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Roles of the plant cell wall in powdery mildew disease resistance in Arabidopsis thaliana: PMR5 (POWDERY MILDEW RESISTANT 5) affects the acetylation of cell wall pectin

Abstract

The pmr5 (powdery mildew resistant 5) mutant was found in a screen for genes involved in susceptibility to Golovinomyces cichoracearum, a biotrophic pathogen that infects Arabidopsis. PMR5 is a member of the TBL (TRICHOME BIREFRINGENCE LIKE) family, which is composed of 46 functionally uncharacterized plant-specific proteins. Initial characterization of this mutant showed that pmr5-mediated disease resistance acts independently of the salicylic acid, jasmonic acid, and ethylene signal transduction pathways, and that there are changes in the pmr5 cell wall that may be linked to the gain of resistance in the mutant. Specifically, PMR5 may be affecting cell wall pectin by acetylation. Characterization of the pmr5 cell wall has revealed changes in pectin composition and a decrease in acetylation. This is corroborated by the ability of heterologously expressed PMR5 protein to bind to pectin, with decreased binding affinity to acetylated pectin. The cell wall and disease phenotypes of the pmr5 mutant may be revealing a potential role of PMR5 in the elusive plant cell wall integrity-signaling pathway. This work summarizes the continuing efforts in both determining the biochemical function of PMR5 and investigating the mechanism behind pmr5-mediated disease resistance.

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