Plants&Bacteria
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Plants&Bacteria
A selection of publications concerning the diverse relationship between plants and microorganisms, with some special atention to plant-pathogenic bacteria.
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The Clavibacter michiganensis subsp. michiganensis–Tomato Interactome Reveals the Perception of Pathogen by the Host and Suggests Mechanisms of Infection

The Clavibacter michiganensis subsp. michiganensis–Tomato Interactome Reveals the Perception of Pathogen by the Host and Suggests Mechanisms of Infection | Plants&Bacteria | Scoop.it

The Gram-positive bacterium Clavibacter michiganensis subsp. michiganensis (Cmm) causes wilt and canker disease of tomato (Solanum lycopersicum). Mechanisms of Cmm pathogenicity and tomato response to Cmm infection are not well understood. To explore the interaction between Cmm and tomato, multidimensional protein identification technology (MudPIT) and tandem mass spectrometry were used to analyze in vitro and in planta generated samples. The results show that during infection Cmm senses the plant environment, transmits signals, induces, and then secretes multiple hydrolytic enzymes, including serine proteases of the Pat-1, Ppa, and Sbt familes, the CelA, XysA, and NagA glycosyl hydrolases, and other cell wall-degrading enzymes. Tomato induction of pathogenesis-related (PR) proteins, LOX1, and other defense-related proteins during infection indicates that the plant senses the invading bacterium and mounts a basal defense response, although partial with some suppressed components including class III peroxidases and a secreted serine peptidase. The tomato ethylene-synthesizing enzyme ACC-oxidase was induced during infection with the wild-typeCmm but not during infection with an endophytic Cmm strain, identifying Cmm-triggered host synthesis of ethylene as an important factor in disease symptom development. The proteomic data were also used to improve Cmm genome annotation, and thousands of Cmm gene models were confirmed or expanded.

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High resolution time-resolved imaging of in vitro Arabidopsis rosette growth

High resolution time-resolved imaging of in vitro Arabidopsis rosette growth | Plants&Bacteria | Scoop.it

Scooped from: The Plant Journal, 2014

Authors:

 

Abstract:

Although the quantitative characterization of growth phenotypes is of key importance for the understanding of essential networks driving plant growth, the majority of growth-related genes is still being identified based on qualitative visual observations and/or single endpoint quantitative measurements. We developed an IGIS, an In vitro Growth Imaging System to perform time-resolved analysis of rosette growth. With this system, Arabidopsis plants are grown in Petri dishes mounted on a rotating disk and pictures from each plate are taken on an hourly basis. Automated image analysis was developed in order to extract several growth-related parameters, such as projected rosette area, rosette relative growth rate, compactness and stockiness, over time. To illustrate the use of the platform and the resulting data, we present the growth response of Col-0 plants subjected to three different mild stress conditions. Although at 19 DAS the reduction in rosette area was relatively similar, the time-lapse analysis demonstrated that plants react differently to salt, osmotic and oxidative stress. Rosette area was altered at different moments during development, but also leaf movement and shape parameters were affected differently. We also used the IGIS to analyze in detail the growth behavior of mutants showing enhanced leaf size. The analysis of several growth-related parameters overtime in these mutants revealed several particularities in growth behavior, underlining the high complexity of leaf growth coordination. These results demonstrate that time-resolved imaging of in vitro rosette growth generates a better understanding of growth phenotypes compared to endpoint measurements.

Freddy Monteiro's insight:

In vitro Growth Imaging System for Arabidopsis development

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Elucidation of a pH-folding switch in the Pseudomonas syringae effector protein AvrPto

Elucidation of a pH-folding switch in the Pseudomonas syringae effector protein AvrPto | Plants&Bacteria | Scoop.it

Scooped from: PNAS, 2009.

Authors: Jennifer E. Dawson, Jolita Šečkutė, Soumya De, Samuel A. Schueler, Aaron B. Oswald and Linda K. Nicholson.

 

Abstract:

Pathogenic bacteria have developed extraordinary strategies for invading host cells. The highly conserved type III secretion system (T3SS) provides a regulated conduit between the bacterial and host cytoplasm for delivery of a specific set of bacterial effector proteins that serve to disrupt host signaling and metabolism for the benefit of the bacterium. Remarkably, the inner diameter of the T3SS apparatus requires that effector proteins pass through in at least a partially unfolded form. AvrPto, an effector protein of the plant pathogen Pseudomonas syringae, adopts a helical bundle fold of low stability (ΔGF→U = 2 kcal/mol at pH 7, 26.6 °C) and offers a model system for chaperone-independent secretion. P. syringae effector proteins encounter a pH gradient as they translocate from the bacterial cytoplasm (mildly acidic) into the host cell (neutral). Here, we demonstrate that AvrPto possesses a pH-sensitive folding switch controlled by conserved residue H87 that operates precisely in the pH range expected between the bacterial and host cytoplasm environments. These results provide a mechanism for how a bacterial effector protein employs an intrinsic pH sensor to unfold for translocation via the T3SS and refold once in the host cytoplasm and provide fundamental insights for developing strategies for delivery of engineered therapeutic proteins to target tissues.


 

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Comparison of the Transcriptomes of Ginger (Zingiber officinale Rosc.) and Mango Ginger (Curcuma amada Roxb.) in Response to the Bacterial Wilt Infection

Comparison of the Transcriptomes of Ginger (Zingiber officinale Rosc.) and Mango Ginger (Curcuma amada Roxb.) in Response to the Bacterial Wilt Infection | Plants&Bacteria | Scoop.it

Scooped from: PLoS One, 2014.

