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Trends in MPMI
Molecular Plant Microbe Interaction
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Identification of nuclear target proteins for S-nitrosylation in pathogen-treated Arabidopsis thaliana cell cultures

Identification of nuclear target proteins for S-nitrosylation in pathogen-treated Arabidopsis thaliana cell cultures | Trends in MPMI | Scoop.it
Highlights



117 nuclear proteins were identified as targets for S-nitrosylation.


Nuclear proteins involved in protein and RNA metabolism are the dominant targets.


In these target proteins 155 S-nitrosylation sites were predicted.


S-Nitrosylation of plant-specific histone deacetylases was demonstrated.

Abstract

Nitric oxide (NO) is a significant signalling molecule involved in the regulation of many different physiological processes in plants. One of the most imperative regulatory modes of action of NO is protein S-nitrosylation—the covalent attachment of an NO group to the sulfur atom of cysteine residues. In this study, we focus on S-nitrosylation of Arabidopsis nuclear proteins after pathogen infection. After treatment of Arabidopsis suspension cell cultures with pathogens, nuclear proteins were extracted and treated with the S-nitrosylating agent S-nitrosoglutathione (GSNO). A biotin switch assay was performed and biotin-labelled proteins were purified by neutravidin affinity chromatography and identified by mass spectrometry. A total of 135 proteins were identified, whereas nuclear localization has been described for 122 proteins of them. 117 of these proteins contain at least one cysteine residue. Most of the S-nitrosylated candidates were involved in protein and RNA metabolism, stress response, and cell organization and division. Interestingly, two plant-specific histone deacetylases were identified suggesting that nitric oxide regulated epigenetic processes in plants. In sum, this work provides a new collection of targets for protein S-nitrosylation in Arabidopsis and gives insight into the regulatory function of NO in the nucleus during plant defense response. Moreover, our data extend the knowledge on the regulatory function of NO in events located in the nucleus.

Via Christophe Jacquet
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Redox rhythm reinforces the circadian clock to gate immune response : Nature : Nature Publishing Group

Redox rhythm reinforces the circadian clock to gate immune response : Nature : Nature Publishing Group | Trends in MPMI | Scoop.it
Recent studies have shown that in addition to the transcriptional circadian clock, many organisms, including Arabidopsis, have a circadian redox rhythm driven by the organism’s metabolic activities1, 2, 3. It has been hypothesized that the redox rhythm is linked to the circadian clock, but the mechanism and the biological significance of this link have only begun to be investigated4, 5, 6, 7. Here we report that the master immune regulator NPR1 (non-expressor of pathogenesis-related gene 1) of Arabidopsis is a sensor of the plant’s redox state and regulates transcription of core circadian clock genes even in the absence of pathogen challenge. Surprisingly, acute perturbation in the redox status triggered by the immune signal salicylic acid does not compromise the circadian clock but rather leads to its reinforcement. Mathematical modelling and subsequent experiments show that NPR1 reinforces the circadian clock without changing the period by regulating both the morning and the evening clock genes. This balanced network architecture helps plants gate their immune responses towards the morning and minimize costs on growth at night. Our study demonstrates how a sensitive redox rhythm interacts with a robust circadian clock to ensure proper responsiveness to environmental stimuli without compromising fitness of the organism.

Via Suayib Üstün
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Frontiers | Does plant immunity play a critical role during initiation of the legume-rhizobium symbiosis? | Plant-Microbe Interaction

Frontiers | Does plant immunity play a critical role during initiation of the legume-rhizobium symbiosis? | Plant-Microbe Interaction | Trends in MPMI | Scoop.it
Plants are exposed to many different microbes in their habitats. These microbes may be benign or pathogenic, but in some cases they are beneficial for the host. The rhizosphere provides an especially rich palette for colonization by beneficial (associative and symbiotic) microorganisms, which raises the question as to how roots can distinguish such ‘friends’ from possible ‘foes’ (i.e., pathogens). Plants possess an innate immune system that can recognize pathogens, through an arsenal of protein receptors, including receptor-like kinases (RLKs) and receptor-like proteins (RLPs) located at the plasma membrane. In addition, the plant host has intracellular receptors (so called NBS-LRR proteins or R proteins) that directly or indirectly recognize molecules released by microbes into the plant cell. A successful cooperation between legume plants and rhizobia leads to beneficial symbiotic interaction. The key rhizobial, symbiotic signaling molecules [lipo-chitooligosaccharide Nod factors (NF)] are perceived by the host legume plant using lysin motif-domain containing RLKs. Perception of the symbiotic NFs trigger signaling cascades leading to bacterial infection and accommodation of the symbiont in a newly formed root organ, the nodule, resulting in a nitrogen-fixing root nodule symbiosis. The net result of this symbiosis is the intracellular colonization of the plant with thousands of bacteria; a process that seems to occur in spite of the immune ability of plants to prevent pathogen infection. In this review, we discuss the potential of the invading rhizobial symbiont to actively avoid this innate immune response, as well as specific examples of where the plant immune response may modulate rhizobial infection and host range.

