Ralstonia solanacearum of tomato
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Ralstonia solanacearum of tomato
Ralstonia solanacearum of tomato
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Frontiers: TALE-Like Effectors Are an Ancestral Feature of the Ralstonia solanacearum Species Complex and Converge in DNA Targeting Specificity (2016)

Frontiers: TALE-Like Effectors Are an Ancestral Feature of the Ralstonia solanacearum Species Complex and Converge in DNA Targeting Specificity (2016) | Ralstonia solanacearum of tomato | Scoop.it

Ralstonia solanacearum, a species complex of bacterial plant pathogens divided into four monophyletic phylotypes, causes plant diseases in tropical climates around the world. Some strains exhibit a broad host range on solanaceous hosts, while others are highly host-specific as for example some banana-pathogenic strains. Previous studies showed that transcription activator-like (TAL) effectors from Ralstonia, termed RipTALs, are capable of activating reporter genes in planta, if these are preceded by a matching effector binding element (EBE). RipTALs target DNA via their central repeat domain (CRD), where one repeat pairs with one DNA-base of the given EBE. The repeat variable diresidue dictates base repeat specificity in a predictable fashion, known as the TALE code. In this work, we analyze RipTALs across all phylotypes of the Ralstonia solanacearum species complex. We find that RipTALs are prevalent in phylotypes I and IV but absent from most phylotype III and II strains (10/12, 8/14, 1/24, and 1/5 strains contained a RipTAL, respectively). RipTALs originating from strains of the same phylotype show high levels of sequence similarity (>98%) in the N-terminal and C-terminal regions, while RipTALs isolated from different phylotypes show 47–91% sequence similarity in those regions, giving rise to four RipTAL classes. We show that, despite sequence divergence, the base preference for guanine, mediated by the N-terminal region, is conserved across RipTALs of all classes. Using the number and order of repeats found in the CRD, we functionally sub-classify RipTALs, introduce a new simple nomenclature, and predict matching EBEs for all seven distinct RipTALs identified. We experimentally study RipTAL EBEs and uncover that some RipTALs are able to target the EBEs of other RipTALs, referred to as cross-reactivity. In particular, RipTALs from strains with a broad host range on solanaceous hosts cross-react on each other’s EBEs. Investigation of sequence divergence between RipTAL repeats allows for a reconstruction of repeat array biogenesis, for example through slipped strand mispairing or gene conversion. Using these studies we show how RipTALs of broad host range strains evolved convergently toward a shared target sequence. Finally, we discuss the differences between TALE-likes of plant pathogens in the context of disease ecology.


Via Kamoun Lab @ TSL
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Rescooped by tianxing84 from Host-Microbe Interactions. Plant Biology.
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Escaping Underground Nets: Extracellular DNases Degrade Plant Extracellular Traps and Contribute to Virulence of the Plant Pathogenic Bacterium Ralstonia solanacearum

Escaping Underground Nets: Extracellular DNases Degrade Plant Extracellular Traps and Contribute to Virulence of the Plant Pathogenic Bacterium  Ralstonia solanacearum | Ralstonia solanacearum of tomato | Scoop.it
Author Summary Plant root tips are covered by a protective sleeve of loosely attached border cells that can release a matrix containing proteins, polysaccharides, and DNA. In animal immune systems, extracellular DNA forms the backbone of neutrophil extracellular traps (NETs) deployed by immune cells to immobilize and kill invading microbes. Some animal pathogens can secrete DNases to degrade NETs and facilitate infection. We found that plant border cells release DNA-containing extracellular traps in response to the high-impact plant pathogenic bacterium Ralstonia solanacearum . R . solanacearum secretes two DNases that free the pathogen from these extracellular traps. The bacterium needs these DNases for full virulence and normal colonization of its host plants. This work reveals that, like animal pathogens, the plant pathogen R . solanacearum can overcome a DNA-based host defense system with secreted enzymes.

Via Tatsuya Nobori
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Two linked pairs of Arabidopsis TNL resistance genes independently confer recognition of bacterial effector AvrRps4 : Nature Communications : Nature Publishing Group

Two linked pairs of Arabidopsis TNL resistance genes independently confer recognition of bacterial effector AvrRps4 : Nature Communications : Nature Publishing Group | Ralstonia solanacearum of tomato | Scoop.it
Plant immunity requires recognition of pathogen effectors by intracellular NB-LRR immune receptors encoded by Resistance (R) genes. Most R proteins recognize a specific effector, but some function in pairs that recognize multiple effectors. Arabidopsis thaliana TIR-NB-LRR proteins RRS1-R and RPS4 together recognize two bacterial effectors, AvrRps4 from Pseudomonas syringae and PopP2 from Ralstonia solanacearum. However, AvrRps4, but not PopP2, is recognized in rrs1/rps4 mutants. We reveal an R gene pair that resembles and is linked to RRS1/RPS4, designated as RRS1B/RPS4B, which confers recognition of AvrRps4 but not PopP2. Like RRS1/RPS4, RRS1B/RPS4B proteins associate and activate defence genes upon AvrRps4 recognition. Inappropriate combinations (RRS1/RPS4B or RRS1B/RPS4) are non-functional and this specificity is not TIR domain dependent. Distinct putative orthologues of both pairs are maintained in the genomes of Arabidopsis thaliana relatives and are likely derived from a common ancestor pair. Our results provide novel insights into paired R gene function and evolution.

