Gac two-component system in Pseudomonas syringae pv. tabaci is required for virulence but not for hypersensitive reaction

Abstract

Pseudomonas syringae pv. tabaci 6605 causes wildfire disease on host tobacco plants. To investigate the regulatory mechanism of the expression of virulence, Gac two-component system-defective mutants, !gacA and !gacS, and a double mutant, !gacA!gacS, were generated. These mutants produced smaller amounts of N-acyl homoserine lactones, required for quorum sensing, had lost swarming motility, and had reduced expression of virulence-related hrp genes and the algT gene required for exopolysaccharide production.The ability of the mutants to cause disease symptoms in their host tobacco plant was remarkably reduced, while they retained the ability to induce hypersensitive reaction (HR) in non-host plants. These results indicated that the Gac two-component system of P. syringae pv.tabaci 6605 is indispensable for virulence on the host plant, but not for HR induction in non-host plants.Marutani et al.,

Regulation of Bacterial Virulence by Csr (Rsm) Systems

“…As is the case for many other plant and animal pathogens, P. syringae secretes a variety of products, including quorum-sensing compounds, phytotoxins, antibiotics, exoproteases, fluorescent pigments, and alginate, which influence infection and disease processes (363). These secreted products as well as biofilm formation, host colonization, and lesion formation are all regulated by the GacS/GacA TCS (364)(365)(366)(367)(368)(369)(370)(371)(372)(373)(374)(375)(376)(377)(378)(379). Furthermore, genetic analyses of various P. syringae pathovars have identified homologs of the RsmA-inhibitory sRNAs RsmX, RsmY, and RsmZ of P. fluorescens, as well as RsmB of P. carotovorum (55).…”

Characterization of each aefR and mexT mutant in Pseudomonas syringae pv. tabaci 6605

“…The expression of ahlI (also called psyI), a gene encoding AHL synthase, is cell densitydependent, and is reduced in the DaefR and DgacA mutant strains (Quiñones et al 2004). The gacA encodes GacA, a response regulator of the Gac two-component system (Heeb and Haas 2001;Marutani et al 2008). However, the expression of aefR was not reduced in the DgacS and DgacA mutant strains (Quiñones et al 2004).…”

Functional analysis of the <italic>aefR</italic> mutation and identification of its binding site in <italic>Pseudomonas syringae</italic> pv. <italic>tabaci</italic> 11528

“…The AHL-mediated quorum-sensing system is regulated by the GacS/ GacA two-component system along with AefR in P. syringae [6,[10][11][12][13]25,26]. To determine the effect of aefR deficiency on AHL production, A. tumefaciens NT1 carrying a lacZ-traG-fused plasmid was used as a biosensor strain.…”

“…A LuxR-type transcriptional regulator, PsyR, is responsible for the response to AHL molecules [8,9]. The best-characterized regulator of AHL production is a GacS/GacA two-component system [10,11], whereas the TetR family transcription factor AefR is required for AHL production [6,12,13]. These two pathways function independently [6].…”