Authors: Duraisamy Prasath, Raveendran Karthika, Naduva Thadath Habeeba, Erinjery Jose Suraby, Ottakandathil Babu Rosana, Avaroth Shaji, Santhosh Joseph Eapen, Uday Deshpande and Muthuswamy Anandaraj

 

Summary:

Bacterial wilt in ginger (Zingiber officinale Rosc.) caused by Ralstonia solanacearum is one of the most important production constraints in tropical, sub-tropical and warm temperature regions of the world. Lack of resistant genotype adds constraints to the crop management. However, mango ginger (Curcuma amada Roxb.), which is resistant to R. solanacearum, is a potential donor, if the exact mechanism of resistance is understood. To identify genes involved in resistance to R. solanacearum, we have sequenced the transcriptome from wilt-sensitive ginger and wilt-resistant mango ginger using Illumina sequencing technology. A total of 26387032 and 22268804 paired-end reads were obtained after quality filtering for C. amada and Z. officinale, respectively. A total of 36359 and 32312 assembled transcript sequences were obtained from both the species. The functions of the unigenes cover a diverse set of molecular functions and biological processes, among which we identified a large number of genes associated with resistance to stresses and response to biotic stimuli. Large scale expression profiling showed that many of the disease resistance related genes were expressed more in C. amada. Comparative analysis also identified genes belonging to different pathways of plant defense against biotic stresses that are differentially expressed in either ginger or mango ginger. The identification of many defense related genes differentially expressed provides many insights to the resistance mechanism to R. solanacearum and for studying potential pathways involved in responses to pathogen. Also, several candidate genes that may underline the difference in resistance to R. solanacearum between ginger and mango ginger were identified. Finally, we have developed a web resource, ginger transcriptome database, which provides public access to the data. Our study is among the first to demonstrate the use of Illumina short read sequencing for de novo transcriptome assembly and comparison in non-model species of Zingiberaceae.

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A Scalable Open-Source Pipeline for Large-Scale Root Phenotyping of Arabidopsis

A Scalable Open-Source Pipeline for Large-Scale Root Phenotyping of Arabidopsis | Plants&Bacteria | Scoop.it

Scooped from: The Plant Cell 2014
Authors: Radka Slovak, Christian Göschl, Xiaoxue Su, Koji Shimotani, Takashi Shiina and Wolfgang Busch

 

Abstract:

 Large-scale phenotyping of multicellular organisms is one of the current challenges in biology. We present a comprehensive and scalable pipeline that allows for the efficient phenotyping of root growth traits on a large scale. This includes a high-resolution, low-cost acquisition setup as well as the automated image processing software BRAT. We assess the performance of this pipeline in Arabidopsis thaliana under multiple growth conditions and show its utility by performing genome-wide association studies on 16 root growth traits quantified by BRAT each day during a 5-d time-course experiment. The most significantly associated genome region for root growth rate is a locus encoding a calcium sensing receptor. We find that loss of function and overexpression of this gene can significantly alter root growth in a growth condition dependent manner and that the minor natural allele of the Calcium Sensor Receptor locus is highly significantly enriched in populations in coastal areas, demonstrating the power of our approach to identify regulators of root growth that might have adaptive relevance.

Freddy Monteiro's insight:

An impressive set-up that SIGNIFICATIVELY reduces the time of image (root length phenotypes) analysis.

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Comparative analysis of type III secreted effector genes reflects divergence of Acidovorax citrulli strains into three distinct lineages

Comparative analysis of type III secreted effector genes reflects divergence of Acidovorax citrulli strains into three distinct lineages | Plants&Bacteria | Scoop.it

Scooped from: Phytopathology 2014

Authors: Mr. Noam Eckshtain-Levi , Mrs. Tamar Munitz , Miss Marija Živanović , Mr. Sy Mamadou Traore , Mrs. Cathrin Spröer , Prof. Bingyu Zhao , Prof. Gregory Welbaum , Dr. Ron Ricardo Walcott PhD , Dr. Johannes Sikorski and Dr. Saul Burdman

 

Abstract:

Acidovorax citrulli causes bacterial fruit blotch (BFB) of cucurbits, a serious economic threat to watermelon (Citrullus lanatus) and melon (Cucumis melo) production worldwide. Based on genetic and biochemical traits, A. citrulli strains have been divided into two distinct groups: group I strains have been mainly isolated from various non-watermelon hosts, while group II strains have been generally isolated from and are highly virulent on watermelon. The pathogen depends on a functional type III secretion system (T3SS) for pathogenicity. Annotation of the genome of the group II strain, AAC00-1, revealed eleven genes encoding putative type III secreted (T3S) effectors. Due to the crucial role of type III secretion for A. citrulli pathogenicity, we hypothesized that group I and II strains differ in their T3S effector repertoire. Comparative analysis of the eleven effector genes from a collection of 22 A. citrulli strains confirmed this hypothesis. Moreover, this analysis led to the identification of a third A. citrulli group, which was supported by DNA:DNA hybridization, DNA fingerprinting, multilocus sequence analysis (MLSA) of conserved genes and virulence assays. The effector genes assessed in this study are homologous of effectors from other plant pathogenic bacteria, mainly belonging to Xanthomonas species and Ralstonia solanacearum. Analyses of the effective number of codons and GC content of effector genes relative to a representative set of housekeeping genes support that these effector genes were acquired by lateral gene transfer. Further investigation is required to identify new T3S effectors of A. citrulli and to determine their contribution to virulence and host preferential association.


Image source: http://departments.agri.huji.ac.il/plantpath/burdman/sb-aac.html

Image credit: Dr. Saul Burdman

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The plant microbiome and its importance for plant and human health - Frontiers in Microbiology

The plant microbiome and its importance for plant and human health - Frontiers in Microbiology | Plants&Bacteria | Scoop.it

Scooped from: Frontiers in Microbiology, 2014

Topic Editors:
Martin Grube, Michael Schloter, Kornelia Smalla and Gabriele Berg.

