Tobacco mosaic virus (TMV)

In the late 19th century, it was known that a disease that threatened the survival of tobacco crops was first demonstrated by D.I. Iwanowski in 1892 that the disease was caused by a filtering pathogen, known as a virus. W.M. Stanley initially believed that the pathogen was a protein, and in 1935 he first isolated a virus-like crystal from the juice of diseased leaves, and eventually understood that this crystal also contained nucleic acids, and determined that it was the pathogen. Tobacco mosaic virus is the first known virus, and it is a milestone in the human exploration of microorganisms.

What is a tobacco mosaic virus?

Tobacco mosaic virus is the causative agent of plant diseases such as tobacco mosaic disease and belongs to Tobamovirus. Tobacco mosaic virus (TMV) is an RNA virus that consists of a single protein shell (capsid) and nucleic acid. Its protein shell is cylindrical and consists of many of the same protein subunits. There is a single-stranded RNA molecule inside the outer shell. Tobacco mosaic virus specifically infects plants, especially tobacco and other Solanaceae plants, and can make these infected leaves appear mottled and stained.

The TMV virion is a straight rod-shaped, about 300 nm long and 15 nm in diameter, with a single-stranded sense RNA genome about 6400 bases long. The genomic RNA of TMV has a tRNA-like structure at the 3' end and a methylated nucleotide cap at the 5' end.

Fig.1 Structural diagram of tobacco Mosaic virus. (Lunn David J., et al.,2 015)

Structure of TMV

The TMV genome encodes four open reading frames (ORFs), two of which produce only one protein molecule due to ribosomal read-through, and these four genes encode replicase (containing methyltransferase [MT] and RNA helicase [Hel] domains), RNA-dependent RNA polymerase, viral movement protein (MP), and capsid protein (CP). The nucleic acid is encapsulated by a capsid composed of 2130 protein subunits, which is a rod-shaped helix structure formed by the self-assembly of capsid proteins, which constitutes the rod-like appearance of tobacco mosaic virus.

Tobacco mosaic virus disease

Tobacco mosaic virus is the causative agent of a variety of plant diseases, especially on solanaceous crops such as tobacco, tomato and pepper. Plants infected with TMV typically experience the following symptoms:

Mottled leaves: Yellow or green mottled areas appear on infected leaves, affecting photosynthesis.

Growth inhibition: Slow growth or even deformity of plants due to viruses interfering with the normal functioning of plant cells.

Malformed fruits: In some cases, plants infected with TMV can produce uneven ripening or misshapen fruits, affecting crop yield and quality.

Transmission of tobacco mosaic virus

Tobacco mosaic virus is transmitted mainly through mechanical damage and human activities. The virus spreads through infected plant residues, tools, hand contact, and friction between plants. The primary infection is caused by diseased residues and other host plants, and also by toxic fertilizers that are not fully decomposed. It is mainly spread by sap. If the disease is slightly rubbed against the diseased leaves, the virus can invade and not invade from the large wound and natural orifice. After invasion, it multiplies in parenchyma cells and then enters the vascular tissue to infect the entire plant. At 22-28 ℃, the infected plants began to show symptoms after 7-14 days. Reinfection is carried out in the field by friction between diseased seedlings and healthy seedlings or agricultural operations. In addition, insects with chewing mouthparts, such as locusts and tobacco worms in tobacco fields, can also transmit TMV virus. The optimal temperature for TMV to occur is 25-27℃, above 38-40 ℃ the invasion is inhibited, and above 27 ℃ or below 10 ℃ the condition disappears.

Tobacco mosaic virus detection

In order to reduce and reduce the harm of the virus to the tobacco industry, the establishment of efficient and sensitive detection technology is the premise of solving the basic problems such as early identification of disease resistance, and will help to study the transmission route and occurrence law of virus diseases, and lay the foundation for scientifically formulating prevention and control strategies.

Monoclonal antibody against tobacco mosaic virus was obtained by monoclonal antibody technology, and a rapid detection method for tobacco mosaic virus was established by colloidal gold labeling technology, immunochromatographic rapid detection technology and SQUID magnetic quantitative determination technology, and TMV colloidal gold rapid test strips for qualitative detection and TMV nanomagnetic bead rapid test strips for quantitative detection were developed, with detection sensitivities of 1 ng/mL and 0.1 ng/mL, respectively. The established method is simple, rapid, sensitive, and specific, and is an effective means for on-site screening of various TMV-free and symptomatic tobacco plants in tobacco seedlings.

Treatment for tobacco mosaic virus

Currently, treatment for tobacco mosaic virus is still very limited. Due to the rapid spread of the virus in plants and its efficient ability to infect, the main strategies for the prevention and control of TMV focus on prevention and suppression with antiviral drugs.

7-Deoxy-trans-dihydronarciclasine: An alkaloid that has been shown to have significant inhibitory effects (IC₅₀ value of 1.80 μM) against tobacco mosaic virus. The compound is not only a potent anti-TMV agent, but also has anti-neuroinflammatory potential. Studies have shown that 7-Deoxy-trans-dihydronarciclasine can reduce the levels of Aβ and APP in the cerebral cortex of Tg2576 mice, exhibiting neuroprotective effects.

Luotonin A: A versatile antiviral and anti-phytopathogenic fungal agent. It exhibits good antiviral activity against TMV and can effectively inhibit the spread of viruses in plants. Luotonin A also has inhibitory effects on topoisomerase I and topoisomerase II, and has certain antitumor activity. Its diverse pharmacological effects make it a potential candidate for the study of plant virus infections.

TMV-IN-2: A chalcone derivative that has been shown to have a significant inhibitory effect on TMV with an EC₅₀ value of 89.9 μg/mL. The antiviral activity of TMV-IN-2 makes it an important compound for inhibiting TMV infection. In addition, the study also showed that TMV-IN-2 has potential in the research of inflammation and oncology.

Summary

Tobacco mosaic virus was one of the first viruses to be discovered and has important scientific and agricultural significance. Although the infection of the virus has caused great harm to agricultural production, through scientific research, people have gradually understood its structure and transmission mechanism, and developed a variety of effective prevention and control methods. With the continuous development of antiviral drugs and disease-resistant varieties, agricultural producers will have more tools and methods to protect the health and yield of their crops in the future to control the spread of tobacco mosaic virus.

Reference

• Lunn, David J., et al., Self-assembly of "patchy" nanoparticles: A versatile approach to functional hierarchical materials. Chemical Science 6.7 (2015): 3663-3673.

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