TOBACCO MOSAIC VIRUS (Genome organization &their replication) TMV is a plant virus which infects a wide range of plants, especially tobacco and other members of the family Solanaceae and cucumbers, and a number of ornamental flowers.

1. Dr. Pawan Kumar Kanaujia
Assistant Professor
Molecular Virology (Theory)
TOBACCO MOSAIC VIRUS
Genome organization &their
replication

2. Tobacco mosaic virus
Healthy tobacco plant Infected by tobacco mosaic virus

3. TMV is a plant virus which infects a wide range of plants,
especially tobacco and other members of the family
Solanaceae.
The infection causes characteristic patterns, that is
"mosaic"-spots and discoloration on the leaves.
TMV was the first virus ever to be discovered & recognized
virus disease of plant in world.
Most common on tobacco crops in India particularly in
states like Andhra Pradesh, Assam, Maharashtra, Odisha,
Tamil Nadu, Uttar Pradesh, etc.
First virus where the protein coat was fully sequenced
into 158 amino acids
TMV was the first plant RNA virus of which complete
genome was sequenced
SIGNIFICANCE OF THE DISEASE

4. ECONOMIC LOSS
It reduces the quality as well as quantity by upto 50% and
upto 30% worldwide, respectively
It has wide range of host
It caused 20% of yield loss in tomato

5. DISTRIBUTION
India is the 2nd largest producer of tobacco with annual
production of 800 million kg
The same virus occur in many other plant
Over 20 different virus disease occur in tobacco in which
mosaic disease is most important
HOST PLANTS
It is known to infect members of nine plant families of 125
individual species
It including tobacco, tomato, pepper (all members of the
useful Solanaceae), cucumbers, and a number of ornamental
flowers.

6. HISTORY
Adolph Mayer began to study the TMV in 1886 for first
time
In 1898, Martinus Willem Beijerinck proposed that tobacco
mosaic virus was caused by an infectious fluid which he
called as virus
In 1935, it was the first virus to be crystallized by
W.H.Stanley

7. Virus classification
(unranked): Virus
Phylum:
Class:
Kitrinoviricota
Alsuviricetes
Order: Martellivirales
Family: Virgaviridae
Genus: Tobamovirus
Species: Tobacco mosaic virus

8. STRUCTURE OF TMV
ELECTRON MICROSCOPIC VIEW OF TMV-160,000× MAGNIFICATION

9. STRUCTURE OF TMV
1. nucleic acid (RNA), 2. capsomer protein (protomer), 3. capsid

10. MORPHOLOGY (STRUCTURE OF TMV)
It is made up of centrally placed ribonucleic acid molecules
covered with a protein coat(called capsid)
Molecular wt. of virion 39x106 daltons.
Rod shaped- 300nm x 18nm (3000 X 180 A
o
)
consist of approx. 6,400 nucleotides
No. of Capsomers- 2130
Capsomers arranged in helix around central hole of 4nm
(40 A
o
) radius.

12.  TMV- single-stranded RNA molecules (spiral coiled to
form helix)
Each capsomer (capsid subunit) is made up of 158 amino
acids.
In one turn the RNA contain 49 nucleotides
 49 protein subunits (capsomer) counting (present) in the
three turns i.e., 49/3 capsomers per turn (16.33 capsomers)
Therefore a single capsomer is linked with 3 nucleotides of
RNA

13. Arrangement of capsomers on RNA

14. GENOME:
Single stranded, unsegmented, positive sense RNA.
The RNA encodes 3 essential proteins out of four
protein-
a) small replicase subunit
b) RNA dependent RNA polymerase
c) Movement protein
d) Coat Protein

15. GENOME ORGANISATION

16. Monopartite, linear, ssRNA(+) genome of 6.3-6.5 kb.
The 5' terminus has a methylated nucleotide cap
(m7G5’pppN).
The 3'-terminus has a tRNA-like structure.
The genome encodes 4 open reading frames(ORFs),
The 4 genes encode
1. a small replicase subunit
2. Replication associated proteins (RNA-dependent RNA
polymerase- RdRp) (two of which produce a single protein
due to ribosomal readthrough of a leaky UAG stop codon)
3. movement protein (MP) and
4. a capsid protein(CP)

