Rhizosphere interactions
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Rescooped by Samira Hassan from Plant-Microbe Symbiosis
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Signal molecules and cell-surface components involved in early stages of the legume–rhizobium interactions

Signal molecules and cell-surface components involved in early stages of the legume–rhizobium interactions | Rhizosphere interactions | Scoop.it
Signaling during early stages of legume–rhizobium symbiosis is of great interest from many years because legumes provide high environmental and agricultural benefits for humans, among them are important sources of food, feed, and biofuel crops.


Over the last decade, our understanding of this “molecular dialog” between both symbiotic partners: host plants and their microsymbionts, has grown immensely, leading to broadening our knowledge of early stages of these plant–microbe interactions.


The availability of reduced nitrogenous compounds in soil is a major limiting factor for plant growth and effectiveness of agricultural crops.


Because of this reason, the process of biological nitrogen fixation conducted by symbiotic soil bacteria collectively called rhizobia is crucial for providing high amounts of nitrogen forms available for plants.


The establishment of symbiosis is a complex process, in which multiple signals and cell-surface compounds derived from both the host plant and bacteria are involved, among them flavonoids and rhizobial lipochitin oligosaccharides play crucial roles.

Via Jean-Michel Ané
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Rescooped by Samira Hassan from Plant roots and rhizosphere
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The anthocyanin reduced Tomato Mutant Demonstrates the Role of Flavonols in Tomato Lateral Root and Root Hair Development

The anthocyanin reduced Tomato Mutant Demonstrates the Role of Flavonols in Tomato Lateral Root and Root Hair Development | Rhizosphere interactions | Scoop.it

This study utilized tomato (Solanum lycopersicum) mutants with altered flavonoid biosynthesis to understand the impact of these metabolites on root development. The mutant anthocyanin reduced (are) has a mutation in the gene encoding FLAVONOID 3-HYDROXYLASE (F3H), the first step in flavonol synthesis, and accumulates higher concentrations of the F3H substrate, naringenin, and lower levels of the downstream products kaempferol, quercetin, myricetin, and anthocyanins, than the wild type. Complementation of are with the p35S:F3H transgene reduced naringenin and increased flavonols to wild-type levels. The initiation of lateral roots is reduced in are, and p35S:F3H complementation restores wild-type root formation. The flavonoid mutant anthocyanin without has a defect in the gene encoding DIHYDROFLAVONOL REDUCTASE, resulting in elevated flavonols and the absence of anthocyanins and displays increased lateral root formation. These results are consistent with a positive role of flavonols in lateral root formation. The are mutant has increased indole-3-acetic acid transport and greater sensitivity to the inhibitory effect of the auxin transport inhibitor naphthylphthalamic acid on lateral root formation. Expression of the auxin-induced reporter (DR5-β-glucuronidase) is reduced in initiating lateral roots and increased in primary root tips of are. Levels of reactive oxygen species are elevated in are root epidermal tissues and root hairs, and are forms more root hairs, consistent with a role of flavonols as antioxidants that modulate root hair formation. Together, these experiments identify positive roles of flavonols in the formation of lateral roots and negative roles in the formation of root hairs through the modulation of auxin transport and reactive oxygen species, respectively.


Via Christophe Jacquet
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Rescooped by Samira Hassan from The Plant Microbiome
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PNAS: Structural basis for regulation of rhizobial nodulation and symbiosis gene expression by the regulatory protein NolR

Nitrogen nodules formed by the symbiosis of rhizobial microbes and legume roots are essential for fixation of nitrogen in the environment. As part of the symbiosis that leads to nodule formation, a series of changes in gene expression of the Rhizobium must occur. The protein NolR is a global regulator of rhizobial genes for symbiosis and nodulation. Here, we describe the three-dimensional structure of this transcription factor in unliganded and DNA bound forms. These structures show how NolR recognizes asymmetric DNA binding sites and reveal a previously unknown mechanism for conformational switching that alters the energetics of interaction to accommodate variable DNA sequences. Two models for the role of NolR in the regulation of nodulation and symbiosis genes are also proposed.
Via Stéphane Hacquard
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Rescooped by Samira Hassan from Rhizobium Research
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Evolution of a symbiotic receptor through gene duplications in the legume-rhizobium mutualism.

