GacS sensor domains pertinent to the regulation of exoproduct formation and to the biocontrol potential of Pseudomonas fluorescens CHA0.
In the root-colonizing biocontrol strain CHA0 of Pseudomonas fluorescens, cell density-dependent synthesis of extracellular, plant-beneficial secondary metabolites and enzymes is positively regulated by the GacS/GacA two-component system. Mutational analysis of the GacS sensor kinase using improved single-copy vectors showed that inactivation of each of the three conserved phosphate acceptor sites caused an exoproduct null phenotype (GacS-), whereas deletion of the periplasmic loop domain had no significant effect on the expression of exoproduct genes. Strain CHA0 is known to synthesize a solvent-extractable extracellular signal that advances and enhances the expression of exoproduct genes during the transition from exponential to stationary growth phase when maximal exoproduct formation occurs. Mutational inactivation of either GacS or its cognate response regulator GacA abolished the strain's response to added signal. Deletion of the linker domain of the GacS sensor kinase caused signal-independent, strongly elevated expression of exoproduct genes at low cell densities. In contrast to the wild-type strain CHA0, the gacS linker mutant and a gacS null mutant were unable to protect tomato plants from crown and root rot caused by Fusarium oxysporum f. sp. radicis-lycopersici in a soil-less microcosm, indicating that, at least in this plant-pathogen system, there is no advantage in using a signal-independent biocontrol strain.
Zuber
Sophie
S
Laboratoire de Biologie Microbienne, Université de Lausanne, CH-1015 Lausanne, Switzerland.
Carruthers
Fiona
F
Keel
Christoph
C
Mattart
Alexandre
A
Blumer
Caroline
C
Pessi
Gabriella
G
Gigot-Bonnefoy
Cécile
C
Schnider-Keel
Ursula
U
Heeb
Stephan
S
Reimmann
Cornelia
C
Haas
Dieter
D
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017124:Conserved Sequence; D005670:Fusarium / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial; D018551:Solanum lycopersicum / Q000382:microbiology; D008969:Molecular Sequence Data; D009154:Mutation; D010572:Pest Control, Biological; D010935:Plant Diseases / Q000382:microbiology; D017434:Protein Structure, Tertiary; D011551:Pseudomonas fluorescens / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; C091100:GacA protein, Bacteria; D014157:Transcription Factors; C074165:lemA protein, bacterial