Dissecting Phosphite-Induced Priming in Arabidopsis Infected withHyaloperonospora arabidopsidis   

Abstract

Phosphite (Phi), a phloem-mobile oxyanion of phosphorous acid (H3PO3), 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.

Rhamnolipids Elicit Defense Responses and Induce Disease Resistance against Biotrophic, Hemibiotrophic, and Necrotrophic Pathogens That Require Different Signaling Pathways in Arabidopsis and Highlight a Central Role for Salicylic Acid

“…Moreover, no enhanced susceptibility to oomycete was observed in npr1-1 (Col-0 background; Bowling et al, 1997). SA-dependent and NPR1-independent resistance responses that limit growth of oomycetes seem to be conserved in RL-induced resistance but not in phosphite-induced protection, which is SA and NPR1 dependent (Massoud et al, 2012). Until now, there was no evidence that ET-dependent responses were normally active in limiting H. arabidopsidis (Glazebrook, 2005), but our data suggest that ET is involved in RLmediated resistance to the oomycete.…”

“…Before our study, few data were available concerning elicitor-induced resistance against H. arabidopsidis. Only recently, Massoud et al (2012) presented evidence that phosphite could prime Arabidopsis defenses against this oomycete. SAdependent defenses are thought to play a role in limiting oomycete growth as demonstrated by experiments carried out in eds5 and sid2 plants (Nawrath and Métraux, 1999).…”

Plant Resistance Inducers against Pathogens in Solanaceae Species—From Molecular Mechanisms to Field Application

“…The importance of the SA pathway in phosphite-IR has been demonstrated in Arabidopsis [135]. In potato it has been reported that phosphite leads to excessive accumulation of hydrogen peroxide and PR1 transcripts [80], which is associated with SA signaling.…”

Impact of abiotic stresses on the protection efficacy of defence elicitors and on metabolic regulation in tomato leaves infected by Botrytis cinerea

“…and yeast ( ). Some of these were already characterized as plant defence elicitors in other plant/pathogen interactions, such as phosphite in / (Massoud et al 2012 ), and Eugenol in tomato/yellow leaf curl virus (Wang et al 2013 ). Despite a good efficacy of those PDE under laboratory conditions, transfer to field conditions is sometimes found inconclusive or too variable (Small et al 2012 ;Dinh et al 2007 ), most probably because, in the field, many external factors can influence the efficacy of elicitor treatments.…”