Evolution of a symbiotic receptor through gene duplications in the legume-rhizobium mutualism. | Rhizosphere interactions | Scoop.it

The symbiosis between legumes and nitrogen-fixing rhizobia co-opted pre-existing endomycorrhizal features. In particular, both symbionts release lipo-chitooligosaccharides (LCOs) that are recognized by LysM-type receptor kinases. We investigated the evolutionary history of rhizobial LCO receptor genes MtLYK3-LjNFR1 to gain insight into the evolutionary origin of the rhizobial symbiosis. We performed a phylogenetic analysis integrating gene copies from nonlegumes and legumes, including the non-nodulating, phylogenetically basal legume Cercis chinensis. Signatures of differentiation between copies were investigated through patterns of molecular evolution. We show that two rounds of duplication preceded the evolution of the rhizobial symbiosis in legumes. Molecular evolution patterns indicate that the resulting three paralogous gene copies experienced different selective constraints. In particular, one copy maintained the ancestral function, and another specialized into perception of rhizobial LCOs. It has been suggested that legume LCO receptors evolved from a putative ancestral defense-related chitin receptor through the acquisition of two kinase motifs. However, the phylogenetic analysis shows that these domains are actually ancestral, suggesting that this scenario is unlikely. Our study underlines the evolutionary significance of gene duplication and subsequent neofunctionalization in MtLYK3-LjNFR1 genes. We hypothesize that their ancestor was more likely a mycorrhizal LCO receptor, than a defense-related receptor kinase.

 

De Mita S, Streng A, Bisseling T, Geurts R. (2014). 

New Phytol. Feb;201(3):961-72.  


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GNOM regulates root hydrotropism and phototropism independently of PIN-mediated auxin transport

GNOM regulates root hydrotropism and phototropism independently of PIN-mediated auxin transport | Rhizosphere interactions | Scoop.it

Abstract

Plant roots exhibit tropisms in response to gravity, unilateral light and moisture gradients. During gravitropism, an auxin gradient is established by PIN auxin transporters, leading to asymmetric growth. GNOM, a guanine nucleotide exchange factor of ARF GTPase (ARF-GEF), regulates PIN localization by regulating subcellular trafficking of PINs. Therefore, GNOM is important for gravitropism. We previously isolated mizu-kussei2 (miz2), which lacks hydrotropic responses; MIZ2 is allelic to GNOM. Since PIN proteins are not required for root hydrotropism in Arabidopsis, the role of GNOM in root hydrotropism should differ from that in gravitropism. To examine this possibility, we conducted genetic analysis of gnommiz2 and gnom trans-heterozygotes. The mutant gnommiz2, which lacks hydrotropic responses, was partially recovered by gnomemb30-1, which lacks GEF activity, but not by gnomB4049, which lacks heterotypic domain interactions. Furthermore, the phototropic response of gnom trans-heterozygotes differed from that of the pin2 mutant allele eir1-1. Moreover, defects in the polarities of PIN2 and auxin distribution in a severe gnom mutant were recovered by gnommiz2. Therefore, an unknown GNOM-mediated vesicle trafficking system may mediate root hydrotropism and phototropism independently of PIN trafficking.

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Auxin biosynthetic gene TAR2 is involved in low nitrogen mediated reprogramming of root architecture in Arabidopsis

Auxin biosynthetic gene TAR2 is involved in low nitrogen mediated reprogramming of root architecture in Arabidopsis | Rhizosphere interactions | Scoop.it

In plants, the plasticity of root architecture in response to nitrogen availability largely determines nitrogen acquisition efficiency. One poorly understood root growth response to low nitrogen availability is an observed increase in the number and length of lateral roots (LRs). Here, we show that low nitrogen-induced Arabidopsis lateral root growth depended on the function of the auxin biosynthesis gene TAR2 (tryptophan aminotransferase related 2). TAR2 was expressed in the pericycle and the vasculature of the mature root zone near the root tip, and was induced under low nitrogen conditions. In the wild type plants, low nitrogen stimulated auxin accumulation in the non-emerged LR primordia with >3 cell layers and LR emergence. Conversely, these low nitrogen-mediated auxin accumulation and root growth responses were impaired in the tar2-c null mutant. Overexpression of TAR2 increased LR numbers under both high and low nitrogen conditions. Our results suggest that TAR2 is required for reprogramming root architecture in response to low nitrogen conditions. This finding suggests a new strategy for improving nitrogen use efficiency through the engineering of TAR2 expression in roots.


