This document summarizes a presentation on plant viruses given by Divya Singh at Narendra Deva University of Agriculture and Technology. The presentation covered the introduction of viruses, characteristics of plant viruses, their structure and morphology, composition, and concluded with key points. Plant viruses are obligate intracellular parasites composed of nucleic acid surrounded by a protective protein coat. They can have various shapes, and nucleic acids that are single or double stranded RNA and DNA. The composition of viruses includes proteins, nucleic acids, and sometimes enzymes.

2. By
Divya Singh
ID. No. : A5205/10/14
Venue : Seminar Hall
Time: : 11:00 AM
Date : 04/09/2015
DEPARTMENT OF PLANT PATHOLOGY
NARENDRA DEVA UNIVERSITY OF AGRICULTURE AND
TECHNOLOGYKUMARGANJ FAIZABAD 224229

3. HIGHLIGHTS
Introduction
Characteristics of plant viruses
 structure and morphology of plant viruses
 Composition of plant viruses
Conclusion

4. Introduction
 A virus is a nucleoprotein that multiplies only in the
living host cells and has ability to cause the disease.
 Viruses are link between living and non living. They
can reproduce and mutate, have nucleic acid like
living organism. It can be crystallized, and not
reproduce outside the living cell like non living.
 Many economically important, destructive diseases
of crops are caused by viruses. e.g. Yellow vein
mosaic of okra , Cauliflower mosaic, Sterility mosaic
of pigeon pea, Bunchy top of banana, Rice tungro
disease, Citrus tristeza disease, Leaf curl of tomato
etc.

5.  Involvement of virus in plant disease was proved by M. W.
Beijerinck(1898) who worked on tobacco mosaic disease.
He concluded that pathogenic agent of the disease was a
“Contagium Vivum Fluidum” which he later called VIRUS.
 W. M. Stanley(1935) isolated virus in a crystalline protein .
He concluded that the virus was an autocatalytic protein
that could multiply within living cells and got nobel prize in
1946.
 F. C. Bawden and N. W. Pirie (1936) proved that TMV was a
nucleoprotein. Nucleic acid in TMV was identified as RNA.
 Gierer and Schramm (1956) showed that TMV nucleic acid
free from its protein coat, could alone cause infection.
 Black (1963) discovered ds- RNA reoviruses.
 B. kassin (1966) discovered satellite virus Tobacco necrosis
satellite virus.
 Shepherd et al (1968) discovered first DNA plant virus
causing Cauliflower mosaic disease.

6. M. W. Beijerinck
Father of Virology

7. Characteristics of plant viruses
Small acellular infectious agent
 Obligate intracellular parasite
Made of nucleic acid and protein. Nucleic acid must
be surrounded by a protective protein coat.
Nucleic acid is DNA or RNA (not both) that may be
single stranded or double stranded, linear or circular.

8. Structure of plant viruses
Viruses consist of nucleic acid
either RNA or DNA, surrounded
by a protein coat called the
capsid.
 The capsid is composed of small
structural units called
capsomeres.
 The capsid protects nucleic acid
from inactivation by the outer
Physical condition.
 Rhabdovirus and Tospo virus groups
are provided with an outer membrane
called envelope inside the membrane
the nucleoprotein core is called
nucleocapsid.
Tobacco mosaic virus
capsid
capsomere
Nucleic acid(RNA)
envelope
nucleocapsid
Tomato spotted wilt virus

9. Monopartite genome, Multipartite genome &
Multicomponent viruses
Monopartite genome : The genome of the
viruses is present as single continuous strand. e.g.
Tobacco mosaic virus, Cauliflower mosaic virus
Multipartite genome : Viruses have two or more
molecular species of nucleic acid encapsidated
within same (Tomato spotted wilt virus) or
separate protein cell. Such genome are referred to
as bi-, tri- or multipartite. e.g. Tobacco rattle virus,
Alfalfa mosaic virus.

10. Multicomponent virus :
The division of the genetic information in to two or
more parts is a feature found in certain group of
RNA viruses. In such multicomponent viruses, all
of the nucleic strand component must be present
in the plant to cause infection.
e.g. Brome mosaic virus, Tobacco ring spot virus

11. Genome type and genome structure of some plant
viruses
Virus Genome type Genome structure
Tobacco mosaic virus (rigid rod) ss- RNA Monopartite
Tobacco rattle virus (rigid rod) ss- RNA Bipartite
Potato mop top virus (rigid rod) ss- RNA Tripartite
Potato virus Y (Flexuous rod) ss- RNA Monopartite
Turnip yellow mosaic virus (Isometric) ss- RNA Monopartite
Tobacco ring spot virus (Isometric) ss- RNA Bipartite
Brome mosaic virus (Isometric) ss- RNA Tripartite
Wound tumor virus (Isometric) ds- RNA Monopartite
Lettuce big vein virus (Rigid rod) ds- RNA Tripartite
Tobacco leaf curl virus (Isometric) ss- DNA Bipartite
Banana bunchy top virus (Isometric) ss- DNA Multipartite
Cauliflower mosaic virus (Isometric) ds- DNA Monopartite

12. Shape and Size
Elongated viruses : Some elongated viruses are rigid
rods about 15 by 300 nm e.g. TMV
But most appear as flexous thread, that are usually 10-
13nm wide and 480-2,000 nm long. e.g. Potato virus Y
Rigid rod shaped TMV Flexous thread like potato virus Y

