Virus-host interactions trategies viruses use to replicate their genomes in susceptible host cells – “replication” trategies viruses use to move their genomes through susceptible host plants – “cell-to-cell movement” trategies viruses use to suppress host defenses
Virus-host interactions. Strategies viruses use to replicate their genomes in susceptible host cells – “replication” Strategies viruses use to move their genomes throughout susceptible host plants – “cell-to-cell movement” -Strategies viruses use to suppress host defenses. - PowerPoint PPT Presentation
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Virus-host interactions
-Strategies viruses use to replicate their genomes in susceptible host cells – “replication”
-Strategies viruses use to move their genomes throughout susceptible host plants – “cell-to-cell movement”
-Strategies viruses use to suppress host defenses
Plant viruses cause many different symptoms
Necrosis
Vein-banding
Little Cherry
Flower BreakingTissue Deformation
Rigid rod Icosahedral/spherical
Flexuous rod
Virions of plant viruses
Plant virus classes
Genes encoded by Tobacco mosaic virus
Viral Pathogenesis
Within the plant, viruses must complete three major steps in orderto infect a susceptible plant host.
Infection ofsingle cells
Cell-to-cellmovement
Long-distancemovement
Replication ReplicationMovement to adjacent cells
ReplicationMovement to adjacent cellsMovement to cells throughout the plant
Early steps in plant virus infection
Huang et al. 2012. Curr. Opin. Virol.
Roles of host factors in (+) RNA virus replication
Huang et al. 2012. Curr. Opin. Virol.
Assembly of viral replication complexes
Mine and Okuno. 2012. Curr. Opin. Virol.
Virus movement
After the virus replicates it has to be able to move to new cellsand new tissues/organs in order to systemically infect
Infection ofsingle cells
Cell-to-cellmovement
Long-distancemovement
Replication ReplicationMovement to adjacent cells
ReplicationMovement to adjacent cellsMovement to cells throughout the plant
General view of virus cell-to-cell and long-distance movement
Hipper et al. 2013. Front. Plant Sci.
Cell-to-cellmovement
ReplicationMovement to adjacent cells
Steps in cell-to-cell movement
1) Viruses need to leave sites of replication
2) Viruses need to locate the plasmodesmata
3) Viruses need to pass through plasmodesmata
Viral encoded “movement proteins (MPs)”facilitate these steps. Most MPs areMultifunctional.
1) MPs are required for movement
2) MPs bind to virus genomes
3) MPs interact with plant cytoskeleton
4) MPs localize to plasmodesmata
5) MPs gate plasmodesmata
Genes encoded by Tobacco mosaic virus
Replication and early steps in movement
Hyodo et al. 2014. Front. Plant Sci.
Plasmodesmata
Lucas. 2006. Virology. 344:169-184
Structure of plasmodesmata and comparison toviral particles
Model for trafficking through plasmodesmata
Lucas. 2006. Virology. 344:169-184
Lucas. 2006. Virology. 344:169-184
Model for TMV movement
Liu and Nelson. 2013. Front. Plant Sci.
Proposed accumulation and movement pathway for TMV
Suppression of host defenses
Successful pathogens overcome innate host defense responses by targeting signaling, defense gene expression, or defense gene function.
-Suppression of RNA silencing
-Breaking throughthrough or breaking down physical or biochemical barriers
-Suppression (or modulation) of basal defense
-Suppression (or modulation) of (R gene–mediated HR or cell death)
The RNA silencing pathways – innate resistance to viruses
RNA silencing is logically an antiviral defense mechanism
Small RNAs corresponding to viruses can be found in infected tissues
Mutation of RNA silencing components can lead to increased virus infection
Viruses must protect themselves against this degradation pathway
Waterhouse (2006) Science 313:54-55
Plant antiviral RNA silencing
Incarbone and Dunoyer. 2013. Trends Plant Sci.
Anti-viral RNA silencing and its supporession by plant viruses
Scholthof (2006) Nat. Rev. Microbiol.
Tombusvirus P19 is a silencing suppressor
Incarbone and Dunoyer. 2013. Trends Plant Sci.
Antiviral RNA silencing: defense and counter defense
Incarbone and Dunoyer. 2013. Trends Plant Sci.
Perturbation of miRNA pathways to enhance resistance or viral pathogenesis
Can virus infection be beneficial?
Roossinck. 2013. PLoS Pathog.
Ling et al. 2013. Virology 446:397
Chung et al. 2008. PNAS. 105:5897
New overlapping viral ORFs
Summary
- Plant viruses encode proteins that direct the replication and movement of their genomes
- Viral replication occurs in association with host membranes and host factors
- Viral movement is directed by movement proteins that serve many functions:binding the viral genometransporting the viral genome to plasmodesmatagating plasmodesmatatrafficking through plasmodesmata