Redox signalling and Plant Symbioses
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Frontiers | Extra-Cellular But Extra-Ordinarily Important for Cells: Apoplastic Reactive Oxygen Species Metabolism | Plant Science

Frontiers | Extra-Cellular But Extra-Ordinarily Important for Cells: Apoplastic Reactive Oxygen Species Metabolism | Plant Science | Redox signalling and Plant Symbioses | Scoop.it
Reactive oxygen species (ROS), by their very nature, are highly reactive, and it is no surprise that they can cause damage to organic molecules. In cells, ROS are produced as byproducts of many metabolic reactions, but plants are prepared for this ROS output. Even though extracellular ROS generation constitutes only a minor part of a cell’s total ROS level, this fraction is of extraordinary importance. In an active apoplastic ROS burst, it is mainly the respiratory burst oxidases and peroxidases that are engaged, and defects of these enzymes can affect plant development and stress responses. It must be highlighted that there are also other less well-known enzymatic or non-enzymatic ROS sources. There is a need for ROS detoxification in the apoplast, and almost all cellular antioxidants are present in this space, but the activity of antioxidant enzymes and the concentration of low-mass antioxidants is very low. The low antioxidant efficiency in the apoplast allows ROS to accumulate easily, which is a condition for ROS signaling. Therefore, the apoplastic ROS/antioxidant homeostasis is actively engaged in the reception and reaction to many biotic and abiotic stresses.
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The rice LysM receptor-like kinase OsCERK1 is required for the perception of short-chain chitin oligomers in arbuscular mycorrhizal signaling

The rice lysin-motif (LysM) receptor-like kinase OsCERK1 is now known to have a dual role in both pathogenic and symbiotic interactions. Following the recent discovery that the Oscerk1 mutant is unable to host arbuscular mycorrhizal (AM) fungi, we have examined whether OsCERK1 is directly involved in the perception of the short-chain chitin oligomers (Myc-COs) identified in AM fungal exudates and shown to activate nuclear calcium (Ca2+) spiking in the rice root epidermis. An Oscerk1 knockout mutant expressing the cameleon NLS-YC2.60 was used to monitor nuclear Ca2+ signaling following root treatment with either crude fungal exudates or purified Myc-COs. Compared with wild-type rice, Ca2+ spiking responses to AM fungal elicitation were absent in root atrichoblasts of the Oscerk1 mutant. By contrast, rice lines mutated in OsCEBiP, encoding the LysM receptor-like protein which associates with OsCERK1 to perceive chitin elicitors of the host immune defense pathway, responded positively to Myc-COs. These findings provide direct evidence that the bi-functional OsCERK1 plays a central role in perceiving short-chain Myc-CO signals and activating the downstream conserved symbiotic signal transduction pathway.

Via Francis Martin, Michael Wrzaczek
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An NADPH Oxidase RBOH Functions in Rice Roots during Lysigenous Aerenchyma Formation under Oxygen-Deficient Conditions. - PubMed - NCBI

Plant Cell. 2017 Apr;29(4):775-790. doi: 10.1105/tpc.16.00976. Epub 2017 Mar 28.
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PBS: The next Green Revolution may rely on microbes (2014)

PBS: The next Green Revolution may rely on microbes (2014) | Redox signalling and Plant Symbioses | Scoop.it

Ian Sanders wants to feed the world. A soft-spoken Brit, Sanders studies fungus genetics in a lab at the University of Lausanne in Switzerland. But fear not, he’s not on a mad-scientist quest to get the world to eat protein pastes made from ground-up fungi. Still, he believes—he’s sure—that these microbes will be critical to meeting the world’s future food needs.

 

Sanders’s eyes widen with delight and almost childlike glee when he talks about a microscopic life form called mycorrhizal fungus, his chosen lifetime research subject. Mycorrhizal fungi live in a tightly wound, mutually beneficial embrace with most plants on the planet. Years of dedication have made Sanders into one of the world’s foremost experts on the genetics of the microbe, and he recently was part of a team that sequenced the first mycorrhizal fungi genome.

 

Despite his drive, Sanders comes across as light-hearted as he teases and jokes with fellow researchers. But he loses his affable smile as he fires off facts about the upcoming food shortage: The world’s population is expected to increase to between 9 billion and 16 billion people. Five million people per year die of direct causes of malnutrition. Three and a half million of those are children under five. Today, we have the means to grow enough food to feed all those people, but we will most certainly need to produce more in the very near future.

 

Sanders may have come up with a way to do just that. He has successfully bred custom varieties of microbes that can help plants produce more food. It’s one of the ultimate goals of farming research—more food with, he hopes, little or no environmental downside.