Via The Sainsbury Lab, Kamoun Lab @ TSL, Christophe Jacquet
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PLOS Genetics: The Nuclear Immune Receptor RPS4 Is Required for RRS1SLH1-Dependent Constitutive Defense Activation in Arabidopsis thaliana (2014)

PLOS Genetics: The Nuclear Immune Receptor RPS4 Is Required for RRS1SLH1-Dependent Constitutive Defense Activation in Arabidopsis thaliana (2014) | Ralstonia solanacearum of tomato | Scoop.it

Plant nucleotide-binding leucine-rich repeat (NB-LRR) disease resistance (R) proteins recognize specific “avirulent” pathogen effectors and activate immune responses. NB-LRR proteins structurally and functionally resemble mammalian Nod-like receptors (NLRs). How NB-LRR and NLR proteins activate defense is poorly understood. The divergently transcribed Arabidopsis R genes, RPS4 (resistance to Pseudomonas syringae 4) and RRS1 (resistance to Ralstonia solanacearum 1), function together to confer recognition of PseudomonasAvrRps4 and Ralstonia PopP2. RRS1 is the only known recessive NB-LRR R gene and encodes a WRKY DNA binding domain, prompting suggestions that it acts downstream of RPS4 for transcriptional activation of defense genes. We define here the early RRS1-dependent transcriptional changes upon delivery of PopP2 via Pseudomonas type III secretion. The Arabidopsis slh1 (sensitive to low humidity 1) mutant encodes an RRS1 allele (RRS1SLH1) with a single amino acid (leucine) insertion in the WRKY DNA-binding domain. Its poor growth due to constitutive defense activation is rescued at higher temperature. Transcription profiling data indicate that RRS1SLH1-mediated defense activation overlaps substantially with AvrRps4- and PopP2-regulated responses. To better understand the genetic basis of RPS4/RRS1-dependent immunity, we performed a genetic screen to identify suppressor of slh1 immunity (sushi) mutants. We show that many sushi mutants carry mutations in RPS4, suggesting that RPS4 acts downstream or in a complex with RRS1. Interestingly, several mutations were identified in a domain C-terminal to the RPS4 LRR domain. Using an Agrobacterium-mediated transient assay system, we demonstrate that the P-loop motif of RPS4 but not of RRS1SLH1 is required for RRS1SLH1 function. We also recapitulate the dominant suppression of RRS1SLH1 defense activation by wild type RRS1 and show this suppression requires an intact RRS1 P-loop. These analyses of RRS1SLH1shed new light on mechanisms by which NB-LRR protein pairs activate defense signaling, or are held inactive in the absence of a pathogen effector.


Via Kamoun Lab @ TSL
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Molecular chaperons and co-chaperons, Hsp90, RAR1, and SGT1 negatively regulate bacterial wilt disease caused by Ralstonia solanacearum in Nicotiana benthamiana

Molecular chaperons and co-chaperons, Hsp90, RAR1, and SGT1 negatively regulate bacterial wilt disease caused by Ralstonia solanacearum in Nicotiana benthamiana | Ralstonia solanacearum of tomato | Scoop.it
Ralstonia solanacearum is the causal agent of bacterial wilt disease. To better understand the molecular mechanisms involved in interaction between Nicotiana benthamiana and R. solanacearum, we focused on Hsp90, RAR1 and SGT1. Appearances of wilt symptom were significantly suppressed in Hsp90, RAR1 and SGT1-silenced plants compared with control plants. In RAR1-silenced plants, population of R. solanacearum increased in a similar manner to control plants. In contrast, multiplication of R. solanacearum was significantly suppressed in Hsp90 and SGT1-silenced plants. In addition, expression of PR genes were increased in Hsp90 and SGT1-silenced plants challenged with R. solanacearum. Therefore, RAR1 might be required for disease development or suppression of disease tolerance. These results also suggested that Hsp90 and/or SGT1 might play an important role in suppression of plant defenses leading to disease susceptibility and disease development.

Via Christophe Jacquet
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Pepper CabZIP63 acts as a positive regulator during Ralstonia solanacearum or high temperature–high humidity challenge in a positive feedback loop with CaWRKY40

Pepper CabZIP63 acts as a positive regulator during Ralstonia solanacearum or high temperature–high humidity challenge in a positive feedback loop with CaWRKY40 | Ralstonia solanacearum of tomato | Scoop.it
CaWRKY40 is known to act as a positive regulator in the response of pepper (Capsicum annuum) to Ralstonia solanacearum inoculation (RSI) or high temperature–high humidity (HTHH), but the underlying mechanism remains elusive. Herein, we report that CabZIP63, a pepper bZIP family member, participates in this process by regulating the expression of CaWRKY40. CabZIP63 was found to localize in the nuclei, be up-regulated by RSI or HTHH, bind to promoters of both CabZIP63 (pCabZIP63) and CaWRKY40 (pCaWRKY40), and activate pCabZIP63- and pCaWRKY40-driven β-glucuronidase expression in a C- or G-box-dependent manner. Silencing of CabZIP63 by virus-induced gene silencing (VIGS) in pepper plants significantly attenuated their resistance to RSI and tolerance to HTHH, accompanied by down-regulation of immunity- or thermotolerance-associated CaPR1, CaNPR1, CaDEF1, and CaHSP24. Hypersensitive response-mediated cell death and expression of the tested immunity- and thermotolerance-associated marker genes were induced by transient overexpression (TOE) of CabZIP63, but decreased by that of CabZIP63-SRDX. Additionally, binding of CabZIP63 to pCaWRKY40 was up-regulated by RSI or HTHH, and the transcript level of CaWRKY40 and binding of CaWRKY40 to the promoters of CaPR1, CaNPR1, CaDEF1 and CaHSP24 were up-regulated by TOE of CabZIP63. On the other hand, CabZIP63 was also up-regulated transcriptionally by TOE of CaWRKY40. The data suggest collectively that CabZIP63 directly or indirectly regulates the expression of CaWRKY40 at both the transcriptional and post-transcriptional level, forming a positive feedback loop with CaWRKY40 during pepper’s response to RSI or HTHH. Altogether, our data will help to elucidate the underlying mechanism of crosstalk between pepper’s response to RSI and HTHH.

