Tobacco mosaic virus

1. Tobacco Mosaic Virus
Dhole N. A.
Department of Botany,
Digambarrao Bindu ACS College, Bhokar

2. • The German Adolf Mayer, working in the Netherlands, who in 1882
first described an important disease of tobacco which he called
tobacco mosaic disease (TMV).
• He showed that the disease was infectious and could be transmitted
to healthy tobacco plants by inoculation with capillary glass tubes
containing sap from diseased plants.
• St. Petersburg, Dmitri Ivanovsky was studying the same disease and
he reported in 1892 that when sap from a diseased tobacco plant was
passed through a bacteria-retaining Chamberland filter.
• This filtrate remained infectious and could be used to infect healthy
tobacco plants.

3. • Ivanovsky was the first person to show that the agent causing the
tobacco mosaic disease passed through a sterilizing filter.
• This gave rise to the subsequent characterization of viruses as
filterable agents.
• Following in the footsteps of Adolf Mayer, Beijerinck in Delft, Holland,
again showed in 1898 that sap from tobacco plants infected with the
mosaic disease was still infectious after filtration through porcelain
filters.
• Beijerinck also demonstrated that the causative agent was able to
diffuse through several millimeters of an agar gel.

4. • Beijerinck called the agent causing the tobacco mosaic disease
a contagium vivum fluidum (a contagious living liquid), in opposition
to a contagium vivum fixum.
• In those days the term contagium was used to refer to any
contagious, disease-causing agent, while the term fixum meant that
the agent was a solid particle.

5. Virus Symptoms in Plants:
• Vein clearing and vein banding
• Ring spots
• Necrosis
• Tissue and unusual excessive growth
• Irregularly shape and size of plant parts
• Develop crumpled blister-areas on plants
• Stunting growth
• Premature death of plant

6. Structure of Tobacco Mosaic Virus (TMV):

7. • In 1935 when Stanley, working at the Rockefeller Institute in Princeton,
obtained needle-like crystals of TMV that were infectious and consisted of
protein.
• The virus contained phosphorus and carbohydrate and actually consisted of
95% protein and 5% RNA.
• TMV thus became the first virus to be purified and shown to be a complex
of protein and nuclei c acid.
• Stanley’s demonstration that TMV was a crystallizable chemical substance
rather than a microorganism, a discovery that earned him the Nobel Prize
in 1946.
• TMV thus became the first virus to be purified and shown to be a complex
of protein and nucleic acid
• In 1939 ,TMV be came the first virus to be visualized in the electron
microscope.
• In 1941, TMV particles were shown to be rods about 280 nm long and 15
nm wide.

8. • TMV particles were shown to be rods about 280 nm long and 15 nm wide.
• X-ray analysis established that the rods were hollow tubes consisting of a
helical array and containing one molecule of RNA deeply embedded in the
protein subunits at a radius of 4 nm.
• The protein coat is technically called ‘capsid’.
• R. Franklin estimated 2,130 sub-units, namely, capsomeres in a complete
helical rod and 49 capsomeres on every three turns of the helix.
• Thus there would be about 130 turns per rod of TMV.
• The length of the TMV particle is controlled by the length of the RNA
molecule which becomes fully coated with protein and is there by
protected from nuclease attack.

9. • The diameter of RNA helix is about 80 Å and the RNA molecule lies
about 50 Å inward from the outer-most surface of the rod.
• The central core of the rod is about 40 Å in diameter.
• Each capsomere is a grape like structure containing about 158 amino
acids.
• The ssRNA is little more in length (about 3300 Å) slightly protruding
from one end of the rod.
• The RNA molecule consists of about 7300 nucleotides.

10. Replication of TMV:
• TMV-infected tissues contain four viral proteins: the 126 kDa and 183
kDa proteins of the replicase complex, the 30 kDa movement protein,
and the 17.6 kDa coat protein.
• TMV replication is initiated by the translation of the viral RNA to
produce the replicase proteins and this leads to the synthesis of
minus-sense and plus-sense copies of the RNA.
• Translation of the viral coat protein gene then occurs leading to the
assembly of progeny virus particles from full-length genomic RNA and
coat protein.
• The translation of the coat protein and movement protein is
controlled by the production of two separate subgenomic mRNAs.

11. • Plant viruses like TMV penetrate and enter the host cells and their
replication completes within such infected host cells.
• Inside the host cell, the protein coat dissociates and viral nucleic acid
becomes free in the cell cytoplasm.
• The studies suggest the viral nucleic acid after becoming free in the
cell cytoplasm, the viral-RNA moves into the nucleus (possibly into
the nucleolus).
• The viral-RNA first induces the formation of specific enzymes called
‘RNA polymerases’ the single-stranded viral-RNA synthesizes an
additional RNA strand called replicative RNA.
• This RNA strand is complementary to the viral genome and serves as
‘template’ for producing new RNA single strands which is the copies
of the parental viral-RNA.

12. • The new viral-RNAs are released from the nucleus into die cytoplasm
and serve as messenger-RNAs (mRNAs).
• Each mRNA, in cooperation with ribosomes and t-RNA of the host cell
directs the synthesis of protein subunits.
• After the desired protein sub-units (capsomeres) have been
produced, the new viral nucleic acid is considered to organize the
protein subunit around it resulting in the formation of complete virus
particle, the virion.
• The host cells remain alive and viruses move from one cell to the
other causing systemic infection.

13. References:
• https://doi.org/10.1016/B978-012374410-4.00595-1
• https://www.biologydiscussion.com/viruses/tobacco-mosaic-virus-
tmv-structure-and-replication/54903
• https://www.yourarticlelibrary.com/virus/tobacco-mosaic-virus-
notes-on-tobacco-mosaic-virus-tmv/6847

14. Thank you