Via Francis Martin, Jennifer Mach
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14-3-3 Proteins in Plant-Pathogen Interactions

14-3-3 Proteins in Plant-Pathogen Interactions | Trends in MPMI | Scoop.it

14-3-3 proteins define a eukaryotic-specific protein family with a general role in signal transduction. Primarily, 14-3-3 proteins act as phosphosensors, binding phosphorylated client proteins and modulating their functions. Since phosphorylation regulates a plethora of different physiological responses in plants, 14-3-3 proteins play roles in multiple signaling pathways, including those controlling metabolism, hormone signaling, cell division, and responses to abiotic and biotic stimuli. Increasing evidence supports a prominent role of 14-3-3 proteins in regulating plant immunity against pathogens at various levels. In this review, potential links between 14-3-3 function and the regulation of plant-pathogen interactions are discussed, with a special focus on the regulation of 14-3-3 proteins in response to pathogen perception, interactions between 14-3-3 proteins and defense-related proteins, and 14-3-3 proteins as targets of pathogen effectors.


Via Christophe Jacquet
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Chloroplasts play a central role in plant defence and are targeted by pathogen effectors

Chloroplasts play a central role in plant defence and are targeted by pathogen effectors | Trends in MPMI | Scoop.it

Microbe associated molecular pattern (MAMP) receptors in plants recognize MAMPs and activate basal defences; however a complete understanding of the molecular and physiological mechanisms conferring immunity remains elusive. Pathogens suppress active defence in plants through the combined action of effector proteins. Here we show that the chloroplast is a key component of early immune responses. MAMP perception triggers the rapid, large-scale suppression of nuclear encoded chloroplast-targeted genes (NECGs). Virulent Pseudomonas syringae effectors reprogramme NECG expression in Arabidopsis, target the chloroplast and inhibit photosynthetic CO2assimilation through disruption of photosystem II. This activity prevents a chloroplastic reactive oxygen burst. These physiological changes precede bacterial multiplication and coincide with pathogen-induced abscisic acid (ABA) accumulation. MAMP pretreatment protects chloroplasts from effector manipulation, whereas application of ABA or the inhibitor of photosynthetic electron transport, DCMU, abolishes the MAMP-induced chloroplastic reactive oxygen burst, and enhances growth of a P. syringae hrpA mutant that fails to secrete effectors.


Via Jennifer Mach
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Feasibility of new breeding techniques for organic farming: Trends in Plant Science

•Organic farming suffers from lower productivity than conventional agriculture because the use of pesticides, herbicides, and fertilizers is restricted.•Rewilding furnishes crops with lost properties that their ancestors once had to tolerate adverse environmental conditions.•Rewilding is in accordance with the values of organic breeding and would contribute to closing the yield gap.•New breeding techniques that involve methods of genetic engineering allow for rewilding in a way that the final crop cannot be distinguished from a crop bred by traditional means.

 

Organic farming is based on the concept of working ‘with nature’ instead of against it; however, compared with conventional farming, organic farming reportedly has lower productivity. Ideally, the goal should be to narrow this yield gap. In this review, we specifically discuss the feasibility of new breeding techniques (NBTs) for rewilding, a process involving the reintroduction of properties from the wild relatives of crops, as a method to close the productivity gap. The most efficient methods of rewilding are based on modern biotechnology techniques, which have yet to be embraced by the organic farming movement. Thus, the question arises of whether the adoption of such methods is feasible, not only from a technological perspective, but also from conceptual, socioeconomic, ethical, and regulatory perspectives.