Via Christophe Jacquet
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BMC Genomics: Repertoire, unified nomenclature and evolution of the Type III effector gene set in the Ralstonia solanacearum species complex (2013)

BMC Genomics: Repertoire, unified nomenclature and evolution of the Type III effector gene set in the Ralstonia solanacearum species complex (2013) | Ralstonia solanacearum of tomato | Scoop.it

Ralstonia solanacearum is a soil-borne beta-proteobacterium that causes bacterial wilt disease in many food crops and is a major problem for agriculture in intertropical regions. R. solanacearum is a heterogeneous species, both phenotypically and genetically, and is considered as a species complex. Pathogenicity of R. solanacearum relies on the Type III secretion system that injects Type III effector (T3E) proteins into plant cells. T3E collectively perturb host cell processes and modulate plant immunity to enable bacterial infection. We provide the catalogue of T3E in the R. solanacearum species complex, as well as candidates in newly sequenced strains. 95 T3E orthologous groups were defined on phylogenetic bases and ordered using a uniform nomenclature. This curated T3E catalog is available on a public website and a bioinformatic pipeline has been designed to rapidly predict T3E genes in newly sequenced strains. Systematical analyses were performed to detect lateral T3E gene transfer events and identify T3E genes under positive selection. Our analyses also pinpoint the RipF translocon proteins as major discriminating determinants among the phylogenetic lineages. Establishment of T3E repertoires in strains representatives of the R. solanacearum biodiversity allowed determining a set of 22 T3E present in all the strains but provided no clues on host specificity determinants. The definition of a standardized nomenclature and the optimization of predictive tools will pave the way to understanding how variation of these repertoires is correlated to the diversification of this species complex and how they contribute to the different strain pathotypes. 

 

Nemo Peeters, Sébastien Carrère, Maria Anisimova, Laure Plener, Anne-Claire Cazalé and Stephane Genin

 

Database interface: https://iant.toulouse.inra.fr/bacteria/annotation/cgi/ralso_effectome/ralso_effectome.cgi


Via Nicolas Denancé
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MPMI: A novel, sensitive method to evaluate potato germplasm for bacterial wilt resistance using a luminescent Ralstonia solanacearum reporter strain (2013)

MPMI: A novel, sensitive method to evaluate potato germplasm for bacterial wilt resistance using a luminescent Ralstonia solanacearum reporter strain (2013) | Ralstonia solanacearum of tomato | Scoop.it

Several breeding programs are under way to introduce resistance to bacterial wilt caused by Ralstonia solanacearum in solanaceous crops. The lack of screening methods allowing easy measurement of pathogen colonization and the inability to detect latent (i.e. symptomless) infections are major limitations when evaluating resistance to this disease in plant germplasm. We describe a new method to study the interaction between R. solanacearum and potato germplasm that overcomes these restrictions. The R. solanacearum strain UY031 was genetically modified to constitutively generate light from a synthetic luxCDABE operon stably inserted in its chromosome. Colonization of this reporter strain on different potato accessions was followed using life imaging. Bacterial detection in planta by this non-disruptive system correlated with the development of wilting symptoms. In addition, we demonstrated that quantitative detection of the recombinant strain using a luminometer can identify latent infections on symptomless potato plants. We have developed a novel, unsophisticated and accurate method for high-throughput evaluation of pathogen colonization in plant populations. We applied this method to compare the behavior of potato accessions with contrasting resistance to R. solanacearum. This new system will be especially useful to detect latency in symptomless parental lines before their inclusion in long-term breeding programs for disease resistance.


Via Kamoun Lab @ TSL
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Gene transcription analysis during interaction between potato and Ralstonia solanacearum

Gene transcription analysis during interaction between potato and Ralstonia solanacearum | Ralstonia solanacearum of tomato | Scoop.it

Scooped from: Russian Journal of Plant Physiology, 2010

Authors: G. C. Li, L. P. Jin, X. W. Wang, K. Y. Xie, Y. Yang, E. A. G. van  der Vossen, S. W. Huang and D. Y. Qu

 

Summary:

Bacterial wilt (BW) caused by Ralstonia solanacearum (Rs) is an important quarantine disease that spreads worldwide and infects hundreds of plant species. The BW defense response of potato is a complicated continuous process, which involves transcription of a battery of genes. The molecular mechanisms of potato-Rs interactions are poorly understood. In this study, we combined suppression subtractive hybridization and macroarray hybridization to identify genes that are differentially expressed during the incompatible interaction between Rs and potato. In total, 302 differentially expressed genes were identified and classified into 12 groups according to their putative biological functions. Of 302 genes, 81 were considered as Rs resistance-related genes based on the homology to genes of known function, and they have putative roles in pathogen recognition, signal transduction, transcription factor functioning, hypersensitive response, systemic acquired resistance, and cell rescue and protection. Additionally, 50 out of 302 genes had no match or low similarity in the NCBI databases, and they may represent novel genes. Of seven interesting genes analyzed via RNA gel blot and semi-quantitative RT-PCR, six were induced, one was suppressed, and all had different transcription patterns. The results demonstrate that the response of potato against Rs is rapid and involves the induction of numerous various genes. The genes identified in this study add to our knowledge of potato resistance to Rs.


Via Freddy Monteiro
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Freddy Monteiro's comment, June 28, 2013 6:21 PM
See also these related publications: http://sco.lt/61d49x
Freddy Monteiro's comment, June 28, 2013 6:25 PM
and http://mbio.asm.org/content/3/4/e00114-12.full
Rescooped by tianxing84 from of Plants & Bacteria (and sometimes other fellows too)
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Ethylene emission and PR protein synthesis in ACC deaminase producing Methylobacterium spp. inoculated tomato plants (Lycopersicon esculentum Mill.) challenged with Ralstonia solanacearum under gre...