17. The virion RNA is infectious and serves as both the genome
and viral messenger RNA. The 5'-proximal ORFs are directly
translated to produce the viral constituents of the replicase
complex.
RdRp is translated through suppression of termination at
the end of ORF1.
The small replicase is involved in replication and acts as
a suppressor of RNA silencing.
(In host, RNA silencing (RNAi) plays antiviral defense. plant virus
encode viral suppressors of RNA silencing (VSRs) which inhibit key
steps of cellular RNAi system)
The movement proteins and the capsid protein are
expressed from separate subgenomic mRNAs.

18. Multiplication Cycle
The reproductive cycle of TMV consists of Five steps as-
1. Entry into host cell
2. Uncoating
3. Intracellular Development
4. Assembly (Maturation)
5. Release

19. Entry into the host cell
TMV can not directly enter the host cell.
It requires damage to plant cells.
It enters through breaches (Gap) in the cell wall.

20. Uncoating
It is a process in which capsid is removed and nucleic acid
is released into the cell cytoplasm.
Nucleic acid of plant viruses enters the host cell cytoplasm
along with capsid.
In the cytoplasm capsid is removed and nucleic acid is
released.
It requires assistment of host enzymes to remove capsids.

21. Intracellular development (biosynthesis)
In order to produce disease, the virus must replicate and
spread to neighbouring cells and then systematically
throughout the plant.
Spreads of virus to neighbouring cells occurs through
microscopic channels in the cell walls called plasmodesmata.
Plasmodesmata-
These are slender structures extending from cell wall which
connects adjacent plant cells.

22. Spread to other parts of the plant by vasculature system (
Xylem and phloem).
The cell to cell movement of virus requires one or more
protein called as “Movement protein”.
Plant viruses uses capsid proteins for encapsulation.

23. Viral Genome Replication
TMV contains SS Positive sense RNA as its genome.
Replication of virion RNA thus involves synthesis of
negative strand RNA using positive strand RNA as a template.
Thus, replication completes in 2 steps-
1) Synthesis of negative strand RNA using positive strand
RNA as a template which forms doubles stranded
intermediate termed as “Replicative form (RF)”.
2) Synthesis of positive strand RNA using negative strand
RNA as a template using virus coded RNA dependent RNA
polymerase.

24. movement
proteins

25. Assembly
Also called Maturation.
After intracellular synthesis of enough no. of capsid
proteins and Virion RNA, virion assembly begins.
It is highly organized process.
Initially Capsid assembly begins when capsomers associate
with 3I end of the RNA.

26. Release
Plant viruses kills their hosts in which they multiply.
They releases by autolysis of host cell which causes death
of cell.

28. Thank you

29. REFERENCES
Alice D and Jeyalakshmi C, 2014, Hand book on Introductory Plant
Pathology, A.E publishers, Coimbatore. pp 250-251
Mehrotra R S and Ashok Agarwal, Fundamentals of Plant
Pathology, McGraw Hill Education Private Limited, New Delhi. pp
348-351
Multiplication of tobacco mosaic virus, Prof. Suraj Dipak Gabale
Assistant professor Vivekanand College, Kolhapur
TOBACCO MOSAIC VIRUS, : Dr. PARTHASARATHY S, Asst. Professor
(Plant Pathology), COLLEGE OF AGRICULTURAL TECHNOLOGY
(Affiliated to Tamil Nadu Agricultural University, Coimbatore3)
Kullapuram (Po),ViaVaigai Dam, Theni-625 562
https://viralzone.expasy.org/51?outline=all_by_species
https://viralzone.expasy.org/891?outline=all_by_protein#:~:text=T
o%20counteract%20host%20RNAi%20antiviral,steps%20of%20cellul
ar%20RNAi%20system%20.