title: Regulatory and Functional Aspects of Indolic Metabolism in Plant Systemic Acquired Resistance.
abstract: Tryptophan-derived, indolic metabolites possess diverse functions in Arabidopsis innate immunity to microbial pathogen infection. Here, we investigate the functional role and regulatory characteristics of indolic metabolism in Arabidopsis systemic acquired resistance (SAR) triggered by the bacterial pathogen Pseudomonas syringae. Indolic metabolism is broadly activated in both P. syringae-inoculated and distant, non-inoculated leaves. At inoculation sites, camalexin, indol-3-ylmethylamine (I3A), and indole-3-carboxylic acid (ICA) are the major accumulating compounds. Camalexin accumulation is positively affected by MYB122, and the cytochrome P450 genes CYP81F1 and CYP81F2. Local I3A production, by contrast, occurs via indole glucosinolate breakdown by PEN2- dependent and independent pathways. Moreover, exogenous application of the defense hormone salicylic acid stimulates I3A generation at the expense of its precursor indol-3-ylmethylglucosinolate (I3M), and the SAR regulator pipecolic acid primes plants for enhanced P. syringae-induced activation of distinct branches of indolic metabolism. In uninfected systemic tissue, the metabolic response is more specific and associated with enhanced levels of the indolics I3A, ICA, and indole-3-carbaldehyde (ICC). Systemic indole accumulation fully depends on functional CYP79B2/3, PEN2, and MYB34/51/122, and requires functional SAR signaling. Genetic analyses suggest that systemically elevated indoles are dispensable for SAR and associated systemic increases of salicylic acid. However, soil-grown but not hydroponically -cultivated cyp79b2/3 and pen2 plants, both defective in indolic secondary metabolism, exhibit pre-induced immunity, which abrogates their intrinsic ability to induce SAR.
authors.affiliation: Department of Biology, Heinrich Heine University Düsseldorf, Universitätsstraße 1, 40225 Düsseldorf, Germany; Cluster of Excellence on Plant Sciences (CEPLAS), Heinrich Heine University Düsseldorf, Universitätsstraße 1, D-40225 Düsseldorf, Germany.
authors.forename: Elia
authors.initials: E
authors.lastname: Stahl
authors.affiliation: Plant Biology Section, University of Fribourg, Route Albert Gockel 3, 1700 Fribourg, Switzerland.
authors.forename: Patricia
authors.initials: P
authors.lastname: Bellwon
authors.affiliation: Department of Biology, Heinrich Heine University Düsseldorf, Universitätsstraße 1, 40225 Düsseldorf, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Huber
authors.affiliation: Plant Biology Section, University of Fribourg, Route Albert Gockel 3, 1700 Fribourg, Switzerland.
authors.forename: Klaus
authors.initials: K
authors.lastname: Schlaeppi
authors.affiliation: Department of Biology, Heinrich Heine University Düsseldorf, Universitätsstraße 1, 40225 Düsseldorf, Germany.
authors.forename: Friederike
authors.initials: F
authors.lastname: Bernsdorff
authors.affiliation: Institut de Chimie, Université de Neuchâtel, Avenue Bellevaux 51, 2007 Neuchâtel, Switzerland.
authors.forename: Armelle
authors.initials: A
authors.lastname: Vallat-Michel
authors.affiliation: Plant Biology Section, University of Fribourg, Route Albert Gockel 3, 1700 Fribourg, Switzerland.
authors.forename: Felix
authors.initials: F
authors.lastname: Mauch
authors.affiliation: Department of Biology, Heinrich Heine University Düsseldorf, Universitätsstraße 1, 40225 Düsseldorf, Germany; Cluster of Excellence on Plant Sciences (CEPLAS), Heinrich Heine University Düsseldorf, Universitätsstraße 1, D-40225 Düsseldorf, Germany. Electronic address: juergen.zeier@uni-duesseldorf.de.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Zeier
mesh_terms: D017360:Arabidopsis / Q000378:metabolism / Q000382:microbiology; D060467:Disease Resistance / Q000235:genetics / Q000502:physiology; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology; D007113:Immunity, Innate / Q000235:genetics / Q000502:physiology; D007211:Indoles / Q000378:metabolism; D010935:Plant Diseases / Q000235:genetics / Q000382:microbiology*; D044224:Pseudomonas syringae / Q000472:pathogenicity; D013844:Thiazoles / Q000378:metabolism; D000094162:Phytoalexins
chemical_list: D007211:Indoles; D013844:Thiazoles; C102405:camalexin; D000094162:Phytoalexins; C012382:indole-3-carboxylic acid
keywords: Arabidopsis thaliana; Pseudomonas syringae; indolic metabolism; systemic acquired resistance