Ethylene emission and PR protein synthesis in ACC deaminase producing Methylobacterium spp. inoculated tomato plants (Lycopersicon esculentum Mill.) challenged with Ralstonia solanacearum under gre... | Ralstonia solanacearum of tomato | Scoop.it

Scooped from: Plant Physiology and Biochemistry, 2013

Authors: Woojong Yima, Sundaram Seshadrib, Kiyoon Kima, Gillseung Leec, Tongmin Sa

 

Summary:

Bacteria of genus Methylobacterium have been found to promote plant growth and regulate the level of ethylene in crop plants. This work is aimed to test the induction of defense responses in tomato against bacterial wilt by stress ethylene level reduction mediated by the ACC deaminase activity of Methylobacterium strains. Under greenhouse conditions, the disease index value in Methylobacterium sp. inoculated tomato plants was lower than control plants. Plants treated with Methylobacterium sp. challenge inoculated with Ralstonia solanacearum (RS) showed significantly reduced disease symptoms and lowered ethylene emission under greenhouse condition. The ACC and ACO (1-aminocyclopropane-1-carboxylate oxidase) accumulation in tomato leaves were significantly reduced with Methylobacterium strains inoculation. While ACC oxidase gene expression was found higher in plants treated with R. solanacearum than Methylobacterium sp. treatment, PR proteins related to induced systemic resistance like β-1,3-glucanase, PAL, PO and PPO were increased in Methylobacterium sp. inoculated plants. A significant increase in β-1,3-glucanase and PAL gene expression was found in all the Methylobacterium spp. treatments compared to the R. solanacearum treatment. This study confirms the activity of Methylobacterium sp. in increasing the defense enzymes by modulating the ethylene biosynthesis pathway and suggests the use of methylotrophic bacteria as potential biocontrol agents in tomato cultivation.


Via Freddy Monteiro
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Mol. Plant Pathol.: Ralstonia solanacearum, a widespread bacterial plant pathogen in the post-genomic era (2013)

Mol. Plant Pathol.: Ralstonia solanacearum, a widespread bacterial plant pathogen in the post-genomic era (2013) | Ralstonia solanacearum of tomato | Scoop.it

Summary

Ralstonia solanacearum is a soil-borne bacterium causing the widespread disease known as bacterial wilt. Ralstonia solanacearum is also the causal agent of Moko disease of banana and brown rot of potato. Since the last R. solanacearum pathogen profile was published 10 years ago, studies concerning this plant pathogen have taken a genomic and post-genomic direction. This was pioneered by the first sequenced and annotated genome for a major plant bacterial pathogen and followed by many more genomes in subsequent years. All molecular features studied now have a genomic flavour. In the future, this will help in connecting the classical field of pathology and diversity studies with the gene content of specific strains. In this review, we summarize the recent research on this bacterial pathogen, including strain classification, host range, pathogenicity determinants, regulation of virulence genes, type III effector repertoire, effector-triggered immunity, plant signalling in response to R. solanacearum, as well as a review of different new pathosystems.

Taxonomy

Bacteria; Proteobacteria; β subdivision; Ralstonia group; genus Ralstonia.

Disease symptoms

Ralstonia solanacearum is the agent of bacterial wilt of plants, characterized by a sudden wilt of the whole plant. Typically, stem cross-sections will ooze a slimy bacterial exudate. In the case of Moko disease of banana and brown rot of potato, there is also visible bacterial colonization of banana fruit and potato tuber.

Disease control

As a soil-borne pathogen, infected fields can rarely be reused, even after rotation with nonhost plants. The disease is controlled by the use of resistant and tolerant plant cultivars. The prevention of spread of the disease has been achieved, in some instances, by the application of strict prophylactic sanitation practices.

Useful websites

Stock centre: International Centre for Microbial Resources—French Collection for Plant-associated Bacteria CIRM-CFBP, IRHS UMR 1345 INRA-ACO-UA, 42 rue Georges Morel, 49070 Beaucouzé Cedex, France, http://www.angers-nantes.inra.fr/cfbp/. Ralstonia Genome browser: https://iant.toulouse.inra.fr/R.solanacearum. GMI1000 insertion mutant library: https://iant.toulouse.inra.fr/R.solanacearumGMI1000/GenomicResources. MaGe Genome Browser: https://www.genoscope.cns.fr/agc/microscope/mage/viewer.php

 

Nemo Peeters, Alice Guidot, Fabienne Vailleau, and Marc Valls


Via Nicolas Denancé
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Phytopathogen type III effectors as probes of biological systems - Microbial Biotechnology

Phytopathogen type III effectors as probes of biological systems - Microbial Biotechnology | Ralstonia solanacearum of tomato | Scoop.it

Amy Huei-Yi Lee; Maggie A. Middleton; David S. Guttman; Darrell Desveaux

 

Summary:

Bacterial phytopathogens utilize a myriad of virulence factors to modulate their plant hosts in order to promote successful pathogenesis. One potent virulence strategy is to inject these virulence proteins into plant cells via the type III secretion system. Characterizing the host targets and the molecular mechanisms of type III secreted proteins, known as effectors, has illuminated our understanding of eukaryotic cell biology. As a result, these effectors can serve as molecular probes to aid in our understanding of plant cellular processes, such as immune signalling, vesicle trafficking, cytoskeleton stability and transcriptional regulation. Furthermore, given that effectors directly and specifically interact with their targets within plant cells, these virulence proteins have enormous biotechnological potential for manipulating eukaryotic systems.


Via Freddy Monteiro
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Freddy Monteiro's curator insight, February 27, 2013 3:34 AM

For quite some time effector proteins started to be regarded as potential molecular tools to investigate cellular processes. This is an expanding field and I hope effector biology may help on our understanding of plant biology and molecular evolution dynamics.

