Extracellular Vesicle-Driven Crosstalk between Legume Plants and Rhizobia: The Peribacteroid Space of Symbiosomes as a Protein Trafficking Interface.

Prokaryotes and eukaryotes secrete extracellular vesicles (EVs) into the surrounding milieu to preserve and transport elevated concentrations of biomolecules across long distances. EVs encapsulate metabolites, DNA, RNA, and proteins, whose abundance and composition fluctuate depending on environmental cues. EVs are involved in eukaryote-to-prokaryote communication owing to their ability to navigate different ecological niches and exchange molecular cargo between the two domains.

Exopolysaccharide is detrimental for the symbiotic performance of Sinorhizobium fredii HH103 mutants with a truncated lipopolysaccharide core.

The nitrogen-fixing rhizobia-legume symbiosis relies on a complex interchange of molecular signals between the two partners during the whole interaction. On the bacterial side, different surface polysaccharides, such as lipopolysaccharide (LPS) and exopolysaccharide (EPS), might play important roles for the success of the interaction. In a previous work we studied two Sinorhizobium fredii HH103 mutants affected in the rkpK and lpsL genes, which are responsible for the production of glucuronic acid and galacturonic acid, respectively.

A complex regulatory network governs the expression of symbiotic genes in HH103.

Introduction: The establishment of the rhizobium-legume nitrogen-fixing symbiosis relies on the interchange of molecular signals between the two symbionts. We have previously studied by RNA-seq the effect of the symbiotic regulators NodD1, SyrM, and TtsI on the expression of the symbiotic genes (the regulon) of HH103 upon treatment with the isoflavone genistein. In this work we have further investigated this regulatory network by incorporating new RNA-seq data of HH103 mutants in two other regulatory genes, and .

DnaJ Is Required for Surface Motility, Stress Tolerance, and for Efficient Nodulation and Symbiotic Nitrogen Fixation.

Bacterial surface motility is a complex microbial trait that contributes to host colonization. However, the knowledge about regulatory mechanisms that control surface translocation in rhizobia and their role in the establishment of symbiosis with legumes is still limited. Recently, 2-tridecanone (2-TDC) was identified as an infochemical in bacteria that hampers microbial colonization of plants.

Non-Ionic Osmotic Stress Induces the Biosynthesis of Nodulation Factors and Affects Other Symbiotic Traits in HH103.

(1) Background: Some rhizobia, such as CIAT 899, activate nodulation genes when grown under osmotic stress. This work aims to determine whether this phenomenon also takes place in HH103. (2) Methods: HH103 was grown with and without 400 mM mannitol.

The Rhizobial Type 3 Secretion System: The Dr. Jekyll and Mr. Hyde in the Rhizobium-Legume Symbiosis.

Rhizobia are soil bacteria that can establish a symbiotic association with legumes. As a result, plant nodules are formed on the roots of the host plants where rhizobia differentiate to bacteroids capable of fixing atmospheric nitrogen into ammonia. This ammonia is transferred to the plant in exchange of a carbon source and an appropriate environment for bacterial survival.

Surface Motility Regulation of HH103 by Plant Flavonoids and the NodD1, TtsI, NolR, and MucR1 Symbiotic Bacterial Regulators.

Bacteria can spread on surfaces to colonize new environments and access more resources. Rhizobia, a group of α- and β-, establish nitrogen-fixing symbioses with legumes that rely on a complex signal interchange between the partners. Flavonoids exuded by plant roots and the bacterial transcriptional activator NodD control the transcription of different rhizobial genes (the so-called regulon) and, together with additional bacterial regulatory proteins (such as TtsI, MucR or NolR), influence the production of different rhizobial molecular signals.

The Gene of HH103 Restores Nodulation Capacity on Bean in a CIAT 899 / Mutant, but the Secondary Symbiotic Regulators , or Prevent HH103 to Nodulate with This Legume.

Rhizobial NodD proteins and appropriate flavonoids induce rhizobial nodulation gene expression. In this study, we show that the gene of HH103, but not the gene, can restore the nodulation capacity of a double / mutant of CIAT 899 in bean plants (). HH103 only induces pseudonodules in beans.

