structure of the virus population at the organ and the plant level. Data suggest that in spite of huge fecundity, the effective numbers of the within-host virus population may be small due to severe population bottlenecks at each stage of plant infection and colonisation, which results in a spatially structured population.
Further reading: Recent Advances in Plant Virology | Virology Publications
Control Measures Against Viruses
Integrated Control Measures Against Viruses and Their Vectors
from Alberto Fereres and Aranzazu Moreno writing in Recent Advances in Plant Virology
Viruses and their vectors produce severe damage to crops worldwide. Of importance are the strategies and tactics used to manage vectors of plant viruses, with special attention to insects, by far the most important type of vector. The philosophy and principles of Integrated Pest Management (IPM) developed long ago can still provide an effective and sustainable way to manage insect vectors of virus diseases of plants. Preventive strategies such as the development of models that forecast virus disease outbreaks together with host plant resistance, cultural and physical tactics are the most effective ways to control nonpersistently-transmitted viruses. A reduction in vector numbers using conventional systemic insecticides or innundative biological control agents can also provide effective control of persistently-transmitted viruses. Recent advances on understanding of the mode of transmission of plant viruses are also a very promising way to develop molecules to block putative virus binding sites within the vector and to avoid virus retention and transmission. Also, the characterization of aphid's salivary components that is underway may facilitate the development of new tools to interfere with the process of transmission of plant viruses.
Further reading: Recent Advances in Plant Virology | Virology Publications
from Alberto Fereres and Aranzazu Moreno writing in Recent Advances in Plant Virology
Viruses and their vectors produce severe damage to crops worldwide. Of importance are the strategies and tactics used to manage vectors of plant viruses, with special attention to insects, by far the most important type of vector. The philosophy and principles of Integrated Pest Management (IPM) developed long ago can still provide an effective and sustainable way to manage insect vectors of virus diseases of plants. Preventive strategies such as the development of models that forecast virus disease outbreaks together with host plant resistance, cultural and physical tactics are the most effective ways to control nonpersistently-transmitted viruses. A reduction in vector numbers using conventional systemic insecticides or innundative biological control agents can also provide effective control of persistently-transmitted viruses. Recent advances on understanding of the mode of transmission of plant viruses are also a very promising way to develop molecules to block putative virus binding sites within the vector and to avoid virus retention and transmission. Also, the characterization of aphid's salivary components that is underway may facilitate the development of new tools to interfere with the process of transmission of plant viruses.
Further reading: Recent Advances in Plant Virology | Virology Publications
NB-LRR Immune Receptors in Plant Virus Defense
NB-LRR Immune Receptors in Plant Virus Defense
from Patrick Cournoyer and Savithramma P. Dinesh-Kumar writing in Recent Advances in Plant Virology
Resistance genes protect plants from infection by viruses and many other classes of pathogens. The dominant, anti-viral R genes that have been cloned thus far encode NB-LRR immune receptors that detect a single viral protein and trigger defense. Many different types of viral proteins are known to elicit defense by corresponding NB-LRRs. Defense often results in a type of localized programmed cell death at the site of attempted pathogen infection known as the hypersensitive response (HR-PCD), but some NB-LRRs confer resistance to viruses without HR-PCD. The activation of NB-LRRs triggers manifold signaling events including reactive oxygen species (ROS) production, nitric oxide (NO) production, calcium (Ca2+) influx, activation of mitogen activated protein kinases (MAPKs), and production of the plant hormones salicylic acid (SA), jasmonic acid (JA), and ethylene. After a successful NB-LRR-mediated defense event, the plant exhibits heightened resistance to future pathogen challenge in a state called systemic acquired resistance.
Further reading: Recent Advances in Plant Virology | Virology Publications
from Patrick Cournoyer and Savithramma P. Dinesh-Kumar writing in Recent Advances in Plant Virology
Resistance genes protect plants from infection by viruses and many other classes of pathogens. The dominant, anti-viral R genes that have been cloned thus far encode NB-LRR immune receptors that detect a single viral protein and trigger defense. Many different types of viral proteins are known to elicit defense by corresponding NB-LRRs. Defense often results in a type of localized programmed cell death at the site of attempted pathogen infection known as the hypersensitive response (HR-PCD), but some NB-LRRs confer resistance to viruses without HR-PCD. The activation of NB-LRRs triggers manifold signaling events including reactive oxygen species (ROS) production, nitric oxide (NO) production, calcium (Ca2+) influx, activation of mitogen activated protein kinases (MAPKs), and production of the plant hormones salicylic acid (SA), jasmonic acid (JA), and ethylene. After a successful NB-LRR-mediated defense event, the plant exhibits heightened resistance to future pathogen challenge in a state called systemic acquired resistance.
