User:Starryoung/Tobacco mosaic virus

Structure
Schematic model of TMV: 1. nucleic acid (RNA), 2. capsomer protein (protomer), 3. capsid

Tobacco mosaic virus has a rod-like appearance. Its capsid is made from 2130 molecules of coat protein and one molecule of genomic single strand RNA, 6400 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 micrograph above). The structural organization of the virus gives stability. The protein monomer consists of 158 amino acids 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. Negatively stained electron microphotographs show a distinct inner channel of radius ~2 nm. The RNA is located at a radius of ~4 nm and is protected from the action of cellular enzymes by the coat protein. X-ray fiber diffraction structure of the intact virus was studied based on an electron density map at 3.6 Å resolution. Inside the capsid helix, near the core, is the coiled RNA molecule, which is made up of 6,395 ±10 nucleotides.

The structure of the virus plays an important role in the recognition of the viral DNA. This happens due to the formation of an obligatory intermediate produced from a protein allows the virus to recognize a specific RNA hairpin structure. The intermediate induces the nucleation of TMV self-assembly by binding with the hairpin structure.

Genome
Genome of tobacco mosaic virus

The TMV genome consists of a 6.3–6.5 kbp single-stranded (ss) RNA. The 3’-terminus has a tRNA-like structure, and the 5’-terminus has a methylated nucleotide cap. (m7G5’pppG). The genome encodes 4 open reading frames (ORFs), two of which produce a single protein due to ribosomal readthrough of a leaky UAG stop codon. The 4 genes encode a  replicase (with methyltransferase [MT] and RNA helicase [Hel] domains), an RNA-dependent RNA polymerase, a so-called movement protein (MP) and a capsid protein (CP). The coding sequence starts with the first reading frame, which is 69 nucleotides away from the 5' end of the RNA.''' The noncoding region at the 5' end can be varied in different individual virions, but there hasn't been any variation found between virions in the noncoding region at the 3' end. '''

Disease cycle
TMV does not have a distinct overwintering structure. Rather, it will over-winter in infected tobacco stalks and leaves in the soil, on the surface of contaminated seed (TMV can even survive in contaminated tobacco products for many years, so smokers can accidentally transmit it by touch, although not in the smoke itself). With the direct contact with host plants through its vectors (normally insects such as aphids and leafhoppers), TMV will go through the infection process and then the replication process.

Infection and transmission
After its multiplication, it enters the neighbouring cells through plasmodesmata. The infection does not spread through contact with insects, but instead spreads by direct contact to the neighboring cells. For its smooth entry, TMV produces a 30 kDamovement protein called P30 which enlarges the plasmodesmata. TMV most likely moves from cell-to-cell as a complex of the RNA, P30, and replicate proteins.

It can also spread through phloem for longer distance movement within the plant. Moreover, TMV can be transmitted from one plant to another by direct contact. Although TMV does not have defined transmission vectors, the virus can be easily transmitted from the infected hosts to the healthy plants by human handling.

Environment
TMV is known as one of the most stable viruses. It has a very wide survival range. As long as the surrounding temperature remains below approximately 40 degrees Celsius, TMV can sustain its stable form. All it needs is a host to infect. If necessary, greenhouses and botanical gardens would provide the most favorable condition for TMV to spread out, due to the high population density of possible hosts and the constant temperature throughout the year. It also could be useful to culture TMV in vitro in sap because it can survive up to 3000 days.

Treatment and management
One of the common control methods for TMV is sanitation, which includes removing infected plants and washing hands in between each planting. Crop rotation should also be employed to avoid infected soil/seed beds for at least two years. As for any plant disease, looking for resistant strains against TMV may also be advised. Furthermore, the cross protection method can be administered, where the stronger strain of TMV infection is inhibited by infecting the host plant with a mild strain of TMV, similar to the effect of a vaccine.

In the past ten years, the application of genetic engineering on a host plant genome has been developed to allow the host plant to produce the TMV coat protein within their cells. It was hypothesized that the TMV genome will be re-coated rapidly upon entering the host cell, thus it prevents the initiation of TMV replication. Later it was found that the mechanism that protects the host from viral genome insertion is through gene silencing.

TMV is inhibited by a product of the myxomycete slime mold Physarum polycephalum. Both tobacco and the beans P. vulgaris and V. sinensis suffered almost no lesioning in vitro from TMV when treated with a P. polycephalum extract.

'Research has shown that Bacillus'' spp. can be used to reduce the severity of symptoms from TMV in tobacco plants. In the study, treated tobacco plants had more growth and less build-up of TMV virions than tobacco plants that hadn't been treated. '''

A research has been conducted by H.Fraenkel-Conrat to show the influence of acetic acid on the Tobacco Mosaic Virus. According to the research, 67% acetic acid resulted as degradation of the virus.

Another possible source of prevention for TMV is the use of salicylic acid. A study completed by a research team at the University of Cambridge found that treating plants with salicylic acid reduced the amount of TMV viral RNAs and viral coat protein present in the tobacco plants. There research showed that salicylic acid most likely was disrupting replication and transcription and more specifically, the RdRp complex.

A research was conducted and revealed that humans have antibodies against Tobacco Mosaic Virus.

Scientific and environmental impact
The large amount of literature about TMV and its choice for many pioneering investigations in structural biology (including 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 several hundred infected tobacco plants in a greenhouse, followed by a few simple laboratory procedures, a scientist can produce several grams of the virus. '''In fact, tobacco mosaic virus is so proliferate that the inclusion bodies can be seen with only a light microscope. '''

James D. Watson, in his memoir The Double Helix, cites his x-ray investigation of TMV's helical structure as an important step in deducing the nature of the DNA molecule.

Applications
Plant viruses can be used to engineer viral vectors, tools commonly used by molecular biologists to deliver genetic material into plant cells; they are also sources of biomaterials and nanotechnology devices. Viral vectors based on TMV include those of the magnICON and TRBO plant expression technologies. Due to its cylindrical shape, high aspect ratio, self-assembling nature, and ability to incorporate metal coatings (nickel and cobalt) into its shell, TMV is an ideal candidate to be incorporated into battery electrodes. Addition of TMV to a battery electrode increases the reactive surface area by an order of magnitude, resulting in an increase in the battery's capacity by up to six times compared to a planar electrode geometry.

Explanation
The bolded sentences are added by Violettemoonlight and the underlines sentences are added by Starryoung.

We added information on scientific and environmental impact and a lot of information in treatment and management especially regarding on acetic acid on TMV. Information was also added on the topics of infection and transmission, structure, and genome. Few resources were added to support the existing article better.