Karrikins from plant smoke modulate bacterial quorum sensing

KARRIKIN INSENSITIVE2 regulates leaf development, root system architecture and arbuscular-mycorrhizal symbiosis in Brachypodium distachyon

KARRIKIN INSENSITIVE2 (KAI2) is an α/β-hydrolase required for plant responses to karrikins, which are abiotic butenolides that can influence seed germination and seedling growth. Although represented by four angiosperm species, loss-of-function kai2 mutants are phenotypically inconsistent and incompletely characterised, resulting in uncertainties about the core functions of KAI2 in plant development. Here we characterised the developmental functions of KAI2 in the grass Brachypodium distachyon using molecular, physiological and biochemical approaches. Bdkai2 mutants exhibit increased internode elongation and reduced leaf chlorophyll levels, but only a modest increase in water loss from detached leaves. Bdkai2 shows increased numbers of lateral roots and reduced root hair growth, and fails to support normal root colonisation by arbuscular-mycorrhizal (AM) fungi. The karrikins KAR₁ and KAR₂ , and the strigolactone (SL) analogue rac-GR24, each elicit overlapping but distinct changes to the shoot transcriptome via BdKAI2. Finally, we show that BdKAI2 exhibits a clear ligand preference for desmethyl butenolides and weak responses to methyl-substituted SL analogues such as GR24. Our findings suggest that KAI2 has multiple roles in shoot development, root system development and transcriptional regulation in grasses. Although KAI2-dependent AM symbiosis is likely conserved within monocots, the magnitude of the effect of KAI2 on water relations may vary across angiosperms.

1-(4-Amino-2-hydroxyphenyl)ethanone from Phomopsis liquidambari showed quorum sensing inhibitory activity against Pseudomonas aeruginosa

Phomopsis liquidambari S47 is an endophytic fungus isolated from the leaves of Punica granatum. Here, we are the first to report a quorum sensing (QS) inhibitor 1-(4-amino-2-hydroxyphenyl)ethanone (AHE) isolated and identified from the metabolites of P. liquidambari S47. Exposure to AHE at sub-MIC concentrations notably suppressed the secretion of acyl-homoserine lactones and virulence factors in Pseudomonas aeruginosa PAO1. To investigate the metabolic variations of P. aeruginosa PAO1 exposed to AHE, magnetic resonance imaging-based metabolomic analysis was performed. AHE treatment created a disturbance in the QS system by suppressing the expressions of QS-related genes. The disturbed QS system resulted in the inhibited activity of antioxidant enzymes and thus enhanced oxidative stress. The vegetable infection assay showed that the virulence of P. aeroginosa PAO1 was attenuated which could be due to the impacts to the amino acid and nucleotide metabolism by enhanced oxidative stress. These findings suggest that AHE has a potential to become an antivirulence "agent" to tackle P. aeruginosa infection. KEY POINTS: • AHE treatment inhibited AHL secretion and virulence factors production. • AHE treatment aggravated oxidative stress and disturbed metabolism. • AHE suppressed QS-related gene expressions and reduced virulence of P. aeruginosa.

Modulation of Bacterial Quorum Sensing by Strigolactones

Strigolactones are plant hormones with multiple roles that act as signaling molecules in many processes in the rhizosphere. In recent years, additional roles of strigolactones in nature have emerged, and here we report that strigolactones are able to modulate bacterial quorum sensing (QS) in the human pathogen Vibrio cholerae.

Inhibition of Quorum Sensing and Virulence in Serratia marcescens by Hordenine

Serratia marcescens NJ01 is a pathogenic bacterium isolated from diseased tomato leaves. Here, we report on the development of a tomato- S. marcescens host-pathogen system as a model to evaluate the effects of hordenine on quorum sensing (QS)-mediated pathogenicity under native conditions. Exposure to hordenine at 25, 50, and 100 μg/mL significantly inhibited the production of acyl-homoserine lactones and the formation of biofilms. Hordenine treatment notably enhanced the susceptibility of the preformed biofilms to ciprofloxacin by reducing the production of extracellular polysaccharides, destroying the architecture of biofilms, and changing the permeability of membranes, as evidenced by the scattered appearance and dominant red fluorescence in the combination-treated biofilms. Furthermore, the addition of hordenine affected the production of virulence factors, influenced the intracellular metabolites, and downregulated the expressions of QS- and biofilm-related genes. The plant infection model indicated that hordenine could significantly attenuate the pathogenicity of S. marcescens NJ01 in tomato plants. Thus, hordenine could act as a potential pesticide or pesticide accelerant in treating crop infections.

Discovery of cytochrome bc1 complex inhibitors inspired by the natural product karrikinolide

Novel and potent inhibitors targeting the cytochrome bc₁ complex were discovered from the natural product karrikinolide for the first time.

Silencing the mob: disrupting quorum sensing as a means to fight plant disease

Bacteria are able to sense their population's density through a cell-cell communication system, termed 'quorum sensing' (QS). This system regulates gene expression in response to cell density through the constant production and detection of signalling molecules. These molecules commonly act as auto-inducers through the up-regulation of their own synthesis. Many pathogenic bacteria, including those of plants, rely on this communication system for infection of their hosts. The finding that the countering of QS-disrupting mechanisms exists in many prokaryotic and eukaryotic organisms offers a promising novel method to fight disease. During the last decade, several approaches have been proposed to disrupt QS pathways of phytopathogens, and hence to reduce their virulence. Such studies have had varied success in vivo, but most lend promising support to the idea that QS manipulation could be a potentially effective method to reduce bacterial-mediated plant disease. This review discusses the various QS-disrupting mechanisms found in both bacteria and plants, as well as the different approaches applied artificially to interfere with QS pathways and thus protect plant health.

Pseudomonas aeruginosa activates the quorum sensing LuxR response regulator through secretion of 2-aminoacetophenone

Specific activation of the LuxR quorum-sensing response regulator by the volatile compound 2-aminoacetophenone, produced by the bacteriumPseudomonas aeruginosa.

Volatiles from nineteen recently genome sequenced actinomycetes

The volatiles from nineteen genome sequenced actinobacteria were analysed by GC/MS and the identified terpenes were correlated to genome data.