Molecular plant pathogenesis: regulation and impacts of bacterial soft rot virulence factors

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Theme: Agriculture and Food SecurityBecause of agriculture and food security ramifications, and strategic policy, BBSRC consider plant pathology as a "vulnerable" research area requiring active DTP investment in skills training, highly appropriate for Cambridge DTP support. Soft rotting Erwinia species (now Pectobacterium and Dickeya species) attack potato crops and various vegetable crops. These pathogens are in the "top ten" of plant pathogenic bacteria for agricultural and research impact. Project: The co-supervisors, George Salmond (Biochemistry) and John Carr (Plant Sciences), collaborated successfully on a project involving the plant pathogen, Pectobacterium (originally Erwinia). The interdepartmental collaboration uncovered a novel bacterial toxin that was necrotic and lethal in Arabidopsis assays done in the Carr laboratory. Production of the bacterial toxin (Nip; necrosis inducing protein) is under quorum sensing (QS) control i.e regulated by a diffusible intercellular chemical signal, N-3-oxohexanoyl homoserine lactone. Nip production is one of multiple virulence determinants in the quorum sensing regulon that plays key roles in plant disease. Other QS regulon members include plant cell wall degrading enzymes (PCWDEs: pectinases, cellulases and proteases) and co-regulated protein secretion machines (Type I and Type II in particular). This project will use transcriptional reporter gene fusion (LacZ, UidA, Gfp) strains of the pathogen (Pectobacterium and, if time allows, Dickeya solani) to investigate regulatory inputs to Nip and PCWDE production. In addition to QS, we will assess new environmental and physiological inputs to toxin elaboration. Some virulence factors are thermoregulated and their cognate genes could also respond to osmolarity, pH and C, N and P nutritional availability. This will be assessed by high throughput screening using appropriate pathogen reporter fusion strains. Importantly, we intend to investigate the impacts of plant signals in pathogen gene induction, initially using plant extracts (Solanum and Arabidopsis) in screening assays to define plant-inducible genes (via high density gene fusion arrays). Plant-inducible gene mutants will be tested in planta for virulence impacts and those exhibiting plant pathology impacts (and/or response to specific environmental or physiological cues) will be examined further. They will be used, with wild type, for proteomic analyses and RNA-seq studies to define wider transcriptional and proteomic impacts of the novel regulators in plant attack. This project will be data-rich, with malleable contingencies and so is ideal for a PhD project. The PhD student will benefit from interdisciplinary co-supervision across two departments. She will acquire core skills in the strategically important area of plant pathology plus underpinning skills in genetics, bioinformatics, and some 'omics technologies (proteomics and RNA-seq). Given the phytopathology skills gap in the UK (as highlighted by the BBSRC) the graduate will be highly employable, in basic research or translational agricultural industries.