Tobacco mosaic virus

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 39x10 6 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.

11. 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

12. Arrangement of capsomers on RNA

13. GENOME: Single stranded, unsegmented , positive sense RNA. The RNA encodes 3 essential proteins out of four protein- small replicase subunit RNA dependent RNA polymerase Movement protein Coat Protein

14. GENOME ORGANISATION

15. 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)

16. 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.

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

18. 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.

19. 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 .

20. 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.

21. 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.

22. 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.

23. movement proteins

24. 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 3 I end of the RNA.

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

26. Thank you

27. 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=To%20counteract%20host%20RNAi%20antiviral,steps%20of%20cellular%20RNAi%20system%20.