Plant virus
Many plant viruses are rod-shaped, with protein discs forming a tube surrounding the viral genome; isometric particles are another common structure.
This and other viruses cause an estimated US$60 billion loss in crop yields worldwide each year.
[2] Plant defenses against viral infection include, among other measures, the use of siRNA in response to dsRNA.
However, after larger inoculation with a large number of bacteria, he failed to develop a mosaic symptom.
In 1898, Martinus Beijerinck, who was a professor of microbiology at the Technical University the Netherlands, put forth his concepts that viruses were small and determined that the "mosaic disease" remained infectious when passed through a Chamberland filter-candle.
Beijerinck referred to the infectious filtrate as a "contagium vivum fluidum", thus the coinage of the modern term "virus".
After the initial discovery of the 'viral concept' there was need to classify any other known viral diseases based on the mode of transmission even though microscopic observation proved fruitless.
The purification (crystallization) of TMV was first performed by Wendell Stanley, who published his findings in 1935, although he did not determine that the RNA was the infectious material.
In the 1950s a discovery by two labs simultaneously proved that the purified RNA of the TMV was infectious which reinforced the argument.
Understanding the virus genetics and protein functions has been used to explore the potential for commercial use by biotechnology companies.
In cases when there is only a single coat protein, the basic structure consists of 60 T subunits, where T is an integer.
Viruses can be spread by direct transfer of sap by contact of a wounded plant with a healthy one.
Such contact may occur during agricultural practices, as by damage caused by tools or hands, or naturally, as by an animal feeding on the plant.
This was shown in part when the old world white fly made it to the United States, where it transferred many plant viruses into new hosts.
Circulative viruses are protected inside aphids by the chaperone protein symbionin, produced by bacterial symbionts.
Many plant viruses encode within their genome polypeptides with domains essential for transmission by insects.
A bridging hypothesis has been proposed to explain how these proteins aid in insect-mediated viral transmission.
The helper component will bind to the specific domain of the coat protein, and then the insect mouthparts – creating a bridge.
[7] A number of virus genera are transmitted, both persistently and non-persistently, by soil borne zoosporic protozoa.
When the growth and development of plants is delayed because of situations like unfavorable weather, there is an increase in the amount of virus infections in seeds.
Little is known about the mechanisms involved in the transmission of plant viruses via seeds, although it is known that it is environmentally influenced and that seed transmission occurs because of a direct invasion of the embryo via the ovule or by an indirect route with an attack on the embryo mediated by infected gametes.
It is unknown how the virus is able to directly invade and cross the embryo and boundary between the parental and progeny generations in the ovule.
Many plants species can be infected through seeds including but not limited to the families Leguminosae, Solanaceae, Compositae, Rosaceae, Cucurbitaceae, Gramineae.
[10] The intracellular life of plant viruses in hosts is still understudied especially the earliest stages of infection.
[11] These comparable lipid alterations inform our expectations and research directions for the lesser understood area of plant viruses.
Besides involvement in the infection process, viral replicase is a directly necessary part of the packaging of RNA viruses' genetic material.
RNA 1, which is 6746 nucleotides long, encodes a single open reading frame (ORF) that produces the 237 kDa protein P237.
Viral vectors based on tobacco mosaic virus include those of the magnICON® and TRBO plant expression technologies.
[19] Building on the market approvals and sales of recombinant virus-based biopharmaceuticals for veterinary and human medicine, the use of engineered plant viruses has been proposed to enhance crop performance and promote sustainable production.
