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J. Bacteriol., 11 1995, 6160-6169, Vol 177, No. 21
M Ullrich, A Penaloza-Vazquez, AM Bailey and CL Bender
Biosynthesis of the phytotoxin coronatine (COR) in Pseudomonas syringae pv.
glycinea PG4180 is regulated by temperature at the transcriptional level. A
3.4-kb DNA fragment from the COR biosynthetic gene cluster restored
temperature-regulated phytotoxin production to Tn5 mutants defective in COR
production. Nucleotide sequence analysis of this fragment revealed three
genes, corS, corP, and corR, which encode a modified two-component
regulatory system consisting of one sensor protein, CorS, and two response
regulator proteins, CorP and CorR. Although only one response regulator,
CorR, had a DNA-binding domain, the phosphate-receiving domains of both
response regulator proteins were highly conserved. Transcriptional fusions
of the corP and corR promoters to a promoterless glucuronidase gene (uidA)
indicated that these two genes are expressed constitutively at 18 and 28
degrees C. In contrast, a corS::uidA fusion exhibited the temperature
dependence previously observed for COR biosynthetic promoters and exhibited
maximal transcriptional activity at 18 degrees C and low activity at 28
degrees C. Furthermore, glucuronidase activity for corS::uidA was decreased
in corP, corR, and corS mutants relative to the levels observed for
PG4180(corS::uidA). This difference was not observed for corP::uidA and
corR::uidA transcriptional fusions since expression of these fusions
remained low and constitutive regardless of the genetic background. The
three regulatory genes functioned in a P. syringae strain lacking the COR
gene cluster to achieve temperature-dependent activation of an introduced
COR biosynthetic promoter, indicating that this triad of genes is the
primary control for COR biosynthesis and responsible for
thermoregulation.(ABSTRACT TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
A modified two-component regulatory system is involved in temperature- dependent biosynthesis of the Pseudomonas syringae phytotoxin coronatine
Department of Plant Pathology, Oklahoma State University, Stillwater 74078-3032, USA.
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