title: Early changes in apoplast composition associated with defence and disease in interactions between Phaseolus vulgaris and the halo blight pathogen Pseudomonas syringae Pv. phaseolicola.
abstract: The apoplast is the arena in which endophytic pathogens such as Pseudomonas syringae grow and interact with plant cells. Using metabolomic and ion analysis techniques, this study shows how the composition of Phaseolus vulgaris leaf apoplastic fluid changes during the first six hours of compatible and incompatible interactions with two strains of P. syringae pv. phaseolicola (Pph) that differ in the presence of the genomic island PPHGI-1. Leaf inoculation with the avirulent island-carrying strain Pph 1302A elicited effector-triggered immunity (ETI) and resulted in specific changes in apoplast composition, including increases in conductivity, pH, citrate, γ-aminobutyrate (GABA) and K(+) , that are linked to the onset of plant defence responses. Other apoplastic changes, including increases in Ca(2+) , Fe(2/3+) Mg(2+) , sucrose, β-cyanoalanine and several amino acids, occurred to a relatively similar extent in interactions with both Pph 1302A and the virulent, island-less strain Pph RJ3. Metabolic footprinting experiments established that Pph preferentially metabolizes malate, glucose and glutamate, but excludes certain other abundant apoplastic metabolites, including citrate and GABA, until preferred metabolites are depleted. These results demonstrate that Pph is well-adapted to the leaf apoplast metabolic environment and that loss of PPHGI-1 enables Pph to avoid changes in apoplast composition linked to plant defences.
authors.affiliation: Department of Plant Sciences, University of Oxford, Oxford, OX1 3RB, UK.|Australian Research Council Centre of Excellence in Plant Energy Biology, The University of Western Australia, Perth, 6009, Australia.
authors.forename: Brendan M
authors.initials: BM
authors.lastname: O'Leary
authors.affiliation: Faculty of Health and Applied Sciences, University of the West of England, Bristol, BS16 1QY, United Kingdom.
authors.forename: Helen C
authors.initials: HC
authors.lastname: Neale
authors.affiliation: Faculty of Agricultural and Nutritional Sciences, Institute of Plant Nutrition and Soil Science, Kiel University, Kiel, 24118, Germany.
authors.forename: Christoph-Martin
authors.initials: CM
authors.lastname: Geilfus
authors.affiliation: School of Biological Sciences, University of Reading, Reading, RG6 6AH, UK.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Jackson
authors.affiliation: Faculty of Health and Applied Sciences, University of the West of England, Bristol, BS16 1QY, United Kingdom.
authors.forename: Dawn L
authors.initials: DL
authors.lastname: Arnold
authors.affiliation: Department of Plant Sciences, University of Oxford, Oxford, OX1 3RB, UK. gail.preston@plants.ox.ac.uk.
authors.forename: Gail M
authors.initials: GM
authors.lastname: Preston
mesh_terms: D054884:Host-Pathogen Interactions; D055432:Metabolomics; D027805:Phaseolus / Q000276:immunology / Q000378:metabolism / Q000382:microbiology*; D010935:Plant Diseases / Q000382:microbiology; D018515:Plant Leaves / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D044224:Pseudomonas syringae / Q000502:physiology*
keywords: GABA; apoplastic washing fluid; citrate; leaf apoplast; metabolic footprinting; metabolomics; plant defence response; plant-microbe interactions