Rescooped by tianxing84 from of Plants & Bacteria (and sometimes other fellows too)
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The importance of colony morphology, and why TZC should be ALWAYS used when working with Ralstonia solanacearum


Via Freddy Monteiro
tianxing84's insight:

For quite some time now I was aware of the different phenotypes you can observe in a plate when you streak Ralstonia solanacearum. Just ecause I was correctly taught, I quickly learnt which clones to select to proceed with my experiments. However... I failed to provide an explanation to colleagues insisting on not using TZC. They claimed that colony morphology was quite obvious without it. I disagreed at the time, and I still do, but now I have a handout for all those with white colonies on their plates.

 

I am finally finding and writing important things on my thesis. And I want it to contain this kind of information as well... because not only my experiments were useful. Those obtained before 1954 may be more important to our labs nowadays.

 

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Freddy Monteiro's curator insight, January 8, 2013 11:15 AM

For quite some time now I was aware of the different phenotypes you can observe in a plate when you streak Ralstonia solanacearum. Just ecause I was correctly taught, I quickly learnt which clones to select to proceed with my experiments. However... I failed to provide an explanation to colleagues insisting on not using TZC. They claimed that colony morphology was quite obvious without it. I disagreed at the time, and I still do, but now I have a handout for all those with white colonies on their plates.

 

I am finally finding and writing important things on my thesis. And I want it to contain this kind of information as well... because not only my experiments were useful. Those obtained before 1954 may be more important to our labs nowadays.

 

Rescooped by tianxing84 from Plant hormones and signaling peptides
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l-Histidine Induces Resistance in Plants to the Bacterial Pathogen Ralstonia solanacearum Partially Through the Activation of Ethylene Signaling

l-Histidine Induces Resistance in Plants to the Bacterial Pathogen Ralstonia solanacearum Partially Through the Activation of Ethylene Signaling | Ralstonia solanacearum of tomato | Scoop.it
Wilt disease in plants, which is caused by the soil-borne bacterial pathogen Ralstonia solanacearum, is one of the most devastating plant diseases. We previously detected bacterial wilt disease-inhibiting activity in an extract from yeast cells. In the present study, we purified this activity and identified one of the substances responsible for the activity as the amino acid histidine. The exogenous application of l-histidine, but not d-histidine, inhibited wilt disease in tomato and Arabidopsis plants without exhibiting any antibacterial activity. l-Histidine induced the expression of genes related to ethylene (ET) biosynthesis and signaling as well as the production of ET in tomato and Arabidopsis plants. l-Histidine-induced resistance to R. solanacearum was partially abolished in ein3-1, an ET-insensitive Arabidopsis mutant line. Resistance to the fungal pathogen Botrytis cinerea, which is known to require ET biosynthesis or signaling, was also induced by exogenously applied l-histidine. These results suggest that l-histidine induces resistance to R. solanacearum and B. cinerea partially through the activation of ET signaling in plants.

Via Christophe Jacquet
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Nature Communications: Two linked pairs of Arabidopsis TNL resistance genes independently confer recognition of bacterial effector ​AvrRps4 (2015)

Nature Communications: Two linked pairs of Arabidopsis TNL resistance genes independently confer recognition of bacterial effector ​AvrRps4 (2015) | Ralstonia solanacearum of tomato | Scoop.it

Plant immunity requires recognition of pathogen effectors by intracellular NB-LRR immune receptors encoded by Resistance (R) genes. Most R proteins recognize a specific effector, but some function in pairs that recognize multiple effectors. Arabidopsis thaliana TIR-NB-LRR proteins RRS1-R and RPS4together recognize two bacterial effectors, AvrRps4 from Pseudomonas syringae and PopP2 from Ralstonia solanacearum. However, AvrRps4, but not PopP2, is recognized in rrs1/rps4 mutants. We reveal an R gene pair that resembles and is linked to RRS1/RPS4, designated as RRS1B/RPS4B, which confers recognition of AvrRps4 but not PopP2. Like RRS1/RPS4, RRS1B/RPS4B proteins associate and activate defence genes upon AvrRps4 recognition. Inappropriate combinations (RRS1/RPS4B or RRS1B/RPS4) are non-functional and this specificity is not TIR domain dependent. Distinct putative orthologues of both pairs are maintained in the genomes of Arabidopsis thalianarelatives and are likely derived from a common ancestor pair. Our results provide novel insights into paired R gene function and evolution.


Via The Sainsbury Lab, Kamoun Lab @ TSL
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The Sainsbury Lab's curator insight, March 6, 2015 3:09 PM

Plant immunity requires recognition of pathogen effectors by intracellular NB-LRR immune receptors encoded by Resistance (R) genes. Most R proteins recognize a specific effector, but some function in pairs that recognize multiple effectors. Arabidopsis thaliana TIR-NB-LRR proteins RRS1-R and RPS4together recognize two bacterial effectors, AvrRps4 from Pseudomonas syringae and PopP2 from Ralstonia solanacearum. However, AvrRps4, but not PopP2, is recognized in rrs1/rps4 mutants. We reveal an R gene pair that resembles and is linked to RRS1/RPS4, designated as RRS1B/RPS4B, which confers recognition of AvrRps4 but not PopP2. Like RRS1/RPS4, RRS1B/RPS4B proteins associate and activate defence genes upon AvrRps4 recognition. Inappropriate combinations (RRS1/RPS4B or RRS1B/RPS4) are non-functional and this specificity is not TIR domain dependent. Distinct putative orthologues of both pairs are maintained in the genomes of Arabidopsis thalianarelatives and are likely derived from a common ancestor pair. Our results provide novel insights into paired R gene function and evolution.