Via Jennifer Mach
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Jennifer Mach's curator insight, May 29, 8:51 AM

Re-wilding: it's a thing!

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Autophagic Degradation of the 26S Proteasome Is Mediated by the Dual ATG8/Ubiquitin Receptor RPN10 in Arabidopsis

Autophagic Degradation of the 26S Proteasome Is Mediated by the Dual ATG8/Ubiquitin Receptor RPN10 in Arabidopsis | Trends in MPMI | Scoop.it

Highlights•

The Arabidopsis 26S proteasome is degraded by ATG8-mediated autophagy

This degradation is induced by nitrogen starvation and proteasome inhibition

Proteasome inhibition stimulates extensive ubiquitylation of the complex

RPN10 acts as a proteaphagy receptor by binding ubiquitylated proteasomes and ATG8

Summary

Autophagic turnover of intracellular constituents is critical for cellular housekeeping, nutrient recycling, and various aspects of growth and development in eukaryotes. Here we show that autophagy impacts the other major degradative route involving the ubiquitin-proteasome system by eliminating 26S proteasomes, a process we termed proteaphagy. Using Arabidopsis proteasomes tagged with GFP, we observed their deposition into vacuoles via a route requiring components of the autophagy machinery. This transport can be initiated separately by nitrogen starvation and chemical or genetic inhibition of the proteasome, implying distinct induction mechanisms. Proteasome inhibition stimulates comprehensive ubiquitylation of the complex, with the ensuing proteaphagy requiring the proteasome subunit RPN10, which can simultaneously bind both ATG8 and ubiquitin. Collectively, we propose that Arabidopsis RPN10 acts as a selective autophagy receptor that targets inactive 26S proteasomes by concurrent interactions with ubiquitylated proteasome subunits/targets and lipidated ATG8 lining the enveloping autophagic membranes.


Via Christophe Jacquet, Suayib Üstün
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Treasure Your Exceptions: Unusual Domains in Immune Receptors Reveal Host Virulence Targets: Cell

Treasure Your Exceptions: Unusual Domains in Immune Receptors Reveal Host Virulence Targets: Cell | Trends in MPMI | Scoop.it

Summary:

A mechanistic understanding of how plant pathogens modulate their hosts is critical for rationally engineered disease resistance in agricultural systems. Two new studies show that genomically paired plant immune receptors have incorporated decoy domains that structurally mimic pathogen virulence targets to monitor attempted host immunosuppression.


Via Freddy Monteiro, Elsa Ballini
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Freddy Monteiro's curator insight, May 21, 1:02 PM

This is a short introduction to the back-to-back pieces:

 

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

 

2. A Receptor Pair with an Integrated Decoy Converts Pathogen Disabling of Transcription Factors to Immunity http://www.cell.com/cell/abstract/S0092-8674%2815%2900442-0

 

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Cell: A Plant Immune Receptor Detects Pathogen Effectors that Target WRKY Transcription Factors (2015)

Cell: A Plant Immune Receptor Detects Pathogen Effectors that Target WRKY Transcription Factors (2015) | Trends in MPMI | Scoop.it

Defense against pathogens in multicellular eukaryotes depends on intracellular immune receptors, yet surveillance by these receptors is poorly understood. Several plant nucleotide-binding, leucine-rich repeat (NB-LRR) immune receptors carry fusions with other protein domains. The Arabidopsis RRS1-R NB-LRR protein carries a C-terminal WRKY DNA binding domain and forms a receptor complex with RPS4, another NB-LRR protein. This complex detects the bacterial effectors AvrRps4 or PopP2 and then activates defense. Both bacterial proteins interact with the RRS1 WRKY domain, and PopP2 acetylates lysines to block DNA binding. PopP2 and AvrRps4 interact with other WRKY domain-containing proteins, suggesting these effectors interfere with WRKY transcription factor-dependent defense, and RPS4/RRS1 has integrated a “decoy” domain that enables detection of effectors that target WRKY proteins. We propose that NB-LRR receptor pairs, one member of which carries an additional protein domain, enable perception of pathogen effectors whose function is to target that domain.

