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Functional overlap of the Arabidopsis leaf and root microbiota

Roots and leaves of healthy plants host taxonomically structured bacterial assemblies, and members of these communities contribute to plant growth and health. We established Arabidopsis leaf- and root-derived microbiota culture collections representing the majority of bacterial species that are reproducibly detectable by culture-independent community sequencing. We found an extensive taxonomic overlap between the leaf and root microbiota. Genome drafts of 400 isolates revealed a large overlap of genome-encoded functional capabilities between leaf- and root-derived bacteria with few significant differences at the level of individual functional categories. Using defined bacterial communities and a gnotobiotic Arabidopsis plant system we show that the isolates form assemblies resembling natural microbiota on their cognate host organs, but are also capable of ectopic leaf or root colonization. While this raises the possibility of reciprocal relocation between root and leaf microbiota members, genome information and recolonization experiments also provide evidence for microbiota specialization to their respective niche.

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BMC Plant Biology | Full text | Influence of rhizobacterial volatiles on the root system architecture and the production and allocation of biomass in the model grass Brachypodium distachyon

Background

Plant growth-promoting rhizobacteria are increasingly being seen as a way of complementing conventional inputs in agricultural systems. The effects on their host plants are diverse and include volatile-mediated growth enhancement. This study sought to assess the effects of bacterial volatiles on the biomass production and root system architecture of the model grass Brachypodium distachyon (L.) Beauv.

Results

An in vitro experiment allowing plant-bacteria interaction throughout the gaseous phase without any physical contact was used to screen 19 bacterial strains for their growth-promotion ability over a 10-day co-cultivation period. Five groups of bacteria were defined and characterised based on their combined influence on biomass production and root system architecture. The observed effects ranged from unchanged to greatly increased biomass production coupled with increased root length and branching. Primary root length was increased only by the volatile compounds emitted by Enterobacter cloacae JM22 and Bacillus pumilus T4. Overall, the most significant results were obtained with Bacillus subtilis GB03, which induced an 81 % increase in total biomass, as well as enhancing total root length, total secondary root length and total adventitious root length by 88.5, 201.5 and 474.5 %, respectively.

Conclusions

This study is the first report on bacterial volatile-mediated growth promotion of a grass plant. Contrasting modulations of biomass production coupled with changes in root system architecture were observed. Most of the strains that increased total plant biomass also modulated adventitious root growth. Under our screening conditions, total biomass production was strongly correlated with the length and branching of the root system components, except for primary root length. An analysis of the emission kinetics of the bacterial volatile compounds is being undertaken and should lead to the identification of the compounds responsible for the observed growth-promotion effects. Within the context of the inherent characteristics of our in vitro system, this paper identifies the next critical experimental steps and discusses them from both a fundamental and an applied perspective.

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Autotransporter-based cell surface display in Gram-negative bacteria, Critical Reviews in Microbiology, Informa Healthcare

Autotransporter-based cell surface display in Gram-negative bacteria, Critical Reviews in Microbiology, Informa Healthcare | My publications | Scoop.it
Cell surface display of proteins can be used for several biotechnological applications such as the screening of protein libraries, whole cell biocatalysis and live vaccine development. Amongst all secretion systems and surface appendages of Gram-negative bacteria, the autotransporter secretion pathway holds great potential for surface display because of its modular structure and apparent simplicity. Autotransporters are polypeptides made up of an N-terminal signal peptide, a secreted or surface-displayed passenger domain and a membrane-anchored C-terminal translocation unit. Genetic replacement of the passenger domain allows for the surface display of heterologous passengers. An autotransporter-based surface expression module essentially consists of an application-dependent promoter system, a signal peptide, a passenger domain of interest and the autotransporter translocation unit. The passenger domain needs to be compatible with surface translocation although till now no general rules have been determined to test this compatibility. The autotransporter technology for surface display of heterologous passenger domains is critically discussed for various applications.


Read More: http://informahealthcare.com/doi/abs/10.3109/1040841X.2013.804032
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Complete Genome Sequence of the Model Rhizosphere Strain Azospirillum brasilense Az39, Successfully Applied in Agriculture

We present the complete genome sequence of Azospirillum brasilense Az39, isolated from wheat roots in the central region of Argentina and used as inoculant in extensive and intensive agriculture during the last four decades. The genome consists of 7.39 Mb, distributed in six replicons: one chromosome, three chromids, and two plasmids.

