Bacterial Molecular Signals in the Sinorhizobium fredii-Soybean Symbiosis

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Abstract

Sinorhizobium ( Ensifer) fredii ( S. fredii) is a rhizobial species exhibiting a remarkably broad nodulation host-range. Thus, S. fredii is able to effectively nodulate dozens of different legumes, including plants forming determinate nodules, such as the important crops soybean and cowpea, and plants forming indeterminate nodules, such as Glycyrrhiza uralensis and pigeon-pea. This capacity of adaptation to different symbioses makes the study of the molecular signals produced by S. fredii strains of increasing interest since it allows the analysis of their symbiotic role in different types of nodule. In this review, we analyze in depth different S. fredii molecules that act as signals in symbiosis, including nodulation factors, different surface polysaccharides (exopolysaccharides, lipopolysaccharides, cyclic glucans, and K-antigen capsular polysaccharides), and effectors delivered to the interior of the host cells through a symbiotic type 3 secretion system.

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Most cited references 140

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Speak, friend, and enter: signalling systems that promote beneficial symbiotic associations in plants.

Giles E D Oldroyd (2013)

Plants associate with a wide range of microorganisms, with both detrimental and beneficial outcomes. Central to plant survival is the ability to recognize invading microorganisms and either limit their intrusion, in the case of pathogens, or promote the association, in the case of symbionts. To aid in this recognition process, elaborate communication and counter-communication systems have been established that determine the degree of ingress of the microorganism into the host plant. In this Review, I describe the common signalling processes used by plants during mutualistic interactions with microorganisms as diverse as arbuscular mycorrhizal fungi and rhizobial bacteria.

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The role of flavonoids in root-rhizosphere signalling: opportunities and challenges for improving plant-microbe interactions.

Samira Hassan, Ulrike Mathesius (2012)

The flavonoid pathway produces a diverse array of plant compounds with functions in UV protection, as antioxidants, pigments, auxin transport regulators, defence compounds against pathogens and during signalling in symbiosis. This review highlights some of the known function of flavonoids in the rhizosphere, in particular for the interaction of roots with microorganisms. Depending on their structure, flavonoids have been shown to stimulate or inhibit rhizobial nod gene expression, cause chemoattraction of rhizobia towards the root, inhibit root pathogens, stimulate mycorrhizal spore germination and hyphal branching, mediate allelopathic interactions between plants, affect quorum sensing, and chelate soil nutrients. Therefore, the manipulation of the flavonoid pathway to synthesize specifically certain products has been suggested as an avenue to improve root-rhizosphere interactions. Possible strategies to alter flavonoid exudation to the rhizosphere are discussed. Possible challenges in that endeavour include limited knowledge of the mechanisms that regulate flavonoid transport and exudation, unforeseen effects of altering parts of the flavonoid synthesis pathway on fluxes elsewhere in the pathway, spatial heterogeneity of flavonoid exudation along the root, as well as alteration of flavonoid products by microorganisms in the soil. In addition, the overlapping functions of many flavonoids as stimulators of functions in one organism and inhibitors of another suggests caution in attempts to manipulate flavonoid rhizosphere signals.

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Molecular basis of symbiotic promiscuity.

X Perret, C. Staehelin, W J Broughton (2000)

Eukaryotes often form symbioses with microorganisms. Among these, associations between plants and nitrogen-fixing bacteria are responsible for the nitrogen input into various ecological niches. Plants of many different families have evolved the capacity to develop root or stem nodules with diverse genera of soil bacteria. Of these, symbioses between legumes and rhizobia (Azorhizobium, Bradyrhizobium, Mesorhizobium, and Rhizobium) are the most important from an agricultural perspective. Nitrogen-fixing nodules arise when symbiotic rhizobia penetrate their hosts in a strictly controlled and coordinated manner. Molecular codes are exchanged between the symbionts in the rhizosphere to select compatible rhizobia from pathogens. Entry into the plant is restricted to bacteria that have the "keys" to a succession of legume "doors". Some symbionts intimately associate with many different partners (and are thus promiscuous), while others are more selective and have a narrow host range. For historical reasons, narrow host range has been more intensively investigated than promiscuity. In our view, this has given a false impression of specificity in legume-Rhizobium associations. Rather, we suggest that restricted host ranges are limited to specific niches and represent specialization of widespread and more ancestral promiscuous symbioses. Here we analyze the molecular mechanisms governing symbiotic promiscuity in rhizobia and show that it is controlled by a number of molecular keys.

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Author and article information

Contributors

Peter M. Gresshoff: Role: Academic Editor

Brett Ferguson: Role: Academic Editor

Journal

Journal ID (nlm-ta): Int J Mol Sci

Journal ID (iso-abbrev): Int J Mol Sci

Journal ID (publisher-id): ijms

Title: International Journal of Molecular Sciences

Publisher: MDPI

ISSN (Electronic): 1422-0067

Publication date (Electronic): 18 May 2016

Publication date Collection: May 2016

Volume: 17

Issue: 5

Electronic Location Identifier: 755

Affiliations

[1 ]Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla, Avenida de Reina Mercedes, 6, 41012 Sevilla, Spain; rsainz@ 123456us.es (J.E.R.-S.); jvinar@ 123456us.es (J.M.V.)

[2 ]Departamento de Química Orgánica, Facultad de Química, Universidad de Sevilla, Profesor García González, 1, 41012 Sevilla, Spain; rcarvaj@ 123456us.es

Author notes

[* ]Correspondence: jlopez@ 123456us.es ; Tel.: +34-954-554-330; Fax: +34-954-557-830

Article

Publisher ID: ijms-17-00755

DOI: 10.3390/ijms17050755

PMC ID: 4881576

PubMed ID: 27213334

SO-VID: ea57412e-15df-4963-b52c-d9ce84be64db

License:

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license ( http://creativecommons.org/licenses/by/4.0/).

Bacterial Molecular Signals in the Sinorhizobium fredii-Soybean Symbiosis

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Abstract

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Higher order chromatin architecture

Most cited references 140

Speak, friend, and enter: signalling systems that promote beneficial symbiotic associations in plants.

The role of flavonoids in root-rhizosphere signalling: opportunities and challenges for improving plant-microbe interactions.

Molecular basis of symbiotic promiscuity.

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