A plant-responsive bacterial-signaling system senses an ethanolamine derivative
Bruna G. Coutinho, Emily Mevers, Amy L. Schaefer, Dale A. Pelletier, Caroline S. Harwood, Jon Clardy, and E. Peter Greenberg
25 September 2018 PNAS 115(39):9785-9790; doi: 10.1073/pnas.1809611115
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 ABCtype 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 PipRdependent 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.
Coutinho, B. G., E. Mevers, A. L. Schaefer, D. A. Pelletier, C. S. Harwood, J. Clardy and E. P. Greenberg (2018). “A plant-responsive bacterial-signaling system senses an ethanolamine derivative.”