 


Via Kamoun Lab @ TSL
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Curr Opin Plant Biol: Inside plant: biotrophic strategies to modulate host immunity and metabolism (2014)

Curr Opin Plant Biol: Inside plant: biotrophic strategies to modulate host immunity and metabolism (2014) | Redox signalling and Plant Symbioses | Scoop.it

Filamentous plant pathogens that establish biotrophic interactions need to avoid plant immune responses. Recent findings from different pathosystems suggest that sufficient suppression of host immunity is based on the modulation of a rather limited number of host targets. Microbial strategies to target host physiology dependent on the duration of biotrophy, the style of host tissue colonization and the degree of interference with plant development. In this article, we present current concepts in biotrophic virulence strategies and discuss mechanisms of pathogen adaptation and effector specialization.


Via Kamoun Lab @ TSL, Francis Martin
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Through the doors of perception to function in arbuscular mycorrhizal symbioses

Through the doors of perception to function in arbuscular mycorrhizal symbioses | Redox signalling and Plant Symbioses | Scoop.it

The formation of an arbuscular mycorrhizal (AM) symbiosis is initiated by the bidirectional exchange of diffusible molecules. While strigolactone hormones, secreted from plant roots, stimulate hyphal branching and fungal metabolism, fungal short-chain chitin oligomers as well as sulfated and nonsulfated lipochitooligosaccharides (s/nsMyc-LCOs) elicit pre-symbiosis responses in the host. Fungal LCO signals are structurally related to rhizobial Nod-factor LCOs. Genome-wide expression studies demonstrated that defined sets of genes were induced by Nod-, sMyc- and nsMyc-LCOs, indicating LCO-specific perception in the pre-symbiosis phase. During hyphopodium formation and the subsequent root colonization, cross-talk between plant roots and AM fungi also involves phytohormones. Notably, gibberellins control arbuscule formation via DELLA proteins, which themselves serve as positive regulators of arbuscule formation. The establishment of arbuscules is accompanied by a substantial transcriptional and post-transcriptional reprogramming of host roots, ultimately defining the unique protein composition of arbuscule-containing cells. Based on cellular expression profiles, key checkpoints of AM development as well as candidate genes encoding transcriptional regulators and regulatory microRNAs were identified. Detailed functional analyses of promoters specified short motifs sufficient for cell-autonomous gene regulation in cells harboring arbuscules, and suggested simultaneous, multi-level regulation of the mycorrhizal phosphate uptake pathway by integrating AM symbiosis and phosphate starvation response signaling.


Via Jean-Michel Ané
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Molecular Genetics of Nodulation Control in Legumes

Professor Peter M. Gresshoff
QAAFI Science Seminar -- 27 May 2014
http://www.uq.edu.au/agriculture/pete...

Most legume plants, such as soybean, are capable of nodulation, that is development of de novo organs called nodules in which the inducing bacterium, broadly called Rhizobium, is captured to allow complex differentiation of both plant and bacterium to facilitate symbiotic nitrogen fixation. This has immense economic as well as ecological and environmental benefits, as nitrogen fertiliser demand is significantly reduced.

The main questions are: how are these structures induced by the bacterium? What genes do legumes possess to facilitate that process? What genes does the plant use to control the development of these nodule structures?

We have used diverse genetic, molecular and physiological methods to generate a functional impression of these overall processes. The seminar will high-light discoveries made by the speaker's research effort over the last 30 years, leading to an in-depth understanding of key processes. Sadly, as in all science, this is just a beginning, and future insights are hoped to elucidate the inability of non-legumes to enter this nitrogen fixation symbiosis.

Via Jean-Michel Ané
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Jean-Michel Ané's curator insight, May 28, 2014 2:09 AM

Great lecture from Peter Gresshoff

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How to say: "RHIZOBIA" in English

This video teaches you how to say "RHIZOBIA" in English.

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A Paradigm for Endosymbiotic Life: Cell Differentiation of Rhizobium Bacteria Provoked by Host Plant Factors - Annual Review of Microbiology, 67(1):611

A Paradigm for Endosymbiotic Life: Cell Differentiation of Rhizobium Bacteria Provoked by Host Plant Factors - Annual Review of Microbiology, 67(1):611 | Redox signalling and Plant Symbioses | Scoop.it
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Possible role of glutamine synthetase in the NO signaling response in root nodules by contributing to the antioxidant defenses

Possible role of glutamine synthetase in the NO signaling response in root nodules by contributing to the antioxidant defenses | Redox signalling and Plant Symbioses | Scoop.it

