title: Ascorbate oxidase-dependent changes in the redox state of the apoplast modulate gene transcript accumulation leading to modified hormone signaling and orchestration of defense processes in tobacco.
abstract: The role of the redox state of the apoplast in hormone responses, signaling cascades, and gene expression was studied in transgenic tobacco (Nicotiana tabacum) plants with modified cell wall-localized ascorbate oxidase (AO). High AO activity specifically decreased the ascorbic acid (AA) content of the apoplast and altered plant growth responses triggered by hormones. Auxin stimulated shoot growth only when the apoplastic AA pool was reduced in wild-type or AO antisense lines. Oxidation of apoplastic AA in AO sense lines was associated with loss of the auxin response, higher mitogen-activated protein kinase activities, and susceptibility to a virulent strain of the pathogen Pseudomonas syringae. The total leaf glutathione pool, the ratio of reduced glutathione to glutathione disulfide, and glutathione reductase activities were similar in the leaves of all lines. However, AO sense leaves exhibited significantly lower dehydroascorbate reductase and ascorbate peroxidase activities than wild-type and antisense leaves. The abundance of mRNAs encoding antioxidant enzymes was similar in all lines. However, the day/night rhythms in the abundance of transcripts encoding the three catalase isoforms were changed in response to the AA content of the apoplast. Other transcripts influenced by AO included photorespiratory genes and a plasma membrane Ca(2+) channel-associated gene. We conclude that the redox state of the apoplast modulates plant growth and defense responses by regulating signal transduction cascades and gene expression patterns. Hence, AO activity, which modulates the redox state of the apoplastic AA pool, strongly influences the responses of plant cells to external and internal stimuli.
authors.affiliation: Crop Performance and Improvement Division , Rothamsted Research, Harpenden, Herts AL5 2JQ, United Kingdom.
authors.forename: Cristina
authors.initials: C
authors.lastname: Pignocchi
authors.forename: Guy
authors.initials: G
authors.lastname: Kiddle
authors.forename: Iker
authors.initials: I
authors.lastname: Hernández
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Foster
authors.forename: Amparo
authors.initials: A
authors.lastname: Asensi
authors.forename: Tahar
authors.initials: T
authors.lastname: Taybi
authors.forename: Jeremy
authors.initials: J
authors.lastname: Barnes
authors.forename: Christine H
authors.initials: CH
authors.lastname: Foyer
mesh_terms: D001204:Ascorbate Oxidase / Q000378:metabolism*; D001483:Base Sequence; D002940:Circadian Rhythm; D017931:DNA Primers; D007210:Indoleacetic Acids / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010937:Plant Growth Regulators / Q000378:metabolism*; D018515:Plant Leaves / Q000201:enzymology; D030821:Plants, Genetically Modified; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D014026:Nicotiana / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D012333:RNA, Messenger; D001204:Ascorbate Oxidase; D020928:Mitogen-Activated Protein Kinases