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Phenotypical and molecular responses of Arabidopsis thaliana roots as a result of inoculation with the auxin-producing bacterium Azospirillum brasilense - Spaepen - 2013 - New Phytologist - Wiley O...

Phenotypical and molecular responses of Arabidopsis thaliana roots as a result of inoculation with the auxin-producing bacterium Azospirillum brasilense - Spaepen - 2013 - New Phytologist - Wiley O... | My publications | Scoop.it

The auxin-producing bacterium Azospirillum brasilense Sp245 can promote the growth of several plant species. The model plant Arabidopsis thaliana was chosen as host plant to gain an insight into the molecular mechanisms that govern this interaction. The determination of differential gene expression in Arabidopsis roots after inoculation with either A. brasilense wild-type or an auxin biosynthesis mutant was achieved by microarray analysis.Arabidopsis thaliana inoculation with A. brasilense wild-type increases the number of lateral roots and root hairs, and elevates the internal auxin concentration in the plant. The A. thaliana root transcriptome undergoes extensive changes on A. brasilense inoculation, and the effects are more pronounced at later time points. The wild-type bacterial strain induces changes in hormone- and defense-related genes, as well as in plant cell wall-related genes. The A. brasilense mutant, however, does not elicit these transcriptional changes to the same extent. There are qualitative and quantitative differences between A. thaliana responses to the wild-type A. brasilense strain and the auxin biosynthesis mutant strain, based on both phenotypic and transcriptomic data. This illustrates the major role played by auxin in the Azospirillum–Arabidopsis interaction, and possibly also in other bacterium–plant interactions.

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Structure and Functions of the Bacterial Microbiota of Plants - Annual Review of Plant Biology, 64(1):807

Structure and Functions of the Bacterial Microbiota of Plants - Annual Review of Plant Biology, 64(1):807 | My publications | Scoop.it

Plants host distinct bacterial communities on and inside various plant organs, of which those associated with roots and the leaf surface are best characterized. The phylogenetic composition of these communities is defined by relatively few bacterial phyla, including Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. A synthesis of available data suggests a two-step selection process by which the bacterial microbiota of roots is differentiated from the surrounding soil biome. Rhizodeposition appears to fuel an initial substrate-driven community shift in the rhizosphere, which converges with host genotype–dependent fine-tuning of microbiota profiles in the selection of root endophyte assemblages. Substrate-driven selection also underlies the establishment of phyllosphere communities but takes place solely at the immediate leaf surface. Both the leaf and root microbiota contain bacteria that provide indirect pathogen protection, but root microbiota members appear to serve additional host functions through the acquisition of nutrients from soil for plant growth. Thus, the plant microbiota emerges as a fundamental trait that includes mutualism enabled through diverse biochemical mechanisms, as revealed by studies on plant growth–promoting and plant health–promoting bacteria.

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Characterization of Esterase A, a Pseudomonas stutzeri A15 Autotransporter

Autotransporters are a widespread family of proteins, generally known as virulence factors produced by Gram-negative bacteria. In this study, the esterase A (EstA) autotransporter of the rice root-colonizing beneficial bacterium Pseudomonas stutzeri A15 was characterized. A multiple sequence alignment identified EstA as belonging to clade II of the GDSL esterase family. Autologous overexpression allowed the investigation of several features of both autotransporter proteins and GDSL esterases. First, the correctly folded autotransporter was shown to be present in the membrane fraction. Unexpectedly, after separation of the membrane fraction, EstA was detected in the N-laurylsarcosine soluble fraction. However, evidence is presented for the surface exposure of EstA based on fluorescent labeling with EstA specific antibodies. Another remarkable feature is the occurrence of a C-terminal leucine residue instead of the canonical phenylalanine or tryptophan residue. Replacement of this residue with a phenylalanine residue reduced the stability of the β-barrel. Regarding the esterase passenger domain, we show the importance of the catalytic triad residues, with the serine and histidine residues being more critical than the aspartate residue. Furthermore, the growth of an estA-negative mutant was not impaired and cell mobility was not disabled compared to the wild type. No specific phenotype was detected for an estA-negative mutant. Overall, P. stutzeri A15 EstA is a new candidate for the surface display of proteins in environmentally relevant biotechnological applications.

