Structure and composition of plant viruses

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.

1. WELCOME

2. Course seminar on Structure and Composition of Plant Viruses 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 viru s (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 100 nm 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 52-75 nm wide and 300-380 nm 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 .

20. 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

21. Structure and composition of viral protein Viral protein consist of amino acids which except proline ; have a general formula R-CH( NH 2 )-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 28000 D)

22. 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

23. 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

24. 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.

25. THANKS