Plant virus control strategies (was:Why we should care about pathogenic viruses in our plants)

Calvin Becker
Sun, 25 Jul 2010 10:47:03 PDT
Hi Lee and list

In response to your question as to whether plants are able to fight viruses or not- from my understanding they are able to. Plant viruses move from cell to cell via the plasmodesmata connecting those cells. Plant viruses produce movement proteins as part of their replication cycle and these movement proteins serve to widen the plasmodesmata connecting neighbouring cells and thus allow the virus through to infect a neighbouring cell. If the plant is able to prevent the action of this viral movement protein, the progeny virions cannot move from cell to cell and hence infection is curtailed. 

Another strategy employed by plants to control viral infection is that of a hypersensitive reaction by the plant to the presence of viral particles. Cells in and near the site of infection die off leading to necrosis of the area and hence elimination of the virus in the plant, provided that this reaction occurs early in the infection process.

Genetic transformation of plants using the bacterium Agrobacterium tumefaciens can be used to introduce viral genes (often those coding for the coat protein of the virus) into the genome of plants susceptible to a certain virus. The viral genes (and hence viral proteins) are expressed along with the plant proteins when transcription and translation of the plant genome occurs. The presence of the viral coat proteins in the plant prime the 'immune system' of the plant to that particular virus and prevent infection of the plant by that virus. Since genes coding for only certain viral proteins are introduced into the plant, the 'virus' does not replicate and harm the plant. 

I hope that this explanation is understandable?

3. Which leads me to a third comment/question: I am not a biologist, 
just someone very scientifically oriented and interested in many aspects 
of science. However, even though I've read and heard a lot about how the 
human body (and animals in general) fights viruses, antibodies, etc., I 
have utterly no knowledge about how or whether plants fight viruses. Do 
they produce antibodies? Do they have some other mechanism to do so? It 
would seem that they have to do something or else by now the entire 
plant kingdom would be either completely infiltrated with evolved 
viruses, or extinct. If there is such a mechanism, wouldn't it be 
possible to develop the equivalent or analog of vaccines for plants? 
They've made vaccines for pet animals and agricultural animals; have 
they tried creating the equivalent of vaccines for important commercial 
crops, and it not, is it because such a thing is not possible? (I 
realize that geophytes are far down the list in importance for making 
"vaccines" against viruses. But I'm curious about why I've never heard 
of medical methods to prevent virus infection in plants.)

--Lee Poulsen
Pasadena, California, USA - USDA Zone 10a

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