 

Panagiotis F. Sarris, Zane Duxbury, Sung Un Huh, Yan Ma, Cécile Segonzac, Jan Sklenar, Paul Derbyshire, Volkan Cevik, Ghanasyam Rallapalli, Simon B. Saucet, Lennart Wirthmueller, Frank L.H. Menke, Kee Hoon Sohn, Jonathan D.G. Jones


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Front. Microbiol.: Phylogenomics of Xanthomonas field strains infecting pepper and tomato reveals diversity in effector repertoires and identifies determinants of host specificity (2015)

Front. Microbiol.: Phylogenomics of Xanthomonas field strains infecting pepper and tomato reveals diversity in effector repertoires and identifies determinants of host specificity (2015) | Trends in MPMI | Scoop.it

Bacterial spot disease of pepper and tomato is caused by four distinct Xanthomonas species and is a severely limiting factor on fruit yield in these crops. The genetic diversity and the type III effector repertoires of a large sampling of field strains for this disease have yet to be explored on a genomic scale, limiting our understanding of pathogen evolution in an agricultural setting. Genomes of sixty-seven Xanthomonas euvesicatoria (Xe), Xanthomonas perforans (Xp), and Xanthomonas gardneri (Xg) strains isolated from diseased pepper and tomato fields in the southeastern and midwestern United States were sequenced in order to determine the genetic diversity in field strains. Type III effector repertoires were computationally predicted for each strain, and multiple methods of constructing phylogenies were employed to understand better the genetic relationship of strains in the collection. A division in the Xp population was detected based on core genome phylogeny, supporting a model whereby the host-range expansion of Xp field strains on pepper is due, in part, to a loss of the effector AvrBsT. Xp-host compatibility was further studied with the observation that a double deletion mutant of AvrBsT and XopQ in Xp experiences a host gain for Nicotiana benthamiana. Extensive sampling of field strains and an improved understanding of effector content will aid in efforts to design disease resistance strategies targeted against highly conserved core effectors.

 

Schwartz AR, Potnis N, Timilsina S, Wilson M, Patane J, Martins J, Minsavage GV, Dahlbeck D, Akhunova A, Almeida N, Vallad GE, Barak JD, White FF, Miller SA, Ritchie D, Goss E, Bart RS, Setubal JC, Jones JB and Staskawicz BJ

 

 


Via Nicolas Denancé, Suayib Üstün
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Utilization of TALEN and CRISPR/Cas9 technologies for gene targeting and modification - Exp. Biol. Med.

Pu et al, 2015

The capability to modify the genome precisely and efficiently offers an extremely useful tool for biomedical research. Recent developments in genome editing technologies such as transcription activator-like effector nuclease and the clustered regularly interspaced short palindromic repeats system have made genome modification available for a number of organisms with relative ease. Here, we introduce these genome editing techniques, compare and contrast each technical approach and discuss their potential to study the underlying mechanisms of human disease using patient-derived induced pluripotent stem cells.


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Frontiers | Proteasome targeting of proteins in Arabidopsis leaf mesophyll, epidermal and vascular tissues | Plant Systems and Synthetic Biology

Protein and transcript levels are partly decoupled as a function of translation efficiency and protein degradation. Selective protein degradation via the Ubiquitin-26S proteasome system (UPS) ensures protein homeostasis and facilitates adjustment of protein abundance during changing environmental conditions. Since individual leaf tissues have specialized functions, their protein composition is different and hence also protein level regulation is expected to differ. To understand UPS function in a tissue-specific context we developed a method termed Meselect to effectively and rapidly separate Arabidopsis thaliana leaf epidermal, vascular and mesophyll tissues. Epidermal and vascular tissue cells are separated mechanically, while mesophyll cells are obtained after rapid protoplasting. The high yield of proteins was sufficient for tissue-specific proteome analyses after inhibition of the proteasome with the specific inhibitor Syringolin A (SylA) and affinity enrichment of ubiquitylated proteins. SylA treatment of leaves resulted in the accumulation of 225 proteins and identification of 519 ubiquitylated proteins. Proteins that were exclusively identified in the three different tissue types are consistent with specific cellular functions. Mesophyll cell proteins were enriched for plastid membrane translocation complexes as targets of the UPS. Epidermis enzymes of the TCA cycle and cell wall biosynthesis specifically accumulated after proteasome inhibition, and in the vascular tissue several enzymes involved in glucosinolate biosynthesis were found to be ubiquitylated. Our results demonstrate that protein level changes and UPS protein targets are characteristic of the individual leaf tissues and that the proteasome is relevant for tissue-specific functions.


