Plant-Microbe Symbiosis
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Choice of hydrogen uptake (Hup) status in legume-rhizobia symbioses | Rhizobium Research

Choice of hydrogen uptake (Hup) status in legume-rhizobia symbioses | Rhizobium Research | Plant-Microbe Symbiosis | Scoop.it
The H2 is an obligate by-product of N-fixation. Recycling of H2 through uptake hydrogenase (Hup) inside the root nodules of leguminous plants is often considered an advantage for plants.
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Plant-Microbe Symbiosis
Beneficial associations between plants and microbes
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INRA - INRA is recruiting more than 30 scientists

INRA - INRA is recruiting more than 30 scientists | Plant-Microbe Symbiosis | Scoop.it
In 2017, INRA will be recruiting 32 research scientists to reinforce its teams. Positions are open to all nationalities. Applications will be open from 26 January to 1st March (for online applications) or 3 March 2017 (for paper applications).

Via Saclay Plant Sciences
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Comparative genomics of Mortierella elongata and its bacterial endosymbiont Mycoavidus cysteinexigens

Comparative genomics of Mortierella elongata and its bacterial endosymbiont Mycoavidus cysteinexigens | Plant-Microbe Symbiosis | Scoop.it
Endosymbiosis of bacteria by eukaryotes is a defining feature of cellular evolution. In addition to well known bacterial origins for mitochondria and chloroplasts, multiple origins of bacterial endosymbiosis are known within the cells of diverse animals, plants, and fungi. Early-diverging lineages of terrestrial fungi harbor endosymbiotic bacteria belonging to the Burkholderiaceae. We sequenced the metagenome of the soil-inhabiting fungus Mortierella elongata and assembled the complete circular chromosome of its endosymbiont, Mycoavidus cysteinexigens, which we place within in a lineage of endofungal symbionts that are sister clade to Burkholderia. The M. elongata strain AG77 genome features a core set of primary metabolic pathways for degradation of simple carbohydrates and lipid biosynthesis, while the M. cysteinexigens (AG77) genome is reduced in size and function. Experiments using antibiotics to cure the endobacterium from the host demonstrate that the fungal host metabolism is highly modulated by presence/absence of M. cysteinexigens. Independent comparative phylogenomic analyses of fungal and bacterial genomes are consistent with an ancient origin for M. elongata – M. cysteinexigens symbiosis, most likely over 350 million years ago and concomitant with the terrestrialization and diversification of fungi and plants

Via Francis Martin
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The ERF Required for Nodulation1 (ERN1) transcription factor is required for infection thread formation in Lotus japonicus 

Several hundred genes are transcriptionally regulated during infection thread formation and development of nitrogen fixing root nodules. We have characterized a set of Lotus japonicus mutants impaired in root nodule formation and found that the causative gene, Ern1, encodes a protein with a characteristic APETALA2/Ethylene Responsive Factor (AP2/ERF) transcription factor domain. Phenotypic characterisation of four ern1 alleles shows that infection pockets are formed but root hair infection threads are absent. Formation of root nodule primordia is delayed and no normal trans-cellular infection threads are found in the infected nodules. Corroborating the role of ERN1 in nodule organogenesis, spontaneous nodulation induced by an autoactive CCaMK and cytokinin induced nodule primordia were not observed in ern1 mutants. Expression of Ern1 is induced in the susceptible zone by Nod factor treatment or rhizobial inoculation. At the cellular level, the pErn1:GUS reporter is highly expressed in root epidermal cells of the susceptible zone and in the cortical cells that form nodule primordia. The genetic regulation of this cellular expression pattern was further investigated in symbiotic mutants. Nod factor induction of Ern1 in epidermal cells was found to depend on Nfr1, Cyclops and Nsp2 but was independent of Nin and Nf-ya1. These results suggest that ERN1 functions as a transcriptional regulator involved in the formation of infection threads and development of nodule primordia, and may coordinate these two processes.

