title: Chloroplasts play a central role in plant defence and are targeted by pathogen effectors.
abstract: Microbe associated molecular pattern (MAMP) receptors in plants recognize MAMPs and activate basal defences; however a complete understanding of the molecular and physiological mechanisms conferring immunity remains elusive. Pathogens suppress active defence in plants through the combined action of effector proteins. Here we show that the chloroplast is a key component of early immune responses. MAMP perception triggers the rapid, large-scale suppression of nuclear encoded chloroplast-targeted genes (NECGs). Virulent Pseudomonas syringae effectors reprogramme NECG expression in Arabidopsis, target the chloroplast and inhibit photosynthetic CO2 assimilation through disruption of photosystem II. This activity prevents a chloroplastic reactive oxygen burst. These physiological changes precede bacterial multiplication and coincide with pathogen-induced abscisic acid (ABA) accumulation. MAMP pretreatment protects chloroplasts from effector manipulation, whereas application of ABA or the inhibitor of photosynthetic electron transport, DCMU, abolishes the MAMP-induced chloroplastic reactive oxygen burst, and enhances growth of a P. syringae hrpA mutant that fails to secrete effectors.
authors.affiliation: Biosciences, College of Life and Environment Sciences, University of Exeter, Exeter EX4 4QD, UK.
authors.forename: Marta
authors.initials: M
authors.lastname: de Torres Zabala
authors.affiliation: Biosciences, College of Life and Environment Sciences, University of Exeter, Exeter EX4 4QD, UK.
authors.forename: George
authors.initials: G
authors.lastname: Littlejohn
authors.affiliation: Biosciences, College of Life and Environment Sciences, University of Exeter, Exeter EX4 4QD, UK.
authors.forename: Siddharth
authors.initials: S
authors.lastname: Jayaraman
authors.affiliation: Biosciences, College of Life and Environment Sciences, University of Exeter, Exeter EX4 4QD, UK.
authors.forename: David
authors.initials: D
authors.lastname: Studholme
authors.affiliation: Biosciences, College of Life and Environment Sciences, University of Exeter, Exeter EX4 4QD, UK.
authors.forename: Trevor
authors.initials: T
authors.lastname: Bailey
authors.affiliation: School of Biological Sciences, University of Essex, Colchester CO4 3SQ, UK.
authors.forename: Tracy
authors.initials: T
authors.lastname: Lawson
authors.affiliation: Max Planck Institute of Molecular Plant Physiology, Am Müehlenberg 1, Potsdam-Golm D-14476, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Tillich
authors.affiliation: Max Planck Institute of Molecular Plant Physiology, Am Müehlenberg 1, Potsdam-Golm D-14476, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Licht
authors.affiliation: Department of Biology I, Botany, Ludwig-Maximilians-Universität München, Groβhaderner Strase 2-4, Planegg-Martinsried D-82152, Germany.
authors.forename: Bettina
authors.initials: B
authors.lastname: Bölter
authors.affiliation: Department of Biology I, Botany, Ludwig-Maximilians-Universität München, Groβhaderner Strase 2-4, Planegg-Martinsried D-82152, Germany.
authors.forename: Laura
authors.initials: L
authors.lastname: Delfino
authors.affiliation: Department of Plant Biology, University of Minnesota, USA.
authors.forename: William
authors.initials: W
authors.lastname: Truman
authors.affiliation: Department of Life Sciences, Imperial College, London SW7 2AZ, UK.
authors.forename: John
authors.initials: J
authors.lastname: Mansfield
authors.affiliation: Biosciences, College of Life and Environment Sciences, University of Exeter, Exeter EX4 4QD, UK.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Smirnoff
authors.affiliation: Biosciences, College of Life and Environment Sciences, University of Exeter, Exeter EX4 4QD, UK.
authors.forename: Murray
authors.initials: M
authors.lastname: Grant