Via Christophe Jacquet
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YUCASIN is a potent inhibitor of YUCCA(s), a key enzyme in auxin biosynthesis

YUCASIN is a potent inhibitor of YUCCA(s), a key enzyme in auxin biosynthesis | Rhizosphere interactions | Scoop.it

Indole-3-acetic acid (IAA), a plant hormone auxin, is biosynthesized from tryptophan. The indole-3-pyruvic acid (IPyA) pathway, involving TAA1 and YUCCA (YUC) enzymes, was recently found to be a major IAA biosynthetic pathway in Arabidopsis. TAA1 catalyzes the conversion of tryptophan to IPyA, and YUC produces IAA from IPyA. Using a chemical biology approach with maize coleoptiles, we identified 5-(4-chlorophenyl)-4H-1,2,4-triazole-3-thiol (yucasin) as a potent inhibitor of IAA biosynthesis in YUC-expressing coleoptile tips. Enzymatic analysis of recombinant AtYUC1-His suggested that yucasin strongly inhibited YUC1-His activity in a competitive manner against the substrate IPyA. Phenotypic analysis of Arabidopsis YUC1 overexpression (35S::YUC1) lines demonstrated that yucasin acts in IAA biosynthesis catalyzed by YUC. Also, 35S::YUC1 seedlings showed resistance to yucasin in root growth. A loss-of-function mutant of TAA1, sav3-2, was hypersensitive to yucasin in root growth and hypocotyl elongation of etiolated seedlings. Yucasin combined with the TAA1 inhibitor L-kynurenine acted additively in Arabidopsis seedlings, producing a phenotype similar to yucasin-treated sav3-2 seedlings, indicating the importance of IAA biosynthesis via the IPyA pathway in root growth and leaf vascular development. The present study showed that yucasin is a potent inhibitor of YUCs that offers an effective tool for analyzing the contribution of IAA biosynthesis via the IPyA pathway to plant development and physiological processes.

 

 


Via Christophe Jacquet
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Rescooped by Samira Hassan from Rhizobium Research
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Enhanced nodulation and nodule development by nolR mutants of Sinorhizobium medicae on specific Medicago host genotypes

Enhanced nodulation and nodule development by nolR mutants of Sinorhizobium medicae on specific Medicago host genotypes | Rhizosphere interactions | Scoop.it

The nolR gene encodes a negatively-acting, transcriptional regulatory protein of core Nod-factor biosynthetic genes in the sinorhizobia. While previous reports showed that nolR modulates Nod-factors production and enhances nodulation speed of Sinorhizobium meliloti on alfalfa, there have been no reports for the symbiotic function of this gene in the S. medicae-Medicago truncatula symbiosis. Here we constructed a nolR mutant of S. medicae WSM419 and evaluated mutant and wild-type strains for their nodulation ability, competitiveness, host specificity, and density-dependent nodulation phenotypes. When the mutant was inoculated at low- and medium-population densities it showed enhanced nodule formation during the initial stages of nodulation. Results of quantitative competitive nodulation assays indicated that a nolR mutant had 2.3-fold greater competitiveness for nodulation on M. truncatula cv. A17 than did the wild-type strain. Moreover, the nodulation phenotype of the nolR mutant differed among Medicago genotypes, and showed significantly enhanced nodule development on Medicago tricycla. Taken together, these results indicated that mutation of nolR in S. medicae positively influenced nodule initiation, competitive nodulation, and nodule development at later nodulation stages. This may allow nolR mutants of S. medicae to have a selective advantage under field conditions

 

Sugawara M, Sadowsky MJ. (2013). Mol Plant Microbe Interact. Nov 27. [Epub ahead of print]


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Jasmonate signalling: a copycat of auxin signalling? - PÉREZ - 2013 - Plant, Cell & Environment -

Jasmonate signalling: a copycat of auxin signalling? - PÉREZ - 2013 - Plant, Cell & Environment - | Rhizosphere interactions | Scoop.it

Plant hormones regulate almost all aspects of plant growth and development. The past decade has provided breakthrough discoveries in phytohormone sensing and signal transduction, and highlighted the striking mechanistic similarities between the auxin and jasmonate (JA) signalling pathways. Perception of auxin and JA involves the formation of co-receptor complexes in which hormone-specific E3-ubiquitin ligases of the SKP1-Cullin-F-box protein (SCF) type interact with specific repressor proteins. Across the plant kingdom, the Aux/IAA and the JASMONATE-ZIM DOMAIN (JAZ) proteins correspond to the auxin- and JA-specific repressors, respectively. In the absence of the hormones, these repressors form a complex with transcription factors (TFs) specific for both pathways. They also recruit several proteins, among which the general co-repressor TOPLESS, and thereby prevent the TFs from activating gene expression. The hormone-mediated interaction between the SCF and the repressors targets the latter for 26S proteasome-mediated degradation, which, in turn, releases the TFs to allow modulating hormone-dependent gene expression. In this review, we describe the similarities and differences in the auxin and JA signalling cascades with respect to the protein families and the protein domains involved in the formation of the pathway-specific complexes.