Via Pierre-Marc Delaux
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Transcriptome profiles reveal gene regulation of peanut (Arachis hypogaea L.) nodulation

Transcriptome profiles reveal gene regulation of peanut (Arachis hypogaea L.) nodulation | Plant-Microbe Symbiosis | Scoop.it
The molecular mechanisms of symbiosis in cultivated peanut with a ‘crack entry’ infection process are largely understudied. In this study, we investigated the root transcriptional profiles of two pairs of non-nodulating (nod−) and nodulating (nod+) sister inbred peanut lines, E4/E5 and E7/E6, and their nod+ parents, F487A and PI262090 during rhizobial infection and nodule initiation by using RNA-seq technology. A total of 143, 101, 123, 215, 182, and 289 differentially expressed genes (DEGs) were identified in nod− E4, E7 and nod+ E5, E6, F487A, and PI262090 after inoculation with Bradyrhizobium sp. Different deficiencies at upstream of symbiotic signaling pathway were revealed in the two nod− genotypes. DEGs specific in nod+ genotypes included orthologs to some known symbiotic signaling pathway genes, such as NFR5, NSP2, NIN, ERN1, and many other novel and/or functionally unknown genes. Gene ontology (GO) enrichment analysis of nod+ specific DEGs revealed 54 significantly enriched GO terms, including oxidation-reduction process, metabolic process, and catalytic activity. Genes related with plant defense systems, hormone biosynthesis and response were particularly enriched. To our knowledge, this is the first report revealing symbiosis-related genes in a genome-wide manner in peanut representative of the ‘crack entry’ species.
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Plastomes on the edge: the evolutionary breakdown of mycoheterotroph plastid genomes

Plastomes on the edge: the evolutionary breakdown of mycoheterotroph plastid genomes | Plant-Microbe Symbiosis | Scoop.it

We examine recent evidence for ratchet-like genome degradation in mycoheterotrophs, plants that obtain nutrition from fungi. Initial loss of the NADH dehydrogenase-like (NDH) complex may often set off an irreversible evolutionary cascade of photosynthetic gene losses. Genes for plastid-encoded subunits of RNA polymerase and photosynthetic enzymes with secondary functions (Rubisco and ATP synthase) can persist initially, with nonsynchronous and quite broad windows in the relative timing of their loss. Delayed losses of five core nonbioenergetic genes (especially trnE and accD, which respectively code for glutamyl tRNA and a subunit of acetyl-CoA carboxylase) probably explain long-term persistence of heterotrophic plastomes. The observed range of changes of mycoheterotroph plastomes is similar to that of holoparasites, although greater diversity of both probably remains to be discovered. These patterns of gene loss/retention can inform research programs on plastome function.


Via Pierre-Marc Delaux
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Improvement of Faba Bean Yield Using Rhizobium/Agrobacterium Inoculant in Low-Fertility Sandy Soil

Abstract: Soil fertility is one of the major limiting factors for crop’s productivity in Egypt and the world in general. Biological nitrogen fixation (BNF) has a great importance as a non-polluting and a cost-effective way to improve soil fertility through supplying N to different agricultural systems. Faba bean (Vicia faba L.) is one of the most efficient nitrogen-fixing legumes that can meet all of their N needs through BNF. Therefore, understanding the impact of rhizobial inoculation and contrasting soil rhizobia on nodulation and N2 fixation in faba bean is crucial to optimize the crop yield, particularly under low fertility soil conditions. This study investigated the symbiotic effectiveness of 17 Rhizobium/Agrobacterium strains previously isolated from different Egyptian governorates in improving the nodulation and N2 fixation in faba bean cv. Giza 843 under controlled greenhouse conditions. Five strains that had a high nitrogen-fixing capacity under greenhouse conditions were subsequently tested in field trials as faba bean inoculants at Ismaillia Governorate in northeast Egypt in comparison with the chemical N-fertilization treatment (96 kg N·ha−1). A starter N-dose (48 kg N·ha−1) was applied in combination with different Rhizobium inoculants. The field experiments were established at sites without a background of inoculation under low fertility sandy soil conditions over two successive winter growing seasons, 2012/2013 and 2013/2014. Under greenhouse conditions, inoculated plants produced significantly higher nodules dry weight, plant biomass, and shoot N-uptake than non-inoculated ones. In the first season (2012/2013), inoculation of field-grown faba bean showed significant improvements in seed yield (3.73–4.36 ton·ha−1) and seed N-yield (138–153 Kg N·ha−1), which were higher than the uninoculated control (48 kg N·ha−1) that produced 2.97 Kg·ha−1 and 95 kg N·ha−1, respectively. Similarly, in the second season (2013/2014), inoculation significantly improved seed yield (3.16–4.68 ton·ha−1) and seed N-yield (98–155 Kg N·ha−1) relative to the uninoculated control (48 kg N·ha−1), which recorded 2.58 Kg·ha−1 and 80 kg N·ha−1, respectively. Interestingly, faba bean inoculated with strain Rlv NGB-FR 126 showed significant increments in seed yield (35%–48%) and seed N-yield (34%–49%) compared to the inorganic N fertilizers treatment (96 kg N·ha−1) over the two cropping seasons, respectively. These results indicate that inoculation of faba bean with effective rhizobial strains can reduce the need for inorganic N fertilization to achieve higher crop yield under low fertility soil conditions.
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Synthetic DNA Synthesis and Assembly: Putting the Synthetic in Synthetic Biology