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N2-Fixing Endophytes of Grasses and Cereals - Ecological Aspects of Nitrogen Metabolism in Plants - Reis - Wiley Online Library

N2-Fixing Endophytes of Grasses and Cereals - Ecological Aspects of Nitrogen Metabolism in Plants - Reis - Wiley Online Library | My publications | Scoop.it
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Plant growth promotion by Azospirillum sp. in sugarcane is influenced by genotype and drought stress - Springer

Plant growth promotion by Azospirillum sp. in sugarcane is influenced by genotype and drought stress - Springer | My publications | Scoop.it

Azospirillum influences growth and development of several crops by producing phytohormones such as auxins which have a major impact on root development. An improved root system leads to better water and nutrient uptake that in turn may influence yield positively. In this study, two agronomically contrasting sugarcane cvs R 570 and M 1176/77 adapted to different agroclimatic zones were inoculated with Azospirillum sp., with and without drought stress, to gauge how far they could benefit from this bacterial association. As early as 103 days after planting, cv M 1176/77 responded positively to inoculation with 15% improved growth (shoot height) and 75% more root dry mass when subjected to drought stress, whereas cv R 570 responded negatively particularly in the absence of drought stress. The significant interaction of cultivar x water regime x Azospirillum inoculation suggests a complex interplay of these factors, possibly involving the indigenous plant auxin pool. Therefore, plant genotype needs to be taken into account when recommending bacterial inoculation for direct plant growth promotion. Furthermore, enhanced growth under sub-optimal water conditions shows clearly the benefits that could be obtained in semi-arid conditions where water deficits frequently occur.

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Applicability of the 16S–23S rDNA internal spacer for PCR detection of the phytostimulatory PGPR inoculant Azospirillum lipoferum CRT1 in field soil - Baudoin - 2009 - Journal of Applied Microbiolo...

Applicability of the 16S–23S rDNA internal spacer for PCR detection of the phytostimulatory PGPR inoculant Azospirillum lipoferum CRT1 in field soil - Baudoin - 2009 - Journal of Applied Microbiolo... | My publications | Scoop.it

Aims: To assess the applicability of the 16S–23S rDNA internal spacer regions (ISR) as targets for PCR detection of Azospirillum ssp. and the phytostimulatory plant growth-promoting rhizobacteria seed inoculant Azospirillum lipoferum CRT1 in soil.

Methods and Results: Primer sets were designed after sequence analysis of the ISR of A. lipoferum CRT1 and Azospirillum brasilense Sp245. The primers fAZO/rAZO targeting the Azospirillum genus successfully yielded PCR amplicons (400–550 bp) from Azospirillum strains but also from certain non-Azospirillum strains in vitro, therefore they were not appropriate to monitor indigenous Azospirillum soil populations. The primers fCRT1/rCRT1 targeting A. lipoferum CRT1 generated a single 249-bp PCR product but could also amplify other strains from the same species. However, with DNA extracts from the rhizosphere of field-grown maize, both fAZO/rAZO and fCRT1/rCRT1 primer sets could be used to evidence strain CRT1 in inoculated plants by nested PCR, after a first ISR amplification with universal ribosomal primers. In soil, a 7-log dynamic range of detection (102–108 CFU g−1 soil) was obtained.

Conclusions: The PCR primers targeting 16S–23S rDNA ISR sequences enabled detection of the inoculant A. lipoferum CRT1 in field soil.

Significance and Impact of the Study: Convenient methods to monitor Azospirillum phytostimulators in the soil are lacking. The PCR protocols designed based on ISR sequences will be useful for detection of the crop inoculant A. lipoferum CRT1 under field conditions.

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Identification of the glutamine synthetase adenylyltransferase of Azospirillum brasilense

Glutamine synthetase, a key enzyme in nitrogen metabolism of both prokaryotes and eukaryotes, is strictly regulated. One means of regulation is the modulation of activity through adenylylation catalyzed by adenylyltransferases. Using PCR primers based on conserved sequences in glutamine synthetase adenylyltransferases, we amplified part of the glnE gene of Azospirillum brasilense Sp7. The complete glnE sequence of A. brasilense Sp245 was retrieved from the draft genome sequence of this organism (http://genomics.ornl.gov/research/azo/). Adenylyltransferase is a bifunctional enzyme consisting of an N-terminal domain responsible for deadenylylation activity and a C-terminal domain responsible for adenylylation activity. Both domains are partially homologous to each other. Residues important for catalytic activity were present in the deduced amino acid sequence of the A. brasilense Sp245 glnE sequence. A glnE mutant was constructed in A. brasilense Sp7 by inserting a kanamycin resistance cassette between the two active domains of the enzyme. The resulting mutant was unable to adenylylate the glutamine synthetase enzyme and was impaired in growth when shifted from nitrogen-poor to nitrogen-rich medium.