Via Christophe Jacquet
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GmFNSII-controlled Soybean Flavone Metabolism Responds to Abiotic Stresses and Regulates Plant Salt Tolerance

GmFNSII-controlled Soybean Flavone Metabolism Responds to Abiotic Stresses and Regulates Plant Salt Tolerance | Rhizosphere interactions | Scoop.it
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Rescooped by Samira Hassan from MycorWeb Plant-Microbe Interactions
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Visualization of plant cell wall lignification using fluorescence-tagged monolignols

Visualization of plant cell wall lignification using fluorescence-tagged monolignols | Rhizosphere interactions | Scoop.it

Lignin is an abundant phenylpropanoid polymer produced by the oxidative polymerization of p-hydroxycinnamyl alcohols (monolignols). Lignification, i.e., deposition of lignin, is a defining feature of secondary cell wall formation in vascular plants, and provides an important mechanism for their disease resistance; however, many aspects of the cell wall lignification process remain unclear partly because of a lack of suitable imaging methods to monitor the process in vivo. In this study, a set of monolignol analogs γ-linked to fluorogenic aminocoumarin and nitrobenzofuran dyes were synthesized and tested as imaging probes to visualize the cell wall lignification process inArabidopsis thaliana and Pinus radiata under various feeding regimens. In particular, we demonstrate that the fluorescence-tagged monolignol analogs can penetrate into live plant tissues and cells, and appear to be metabolically incorporated into lignifying cell walls in a highly specific manner. The localization of the fluorogenic lignins synthesized during the feeding period can be readily visualized by fluorescence microscopy and is distinguishable from the other wall components such as polysaccharides as well as the pre-existing lignin that was deposited earlier in development.


Via Francis Martin
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Thiol-based redox signaling in the nitrogen-fixing symbiosis

Thiol-based redox signaling in the nitrogen-fixing symbiosis | Rhizosphere interactions | Scoop.it

In nitrogen poor soils legumes establish a symbiotic interaction with rhizobia that results in the formation of root nodules. These are unique plant organs where bacteria differentiate into bacteroids, which express the nitrogenase enzyme complex that reduces atmospheric N 2 to ammonia. Nodule metabolism requires a tight control of the concentrations of reactive oxygen and nitrogen species (RONS) so that they can perform useful signaling roles while avoiding nitro-oxidative damage. In nodules a thiol-dependent regulatory network that senses, transmits and responds to redox changes is starting to be elucidated. A combination of enzymatic, immunological, pharmacological and molecular analyses has allowed us to conclude that glutathione and its legume-specific homolog, homoglutathione, are abundant in meristematic and infected cells, that their spatio-temporally distribution is correlated with the corresponding (homo)glutathione synthetase activities, and that they are crucial for nodule development and function. Glutathione is at high concentrations in the bacteroids and at moderate amounts in the mitochondria, cytosol and nuclei. Less information is available on other components of the network. The expression of multiple isoforms of glutathione peroxidases, peroxiredoxins, thioredoxins, glutaredoxins and NADPH-thioredoxin reductases has been detected in nodule cells using antibodies and proteomics. Peroxiredoxins and thioredoxins are essential to regulate and in some cases to detoxify RONS in nodules. Further research is necessary to clarify the regulation of the expression and activity of thiol redox-active proteins in response to abiotic, biotic and developmental cues, their interactions with downstream targets by disulfide-exchange reactions, and their participation in signaling cascades. The availability of mutants and transgenic lines will be crucial to facilitate systematic investigations into the function of the various proteins in the legume-rhizobial symbiosis.

 

Frendo P, Matamoros MA, Alloing G, Becana M. (2013). Front Plant Sci. Sep 26;4:376.