 

About: 

The study of plant-microbe associations by new techniques has significantly improved our understanding of the structure and specificity of the plant microbiome. Yet, microbiome function and the importance of the plant’s microbiome in the context of human and plant health are largely unexplored. Comparable with our human microbiome, millions of microbes inhabit plants, forming complex ecological communities that influence plant growth and health through its collective metabolic activities and host interactions. Viewing the microbiota from an ecological perspective can provide insight into how to promote plant health and stress tolerance of their hosts or how to adapt to a changing climate by targeting this microbial community. Moreover, the plant microbiome has a substantial impact on human health by influencing our gut microbiome by eating raw plants such as lettuce and herbs and but also by influencing the microbiome of our environment through airflow. This research topic will highlight the current knowledge regarding plant microbiomes, their specificity, diversity and function. Especially welcome are articles focused on the microbiomes of fresh edible plants and their impact on human health. Furthermore all applied aspects studying the management of plant microbiomes to enhance plant growth, health quality and stress tolerance are encouraged.

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Jean-Michel Ané's curator insight, May 4, 11:28 AM

Interesting topic. 

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Proteomic comparison of Ralstonia solanacearum strains reveals temperature dependent virulence factors

Proteomic comparison of Ralstonia solanacearum strains reveals temperature dependent virulence factors | Plants&Bacteria | Scoop.it

Scooped from: BMC Genomics, 2014
Authors: Ana M Bocsanczy, Ute CM Achenbach, Arianna Mangravita-Novo, Marjorie Chow and David J Norman

 

Summary:
Background
Ralstonia solanacearum, the causal agent of bacterial wilt, is a genetically diverse bacterial plant pathogen present in tropical and subtropical regions of the world that infects more than 200 plant species, including economically important solanaceous crops. Most strains of R. solanacearum are only pathogenic at temperatures between 25 to 30°C with strains that can cause disease below 20°C considered a threat to agriculture in temperate areas. Identifying key molecular factors that distinguish strains virulent at cold temperatures from ones that are not is needed to develop effective management tools for this pathogen. We compared protein profiles of two strains virulent at low temperature and two strains not virulent at low temperature when incubated in the rhizosphere of tomato seedlings at 30 and 18°C using quantitative 2D DIGE gel methods. Spot intensities were quantified and compared, and differentially expressed proteins were sequenced and identified by mass spectrometry (MS/MS).
Results
Four hundred and eighteen (418) differentially expressed protein spots sequenced produced 101 unique proteins. The identified proteins were classified in the Gene Ontology biological processes categories of metabolism, cell processes, stress response, transport, secretion, motility, and virulence. Identified virulence factors included catalase (KatE), exoglucanase A (ChbA), drug efflux pump, and twitching motility porin (PilQ). Other proteins identified included two components of a putative type VI secretion system. We confirmed differential expression of 13 candidate genes using real time PCR techniques. Global regulators HrpB and HrpG also had temperature dependent expression when quantified by real time PCR.
Conclusions
The putative involvement of the identified proteins in virulence at low temperature is discussed. The discovery of a functional type VI secretion system provides a new potential virulence mechanism to explore. The global regulators HrpG and HrpB, and the protein expression profiles identified suggest that virulence at low temperatures can be partially explained by differences in regulation of virulence factors present in all the strains.

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Freddy Monteiro's comment, April 27, 5:33 PM
More on how bacteria senses temperature: An amazing example: http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.1002153
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Xanthomonas perforans Colonization Influences Salmonella enterica in the Tomato Phyllosphere

Xanthomonas perforans Colonization Influences Salmonella enterica in the Tomato Phyllosphere | Plants&Bacteria | Scoop.it

Scooped from: Applied Environmental Microbiology, 2014.

Authors: Neha Potnis, José Pablo Soto-Arias, Kimberly N. Cowles, Ariena H. C. van Bruggen, Jeffrey B. Jones and Jeri D. Barak

 

Summary:

Salmonella enterica rarely grows on healthy, undamaged plants, but its persistence is influenced by bacterial plant pathogens. The interactions betweenS. enterica, Xanthomonas perforans (a tomato bacterial spot pathogen), and tomato were characterized. We observed that virulent X. perforans, which establishes disease by suppressing pathogen-associated molecular pattern (PAMP)-triggered immunity that leads to effector-triggered susceptibility, created a conducive environment for persistence of S. enterica in the tomato phyllosphere, while activation of effector-triggered immunity by avirulent X. perforans resulted in a dramatic reduction in S. enterica populations. S. entericapopulations persisted at ∼10 times higher levels in leaves coinoculated with virulent X. perforans than in those where S. enterica was applied alone. In contrast, S. enterica populations were ∼5 times smaller in leaves coinoculated with avirulent X. perforans than in leaves inoculated with S. enterica alone. Coinoculation with virulent X. perforans increased S. enterica aggregate formation; however, S. enterica was not found in mixed aggregates with X. perforans. Increased aggregate formation by S. enterica may serve as the mechanism of persistence on leaves cocolonized by virulent X. perforans. S. enterica association with stomata was altered by X. perforans; however, it did not result in appreciable populations of S. enterica in the apoplast even in the presence of large virulent X. perforans populations. Gene-for-gene resistance against X. perforans successively restricted S. enterica populations. Given the effect of this interaction, breeding for disease-resistant cultivars may be an effective strategy to limit both plant disease and S. enterica populations and, consequently, human illness.

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A Synthetic Community Approach Reveals Plant Genotypes Affecting the Phyllosphere Microbiota

A Synthetic Community Approach Reveals Plant Genotypes Affecting the Phyllosphere Microbiota | Plants&Bacteria | Scoop.it

Scooped from: PLOS Genetics, 2014.

Authors: Natacha Bodenhausen, Miriam Bortfeld-Miller, Martin Ackermann and Julia A. Vorholt.