Via Suayib Üstün
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Plant immunity triggered by engineered in vivo release of oligogalacturonides, damage-associated molecular patterns

Plant immunity triggered by engineered in vivo release of oligogalacturonides, damage-associated molecular patterns | Trends in MPMI | Scoop.it
Significance

Damage-associated molecular patterns (DAMPs), released from host tissues as a consequence of pathogen attack, have been proposed as endogenous activators of immune responses in both animals and plants. Oligogalacturonides (OGs), oligomers of α-1,4–linked galacturonic acid generated in vitro by the partial hydrolysis of pectin, have been shown to function as potent elicitors of immunity when they are applied exogenously to plant tissues. However, there is no direct evidence that OGs can be produced in vivo or that they function as immune elicitors. This report provides the missing evidence that OGs can be generated in planta and can function as DAMPs in the activation of plant immunity.
Abstract

Oligogalacturonides (OGs) are fragments of pectin that activate plant innate immunity by functioning as damage-associated molecular patterns (DAMPs). We set out to test the hypothesis that OGs are generated in planta by partial inhibition of pathogen-encoded polygalacturonases (PGs). A gene encoding a fungal PG was fused with a gene encoding a plant polygalacturonase-inhibiting protein (PGIP) and expressed in transgenic Arabidopsis plants. We show that expression of the PGIP–PG chimera results in the in vivo production of OGs that can be detected by mass spectrometric analysis. Transgenic plants expressing the chimera under control of a pathogen-inducible promoter are more resistant to the phytopathogens Botrytis cinerea, Pectobacterium carotovorum, and Pseudomonas syringae. These data provide strong evidence for the hypothesis that OGs released in vivo act as a DAMP signal to trigger plant immunity and suggest that controlled release of these molecules upon infection may be a valuable tool to protect plants against infectious diseases. On the other hand, elevated levels of expression of the chimera cause the accumulation of salicylic acid, reduced growth, and eventually lead to plant death, consistent with the current notion that trade-off occurs between growth and defense.

Via Christophe Jacquet
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Rice Blast on Facebook

Rice Blast on Facebook | Trends in MPMI | Scoop.it
Rice blast disease is caused by the fungus Magnaporthe oryzae (synonym Pyricularia oryzae).

Via Elsa Ballini
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Lipids in salicylic acid-mediated defense in plants: focusing on the roles of phosphatidic acid and phosphatidylinositol 4-phosphate

Lipids in salicylic acid-mediated defense in plants: focusing on the roles of phosphatidic acid and phosphatidylinositol 4-phosphate | Trends in MPMI | Scoop.it
Plants have evolved effective defense strategies to protect themselves from various pathogens. Salicylic acid (SA) is an essential signaling molecule that mediates pathogen-triggered signals perceived by different immune receptors to induce downstream defense responses. While many proteins play essential roles in regulating SA signaling, increasing evidence also supports important roles for signaling phospholipids in this process. In this review, we collate the experimental evidence in support of the regulatory roles of two phospholipids, phosphatidic acid (PA) and phosphatidylinositol 4-phosphate (PI4P), and their metabolizing enzymes in plant defense, and examine the possible mechanistic interaction between phospholipid signaling and SA-dependent immunity with a particular focus on the immunity-stimulated biphasic PA production that is reminiscent of and perhaps mechanistically connected to the biphasic reactive oxygen species (ROS) generation and SA accumulation during defense activation.