 


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

Hijacking of leguminous nodulation signaling by the rhizobial type III secretion system | Rhizosphere interactions | Scoop.it

Root–nodule symbiosis between leguminous plants and nitrogen-fixing bacteria (rhizobia) involves molecular communication between the two partners. Key components for the establishment of symbiosis are rhizobium-derived lipochitooligosaccharides (Nod factors; NFs) and their leguminous receptors (NFRs) that initiate nodule development and bacterial entry. Here we demonstrate that the soybean microsymbiont Bradyrhizobium elkanii uses the type III secretion system (T3SS), which is known for its delivery of virulence factors by pathogenic bacteria, to promote symbiosis. Intriguingly, wild-type B. elkanii, but not the T3SS-deficient mutant, was able to form nitrogen-fixing nodules on soybean nfr mutant En1282. Furthermore, even the NF-deficient B. elkanii mutant induced nodules unless T3SS genes were mutated. Transcriptional analysis revealed that expression of the soybean nodulation-specific genes ENOD40 and NIN was increased in the roots of En1282 inoculated with B. elkanii but not with its T3SS mutant, suggesting that T3SS activates host nodulation signaling by bypassing NF recognition. Root-hair curling and infection threads were not observed in the roots of En1282 inoculated with B. elkanii, indicating that T3SS is involved in crack entry or intercellular infection. These findings suggest that B. elkanii has adopted a pathogenic system for activating host symbiosis signaling to promote its infection.


Via Christophe Jacquet
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Christophe Jacquet's curator insight, October 16, 2013 2:11 AM

The dark side of Rhizobium...

Rescooped by Samira Hassan from Plant immunity and legume symbiosis
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NODULE INCEPTION creates a long-distance negative feedback loop involved in homeostatic regulation of nodule organ production

NODULE INCEPTION creates a long-distance negative feedback loop involved in homeostatic regulation of nodule organ production | Rhizosphere interactions | Scoop.it
Significance

Long-range organ-to-organ communications are important for the coordination of development and environmental adaptation in multicellular organisms, particularly plants that continuously produce postembryonic lateral organs in various environmental conditions. The substance of homeostatic regulation of organ development via long-distance signals has not yet been identified, however. Legumes use an autoregulatory negative-feedback system involving root–shoot communication to maintain optimal numbers of nodules by systemically suppressing nodulation. We show that a transcription factor, NODULE INCEPTION (NIN), an essential inducer for nodule primordium formation, directly activates genes encoding small peptides that act as root-derived long-distance mobile signals, leading to repression of endogenous NIN though the root–shoot communication and resulting in systemic suppression of nodulation. We demonstrate that an autoregulatory negative-feedback loop homeostatically regulates nodule production via this long-range signaling.
Abstract

Autoregulatory negative-feedback loops play important roles in fine-balancing tissue and organ development. Such loops are composed of short-range intercellular signaling pathways via cell–cell communications. On the other hand, leguminous plants use a long-distance negative-feedback system involving root–shoot communication to control the number of root nodules, root lateral organs that harbor symbiotic nitrogen-fixing bacteria known as rhizobia. This feedback system, known as autoregulation of nodulation (AON), consists of two long-distance mobile signals: root-derived and shoot-derived signals. Two Lotus japonicus CLAVATA3/ENDOSPERM SURROUNDING REGION (CLE)-related small peptides, CLE ROOT SIGNAL1 (CLE-RS1) and CLE-RS2, function as root-derived signals and are perceived by a shoot-acting AON factor, the HYPERNODULATION ABERRANT ROOT FORMATION1 (HAR1) receptor protein, an ortholog of Arabidopsis CLAVATA1, which is responsible for shoot apical meristem homeostasis. This peptide–receptor interaction is necessary for systemic suppression of nodulation. How the onset of nodulation activates AON and how optimal nodule numbers are maintained remain unknown, however. Here we show that an RWP-RK–containing transcription factor, NODULE INCEPTION (NIN), which induces nodule-like structures without rhizobial infection when expressed ectopically, directly targets CLE-RS1 and CLE-RS2. Roots constitutively expressing NIN systemically repress activation of endogenous NIN expression in untransformed roots of the same plant in a HAR1-dependent manner, leading to systemic suppression of nodulation and down-regulation of CLE expression. Our findings provide, to our knowledge, the first molecular evidence of a long-distance autoregulatory negative-feedback loop that homeostatically regulates nodule organ formation.

Via Christophe Jacquet
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Abscisic Acid and LATERAL ROOT ORGAN DEFECTIVE/...

Abscisic Acid and LATERAL ROOT ORGAN DEFECTIVE/... | Rhizosphere interactions | Scoop.it
Abscisic acid (ABA) modulates root growth in plants grown under normal and stress conditions and can rescue the root growth defects of the Medicago truncatula lateral root-organ defective (latd) mutant.