Nitric oxide (NO) is emerging as an important regulatory player in the Rhizobium-legume symbiosis. The occurrence of NO during several steps of the symbiotic interaction suggests an important, but yet unknown, signaling role of this molecule for root nodule formation and functioning. The identification of the molecular targets of NO is key for the assembly of the signal transduction cascade that will ultimately help to unravel NO function. We have recently shown that the key nitrogen assimilatory enzyme glutamine synthetase (GS) is a molecular target of NO in root nodules of Medicago truncatula, being post-translationally regulated by tyrosine nitration in relation to nitrogen fixation. In functional nodules of M. truncatula NO formation has been located in the bacteroid containing cells of the fixation zone, where the ammonium generated by bacterial nitrogenase is released to the plant cytosol and assimilated into the organic pools by plant GS. We propose that the NO-mediated GS post-translational inactivation is connected to nitrogenase inhibition induced by NO and is related to metabolite channeling to boost the nodule antioxidant defenses. Glutamate, a substrate for GS activity is also the precursor for the synthesis of glutathione (GSH), which is highly abundant in root nodules of several plant species and known to play a major role in the antioxidant defense participating in the ascorbate/GSH cycle. Existing evidence suggests that upon NO-mediated GS inhibition, glutamate could be channeled for the synthesis of GSH. According to this hypothesis, GS would be involved in the NO-signaling responses in root nodules and the NO-signaling events would meet the nodule metabolic pathways to provide an adaptive response to the inhibition of symbiotic nitrogen fixation by reactive nitrogen species.

 

Silva L, Carvalho H. (2013). Front Plant Sci. Sep 19;4:372


Via IvanOresnik
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An endogenous artificial microRNA system for unraveling the function of root endosymbioses related genes in Medicago truncatula (BMC plant biology 2013)

An endogenous artificial microRNA system for unraveling the function of root endosymbioses related genes in Medicago truncatula (BMC plant biology 2013) | Redox signalling and Plant Symbioses | Scoop.it
Legumes have the unique capacity to undergo two important root endosymbioses: the root nodule symbiosis and the arbuscular mycorrhizal symbiosis. Medicago truncatula is widely used to unravel the functions of genes during these root symbioses.

Via Olivier ANDRE
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Mycorrhiza-induced resistance: more than the sum of its parts?

Mycorrhiza-induced resistance: more than the sum of its parts? | Redox signalling and Plant Symbioses | Scoop.it
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Molecular link between auxin and ROS-mediated polar growth. - PubMed - NCBI

Proc Natl Acad Sci U S A. 2017 May 16;114(20):5289-5294. doi: 10.1073/pnas.1701536114. Epub 2017 May 1.
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Plant Cell: Interplay of Plasma Membrane and Vacuolar Ion Channels, Together with BAK1, Elicits Rapid Cytosolic Calcium Elevations in Arabidopsis during Aphid Feeding (2017)

Plant Cell: Interplay of Plasma Membrane and Vacuolar Ion Channels, Together with BAK1, Elicits Rapid Cytosolic Calcium Elevations in Arabidopsis during Aphid Feeding (2017) | Redox signalling and Plant Symbioses | Scoop.it

A transient rise in cytosolic calcium ion concentration is one of the main signals used by plants in perception of their environment. The role of calcium in the detection of abiotic stress is well documented; however, its role during biotic interactions remains unclear. Here, we use a fluorescent calcium biosensor (GCaMP3) in combination with the green peach aphid (Myzus persicae) as a tool to study Arabidopsis thaliana calcium dynamics in vivo and in real time during a live biotic interaction. We demonstrate rapid and highly-localised plant calcium elevations around the feeding sites of M. persicae, and by monitoring aphid feeding behaviour electrophysiologically we demonstrate that these elevations correlate with aphid probing of epidermal and mesophyll cells. Furthermore, we dissect the molecular mechanisms involved, showing that interplay between the plant defence co-receptor BRASSINOSTEROID INSENSITIVE-ASSOCIATED KINASE 1 (BAK1), the plasma membrane ion channels GLUTAMATE RECEPTOR-LIKE 3.3 and 3.6 (GLR3.3 and GLR3.6) and the vacuolar ion channel TWO-PORE CHANNEL 1 (TPC1) mediate these calcium elevations. Consequently, we identify a link between plant perception of biotic threats by BAK1, cellular calcium entry mediated by GLRs, and intracellular calcium release by TPC1 during a biologically relevant interaction.


