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A LuxR homolog in a cottonwood tree endophyte that activates gene expression in response to a plant signal or specific peptides

Journal Article · · mBio (Online)
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  1. Univ. of Washington, Seattle, WA (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. International Centre for Genetic Engineering and Biotechnology, Trieste (Italy)
+ Show Author Affiliations
Homologs of the LuxR acyl-homoserine lactone (AHL) quorum-sensing signal receptor are prevalent in Proteobacteria isolated from roots of the Eastern cottonwood tree, Populus deltoides. Many of these isolates possess an orphan LuxR homolog, closely related to OryR from the rice pathogen Xanthomonas oryzae. OryR does not respond to AHL signals but, instead, responds to an unknown plant compound. We discovered an OryR homolog, PipR, in the cottonwood endophyte Pseudomonas sp. strain GM79. The genes adjacent to pipR encode a predicted ATP-binding cassette (ABC) peptide transporter and peptidases. We purified the putative peptidases, PipA and AapA, and confirmed their predicted activities. A transcriptional pipA-gfp reporter was responsive to PipR in the presence of plant leaf macerates, but it was not influenced by AHLs, similar to findings with OryR. We found that PipR also responded to protein hydrolysates to activate pipA-gfp expression. Among many peptides tested, the tripeptide Ser-His-Ser showed inducer activity but at relatively high concentrations. An ABC peptide transporter mutant failed to respond to leaf macerates, peptone, or Ser-His-Ser, while peptidase mutants expressed higher-than-wild-type levels of pipA-gfp in response to any of these signals. Our studies are consistent with a model where active transport of a peptidelike signal is required for the signal to interact with PipR, which then activates peptidase gene expression. As a result, the identification of a peptide ligand for PipR sets the stage to identify plant-derived signals for the OryR family of orphan LuxR proteins.
Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE Office of Science (SC)
Grant/Contract Number:
AC05-00OR22725
OSTI ID:
1324202
Journal Information:
mBio (Online), Journal Name: mBio (Online) Journal Issue: 4 Vol. 7; ISSN 2150-7511
Publisher:
American Society for MicrobiologyCopyright Statement
Country of Publication:
United States
Language:
English

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Beneficial Effects of Bacterial Endophytes on Forest Tree Species book January 2017
Evolution of LuxR solos in bacterial communication: receptors and signals journal November 2019
Progress in and promise of bacterial quorum sensing research journal November 2017
A plant-responsive bacterial-signaling system senses an ethanolamine derivative journal September 2018
A novel LuxR‐type solo of Sinorhizobium meliloti , NurR, is regulated by the chromosome replication coordinator, DnaA and activates quorum sensing journal June 2019
Virulence Factor Identification in the Banana Pathogen Dickeya zeae MS2 journal September 2019
Exploration of the Biosynthetic Potential of the Populus Microbiome journal October 2018
luxR Homolog-Linked Biosynthetic Gene Clusters in Proteobacteria journal March 2018
Comparative Transcriptomics of Bacillus mycoides Strains in Response to Potato-Root Exudates Reveals Different Genetic Adaptation of Endophytic and Soil Isolates journal August 2017

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