 

Summary:

The identity of plant host genetic factors controlling the composition of the plant microbiota and the extent to which plant genes affect associated microbial populations is currently unknown. Here, we use a candidate gene approach to investigate host effects on the phyllosphere community composition and abundance. To reduce the environmental factors that might mask genetic factors, the model plant Arabidopsis thaliana was used in a gnotobiotic system and inoculated with a reduced complexity synthetic bacterial community composed of seven strains representing the most abundant phyla in the phyllosphere. From a panel of 55 plant mutants with alterations in the surface structure, cell wall, defense signaling, secondary metabolism, and pathogen recognition, a small number of single host mutations displayed an altered microbiota composition and/or abundance. Host alleles that resulted in the strongest perturbation of the microbiota relative to the wild-type were lacs2 and pec1. These mutants affect cuticle formation and led to changes in community composition and an increased bacterial abundance relative to the wild-type plants, suggesting that different bacteria can benefit from a modified cuticle to different extents. Moreover, we identified ein2, which is involved in ethylene signaling, as a host factor modulating the community's composition. Finally, we found that different Arabidopsis accessions exhibited different communities, indicating that plant host genetic factors shape the associated microbiota, thus harboring significant potential for the identification of novel plant factors affecting the microbiota of the communities.

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The Role of Autophagy in Chloroplast Degradation and Chlorophagy in Immune Defenses during Pst DC3000 (AvrRps4) Infection

The Role of Autophagy in Chloroplast Degradation and Chlorophagy in Immune Defenses during Pst DC3000 (AvrRps4) Infection | Plants&Bacteria | Scoop.it

Scooped from: PLOS One, 2014

Authors: Junjian Dong and Wenli Chen


Summary:

Background

Chlorosis of leaf tissue normally observed during pathogen infection may result from the degradation of chloroplasts. There is a growing evidence to suggest that the chloroplast plays a significant role during pathogen infection. Although most degradation of the organelles and cellular structures in plants is mediated by autophagy, its role in chloroplast catabolism during pathogen infection is largely unknown.

Results

In this study, we investigated the function of autophagy in chloroplast degradation during avirulent Pst DC3000 (AvrRps4) infection. We examined the expression of defensive marker genes and suppression of bacterial growth using the electrolyte leakage assay in normal light (N) and low light (L) growing environments of wild-type and atg5-1 plants during pathogen treatment. Stroma-targeted GFP proteins (CT-GFP) were observed with LysoTracker Red (LTR) staining of autophagosome-like structures in the vacuole. The results showed that Arabidopsis expressed a significant number of small GFP-labeled bodies when infected with avirulent Pst DC3000 (AvrRps4). While barely detectable, there were small GFP-labeled bodies in plants with the CT-GFP expressing atg5-1 mutation. The results showed that chloroplast degradation depends on autophagy and this may play an important role in inhibiting pathogen growth.

Conclusion

Autophagy plays a role in chloroplast degradation in Arabidopsis during avirulent Pst DC3000 (AvrRps4) infection. Autophagy dependent chloroplast degradation may be the primary source of reactive oxygen species (ROS) as well as the pathogen-response signaling molecules that induce the defense response.


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Identification of Genes Differentially Expressed between Resistant and Susceptible Tomato Lines during Time-Course Interactions with Xanthomonas perforans Race T3

Identification of Genes Differentially Expressed between Resistant and Susceptible Tomato Lines during Time-Course Interactions with Xanthomonas perforans Race T3 | Plants&Bacteria | Scoop.it

Scooped from: PLOS One, 2014

Authors: Heshan Du, Wenhui Li, Yuqing Wang, Wencai Yang.


Abstract:

Bacterial spot caused by several Xanthomonas sp. is one of the most devastating diseases in tomato (Solanum lycopersicum L.). The genetics of hypersensitive resistance to X. perforans race T3 has been intensively investigated and regulatory genes during the infection of race T3 have been identified through transcriptional profiling. However, no work on isolating regulatory genes for field resistance has been reported. In this study, cDNA-amplified fragment length polymorphism technique was used to identify differentially expressed transcripts between resistant tomato accession PI 114490 and susceptible variety OH 88119 at 3, 4 and 5 days post-inoculation of the pathogen. Using 256 selective primer combinations, a total of 79 differentially expressed transcript-derived fragments (TDFs) representing 71 genes were obtained. Of which, 60 were up-regulated and 4 were down-regulated in both tomato lines, 4 were uniquely up-regulated and 2 were uniquely down-regulated in PI 114490, and 1 was specifically up-regulated in OH 88119. The expression patterns of 19 representative TDFs were further confirmed by semi-quantitative and/or quantitative real time RT-PCR. These results suggested that the two tomato lines activated partly similar defensive mechanism in response to race T3 infection. The data obtained here will provide some fundamental information for elucidating the molecular mechanism of response to race T3 infection in tomato plants with field resistance.

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The Carboxy-terminus of BAK1 regulates kinase activity and is required for normal growth of Arabidopsis

The Carboxy-terminus of BAK1 regulates kinase activity and is required for normal growth of Arabidopsis | Plants&Bacteria | Scoop.it

Scooped from: Front. Plant Sci., 2014

Authors: Man-Ho Oh, Xuejun Wang, Sang Yeol Kim, Xia Wu, Steven D. Clouse and Steven C. Huber

 

Abstract:

