A pattern-triggered immunity-related phenolic, acetosyringone, boosts rapid inhibition of a diverse set of plant pathogenic bacteria

Abstract

Background Acetosyringone (3,5-dimethoxy-4-hydroxyacetophenone, AS) is a syringyl-type phenolic compound rarely found in plants in free form. It has been shown earlier to inhibit the growth of Pseudomonas bacteria in the presence of hydrogen peroxide and peroxidase (AS mix). Results We detected elevated levels of free AS in Nicotiana tabacum and N. benthamiana plants after inducing pattern-triggered immunity (PTI) by injecting bacterial elicitor flg22, or pathogenicity-mutant Pseudomonas syringae pv. syringae 61 hrcC- bacteria; but not after inoculations with compatible or incompatible pathogens at the time of PTI onset. In this study, we demonstrate that the antibacterial effect of the AS mix is general, as growth of several Gram-negative and -positive phytopathogenic bacteria was characteristically inhibited. The inhibition of bacterial metabolism by the AS mix was rapid, shown by the immediate drop of luminescence intensity of P. syringae pv. tomato DC3000 lx strain after addition of AS mix. The mechanism of the bacteriostatic effect was investigated using fluorescent reporter dye assays. SYTOX Green experiments supported others’ previous findings that the AS mix does not result in membrane permeabilization. Moreover, we observed that the mode of action could be depolarization of the bacterial cell membrane, as shown by assays carried out with the voltage sensitive dye DIBAC4(3). Conclusions Level of free acetosyringone is elevated during plant PTI responses in tobacco leaves (N. tabacum and N. benthamiana). When combined with hydrogen peroxide and peroxidase (AS mix), components of the mix act synergistically to inhibit bacterial metabolism and proliferation rapidly in a wide range of plant pathogens. This effect is related to depolarization rather than to permeabilization of the bacterial cell membrane. Similar AS mixture to the in vivo model might form locally at sites of invading bacterial attachment to the plant cells and the presence of acetosyringone might have an important role in the inhibition of bacterial proliferation during PTI.

Improved Canker Processing and Viability Droplet Digital PCR Allow Detection of Erwinia amylovora Viable Nonculturable Cells in Apple Bark

“…In this regard, Mock et al demonstrated that the oxidation of acetosyringone in the presence of hydrogen peroxide and peroxidase induces the VBNC state in Pseudomonas syringae pathovars [ 62 ]. Acetosyringone is a pattern-triggered immunity-related phenolic compound present in the apoplast of tobacco and other plant species [ 63 ], the oxidation of which also leads to growth inhibition in Agrobacterium tumefaciens , Clavibacter michiganensis subsp. Michiganensis, Pectobacterium carotovorum subsp.…”

“…Carotovorum, and Xanthomonas campestris pv. campestris [ 63 ]. E. amylovora triggers an oxidative burst during compatible interactions [ 64 , 65 ], so exposure to oxidized acetosyringone or other phenolic compounds in the bark might explain the results we observed in this work.…”

Multimodal Spectroscopic Studies to Evaluate the Effect of Nod-Factor-Based Fertilizer on the Maize (Zea mays) Stem

“…Their mechanism of action on non-legume plants was proposed by Liang et al 41 They showed that nod factors suppress the innate immune response of the plants by suppressing microbe-associated molecular pattern-triggered immunity. Since pattern-triggered immunity was shown to increase the concentration of phenolic acids, 42 the expected effect of the biofertilizer would be the decrease of total phenolic content. Indeed, we observed significantly decreased total phenolic content of plants that were seed coated with purified biofertilizer (which was expected), but also in plants that were foliar sprayed with a water fraction of the bacterial medium (which we did not expect).…”

Redox Active Plant Phenolic, Acetosyringone, for Electrogenetic Signaling

“…Oxidized acetosyringone imparts oxidative stress on E. coli Perhaps oxidized AS inhibits pathogen invasion of plants by increasing toxicity towards microbes [41]. While E. coli is not a typical plant pathogen, we performed a colony count assay after treating E. coli with PB, AS, and oxidized AS (Fig.…”