Linalool reduces the virulence of Pseudomonas syringae pv. tomato DC 3000 by modulating the PsyI/PsyR quorum-sensing system

Quorum sensing modulatory effect of linalool was tested for the first time against Pseudomonas syringae pv. tomato DC 3000, a bacterial plant pathogen responsible for causing huge losses worldwide. DC 3000 extensively regulates its virulence traits through quorum sensing mechanism involving expression of psyI, an acyl-homoserine lactone (AHL) synthase gene and psyR, a luxR-type regulator. In this study, exposure of DC 3000 to 80 ppm linalool concentration resulted in reduced biofilm formation, hampered motility, decreased AHL production, and reduced secretion of plant cell wall-degrading enzymes followed by negligible effect on the bacterial count and its metabolic activity. Extracellular polymeric substances (EPS), which play a crucial role in the development of biofilm and subsequent infection was significantly reduced which was further confirmed by Fourier Transform Infrared Spectroscopy. The qRT PCR analysis of the gene expression analysis of virulence genes (syringafactin production gene syfA, type III secretion system gene hrpA, flagellar genes fleQ and fliC, and coronatine production gene cfl unveiled significant downregulation of the same under Lin 80 ppm concentration. To further confirm the aforementioned possibilities, docking simulations run between PsyR and linalool suggested a strong interaction with the developed protein model. Overall, the treatment of DC 3000 with Lin 80 ppm affected the phenotypic and genotypic expressions associated with quorum sensing, thereby significantly reducing the infection rate as observed in in-vivo plant assay.