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Characterization of a novel rapid response elicited in Arabidopsis by a compatible plant pathogen

Reference	BB/C005562/1
Principal Investigator / Supervisor	Dr Joel Milner
Co-Investigators / Co-Supervisors	Professor Gary Loake, Professor Ari Sadanandom
Institution	University of Glasgow
Department	School of Life Sciences
Funding type	Research
Value (£)	283,567
Status	Completed
Type	Research Grant
Start date	01/03/2005
End date	31/08/2008
Duration	42 months

Abstract

Viruses are important pathogens of economically important plants, and virus diseases are responsible for economic losses running into billions of pounds per year. although it is compatible interactions that are responsible for such losses, with the exception of gene silencing, host responses to compatible virus infections, and the molecular mechanisms by which plants defend themselves against such infections are poorly characterised. Using the infection of Arabidopsis by cauliflower mosaic virus (CaMV) as a model pathosystem with which to study compatible host-virus interactions, we have recently identified a previously unknown response to infection by a compatible virus. This response, which we term the rapid systemic response (RSR) involves the up-regulation at sites distant to the inoculated leaf, of marker reporter genes for the presence of reactive oxygen intermediates (ROS) and ethylene-signalling. Virus capsid protein(s) act as the elicitor of the response, which occurs within 2 h of inoculation, is accompanied by the accumulation of H202, and involves a systemic signal which is not virus. Several mutants, including two defective in ethylene response, are deficient in the RSR, and are also substantially less susceptible than wild-type Arabidopsis to CaMV. These and other results lead us to suggest that the RSR forms part of a hitherto unidentified early warning response mechanism that reacts to the presence of foreign pathogen-associated proteins. Our overall objectives are: to determine the extent to which other pathogens can elicits the RSR; to characterise the signalling pathways involved; to determine the molecular mechanisms by which they are elicited (or suppressed); and to establish how they control virus multiplication and or spread. In particular we aim to establish the roles played by ethylene and ROS as signalling intermediates. To achieve these aims, we propose to take three different approaches, to be carried out in parallel in Glasgow and Edinburgh: Firstly, we propose to use luminescence to characterise the expression of reporter genes GST1::LUC (a marker for ROS) and PDF1.2::LUC (a marker for ethylene JA defence) to infection by three other viruses (for two of which Arabidopsis is a host) two compatible fungal pathogens, and a compatible bacterial pathogen. We will use staining to identify H202 accumulation in response to infection. We will extend these studies to characterising the patterns of Luciferase activity in ethylene response and rboh mutant backgrounds. We have already established the timing and patterns of expression of these reporters in wild-type Arabidopsis, and have shown that such mutants are deficient in local and systemic H202 accumulation in response to CaMV-inoculation. Here we will determine the role of the mutant genes, and their associated signalling pathways, in the signalling and propagation of the RSR. We will characterise the role of CaMV structural proteins as elicitors. Expression plasmids with the coding regions for the major and minor capsid proteins under the control of a 35S promoter will be constructed. Particle bombardment will be used to transiently express these constructs in GST1::LUC reporter plants and we will test for the ability to elicit systemic luciferase activity. We will extend these studies to expressing domains of the capsid proteins. Our objectives will be to identify the precise domains that are recognised by the plant. We also aim to identify plant-encoded proteins that are candidates for receptors that can recognise these domains. We will carry out yeast two-hybrid analysis using the elicitor domains as the bait. In a second approach we will transiently express the elicitor by particle bombardment and will use immunoprecipitation to identify interactors with the elicitor protein. We anticipate that these studies will lead to the identification of novel approaches for engineering virus tolerance into plants.

Summary

unavailable

Committee	Closed Committee - Plant & Microbial Sciences (PMS)
Research Topics	Crop Science, Microbiology, Plant Science
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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