Tuesday, 3 April 2012

Virus-induced gene silencing: a versatile tool for discovery of gene functions in plants- Rahib AZWAD (42941804)


What is VIGS?
Virus Induced Gene Slicing (VIGS) is a tool that uses the RNA defence mechanism in a plant so that we can link a gene to what it does in a plant. So whenever a plant cell is infected, the defence mechanism, which is basically the short interfering strands of RNA (siRNA), attacks the single stranded RNA (ssRNA) of the virus cell, and this basically slows down the replication process in the virus cell [Purkayastha A, Dasgupta I, (2009)]. So what happens in VIGS is that the virus cell is injected with a specific gene of the plant. And so when the defence mechanism of plants activates and attacks the virus containing its own gene, the plant essentially messes up its own genome and the ability to produce a specific protein [Lu R ,Martin-Hernandez A, Peart J, Malcuit I, Baulcombe D. (2003)]. No protein means that the plant doesn’t function properly and there is a physical change.  This means that we can link that gene we injected into the virus with the physical change that occurred. 

This process is explained in more detail in the 2009 journal article Virus-induced gene silencing: a versatile tool for discovery of gene functions in plants http://www.ncbi.nlm.nih.gov/pubmed/19783452

So for example, let’s say I injected a virus with a gene I had no clue about. I then injected the virus into the plant. After 2-3 weeks I see that the plants stem is flaccid. I now know that the plant gene I injected into the virus is responsible for keeping the rigid structure of plants.
Left: shows the effects when the tomato plant has the gene ALC1 silenced.

Source: Wangdi T et al (2010), A Virus-Induced Gene Silencing Screen Identifies a Role for Thylakoid Formation1 in Pseudomonas syringae pv tomato Symptom Development in Tomato and Arabidopsis [journal article]

Recent developments
Since VIGS was first used, the functions of a large variety of genes belonging to plant development, defence mechanisms and stress response mechanisms have been identified. And as technology is progressing, we have discovered various techniques to infect a plant host cell. We can do this by spraying it on the plant, directly injecting it into the fruit or stem, or even putting it into the soil so it is sucked up by the roots [Voinnet O (2001)]. On top of this new viruses have been discovered such as the African cassava mosaic virus (ACMV) and these new viruses allow for a wider range of genes to be silenced in a wider range of plants [Voinnet O (2001)]. These are just a few technological developments and there are more explained in detail in Voinnet’s 2001 article RNA silencing as a plant immune system against viruses http://www.ncbi.nlm.nih.gov/pubmed/11485817

Pros and Cons
The main advantage of VIGS is that it’s a simple process, and the results can be produced within 2-3 weeks of infection. But it does have a limitation: it will not work with plants that are resistant to viruses [Purkayastha A, Dasgupta I. (2009)].  
And so we can see that VIGS is a quick and reliable tool for reverse genetics in plants. Due to this technology we have been able to silence and identify the functions of a wide variety of genes in plants and I believe it is possible that VIGS will grow in importance in plant genetics in the near future as it will be applied to a wider variety of plants.

References

Purkayastha A, Dasgupta I. (2009) Virus-induced gene silencing: a versatile tool for discovery of gene functions in plants http://www.ncbi.nlm.nih.gov/pubmed/19783452 [online](accessed 18 March 2012)

Lu R ,Martin-Hernandez A, Peart J, Malcuit I, Baulcombe D. (2003) Virus-induced gene silencing in plants http://www.sciencedirect.com/science/article/pii/S1046202303000379 [online](accessed 18 March 2012)

Voinnet O (2001) RNA silencing as a plant immune system against viruses http://www.ncbi.nlm.nih.gov/pubmed/11485817, TRENDS in Genetics Vol.17 No.8 pp 449-459

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