Principal Supervisor: Professor Murray Grant - SLS
Co-supervisors: Dr Patrick Schäfer - SLS
PhD project title: Getting the message across – understanding systemic signalling for global food security
University of Registration: Warwick
Given that > 25% of global crop production is currently lost to plant pathogens, an intimate understanding of plant defence mechanisms will significantly assist efforts to ensure global food security for our next generations. Plant disease resistance gene (R) products activate a rapid hypersensitive cell death programme that contains the pathogen. Simultaneously, R proteins also activate a systemic immune response in which naive tissues are more immune to a range of diverse pathogens. There is enormous biotechnological potential to enhance crop yields if we can understand the mechanisms underlying plant systemic immunity.
Plants lack a circulatory system. Long distance communication requires signal(s) generation in the local sensing organ, its translocation, delivery to, and decoding of, in the appropriate distal responding tissue. Implicit in this are both specificity and directionality. Such signals can only be delivered through the phloem, xylem or via volatile compounds. Although it is relatively easy to apply a local stress and record endpoint responses (more resistant or more susceptible than controls), our knowledge of the nature and perception of mobile signals delivered via any one of these avenues is at best rudimentary.
This is a truly multidisciplinary project. It will initially use the model pathosystem, Arabidopsis thaliana and Pseudomonas syringae carrying the virulence gene avrRpm1. Avirulent DC3000avrRpm1 but not virulent DC3000 activates rapid systemic signalling 3.5 h after infection (A). Hormonal cross talk is probably central to establishing global immunity. Indeed, transcriptomic profiling has implicated phytohormone networks in systemic immunity and susceptibility. Our data suggest a very dynamic temporal nature to transcriptional reprogramming in systemic responding naïve leaves. Using a combination of transcript profiling and whole plant live imaging, we now have strong preliminary evidence that the propagating signal is most likely a novel jasmonate derivative and mechanistically may be related to wounding (B, C). But we also know that the signalling is multicomponent, one unexpected component being an electrical signal generated shortly after R protein activation.
More recently it has been reported that virulent pathogens also modulate defence in systemic leaves, however this is particularly controversial with conflicting reports suggesting enhanced and suppressed immunity.
We will examine the nature of the RPM1 generated systemic signal and its dynamics from the initial stages of propagation to signal decoding in systemic responding leaves. The exciting opportunity to explore this remarkable, yet challenging, component of plant defence is now possible because of the availability of a range of unique systemic reporter constructs only recently developed in the Grant lab, combined with existing transcript data from systemically responding tissues and electrophysiological data.
The project will use these reporter lines, now additionally generated in Arabidopsis defence mutants. It will also use new lines with native-promoter transcriptional fusions to YFP and GFP to visualise the subcellular localisation and how signals move between cells of the petiole. As timing of signal generation and the spatial dynamics of signal perception are resolved, and as we confirm the core mutants lines that modulate these signals, the project will evolve to use one or more of a combination of untargeted metabolite or transcript profiling of phloem or responding systemic leaves. Emerging results will provide new insights into the complexities of communication in plants, both intracellularly and within the whole plant. The latter stages of the project will follow in the direction of the most interesting outcomes.
BBSRC Strategic Research Priority: Food security
Techniques that will be undertaken during the project:
- Plant pathology – local infection and systemic immune assays including bacterial enumeration.
- Bioimaging – both whole plant transcriptional dynamics using luciferase based assays and sub-cellular transport using YFP & GFP derivatives.
- Electrophysiology – basic electrophysiology looking at electrical potentials generated during challenges in different mutants.
- Basic plant genetics and reverse genetics.
- Transcriptomic profiling and data analysis Metabolomics.
- Application of both targeted – hormones - and untargeted profiling on phloem exudates and systemic responding leaves.
Contact: Professor Murray Grant, University of Warwick