Rhizobial Exopolysaccharides: Genetic Regulation of Their Synthesis and Relevance in Symbiosis with Legumes.

Rhizobia are soil proteobacteria able to engage in a nitrogen-fixing symbiotic interaction with legumes that involves the rhizobial infection of roots and the bacterial invasion of new organs formed by the plant in response to the presence of appropriate bacterial partners. This interaction relies on a complex molecular dialogue between both symbionts. Bacterial -acetyl-glucosamine oligomers called Nod factors are indispensable in most cases for early steps of the symbiotic interaction.

The Sinorhizobium fredii HH103 type III secretion system effector NopC blocks nodulation with Lotus japonicus Gifu.

The broad-host-range bacterium Sinorhizobium fredii HH103 cannot nodulate the model legume Lotus japonicus Gifu. This bacterium possesses a type III secretion system (T3SS), a specialized secretion apparatus used to deliver effector proteins (T3Es) into the host cell cytosol to alter host signaling and/or suppress host defence responses to promote infection. However, some of these T3Es are recognized by specific plant receptors and hence trigger a strong defence response to block infection.

Structure of the unusual HH103 lipopolysaccharide and its role in symbiosis.

Rhizobia are soil bacteria that form important symbiotic associations with legumes, and rhizobial surface polysaccharides, such as K-antigen polysaccharide (KPS) and lipopolysaccharide (LPS), might be important for symbiosis. Previously, we obtained a mutant of HH103, , that does not produce KPS, a homopolysaccharide of a pseudaminic acid derivative, but whose LPS electrophoretic profile was indistinguishable from that of the WT strain. We also previously demonstrated that the HH103 operon is responsible for 5-acetamido-3,5,7,9-tetradeoxy-7-(3-hydroxybutyramido)-l--l--nonulosonic acid [Pse5NAc7(3OHBu)] production and is involved in HH103 KPS and LPS biosynthesis and that an HH103 mutant cannot produce KPS and displays an altered LPS structure.

Deciphering the Symbiotic Significance of Quorum Sensing Systems of HH103.

Quorum sensing (QS) is a bacterial cell-to-cell signaling mechanism that collectively regulates and synchronizes behaviors by means of small diffusible chemical molecules. In rhizobia, QS systems usually relies on the synthesis and detection of -acyl-homoserine lactones (AHLs). In the model bacterium functions regulated by the QS systems TraI-TraR and SinI-SinR(-ExpR) include plasmid transfer, production of surface polysaccharides, motility, growth rate and nodulation.

Regulation of Protein Secretion Systems Mediated by Cyclic Diguanylate in Plant-Interacting Bacteria.

The ubiquitous second messenger cyclic diguanylate (c-di-GMP) is involved in the regulation of different processes in bacteria. In phytopathogens, intracellular fluctuations in the concentration of this molecule contribute to the lifestyle switching from a motile and virulent stage to a sessile and biofilm-forming phase. Among the virulence mechanisms used by bacterial pathogens, different specific type secretion systems (TSSs) and the effector proteins that they translocate are included.

Transcriptomic Studies Reveal that the Serine/Threonine Protein Phosphatase PssZ has a Role in the Synthesis of Cell-Surface Components, Nutrient Utilization, and Other Cellular Processes.

bv. is a soil bacterium capable of establishing symbiotic associations with clover plants ( spp.).

Sinorhizobium fredii HH103 nolR and nodD2 mutants gain capacity for infection thread invasion of Lotus japonicus Gifu and Lotus burttii.

Sinorhizobium fredii HH103 Rif , a broad-host-range rhizobial strain, forms ineffective nodules with Lotus japonicus but induces nitrogen-fixing nodules in Lotus burttii roots that are infected by intercellular entry. Here we show that HH103 Rif nolR or nodD2 mutants gain the ability to induce infection thread formation and to form nitrogen-fixing nodules in L. japonicus Gifu.

HH103 RirA Is Required for Oxidative Stress Resistance and Efficient Symbiosis with Soybean.