The chemical synthesis of DNA oligonucleotides and their assembly into synthons, genes, circuits, and even entire genomes by gene synthesis methods has become an enabling technology for modern molecular biology and enables the design, build, test, learn, and repeat cycle underpinning innovations in synthetic biology. In this perspective, we briefly review the techniques and technologies that enable the synthesis of DNA oligonucleotides and their assembly into larger DNA constructs with a focus on recent advancements that have sought to reduce synthesis cost and increase sequence fidelity. The development of lower-cost methods to produce high-quality synthetic DNA will allow for the exploration of larger biological hypotheses by lowering the cost of use and help to close the DNA read–write cost gap.

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Bacillus subtilis Early Colonization of Arabidopsis thaliana Roots Involves Multiple Chemotaxis Receptors

Bacillus subtilis Early Colonization of Arabidopsis thaliana Roots Involves Multiple Chemotaxis Receptors | Plant-Microbe Symbiosis | Scoop.it
Colonization of plant roots by Bacillus subtilis is mutually beneficial to plants and bacteria. Plants can secrete up to 30% of their fixed carbon via root exudates, thereby feeding the bacteria, and in return the associated B. subtilis bacteria provide the plant with many growth-promoting traits. Formation of a biofilm on the root by matrix-producing B. subtilis is a well-established requirement for long-term colonization. However, we observed that cells start forming a biofilm only several hours after motile cells first settle on the plant. We also found that intact chemotaxis machinery is required for early root colonization by B. subtilis and for plant protection. Arabidopsis thaliana root exudates attract B. subtilis in vitro, an activity mediated by the two characterized chemoreceptors, McpB and McpC, as well as by the orphan receptor TlpC. Nonetheless, bacteria lacking these chemoreceptors are still able to colonize the root, suggesting that other chemoreceptors might also play a role in this process. These observations suggest that A. thaliana actively recruits B. subtilis through root-secreted molecules, and our results stress the important roles of B. subtilis chemoreceptors for efficient colonization of plants in natural environments. These results demonstrate a remarkable strategy adapted by beneficial rhizobacteria to utilize carbon-rich root exudates, which may facilitate rhizobacterial colonization and a mutualistic association with the host.

IMPORTANCE Bacillus subtilis is a plant growth-promoting rhizobacterium that establishes robust interactions with roots. Many studies have now demonstrated that biofilm formation is required for long-term colonization. However, we observed that motile B. subtilis mediates the first contact with the roots. These cells differentiate into biofilm-producing cells only several hours after the bacteria first contact the root. Our study reveals that intact chemotaxis machinery is required for the bacteria to reach the root. Many, if not all, of the B. subtilis 10 chemoreceptors are involved in the interaction with the plant. These observations stress the importance of root-bacterium interactions in the B. subtilis lifestyle.

