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Department of Plant Sciences

Aspirin's parent and RNA silencing jointly protect plants from TMV

Salicylic acid (SA: the parent compound of aspirin) is an important plant hormone that is needed by plants for defence against a wide range of disease-causing micro-organisms.  A lot is known about how SA helps plants to defeat invasion by bacteria and fungi but how this vital defence signal protects plants from infection by viruses remains much more mysterious.  However, it is known that SA increases expression of a gene called RNA-dependent RNA polymerase 1 (RDR1).  The RDR1 gene encodes an enzyme that is thought to help degrade viral RNA genomes through an important process called RNA silencing.  Sam Lee and colleagues in John Carr’s lab, and in collaboration with Rick Nelson at the Noble Foundation (Oklahoma, USA), showed that in the plant Nicotiana benthamiana RDR1 activity protects plants from being killed by tobacco mosaic virus.  RDR1 does this by preventing entry of the virus into the plant’s ‘meristem’; a region of tissue that contains a plant’s stem cells*, from which all other cell types develop (see illustration).  The ability of RDR1 to restrict the spread of virus into this region of precious progenitor cells is enhanced by SA and the researchers present evidence that SA does this by enhancing RDR1 enzyme activity. The work is published in BMC Plant Biology.  

Lee, W.S., Fu, S.F., Li, Z., Murphy, A.M., Dobson, E.A., Garland, L., Chaluvadi, S.R., Lewsey, M.G., Nelson, R.S., and Carr, J.P. Salicylic acid treatment and expression of an RNA-dependent RNA polymerase 1 transgene inhibit lethal symptoms and meristem invasion during tobacco mosaic virus infection in Nicotiana benthamiana. BMC Plant Biology 2016 16:15


*Note that these ‘pluripotent’ stem cells should not be confused with cells that happen to be in the stem of the plant.





Panel A shows high magnification images of the vicinity of the meristem for control (non-transgenic) plants and plants modified to express a gene for RDR1 (MtRDR1-transgenic). The plants were infected with tobacco mosaic virus engineered to express the green fluorescent protein (TMV-GFP). Under ultraviolet illumination uninfected tissue appears red in colour but tissue infected with TMV-GFP looks bright green. Expression of RDR1, or treatment with salicylic acid (SA), prevents entry of the TMV-GFP into this region.

In Panel B, longer sections of RDR1-expressing plants are shown and illustrate that a combination of SA treatment and RDR1 expression increases the protection of the meristem region from viral invasion.

Panel C shows how this combination of RDR1 expression and SA treatment prevents TMV from killing the plants and even allows them to recover from the virus-induced disease.