title: Dissecting phosphite-induced priming in Arabidopsis infected with Hyaloperonospora arabidopsidis.
abstract: Phosphite (Phi), a phloem-mobile oxyanion of phosphorous acid (H(3)PO(3)), protects plants against diseases caused by oomycetes. Its mode of action is unclear, as evidence indicates both direct antibiotic effects on pathogens as well as inhibition through enhanced plant defense responses, and its target(s) in the plants is unknown. Here, we demonstrate that the biotrophic oomycete Hyaloperonospora arabidopsidis (Hpa) exhibits an unusual biphasic dose-dependent response to Phi after inoculation of Arabidopsis (Arabidopsis thaliana), with characteristics of indirect activity at low doses (10 mm or less) and direct inhibition at high doses (50 mm or greater). The effect of low doses of Phi on Hpa infection was nullified in salicylic acid (SA)-defective plants (sid2-1, NahG) and in a mutant impaired in SA signaling (npr1-1). Compromised jasmonate (jar1-1) and ethylene (ein2-1) signaling or abscisic acid (aba1-5) biosynthesis, reactive oxygen generation (atrbohD), or accumulation of the phytoalexins camalexin (pad3-1) and scopoletin (f6'h1-1) did not affect Phi activity. Low doses of Phi primed the accumulation of SA and Pathogenesis-Related protein1 transcripts and mobilized two essential components of basal resistance, Enhanced Disease Susceptibility1 and Phytoalexin Deficient4, following pathogen challenge. Compared with inoculated, Phi-untreated plants, the gene expression, accumulation, and phosphorylation of the mitogen-activated protein kinase MPK4, a negative regulator of SA-dependent defenses, were reduced in plants treated with low doses of Phi. We propose that Phi negatively regulates MPK4, thus priming SA-dependent defense responses following Hpa infection.
authors.affiliation: Institut de Biologie des Plantes, CNRS-Université Paris-Sud 11, UMR 8618, 91405 Orsay cedex, France.
authors.forename: Kamal
authors.initials: K
authors.lastname: Massoud
authors.forename: Thierry
authors.initials: T
authors.lastname: Barchietto
authors.forename: Thomas
authors.initials: T
authors.lastname: Le Rudulier
authors.forename: Laurane
authors.initials: L
authors.lastname: Pallandre
authors.forename: Laure
authors.initials: L
authors.lastname: Didierlaurent
authors.forename: Marie
authors.initials: M
authors.lastname: Garmier
authors.forename: Françoise
authors.initials: F
authors.lastname: Ambard-Bretteville
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Seng
authors.forename: Patrick
authors.initials: P
authors.lastname: Saindrenan
mesh_terms: D000040:Abscisic Acid / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism / Q000382:microbiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D003517:Cyclopentanes / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D060467:Disease Resistance; D004305:Dose-Response Relationship, Drug; D005030:Ethylenes / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D007211:Indoles / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism; D009868:Oomycetes / Q000187:drug effects / Q000472:pathogenicity*; D054883:Oxylipins / Q000378:metabolism; D017905:Phosphites / Q000494:pharmacology*; D010766:Phosphorylation; D010935:Plant Diseases / Q000382:microbiology*; D057865:Plant Immunity; D020156:Salicylic Acid / Q000378:metabolism; D012603:Scopoletin / Q000378:metabolism; D015398:Signal Transduction; D013844:Thiazoles / Q000378:metabolism; D000094162:Phytoalexins
chemical_list: D000040:Abscisic Acid; D029681:Arabidopsis Proteins; D003517:Cyclopentanes; D004268:DNA-Binding Proteins; D005030:Ethylenes; D007211:Indoles; D020928:Mitogen-Activated Protein Kinases; D054883:Oxylipins; D017905:Phosphites; D020156:Salicylic Acid; D012603:Scopoletin; D013844:Thiazoles; C118837:EDS1 protein, Arabidopsis; C102405:camalexin; D000094162:Phytoalexins; C011006:jasmonic acid; C036216:ethylene; C436292:AtMPK4 protein, Arabidopsis