Via Ryohei Thomas Nakano
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Comparison of arbuscular mycorrhizal fungal effects on the heavy metal uptake of a host and a non-host plant species in contact with extraradical mycelial network

Comparison of arbuscular mycorrhizal fungal effects on the heavy metal uptake of a host and a non-host plant species in contact with extraradical mycelial network | Plant-Microbe Symbiosis | Scoop.it
The effects of inoculation with an arbuscular mycorrhizal (AM) fungus on Cd and Ni tolerance and uptake in Medicago sativa, an AM host, and Sesuvium portulacastrum, a non-host plant, were investigated in a greenhouse experiment. The plants were cultivated in sterilized sand in a two-compartmented system, which prevented root competition but enabled colonization of the whole substrate by AM fungal extraradical mycelium. M. sativa was either left non-inoculated or inoculated with the AM fungus Rhizophagus irregularis, and both plants were either cultivated without heavy metal (HM) addition or supplied with cadmium (Cd) or nickel (Ni), each in two doses. Additional pots with singly cultivated plants were established to control for the effect of the co-cultivation. AM significantly enhanced the growth of M. sativa and substantially increased its uptake of both HMs. The roots of S. portulacastrum became colonized by AM fungal hyphae and vesicles. The presence of the AM fungus in the cultivation system tended to increase the HM uptake of S. portulacastrum, but the effect was less consistent and pronounced than that in M. sativa. We conclude that AM fungal mycelium radiating from M. sativa did not negatively affect the growth and HM uptake of S. portulacastrum. On the contrary, we hypothesize that it stimulated the absorption and translocation of Cd and Ni in the non-host species. Thus, our results suggest that AM fungal mycelium radiating from mycorrhizal plants does not decrease the HM uptake of non-host plants, many of which are considered promising candidate plants for phytoremediation.

Via Christophe Jacquet
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Reproducibility: A tragedy of errors

Reproducibility: A tragedy of errors | Plant-Microbe Symbiosis | Scoop.it
Just how error-prone and self-correcting is science? We have spent the past 18 months getting a sense of that.


Scientific method: Statistical errors
We are a group of researchers working on obesity, nutrition and energetics. In the summer of 2014, one of us (D.B.A.) read a research paper in a well-regarded journal estimating how a change in fast-food consumption would affect children's weight, and he noted that the analysis applied a mathematical model that overestimated effects by more than tenfold. We and others submitted a letter1 to the editor explaining the problem. Months later, we were gratified to learn that the authors had elected to retract their paper. In the face of popular articles proclaiming that science is stumbling, this episode was an affirmation that science is self-correcting.
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The Critical Thinking Skills Cheatsheet [Infographic] via GDC

The Critical Thinking Skills Cheatsheet [Infographic] via GDC | Plant-Microbe Symbiosis | Scoop.it
We'd like to share this critical thinking skills cheatsheet for you to use with your students. Get them asking questions on any topic!

Via Tom D'Amico (@TDOttawa)
Jean-Michel Ané's insight:

Easily applicable to grant proposals...

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John Rudkin's curator insight, December 17, 2016 12:47 PM
Useful checklist to keep you on the straight and narrow...
Walter Gassenferth's curator insight, December 18, 2016 3:38 AM

Lucid post, presenting interesting data. For those who speak Portuguese or Spanish and are interested in education in business, please visit http://www.quanticaconsultoria.com

Ron McIntyre's curator insight, December 19, 2016 2:14 PM

Interesting insights?

Rescooped by Jean-Michel Ané from MycorWeb Plant-Microbe Interactions
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Lipid metabolic changes in an early divergent fungus govern the establishment of a mutualistic symbiosis with endobacteria

Lipid metabolic changes in an early divergent fungus govern the establishment of a mutualistic symbiosis with endobacteria | Plant-Microbe Symbiosis | Scoop.it
The recent accumulation of newly discovered fungal–bacterial mutualisms challenges the paradigm that fungi and bacteria are natural antagonists. To understand the mechanisms that govern the establishment and maintenance over evolutionary time of mutualisms between fungi and bacteria, we studied a symbiosis of the fungus Rhizopus microsporus (Mucoromycotina) and its Burkholderia endobacteria. We found that nonhost R. microsporus, as well as other mucoralean fungi, interact antagonistically with endobacteria derived from the host and are not invaded by them. Comparison of gene expression profiles of host and nonhost fungi during interaction with endobacteria revealed dramatic changes in expression of lipid metabolic genes in the host. Analysis of the host lipidome confirmed that symbiosis establishment was accompanied by specific changes in the fungal lipid profile. Diacylglycerol kinase (DGK) activity was important for these lipid metabolic changes, as its inhibition altered the fungal lipid profile and caused a shift in the host–bacterial interaction into an antagonism. We conclude that adjustments in host lipid metabolism during symbiosis establishment, mediated by DGKs, are required for the mutualistic outcome of the Rhizopus–Burkholderia symbiosis. In addition, the neutral and phospholipid profiles of R. microsporus provide important insights into lipid metabolism in an understudied group of oleaginous Mucoromycotina. Lastly, our study revealed that the DGKs involved in the symbiosis form a previously uncharacterized clade of DGK domain proteins.