Binding of brassinolide to the brassinosteroid-insenstive 1(BRI1) receptor kinase promotes interaction with its co-receptor, BRI1-associated receptor kinase 1 (BAK1). Juxtaposition of the kinase domains that occurs then allows reciprocal transphosphorylation and activation of both kinases, but details of that process are not entirely clear. In the present study we show that the carboxy (C)-terminal polypeptide of BAK1 may play a role. First, we demonstrate that the C-terminal domain is a strong inhibitor of the transphosphorylation activity of the recombinant BAK1 cytoplasmic domain protein. However, recombinant BAK1 lacking the C-terminal domain is unable to transactivate the peptide kinase activity of BRI1 in vitro. Thus, the C-terminal domain may play both a positive and negative role. Interestingly, a synthetic peptide corresponding to the full C-terminal domain (residues 576–615 of BAK1) interacted with recombinant BRI1 in vitro, and that interaction was enhanced by phosphorylation at the Tyr-610 site. Expression of a BAK1 C-terminal domain truncation (designated BAK1-ΔCT-Flag) in transgenic Arabidopsis plants lacking endogenous bak1 and its functional paralog, bkk1, produced plants that were wild type in appearance but much smaller than plants expressing full-length BAK1-Flag. The reduction in growth may be attributed to a partial inhibition of BR signaling in vivo as reflected in root growth assays but other factors are likely involved as well. Our working model is that in vivo, the inhibitory action of the C-terminal domain of BAK1 is relieved by binding to BRI1. However, that interaction is not essential for BR signaling, but other aspects of cellular signaling are impacted when the C-terminal domain is truncated and result in inhibition of growth. These results increase the molecular understanding of the C-terminal domain of BAK1 as a regulator of kinase activity that may serve as a model for other receptor kinases.

 

Freddy Monteiro's insight:

Tyr phosphorilation of BAK1 Tyr residues upon deletion of C-terminal domain and interaction with BRI1

 

It may be interesting to read this beforehand:

Oh et al. Tyrosine phosphorylation of the BRI1 receptor kinase emerges as a component of brassinosteroid signaling in Arabidopsis. PNAS 2009. http://www.pnas.org/content/106/2/658.long

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Alteration of gene expression profile in the roots of wild diploid Arachis duranensis inoculated with Ralstonia solanacearum

Alteration of gene expression profile in the roots of wild diploid Arachis duranensis inoculated with Ralstonia solanacearum | Plants&Bacteria | Scoop.it

Scooped from: Plant Pathology, 2014

Authors:     Y. N. Chen, X. P. Ren, X. J. Zhou, L. Huang, J. Q. Huang, L. Y. Yan, Y. Lei, Y Qi, W. H. Wei and H. F. Jiang

 

Abstract

Bacterial wilt caused by Ralstonia solanacearum is a serious disease of peanut (Arachis hypogaea) in China. However, the molecular basis of peanut resistance to R. solanacearum is poorly understood. Arachis duranensis, a wild diploid species of the genus Arachis, has been proven to be resistant to bacterial wilt, and thus holds valuable potential for understanding the mechanism of resistance to bacterial wilt and genetic improvement of peanut disease resistance. Here, suppression subtractive hybridization (SSH) and macroarray hybridization were employed to detect differentially expressed genes (DEGs) in the roots of A. duranensis after R. solanacearum inoculation. A total of 317 unique genes were obtained, 265 of which had homologues and functional annotations. KEGG analysis revealed that a large proportion of these unigenes are mainly involved in the biosynthesis of phytoalexins, particularly in the biosynthetic pathways of terpenoids and flavonoids. Subsequent real-time polymerase chain reaction (PCR) analysis showed that the terpenoid and flavonoid synthesis-related genes showed higher expression levels in a resistant genotype of A. duranensis than in a susceptible genotype, indicating that the terpenoids and flavonoids probably played a fundamental role in the resistance of A. duranensis to R. solanacearum. This study provides an overview of the gene expression profile in the roots of wild Arachis species in response to R. solanacearum infection. Moreover, the related candidate genes are also valuable for the further study of the molecular mechanisms of resistance to R. solanacearum.

Freddy Monteiro's insight:

Terpenoids and flavonoids MIGHT be responsible for resistance of Arachis duranensis to R. solanacearum.

There's room for more studies.

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Molecular Steps in the Immune Signaling Pathway Evoked by Plant Elicitor Peptides: Ca2+-Dependent Protein Kinases, Nitric Oxide, and Reactive Oxygen Species Are Downstream from the Early Ca2+ Signal

Molecular Steps in the Immune Signaling Pathway Evoked by Plant Elicitor Peptides: Ca2+-Dependent Protein Kinases, Nitric Oxide, and Reactive Oxygen Species Are Downstream from the Early Ca2+ Signal | Plants&Bacteria | Scoop.it

Scooped from: Plant Physiology, 2013.

Authors: Yi Ma, Yichen Zhao, Robin K. Walker and Gerald A. Berkowitz.

 

Abstract:

Endogenous plant elicitor peptides (Peps) can act to facilitate immune signaling and pathogen defense responses. Binding of these peptides to the Arabidopsis (Arabidopsis thaliana) plasma membrane-localized Pep receptors (PEPRs) leads to cytosolic Ca2+ elevation, an early event in a signaling cascade that activates immune responses. This immune response includes the amplification of signaling evoked by direct perception of pathogen-associated molecular patterns by plant cells under assault. Work included in this report further characterizes the Pep immune response and identifies new molecular steps in the signal transduction cascade. The PEPR coreceptor BRASSINOSTEROID-INSENSITIVE1 Associated Kinase1 contributes to generation of the Pep-activated Ca2+ signal and leads to increased defense gene expression and resistance to a virulent bacterial pathogen. Ca2+-dependent protein kinases (CPKs) decode the Ca2+ signal, also facilitating defense gene expression and enhanced resistance to the pathogen. Nitric oxide and reduced nicotinamide adenine dinucleotide phosphate oxidase-dependent reactive oxygen species generation (due to the function of Respiratory Burst Oxidase Homolog proteins D and F) are also involved downstream from the Ca2+ signal in the Pep immune defense signal transduction cascade, as is the case with BRASSINOSTEROID-INSENSITIVE1 Associated Kinase1 and CPK5, CPK6, and CPK11. These steps of the pathogen defense response are required for maximal Pep immune activation that limits growth of a virulent bacterial pathogen in the plant. We find a synergism between function of the PEPR and Flagellin Sensing2 receptors in terms of both nitric oxide and reactive oxygen species generation. Presented results are also consistent with the involvement of the secondary messenger cyclic GMP and a cyclic GMP-activated Ca2+-conducting channel in the Pep immune signaling pathway.