Rescooped by tianxing84 from Plant immunity and legume symbiosis
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A Receptor Pair with an Integrated Decoy Converts Pathogen Disabling of Transcription Factors to Immunity: Cell

A Receptor Pair with an Integrated Decoy Converts Pathogen Disabling of Transcription Factors to Immunity: Cell | Ralstonia solanacearum of tomato | Scoop.it

Summary:

Microbial pathogens infect host cells by delivering virulence factors (effectors) that interfere with defenses. In plants, intracellular nucleotide-binding/leucine-rich repeat receptors (NLRs) detect specific effector interference and trigger immunity by an unknown mechanism. The Arabidopsis-interacting NLR pair, RRS1-R with RPS4, confers resistance to different pathogens, including Ralstonia solanacearum bacteria expressing the acetyltransferase effector PopP2. We show that PopP2 directly acetylates a key lysine within an additional C-terminal WRKY transcription factor domain of RRS1-R that binds DNA. This disrupts RRS1-R DNA association and activates RPS4-dependent immunity. PopP2 uses the same lysine acetylation strategy to target multiple defense-promoting WRKY transcription factors, causing loss of WRKY-DNA binding and transactivating functions needed for defense gene expression and disease resistance. Thus, RRS1-R integrates an effector target with an NLR complex at the DNA to switch a potent bacterial virulence activity into defense gene activation.


Via Freddy Monteiro, Christophe Jacquet
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Freddy Monteiro's curator insight, May 21, 2015 12:55 PM

See also the back-to-back paper:

A Plant Immune Receptor Detects Pathogen Effectors that Target WRKY Transcription Factors. www.cell.com/cell/abstract/S0092-8674(15)00441-9

 

See also the preview:

Treasure Your Exceptions: Unusual Domains in Immune Receptors Reveal Host Virulence Targets. http://www.cell.com/cell/abstract/S0092-8674%2815%2900566-8

Rescooped by tianxing84 from Plant pathogens and pests
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PLOS ONE: Defining the Metabolic Functions and Roles in Virulence of the rpoN1 and rpoN2 Genes in Ralstonia solanacearum GMI1000

PLOS ONE: Defining the Metabolic Functions and Roles in Virulence of the rpoN1 and rpoN2 Genes in Ralstonia solanacearum GMI1000 | Ralstonia solanacearum of tomato | Scoop.it
The alternative sigma factor RpoN is a unique regulator found among bacteria. It controls numerous processes that range from basic metabolism to more complex functions such as motility and nitrogen fixation. Our current understanding of RpoN function is largely derived from studies on prototypical bacteria such as Escherichia coli. Bacillus subtilis and Pseudomonas putida. Although the extent and necessity of RpoN-dependent functions differ radically between these model organisms, each bacterium depends on a single chromosomal rpoN gene to meet the cellular demands of RpoN regulation. The bacterium Ralstonia solanacearum is often recognized for being the causative agent of wilt disease in crops, including banana, peanut and potato. However, this plant pathogen is also one of the few bacterial species whose genome possesses dual rpoN genes. To determine if the rpoN genes in this bacterium are genetically redundant and interchangeable, we constructed and characterized ΔrpoN1, ΔrpoN2 and ΔrpoN1 ΔrpoN2 mutants of R. solanacearum GMI1000. It was found that growth on a small range of metabolites, including dicarboxylates, ethanol, nitrate, ornithine, proline and xanthine, were dependent on only the rpoN1 gene. Furthermore, the rpoN1 gene was required for wilt disease on tomato whereas rpoN2 had no observable role in virulence or metabolism in R. solanacearum GMI1000. Interestingly, plasmid-based expression of rpoN2 did not fully rescue the metabolic deficiencies of the ΔrpoN1 mutants; full recovery was specific to rpoN1. In comparison, only rpoN2 was able to genetically complement a ΔrpoN E. coli mutant. These results demonstrate that the RpoN1 and RpoN2 proteins are not functionally equivalent or interchangeable in R. solanacearum GMI1000.

Via Christophe Jacquet
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CaWRKY6 transcriptionally activates CaWRKY40, regulates Ralstonia solanacearum resistance, and confers high-temperature and high-humidity tolerance in pepper

CaWRKY6 transcriptionally activates CaWRKY40, regulates Ralstonia solanacearum resistance, and confers high-temperature and high-humidity tolerance in pepper | Ralstonia solanacearum of tomato | Scoop.it
High temperature (HT), high humidity (HH), and pathogen infection often co-occur and negatively affect plant growth. However, these stress factors and plant responses are generally studied in isolation. The mechanisms of synergistic responses to combined stresses are poorly understood. We isolated the subgroup IIb WRKY family member CaWRKY6 from Capsicum annuum and performed quantitative real-time PCR analysis. CaWRKY6 expression was upregulated by individual or simultaneous treatment with HT, HH, combined HT and HH (HTHH), and Ralstonia solanacearum inoculation, and responded to exogenous application of jasmonic acid (JA), ethephon, and abscisic acid (ABA). Virus-induced gene silencing of CaWRKY6 enhanced pepper plant susceptibility to R. solanacearum and HTHH, and downregulated the hypersensitive response (HR), JA-, ethylene (ET)-, and ABA-induced marker gene expression, and thermotolerance-associated expression of CaHSP24, ER-small CaSHP, and Chl-small CaHSP. CaWRKY6 overexpression in pepper attenuated the HTHH-induced suppression of resistance to R. solanacearum infection. CaWRKY6 bound to and activated the CaWRKY40 promoter in planta, which is a pepper WRKY that regulates heat-stress tolerance and R. solanacearum resistance. CaWRKY40 silencing significantly blocked HR-induced cell death and reduced transcriptional expression of CaWRKY40. These data suggest that CaWRKY6 is a positive regulator of R. solanacearum resistance and heat-stress tolerance, which occurs in part by activating CaWRKY40.

