title: Secreted fungal effector lipase releases free fatty acids to inhibit innate immunity-related callose formation during wheat head infection.
abstract: The deposition of the (1,3)-β-glucan cell wall polymer callose at sites of attempted penetration is a common plant defense response to intruding pathogens and part of the plant's innate immunity. Infection of the Fusarium graminearum disruption mutant Δfgl1, which lacks the effector lipase FGL1, is restricted to inoculated wheat (Triticum aestivum) spikelets, whereas the wild-type strain colonized the whole wheat spike. Our studies here were aimed at analyzing the role of FGL1 in establishing full F. graminearum virulence. Confocal laser-scanning microscopy revealed that the Δfgl1 mutant strongly induced the deposition of spot-like callose patches in vascular bundles of directly inoculated spikelets, while these callose deposits were not observed in infections by the wild type. Elevated concentrations of the polyunsaturated free fatty acids (FFAs) linoleic and α-linolenic acid, which we detected in F. graminearum wild type-infected wheat spike tissue compared with Δfgl1-infected tissue, provided clear evidence for a suggested function of FGL1 in suppressing callose biosynthesis. These FFAs not only inhibited plant callose biosynthesis in vitro and in planta but also partially restored virulence to the Δfgl1 mutant when applied during infection of wheat spikelets. Additional FFA analysis confirmed that the purified effector lipase FGL1 was sufficient to release linoleic and α-linolenic acids from wheat spike tissue. We concluded that these two FFAs have a major function in the suppression of the innate immunity-related callose biosynthesis and, hence, the progress of F. graminearum wheat infection.
authors.affiliation: Molecular Phytopathology and Genetics, Biocenter Klein Flottbek, University of Hamburg, 22609 Hamburg, Germany.
authors.forename: Antje
authors.initials: A
authors.lastname: Blümke
authors.forename: Christian
authors.initials: C
authors.lastname: Falter
authors.forename: Cornelia
authors.initials: C
authors.lastname: Herrfurth
authors.forename: Björn
authors.initials: B
authors.lastname: Sode
authors.forename: Rainer
authors.initials: R
authors.lastname: Bode
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Schäfer
authors.forename: Ivo
authors.initials: I
authors.lastname: Feussner
authors.forename: Christian A
authors.initials: CA
authors.lastname: Voigt
mesh_terms: D003847:Deoxyglucose / Q000494:pharmacology; D005230:Fatty Acids, Nonesterified / Q000494:pharmacology*; D005670:Fusarium / Q000201:enzymology* / Q000472:pathogenicity / Q000502:physiology; D005936:Glucans / Q000378:metabolism*; D005964:Glucosyltransferases / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism; D007113:Immunity, Innate / Q000187:drug effects*; D008049:Lipase / Q000378:metabolism*; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D010935:Plant Diseases / Q000276:immunology / Q000382:microbiology*; D057865:Plant Immunity / Q000187:drug effects; D014908:Triticum / Q000187:drug effects / Q000276:immunology* / Q000382:microbiology*; D014774:Virulence / Q000187:drug effects
chemical_list: D005230:Fatty Acids, Nonesterified; D005936:Glucans; D049452:Green Fluorescent Proteins; C048306:callose; D003847:Deoxyglucose; D005964:Glucosyltransferases; C020570:1,3-beta-glucan synthase; D008049:Lipase