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OsCERK1-mediated chitin perception and immune signaling requires Receptor-like Cytoplasmic Kinase 185 to activate a MAPK cascade in rice

Conserved pathogen-associated molecular patterns (PAMPs), such as chitin, are perceived by pattern recognition receptors (PRRs) located at the host cell surface and trigger rapid activation of mitogen-activated protein kinase (MAPK) cascades, which is required for plant resistance to pathogens. However, the direct link from PAMP perception to MAPK activation in plants is elusive. Here, we found that the PRR-associated receptor-like cytoplasmic kinase Oryza sativa RLCK185 transmits immune signaling from the PAMP receptor OsCERK1 to a MAPK signaling cascade through interaction with a MAPK kinase kinase, OsMAPKKKε, which is the initial kinase of the MAPK cascade. OsRLCK185 interacts with and phosphorylates the C-terminal regulatory domain of OsMAPKKKε. Coexpression of phosphomimetic OsRLCK185 and OsMAPKKKε activates MAPK3/6 phosphorylation in Nicotiana benthamiana leaves. OsMAPKKKε interacts with and phosphorylates OsMKK4, a key MAPK kinase that transduces the chitin signal. OsMAPKKKε overexpression increases chitin-induced MAPK3/6 activation. OsMAPKKKε knockdown compromises chitin-induced MAPK3/6 activation and resistance to rice blast fungus. These findings suggest a phospho-signaling pathway from cell surface chitin perception to intracellular activation of a MAPK cascade in rice.


Via Pierre-Marc Delaux
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Nod factors potentiate auxin signaling for transcriptional regulation and lateral root formation in Medicago truncatula

Nod factors potentiate auxin signaling for transcriptional regulation and lateral root formation in Medicago truncatula | Plant-Microbe Symbiosis | Scoop.it
Nodulation (Nod) factors (NFs) are symbiotic molecules produced by rhizobia that are essential for establishment of the rhizobium–legume endosymbiosis. Purified NFs can stimulate lateral root formation (LRF) in Medicago truncatula, but little is known about the molecular mechanisms involved. Using a combination of reporter constructs, pharmacological and genetic approaches, we show that NFs act on early steps of LRF in M. truncatula, independently of the ethylene signaling pathway and of the cytokinin receptor MtCRE1, but in interaction with auxin. We conducted a whole-genome transcriptomic study upon NF and/or auxin treatments, using a lateral root inducible system adapted for M. truncatula. This revealed a large overlap between NF and auxin signaling and, more interestingly, synergistic interactions between these molecules. Three groups showing interaction effects were defined: group 1 contained more than 1500 genes responding specifically to the combinatorial treatment of NFs and auxin; group 2 comprised auxin-regulated genes whose expression was enhanced or antagonized by NFs; and in group 3 the expression of NF regulated genes was antagonized by auxin. Groups 1 and 2 were enriched in signaling and metabolic functions, which highlights important crosstalk between NF and auxin signaling for both developmental and symbiotic processes.
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Elucidating rhizosphere processes by mass spectrometry – A review

Elucidating rhizosphere processes by mass spectrometry – A review | Plant-Microbe Symbiosis | Scoop.it
The presented review discusses state-of-the-art mass spectrometric methods, which have been developed and applied for investigation of chemical processes in the soil-root interface, the so-called rhizosphere. Rhizosphere soil's physical and chemical characteristics are to a great extent influenced by a complex mixture of compounds released from plant roots, i.e. root exudates, which have a high impact on nutrient and trace element dynamics in the soil-root interface as well as on microbial activities or soil physico-chemical characteristics. Chemical characterization as well as accurate quantification of the compounds present in the rhizosphere is a major prerequisite for a better understanding of rhizosphere processes and requires the development and application of advanced sampling procedures in combination with highly selective and sensitive analytical techniques. During the last years, targeted and non-targeted mass spectrometry-based methods have emerged and their combination with specific separation methods for various elements and compounds of a wide polarity range have been successfully applied in several studies. With this review we critically discuss the work that has been conducted within the last decade in the context of rhizosphere research and elemental or molecular mass spectrometry emphasizing different separation techniques as GC, LC and CE. Moreover, selected applications such as metal detoxification or nutrient acquisition will be discussed regarding the mass spectrometric techniques applied in studies of root exudates in plant-bacteria interactions. Additionally, a more recent isotope probing technique as novel mass spectrometry based application is highlighted.