Via Jean-Michel Ané
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BBC Radio 4 - Frontiers, Nitrogen Fixing

BBC Radio 4 - Frontiers, Nitrogen Fixing | Rhizosphere interactions | Scoop.it
Prof Andrea Sella looks at efforts to reduce our dependence on the Haber-Bosch process.

Via IvanOresnik
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IvanOresnik's curator insight, December 6, 2013 8:31 AM

Worth a listen.  Pitched toward a generalist.

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PLOS Pathogens: Identification of Novel Target Genes for Safer and More Specific Control of Root-Knot Nematodes from a Pan-Genome Mining (2013)

PLOS Pathogens: Identification of Novel Target Genes for Safer and More Specific Control of Root-Knot Nematodes from a Pan-Genome Mining (2013) | Rhizosphere interactions | Scoop.it

Root-knot nematodes are globally the most aggressive and damaging plant-parasitic nematodes. Chemical nematicides have so far constituted the most efficient control measures against these agricultural pests. Because of their toxicity for the environment and danger for human health, these nematicides have now been banned from use. Consequently, new and more specific control means, safe for the environment and human health, are urgently needed to avoid worldwide proliferation of these devastating plant-parasites. Mining the genomes of root-knot nematodes through an evolutionary and comparative genomics approach, we identified and analyzed 15,952 nematode genes conserved in genomes of plant-damaging species but absent from non target genomes of chordates, plants, annelids, insect pollinators and mollusks. Functional annotation of the corresponding proteins revealed a relative abundance of putative transcription factors in this parasite-specific set compared to whole proteomes of root-knot nematodes. This may point to important and specific regulators of genes involved in parasitism. Because these nematodes are known to secrete effector proteins in planta, essential for parasitism, we searched and identified 993 such effector-like proteins absent from non-target species. Aiming at identifying novel targets for the development of future control methods, we biologically tested the effect of inactivation of the corresponding genes through RNA interference. A total of 15 novel effector-like proteins and one putative transcription factor compatible with the design of siRNAs were present as non-redundant genes and had transcriptional support in the model root-knot nematode Meloidogyne incognita. Infestation assays with siRNA-treated M. incognita on tomato plants showed significant and reproducible reduction of the infestation for 12 of the 16 tested genes compared to control nematodes. These 12 novel genes, showing efficient reduction of parasitism when silenced, constitute promising targets for the development of more specific and safer control means.


Via Kamoun Lab @ TSL, Guogen Yang
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Arjen ten Have's curator insight, November 20, 2013 4:13 PM

My guess this is a rather stringent protocol. There will be many cool targets at intermediate levels of the filtration flow! But obviously a great piece of work. Love its simplicity! (likely much of the work actually performed is not shown).

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Plant J: Rhizobial infection does not require cortical expression of upstream common symbiosis genes responsible for the induction of Ca2+ spiking

Plant J: Rhizobial infection does not require cortical expression of upstream common symbiosis genes responsible for the induction of Ca2+ spiking | Rhizosphere interactions | Scoop.it

For the establishment of an effective root nodule symbiosis, a  coordinated regulation of the infection processes between the epidermis and cortex is required. However, it remains unclear whether the symbiotic genes identified so far are involved in epidermal and/or cortical infection, e.g. epidermal and cortical infection thread formation or cortical cell division. To analyze the symbiotic gene requirements of the infection process, we have developed an epidermis-specific expression system (pEpi expression system) and examined the symbiotic genes NFR1, NFR5, NUP85, NUP133, CASTOR, POLLUX, CCaMK, CYCLOPS, NSP1 and NSP2 for involvement in the infection process in the epidermis and cortex. Our study shows that expression of the upstream common symbiosis genes CASTOR, POLLUX, NUP85 and NUP133 in the epidermis is sufficient to induce formation of infection threads and cortical cell division, leading to the development of fully effective nodules. Our system also shows a requirement of CCaMK, CYCLOPS, NSP1 and NSP2 for the entire nodulation process, and the different contributions of NFR1 and NFR5 to cortical infection thread formation. Based on these analyses using the pEpi expression system, we propose a functional model of symbiotic genes for epidermal and cortical infection.

