Bacterial Biosensors for in Vivo Spatiotemporal Mapping of Root Secretion.

Francesco Pini,Jason J Terpolilli,J Allan Downie,Marcela Mendoza-Suárez,Jakub Tomek,Philip S Poole,Alison K East,Anne Edwards,Corinne Appia-Ayme,Ramakrishnan Karunakaran,Joshua Roworth

doi:10.1104/pp.16.01302

Francesco Pini, Jason J Terpolilli + Show 9 more

Open Access

https://doi.org/10.1104/pp.16.01302

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Journal: Plant physiology	Publication Date: May 11, 2017
Citations: 80	License type: CC BY 4.0

Affiliation: John Innes Centre, University of Oxford

Abstract

Plants engineer the rhizosphere to their advantage by secreting various nutrients and secondary metabolites. Coupling transcriptomic and metabolomic analyses of the pea (Pisum sativum) rhizosphere, a suite of bioreporters has been developed in Rhizobium leguminosarum bv viciae strain 3841, and these detect metabolites secreted by roots in space and time. Fourteen bacterial lux fusion bioreporters, specific for sugars, polyols, amino acids, organic acids, or flavonoids, have been validated in vitro and in vivo. Using different bacterial mutants (nodC and nifH), the process of colonization and symbiosis has been analyzed, revealing compounds important in the different steps of the rhizobium-legume association. Dicarboxylates and sucrose are the main carbon sources within the nodules; in ineffective (nifH) nodules, particularly low levels of sucrose were observed, suggesting that plant sanctions affect carbon supply to nodules. In contrast, high myo-inositol levels were observed prior to nodule formation and also in nifH senescent nodules. Amino acid biosensors showed different patterns: a γ-aminobutyrate biosensor was active only inside nodules, whereas the phenylalanine bioreporter showed a high signal also in the rhizosphere. The bioreporters were further validated in vetch (Vicia hirsuta), producing similar results. In addition, vetch exhibited a local increase of nod gene-inducing flavonoids at sites where nodules developed subsequently. These bioreporters will be particularly helpful in understanding the dynamics of root exudation and the role of different molecules secreted into the rhizosphere.

Highlights

Plants engineer the rhizosphere to their advantage by secreting various nutrients and secondary metabolites
The perception of environmental signals plays a pivotal role in the association between plants and bacteria (Pini et al, 2011), and R. leguminosarum bv viciae modifies its transcriptomic profile in different rhizospheres (Ramachandran et al, 2011)
Induction of the expression of genes encoding transporters in the presence of their transported solute led to the identification of the substrates of many ATP-binding cassette (ABC) and tripartite ATP-independent periplasmic transporter systems of Sinorhizobium meliloti (Mauchline et al, 2006)

Summary

Introduction

Plants engineer the rhizosphere to their advantage by secreting various nutrients and secondary metabolites. Vetch exhibited a local increase of nod gene-inducing flavonoids at sites where nodules developed subsequently These bioreporters will be helpful in understanding the dynamics of root exudation and the role of different molecules secreted into the rhizosphere. Improvement of the technologies available and an increased knowledge of the bacterial transcriptomic response to roots give us the chance to develop a suite of biosensors These biosensors have been constructed using Rhizobium leguminosarum bv viciae. Pea and hairy vetch (Vicia hirsuta) plants have been used, allowing us to monitor both the rhizosphere and the process of nodulation Applications of this methodology will be multiple and are not restricted to leguminous plants (e.g. screening plant mutant libraries for those altered in secretion from roots or observing different exudations during seed germination)

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