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Arbuscular mycorrhizal fungal community composition is altered by long‐term litter removal but not litter addition in a lowland tropical forest

Tropical forest productivity is sustained by the cycling of nutrients through decomposing organic matter. Arbuscular mycorrhizal (AM) fungi play a key role in the nutrition of tropical trees, yet there has been little experimental investigation into the role of AM fungi in nutrient cycling via decomposing organic material in tropical forests.
We evaluated the responses of AM fungi in a long-term leaf litter addition and removal experiment in a tropical forest in Panama. We described AM fungal communities using 454-pyrosequencing, quantified the proportion of root length colonised by AM fungi using microscopy, and estimated AM fungal biomass using a lipid biomarker.
AM fungal community composition was altered by litter removal but not litter addition. Root colonisation was substantially greater in the superficial organic layer compared with the mineral soil. Overall colonisation was lower in the litter removal treatment, which lacked an organic layer. There was no effect of litter manipulation on the concentration of the AM fungal lipid biomarker in the mineral soil.
We hypothesise that reductions in organic matter brought about by litter removal may lead to AM fungi obtaining nutrients from recalcitrant organic or mineral sources in the soil, besides increasing fungal competition for progressively limited resources.
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Activation of a calcium-dependent protein kinase involved in the Azospirillum growth promotion in rice

Rice seedlings (Oryza sativa) inoculated with the plant growth-promoting rhizobacteria Azospirillum brasilense FT326 showed an enhanced development of the root system 3 days after inoculation. Later on, a remarkable enlargement of shoots was also evident. An increase in the Ca2+-dependent histone kinase activity was also detected as a result of inoculation. The biochemical characterization and Western-blot analysis of the kinase strongly supports the hypothesis that it belongs to a member of the rice CDPK family. The fact that the amount of the protein did not change upon inoculation seems to indicate that a posttranslational activation is responsible for the change in the enzymatic activity. An in-gel kinase experiment identified a 46 kDa CDPK like protein kinase as a putative component of the signal transduction pathway triggered by Azospirillum inoculation. To our knowledge, this is the first report on the possible involvement of a Ca2+-dependent protein kinase in promotion of rice plants growth by A. brasilense.

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Salinity stress alleviation using arbuscular mycorrhizal fungi. A review

Salinity is one of the most severe environmental stress as it decreases crop production of more than 20% of irrigated land worldwide. Hence, it is important to develop salt-tolerant crops. Understanding the mechanisms that enable plant growth under saline conditions is therefore required. Acclimation of plants to salinized conditions depends upon activation of cascades of molecular networks involved in stress sensing, signal transduction, and the expression of specific stress-related genes and metabolites. The stress signal is first perceived at the membrane level by the receptors and then transduced in the cell to switch on the stress-responsive genes which mediate stress tolerance. In addition to stress-adaptative mechanisms developed by plants, arbuscular mycorrhizal fungi have been shown to improve plant tolerance to abiotic environmental factors such as salinity. In this review, we emphasize the significance of arbuscular mycorrhizal fungi alleviation of salt stress and their beneficial effects on plant growth and productivity. Although salinity can affect negatively arbuscular mycorrhizal fungi, many reports show improved growth and performance of mycorrhizal plants under salt stress conditions. These positive effects are explained by improved host plant nutrition, higher K+/Na+ ratios in plant tissues and a better osmotic adjustment by accumulation of compatible solutes such as proline, glycine betaine, or soluble sugars. Arbuscular mycorrhizal plants also improve photosynthetic- and water use efficiency under salt stress. Arbuscular mycorrhizal plants enhance the activity of antioxidant enzymes in order to cope with the reactive oxygen species generated by salinity. At the molecular level, arbuscular mycorrhizal symbiosis regulates the expression of plant genes involved in the biosynthesis of proline, of genes encoding aquaporins, and of genes encoding late embryogenesis abundant proteins, with chaperone activity. The regulation of these genes allows mycorrhizal plants to maintain a better water status in their tissues. Gene expression patterns suggest that mycorrhizal plants are less strained by salt stress than non-mycorrhizal plants. In contrast, scarce information is available on the possible regulation by the arbuscular mycorrhizal symbiosis of plant genes encoding Na+/H+ antiporters or cyclic nucleotide-gated channels. These genes encode proteins with a key role in the regulation of uptake, distribution and compartimentation of sodium and other ions within the plant, and are major determinants for the salt sensitiveness of a plant. Thus, we propose that investigating the participation of cation proton antiporters and cyclic nucleotide-gated channels on arbuscular mycorrhizal symbiosis under salinity is a promising field that should shed further light on new mechanisms involved in the enhanced tolerance of mycorrhizal plants to salt stress.

