Plant Pathogens
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
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
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