13. Spherical viruses:
Most spherical viruses are polyhedral (isometric) ranging 17-60
nm in diameter. e.g. Turnip yellow mosaic virus (TYNV),
Cauliflower mosaic virus (CaMV).
Tomato spotted wilt virus is surrounded by a membrane and has
a flexible spherical shape about 100nm in diameter.
Spherical particle of CaMV
Twined isometric particles of
Tomato leaf curl virus

14. Bacilliform viruses
These are short bacillus like cylindrical rods that are
about 52-75nm wide and 300-380nm long. e.g.
Rhabdovirus, Rice tungro bacilliform virus (RTBV).
Bacilliform particle of Alfalfa
mosaic virus
RTBV

15. Size and shape of some plant viruses
Virus Particle Shape Size (nm)
Tobacco necrosis satellite virus (Smallest
plant virus)
Isometric 17
Cowpea mosaic virus Isometric 24
Turnip yellow mosaic virus Isometric 28-30
Cauliflower mosaic virus Isometric 50
Alfalfa mosaic virus Bacilliform 28-58 x 18
Wound tumor virus Isometric 60
Tobacco mosaic virus Rigid rod 300 x 18
Potato virus X Flexuous rod 470-580 x 13
Potato virus Y Flexuous rod 680-900 x 11
Citrus tristeza virus (Longest plant virus) Flexuous rod 2000 x 10-12

16. Chemical composition of plant viruses
• Protein (capsid)
• Capsomere
• Nucleic acid
•RNA
•+ve sense RNA
• -ve sense RNA
• ss- RNA
•ds- RNA
 DNA
 ds- DNA
 ss- RNA

17. Composition of viruses
• Protein
Makes up 60-95 % of the virion
• Nucleic acid
Makes up 5-40 % of the virion
Spherical virus- 20-40 %
Elongated virus- 5-6%
• Some viruses contain small amount of
enzyme and membrane lipid.

18. % of Nucleic acid and Protein in some plant viruses
Virus % Nucleic
acid
% Protein Particle shape
Tobacco mosaic virus 5 95 rigid rod
Potato virus X 6 94 flexuous rod
Potato virus Y 5 95 flexuous rod
Beet yellow virus 5 95 flexuous rod
Cauliflower mosaic virus 17 83 spherical
Wound tumor virus 22 78 spherical
Turnip yellow mosaic virus 35 65 spherical

19. Structure and composition of viral nucleic acid
 The nucleic acid of most plant viruses consist of RNA,
such as TMV and Potyvirus , but many viruses consist
of DNA for example ; Cauliflower mosaic virus ,
Tobacco and Tomato leaf curl virus.
RNA and DNA may be single – stranded or double
stranded.
e.g. Tobacco mosaic virus (ss-RNA)
Lettuce big vein virus (ds-RNA)
Mung bean yellow mosaic virus (ss-DNA)
Cauliflower mosaic virus (ds-DNA)
Both RNA and DNA are long chain of nucleotides.

22.  The size of both RNA and DNA is expressed as the
number of bases i.e. Kilo bases (kb) for the ssRNA and
ssDNA or Kilo base pairs (kbp) for dsRNA and dsDNA.
Virus Genome type No. Of bases
Tobacco mosaic virus ss -RNA 6.4 kb
Bean common mosaic virus ss- RNA 10 kb
Rice tungro spherical viruses ss-RNA 12.4 kb
Cauliflower mosaic virus ds- DNA 8.0 kbp
Tobacco leaf curl virus ss-DNA 2.4-2.8 kb

23. Structure and composition of viral protein
 Viral protein consist of amino acids which except
proline; have a general formula R-CH( NH2)-COOH
 The amino acids are linked in linear sequence by peptide
bonds between their amino and corboxyl groups.
 The linear primary sequence of amino acid is folds in
three dimensions in to structure of maximum stability
in their environment.
 The virus coat protein may contain 150 -600 amino
acids and range in molecular weight about 17000-
1,80,000 Dalton. e.g. The protein subunit of TMV consist
of 158 amino acids in a constant sequence and has mass
of 17,600 Dalton.
BCMV – 290 amino acids (M-Wt 28000D)

25.  Protein sub units are arranged in helix in rod shaped
viruses. e.g. TMV
 In polyhedral viruses the protein subunit are packed
tightly in arrangement that produce 20 faces and
form a shell. e.g. TYMV(Turnip yellow mosaic virus)
TYMV
TMV

26. Viruses like pathogen associated with plant disease
Viroids : Small (250 – 400 nucleotide ), naked, single-
stranded, circular RNAs capable of causing disease in
plant by themselves. e.g. Potato spindle tuber viroid, Citrus
exocortis viroid
Satellite viruses : Virus associated with certain typical
viruses (helper virus) and depend on the later for
multiplication and plant infection. e.g. Tobacco necrosis
satellite virus
Satellite RNAs : Small, linear RNAs found in virions of
certain multicomponent viruses may increase or decrease
the severity of viral infection. e.g. satellite RNA (CMV-
RNA5) associated with Cucumber mosaic virus

27. Conclusion
 Virus is chemically a nucleoprotein that multiplies
only in the living cells and has ability to cause disease.
 Nucleic acid may be RNA or DNA that is surrounded
by a protective protein coat called capsid.
 Plant viruses may be elongated, spherical and
bacilliform in shape.
 The nucleic acids RNA and DNA may be single
stranded or double stranded.
 Nucleic acid % is lower in elongated viruses where as
spherical viruses contain higher % of nucleic acid.