Via Christophe Jacquet
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Rescooped by tianxing84 from Plant immunity and legume symbiosis
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CaCDPK15 positively regulates pepper responses to Ralstonia solanacearum inoculation and forms a positive-feedback loop with CaWRKY40 to amplify defense signaling

CaCDPK15 positively regulates pepper responses to Ralstonia solanacearum inoculation and forms a positive-feedback loop with CaWRKY40 to amplify defense signaling | Ralstonia solanacearum of tomato | Scoop.it
CaWRKY40 is a positive regulator of pepper (Capsicum annum) response to Ralstonia solanacearum inoculation (RSI), but the underlying mechanism remains largely unknown. Here, we functionally characterize CaCDPK15 in the defense signaling mediated by CaWRKY40. Pathogen-responsive TGA, W, and ERE boxes were identified in the CaCDPK15 promoter (pCaCDPK15), and pCaCDPK15-driven GUS expression was significantly enhanced in response to RSI and exogenously applied salicylic acid, methyl jasmonate, abscisic acid, and ethephon. Virus-induced gene silencing (VIGS) of CaCDPK15 significantly increased the susceptibility of pepper to RSI and downregulated the immunity-associated markers CaNPR1, CaPR1, and CaDEF1. By contrast, transient CaCDPK15 overexpression significantly activated hypersensitive response associated cell death, upregulated the immunity-associated marker genes, upregulated CaWRKY40 expression, and enriched CaWRKY40 at the promoters of its targets genes. Although CaCDPK15 failed to interact with CaWRKY40, the direct binding of CaWRKY40 to pCaCDPK15 was detected by chromatin immunoprecipitation, which was significantly potentiated by RSI in pepper plants. These combined results suggest that RSI in pepper induces CaCDPK15 and indirectly activates downstream CaWRKY40, which in turn potentiates CaCDPK15 expression. This positive-feedback loop would amplify defense signaling against RSI and efficiently activate strong plant immunity.

Via Christophe Jacquet
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BMC Genomics: Repertoire, unified nomenclature and evolution of the Type III effector gene set in the Ralstonia solanacearum species complex (2013)

BMC Genomics: Repertoire, unified nomenclature and evolution of the Type III effector gene set in the Ralstonia solanacearum species complex (2013) | Ralstonia solanacearum of tomato | Scoop.it

Background. Ralstonia solanacearum is a soil-borne beta-proteobacterium that causes bacterial wilt disease in many food crops and is a major problem for agriculture in intertropical regions. R. solanacearum is a heterogeneous species, both phenotypically and genetically, and is considered as a species complex. Pathogenicity of R. solanacearum relies on the Type III secretion system that injects Type III effector (T3E) proteins into plant cells. T3E collectively perturb host cell processes and modulate plant immunity to enable bacterial infection.

 

Results. We provide the catalogue of T3E in the R. solanacearum species complex, as well as candidates in newly sequenced strains. 94 T3E orthologous groups were defined on phylogenetic bases and ordered using a uniform nomenclature. This curated T3E catalog is available on a public website and a bioinformatic pipeline has been designed to rapidly predict T3E genes in newly sequenced strains. Systematical analyses were performed to detect lateral T3E gene transfer events and identify T3E genes under positive selection. Our analyses also pinpoint the RipF translocon proteins as major discriminating determinants among the phylogenetic lineages.

 

Conclusions. Establishment of T3E repertoires in strains representatives of the R. solanacearum biodiversity allowed determining a set of 22 T3E present in all the strains but provided no clues on host specificity determinants. The definition of a standardized nomenclature and the optimization of predictive tools will pave the way to understanding how variation of these repertoires is correlated to the diversification of this species complex and how they contribute to the different strain pathotypes.


Via Kamoun Lab @ TSL
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Nat. Commun.: Plant immune response to pathogens differs with changing temperatures (2013)

Nat. Commun.: Plant immune response to pathogens differs with changing temperatures (2013) | Ralstonia solanacearum of tomato | Scoop.it

Temperature fluctuation is a key determinant for microbial invasion and host evasion. In contrast to mammals that maintain constant body temperature, plant temperature oscillates on a daily basis. It remains elusive how plants operate inducible defenses in response to temperature fluctuation. Here we report that ambient temperature changes lead to pronounced shifts of the following two distinct plant immune responses: pattern-triggered immunity (PTI) and effector-triggered immunity (ETI). Plants preferentially activate ETI signaling at relatively low temperatures (10–23 °C), whereas they switch to PTI signaling at moderately elevated temperatures (23–32 °C). The Arabidopsis arp6 and hta9hta11 mutants, phenocopying plants grown at elevated temperatures, exhibit enhanced PTI and yet reduced ETI responses. As the secretion of bacterial effectors favours low temperatures, whereas bacteria multiply vigorously at elevated temperatures accompanied with increased microbe-associated molecular pattern production, our findings suggest that temperature oscillation might have driven dynamic co-evolution of distinct plant immune signaling responding to pathogen physiological changes.

 

Cheng Cheng, Xiquan Gao, Baomin Feng, Jen Sheen, Libo Shan & Ping He


Via Nicolas Denancé
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Rescooped by tianxing84 from of Plants & Bacteria (and sometimes other fellows too)
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Ethylene emission and PR protein synthesis in ACC deaminase producing Methylobacterium spp. inoculated tomato plants (Lycopersicon esculentum Mill.) challenged with Ralstonia solanacearum under gre...