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Thermo-Regulation of Genes Mediating Motility and Plant Interactions in Pseudomonas syringae

Thermo-Regulation of Genes Mediating Motility and Plant Interactions in Pseudomonas syringae | Plants&Bacteria | Scoop.it

Scooped from: PLOS ONE, 2013

Authors:  Kevin L. Hockett, Adrien Y. Burch and Steven E. Lindow

 

Abstract:

Pseudomonas syringae is an important phyllosphere colonist that utilizes flagellum-mediated motility both as a means to explore leaf surfaces, as well as to invade into leaf interiors, where it survives as a pathogen. We found that multiple forms of flagellum-mediated motility are thermo-suppressed, including swarming and swimming motility. Suppression of swarming motility occurs between 28° and 30°C, which coincides with the optimal growth temperature of P. syringae. Both fliC (encoding flagellin) and syfA (encoding a non-ribosomal peptide synthetase involved in syringafactin biosynthesis) were suppressed with increasing temperature. RNA-seq revealed 1440 genes of the P. syringae genome are temperature sensitive in expression. Genes involved in polysaccharide synthesis and regulation, phage and IS elements, type VI secretion, chemosensing and chemotaxis, translation, flagellar synthesis and motility, and phytotoxin synthesis and transport were generally repressed at 30°C, while genes involved in transcriptional regulation, quaternary ammonium compound metabolism and transport, chaperone/heat shock proteins, and hypothetical genes were generally induced at 30°C. Deletion of flgM, a key regulator in the transition from class III to class IV gene expression, led to elevated and constitutive expression of fliC regardless of temperature, but did not affect thermo-regulation of syfA. This work highlights the importance of temperature in the biology of P. syringae, as many genes encoding traits important for plant-microbe interactions were thermo-regulated.

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Regulatory network of hrp gene expression in Xanthomonas oryzae pv. oryzae

Regulatory network of hrp gene expression in Xanthomonas oryzae pv. oryzae | Plants&Bacteria | Scoop.it

Scooped from: Journal of General Plant Pathology, 2014

Authors: Seiji Tsuge, Ayako Furutani, Yumi Ikawa

 

Abstract:

Like other plant-pathogenic bacteria, Xanthomonas oryzae pv. oryzae, the causal agent of bacterial leaf blight of rice, has hrp genes that are indispensable for its virulence. The hrp genes are involved in the construction of the type III secretion (T3S) apparatus, through which dozens of virulence-related proteins, called effectors, are directly secreted into plant cells to suppress and disturb plant immune systems and/or induce plant susceptibility genes. The expression of hrp genes is strictly regulated and induced only in plants and in certain nutrient-poor media. Two proteins, HrpG and HrpX, are known as key regulators for hrp gene expression. Great efforts by many researchers have revealed unexpectedly that, besides HrpG and HrpX, many regulators are involved in this regulation, some of which also regulate the expression of virulence-related genes other than hrp. Moreover, it has been found that HrpG and HrpX regulate not only hrp genes and effector genes but also genes unrelated to the T3S system. These findings suggest that the expression of the hrp gene is orchestrally regulated with other virulence-related genes by a complicated, sophisticated regulatory network in X. oryzaepv. oryzae.

Freddy Monteiro's insight:

there you are HrcC!

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Interplay among Pseudomonas syringae HrpR, HrpS and HrpV proteins for regulation of the Type Three Secretion System

Interplay among Pseudomonas syringae HrpR, HrpS and HrpV proteins for regulation of the Type Three Secretion System | Plants&Bacteria | Scoop.it
Authors: Milija Jovanovic*, Edward Lawton, Jörg Schumacher andMartin BuckAbstractPs. syringae pv tomato DC3000, a plant pathogenic gram negative bacterium, employs the Type III Secretion System (T3SS) to cause disease in tomato and Arabidopsis and to induce the hypersensitive response in non-host plants. The expression of T3SS is regulated by the HrpL extracytoplasmic sigma factor. Expression of HrpL is controlled by transcriptional activators HrpR and HrpS and negative regulator HrpV. In this study we analysed the organization of HrpRS and HrpV regulatory proteins and interplay between them. We identified one key residue I26 in HrpS required for repression by HrpV. Substitution of I26 in HrpS abolishes its interaction with HrpV, impairs interactions between HrpS and HrpR and the self-association of HrpS. We show that HrpS self-associates and can associate simultaneously with HrpR and HrpV. We now propose that HrpS has a central role in the assembly of the regulatory HrpRSV complex. Deletion analysis of HrpR and HrpS proteins showed that C-terminal parts of HrpR and HrpS confer determinants indispensable for their self-assembly.
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PODCAST: How bacteria turn plants into zombies discussed in TWIM (This Week in Microbiology)

PODCAST: How bacteria turn plants into zombies discussed in TWIM (This Week in Microbiology) | Plants&Bacteria | Scoop.it

"Vincent Racaniello, Elio Schaechter, Michael Schmidt, and Michele Swanson review how a pathogen promotes plant attractiveness to insect vectors, and activation of sensory neurons that modulate pain and inflammation by bacterial infection". Source: http://feeds.feedburner.com/twim


"This Week in Microbiology (TWiM) is a podcast about unseen life on Earth hosted by Vincent Racaniello and friends. Following in the path of his successful shows 'This Week in Virology' (TWiV) and 'This Week in Parasitism' (TWiP), Racaniello and guests produce an informal yet informative conversation about microbes which is accessible to everyone, no matter what their science background". Source: http://www.microbeworld.org/podcasts/this-week-in-microbiology



