title: Transcriptional activation and production of tryptophan-derived secondary metabolites in arabidopsis roots contributes to the defense against the fungal vascular pathogen Verticillium longisporum.
abstract: The soil-borne fungal pathogen Verticillium longisporum causes vascular disease on Brassicaceae host plants such as oilseed rape. The fungus colonizes the root xylem and moves upwards to the foliage where disease symptoms become visible. Using Arabidopsis as a model for early gene induction, we performed root transcriptome analyses in response to hyphal growth immediately after spore germination and during penetration of the root cortex, respectively. Infected roots showed a rapid reprogramming of gene expression such as activation of transcription factors, stress-, and defense-related genes. Here, we focused on the highly coordinated gene induction resulting in the production of tryptophan-derived secondary metabolites. Previous studies in leaves showed that enzymes encoded by CYP81F2 and PEN2 (PENETRATION2) execute the formation of antifungal indole glucosinolate (IGS) metabolites. In Verticillium-infected roots, we found transcriptional activation of CYP81F2 and the PEN2 homolog PEL1 (PEN2-LIKE1), but no increase in antifungal IGS breakdown products. In contrast, indole-3-carboxylic acid (I3CA) and the phytoalexin camalexin accumulated in infected roots but only camalexin inhibited Verticillium growth in vitro. Whereas genetic disruption of the individual metabolic pathways leading to either camalexin or CYP81F2-dependent IGS metabolites did not alter Verticillium-induced disease symptoms, a cyp79b2 cyp79b3 mutant impaired in both branches resulted in significantly enhanced susceptibility. Hence, our data provide an insight into root-specific early defenses and suggest tryptophan-derived metabolites as active antifungal compounds against a vascular pathogen.
authors.affiliation: Julius-Maximilians-Universität Würzburg, Julius-von-Sachs-Institut, Pharmazeutische Biologie, Julius-von-Sachs-Platz 2, 97082 Würzburg, Germany.
authors.forename: Tim
authors.initials: T
authors.lastname: Iven
authors.forename: Stefanie
authors.initials: S
authors.lastname: König
authors.forename: Seema
authors.initials: S
authors.lastname: Singh
authors.forename: Susanna A
authors.initials: SA
authors.lastname: Braus-Stromeyer
authors.forename: Matthias
authors.initials: M
authors.lastname: Bischoff
authors.forename: Lutz F
authors.initials: LF
authors.lastname: Tietze
authors.forename: Gerhard H
authors.initials: GH
authors.lastname: Braus
authors.forename: Volker
authors.initials: V
authors.lastname: Lipka
authors.forename: Ivo
authors.initials: I
authors.lastname: Feussner
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Dröge-Laser
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology* / Q000502:physiology; D005961:Glucosinolates / Q000378:metabolism; D007211:Indoles / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D010935:Plant Diseases / Q000382:microbiology; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology* / Q000502:physiology; D013312:Stress, Physiological / Q000235:genetics; D013844:Thiazoles / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014364:Tryptophan / Q000378:metabolism*; D020172:Verticillium / Q000502:physiology*; D000094162:Phytoalexins
chemical_list: D005961:Glucosinolates; D007211:Indoles; D013844:Thiazoles; D014364:Tryptophan; C102405:camalexin; D000094162:Phytoalexins