Erakina

tobacco mosaic virus – Erakina

Published Date : February 14, 2022

The first viral virus to be discovered, purified, crystallised, and sequenced – the tobacco mosaic virus is indeed worth knowing about.

Scientific viral classification

Kingdom – orthornavirae

Phylum – Kitrinoviricota

class-Alsuviricetes

Order-martellivirales

Family- virgaviridae

Genus- tobamovirus

Species – tobacco mosaic virus

A helical structure – open to genetic modifications

tobacco mosaic viral plant

 diagrammatic representation of TMV

The virus is a rodlike, submicroscopic particle with a rigid piece of nucleic acid, the ribose nucleic acid encased in a protein coat.[viral] It has a length of around 300 nm and a diameter of 18 nm.[viral] The capsids contain 2130 identical subunits of protein which facilitate the formation of a helical structure by assembling around the nucleic acid.[viral]

Dates back to the colonial era 

Tobacco was grown as a cash crop in America. Due to intensive cultivation, tobacco depleted the soil and left it vulnerable to diseases. One such disease was found in the early 19th century.[viral] It was then named “Amulatamiento” (the tobacco leaf appeared as mulatto or a mixture) 

A healthy leaf vs. an infected leaf

close up of a healthy leaf and an infected one

Green areas with a mosaic pattern.[viral] This caused the plants to take a laden-grey colour and the tobacco turned extremely bitter. In 1879, the disease was named ‘ mosaic disease of tobacco’ by Adolph Mayer. Later a Russian biologist named Dmitry Ivanovsky investigated the mosaic disease and found that it was caused by a virus. This was confirmed by the Dutch botanist William Beijerick.

Subsequently, the virus was studied in detail and proved to be composed of a single-stranded RNA virus of filamentous morphology.

Mechanical transmission – spreads by abrasion

It has the potential to affect 350 different species of plants. Sucking insects do not spread the virus while chewing insects do. The virus can multiply in a living cell but can survive in a dormant state in dead tissues. Thus, the virus can infect growing plants for years even after the infected plant part is dead. This is rare in other viruses.

Vegetative propagation perpetuates the virus. It can  survive on surfaces, and in the dried plant sap. Tobacco products may carry TMV. In cigarette making, repeated heating inactivates most of it. However, it is not transmitted through the smoke of burning tobacco.

Accumulation – disassembly- replication-cellular motion

Mechanical wounds that open up the plasma membrane are a doorway to the virus. Once the virus enters the cell, it accumulates itself by disassembling and reaches the cytoplasm through intra-cellular motion and then it replicates to undergo inter-cellular motion.

Mosaic patches and the other symptoms

The plants infected with TMV show different features based on the species type. In a few plants,the symptoms are masked while a few of them clearly show them. Stunting, mosaic patterns of light and dark patches on the leaf, malformation of leaves, and distinct yellowing are a few of them.

Applications in the modern technology

Apart from being first discovered, crystallised and sequenced, the virus is also the first one to be genetically modified and finds application in bioengineering.

Internal links:

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By Pooja kumari sha

By Pooja kumari sha

Date: 10/01/22

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