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Original research article: http://www.nature.com/nature/journal/v508/n7495/full/508152c.html

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Salmonella enterica induces and subverts the plant immune system

Salmonella enterica induces and subverts the plant immune system | Plants&Bacteria | Scoop.it

Scooped from: Frontiers in Microbiology, 2014

Authors: Ana V. García and Heribert Hirt

 

Summary:

Infections with Salmonella enterica belong to the most prominent causes of food poisoning and infected fruits and vegetables represent important vectors for salmonellosis. Whereas it was shown that plants raise defense responses against Salmonella, these bacteria persist and proliferate in various plant tissues. Recent reports shed light into the molecular interaction between plants and Salmonella, highlighting the defense pathways induced and the means used by the bacteria to escape the plant immune system and accomplish colonization. It was recently shown that plants detect Salmonella pathogen-associated molecular patterns (PAMPs), such as the flagellin peptide flg22, and activate hallmarks of the defense program known as PAMP-triggered immunity (PTI). Interestingly, certain Salmonella strains carry mutations in the flg22 domain triggering PTI, suggesting that a strategy of Salmonella is to escape plant detection by mutating PAMP motifs. Another strategy may rely on the type III secretion system (T3SS) as T3SS mutants were found to induce stronger plant defense responses than wild type bacteria. Although Salmonella effector delivery into plant cells has not been shown, expression of Salmonella effectors in plant tissues shows that these bacteria also possess powerful means to manipulate the plant immune system. Altogether, the data gathered suggest that Salmonella triggers PTI in plants and evolved strategies to avoid or subvert plant immunity.

Freddy Monteiro's insight:

Provocative....

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Decreased abundance of type III secretion system-inducing signals in Arabidopsis mkp1 enhances resistance against Pseudomonas syringae

Decreased abundance of type III secretion system-inducing signals in Arabidopsis mkp1 enhances resistance against Pseudomonas syringae | Plants&Bacteria | Scoop.it

Abstract

Genes encoding the virulence-promoting type III secretion system (T3SS) in phytopathogenic bacteria are induced at the start of infection, indicating that recognition of signals from the host plant initiates this response. However, the precise nature of these signals and whether their concentrations can be altered to affect the biological outcome of host–pathogen interactions remain speculative. Here we use a metabolomic comparison of resistant and susceptible genotypes to identify plant-derived metabolites that induce T3SS genes in Pseudomonas syringae pv tomato DC3000 and report that mapk phosphatase 1 (mkp1), an Arabidopsis mutant that is more resistant to bacterial infection, produces decreased levels of these bioactive compounds. Consistent with these observations, T3SS effector expression and delivery by DC3000 was impaired when infecting the mkp1 mutant. The addition of bioactive metabolites fully restored T3SS effector delivery and suppressed the enhanced resistance in the mkp1 mutant. Pretreatment of plants with pathogen-associated molecular patterns (PAMPs) to induce PAMP-triggered immunity (PTI) also restricts T3SS effector delivery and enhances resistance by unknown mechanisms, and the addition of the bioactive metabolites similarly suppressed both aspects of PTI. Together, these results demonstrate that DC3000 perceives multiple signals derived from plants to initiate its T3SS and that the level of these host-derived signals impacts bacterial pathogenesis.


Via Suayib Üstün, Jim Alfano
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HrcT is a key component of the type III secretion system in Xanthomonas and also regulates the expression of the key hrp transcriptional activator HrpX

HrcT is a key component of the type III secretion system in Xanthomonas and also regulates the expression of the key hrp transcriptional activator HrpX | Plants&Bacteria | Scoop.it

Scooped from: Applied and Environmental Microbiology, 2014

Authors: Zhi-Yang Liu, Li-Fang Zou, Xiao-Bo Xue, Lu-Lu Cai, Wen-Xiu Ma, Li Xiong, Zhi-Yuan Ji and Gong-You Chen.

 

Summary:

The type III secretion system (T3SS), encoded by hrp (hypersensitive response and pathogenicity) genes in Gram-negative phytopathogenic bacteria, delivers repertoires of T3SS effectors (T3SEs) into plant cells to trigger the hypersensitive response (HR) in nonhost or resistant host plants and promote pathogenicity in susceptible plants. The expression of hrp genes in Xanthomonas is regulated by two key regulatory proteins, HrpG and HrpX. However, the interactions between hrp gene products in directing T3SE secretion are largely unknown. Here we demonstrated that HrcT of X. oryzae pv. oryzicola (Xoc) functions as a T3SS component and positively regulates the expression of hrpX. Transcription of hrcT occurs via two distinct promoters, one is with the hrpB operon (T1) and the second (T3) within hrpB7. Via either T1 or T3 promoter, the defect in Hrp phenotype by hrcT deletion was restored in the presence of hrcT only from Xanthomonas species, but not other phytopathogenic bacteria. An N-terminally truncated HrcT was able to bind the hrpX promoter and activate the expression of hrpX, supporting that HrcT is a positive regulator of hrpX. A revised model showing the regulatory interactions between HrcT, HrpX and HrpG is proposed.

Freddy Monteiro's insight:

Glad to know I was following the right path... it was a question of time before seeing this fine-tuning mechanisms described in plant pathogenic bacteria. This is a MUST reference for genetic studies of pathogenicity.