Via Kamoun Lab @ TSL, Michael Wrzaczek
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Reprogramming of plant cells by filamentous plant-colonizing microbes - Doehlemann - 2014 - New Phytologist - Wiley Online Library

Reprogramming of plant cells by filamentous plant-colonizing microbes - Doehlemann - 2014 - New Phytologist - Wiley Online Library | Redox signalling and Plant Symbioses | Scoop.it

Although phylogenetically unrelated, filamentous oomycetes and fungi establish similar structures to colonize plants and they represent economically the most important microbial threat to crop production. In mutualistic interactions established by root-colonizing fungi, clear differences to pathogens can be seen, but there is mounting evidence that their infection strategies and molecular interactions have certain common features. To infect the host, fungi and oomycetes employ similar strategies to circumvent plant innate immunity. This process involves the suppression of basal defence responses which are triggered by the perception of conserved molecular patterns. To establish biotrophy, effector proteins are secreted from mutualistic and pathogenic microbes to the host tissue, where they play central roles in the modulation of host immunity and metabolic reprogramming of colonized host tissues. This review article discusses key effector mechanisms of filamentous pathogens and mutualists, how they modulate their host targets and the fundamental differences or parallels between these different interactions. The orchestration of effector actions during plant infection and the importance of their localization within host tissues are also discussed.


Via Jean-Michel Ané, Francis Martin
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Jean-Michel Ané's curator insight, July 24, 2014 12:53 PM

Piriformospora indica a mutualistic fungus... ha ha ha... very funny!

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BMC Plant Biology | Abstract | Identification of a dominant gene in Medicago truncatula that restricts nodulation by Sinorhizobium meliloti strain Rm41

Leguminous plants are able to form a root nodule symbiosis with nitrogen-fixing soil bacteria called rhizobia. This symbiotic association shows a high level of specificity. Beyond the specificity for the legume family, individual legume species/genotypes can only interact with certain restricted group of bacterial species or strains. Specificity in this system is regulated by complex signal exchange between the two symbiotic partners and thus multiple genetic mechanisms could be involved in the recognition process. Knowledge of the molecular mechanisms controlling symbiotic specificity could enable genetic improvement of legume nitrogen fixation, and may also reveal the possible mechanisms that restrict root nodule symbiosis in non-legumes.
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Frontiers | Building the crops of tomorrow: advantages of symbiont-based approaches to improving abiotic stress tolerance | Microbial Symbioses

Frontiers | Building the crops of tomorrow: advantages of symbiont-based approaches to improving abiotic stress tolerance | Microbial Symbioses | Redox signalling and Plant Symbioses | Scoop.it

The exponential growth in world population is feeding a steadily increasing global need for arable farmland, a resource that is already in high demand. This trend has led to increased farming on subprime arid and semi-arid lands, where limited availability of water and a host of environmental stresses often severely reduce crop productivity. The conventional approach to mitigating the abiotic stresses associated with arid climes is to breed for stress-tolerant cultivars, a time and labor intensive venture that often neglects the complex ecological context of the soil environment in which the crop is grown. In recent years, studies have attempted to identify microbial symbionts capable of conferring the same stress-tolerance to their plant hosts, and new developments in genomic technologies have greatly facilitated such research. Here, we highlight many of the advantages of these symbiont-based approaches and argue in favor of the broader recognition of crop species as ecological niches for a diverse community of microorganisms that function in concert with their plant hosts and each other to thrive under fluctuating environmental conditions.


Via Kemen Lab, Stéphane Hacquard
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Sylvia Singh's thesis


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Jean-Michel Ané's curator insight, June 3, 2014 11:47 AM

Very interesting things inside...

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Molecular cloning and functional analysis of a H+-dependent phosphate transporter gene from the ectomycorrhizal fungus Boletus edulis in southwest China

Molecular cloning and functional analysis of a H+-dependent phosphate transporter gene from the ectomycorrhizal fungus Boletus edulis in southwest China | Redox signalling and Plant Symbioses | Scoop.it

Phosphate transporters (PTs), as entry points for phosphorus (P) in various organisms, are involved in a number of fundamental processes of P nutrition such as phosphate uptake, transport and transfer. In the present study, a PT gene 1,632 bp long (named BePT) was cloned, identified, and functionally characterized from an ectomycorrhizal fungus Boletus edulis. BePT was expected to encode a polypeptide with 543 amino acid residues. The BePT polypeptide belonged to the major facilitator superfamily (MFS) and showed a high degree of sequence identity to the Pht1 family of known high-affinity PTs. A topology model revealed that BePT exhibited twelve transmembrane helices, divided into two halves and connected by a large hydrophilic loop in the middle. A yeast mutant complementation analysis suggested that BePT was a functional PT which mediated orthophosphate uptake of yeast at micromolar concentrations. GFP-BePTfusion proteins expressed were extensively restricted to the plasma membrane in BePT transformed yeast, and its activity was dependent on electrochemical membrane potential. In vitro, qPCR confirmed that B. edulis significantly up-regulated the expression of the BePT at lower phosphorus availability, which may enhance phosphate uptake and transport under phosphate starvation. Our results suggest that BePT plays a key role in phosphate acquisition in the ectomycorrhizal fungus B. edulis.


