Plant-Bacterial Communication

We are working to understand how chemical signaling in the root microbiome contributes to the biology of the Eastern Cottonwood tree, Populus deltoides. We are also interested in the fundamental question of how bacteria sense plant-released chemicals. Poplar is a promising biofuel plant because it grows very fast and can thrive in marginal soils. Working in collaboration with E. Peter Greenberg and scientists at Oak Ridge National Laboratory, we have recently identified an effector of one member of a plant-responsive PipR-family of transcription factors present in many plant pathogens and symbionts. This compound (abbreviated HEHEAA) requires a specific transporter for import into bacterial cells. We solved crystal structures of one component of the transporter bound and unbound by HEHEAA. This led to the discovery that a close homolog of the transporter protein cannot bind HEHEAA, implying there are other effector compound(s) for the widespread PipR signaling system family. Understanding the molecular details for these plant-responsive systems could identify a means of controlling plant colonization.

In other work, we found that acyl-homoserine lactone (AHL)-type quorum sensing (QS) genes are prevalent in the genomes of Proteobacteria isolated from Poplar roots. Quorum sensing is a cell-to-cell signaling system, which allows bacteria to control transcription in a cell density-dependent manner. We are engaged in identifying new AHL-type QS signals and in looking at the microbial functions that they regulate.