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Indole-3-acetic acid-regulated genes in Rhizobium etli CNPAF512 - Spaepen - 2008 - FEMS Microbiology Letters - Wiley Online Library

Indole-3-acetic acid-regulated genes in Rhizobium etli CNPAF512 - Spaepen - 2008 - FEMS Microbiology Letters - Wiley Online Library | My publications | Scoop.it

In the rhizosphere and their interaction with plants rhizobia encounter many different plant compounds, including phytohormones like auxins. Moreover, some rhizobial strains are capable of producing the auxin, indole-3-acetic acid (IAA). However, the role of IAA for the bacterial partner in the legume–Rhizobium symbiosis is not known. To identify the effect of IAA on rhizobial gene expression, a transposon (mTn5gusA-oriV) mutant library of Rhizobium etli, enriched for mutants that show differential gene expression under microaerobiosis and/or addition of nodule extracts as compared with control conditions, was screened for altered gene expression upon IAA addition. Four genes were found to be regulated by IAA. These genes appear to be involved in plant signal processing, motility or attachment to plant roots, clearly demonstrating a distinct role for IAA in legume–Rhizobium interactions.

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Second-order nonlinear optical properties of fluorescent proteins for second-harmonic imaging - Journal of Materials Chemistry (RSC Publishing)

The second-order nonlinear optical properties of three fluorescent proteins (FPs) (green, EGFP; yellow, EYFP; and red, DsRed) have been experimentally determined by frequency-resolved femtosecond hyper-Rayleigh scattering. As expected, DsRed, with its lower-energy bandgap between ground and excited state, exhibits the largest intrinsic hyperpolarizability. The anomalously low first hyperpolarizability for the yellow variant has been rationalized in terms of the centrosymmetrical arrangement between the phenolic Tyr203 (Tyr = tyrosine) residue and the chromophoric Tyr66 moiety, leaving the small imidazolinone moiety as the only effective non-centrosymmetric chromophore for second-order nonlinear effects. The experimental findings are corroborated by high-level computational results and suggest molecular engineering strategies to produce a full rainbow of FPs with enhanced nonlinear optical properties.

 

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Auxin Signaling in Azospirillum brasilense: A Proteome Analysis - Biological Nitrogen Fixation

Auxin Signaling in Azospirillum brasilense: A Proteome Analysis - Biological Nitrogen Fixation | My publications | Scoop.it

The auxin indole-3-acetic acid (IAA) is one of the best studied phytohormones in plants. IAA also has an important role in microbe–plant interactions and in microbial signaling. Here, we report a proteome analysis of Azospirillum brasilense Sp245 identifying differential expressed proteins by comparing the proteome of the wild-type strain to that of an auxin-impaired mutant (knock-out mutant in key gene, ipdC, of IAA biosynthesis). This analysis could pinpoint eight proteins involved in auxin signaling in A. brasilense, pointing toward a role in stress resistance or in the adaptation to the plant–environment interaction.

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Microbiota and Host Nutrition across Plant and Animal Kingdoms: Cell Host & Microbe

Microbiota and Host Nutrition across Plant and Animal Kingdoms: Cell Host & Microbe | My publications | Scoop.it

Plants and animals each have evolved specialized organs dedicated to nutrient acquisition, and these harbor specific bacterial communities that extend the host’s metabolic repertoire. Similar forces driving microbial community establishment in the gut and plant roots include diet/soil-type, host genotype, and immune system as well as microbe-microbe interactions. Here we show that there is no overlap of abundant bacterial taxa between the microbiotas of the mammalian gut and plant roots, whereas taxa overlap does exist between fish gut and plant root communities. A comparison of root and gut microbiota composition in multiple host species belonging to the same evolutionary lineage reveals host phylogenetic signals in both eukaryotic kingdoms. The reasons underlying striking differences in microbiota composition in independently evolved, yet functionally related, organs in plants and animals remain unclear but might include differences in start inoculum and niche-specific factors such as oxygen levels, temperature, pH, and organic carbon availability.

