A Volatile Signal Controls Virulence in the Plant Pathogen Pseudomonas syringae pv. syringae and a Strategy for Infection Control in Organic Farming

Abstract

<div><div><div><p>Pseudomonas syringae is an important pathogen of many agriculturally valuable crops. Among the various pathovars described P. syringae pv. syringae (Pss) has a particularly wide host range, infecting primarily woody and herbaceous host plants. The ability of Pss to cause bacterial apical necrosis of mango trees is dependent on the production of the antimetabolite toxin mangotoxin. The production of this toxin was shown to be regulated by a self-produced signaling molecule. In this study, we determined the structure of the Pss signal molecule belonging to the recently described family of diazeniumdiolate communication molecules. Employing a targeted mass spectrometry-based approach, we provide experimental evidence that the major signal produced by Pss is the volatile compound leudiazen, which controls mangotoxin production and virulence in a detached tomato leaflet infection model. Experimental results demonstrate that KMnO4 solution inactivates leudiazen and that treatment of infected leaves with KMnO<sub>4</sub> abolishes necrosis. This strategy represents the first example of chemically degrading a signaling molecule to interfere with bacterial communication. The application of KMnO4 solution, which is regulatorily approved in organic farming, may constitute an environmentally friendly strategy to control Pss infections.</p></div></div></div>

Regulation of Plant Mineral Nutrition by Signal Molecules

“…Based on the homology observed among ham operons, it was suggested that members of the genera Pseudomonas , Pandorea, and Burkholderia may use the diffusible signal molecule—valdiazen (valinol diazeniumdiolate), which autoregulates its own biosynthesis and also of fragin. Fragin is a metallophore and its metal chelating ability is responsible for its antifungal property [ 184 , 185 , 186 ].…”

The Pbo Cluster from Pseudomonas syringae pv. Phaseolicola NPS3121 Is Thermoregulated and Required for Phaseolotoxin Biosynthesis

“…A second more realistic possibility is that the Pbo cluster is participating in the regulation of phaseolotoxin biosynthesis, particularly considering the complexity of the regulatory circuitry involved. This putative regulatory activity could then be similar to the regulation of the antimetabolite toxin mangotoxin by the volatile compound leudiazen, which belongs to the family of diazeniumdiolate communication molecules [ 37 ]. The biosynthesis of leudiazen requires the mgoBCAD operon, which consists of four genes coding for two predicted oxygenases, an NRPS and a putative polyketide cyclase/dehydratase [ 38 ].…”

“…The biosynthesis of leudiazen requires the mgoBCAD operon, which consists of four genes coding for two predicted oxygenases, an NRPS and a putative polyketide cyclase/dehydratase [ 38 ]. Besides mangotoxin biosynthesis, leudiazen also impacts virulence and likely other phenotypic traits, and this is likely the reason why homologs of the mgo operon are present in diverse pseudomonads and other bacteria [ 37 , 39 ]. Thus, it is conceivable that the putative secondary metabolite produced by the Pbo cluster is also a signaling molecule regulating phaseolotoxin biosynthesis; likewise, its potential implication in regulating other phenotypes would also explain the presence of the Pbo island in bacteria that do not synthesize phaseolotoxin.…”