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PLoS ONE: Real Time Live Imaging of Phytopathogenic Bacteria Xanthomonas campestris pv. campestris MAFF106712 in ‘Plant Sweet Home’ (2014)

PLoS ONE: Real Time Live Imaging of Phytopathogenic Bacteria Xanthomonas campestris pv. campestris MAFF106712 in ‘Plant Sweet Home’ (2014) | Plants&Bacteria | Scoop.it

Xanthomonas is one of the most widespread phytobacteria, causing diseases on a variety of agricultural plants. To develop novel control techniques, knowledge of bacterial behavior inside plant cells is essential. Xanthomonas campestris pv. campestris, a vascular pathogen, is the causal agent of black rot on leaves of Brassicaceae, including Arabidopsis thaliana. Among the X. campestris pv. campestris stocks in the MAFF collection, we selected XccMAFF106712 as a model compatible pathogen for the A. thaliana reference ecotype Columbia (Col-0). Using modified green fluorescent protein (AcGFP) as a reporter, we observed real time XccMAFF106712 colonization in planta with confocal microscopy. AcGFP-expressing bacteria colonized the inside of epidermal cells and the apoplast, as well as the xylem vessels of the vasculature. In the case of the type III mutant, bacteria colonization was never detected in the xylem vessel or apoplast, though they freely enter the xylem vessel through the wound. After 9 days post inoculation with XccMAFF106712, the xylem vessel became filled with bacterial aggregates. This suggests that Xcc colonization can be divided into main four steps, (1) movement in the xylem vessel, (2) movement to the next cell, (3) adhesion to the host plant cells, and (4) formation of bacterial aggregates. The type III mutant abolished at least steps (1) and (2). Better understanding of Xcc colonization is essential for development of novel control techniques for black rot.

 

Chiharu Akimoto-Tomiyama,  Ayako Furutani,  Hirokazu Ochiai

 


Via Nicolas Denancé
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Freddy Monteiro's comment, April 17, 9:21 AM
"Real-time imaging of showing release of bacteria from the xylem vessel is shown in Movies S8, S9. The bacteria seemed to be aggregated inside the xylem vessel 9 days post inoculation (Figures 7B, S2, Movie S9), with the size of the aggregates depending on each xylem vessel. Notably, the size of the aggregates within a single xylem vessel was relatively consistent. In contrast, bacteria from a xylem vessel only 6 days post inoculation (Figure 7A, Movie S8) seemed not to make such bacterial aggregates, but rather to remain as single cells. The size of bacterial aggregates was measured as pixels of the area showing AcGFP fluorescence, demonstrating the size of the aggregates dramatically increases between 6 and 9 days (Figure 7C). We also noted that the released bacterial aggregates did not move, while single bacteria moved vigorously (Movie S10). At 6 days post inoculation, the infected site in the xylem vessel appeared transversely extended (Movie S4) and most of the bacteria did not move (Movie S3). From these observations, we conclude that active single bacteria with high motility move freely inside the xylem vessel, and upon finding a suitable niche (such as one with a low abundance of other bacteria), they adhere to the plant cells and starts multiplying"
Freddy Monteiro's comment, April 17, 9:24 AM
I find that excerpt very interesting. A similar discussion was held in my PhD defense regarding R.solanacearum infection. This is a nice piece of work =)
Suayib Üstün's comment, April 18, 8:17 AM
interesting, however citation 46 is wrong. should be üstün et al., 2013. ;-)
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Commonalities and differences of T3SSs in rhizobia and plant pathogenic bacteria

Commonalities and differences of T3SSs in rhizobia and plant pathogenic bacteria | Plants&Bacteria | Scoop.it

Scooped from: Front Plant Sci., 2014

Author: Anastasia P. Tampakaki

 

Summary:

Plant pathogenic bacteria and rhizobia infect higher plants albeit the interactions with their hosts are principally distinct and lead to completely different phenotypic outcomes, either pathogenic or mutualistic, respectively. Bacterial protein delivery to plant host plays an essential role in determining the phenotypic outcome of plant-bacteria interactions. The involvement of type III secretion systems (T3SSs) in mediating animal- and plant-pathogen interactions was discovered in the mid-80’s and is now recognized as a multiprotein nanomachine dedicated to trans-kingdom movement of effector proteins. The discovery of T3SS in bacteria with symbiotic lifestyles broadened its role beyond virulence. In most T3SS-positive bacterial pathogens, virulence is largely dependent on functional T3SSs, while in rhizobia the system is dispensable for nodulation and can affect positively or negatively the mutualistic associations with their hosts. This review focuses on recent comparative genome analyses in plant pathogens and rhizobia that uncovered similarities and variations among T3SSs in their genetic organization, regulatory networks and type III secreted proteins and discusses the evolutionary adaptations of T3SSs and type III secreted proteins that might account for the distinguishable phenotypes and host range characteristics of plant pathogens and symbionts.

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HopZ4 from Pseudomonas syringae, a member of the HopZ type III effector family from the YopJ superfamily, inhibits the proteasome in plants

HopZ4 from Pseudomonas syringae, a member of the HopZ type III effector family from the YopJ superfamily, inhibits the proteasome in plants | Plants&Bacteria | Scoop.it

The YopJ-family of type III effector (T3E) proteins is one of the largest and widely distributed families of effector proteins whose members are highly diversified in virulence functions. In the present study, HopZ4, a member of the YopJ-family of T3Es from the cucumber pathogen Pseudomonas syringae pv. lachrymans is described. HopZ4 shares high sequence similarity with the Xanthomonas T3E XopJ and a functional analysis suggests a conserved virulence function between these two T3Es. As has previously shown for XopJ, HopZ4 interacts with the proteasomal subunit RPT6 in yeast and in planta to inhibit proteasome activity during infection. The inhibitory effect on the proteasome is dependent on localization of HopZ4 to the plasma membrane as well as on an intact catalytic triad of the effector protein. Furthermore, HopZ4 is able to complement loss of XopJ in Xanthomonas as it prevents precocious host cell death during a compatible interaction of Xanthomonas with pepper. The data presented here suggest that different bacterial species employ inhibition of the proteasome as a virulence strategy by making use of conserved T3Es from the YopJ-family of bacterial effector proteins.


Via Suayib Üstün
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