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Plant Hormones Produced by Microbes - Springer

Plant Hormones Produced by Microbes - Springer | My publications | Scoop.it

Plant hormones or phytohormones are historically classified into five major classes: auxins, cytokinins, gibberellins, abscisic acid and ethylene. Nowadays, many other phytohormones have been identified. Diverse microbial species possess the ability to produce phytohormones, with most data accumulated for the production and role of auxin. In this chapter the microbial biosynthesis, its regulation and the role of the different phytohormones in the interaction with the plant are discussed. Microbial phytohormonal production is a potent mechanism to alter plant physiology, leading to diverse outcomes from pathogenesis to promotion of plant growth. However, genetic evidence for the role of many phytohormones in microbe-plant interactions is still lacking, thus questioning the importance of the microbial production. Targeted approaches focusing on genetic evidence for the role of phytohormones together with plant experiments in an agronomic setting will allow unraveling the importance and potential of this fascinating microbial trait.

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BMC Plant Biology | Full text | Tissue specific analysis reveals a differential organization and regulation of both ethylene biosynthesis and E8 during climacteric ripening of tomato

Background

Solanum lycopersicum or tomato is extensively studied with respect to the ethylene metabolism during climacteric ripening, focusing almost exclusively on fruit pericarp. In this work the ethylene biosynthesis pathway was examined in all major tomato fruit tissues: pericarp, septa, columella, placenta, locular gel and seeds. The tissue specific ethylene production rate was measured throughout fruit development, climacteric ripening and postharvest storage. All ethylene intermediate metabolites (1-aminocyclopropane-1-carboxylic acid (ACC), malonyl-ACC (MACC) and S-adenosyl-L-methionine (SAM)) and enzyme activities (ACC-oxidase (ACO) and ACC-synthase (ACS)) were assessed.

Results

All tissues showed a similar climacteric pattern in ethylene productions, but with a different amplitude. Profound differences were found between tissue types at the metabolic and enzymatic level. The pericarp tissue produced the highest amount of ethylene, but showed only a low ACC content and limited ACS activity, while the locular gel accumulated a lot of ACC, MACC and SAM and showed only limited ACO and ACS activity. Central tissues (septa, columella and placenta) showed a strong accumulation of ACC and MACC. These differences indicate that the ethylene biosynthesis pathway is organized and regulated in a tissue specific way. The possible role of inter- and intra-tissue transport is discussed to explain these discrepancies. Furthermore, the antagonistic relation between ACO and E8, an ethylene biosynthesis inhibiting protein, was shown to be tissue specific and developmentally regulated. In addition, ethylene inhibition by E8 is not achieved by a direct interaction between ACO and E8, as previously suggested in literature.

Conclusions

The Ethylene biosynthesis pathway and E8 show a tissue specific and developmental differentiation throughout tomato fruit development and ripening.

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PLOS Pathogens: Structural Determinants for Activity and Specificity of the Bacterial Toxin LlpA

PLOS Pathogens: Structural Determinants for Activity and Specificity of the Bacterial Toxin LlpA | My publications | Scoop.it

In their natural environments, microorganisms compete for space and nutrients, and a major strategy to assist in niche colonization is the deployment of antagonistic compounds directed at competitors, such as secondary metabolites (antibiotics) and antibacterial peptides or proteins (bacteriocins). The latter selectively kill closely related bacteria, which is also the case for members of the LlpA family. Here, we investigate the structure-function relationship for the prototype LlpABW from a saprophytic plant-associated Pseudomonas whose genus-specific target spectrum includes several phytopathogenic pseudomonads. By determining the 3D structure of this protein, we could assign LlpA to the so-called monocot mannose-binding lectin (MMBL) family, representing its first prokaryotic member, and also add a new type of protective function, as the eukaryotic MMBL members have been linked with antiviral, antifungal, nematicidal or insecticidal activities. For the protein containing two similarly folded domains, we constructed site-specific mutants affected in carbohydrate binding and domain chimers from LlpA homologues to show that mannose-specific sugar binding mediated by one domain is required for activity and that the other domain determines target strain specificity. The strategy that evolved for these bacteriocins is reminiscent of the one used by mammalian bactericidal proteins of the RegIII family that recruited a C-type lectin fold to kill bacteria.

