Tobacco mosaic virus
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2008-07-06T23:28:49Z
Wybot
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robot Modifying: [[es:Tobacco mosaic virus]]
{{Taxobox
| image = Tobacco Mosaic Virus structure.png
| image_size = 300px
| image_caption = A monomeric unit of the much larger Tobacco Mosaic Virus
| virus_group = iv
| genus = ''[[Tobamovirus]]''
| species = '''''Tobacco mosaic virus'''''
}}
'''Tobacco mosaic virus''' (TMV) is an [[RNA virus]] that infects [[plant]]s, especially [[tobacco]] and other members of the family [[Solanaceae]]. The [[infection]] causes characteristic patterns (mottling and discoloration) on the [[Leaf|leaves]] (thus the name). TMV was the first [[virus]] to be discovered. Although it was known from the late 19<sup>th</sup> century that an [[infectious disease]] was damaging tobacco crops, it was not until 1930 that the infectious agent was determined to be a virus.
==History==
In 1883 [[Adolf Mayer]] first described the disease that could be transferred between plants, similar to [[bacterium|bacterial]] infections<ref name = "zaitlin">[http://www.apsnet.org/education/feature/TMV/pdfs/zaitlin.pdf Microsoft Word - Chapter 7.doc<!-- Bot generated title -->]</ref>. [[Dimitri Ivanowski]] gave the first concrete evidence for the existence of a non-bacterial infectious agent, showing that infected sap remained infectious even after filtering through [[Chamberland filter]] candles, in 1892. However, he remained convinced despite repeated failures to produce evidence, that bacteria where the infectious agent. In 1898, [[Martinus Beijerinck]] showed that a filtered, bacteria-free culture medium still contained the infectious agent<ref name = "zaitlin"/>. [[Wendell Meredith Stanley]] crystallized the virus in 1935 and showed that it remains active even after crystallization<ref name = "zaitlin"/>. For his work, he was awarded 1/4 of the [[Nobel Prize in Chemistry]] in 1946<ref>[http://nobelprize.org/nobel_prizes/chemistry/laureates/1946/stanley-bio.html Wendell M. Stanley - Biography<!-- Bot generated title -->]</ref>, even though it was later shown some of his conclusions (in particular, that the crystals were pure protein, and assembled by [[autocatalysis]]) were incorrect.<ref>[http://www.jstor.org/view/00211753/ap010239/01a00030/0] Kay, L.E. (1986). W. M. Stanley's Crystallization of the Tobacco Mosaic Virus, 1930-1940. Isis 77: 450-472.</ref> The first electron microscopical images of TMV were made in 1939 by Gustav Kausche, Edgar Pfankuch and [[Helmut Ruska]] - the brother of Nobel Prize winner [[Ernst Ruska]].<ref>G.A. Kausche, E. Pfankuch and H. Ruska (1939), Die Sichtbarmachung von pflanzlichem Virus im Übermikroskop, Naturwissenschaften 27: 292-299.</ref> In 1955, [[Heinz Fraenkel-Conrat]] and [[Robley Williams]] showed that purified TMV RNA and its [[capsid]] (coat) protein assemble by themselves to functional viruses, indicating that this is the most stable structure (the one with the lowest free energy), and likely the natural assembly mechanism within the host cell.
The crystallographer [[Rosalind Franklin]] worked for Stanley for about a month at [[University of California, Berkeley|Berkeley]], and later designed and built a model of TMV for the [[1958 World's Fair]] at [[Brussels]]. In [[1958]], she speculated that the virus was hollow, not solid, and hypothesized that the [[RNA]] of TMV is single-stranded. This conjecture was proven to be correct after her death and is now know to be the + strand.
==Structure==
[[Image:Tobacco mosaic virus structure.png|300px|thumb|right|Schematic model of TMV: 1. nucleic acid ([[RNA]]), 2. capsomer (protomer), 3. [[capsid]].]]
[[Image:TobaccoMosaicVirus.jpg||thumb|right|Electron micrograph of TMV particles stained to enhance visibility at 160,000x magnification.]]
