A bacterial chemoreceptor that mediates chemotaxis to two different plant hormones

Abstract

Summary Indole‐3‐acetic acid (IAA) is the main naturally occurring auxin and is produced by organisms of all kingdoms of life. In addition to the regulation of plant growth and development, IAA plays an important role in the interaction between plants and growth‐promoting and phytopathogenic bacteria by regulating bacterial gene expression and physiology. We show here that an IAA metabolizing plant‐associated Pseudomonas putida isolate exhibits chemotaxis to IAA that is independent of auxin metabolism. We found that IAA chemotaxis is based on the activity of the PcpI chemoreceptor and heterologous expression of pcpI conferred IAA taxis to different environmental and human pathogenic isolates of the Pseudomonas genus. Using ligand screening, microcalorimetry and quantitative chemotaxis assays, we found that PcpI failed to bind IAA directly, but recognized and mediated chemoattractions to various aromatic compounds, including the phytohormone salicylic acid. The expression of pcpI and its role in the interactions with plants was also investigated. PcpI extends the range of central signal molecules recognized by chemoreceptors. To our knowledge, this is the first report on a bacterial receptor that responds to two different phytohormones. Our study reinforces the multifunctional role of IAA and salicylic acid as intra‐ and inter‐kingdom signal molecules.

The pH Robustness of Bacterial Sensing

“…The E. coli maltose-binding protein (MBP) is a primary model to study SBPs ( 48 , 49 ). We have used E. coli MBP and E6B08_RS28125, an amino acid-sensing SBP of P. putida ( 50 ), as models to study the pH robustness of ligand recognition in solute-binding proteins. Like the periplasmic LBDs, MBP and E6B08_RS28125 show extraordinary pH robustness and recognized their ligands, D-maltose and l -ornithine, respectively, over ranges of 8.5 and 8.0 pH units, respectively ( Fig.…”

Pseudomonas syringae pv. tomato infection of tomato plants is mediated by GABA and l‐Pro chemoperception

“…Complementation of the PsPto‐ pscC mutant with pscC provided in trans resulted in a chemotaxis phenotype that was superior in its magnitude to the WT strain (Figure S3). Expression in trans from multicopy plasmids enhances cellular chemoreceptor levels and previous studies following a similar approach have also reported an increase in the magnitude of the chemotactic response (Fernández et al, 2016; Hida et al, 2020; Rico‐Jiménez et al, 2022).…”

Auxin production in the green alga Chlamydomonas involves an extracellular L-amino acid oxidase and supports algal-bacterial mutualism with methylobacteria

“…IAA can be metabolized by rhizospheric bacteria (Donoso et al, 2017; Ebenau-Jehle et al, 2012; Lin et al, 2012; Scott et al, 2013), some of which like Pseudomonas putida show chemotaxis towards the auxin (Rico-Jiménez et al, 2022; Scott et al, 2013). Thus, IAA production by Chlamydomonas may attract and feed bacteria that could potentially be beneficially self-serving.…”