 

 

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Microbial Cell Factories | Full text | Probing the applicability of autotransporter based surface display with the EstA autotransporter of Pseudomonas stutzeri A15

Background

Autotransporters represent a widespread family of secreted proteins in Gram-negative bacteria. Their seemingly easy secretion mechanism and modular structure make them interesting candidates for cell surface display of heterologous proteins. The most widely applied host organism for this purpose is Escherichia coli. Pseudomonas stutzeri A15 is an interesting candidate host for environmentally relevant biotechnological applications. With the recently characterized P. stutzeri A15 EstA autotransporter at hand, all tools for developing a surface display system for environmental use are available. More general, this system could serve as a case-study to test the broad applicability of autotransporter based surface display.

Results

Based on the P. stutzeri A15 EstA autotransporter β-domain, a surface display expression module was constructed for use in P. stutzeri A15. Proof of concept of this module was presented by successful surface display of the original EstA passenger domain, which retained its full esterase activity. Almost all of the tested heterologous passenger domains however were not exposed at the cell surface of P. stutzeri A15, as assessed by whole cell proteinase K treatment. Only for a beta-lactamase protein, cell surface display in P. stutzeri A15 was comparable to presentation of the original EstA passenger domain. Development of expression modules based on the full-length EstA autotransporter did not resolve these problems.

Conclusions

Since only one of the tested heterologous passenger proteins could be displayed at the cell surface of P. stutzeri A15 to a notable extent, our results indicate that the EstA autotransporter cannot be regarded as a broad spectrum cell surface display system in P. stutzeri A15.

 

 

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Transcriptome Analysis of the Rhizosphere Bacterium Azospirillum brasilense Reveals an Extensive Auxin Response - Springer

Transcriptome Analysis of the Rhizosphere Bacterium Azospirillum brasilense Reveals an Extensive Auxin Response - Springer | My publications | Scoop.it

The rhizosphere bacterium Azospirillum brasilense produces the auxin indole-3-acetic acid (IAA) through the indole-3-pyruvate pathway. As we previously demonstrated that transcription of the indole-3-pyruvate decarboxylase (ipdC) gene is positively regulated by IAA, produced by A. brasilense itself or added exogenously, we performed a microarray analysis to study the overall effects of IAA on the transcriptome of A. brasilense. The transcriptomes of A. brasilense wild-type and the ipdC knockout mutant, both cultured in the absence and presence of exogenously added IAA, were compared.

Interfering with the IAA biosynthesis/homeostasis in A. brasilense through inactivation of the ipdC gene or IAA addition results in much broader transcriptional changes than anticipated. Based on the multitude of changes observed by comparing the different transcriptomes, we can conclude that IAA is a signaling molecule in A. brasilense. It appears that the bacterium, when exposed to IAA, adapts itself to the plant rhizosphere, by changing its arsenal of transport proteins and cell surface proteins. A striking example of adaptation to IAA exposure, as happens in the rhizosphere, is the upregulation of a type VI secretion system (T6SS) in the presence of IAA. The T6SS is described as specifically involved in bacterium–eukaryotic host interactions. Additionally, many transcription factors show an altered regulation as well, indicating that the regulatory machinery of the bacterium is changing.

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Auxin and Plant-Microbe Interactions

Auxin and Plant-Microbe Interactions | My publications | Scoop.it

Microbial synthesis of the phytohormone auxin has been known for a long time. This property is best documented for bacteria that interact with plants because bacterial auxin can cause interference with the many plant developmental processes regulated by auxin. Auxin biosynthesis in bacteria can occur via multiple pathways as has been observed in plants. There is also increasing evidence that indole-3-acetic acid (IAA), the major naturally occurring auxin, is a signaling molecule in microorganisms because IAA affects gene expression in some microorganisms. Therefore, IAA can act as a reciprocal signaling molecule in microbe-plant interactions. Interest in microbial synthesis of auxin is also increasing in yet another recently discovered property of auxin in Arabidopsis. Down-regulation of auxin signaling is part of the plant defense system against phytopathogenic bacteria. Exogenous application of auxin, e.g., produced by the pathogen, enhances susceptibility to the bacterial pathogen.

