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Nucloeside decoys – a novel pathogen strategy to infect plants

Primary Supervisor: Professor Murray Grant, School of Life Sciences

Secondary supervisor: Dr Lijiang Song (Chemistry)

PhD project title: Nucloeside decoys – a novel pathogen strategy to infect plants

University of Registration: University of Warwick

Project outline:

  1. Plant disease resistance (R) genes are widely deployed in plant breeding to help mitigate global crop losses to pests and pathogens. Unfortunately, resistance is often overcome in the field as pathogens evolve ever sophisticated methods of deploying multi-functional “effectors” - key elements of the pathogens armoury that work collectively to avoid detection and suppress host immunity.

    Despite having cloned R proteins more than 25 years ago, until 12 months ago we had little idea how these functioned. A recent major research breakthrough showed that the amino terminal TIR, (Toll Interleukin 1) domain of “T”NL class of disease resistance proteins dimerises to generate a complex capable of cleaving NADH or NADPH, key energy sources for cells. Critically, this “NADase” activity was essential to activate disease resistance. While animal and bacteria TIR domains have similar NADase enzymatic activities, the products appear to differ. Plants produce a compound called v-cADPR (variant cyclic ADP Ribose).

    Remarkably, our research on the metabolic transition from defence to disease, specifically looking at how the bacterial plant pathogen Pseudomonas syringae overcomes host defences identified a molecule, which we call “540” based on its molecular mass, which is of identical molecular mass to v-cADPR formed by activated TNL disease resistance proteins. Critically, it has a different retention time, as also does the bacterial TIR produced v-cADPR suggesting some very subtle structural variations probably confer quite different specificities. To date, it is unclear whether either the TNL produced plant or bacterial v-cADPR have any biological activity.

    Importantly, we had previously published two key pieces of evidence.

    Equally fascinatingly, disease causing bacteria also induce a very specific locus of truncated TNL genes. This appears counterintuitive. Why induce R genes? We know disease causing bacteria rapidly suppress a reactive oxygen burst in the chloroplast. This would lead to increased NADP+, a substrate for NADase substrate. Collectively these data suggest that

    bacterial effectors induce the truncated TNLs to mop up accumulating NADP+ and will test this using a variety of methods.

    So why is this exciting? First, plant TIR-domain resistant proteins confer resistance against a vast array of plant pathogens including bacteria, fungi, oomycetes and viruses. We predict that pathogens hijack these tTNLs to sequester NADP/H to prevent activation – if correct this is a paradigm changing discovery.

    The project suits an enthusiastic and motivated chemistry orientated student with an interest in cutting edge discovery work which could make a real difference to future Food Security. Along the journey, the project will provide a training in a wide range of techniques –protein expression, biochemical assays, HPLC, mass spectrometry and NMR providing an ideal foundation for future career opportunities

BBSRC Strategic Research Priority: Understanding the Rules of Life: Plant Science

    Techniques that will be undertaken during the project:

    • A diverse range of analytical skills including HPLC, mass spectrometry (quadrupole time of flight and triple quadrupole), NMR.

    • Biochemistry techniques such as protein expression and enzyme assays.

    • Fundamental microbiology training for plant-pathogen assays.

    Contact: Professor Murray Grant, University of Warwick