Hayashi T, Shimoda Y, Sato S, Tabata S, Ipmaizumi-Anraku H, Hayashi M, The Plant Journal 12 Dec 2013

DOI: 10.1111/tpj.12374


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Developmental Cell - Auxin-Callose-Mediated Plasmodesmal Gating Is Essential for Tropic Auxin Gradient Formation and Signaling

Developmental Cell - Auxin-Callose-Mediated Plasmodesmal Gating Is Essential for Tropic Auxin Gradient Formation and Signaling | Rhizosphere interactions | Scoop.it

HighlightsGSL8 controls plasmodesmata (PD) callose deposition, essential for tropic responseGSL8 RNAi lines show increased PD permeability and auxin diffusion via PDAuxin-ARF7-callose-mediated PD gating is essential for tropic auxin responseAuxin could regulate symplasmic delivery of a wide range of signaling agentsSummary

In plants, auxin functions as a master controller of development, pattern formation, morphogenesis, and tropic responses. A sophisticated transport system has evolved to allow the establishment of precise spatiotemporal auxin gradients that regulate specific developmental programs. A critical unresolved question relates to how these gradients can be maintained in the presence of open plasmodesmata that allow for symplasmic exchange of essential nutrients and signaling macromolecules. Here we addressed this conundrum using genetic, physiological, and cell biological approaches and identified the operation of an auxin-GSL8 feedback circuit that regulates the level of plasmodesmal-localized callose in order to locally downregulate symplasmic permeability during hypocotyl tropic response. This system likely involves a plasmodesmal switch that would prevent the dissipation of a forming gradient by auxin diffusion through the symplasm. This regulatory system may represent a mechanism by which auxin could also regulate symplasmic delivery of a wide range of signaling agents.


Via Suayib Üstün
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Proteome reference maps of the Lotus japonicus nodule and root.

Proteome reference maps of the Lotus japonicus nodule and root. | Rhizosphere interactions | Scoop.it

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.

 

Dam S, Dyrlund TF, Ussatjuk A, Jochimsen B, Nielsen K, Goffard N, Ventosa M, Lorentzen A, Gupta V, Andersen SU, Enghild JJ, Ronson CW, Roepstorff P,Stougaard J. (2013). Proteomics. Nov 29. [Epub ahead of print]

 


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From β- to α-Proteobacteria: The Origin and Evolution of Rhizobial Nodulation Genes nodIJ

From β- to α-Proteobacteria: The Origin and Evolution of Rhizobial Nodulation Genes nodIJ | Rhizosphere interactions | Scoop.it

Although many α- and some β-proteobacterial species are symbiotic with legumes, the evolutionary origin of nitrogen-fixing nodulation remains unclear. We examined α- and β-proteobacteria whose genomes were sequenced using large-scale phylogenetic profiling and revealed the evolutionary origin of two nodulation genes. These genes, nodI and nodJ(nodIJ), play key roles in the secretion of Nod factors, which are recognized by legumes during nodulation. We found that only the nodulating β-proteobacteria, including the novel strains isolated in this study, possess both nodIJ and their paralogous genes (DRA-ATPase/permease genes). Contrary to the widely accepted scenario of the α-proteobacterial origin of rhizobia, our exhaustive phylogenetic analysis showed that the entire nodIJ clade is included in the clade of Burkholderiaceae DRA-ATPase/permease genes, that is, the nodIJ genes originated from gene duplication in a lineage of the β-proteobacterial family. After duplication, the evolutionary rates of nodIJ were significantly accelerated relative to those of homologous genes, which is consistent with their novel function in nodulation. The likelihood analyses suggest that this accelerated evolution is not associated with changes in either nonsynonymous/synonymous substitution rates or transition/transversion rates, but rather, in the GC content. Although the low GC content of the nodulation genes has been assumed to reflect past horizontal transfer events from donor rhizobial genomes with low GC content, no rhizobial genome with such low GC content has yet been found. Our results encourage a reconsideration of the origin of nodulation and suggest new perspectives on the role of the GC content of bacterial genes in functional adaptation.

 

Mol Biol Evol (2013) doi: 10.1093/molbev/mst153First published online: September 11, 2013


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IvanOresnik's curator insight, October 15, 2013 11:30 AM

I would like to thank Ann Hirsch for bringing this paper to my attention.  

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Time-lapse film of the infection of clover root hairs by rhizobia

Time-lapse film of the infection of clover root hairs by rhizobia | Rhizosphere interactions | Scoop.it
Note that the root hair is curled, one of the first visible steps of the compatible nodulation reaction. The arrows point to the end of the growing infection thread during the infection process. The tubular infection thread is the means by which the rhizobia gain entry into the root. Once the thread exits the root hair, it ramifies into the root cortex, finally ending at a cortical cell that will become infected. Time lapse film kindly provided by Drs. S. Higashi and M. Abe, Kagoshima University, Japan.

