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Plant viruses are viruses affecting plants.
Plant viruses, like all other viruses, are obligate intracellular parasites that do not have the molecular machinery to replicate without the host. The plant viruses are defined as viruses pathogenic to higher plants. While this article does not intend to list all plant viruses, it discusses some important viruses as well as their uses in plant molecular biology.
Over view
Plant Viruses are not nearly as well understood as the animal counterparts, this is ironic as the first virus to be discovered (see below) was the Tobacco Mosaic Virus (TMV) as well as the fact that they have a predicted US$ 6 x 1010 per year economic influence on crops worldwide.
History
The discovery of plant viruses causing disease is often accredited to Martinus Beijerinck who discoved, in 1889, that even after passing infective tree sap through a porcelain filter remained infectious but was sterile of microorganisms.
After the initial discovery of the ‘viral concept’ there was need to classify any other know viral diseases based on the mode of transmission even though microscopic observation proved fruitless. In 1939 Holmes published a classification list of 129 plant viruses. This was expanded and in 1999 there were 977 officially recognised, and some provisional, plant species.
The purification of the TMV (the first purification) was first performed by Wendell Stanley, who published his findings in 1936. He later was accredited with the Nobel Prize in Chemistry in 1946. In the 1950s a discovery by two labs simultaneously proved that the purified RNA of the TMV was infectious which reinforced the argument, that had a lot of opposition at the time, that RNA was carrying genetic information to code for the production of new infectious partials.
More recently the research has been focused on the manipulation and modification of plant virus genomes do discover function and for commercial gain in the agriculture business by using viral-derived sequences to provide understanding of novel forms of resistance. The recent boom in technology allowing humans to manipulate plant viruses has really helped bring the subject out of an Aristolean science age (observation and description of the subject matter) and into the 21st centaury.
Size, Structure and Anatomy
Plant and Animal viruses do have a lot in common with each other; however, there are some differences worth noting this is due to the differing host environment and strategies to combat host infection. Most of the virus types that have been discovered infecting plants are single-stranded RNA viruses, and have rod-shaped capsids with protein units arranged in a spiral.
Initial Infection - There are two major ways the viral diseases may spread: horizontal transmission and vertical transmission. Horizontal transmission means that the infection comes from the outside, usually through damage done to the plant by vegetative propagation, grafting, vectors (some viruses can propagate in plant host and vector animal) or mechanical transmission. Vertical transmission refers to the plant inheriting the disease from a parent; this is often via seed but is not as prevalent as horizontal transmission. Plant viruses frequently have the ability to stunt growth and diminish crop yield.
Well Understood Plant Viruses
Tobacco mosaic virus (TMV) and Cauliflower mosaic virus (CaMV) are frequently used in plant molecular biology. Of special interest is the CaMV 35S promoter, which is a very strong promoter most frequently used in plant transformations.
External links
- Plant Viruses Online, a full list of plant viruses
- Virology page based on Plant Viruses, University of Leicester
References
Milton Zaitlin and Peter Palukaitis (2000), Advances IN Understanding Plant Viruses AND Viruas Diseases. Vol. 38: 117-143 (doi:10.1146/annurev.phyto.38.1.117)
Milton Zaitlin (1998), Discoveries in Plant Biology, New York 14853, USA. Pp.: 105-110. S.D Kung and S. F. Yang (eds).
"Plant virus"