A viral counter defence protein as a probe for cross-talk or functional overlap between host defence pathways.

Lead Research Organisation: University of Cambridge
Department Name: Plant Sciences


Cucumber mosaic virus (CMV) is remarkable in that it attacks more crop and wild plant species than any other and it is one of the two most important viruses of field-grown and glasshouse horticultural crops in the UK and worldwide. An essential contributor to the success of CMV is a recently discovered factor called the 2b protein. This viral protein carries out several tasks but its most important is subverting disease resistance. We know that the 2b protein can inhibit the action of two types of resistance mechanism. One of these is called systemic acquired resistance, in which an attack by one disease-causing organism may stimulate a higher degree of resistance to a very broad range of diverse micro-organisms (viruses, fungi, bacteria). The other resistance mechanism defeated by the 2b protein is based on RNA interference, a phenomenon in which viral genetic material is recognised as foreign and broken down. We will determine how the 2b protein affects two apparently very different defence systems and if, in the process of disrupting systemic acquired resistance against virus infection, the 2b also has the potential to increase the susceptibility of plants to other disease causing micro-organisms.

Technical Summary

The Cucumber mosaic virus 2b protein is a suppressor of RNAi-mediated silencing of the virus. But it also subverts induced virus resistance mechanism(s) regulated by the plant signal chemical salicylic acid (SA), a key signal in the induction of systemic acquired resistance. This suggests that the two forms of resistance overlap and that the 2b protein is targeting a component common to both types of resistance. Although the effect of the 2b protein on SA-induced resistance has been known for four years it has never been determined exactly how it exerts its effects on this resistance pathway. In this project we will identify: 1. The mechanism(s) of 2b-mediated subversion of SA-induced virus resistance; 2. whether or not the functional domains of the 2b protein involved in subversion of SA-induced resistance are the same as, or different from, those that function in subversion of RNAi-mediated resistance, and 3. If the CMV 2b protein affects resistance to non-viral pathogens via SA as well as non-SA dependent signalling pathways such as those controlled primarily by ethylene and jasmonate.


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Harvey JJ (2011) An antiviral defense role of AGO2 in plants. in PloS one

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Lewsey M (2007) Selective targeting of miRNA-regulated plant development by a viral counter-silencing protein. in The Plant journal : for cell and molecular biology

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Lewsey M (2009) The Role of the Cucumber mosaic virus 2b Protein in Viral Movement and Symptom Induction in Molecular Plant-Microbe Interactions®

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Lewsey MG (2010) Disruption of two defensive signaling pathways by a viral RNA silencing suppressor. in Molecular plant-microbe interactions : MPMI

Description A full report on this grant was provided via JeS more than 2 years ago.
Exploitation Route A full report on this grant was provided via JeS more than 2 years ago.
Sectors Agriculture, Food and Drink

Description The work from this grant led directly to projects revealing that viral proteins (such as the 2b protein, which was the focus of this award) affect the interactions of infected plants with insects. This is important because most plant viruses are insect-transmitted. Indeed, since this award, our group and groups in the US and China have found that viruses use factors, including the 2b protein to enhance the likelihood of transmission to new hosts (see review Groen, S.C., Wamonje, F.O., Murphy, A.M. and Carr, J.P. (2017). Engineering resistance to virus transmission. Current Opinion in Virology 26:20-27.). Indeed a major focus of our current work is attempting to utilize these ideas to findings to improve practical protection of crops against aphid-transmitted viruses in Africa. This work also led us to investigate the intriguing possibility that the 2b protein affects interactions of plant with pollinators - with potential effects on the co-evolution of plants and viruses. This led us to obtaining Leverhulme Trust Funding to investigate this (see Groen S.C., Jiang S., Murphy, A.M., Cunniffe N.J., Westwood, J.H., Davey, M.P., Bruce, T.J.A., Caulfield, J.C., Furzer, O.J., Reed, A., Robinson, S.I., Miller, E., Davis C.N., Pickett, J.A., Whitney, H.M., Glover, B.J., and Carr, J.P. (2016) Virus infection of plants alters pollinator preference: A payback for susceptible hosts? PLoS Pathogens 12(8): e1005790 http://dx.plos.org/10.1371/journal.ppat.1005790). The work led to major attention in the international media.
First Year Of Impact 2009
Sector Agriculture, Food and Drink
Impact Types Cultural