Department of Plant Sciences

Dr John Carr

Find out more about John Carr and his Group or email John.Carr@plantsci.cam.ac.uk

Project titles:

  1. Induced resistance to pathogens
  2. The interactions between plants, viruses and the insects that transmit viruses
  3. A novel signal molecule controlling plant resistance to viruses, fungi and bacteria, as well as to abiotic stresses
 

Molecular studies of induced resistance to plant viruses and their vectors

Project Title: Induced resistance to pathogens

Supervisor: Dr J. Carr

Project outline:

One of our long-term objectives is to understand why some plants are able to actively resist pathogens, while others remain susceptible. It is important to study the molecular detail of plant-microbe interactions if we wish to develop new, effective, and environmentally friendly crop protection methods. SA is an important signal compound in plants. It has roles in such apparently diverse phenomena as flowering, senescence and defence against pathogens. SA is a key component of the signal transduction pathway that activates resistance against many plant pathogens: fungi, bacteria, and viruses. Our laboratory has shown that the signal transduction pathway branches down-stream of SA, with one branch leading to resistance to viruses and the other leading to induction of resistance to bacterial and fungal pathogens. Interestingly, this pathway can activate resistance to both virus replication and movement. In addition, SA can induce the expression of an RNA dependent RNA polymerase that may play a role in inducing the sequence-specific destruction (RNA silencing) of viral RNAs. We want to find out how these various antiviral effects are co-ordinated with each other and with resistance to non-viral pathogens.

Currently, we are most interested in finding out how RNA silencing contributes to SA mediated defence against viruses. This will be approached in two ways. Firstly, we will examine how mutations affecting the plant’s RNA silencing machinery affect SA induced resistance. Secondly, we will investigate how viruses overcome SA induced resistance and determine if this is achieved by inhibiting silencing. For example, cucumber mosaic virus encodes a protein, 2b, that inhibits RNA silencing and SA induced resistance. We will determine specifically which SA-induced virus resistance mechanism(s) are subverted by 2b (replication, cell-to-cell movement etc) and use mutagenesis to identify functional domain(s) of the 2b protein responsible for subverting SA-induced resistance and determine if these are the same domains governing subversion of RNAi. We will also determine whether 2b subverts induced resistance to pathogens other than viruses (fungi, bacteria).

See Research or email: John.Carr@plantsci.cam.ac.uk

 

Project Title: The interactions between plants, viruses and the insects that transmit viruses

Supervisor: Dr J. Carr

Project outline:

Aphids are the single most important group of invertebrates transmitting viruses from plant to plant. Most crops have limited resistance to aphids and protection of crops using insecticides is becoming more difficult through the emergence of insecticide-resistant aphids. Novel, less environmentally damaging means f protecting crops from aphids and the viruses they carry are needed.

In collaboration with Dr Mark Stevens (Brooms Barn Research Station) and Professor Alison Smith (of this Department) we are investigating how viruses manipulate plant gene expression and metabolism in order to influence the behaviour and survival of aphids. It is now known that in certain cases virus infection alters the attractiveness of plants to aphids and/or the growth of aphid populations on colonised plants. This was demonstrated in potato (Eigenbrode et al Proc Roy Soc B 269: 455, 2002) and in model plants (this group, unpublished) and most likely involves changes in the metabolite profiles of the plants. We will identify viruses and viral gene product(s) of that elicit changes in insect responses (feeding behaviour and reproduction). In addition we will investigate how viruses alter defensive signalling and metabolism in the host and identify gene products or low molecular weight chemicals that affect aphids.

See Research or email: John.Carr@plantsci.cam.ac.uk

 

Project Title: A novel signal molecule controlling plant resistance to viruses, fungi and bacteria, as well as to abiotic stresses

Supervisors: Dr John Carr and Dr David Hanke

Project outline:

The sugar phosphate phytic acid (myo-inositol hexakisphosphate) is present in all plants and used in seeds and other storage tissues as a reserve for phosphate. Because phytic acid in the diet can have beneficial as well as deleterious influences on human health, and because the release of too much phytic acid in agricultural waste can exacerbate water pollution, various research groups have attempted to generate crop varieties with a modified content of phytate. While investigating lines of transgenic potato and Arabidopsis plants with decreased levels of phytate we serendipitously discovered that phytate is an important signalling molecule that regulates basal resistance to viral, bacterial and fungal pathogens of plants (Murphy et al., 2008) and influences the resistance of plants to abiotic stress (Otto et al., manuscript in preparation).