Further reading: Recent Advances in Plant Virology | Virology Publications
RNA Silencing in Plants and Viral Suppressors
Category: RNA | Plant Science
RNA Silencing in Plants and the Role of Viral Suppressors
from Ana Giner, Juan Jose Lopez-Moya and Lorant Lakatos writing in RNA Interference and Viruses
The term RNA silencing refers to several pathways present in eukaryotic organisms that lead to the sequence specific elimination or functional blocking of RNAs with homology to double stranded RNAs (dsRNAs) that have previously triggered the mechanism. Besides playing important roles in developmental control, RNA silencing forms part of the defence against viruses in plants, acting as a potent antiviral mechanism. To escape from the RNA silencing-based defence, most plant viruses make use of different strategies, the most common relying in the action of viral proteins with the capacity to suppress RNA silencing. The characterization of these viral suppressors is providing useful insights to understand how RNA silencing works, revealing components and steps in the silencing pathways.
Further reading: Recent Advances in Plant Virology | RNA Interference and Viruses | RNA and the Regulation of Gene Expression
from Ana Giner, Juan Jose Lopez-Moya and Lorant Lakatos writing in RNA Interference and Viruses
The term RNA silencing refers to several pathways present in eukaryotic organisms that lead to the sequence specific elimination or functional blocking of RNAs with homology to double stranded RNAs (dsRNAs) that have previously triggered the mechanism. Besides playing important roles in developmental control, RNA silencing forms part of the defence against viruses in plants, acting as a potent antiviral mechanism. To escape from the RNA silencing-based defence, most plant viruses make use of different strategies, the most common relying in the action of viral proteins with the capacity to suppress RNA silencing. The characterization of these viral suppressors is providing useful insights to understand how RNA silencing works, revealing components and steps in the silencing pathways.
Further reading: Recent Advances in Plant Virology | RNA Interference and Viruses | RNA and the Regulation of Gene Expression
Vector-mediated Transmission
Category: Virology
Functions of Virus and Host Factors During Vector-mediated Transmission
from Stéphane Blanc and Martin Drucker writing in Recent Advances in Plant Virology
Most plant viruses are transmitted by living vectors that transport viruses to a new host plant. One discriminates between circulative transmission, where viruses must pass through the vector interior and are usually inoculated with the saliva on a healthy plant, and non-circulative transmission, where viruses do not need to pass through the vector interior but are directly inoculated from the mouth parts into a new host. Especially transmission of non-circulative viruses has been regarded as a simple process where a vector more or less accidentally transports the virus. However, it becomes more and more evident that this scenario is unlikely, because transmission constitutes a dramatic bottleneck of the virus life cycle, where only very few viral genomes pass to a new host, and where a given virus must do everything to ensure successful transmission. Viruses, also in non-circulative transmission, deliberately manipulate their hosts and vectors in often very unexpected ways to optimise their transmission.
Further reading: Recent Advances in Plant Virology | Virology Publications
from Stéphane Blanc and Martin Drucker writing in Recent Advances in Plant Virology
Most plant viruses are transmitted by living vectors that transport viruses to a new host plant. One discriminates between circulative transmission, where viruses must pass through the vector interior and are usually inoculated with the saliva on a healthy plant, and non-circulative transmission, where viruses do not need to pass through the vector interior but are directly inoculated from the mouth parts into a new host. Especially transmission of non-circulative viruses has been regarded as a simple process where a vector more or less accidentally transports the virus. However, it becomes more and more evident that this scenario is unlikely, because transmission constitutes a dramatic bottleneck of the virus life cycle, where only very few viral genomes pass to a new host, and where a given virus must do everything to ensure successful transmission. Viruses, also in non-circulative transmission, deliberately manipulate their hosts and vectors in often very unexpected ways to optimise their transmission.
Further reading: Recent Advances in Plant Virology | Virology Publications
Movement of Viruses Via the Plant Phloem
Category: Virology | Plant Science
Systemic Movement of Viruses Via the Plant Phloem
from Vicente Pallás, Ainhoa Genovés, M. Amelia Sánchez-Pina and José Antonio Navarro writing in Recent Advances in Plant Virology
The incorporation of non invasive techniques has allowed remarkable progress in our understanding of the vascular transport of plant viruses. Indeed, approximately seventy-five percent of reports about this topic have been published after the first use of the jellyfish green fluorescent protein (GFP) in plant virology. In the last two decades, a very detailed picture of the viral determinants involved in phloem transport of plant viruses has been obtained. However, we realize that most virus-host interactions are pathosystem-specific and, consequently, the identification of common host factors involved in phloem transport of plant viruses is the exception rather than the rule. In addition, we are still far from obtaining a clear picture of how environmental factors influence the vascular invasion of plants by these pathogens. A recent publication reviews the progress made in understanding the viral determinants involved in vascular transport of viruses and the pathways followed by viruses during systemic movement, and focuses on host and environmental conditions that influence the final distribution of viruses in the plant.