Via Christophe Jacquet
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Salicylic acid biosynthesis is enhanced and contributes to increased biotrophic pathogen resistance in Arabidopsis hybrids : Nature Communications : Nature Publishing Group

Salicylic acid biosynthesis is enhanced and contributes to increased biotrophic pathogen resistance in Arabidopsis hybrids : Nature Communications : Nature Publishing Group | Trends in MPMI | Scoop.it
Heterosis, the phenotypic superiority of a hybrid over its parents, has been demonstrated for many traits in Arabidopsis thaliana, but its effect on defence remains largely unexplored. Here, we show that hybrids between some A. thaliana accessions show increased resistance to the biotrophic bacterial pathogen Pseudomonas syringae pv. tomato (Pst) DC3000. Comparisons of transcriptomes between these hybrids and their parents after inoculation reveal that several key salicylic acid (SA) biosynthesis genes are significantly upregulated in hybrids. Moreover, SA levels are higher in hybrids than in either parent. Increased resistance to Pst DC3000 is significantly compromised in hybrids of pad4 mutants in which the SA biosynthesis pathway is blocked. Finally, increased histone H3 acetylation of key SA biosynthesis genes correlates with their upregulation in infected hybrids. Our data demonstrate that enhanced activation of SA biosynthesis in A. thaliana hybrids may contribute to their increased resistance to a biotrophic bacterial pathogen.

Via Christophe Jacquet
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Microbiology and Molecular Biology Reviews: Oomycete Interactions with Plants: Infection Strategies and Resistance Principles (2015)

Microbiology and Molecular Biology Reviews: Oomycete Interactions with Plants: Infection Strategies and Resistance Principles (2015) | Trends in MPMI | Scoop.it

The Oomycota include many economically significant microbial pathogens of crop species. Understanding the mechanisms by which oomycetes infect plants and identifying methods to provide durable resistance are major research goals. Over the last few years, many elicitors that trigger plant immunity have been identified, as well as host genes that mediate susceptibility to oomycete pathogens. The mechanisms behind these processes have subsequently been investigated and many new discoveries made, marking a period of exciting research in the oomycete pathology field. This review provides an introduction to our current knowledge of the pathogenic mechanisms used by oomycetes, including elicitors and effectors, plus an overview of the major principles of host resistance: the established R gene hypothesis and the more recently defined susceptibility (S) gene model. Future directions for development of oomycete-resistant plants are discussed, along with ways that recent discoveries in the field of oomycete-plant interactions are generating novel means of studying how pathogen and symbiont colonizations overlap.


Via Kamoun Lab @ TSL, Niklaus Grunwald, Jennifer Mach
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RiboTALE: A modular, inducible system for accurate gene expression control - Sci. Reports

RiboTALE: A modular, inducible system for accurate gene expression control - Sci. Reports | Trends in MPMI | Scoop.it

(via T. Schreiber, thx)

Rai et al, 2015

A limiting factor in synthetic gene circuit design is the number of independent control elements that can be combined together in a single system. Here, we present RiboTALEs, a new class of inducible repressors that combine the specificity of TALEs with the ability of riboswitches to recognize exogenous signals and differentially control protein abundance. We demonstrate the capacity of RiboTALEs, constructed through different combinations of TALE proteins and riboswitches, to rapidly and reproducibly control the expression of downstream targets with a dynamic range of 243.7 ± 17.6-fold, which is adequate for many biotechnological applications.


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Capping protein integrates multiple MAMP signalling pathways to modulate actin dynamics during plant innate immunity : Nature Communications : Nature Publishing Group

Capping protein integrates multiple MAMP signalling pathways to modulate actin dynamics during plant innate immunity : Nature Communications : Nature Publishing Group | Trends in MPMI | Scoop.it
Plants and animals perceive diverse microbe-associated molecular patterns (MAMPs) via pattern recognition receptors and activate innate immune signalling. The actin cytoskeleton has been suggested as a target for innate immune signalling and a key transducer of cellular responses. However, the molecular mechanisms underlying actin remodelling and the precise functions of these rearrangements during innate immunity remain largely unknown. Here we demonstrate rapid actin remodelling in response to several distinct MAMP signalling pathways in plant epidermal cells. The regulation of actin dynamics is a convergence point for basal defence machinery, such as cell wall fortification and transcriptional reprogramming. Our quantitative analyses of actin dynamics and genetic studies reveal that MAMP-stimulated actin remodelling is due to the inhibition of capping protein (CP) by the signalling lipid, phosphatidic acid. In addition, CP promotes resistance against bacterial and fungal phytopathogens. These findings demonstrate that CP is a central target for the plant innate immune response.

Via Suayib Üstün
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Repression of microRNA biogenesis by silencing of OsDCL1 activates the basal resistance to Magnaporthe oryzae in rice

Highlights



OsDCL1 RNAi lines showed enhanced resistance to rice blast.


