Co-option of bacterial quorum sensing for interkingdom signaling
B. GONCALVES COUTINHO (1), A. Schaefer (2), Y. Oda (2), D. Pelletier (3), V. Venturi (4), C. Harwood (2) (1) University of Washington, U.S.A.; (2) University of Washington, U.S.A.; (3) Oak Ridge National Laboratory, U.S.A.; (4) ICGEB, Italy

Some plant-associated bacteria sense their host by detecting an unknown plant signal recognized by a LuxR-subfamily of transcription factors. Genes coding for members of this subfamily are all linked to a gene coding for a putative proline iminopeptidase. This interkingdom signaling system is important for mutualists and pathogens. We describe a transcription factor we call PipR, in the Populus root endophyte Pseudomonas sp. GM79. The genes flanking pipR code for proteins annotated as peptidases and an ABC-type peptide transporter. Like its homologs, PipR activates one of its linked peptidase gene (pipA) in response to plant leaf macerates. GM79 peptidase mutants show increased PipR activation of pip. Plant-macerate induction of pip was lost in ABC-type transporter-defective mutants, suggesting that the plant signal is actively transported. The involvement of a putative peptide transporter in the PipR system suggested that the plant signal might be a peptide. In fact protein hydrolysates (peptone) and a specific tripeptide can serve in place of plant macerates to activate pip in a PipR-dependent manner. We also show that the periplasmic binding protein component of the ABC-type transporter can bind the plant and peptone signal(s) tightly and we are using it as a tool to purify and characterize the signal(s). Understanding these plant-responsive LuxR homologs and their plant signals is important as they occur in dozens of bacteria associated with economically important crops.

Abstract Number: C22-3, P8-230
Session Type: Concurrent