Arabidopsis has three a family of three genes encoding isoforms of the enzyme that catalyses the first step in the biosynthesis of phytate, the enzyme myo-inositol 3-phosphate synthase (AtIPS1–3). Plants with a mutation in the gene AtIPS2 (atips2 mutants) plants were hypersusceptible to the RNA viruses tobacco mosaic virus, turnip mosaic virus, cucumber mosaic virus and the DNA virus cauliflower mosaic virus, as well as to the fungus Botrytis cinerea and to the bacterial pathogen Pseudomonas syringae. In fact, these plants were as hypersusceptible to infection as plants unable to accumulate salicylic acid (SA), which is an indication of the importance of phytic acid in defensive signal transduction. In contrast, atips1 mutants were not hypersusceptible to pathogens but these mutant plants were more susceptible to abiotic stresses. Analysis of the promoter and protein-coding sequences of the AtIPS1 and AtIPS2 genes suggest that the two versions of IPS may be produced in different tissues of a plant and/or accumulate in different compartments within the plant cell. This suggests that different pools of phytate (occurring in different sub-cellular organelles or different plant tissues) may regulate separate signalling pathways regulating pathogen resistance (AtIPS2) or stress responses (AtIPS1). The aim of the project will be: to identify the sites of localization of AtIPS1 and AtIPS2, to identify a role for IPS3, and to determine whether or not the levels of phytate in plants can be altered without damaging a plant’s ability to combat pathogen infection or abiotic stress.

Reference

  1. Murphy, A.M., Otto, B., Brearley, C.A., Carr, J.P. & Hanke, D.E. (2008) A role for inositol hexakisphosphate in the maintenance of basal resistance to plant pathogens. Plant Journal in press

See John Carr's Research or email John.Carr@plantsci.cam.ac.uk
See David Hanke's Research or email: David.Hanke@plantsci.cam.ac.uk

Selected Group publications

Review Articles

  1. Murphy, A.M., Gilliland, A., Wong, C.E., West, J., Singh, D.P. & Carr, J.P. (2001) Induced resistance to viruses. European Journal of Plant Pathology 107, 121-128.
  2. Murphy, A. M., Chivasa, S., Singh, D.P. & Carr, J. P. (1999) Salicylic acid-induced resistance to viruses and other pathogens: a parting of the ways? Trends in Plant Sciences 4, 155-160.
  3. Singh, D.P. Moore,C.A. Gilliland, A. & Carr, J.P. (2004). Activation of multiple anti-viral defence mechanisms by salicylic acid. Molecular Plant Pathology 5: 57-63.

Research Papers

  1. Ziebell, H., Payne, T., Berry, J.O., Walsh, J.A. & Carr, J.P. (2007). A cucumber mosaic virus mutant lacking the 2b counter-defence protein gene provides protection against wild-type strains. Journal of General Virology 88: 2862-2871.
  2. Lewsey, M., Robertson, F.C., Canto, T., Palukaitis, P. & Carr, J.P. (2007). Selective targeting of miRNA-regulated plant development by a viral counter-silencing protein. Plant Journal 50: 240-252.
  3. Handford, M.G. & Carr, J.P. (2007). A defect in carbohydrate metabolism ameliorates symptom severity in virus-infected Arabidopsis thaliana. Journal of General Virology 88: 337-341.
  4. Huang, W.E., Huang, L., Preston, G., Naylor, M., Carr, J.P., Li, Y., Singer, A.C., Whiteley, A.S. & Wang, H. (2006). Quantitative in situ assay of salicylic acid in tobacco leaves using a genetically modified biosensor strain of Acinetobacter sp. ADP1. Plant Journal 46:1073-1083.
  5. Mayers, C.N., Lee, K-.C., Moore, C.A., Wong, S-.K. & Carr, J.P. (2005). Salicylic acid-induced resistance to Cucumber mosaic virus in squash and Arabidopsis thaliana: Contrasting mechanisms of induction and antiviral action. Molecular Plant-Microbe Interactions 18: 428-434.
  6. Murphy, A. M., Gilliland, A., York, C. J., Hyman, B., & Carr, J. P. (2004). High-level expression of alternative oxidase protein sequences enhances the spread of viral vectors in resistant and susceptible plants. Journal of General Virology 85: 3777-3786.
  7. Gilliland, A., Singh, D.P., Hayward, J.M., Moore, C.A., Murphy, A.M., York, C.J., Slator, J. & Carr, J.P. (2003). Genetic modification of alternative respiration has differential effects on antimycin A-induced versus salicylic acid-induced resistance to Tobacco mosaic virus. Plant Physiology 132: 1518-1528.
  8. Soards, A.J., Murphy, A.M., Palukaitis, P. & Carr, J.P. (2002) Virulence and differential local and systemic spread of Cucumber mosaic virus in tobacco are affected by the CMV 2b protein. Molecular Plant-Microbe Interactions 15: 647-653.
  9. Murphy, A.M. & Carr, J.P. (2002) Salicylic acid has cell-specific effects on Tobacco mosaic virus replication and cell-to-cell movement. Plant Physiology 128: 552-563.
  10. Wong, C.E., Carson, R.A.J. & Carr, J.P. (2002) Chemically-induced virus resistance in Arabidopsis thaliana is independent of pathogenesis-related protein expression and the NPR1 gene. Molecular Plant-Microbe Interactions 15: 75-81.