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A novel suppressor of plant defence?

Principal Supervisor: Professor Murray Grant

Co-supervisor: Dr Lijiang Song (Chemistry)

PhD project title: A novel suppressor of plant defence?

University of Registration: University of Warwick

Project outline:

With the human population projected to reach 9 billion in 2050, unsustainable demands will be placed on global agriculture to meet future food requirements. This will NOT be met by improvements previous accrued through traditional routes of plant breeding and energy intensive agriculture. Significant progress could be made through improved plant disease resistance. While current work primarily addresses genomic approaches geared towards improving basal or inducible disease resistance mechanisms, our knowledge of the nature of the small molecules that activate or attenuate defence responses is rudimentary.

This project builds on recent work using novel untargeted mass spectrometry profiling of diseased tissue.

Untargetted profiling of Arabidopsis thaliana leaves infected with Pseudomonas syringae identified discriminant metabolites that are associated with disease progression. The most discriminant metabolite identified belonged to a family of closely related diribosyl adenosines (hereafter referred to as diRAs). Uniquely, these diRAs rapidly and specifically increase in diseased tissue, the most abundant compound being identified as 3-O-β-D-ribofuranosyl adenosine.

3-O-β-D-ribofuranosyl adenosine is unique and targeted studies have identified pathogen induced diRAs in other plants inferring a global role in pathogenesis. The diRAs are rapidly induced to a high levels upon bacterial infection, by far the earliest and most prominent discriminatory molecule we have identified to date.

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The unique nature of these disaccharide nucleosides and their derivatives raises many questions with respect to their role in plant defence, including the fact that P. syringae contains at least 4 effector proteins delivered into the plant cell that have ribosylation activity. We hypothesise that diRAs are the direct product of activity of bacterial ribosyl-transferases and hence are mechanistically involved in suppression of plant immunity.

The project will involve the characterisation of purified diRAs to identify their biological function using HPLC, NMR, bacterial infection assays and generation of transgenic plants.

BBSRC Strategic Research Priority: Food Security

Techniques that will be undertaken during the project:

  • Transgenic plants (expressing effectors, or loss/reduction of function of NAD metabolic enzymes)
  • Microbiology (infection and enumeration of infected leaves)
  • Mass spectrometry profiling
  • Preparative HPLC fractionation
  • NMR structural identification

Contact: Professor Murray Grant, University of Warwick