A negative feedback loop between miR162a and OsDCL1 was identified.


Differentially expressed miRNAs responsive to rice blast infection were identified.


PR and PTI responsive genes were constitutively activated in OsDCL1 RNAi lines.

Abstract

The RNaseIII enzyme Dicer-like 1 (DCL1) processes the microRNA biogenesis and plays a determinant role in plant development. In this study, we reported the function of OsDCL1 in the immunity to rice blast, the devastating disease caused by the fungal pathogen, Magnaporthe oryzae. Expression profiling demonstrated that different OsDCLs responded dynamically and OsDCL1 reduced its expression upon the challenge of rice blast pathogen. In contrast, miR162a predicted to target OsDCL1 increased its expression, implying a negative feedback loop between OsDCL1 and miR162a in rice. In addition to developmental defects, the OsDCL1-silencing mutants showed enhanced resistance to virulent rice blast strains in a non-race specific manner. Accumulation of hydrogen peroxide and cell death were observed in the contact cells with infectious hyphae, revealing that silencing of OsDCL1 activated cellular defense responses. In OsDCL1 RNAi lines, 12 differentially expressed miRNAs were identified, of which 5 and 7 were down- and up-regulated, respectively, indicating that miRNAs responded dynamically in the interaction between rice and rice blast. Moreover, silencing of OsDCL1 activated the constitutive expression of defense related genes. Taken together, our results indicate that rice is capable of activating basal resistance against rice blast by perturbing OsDCL1-dependent miRNA biogenesis pathway.

Via Christophe Jacquet
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Cell: A Receptor Pair with an Integrated Decoy Converts Pathogen Disabling of Transcription Factors to Immunity (2015)

Cell: A Receptor Pair with an Integrated Decoy Converts Pathogen Disabling of Transcription Factors to Immunity (2015) | Trends in MPMI | Scoop.it

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.

 

Clémentine Le Roux, Gaëlle Huet, Alain Jauneau, Laurent Camborde, Dominique Trémousaygue, Alexandra Kraut, Binbin Zhou, Marie Levaillant, Hiroaki Adachi, Hirofumi Yoshioka, Sylvain Raffaele, Richard Berthomé, Yohann Couté, Jane E. Parker, Laurent Deslandes


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Growing rice in controlled environments

Growing rice in controlled environments | Trends in MPMI | Scoop.it
Rice (Oryza sativa) is less frequently used in basic research than Arabidopsis, although rice is a valuable model system for many monocot crops and possesses a high genetic variability in physiologically as well as agriculturally relevant features such as abiotic stress tolerance, nutrient efficiency and flower time control. A reason is the seemingly difficult cultivation of rice outside the rice production area. This review aims to assist newcomers to the field to develop cultivation protocols for their local controlled environment. The main challenges are high light demands, photoperiodicity and low micronutrient efficiency. The nutrient efficiency problem can be overcome by adding micronutrient fertiliser to potting substrates and keeping the soil waterlogged to increase micronutrient availability and mobility. Cultivation of rice on adjusted hydroponic solutions with high iron concentration provides the basis for successful heavy isotope labelling. Many rice cultivars need high light intensities in combination with short-day conditions to complete their life cycle. However, some photoperiod-insensitive cultivars will flower even under relatively low light intensities. In highly photoperiod-sensitive cultivars, like Nipponbare, flowering can be induced by a limited period of short-day treatment in the sensitive period, after which the cultivation can be continued in long-day conditions. The life cycle of many cultivars is completed in 90 to 120 days, its length being thus comparable to Arabidopsis and shorter than in other cereals. In conclusion, with the right cultivation technique, rice is an amiable model species for researchers beyond the rice area too.

Via Jean-Michel Ané, Jennifer Mach
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Can This Scientist Unite Genetic Engineers and Organic Farmers?

