Early changes in apoplast composition associated with defence and disease in interactions between Phaseolus vulgaris and the halo blight pathogen Pseudomonas syringae Pv. phaseolicola |
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| Authors: | Brendan M O'Leary Helen C Neale Christoph‐Martin Geilfus Robert W Jackson Dawn L Arnold Gail M Preston |
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| Affiliation: | 1. Department of Plant Sciences, University of Oxford, Oxford, UK;2. Australian Research Council Centre of Excellence in Plant Energy Biology, The University of Western Australia, Perth, Australia;3. Faculty of Health and Applied Sciences, University of the West of England, Bristol, United Kingdom;4. Faculty of Agricultural and Nutritional Sciences, Institute of Plant Nutrition and Soil Science, Kiel University, Kiel, Germany;5. School of Biological Sciences, University of Reading, Reading, UK |
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| 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 Ca2+, Fe2/3+ Mg2+, 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. |
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| Keywords: | apoplastic washing fluid citrate GABA leaf apoplast metabolic footprinting metabolomics plant defence response plant– microbe interactions |
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