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Title: Properties of Viruses


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Tom German 637 Russell Lab 262-2956 tlg_at_entomology
.wisc.edu Virology/Virus Vector Relationships

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Billions
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Tulip Flower Break Virus
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Tobacco Mosaic Virus (TMV) has played a central
role in the history of virology
The germ theory gained acceptance in the 19th
century with a recognition of bacteria as
infectious agents of disease.
- -Louis Pasteur -Robert Lister -Robert Koch
(1876, 1882)
Infectious filterable agents -Tobacco mosaic
disease (1886-1898) - Mayer - Ivanowski -
Beijerinck Stanley 1935
Bawdin Pirie 50s
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Tobacco mosaic virus (TMV) symptoms on tobacco
From Mathews Plant Virology, Fourth Edition, 2001
http//www.apsnet.org/education/k-12plantpathways/
TeachersGuide/Activities/TMV/purpose.htm
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Tospovirus Symptoms
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Potato Leaf Roll Virus (PLRV) and Net Necrosis
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Tobacco Rattle Virus
Corky Ringspot Disease
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Potato Virus Y complex
PVYntn
PVYo
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Maize fine streak virus causes fine chlorotic
streaks and dwarfing on maize.
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Cucumber mosaic virus (CMV)
Rugosity
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Fig. 10. TMV infection of plants with or without
the dominant N gene. (Left) Systemic mosaic
symptoms of TMV infection on nn tobacco plants.
(Right) Localized necrotic lesions typical of the
hypersensitive response on a leaf from a
TMV-infected tobacco plant carrying the N gene.
Photographs courtesy of Dr. Milt Zaitlin, Cornell
University.
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CMV-Fny CMV-M
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PVX PVY PVY ONLY
PVX ONLY
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Symptoms of Viroid Diseases
CCCVd
PSTVd
CSVd
CEVd
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The RNA genomes of viroids are 246-375
nucleotides in length and share many
similarities They are all single stranded
covalent circles There is extensive
intramolecular base pairing A DNA-directed RNA
polymerase makes both plus and minus strands
Replication does not depend on the presence of
a helper virus No proteins are encoded
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Circular and linear forms of the Potato Spindle
Tuber Viroid observed using a nucleic acid
spreading technique followed by high angle
shadowing with platinum metal.Magnified
350,000X.
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Host Range
Host range the Viral Perspective
  • Wide host range One virus infects more than one
    plant species  
  • Narrow host range Some viruses are host specific 

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Host TRange
The Plant Perspective
  • Each plant species is usually susceptible to
    several different kinds of viruses
  • A plant can be infected with more than one kind
    of virus at the same time
  • mixed infections
  • synergistic effect

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VIRUSEGeneS!! What they are ??
General Characteristics of Viruses
  • Nucleoprotein
  • nucleic acid surrounded by a protein coat
  • acellular, lacks a metabolism of its own
  • Obligate parasites
  • can only multiply in living cell
  • has the ability to cause disease
  • Submicroscopic
  • too small to be seen individually with a light
    microscope
  • electron microscope (EM)

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Viruses The Ultimate Parasites
  • No physiologic activity
  • No energy production
  • Do not divide
  • Do not produce any kind of specialized
    reproductive structures
  • Multiply by inducing host cells to make more virus

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  • Cause disease by utilizing cellular
  • substances during multiplication
  • Interfering with host metabolism and
    developmental regulation
  • Do not consume cells or kill them with toxins

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Viruses The Ultimate Parasites
  • Smaller than the smallest prokaryotic cell
  • Variable size range
  • small--25 nm
  • larger--300 nm

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Fig. 3. Classification of plant viruses. From
Van Regenmortel, M.H.V., Fauquet, C.M., Bishop,
D. et al. (1999). Virus Taxonomy Seventh Report
of the International Committee on Taxonomy of
Viruses.
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Luteoviruses / Potyviruses
Geminiviruses
Tobacco mosaic virus
Tospoviruses
Rhabdoviruses
The Big Picture Book of Viruses
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Plant Viruses Nucleic Acids
ss RNA viruses () RNA Tobacco mosaic virus
(-) RNA Tomato spotted wilt virus ds RNA
viruses Rice fiji disease virus ds DNA
viruses Cauliflower mosaic virus ss DNA
viruses Tomato yellow leaf curl virus
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What it is a VIRION?
  • The Infectious viral Unit
  • Monopartite one type of virus particles
  • Multicomponent (split genomes)
  • bipartite two types of virus particles
  • tripartite three types of virus particles
  • All must be in plant for disease development
  • Different length rods
  • Different density isometric particles

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Multipartite/Multiparticulate
BMV
TRV
TMV
AMV
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Multipartite genome
  • Brome mosaic virus
  • The genome is segmented tripartite, segments are
    distributed among 3 particles

RNA 3
RNA 1
RNA 2
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Fig. 20. Structure and genome organization of
sonchus yellow net virus (SYNV), a
nucleorhabdovirus. From Jackson et al. (1999)
Encyc. of Virology (3rd Edition), pp. 1531-1541
with permission.
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Icosahedral structure of viruses in the
Bromoviridae
For these types of icosahedral viruses (T3),
virions consist of 180 coat protein subunits
Speir et al., Structure 363-78 (1995)
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Speir et al., Structure 363-78 (1995)
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Coat Protein
  • Provides protective sheathing for NA
  • Determines vector transmissibility
  • Determines symptoms
  • Assembly
  • Inclusion bodies

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Coat protein Composition?
  • Protein shell composed of repeating subunits,
    constant for a given virus
  • TMV protein subunit 158 amino acids
  • Protein subunits arranged in a helix
  • Diameter 18 nm
  • Central hole diameter 4 nm
  • NA packed tightly between the helices
  • NA in polyhedral viruses folded in unknown matter
    inside the shell

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Diagnosis and Identification
Symptoms
  • Virus morphology
  • Viral nucleic acid components
  • Viral Protein characteristics
  • ELISA
  • Protein physical properties
  • Inclusion Bodies in infected cells

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Cucumber Mosaic Virus
Three genomic RNAs
Single Coat Protein
Isometric Virions
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Enzyme Linked Immunosorbent Assay ELISA
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Light Microscopic Identification
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