Can This Scientist Unite Genetic Engineers and Organic Farmers? | Trends in MPMI | Scoop.it
Pamela Ronald isolates genes in rice that feeds millions. Her integrative approach to agriculture could be an even bigger game-changer.
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The Barley Powdery Mildew Candidate Secreted Effector Protein CSEP0105 Inhibits the Chaperone Activity of a Small Heat Shock Protein

The Barley Powdery Mildew Candidate Secreted Effector Protein CSEP0105 Inhibits the Chaperone Activity of a Small Heat Shock Protein | Trends in MPMI | Scoop.it
Pathogens secrete effector proteins to establish a successful interaction with their host. Here, we describe two barley (Hordeum vulgare) powdery mildew candidate secreted effector proteins, CSEP0105 and CSEP0162, which contribute to pathogen success and appear to be required during or after haustorial formation. Silencing of either CSEP using host-induced gene silencing significantly reduced the fungal haustorial formation rate. Interestingly, both CSEPs interact with the barley small heat shock proteins, Hsp16.9 and Hsp17.5, in a yeast two-hybrid assay. Small heat shock proteins are known to stabilize several intracellular proteins, including defense-related signaling components, through their chaperone activity. CSEP0105 and CSEP0162 localized to the cytosol and the nucleus of barley epidermal cells, whereas Hsp16.9 and Hsp17.5 are cytosolic. Intriguingly, only those specific CSEPs changed localization and became restricted to the cytosol when coexpressed with Hsp16.9 and Hsp17.5, confirming the CSEP-small heat shock protein interaction. As predicted, Hsp16.9 showed chaperone activity, as it could prevent the aggregation of Escherichia coli proteins during thermal stress. Remarkably, CSEP0105 compromised this activity. These data suggest that CSEP0105 promotes virulence by interfering with the chaperone activity of a barley small heat shock protein essential for defense and stress responses.

Via Christophe Jacquet
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The genome of cultivated sweet potato contains Agrobacterium T-DNAs with expressed genes: An example of a naturally transgenic food crop

The genome of cultivated sweet potato contains Agrobacterium T-DNAs with expressed genes: An example of a naturally transgenic food crop | Trends in MPMI | Scoop.it
Significance

We communicate the rather remarkable observation that among 291 tested accessions of cultivated sweet potato, all contain one or more transfer DNA (T-DNA) sequences. These sequences, which are shown to be expressed in a cultivated sweet potato clone (“Huachano”) that was analyzed in detail, suggest that an Agrobacterium infection occurred in evolutionary times. One of the T-DNAs is apparently present in all cultivated sweet potato clones, but not in the crop’s closely related wild relatives, suggesting the T-DNA provided a trait or traits that were selected for during domestication. This finding draws attention to the importance of plant–microbe interactions, and given that this crop has been eaten for millennia, it may change the paradigm governing the “unnatural” status of transgenic crops.
Abstract

Agrobacterium rhizogenes and Agrobacterium tumefaciens are plant pathogenic bacteria capable of transferring DNA fragments [transfer DNA (T-DNA)] bearing functional genes into the host plant genome. This naturally occurring mechanism has been adapted by plant biotechnologists to develop genetically modified crops that today are grown on more than 10% of the world’s arable land, although their use can result in considerable controversy. While assembling small interfering RNAs, or siRNAs, of sweet potato plants for metagenomic analysis, sequences homologous to T-DNA sequences from Agrobacterium spp. were discovered. Simple and quantitative PCR, Southern blotting, genome walking, and bacterial artificial chromosome library screening and sequencing unambiguously demonstrated that two different T-DNA regions (IbT-DNA1 and IbT-DNA2) are present in the cultivated sweet potato (Ipomoea batatas [L.] Lam.) genome and that these foreign genes are expressed at detectable levels in different tissues of the sweet potato plant. IbT-DNA1 was found to contain four open reading frames (ORFs) homologous to the tryptophan-2-monooxygenase (iaaM), indole-3-acetamide hydrolase (iaaH), C-protein (C-prot), and agrocinopine synthase (Acs) genes of Agrobacterium spp. IbT-DNA1 was detected in all 291 cultigens examined, but not in close wild relatives. IbT-DNA2 contained at least five ORFs with significant homology to the ORF14, ORF17n, rooting locus (Rol)B/RolC, ORF13, and ORF18/ORF17n genes of A. rhizogenes. IbT-DNA2 was detected in 45 of 217 genotypes that included both cultivated and wild species. Our finding, that sweet potato is naturally transgenic while being a widely and traditionally consumed food crop, could affect the current consumer distrust of the safety of transgenic food crops.

Via Christophe Jacquet
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