Dissecting Phosphite-Induced Priming in Arabidopsis Infected with Hyaloperonospora arabidopsidis

• Published in: Plant physiology (Bethesda) 2012-05, Vol.159 (1), p.286-298
• Main Authors: Massoud, Kamal, Barchietto, Thierry, Le Rudulier, Thomas, Pallandre, Laurane, Didierlaurent, Laure, Garmier, Marie, Ambard-Bretteville, Françoise, Seng, Jean-Marc, Saindrenan, Patrick
• Format: Article
• Language: English
• Subjects: Abscisic Acid - genetics; Abscisic Acid - metabolism; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis - microbiology; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Biological and medical sciences; Cyclopentanes - metabolism; Disease Resistance; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Dose-Response Relationship, Drug; Ethylenes - metabolism; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Plant; Indoles - metabolism; Infections; Inoculation; Mitogen-Activated Protein Kinases - genetics; Mitogen-Activated Protein Kinases - metabolism; Mode of action; Oomycetes; Oomycetes - drug effects; Oomycetes - pathogenicity; Oxylipins - metabolism; Pathogens; Phosphites - pharmacology; Phosphorylation; Phytopathology. Animal pests. Plant and forest protection; Plant cells; Plant Diseases - microbiology; Plant Immunity; Plant physiology and development; Plant spores; Plants; PLANTS INTERACTING WITH OTHER ORGANISMS; Salicylic Acid - metabolism; Scopoletin - metabolism; Signal Transduction; Spores; Thiazoles - metabolism
• ISSN: 0032-0889; 1532-2548; 1532-2548
• DOI: 10.1104/pp.112.194647

Phosphite (Phi), a phloem-mobile oxyanion of phosphorous acid (H₂PO₂), 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.