Members of contain a homologue of the iron-responsive regulatory protein RirA. In different bacteria, RirA acts as a repressor of iron uptake systems under iron-replete conditions and contributes to ameliorate cell damage during oxidative stress. In and , mutations in do not impair symbiotic nitrogen fixation.

Strains HH103 and NGR234 Form Nitrogen Fixing Nodules With Diverse Wild Soybeans () From Central China but Are Ineffective on Northern China Accessions.

indigenous populations are prevalent in provinces of Central China whereas species (, , , and others) are more abundant in northern and southern provinces. The symbiotic properties of different soybean rhizobia have been investigated with 40 different wild soybean () accessions from China, Japan, Russia, and South Korea. Bradyrhizobial strains nodulated all the wild soybeans tested, albeit efficiency of nitrogen fixation varied considerably among accessions.

Hanks-Type Serine/Threonine Protein Kinases and Phosphatases in Bacteria: Roles in Signaling and Adaptation to Various Environments.

Reversible phosphorylation is a key mechanism that regulates many cellular processes in prokaryotes and eukaryotes. In prokaryotes, signal transduction includes two-component signaling systems, which involve a membrane sensor histidine kinase and a cognate DNA-binding response regulator. Several recent studies indicate that alternative regulatory pathways controlled by Hanks-type serine/threonine kinases (STKs) and serine/threonine phosphatases (STPs) also play an essential role in regulation of many different processes in bacteria, such as growth and cell division, cell wall biosynthesis, sporulation, biofilm formation, stress response, metabolic and developmental processes, as well as interactions (either pathogenic or symbiotic) with higher host organisms.

Mutation in the Gene Negatively Impacts Exopolysaccharide Synthesis, Surface Properties, and Symbiosis of bv. with Clover.

bv. is a soil bacterium capable of establishing a nitrogen-fixing symbiosis with clover plants ( spp.).

Transcriptomic Studies of the Effect of nod Gene-Inducing Molecules in Rhizobia: Different Weapons, One Purpose.

Simultaneous quantification of transcripts of the whole bacterial genome allows the analysis of the global transcriptional response under changing conditions. RNA-seq and microarrays are the most used techniques to measure these transcriptomic changes, and both complement each other in transcriptome profiling. In this review, we exhaustively compiled the symbiosis-related transcriptomic reports (microarrays and RNA sequencing) carried out hitherto in rhizobia.

Regulatory Elements Located in the Upstream Region of the Rhizobium leguminosarum rosR Global Regulator Are Essential for Its Transcription and mRNA Stability.

bv. is a soil bacterium capable of establishing a symbiotic relationship with clover ( spp.).

Studies of rhizobial competitiveness for nodulation in soybean using a non-destructive split-root system.

Split-root systems (SRS) constitute an appropriate methodology for studying the relevance of both local and systemic mechanisms that participate in the control of rhizobia-legume symbioses. In fact, this kind of approach allowed to demonstrate the autoregulation of nodulation (AON) systemic response in soybean in the 1980s. In SRS, the plant main root is cut and two lateral roots that emerge from the seedlings after root-tip removal are confined into separate compartments.

Sinorhizobium fredii HH103 Invades Lotus burttii by Crack Entry in a Nod Factor-and Surface Polysaccharide-Dependent Manner.

Sinorhizobium fredii HH103-Rif, a broad host range rhizobial strain, induces nitrogen-fixing nodules in Lotus burttii but ineffective nodules in L. japonicus. Confocal microscopy studies showed that Mesorhizobium loti MAFF303099 and S.

Exopolysaccharide Production by Sinorhizobium fredii HH103 Is Repressed by Genistein in a NodD1-Dependent Manner.

In the rhizobia-legume symbiotic interaction, bacterial surface polysaccharides, such as exopolysaccharide (EPS), lipopolysaccharide (LPS), K-antigen polysaccharide (KPS) or cyclic glucans (CG), appear to play crucial roles either acting as signals required for the progression of the interaction and/or preventing host defence mechanisms. The symbiotic significance of each of these polysaccharides varies depending on the specific rhizobia-legume couple. In this work we show that the production of exopolysaccharide by Sinorhizobium fredii HH103, but not by other S.