Ethylene emission and PR protein synthesis in ACC deaminase producing Methylobacterium spp. inoculated tomato plants (Lycopersicon esculentum Mill.) challenged with Ralstonia solanacearum under gre... | Ralstonia solanacearum of tomato | Scoop.it

Scooped from: Plant Physiology and Biochemistry, 2013

Authors: Woojong Yima, Sundaram Seshadrib, Kiyoon Kima, Gillseung Leec, Tongmin Sa

 

Summary:

Bacteria of genus Methylobacterium have been found to promote plant growth and regulate the level of ethylene in crop plants. This work is aimed to test the induction of defense responses in tomato against bacterial wilt by stress ethylene level reduction mediated by the ACC deaminase activity of Methylobacterium strains. Under greenhouse conditions, the disease index value in Methylobacterium sp. inoculated tomato plants was lower than control plants. Plants treated with Methylobacterium sp. challenge inoculated with Ralstonia solanacearum (RS) showed significantly reduced disease symptoms and lowered ethylene emission under greenhouse condition. The ACC and ACO (1-aminocyclopropane-1-carboxylate oxidase) accumulation in tomato leaves were significantly reduced with Methylobacterium strains inoculation. While ACC oxidase gene expression was found higher in plants treated with R. solanacearum than Methylobacterium sp. treatment, PR proteins related to induced systemic resistance like β-1,3-glucanase, PAL, PO and PPO were increased in Methylobacterium sp. inoculated plants. A significant increase in β-1,3-glucanase and PAL gene expression was found in all the Methylobacterium spp. treatments compared to the R. solanacearum treatment. This study confirms the activity of Methylobacterium sp. in increasing the defense enzymes by modulating the ethylene biosynthesis pathway and suggests the use of methylotrophic bacteria as potential biocontrol agents in tomato cultivation.


Via Freddy Monteiro
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Breaking the DNA-binding code of Ralstonia solanacearum TAL effectors provides new possibilities to generate plant resistance genes against bacterial wilt disease - New Phytologist

(Via T. Lahaye & T. Schreiber) De Lange et al 2013 Ralstonia solanacearum is a devastating bacterial phytopathogen with a broad host range. Ralstonia solanacearum injected effector proteins (Rips) are key to the successful invasion of host plants. We have characterized Brg11(hrpB-regulated 11), the first identified member of a class of Rips with high sequence similarity to the transcription activator-like (TAL) effectors of Xanthomonas spp., collectively termed RipTALs. Fluorescence microscopy of in planta expressed RipTALs showed nuclear localization. Domain swaps between Brg11 and Xanthomonas TAL effector (TALE) AvrBs3 (avirulence protein triggering Bs3 resistance) showed the functional interchangeability of DNA-binding and transcriptional activation domains. PCR was used to determine the sequence of brg11 homologs from strains infecting phylogenetically diverse host plants. Brg11 localizes to the nucleus and activates promoters containing a matching effector-binding element (EBE). Brg11 and homologs preferentially activate promoters containing EBEs with a 5′ terminal guanine, contrasting with the TALE preference for a 5′ thymine. Brg11 and other RipTALs probably promote disease through the transcriptional activation of host genes. Brg11 and the majority of homologs identified in this study were shown to activate similar or identical target sequences, in contrast to TALEs, which generally show highly diverse target preferences. This information provides new options for the engineering of plants resistant to R. solanacearum.


Via dromius, Nicolas Denancé
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Pathogenomics of the Ralstonia solanacearum Species Complex - Annual Review of Phytopathology

Pathogenomics of the Ralstonia solanacearum Species Complex - Annual Review of Phytopathology | Ralstonia solanacearum of tomato | Scoop.it

Stéphane Genin and Timothy P. Denny

 

A great review to catch up with the genomic analysis of the Ralstonia solanacearum scpecies complex, pathogen evolution and the sofisticated network of regulators controlling pathogenesis.

It comes just in the right time, in my opinion. Both, as stated by the authors, to refine functional studies, but also to provide a refreshed and comprehensive state of the art in the field.

 

Abstract:

Ralstonia solanacearum is a major phytopathogen that attacks many crops and other plants over a broad geographical range. The extensive genetic diversity of strains responsible for the various bacterial wilt diseases has in recent years led to the concept of an R. solanacearum species complex. Genome sequencing of more than 10 strains representative of the main phylogenetic groups has broadened our knowledge of the evolution and speciation of this pathogen and led to the identification of novel virulence-associated functions. Comparative genomic analyses are now opening the way for refined functional studies. The many molecular determinants involved in pathogenicity and host-range specificity are described, and we also summarize current understanding of their roles in pathogenesis and how their expression is tightly controlled by an intricate virulence regulatory network.


Via Freddy Monteiro
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Freddy Monteiro's curator insight, February 24, 2013 2:15 PM

I hadn't notice this sentence before:

"Even though the known regulatory networks in R. solanacearum are already quite complex, you ain’t seen nothin’ yet!"

 

 

Amanzing!!

Rescooped by tianxing84 from Plants and Microbes
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New Phytologist: Medicago truncatula DNF2 is a PI-PLC-XD-containing protein required for bacteroid persistence and prevention of nodule early senescence and defense-like reactions (2012)

New Phytologist: Medicago truncatula DNF2 is a PI-PLC-XD-containing protein required for bacteroid persistence and prevention of nodule early senescence and defense-like reactions (2012) | Ralstonia solanacearum of tomato | Scoop.it

 

Medicago truncatula and Sinorhizobium meliloti form a symbiotic association resulting in the formation of nitrogen-fixing nodules. Nodule cells contain large numbers of bacteroids which are differentiated, nitrogen-fixing forms of the symbiotic bacteria. In the nodules, symbiotic plant cells home and maintain hundreds of viable bacteria. In order to better understand the molecular mechanism sustaining the phenomenon, we searched for new plant genes required for effective symbiosis.We used a combination of forward and reverse genetics approaches to identify a gene required for nitrogen fixation, and we used cell and molecular biology to characterize the mutant phenotype and to gain an insight into gene function.The symbiotic gene DNF2 encodes a putative phosphatidylinositol phospholipase C-like protein. Nodules formed by the mutant contain a zone of infected cells reduced to a few cell layers. In this zone, bacteria do not differentiate properly into bacteroids. Furthermore, mutant nodules senesce rapidly and exhibit defense-like reactions.This atypical phenotype amongst Fix− mutants unravels dnf2 as a new actor of bacteroid persistence inside symbiotic plant cells.


Via Kamoun Lab @ TSL
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