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Jean-Michel Ané's curator insight, November 2, 2013 6:46 PM

Cool video but a bit slow to load... I'll probably use it for teaching.

IvanOresnik's curator insight, November 6, 2013 1:08 PM

Even though I have seen many infection threads, I still find it fascinating to watch this video.

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The Strawberry Pathogenesis-Related 10 (PR-10) Fra a proteins control flavonoid biosynthesis by binding to metabolic intermediates

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Current Biology - Cytokinin Induces Cell Division in the Quiescent Center of the Arabidopsis Root Apical Meristem

Current Biology - Cytokinin Induces Cell Division in the Quiescent Center of the Arabidopsis Root Apical Meristem | Rhizosphere interactions | Scoop.it

HighlightsCytokinin represses the expression of key regulators of root meristem functionType B ARRs can directly mediate cytokinin repression of gene expressionElevated cytokinin phenocopies disruption of the LAX2 gene in the root tipCytokinin regulates QC cell division in part by repression of LAX2 expressionSummaryBackground

In the root apical meristem, which contains the stem cells that feed into root development, the phytohormones auxin and cytokinin play opposing roles, with auxin promoting cell division and cytokinin promoting cell differentiation. Cytokinin acts in the root tip in part by modulating auxin transport through regulation of the level of the PIN auxin efflux carriers. Auxin plays a key role in the specification of the quiescent center (QC), which is essential for maintaining the stem cell fate of the surrounding cells.

Results

We demonstrate that cytokinin promotes cell division in the QC, which is generally mitotically inactive. Cytokinin downregulates the expression of several key regulatory genes in the root tip, including SCARECROW, WOX5, and the auxin influx carriers AUX1 and LAX2. The decrease in LAX2 expression in response to cytokinin requires ARR1 and ARR12, two type B ARRs that mediate the primary transcriptional response to cytokinin. ARR1 was found to bind directly to the LAX2 gene in vivo, which indicates that type B ARRs directly regulate genes that are repressed by cytokinin. Disruption of the LAX2 gene results in a phenotype similar to that observed in response to cytokinin, including increased division of the cells in the QC and decreased expression of WOX5 and the auxin response reporter DR5.

Conclusions

Cytokinin acts to regulate auxin distribution in the root apical meristem by regulating both the PINs and LAX2. This redistribution of auxin, potentially coupled with other auxin-independent effects of cytokinin, regulates the mitotic activity in the QC.


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CERBERUS and NSP1 of Lotus japonicus are Common Symbiosis Genes that Modulate Arbuscular Mycorrhiza Development

CERBERUS and NSP1 of Lotus japonicus are Common Symbiosis Genes that Modulate Arbuscular Mycorrhiza Development | Rhizosphere interactions | Scoop.it

Arbuscular mycorrhizal symbiosis (AMS) and root nodule symbiosis (RNS) are mutualistic plant–microbe interactions that confer nutritional benefits to both partners. Leguminous plants possess a common genetic system for intracellular symbiosis with AM fungi and with rhizobia. Here we show that CERBERUS and NSP1, which respectively encode an E3 ubiquitin ligase and a GRAS transcriptional regulator and which have previously only been implicated in RNS, are involved in AM fungal infection in Lotus japonicus. Hyphal elongation along the longitudinal axis of the root was reduced in the cerberus mutant, giving rise to a lower colonization level. Knockout ofNSP1 decreased the frequency of plants colonized by AM fungi or rhizobia. CERBERUS and NSP1 showed different patterns of expression in response to infection with symbiotic microbes. A low constitutive level ofCERBERUS expression was observed in the root and an increased level ofNSP1 expression was detected in arbuscule-containing cells. Induction of AM marker gene was triggered in both cerberus and nsp1 mutants by infection with symbiotic microbes; however, the mutants showed a weaker induction of marker gene expression than the wild type, mirroring their lower level of colonization. The common symbiosis genes are believed to act in an early signaling pathway for recognition of symbionts and for triggering early symbiotic responses. Our quantitative analysis of symbiotic phenotypes revealed developmental defects of the novel common symbiosis mutants in both symbioses, which demonstrates that common symbiosis mechanisms also contribute to a range of functions at later or different stages of symbiont infection.


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