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Proteome reference maps of the Lotus japonicus nodule and root

Legume symbiosis with rhizobia results in the formation of a specialized organ, the root nodule, where atmospheric dinitrogen is reduced to ammonia. In Lotus japonicus (Lotus), several genes involved in nodule development or nodule function have been defined using biochemistry, genetic approaches, and high throughput transcriptomics. We have employed proteomics to further understand nodule development. Two developmental stages representing nodules prior to nitrogen fixation (white) and mature nitrogen fixing nodules (red) were compared with roots. In addition, the proteome of a spontaneous nodule formation mutant (snf1) was determined. From nodules and roots, 780 and 790 protein spots from 2D gels were identified and approximately 45% of the corresponding unique gene accessions were common. Including a previous proteomics set from Lotus pod and seed, the common gene accessions were decreased to 7%. Interestingly, an indication of more pronounced post translational modifications in nodules than in roots was determined. Between the two nodule developmental stages, higher levels of pathogen related 10 proteins, HSP's, and proteins involved in redox processes were found in white nodules, suggesting a higher stress level at this developmental stage. In contrast, protein spots corresponding to nodulins such as leghemoglobin, asparagine synthetase, sucrose synthase, and glutamine synthetase were prevalent in red nodules. The distinct biochemical state of nodules was further highlighted by the conspicuous presence of several nitrilases, ascorbate metabolic enzymes and putative rhizobial effectors.


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Hijacking of leguminous nodulation signaling by the rhizobial type III secretion system

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The Nod factor hydrolase of Medicago truncatula: Characterization of an enzyme specifically cleaving rhizobial nodulation signals

Nodule formation induced by nitrogen-fixing rhizobia depends on bacterial nodulation factors (NFs), modified chitin oligosaccharides with a fatty acid moiety. Certain NFs can be cleaved and inactivated by plant chitinases. However, the most abundant NF of Sinorhizobium meliloti, an O-acetylated and sulphated tetramer, is resistant to hydrolysis by all plant chitinases tested so far. Nevertheless, this NF is rapidly degraded in the host rhizosphere. Here, we identify and characterize MtNFH1 (Medicago truncatula Nod factor hydrolase 1), a legume enzyme structurally related to defense-related class V chitinases (glycoside hydrolase family 18). MtNFH1 lacks chitinase activity but efficiently hydrolyzes all tested NFs of S. meliloti. The enzyme shows a high cleavage preference, releasing exclusively lipo-disaccharides from NFs. Substrate specificity and kinetic properties of MtNFH1 were compared to those of class V chitinases from Arabidopsis thaliana and Nicotiana tabacum, which cannot hydrolyze tetrameric NFs of S. meliloti. The Michaelis-Menten constants of MtNFH1 for NFs are in the micromolar concentration range, whereas non-modified chitin oligosaccharides represent neither substrates nor inhibitors for MtNFH1. The three-dimensional structure of MtNFH1 was modeled on the basis of the known structure of class V chitinases. Docking simulation of NFs to MtNFH1 predicted a distinct binding cleft for the fatty acid moiety, which is absent in the class V chitinases. Point mutation analysis confirmed the modeled NF-MtNFH1 interaction. Silencing of MtNFH1 by RNA interference resulted in reduced NF degradation in the rhizosphere of M. truncatula. In conclusion, we have found a novel legume hydrolase that specifically inactivates NFs.


Via Jean-Michel Ané
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Agriculture : La culture de la luzerne redevient à la mode - France 3 Basse-Normandie

Agriculture : La culture de la luzerne redevient à la mode  - France 3 Basse-Normandie | Redox signalling and Plant Symbioses | Scoop.it
Elle avait peu à peu disparu des prairies. Mais aujourd'hui elle redevient une graminé appréciée et cultivée par les agriculteurs. Autonomie économique, traçabilité, vision écologique...
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Leguminous trees can help in restoration of denuded forests by nitrogen fixation - Pentagon Post

Leguminous trees can help in restoration of denuded forests by nitrogen fixation - Pentagon Post | Redox signalling and Plant Symbioses | Scoop.it
Pentagon Post Leguminous trees can help in restoration of denuded forests by nitrogen fixation Pentagon Post A recent study conducted by the Princeton University has found a unique symbiosis between trees in the leguminous family and the...
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