Further reading: Recent Advances in Plant Virology | Virology Publications
from Vicente Pallás, Ainhoa Genovés, M. Amelia Sánchez-Pina and José Antonio Navarro writing in Recent Advances in Plant Virology
The incorporation of non invasive techniques has allowed remarkable progress in our understanding of the vascular transport of plant viruses. Indeed, approximately seventy-five percent of reports about this topic have been published after the first use of the jellyfish green fluorescent protein (GFP) in plant virology. In the last two decades, a very detailed picture of the viral determinants involved in phloem transport of plant viruses has been obtained. However, we realize that most virus-host interactions are pathosystem-specific and, consequently, the identification of common host factors involved in phloem transport of plant viruses is the exception rather than the rule. In addition, we are still far from obtaining a clear picture of how environmental factors influence the vascular invasion of plants by these pathogens. A recent publication reviews the progress made in understanding the viral determinants involved in vascular transport of viruses and the pathways followed by viruses during systemic movement, and focuses on host and environmental conditions that influence the final distribution of viruses in the plant.
Further reading: Recent Advances in Plant Virology | Virology Publications
Plasmodesmata and Virus Movement
Category: Virology
Plasmodesmata as Active Conduits for Virus Cell-to-Cell Movement
from Lourdes Fernandez-Calvino, Christine Faulkner and Andy Maule writing in Recent Advances in Plant Virology
It has been known for many decades that viruses need to exploit plasmodesmata as channels of cytoplasmic connectivity through plant cell walls. However, we do not yet understand the molecular mechanisms involved in moving a single infectious entity from cell to cell, although it is clear that virus-encoded movement proteins play a central role. Major progress has been made in identifying movement proteins, their associations with subcellular structures/organelles, and their biochemical properties with respect to nucleic acid-binding and physical associations with host and other viral proteins. These studies reveal a specificity in functional evolution where viruses share some similarities in their movement strategies with near and far phylogenetic groups but show few examples of processes that might apply to all or many individual viruses. Plasmodesmata also provide channels for cellular communication essential for plant growth, development and defense. As such, there is increasing attention aimed at resolving their constituent components necessary for structure and function. With the limited success of genetic screens, proteomic analysis of biochemically-enriched plasmodesmal fractions has also been pursued. Through the identification of plasmodesmal proteins we will have the opportunity to understand how movement proteins bring about the massive changes in the physical behaviour of plasmodesmata that result in the translocation of the macromolecular complexes responsible for virus infectivity.
Further reading: Recent Advances in Plant Virology | Virology Publications
from Lourdes Fernandez-Calvino, Christine Faulkner and Andy Maule writing in Recent Advances in Plant Virology
It has been known for many decades that viruses need to exploit plasmodesmata as channels of cytoplasmic connectivity through plant cell walls. However, we do not yet understand the molecular mechanisms involved in moving a single infectious entity from cell to cell, although it is clear that virus-encoded movement proteins play a central role. Major progress has been made in identifying movement proteins, their associations with subcellular structures/organelles, and their biochemical properties with respect to nucleic acid-binding and physical associations with host and other viral proteins. These studies reveal a specificity in functional evolution where viruses share some similarities in their movement strategies with near and far phylogenetic groups but show few examples of processes that might apply to all or many individual viruses. Plasmodesmata also provide channels for cellular communication essential for plant growth, development and defense. As such, there is increasing attention aimed at resolving their constituent components necessary for structure and function. With the limited success of genetic screens, proteomic analysis of biochemically-enriched plasmodesmal fractions has also been pursued. Through the identification of plasmodesmal proteins we will have the opportunity to understand how movement proteins bring about the massive changes in the physical behaviour of plasmodesmata that result in the translocation of the macromolecular complexes responsible for virus infectivity.
Further reading: Recent Advances in Plant Virology | Virology Publications
Plant RNA Viruses
Replication of Plant RNA Viruses
from Peter D. Nagy and Judit Pogany writing in Recent Advances in Plant Virology
Among plant viruses, the positive-stranded RNA [(+)RNA] viruses are the largest group, and the most widespread. The central step in the infection cycle of (+)RNA viruses is RNA replication, which is carried out by virus-specific replicase complexes consisting of viral RNA-dependent RNA polymerase, one or more auxiliary viral replication proteins, and a number of co-opted host factors. Viral replicase complexes assemble in specialized membranous compartments in infected cells. Sequestering the replicase complexes is not only helpful for rapid production of a large number of viral (+)RNA progeny, but it also facilitates avoiding recognition by the host¹s anti-viral surveillance system, and it provides protection from degradation of the viral RNA. Successful viral replication is followed by cell-to-cell and long-distance movement throughout the plant, as well as encapsidation of the (+)RNA progeny to facilitate transmission to new plants. A recent review provides an overview of our current understanding of the molecular mechanisms in plant (+)RNA virus replication. Recent significant progress in this research area is based on development of powerful in vivo and in vitro methods, including replicase assays, reverse genetic approaches, intracellular localization studies, genome-wide screens for co-opted host factors and the use of plant or yeast model hosts.
