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Proc Natl Acad Sci U S A. 2018 Sep 25;115(39):9785-9790. doi: 10.1073/pnas.1809611115. Epub 2018 Sep 6.

A plant-responsive bacterial-signaling system senses an ethanolamine derivative.

Author information

1
Department of Microbiology, University of Washington, Seattle, WA 98195.
2
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115.
3
Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830.
4
Department of Microbiology, University of Washington, Seattle, WA 98195; epgreen@uw.edu.

Abstract

Certain plant-associated Proteobacteria sense their host environment by detecting an unknown plant signal recognized by a member of a LuxR subfamily of transcription factors. This interkingdom communication is important for both mutualistic and pathogenic interactions. The Populus root endophyte Pseudomonas sp. GM79 possesses such a regulator, named PipR. In a previous study we reported that PipR activates an adjacent gene (pipA) coding for a proline iminopeptidase in response to Populus leaf macerates and peptides and that this activation is dependent on a putative ABC-type transporter [Schaefer AL, et al. (2016) mBio 7:e01101-16]. In this study we identify a chemical derived from ethanolamine that induces PipR activity at picomolar concentrations, and we present evidence that this is the active inducer present in plant leaf macerates. First, a screen of more than 750 compounds indicated ethanolamine was a potent inducer for the PipR-sensing system; however, ethanolamine failed to bind to the periplasmic-binding protein (PBP) required for the signal response. This led us to discover that a specific ethanolamine derivative, N-(2-hydroxyethyl)-2-(2-hydroxyethylamino) acetamide (HEHEAA), binds to the PBP and serves as a potent PipR-dependent inducer. We also show that a compound, which coelutes with HEHEAA in HPLC and induces pipA gene expression in a PipR-dependent manner, can be found in Populus leaf macerates. This work sheds light on how plant-associated bacteria can sense their environment and on the nature of inducers for a family of plant-responsive LuxR-like transcription factors found in plant-associated bacteria.

KEYWORDS:

LuxR homolog; ethanolamine; plant–microbe interactions; quorum sensing; transcription activator

PMID:
30190434
PMCID:
PMC6166808
[Available on 2019-03-25]
DOI:
10.1073/pnas.1809611115
[Indexed for MEDLINE]

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