A Plant-Responsive Bacterial Signaling System Senses an Ethanolamine Derivative

The Science

To identify a more active PipR coinducer of pipA expression using Pseudomonas GM79 with ΔpipA ΔaapA mutations containing pPpipA-gfp.

The Impact

Advance the understanding of non–acyl-HSL–responsive LuxR homologs and how these transcription factors might be responding to their plant host environments.


  • Identified N-(2-hydroxyethyl)-2-(2-hydroxyethylamino) acetamide (HEHEAA) as the compound that binds to the ABC transporter and serves as a potent (pM) PipR-dependent inducer.
  • Bioassay-active material in Populus leaf macerates co-elutes with HEHEAA by HPLC fractionation, suggesting HEHEAA is present in plant macerates.
  • HEHEAA forms spontaneously from ethanolamine (EA), a component of plant phospholipids.
  • Identification of a GM79 PipR activator sets the stage for understanding interkingdom signaling and for identifying plant-derived signals for other PipR receptors, which are present in dozens of bacterial species associated with economically important plants.


Coutinho, B.G., E. Mevers, A. L. Schaefer, C. S. Harwood, J. Clardy, and E. P. Greenberg. 2018. “A Plant-Responsive Bacterial-Signaling System Senses an Ethanolamine Derivative,” Proceedings of the National Academy of Sciences USA 115(39), 9785–90. DOI:10.1073/pnas.1809611115.