 

 

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NONLINEAR OPTICAL PROPERTIES OF mSTRAWBERRY AND mCHERRY FOR SECOND HARMONIC IMAGING (World Scientific)

NONLINEAR OPTICAL PROPERTIES OF mSTRAWBERRY AND mCHERRY FOR SECOND HARMONIC IMAGING (World Scientific) | My publications | Scoop.it
The second-order nonlinear optical properties of two monomeric red fluorescent proteins, mStrawberry and mCherry, have been experimentally determined by frequency-resolved femtosecond hyper-Rayleigh scattering. These proteins were found to exhibit a stronger nonlinear response than the previously described eGFP, eYFP and DsRed,1 confirming the trend that fluorophores with a more extended conjugated system, or a lower-energy band gap between ground and excited state, exhibit a larger static hyperpolarizability (β0). Furthermore, these experimental data were complemented with quantum chemical calculations. A discrepancy was observed between experimental and theoretical results, but this could be explained by the chromophore model extracted from the available X-ray diffraction data. While eGFP showed a larger dynamic experimental response (βHRS) due to the highest resonance enhancement, we measured an even higher signal for mCherry. Furthermore, mCherry also shows a better separation of the second harmonic signal and two-photon excited fluorescent signal, making this the preferred fluorescent protein for second harmonic imaging at 800 nm so far.


Read More: http://www.worldscientific.com/doi/abs/10.1142/S0218863510005054
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Wheat growth promotion through inoculation with an ammonium-excreting mutant of Azospirillum brasilense - Springer

Wheat growth promotion through inoculation with an ammonium-excreting mutant of Azospirillum brasilense - Springer | My publications | Scoop.it

Azospirillum brasilense is a diazotrophic bacterium and one of the best studied plant-growth-promoting bacterium living in close association with several agronomically important crops. The production of plant-growth-regulating substances is a main mechanism of plant growth stimulation, although other mechanisms have also been proposed. Nitrogen transfer from the bacterium to the plant is one among the other possible mechanisms of plant growth stimulation. In this study, we investigated, by means of a greenhouse trial with winter wheat inoculation, the effect of a point mutation in the ammonium binding site of the A. brasilense glutamine synthetase. The glutamine synthetase is one of the main ammonium-assimilating enzymes and mutations in this enzyme generally result in the release of ammonium from the bacterium to its environment. The ammonium-excreting mutant used in this study was shown to perform better than the wild-type A. brasilense strain with respect to wheat growth parameters and yield. In the greenhouse conditions used, this effect was independent of the way fertilizer was applied.

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Effects of Azospirillum brasilense with genetically modified auxin biosynthesis gene ipdC upon the diversity of the indigenous microbiota of the wheat rhizosphere

The phytostimulatory properties of Azospirillum inoculants, which entail production of the phytohormone indole-3-acetic acid (IAA), can be enhanced by genetic means. However, it is not known whether this could affect their interactions with indigenous soil microbes. Here, wheat seeds were inoculated with the wild-type strain Azospirillum brasilense Sp245 or one of three genetically modified (GM) derivatives and grown for one month. The GM derivatives contained a plasmid vector harboring the indole-3-pyruvate/phenylpyruvate decarboxylase gene ipdC (IAA production) controlled either by the constitutive promoter PnptII or the root exudate-responsive promoter PsbpA, or by an empty vector (GM control). All inoculants displayed equal rhizosphere population densities. Only inoculation with either ipdC construct increased shoot biomass compared with the non-inoculated control. At one month after inoculation, automated ribosomal intergenic spacer analysis (ARISA) revealed that the effect of the PsbpA construct on bacterial community structure differed from that of the GM control, which was confirmed by 16S rDNA-based denaturing gradient gel electrophoresis (DGGE). The fungal community was sensitive to inoculation with the PsbpA construct and especially the GM control, based on ARISA data. Overall, fungal and bacterial communities displayed distinct responses to inoculation of GM A. brasilense phytostimulators, whose effects could differ from those of the wild-type.

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Brominated phenols as auxin-like molecules

2,6-Dibromophenol (DBP) was reported as an auxin-like molecule using molecular quantum similarity measures. In this study, the auxin activity of this molecule and its chlorinated homologue is further determined using a bacterial biosensor: the auxin-inducible ipdC promoter of Azospirillum brasilense. We were able to demonstrate that DBP can induce gene expression, but to a lesser extent than the auxin indole-3-acetic acid (IAA) and that DBP is not an antagonist for the IAA signalling pathway. To investigate the role of the bromine groups, the molecule 2,6-dichlorophenol (DCP) was also tested for gene expression induction. However, no induction could be observed. In a second part, DBP and other molecules were modelled in the auxin-binding pocket of the plant auxin receptor TIR1 to evaluate theoretical binding energies. Both DBP and its chlorinated homologue DCP are not strong ligands compared to other known auxins such as IAA. The importance of a carboxylated side chain for optimal binding (and probably auxin activity) was demonstrated.

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