Further reading: Recent Advances in Plant Virology | Virology Publications | RNA and the Regulation of Gene Expression
from Peter D. Nagy and Judit Pogany writing in Recent Advances in Plant Virology
Among plant viruses, the positive-stranded RNA [(+)RNA] viruses are the largest group, and the most widespread. The central step in the infection cycle of (+)RNA viruses is RNA replication, which is carried out by virus-specific replicase complexes consisting of viral RNA-dependent RNA polymerase, one or more auxiliary viral replication proteins, and a number of co-opted host factors. Viral replicase complexes assemble in specialized membranous compartments in infected cells. Sequestering the replicase complexes is not only helpful for rapid production of a large number of viral (+)RNA progeny, but it also facilitates avoiding recognition by the host¹s anti-viral surveillance system, and it provides protection from degradation of the viral RNA. Successful viral replication is followed by cell-to-cell and long-distance movement throughout the plant, as well as encapsidation of the (+)RNA progeny to facilitate transmission to new plants. A recent review provides an overview of our current understanding of the molecular mechanisms in plant (+)RNA virus replication. Recent significant progress in this research area is based on development of powerful in vivo and in vitro methods, including replicase assays, reverse genetic approaches, intracellular localization studies, genome-wide screens for co-opted host factors and the use of plant or yeast model hosts.
Further reading: Recent Advances in Plant Virology | Virology Publications | RNA and the Regulation of Gene Expression
Plant Virology
Carole Caranta, Miguel A. Aranda, Mark Tepfer and J.J. Lopez-Moya (INRA-UR , Génétique et Amélioration des Fruits et Légumes, Montfavet cedex, France;Centro de Edafología y Biología Aplicada del Segura (CEBAS), CSIC, Espinardo, Murcia, Spain;Laboratoire de Biologie Cellulaire, INRA, F Versailles Cedex, France;IBMB, Centre for Research in Agricultural Genomics (CRAG) CSIC-IRTA-UAB, Barcelona, Spain, respectively) present a new book on Recent Advances in Plant Virology
Viruses that infect plants are responsible for reduction in both yield and quality of crops around the world, and are thus of great economic importance. This has provided the impetus for the extensive research into the molecular and cellular biology of these pathogens and into their interaction with their plant hosts and their vectors. However interest in plant viruses extends beyond their ability to damage crops. Many plant viruses, for example tobacco mosaic virus, have been used as model systems to provide basic understanding of how viruses express genes and replicate. Others permitted the elucidation of the processes underlying RNA silencing, now recognised as a core epigenetic mechanism underpinning numerous areas of biology.
This book attests to the huge diversity of research in plant molecular virology. Written by world authorities in the field, the book opens with two chapters on the translation and replication of viral RNA. Following chapters cover topics such as viral movement within and between plants, plant responses to viral infection, antiviral control measures, virus evolution, and newly emerging plant viruses. To close there are two chapters on biotechnological applications of plant viruses. Throughout the book the focus is on the most recent, cutting-edge research, making this book essential reading for everyone, from researchers and scholars to students, working with plant viruses.
Viruses that infect plants are responsible for reduction in both yield and quality of crops around the world, and are thus of great economic importance. This has provided the impetus for the extensive research into the molecular and cellular biology of these pathogens and into their interaction with their plant hosts and their vectors. However interest in plant viruses extends beyond their ability to damage crops. Many plant viruses, for example tobacco mosaic virus, have been used as model systems to provide basic understanding of how viruses express genes and replicate. Others permitted the elucidation of the processes underlying RNA silencing, now recognised as a core epigenetic mechanism underpinning numerous areas of biology.
This book attests to the huge diversity of research in plant molecular virology. Written by world authorities in the field, the book opens with two chapters on the translation and replication of viral RNA. Following chapters cover topics such as viral movement within and between plants, plant responses to viral infection, antiviral control measures, virus evolution, and newly emerging plant viruses. To close there are two chapters on biotechnological applications of plant viruses. Throughout the book the focus is on the most recent, cutting-edge research, making this book essential reading for everyone, from researchers and scholars to students, working with plant viruses.
 | Edited by: Carole Caranta, Miguel A. Aranda, Mark Tepfer and J.J. Lopez-Moya ISBN: 978-1-904455-75-2 Publisher: Caister Academic Press Publication Date: February 2011 Cover: hardback |