Virus host interactions - PowerPoint PPT Presentation

1 / 32
About This Presentation
Title:

Virus host interactions

Description:

susceptible host plants 'cell-to-cell movement' ... Little Cherry. Flower Breaking. Tissue Deformation. Symptoms of TMV in Tomato ... – PowerPoint PPT presentation

Number of Views:83
Avg rating:3.0/5.0
Slides: 33
Provided by: stevew88
Category:

less

Transcript and Presenter's Notes

Title: Virus host interactions


1
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

2
Plant viruses cause many different symptoms
Little Cherry
Tissue Deformation
3
Symptoms of TMV in Tomato
Strains of TMV infect tomato and cause poor
yield, distorted fruits, delayed fruit ripening
and various fruit discoloration problems that
affect market values.
4
Virions of plant viruses
5
Plant virus genomes
6
Genes encoded by Tobacco mosaic virus
7
Tobacco etch virus genome
SP6
HC-Pro
P1
P3
CI
6
NIa
NIb
Cap
TEV7DA-CMK
(E N L Y F Q S)
NcoI
ClaI
MluI
KpnI
NIa site
bar GFP GUS
TEV-bar TEV-GFP TEV-GUS
GUS
GFP
bar
GUS beta-glucuronidase (turns colorless
substrate to blue precipitate), quantitative GFP
green fluorescent protein (fluoresces green
under ultra violet light), non-destructive bar
basta resistance (herbicides containing basta or
glufosinate), easy selection
8
Viral Pathogenesis
Within the plant, viruses must complete three
major steps in order to infect a susceptible
plant host.
Infection of single cells
Cell-to-cell movement
Long-distance movement
  • Replication
  • Replication
  • Movement to
  • adjacent cells
  • Replication
  • Movement to
  • adjacent cells
  • Movement to
  • cells throughout
  • the plant

9
General features of viral replication
Infection of single cells
  • Steps involved in positive-stranded
  • RNA virus replication
  • 1) Virus enters cells and 2) is uncoated
  • 3) Viral genomic RNA is translated to
  • produce replicase proteins
  • 4) (-)-strand synthesis
  • 5) ()-strand synthesis of sub-genomic RNAs
  • 6) Synthesis of viral proteins
  • 7) Assembly into virions
  • 8) Movement as ribonucleoprotein complexes
  • (doesnt have to be particles!)

10
Genes encoded by Tobacco mosaic virus
11
Role of the host in replication
Host proteins and structures are associated with
sites of viral replication and with replicase
proteins
Basic strategies used so far
  • Cell Biology
  • Biochemistry
  • Forward and reverse genetics in plants and
    heterologous organisms,
  • such as yeast

12
Viral RNA colocalizes with BiP marker for
endoplasmic reticulum (ER) TMV replicates in
association with the endoplasmic reticulum
Mas and Beachy. (1999) J. Cell Biology, 147 (5),
945958
13
Replication of brome mosaic virus (BMV) in yeast
A system to discover host components involved in
viral replication
1a2a directed RNA replication
X URA3 (select for growth without uracil, or
against growth in
5-fluoroorotic acid)
CP, CAT, or GUS (assay for sgRNA synthesis and
translation)
1a and 2a expressed from 2m plasmids (ADH
promoter driver)
5-UTR and 3-UTR sequences missing, so cannot
replicate
in vitro transcribed RNA 3 originally transfected
in yeast
From Ishikawa et al. (1997) PNAS 94 13810.
14
Composition of fatty acids is critical
for replication of brome mosaic virus in yeast
cells-genetic support for importance of host
membranes in viral replication
BMV RNA3-GUS and -CAT are not replicated in oleic
acid deficient yeast (decreased 181
UFA/ increased 160 SFA)
BMV replication is restored by complementing
ole1 mutation. Genetic proof of requirement for
oleic acid.
Lee et al. JOURNAL OF VIROLOGY, Mar. 2001, p.
20972106
15
Spherules form the sites of viral replication in
yeast, not well-developed in oleic acid mutants
Lee and Ahlquist. 2003. J. Virol. 7712819-12828
16
General RNA virus replication strategy
Ahlquist et al. 2003. J. Virol. 778181-8186
17
Virus movement
After the virus replicates it has to be able to
move to new cells and new tissues/organs in order
to systemically infect
Infection of single cells
Cell-to-cell movement
Long-distance movement
  • Replication
  • Replication
  • Movement to
  • adjacent cells
  • Replication
  • Movement to
  • adjacent cells
  • Movement to
  • cells throughout
  • the plant

18
Virus movement pathway
From Carrington et al. (1996) Plant Cell Vol. 8
(10)1669-1681
19
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

Cell-to-cell movement
  • Viral encoded movement proteins (MPs)
  • facilitate these steps. Most MPs are
  • Multifunctional.
  • MPs are required for movement
  • MPs bind to virus genomes
  • MPs interact with plant cytoskeleton
  • MPs localize to plasmodesmata
  • MPs gate plasmodesmata
  • Replication
  • Movement to
  • adjacent cells

20
Plasmodesmata
Lucas. 2006. Virology. 344169-184
21
Structure of plasmodesmata and comparison
to viral particles
22
Genes encoded by Tobacco mosaic virus
23
Viral movement proteins
Lucas. 2006. Virology. 344169-184
24
Model for trafficking through plasmodesmata
Lucas. 2006. Virology. 344169-184
25
Role for cytoskeleton in TMV movement
26
Model for TMV movement
Lucas. 2006. Virology. 344169-184
27
Model for Hordeivirus and Potexvirus movement
Lucas. 2006. Virology. 344169-184
28
Another model for TMV movement that couples
movement to replication
Kawakami et al. 2004. Proc. Natl. Acad. Sci. USA
1016291-6
29
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 genome
  • transporting the viral genome to plasmodesmata
  • gating plasmodesmata
  • trafficking through plasmodesmata
  • Viral movement proteins interact with host
    proteins to accomplish their functions
  • cytoskeleton
  • kinases
  • chaperones
  • docking proteins

30
BMV 1a replicase protein localizes to the
appropriate subcellular membranes, but does not
induce spherule formation in oleic acid deficient
mutants
Lee and Ahlquist. 2003. J. Virol. 7712819-12828
31
Distribution of viral RNA at various stages
after infection by TMV
Mas and Beachy. (1999) J. Cell Biology, 147 (5),
945958
32
Replicase and viral RNA colocalize early in
infection
Mas and Beachy. (1999) J. Cell Biology, 147 (5),
945958
Write a Comment
User Comments (0)
About PowerShow.com