Genetic evidence that the gacA gene encodes the cognate response regulator for the lemA sensor in Pseudomonas syringae

Abstract

Mutational analysis of the bean-pathogenic Pseudomonas syringae pv. syringae strain B728a has led to the genetic identification of the gacA gene as encoding the response regulator for the unlinked lemA sensor kinase. The analysis of a collection of spontaneous mutants of P. syringae pv. syringae suggested that the gacA gene was involved in lesion formation and the production of protease and syringomycin. The gacA gene originally was identified as a regulator of extracellular antibiotic production by Pseudomonas fluorescens, and the predicted GacA protein is a member of the FixJ family of bacterial response regulators. The sequence of the putative B728a GacA protein revealed 92% identity with the P. fluorescens GacA protein. An insertional mutation within the P. syringae pv. syringae gacA gene abrogated lesion formation on beans, production of extracellular protease, and production of the toxin syringomycin, the same phenotypes affected by a lemA mutation. DNA sequence analysis identified the P. syringae pv. syringae uvrC gene immediately downstream of the gacA gene, an arrangement conserved in P. fluorescens and Escherichia coli. The gacA insertional mutant was sensitive to UV, presumably because of polarity on transcription of the downstream uvrC gene. Southwestern (DNA-protein) analysis revealed that the lemA and gacA genes were required for the full expression of a DNA binding activity.

The global activator GacA of Pseudomonas aeruginosa PAO positively controls the production of the autoinducer N‐butyryl‐homoserine lactone and the formation of the virulence factors pyocyanin, cyanide, and lipase

“…2). Furthermore, the GacA proteins of P. syringae (Rich et al, 1994) and P. viridiflava (Liao et al, 1996) showed 99% identity with each other and 89% identity with GacA of P. aeruginosa (Fig. 2).…”

“…GacA is part of a two-component system and belongs to the FixJ family of response regulators (Laville et al, 1992). The cognate sensor appears to be the transmembrane protein LemA (Hrabak and Willis, 1992;Rich et al, 1994). Both the gacA and lemA genes are highly conserved in fluorescent pseudomonads (Liao et al, 1994;Corbell and Loper, 1995;Grewal et al, 1995).…”

“…In strains of P. fluorescens (Laville et al, 1992;Gaffney et al, 1994;Sacherer et al, 1994), Pseudomonas syringae (Rich et al, 1994) and Pseudomonas viridiflava (Liao et al, 1994(Liao et al, , 1996, the global regulator GacA is strictly required for the production of antibiotics, toxins, and several lytic exoenzymes. GacA is part of a two-component system and belongs to the FixJ family of response regulators (Laville et al, 1992).…”

The global regulator GacA of Pseudomonas fluorescens CHA0 is required for suppression of root diseases in dicotyledons but not in Gramineae

“…The response-regulator GacA and the corresponding sensor LemA are components of a highly conserved signal pathway within the genus Pseudomonas (Gaffney et al, 1994;Rich et al, 1994;Corbell & Loper, 1995;Haas & Carruthers, 1996, Université de Lausanne, Switzerland, personal communication). GacA is a response regulator in the Fix-DegU family of two-component regulatory systems Gaffney et al, 1994) and a conserved regulator of virulence factors in Pseudomonas aeruginosa (Rahme et al, 1995).…”

Three small RNAs jointly ensure secondary metabolism and biocontrol in Pseudomonas fluorescens CHA0

“…Among the factors that influence the expression of these small RNAs, the DNA-binding protein GacA stands out as a major activator (19,20). The response regulator GacA is activated by phosphorylation from the cognate membrane-bond sensor GacS (21)(22)(23)(24).…”