Tobacco mosaic virus

Tobacco mosaic virus (TMV) is a positive-sense single stranded RNA virus species in the genus Tobamovirus that infects a wide range of plants, especially tobacco and other members of the family Solanaceae. The infection causes characteristic patterns, such as 'mosaic'-like mottling and discoloration on the leaves (hence the name). TMV was the first virus to be discovered and has been fundamental in the study of virology.

History

The existence of TMV was first hypothesized by Dmitry Ivanovsky in 1892 after he observed an infectious agent, which could pass through a porcelain filter that blocked all known bacteria. Later in 1898, Martinus Beijerinck showed that the infectious agent could reproduce and concluded it was a new form of infectious agent. This discovery was the first conclusive proof of the existence of viruses.

Structure

TMV is a rod-shaped virus, measuring about 300 nm in length and 18 nm in diameter. The virus is composed of a single-stranded RNA genome enclosed in a protective coat of protein. The protein coat is made up of about 2,130 identical protein subunits, each of which binds to and protects a specific section of the viral RNA.

Transmission and Infection

TMV is transmitted mechanically through wounds in the plant's surface. The virus can survive in dried plant material for many years and can also be transmitted through contaminated hands and tools. Once inside the host, the virus uses the host's own machinery to replicate itself. The virus can spread throughout the plant, causing systemic infection.

Symptoms and Impact

The most characteristic symptom of TMV infection is a 'mosaic' pattern of discoloration on the leaves, which gives the virus its name. Other symptoms can include stunted growth and a reduction in the quantity and quality of harvested product. TMV can cause significant economic losses in a wide range of crops.

Control and Management

Control of TMV primarily involves prevention, including the use of virus-free seeds and plants, regular disinfection of tools, and good agricultural practices. There are also a number of resistant plant varieties available. Once a plant is infected, there is no cure and the plant will typically need to be destroyed to prevent the spread of the virus.

In Science

TMV has been fundamental in the study of virology. It was the first virus to be crystallized, allowing its structure to be studied in detail. It was also the first virus to be synthesized chemically.