Staphylococcus aureus pathogenicity on Arabidopsis thaliana is mediated either by a direct effect of salicylic acid on the pathogen or by SA‐dependent, NPR1‐independent host responses

Abstract

SummaryStaphylococcus aureus is a ubiquitous gram-positive bacterium that can cause superficial to serious systemic infections in animals and humans. Here we report the development of a plant infection model to study the pathogenesis of this bacterium. Three global regulatory mutants, RN6911 (agr) and an alpha-toxin mutant defective in biofilm formation (DU1090) which are attenuated in animal pathogenesis, were also attenuated in their ability to infect plants, suggesting that these regulators that mediate synthesis of virulence factors essential for animal pathogenesis are also required for plant pathogenesis. Further, using Arabidopsis plants altered in defense responses such as the transgenic lines NahG [defective in salicylic acid (SA) accumulation], and 35S-LOX2()) (defective in jasmonic acid production and hyper-accumulator of SA), and mutants ics1 (depleted in SA accumulation), and npr1-1 (non-expressor of pathogenesis-related protein) we show that resistance of Arabidopsis to typical plant pathogens and the animal pathogen S. aureus is conserved and is mediated by SA. The data presented here suggest that Arabidopsis thaliana resistance to S. aureus is mediated either by a direct effect of SA on the pathogen, specifically one that affects the attachment/aggregate formation on the root surface and reduces the pathogen's virulence, or by SA-dependent, NPR1-independent host responses.

The plant signal salicylic acid shuts down expression of the vir regulon and activates quormone-quenching genes in Agrobacterium

“…Such a combinatorial line of defense has also been implicated in Arabidopsis resistance to Staphylococcus aureus infection (26). The dramatic restoration of Agrobacterium virulence by a constitutively active VirA makes it highly unlikely that the level of SA produced by even the most resistant mutant is blocking tumorigenesis merely by affecting bacterial viability.…”

“…SA-induced PR gene expression and systemic acquired resistance occur primarily through a signaling pathway involving the transcriptional activator NPR1. Mutant npr1-1 plants are defective in this signaling and exhibit decreased PR gene expression (25), although they accumulate at least WT SA levels in response to infection by various pathogens (26). We tested whether SA levels and NPR1-dependent activation of systemic acquired resistance affected the ability of WT Agrobacterium (strains A208 and A348) to form tumors on root segments.…”

Differential interaction of Salmonella enterica serovars with lettuce cultivars and plant-microbe factors influencing the colonization efficiency

“…However, only few studies have investigated the physiological or molecular interaction between human pathogenic bacteria and plants (Plotnikova et al, 2000;Iniguez et al, 2005;Prithiviraj et al, 2005;Kutter et al, 2006;Klerks et al, 2007). Even fewer studies have been described concerning the conditions required for plant colonization by these pathogens (Toth et al, 2006, Brandl, 2006.…”

Bacteria-derived Peptidoglycans Constitute Pathogen-associated Molecular Patterns Triggering Innate Immunity in Arabidopsis

“…We thus inquired about the ability of plants to recognize and respond to PGN from the Gram-positive bacterium S. aureus, that is found as root-associated bacterium in the rhizosphere of many plants and was recently shown to be pathogenic on A. thaliana (27,42,43). A typical and well characterized plant response to pathogen infection or treatment with PAMPs is the induction of genes encoding pathogenesis-related (PR) proteins (44), such as PR-1.…”

“…Treatment with PGN from the phytopathogenic Gram-positive bacterium S. aureus (27) results in the activation of plant defense responses such as medium alkalinization, elevation of cytoplasmic calcium concentrations, NO production, the activation of MAPKs, the accumulation of camalexin and the induction of various defense-related genes. Interestingly, even though a comparison of the defense responses triggered by PGN and the structurally closely related glycan chitin showed a strong overlap, our results indicate that PGN and chitin engage different perception systems.…”