title: Tryptophan-derived secondary metabolites in Arabidopsis thaliana confer non-host resistance to necrotrophic Plectosphaerella cucumerina fungi.
abstract: A defence pathway contributing to non-host resistance to biotrophic fungi in Arabidopsis involves the synthesis and targeted delivery of the tryptophan (trp)-derived metabolites indol glucosinolates (IGs) and camalexin at pathogen contact sites. We have examined whether these metabolites are also rate-limiting for colonization by necrotrophic fungi. Inoculation of Arabidopsis with adapted or non-adapted isolates of the ascomycete Plectosphaerella cucumerina triggers the accumulation of trp-derived metabolites. We found that their depletion in cyp79B2 cyp79B3 mutants renders Arabidopsis fully susceptible to each of three tested non-adapted P. cucumerina isolates, and super-susceptible to an adapted P. cucumerina isolate. This assigns a key role to trp-derived secondary metabolites in limiting the growth of both non-adapted and adapted necrotrophic fungi. However, 4-methoxy-indol-3-ylmethylglucosinolate, which is generated by the P450 monooxygenase CYP81F2, and hydrolyzed by PEN2 myrosinase, together with the antimicrobial camalexin play a minor role in restricting the growth of the non-adapted necrotrophs. This contrasts with a major role of these two trp-derived phytochemicals in limiting invasive growth of non-adapted biotrophic powdery mildew fungi, thereby implying the existence of other unknown trp-derived metabolites in resistance responses to non-adapted necrotrophic P. cucumerina. Impaired defence to non-adapted P. cucumerina, but not to the non-adapted biotrophic fungus Erysiphe pisi, on cyp79B2 cyp79B3 plants is largely restored in the irx1 background, which shows a constitutive accumulation of antimicrobial peptides. Our findings imply differential contributions of antimicrobials in non-host resistance to necrotrophic and biotrophic pathogens.
authors.affiliation: Centro de Biotecnología y Genómica de Plantas (UPM-INIA), Universidad Politécnica de Madrid, Campus Montegancedo, E-28223-Pozuelo de Alarcón, Madrid, Spain.
authors.forename: Andrea
authors.initials: A
authors.lastname: Sanchez-Vallet
authors.forename: Brisa
authors.initials: B
authors.lastname: Ramos
authors.forename: Paweł
authors.initials: P
authors.lastname: Bednarek
authors.forename: Gemma
authors.initials: G
authors.lastname: López
authors.forename: Mariola
authors.initials: M
authors.lastname: Piślewska-Bednarek
authors.forename: Paul
authors.initials: P
authors.lastname: Schulze-Lefert
authors.forename: Antonio
authors.initials: A
authors.lastname: Molina
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D001203:Ascomycota / Q000472:pathogenicity*; D018744:DNA, Plant / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D007113:Immunity, Innate; D007211:Indoles / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010935:Plant Diseases / Q000276:immunology* / Q000382:microbiology; D013844:Thiazoles / Q000378:metabolism; D014364:Tryptophan / Q000378:metabolism*; D000094162:Phytoalexins
chemical_list: D018744:DNA, Plant; D007211:Indoles; D013844:Thiazoles; D014364:Tryptophan; C102405:camalexin; D000094162:Phytoalexins