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J. Mol. Micro. Biotechnol. 4: 191-196
Control of Temperature-Responsive Synthesis of the Phytotoxin Coronatine in Pseudomonas syringae by the Unconventional Two-Component System CorRPS
Angela V. Smirnova, Ling Wang, Bettina Rohde, Ina Budde, Helge Weingart, and Matthias S. Ullrich
The phytopathogen Pseudomonas syringae produces the phytotoxin coronatine (COR) as a major virulence factor. COR and its precursor, coronafacic acid, function as molecular mimics of the plant signaling molecule jasmonate. A 32.8-kb plasmidborne gene cluster mediates COR biosynthesis, which is optimal at 18°C and non-detectable at 28°C, the optimal growth temperature for P. syringae. The thermoregulation is mediated at the transcriptional level by an unconventional two-component regulatory system consisting of a histidine protein kinase, CorS, and two transcriptional activators, CorR and CorP. Dissection of this regulatory triad revealed that CorR binds to its target sequences in a thermoresponsive manner and that its DNA-binding activity is controlled by CorS. A Preliminary model for thermo-sensing by CorS is proposed based on its membrane topology and the analysis of translational fusions of CorS to reporter enzymes at different temperatures. CorP lacks a typical helix-turn-helix motif but possibly functions as a modulator of CorR or CorS activity. The thermoregulation of COR biosynthetic genes is widespread among various COR-producing P. syringae strains. Post-translational processes also contribute to the thermo-responsiveness of COR production. Additionally, COR synthesis in P. syringae is influenced by nutrient availability, rpoN encoding the alternative sigma factor s54, and HrpV, a negative regulator of hrp gene expression, suggesting a complex regulatory network governing phytotoxin synthesis.-
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