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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