Structural analyses and dynamics of soluble and cell wall-bound phenolics in a broad spectrum resistance to the powdery mildew fungus in barley.
High pressure liquid chromatography profiles of barley leaf epidermal soluble and cell wall-bound phenolics were analyzed in response to challenge with the fungal pathogen Erysiphe graminis f. sp. hordei. Only one soluble phenolic was found to accumulate differentially in a broad spectrum resistance reaction controlled by mlo resistance alleles in comparison to susceptible near isogenic Mlo lines. Structural analysis identified this compound as a novel phenolic conjugate, p-coumaroyl-hydroxyagmatine (p-CHA). p-CHA but not the nonhydroxylated derivative p-coumaroylagmatine exhibited antifungal activity both in vitro and in vivo. The accumulation of p-CHA in epidermal tissue correlated tightly with fungal penetration attempts of attacked host cells. Furthermore, upon penetration, epidermal cell wall-bound phenolics became resistant to saponification at sites of attempted fungal ingress (papilla), indicating a change in, or the addition of, different chemical bonding types. The switch in saponification sensitivity occurred at least 2 h earlier in the mlo-incompatible than in the Mlo-compatible interaction. Our results suggest that p-CHA and the speed of papillae compaction play important roles in non-race-specific powdery mildew defense.
von Röpenack
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Sainsbury Laboratory, John Innes Centre, Colney Lane, NR4 7UH Norwich, United Kingdom.
Parr
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Schulze-Lefert
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D000483:Alleles; D000890:Anti-Infective Agents / Q000032:analysis* / Q000737:chemistry / Q000494:pharmacology; D001203:Ascomycota / Q000187:drug effects / Q000472:pathogenicity*; D002473:Cell Wall / Q000737:chemistry; D002480:Cellulase; D002851:Chromatography, High Pressure Liquid; D003600:Cytosol / Q000737:chemistry; D001467:Hordeum / Q000737:chemistry / Q000235:genetics* / Q000382:microbiology*; D007113:Immunity, Innate; D008826:Microbial Sensitivity Tests; D015394:Molecular Structure; D010636:Phenols / Q000032:analysis* / Q000737:chemistry / Q000494:pharmacology*; D018515:Plant Leaves; D018629:Spectrometry, Mass, Secondary Ion
D000890:Anti-Infective Agents; D010636:Phenols; D002480:Cellulase