PsrA, the Pseudomonas sigma regulator, controls regulators of epiphytic fitness, quorum-sensing signals, and plant interactions in Pseudomonas syringae pv. tomato strain DC3000.
Pseudomonas syringae pv. tomato strain DC3000, a pathogen of tomato and Arabidopsis, occurs as an epiphyte. It produces N-acyl homoserine lactones (AHLs) which apparently function as quorum-sensing signals. A Tn5 insertion mutant of DC3000, designated PsrA(-) (Psr is for Pseudomonas sigma regulator), overexpresses psyR (a LuxR-type regulator of psyI) and psyI (the gene for AHL synthase), and it produces a ca. 8-fold-higher level of AHL than does DC3000. The mutant is impaired in its ability to elicit the hypersensitive reaction and is attenuated in its virulence in tomato. These phenotypes correlate with reduced expression of hrpL, the gene for an alternate sigma factor, as well as several hrp and hop genes during early stages of incubation in a Hrp-inducing medium. PsrA also positively controls rpoS, the gene for an alternate sigma factor known to control various stress responses. By contrast, PsrA negatively regulates rsmA1, an RNA-binding protein gene known to function as negative regulator, and aefR, a tetR-like gene known to control AHL production and epiphytic fitness in P. syringae pv. syringae. Gel mobility shift assays and other lines of evidence demonstrate a direct interaction of PsrA protein with rpoS promoter DNA and aefR operator DNA. In addition, PsrA negatively autoregulates and binds the psrA operator. In an AefR(-) mutant, the expression of psyR and psyI and AHL production are lower than those in DC3000, the AefR(+) parent. In an RpoS(-) mutant, on the other hand, the levels of AHL and transcripts of psyR and psyI are much higher than those in the RpoS(+) parent, DC3000. We present evidence, albeit indirect, that the RpoS effect occurs via psyR. Thus, AefR positively regulates AHL production, whereas RpoS has a strong negative effect. We show that AefR and RpoS do not regulate PsrA and that the PsrA effect on AHL production is exerted via its cumulative, but independent, effects on both AefR and RpoS.
Chatterjee
Asita
A
Division of Plant Sciences, University of Missouri-Columbia, Columbia, MO 65211, USA. chatterjeeas@missouri.edu
Cui
Yaya
Y
Hasegawa
Hiroaki
H
Chatterjee
Arun K
AK
D015107:4-Butyrolactone / Q000031:analogs & derivatives / Q000096:biosynthesis; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D024202:Electrophoretic Mobility Shift Assay; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics / Q000502:physiology*; D008025:Ligases / Q000096:biosynthesis; D018551:Solanum lycopersicum / Q000382:microbiology*; D016254:Mutagenesis, Insertional; D009875:Operator Regions, Genetic; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D044224:Pseudomonas syringae / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology*; D053038:Quorum Sensing / Q000502:physiology*; D016601:RNA-Binding Proteins / Q000096:biosynthesis; D012808:Sigma Factor / Q000096:biosynthesis; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D014774:Virulence / Q000235:genetics
D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; C085855:HrpL protein, Pseudomonas syringae; C430183:PsrA protein, Pseudomonas; D016601:RNA-Binding Proteins; D012808:Sigma Factor; D014157:Transcription Factors; C069567:sigma factor KatF protein, Bacteria; C088386:homoserine lactone; D008025:Ligases; C449816:N-acylhomoserine lactone synthase; D015107:4-Butyrolactone