Tobacco mosaic virus General Presentation

This Presentation is intended to give a idea of what TMV virus is all about
Presenter name Sudha Pandey

1. Tobacco mosaic virus Name : Sudha s. pandey Class : MS c Part 1 Roll no. : 3 College : Institute of science, Dr. Homi bhabha state university

2. CONTENTS Tobacco Mosaic Virus. History. Symptoms. Capsid Assembly. Genome Organization. Replication. 3/28/2021 Sudha S. Pandey 2

3. Tobacco Mosaic Virus . TMV (Tobacco mosaic virus) is the most serious pathogen causing mosaic on tobacco leaves. TMV is the most resistant virus known so far of which the thermal death point is 90 °C for 10 minutes . The tobacco mosaic virus affects all dicotyledonous plants of which most important are tobacco and tomato. The tobacco mosaic virus affects photosynthetic tissue of the host leading to distortion, blistering and necrosis. It also causes dwarfing of affected plants. 3/28/2021 Sudha S. Pandey 3

4. History In 1882, Adolf Mayer first described an important disease of tobacco which he called tobacco mosaic disease. 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 . 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 filter, the filtrate remained infectious and could be used to infect healthy tobacco plants. 3/28/2021 Sudha S. Pandey 4

5. Ivanovsky was the first person to show that the agent causing the tobacco mosaic disease passed through a sterilizing filter and this gave rise to the subsequent characterization of viruses as filterable agents . Beijerinck in Holland, again showed in 1898 that sap from tobacco plants infected with the mosaic disease was still infectious after filtration through porcelain filters. In 1935 Stanley , obtained needle-like crystals of TMV that were infectious and consisted of protein. In 1939, TMV became the first virus to be visualized in the electron microscope and in 1941, TMV particles were shown to be rods about 280 nm long and 18 nm wide. 3/28/2021 Sudha S. Pandey 5

6. Symptoms The symptom is systemic mosaic type. The primary symptom on young leaves is faint circular chlorotic lesions appear with gradual vein clearing. This is followed by the development of characteristic systemic mosaic. With the maturity of the leaves, abnormally dark-green spots appear which develop into ir­regular crumpled blister-like areas.   3/28/2021 Sudha S. Pandey 6 Healthy Leaf TMV infected leaf

7. Structure TMV is a simple rod-shaped helical virus (Fig. 13.20) consisting of centrally located single- stranded RNA (5.6%) enveloped by a protein coat (94.4%). The rod is considered to be 2,800 Å (280 nm) in length and about 180 Å (18 nm) in diameter . 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 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 and having a molecular weight of 17,000 Dalton. 3/28/2021 Sudha S. Pandey 7 1 Armstrong ( Å ) = 0.1 Nanometer (nm)

8. 3/28/2021 Sudha S. Pandey 8

9. Capsid Assembly. One of the many surprises found during the study of TMV was its mode of assembly. If you mix the RNA and capsid proteins together, they spontaneously form functional viruses . First, the TMV protein forms a two-layer disk, with 17 proteins in each ring. A special initiation sequence in the RNA then binds in the hole at the center. This causes the disk to dislocate, forming a lockwasher shaped ring with 49 subunits per 3 turn . The remaining subunits then stack on this structure, elongating until the RNA is covered . 3/28/2021 Sudha S. Pandey 9

10. 3/28/2021 Sudha S. Pandey 10 Capsid Assembly video

11. Genome Organization The  TMV genome  consists of a 6.3–6.5 kb single-stranded ( ss ) RNA. The 3'-terminus has a tRNA -like  structure , and the 5' terminus has a methylated nucleotide cap . The genome contains about 6400 nucleotides, with molecular weight of 2.1 X . The RNA encodes 3 essential proteins. RNA dependent RNA polymerase. Movement Protein. Coat protein.   3/28/2021 Sudha S. Pandey 11

12. Replication The  replication  of  tobacco mosaic virus  ( TMV ) RNA involves synthesis of a negative-strand RNA using the genomic positive-strand RNA as a template, followed by the synthesis of positive-strand RNA on the negative-strand RNA templates . 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.  3/28/2021 Sudha S. Pandey 12

13. Now these replicative RNA synthesis new the ssRNA which will be released into the cytoplasm which along with ribosomes new protein subunits( capsomeres ) are synthesised. After the desired protein subunits (Capsomeres) are formed, the new viral nucleic acid is considered to organize the protein subunit around it resulting in the formation of complete virus particle, the virion . No ‘lysis’ of the host cell, as seen in case of virulent bacteriophages, takes place. The host ells remain alive and viruses move from one cell to the other causing systemic infection.  3/28/2021 Sudha S. Pandey 13

14. 3/28/2021 Sudha S. Pandey 14

15. Reference… Tobacco mosaic virus: Introduction, Structure & Replication by Biology Discussion. Microbiology Textbook : R.C. Dubey & M.K. Maheshwari. Diagrams from Biology discussion. 3/28/2021 Sudha S. Pandey 15