Tobacco mosaic virus has a rod-like appearance. Its capsid is made from 2130 molecules of coat protein (see image above) and one molecule of genomic RNA 6390 bases long. The coat protein self assembles into the rod like helical structure (16.3 proteins per helix turn) around the RNA which forms a hairpin loop structure (see the [[Electron Microscope|Electron Micrograph]] below). The protein monomer consists of 158 aminoacids which are assembled into four main alpha-helices, which are joined by a prominent loop proximal to the axis of the virion. Virions are ~300 nm in length and ~18 nm in diameter.<ref>{{cite book
| last = Stryer
| first = Lubert
| authorlink = Lubert Stryer
| title = Biochemistry
| publisher = [[W. H. Freeman and Company]]
| series = Third Edition
| year = 1988
| isbn = 0-7167-1843-X}}</ref> Negatively stained electron microphotographs show a distinct inner channel of ~4 nm. The RNA is located at a radius of ~6 nm and is protected from the action of cellular enzymes by the coat protein. There are three RNA nucleotides per protein monomer.<ref>{{cite journal
| title = The tobacco mosaic virus particle: structure and assembly
| last = Klug
| first = Aaron
| authorlink = Aaron Klug
| journal = Philosophical Transactions of the Royal Society B: Biological Sciences
| date = March 1999
| volume = 354
| pages = 531–535
| issue = 1383
| url = http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1692534
| doi = 10.1098/rstb.1999.0404
| pmid = 10212932}}</ref>
==Replication==
When it enters the host, it enters as single stranded RNA and has a temporary double stranded intermediate. Its RNA directs the synthesis of viral proteins by the host machinery. After the RNA and the protein is produced, they undergo self assembly. After the assembly of capsomeres and RNA, they are released outside the cell after the [[lysis]] and death of the host. These newly synthesized viruses continue on to infect other cells.
==Infection==
When TMV infects a tobacco plant, the virus enters the plant cell and the virus replicates. After its multiplication, it enters the neighboring cells through [[plasmodesmata]]. For its smooth entry, TMV produces a 30,000 [[Dalton]] protein called P30 which tends to enlarge the plasmodesmata and allows their free entry to the neighboring cells.
The first symptom of this virus disease is a light green coloration between the veins of young leaves. This is followed quickly by the development of a “mosaic” or mottled pattern of light and dark green areas in the leaves. These symptoms develop quickly and are more pronounced on younger leaves. Mosaic does not result in plant death, but if infection occurs early in the season, plants are stunted. Lower leaves are subjected to “mosaic burn” especially during periods of hot and dry weather. In these cases, large dead areas develop in the leaves. This constitutes one of the most destructive phases of tobacco mosaic virus infection. Infected leaves may be crinkled, puckered, or enlongated.
==Scientific and Environmental Impact==
In plants, tobacco mosaic virus leads to severe crop losses<ref>[http://www.ces.ncsu.edu/depts/pp/notes/oldnotes/tb1.htm TB01<!-- Bot generated title -->]</ref>. It is known to infect members of nine plant families, and at least 125 individual species, including tobacco, tomato, pepper, cucumbers, and a number of ornamental flowers.<ref>[http://www.extension.umn.edu/distribution/horticulture/DG1168.html Tomato-Tobacco Mosaic Virus Disease<!-- Bot generated title -->]</ref> There are many different strains.
The large amount of literature about TMV and its choice for many pioneering investigations in structural molecular biology, X-ray diffraction, virus assembly and disassembly, and so on, are fundamentally due to the large quantities that can be obtained, plus the fact that it does not infect animals. After growing a few infected tobacco plants in a greenhouse and a few simple laboratory procedures, a scientist can easily produce several grams of virus. As result of this, TMV can be treated almost as an organic chemical, rather than an infective agent.{{Verify source|date=May 2008}}
==References==
<references />
flue-cured tobacco field manual published R.J.Reynolds Tobacco Company Winston-Salem,North Carolina, 1995
==Further reading==
*Creager, Angela N. ''The Life of a Virus: Tobacco Mosaic Virus as an Experimental Model, 1930-1965.'' Chicago, IL: University of Chicago Press, 2002.
== External links ==
{{commonscat}}
* [http://www.biotecnika.googlepages.com/tmv.html Tobacco Mosaic Virus-Details]
* [http://www.dpvweb.net/dpv/showdpv.php?dpvno=370 Description of plant viruses - TMV] - contains information on symptoms, hosts species, purification etc.
* [http://www.extension.umn.edu/distribution/horticulture/DG1168.html] Further information
* [http://www.ncbi.nlm.nih.gov/ICTVdb/Images/Milne/tobamo1.htm] Electron microscope image of TM
[[Category:Tobacco]]
[[Category:Viruses]]
[[Category:Model organisms]]
[[Category:Plant pathogens and diseases]]
[[Category:Tobacco diseases]]
[[Category:Microbiology]]
[[ca:Virus del mosaic del tabac]]
[[de:Tabakmosaikvirus]]
[[es:Tobacco mosaic virus]]
[[fr:Virus de la mosaïque du tabac]]
[[ko:담배모자이크바이러스]]
[[hr:Virus mozaika duhana]]
[[it:Virus del mosaico del tabacco]]
[[he:מוזאיקת הטבק]]
[[lt:Tabako mozaikos virusas]]
[[ja:タバコモザイクウイルス]]
[[pl:Wirus mozaiki tytoniu]]
[[sk:Vírus tabakovej mozaiky]]
[[tr:Tütün mozaik virüsü]]
[[zh:菸草鑲嵌病毒]]