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Bob Reeves's curator insight, January 9, 6:53 AM
Here in Ontario, we'll be testing to see if mycorrhizae can help reduce the stresses caused by road salt application on boulevard and highway plantings.
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Positive Gene Regulation by a Natural Protective miRNA Enables Arbuscular Mycorrhizal Symbiosis

Positive Gene Regulation by a Natural Protective miRNA Enables Arbuscular Mycorrhizal Symbiosis | Plant-Microbe Symbiosis | Scoop.it
Arbuscular mycorrhizal (AM) symbiosis associates most plants with fungi of the phylum Glomeromycota. The fungus penetrates into roots and forms within cortical cell branched structures called arbuscules for nutrient exchange. We discovered that miR171b has a mismatched cleavage site and is unable to downregulate the miR171 family target gene, LOM1 (LOST MERISTEMS 1). This mismatched cleavage site is conserved among plants that establish AM symbiosis, but not in non-mycotrophic plants. Unlike other members of the miR171 family, miR171b stimulates AM symbiosis and is expressed specifically in root cells that contain arbuscules. MiR171b protects LOM1 from negative regulation by other miR171 family members. These findings uncover a unique mechanism of positive post-transcriptional regulation of gene expression by miRNAs and demonstrate its relevance for the establishment of AM symbiosis.
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Very nice work

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Rescooped by Jean-Michel Ané from Plant immunity and legume symbiosis
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Function and evolution of a Lotus japonicus AP2/ERF family transcription factor that is required for development of infection threads

Function and evolution of a Lotus japonicus AP2/ERF family transcription factor that is required for development of infection threads | Plant-Microbe Symbiosis | Scoop.it
Legume-rhizobium symbiosis is achieved by two major events evolutionarily acquired: root hair infection and organogenesis. Infection thread (IT) development is a distinct element for rhizobial infection. Through ITs, rhizobia are efficiently transported from infection foci on root hairs to dividing meristematic cortical cells. To unveil this process, we performed genetic screening using Lotus japonicus MG-20 and isolated symbiotic mutant lines affecting nodulation, root hair morphology, and IT development. Map-based cloning identified an AP2/ERF transcription factor gene orthologous to Medicago truncatula ERN1. LjERN1 was activated in response to rhizobial infection and depended on CYCLOPS and NSP2. Legumes conserve an ERN1 homolog, ERN2, that functions redundantly with ERN1 in M. truncatula. Phylogenetic analysis showed that the lineages of ERN1 and ERN2 genes originated from a gene duplication event in the common ancestor of legume plants. However, genomic analysis suggested the lack of ERN2 gene in the L. japonicus genome, consistent with Ljern1 mutants exhibited a root hair phenotype that is observed in ern1/ern2 double mutants in M. truncatula. Molecular evolutionary analysis suggested that the nonsynonymous/synonymous rate ratios of legume ERN1 genes was almost identical to that of non-legume plants, whereas the ERN2 genes experienced a relaxed selective constraint.

Via Christophe Jacquet
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Rescooped by Jean-Michel Ané from Impact of plant domestication on rhizosphere microbiome
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Successional Trajectories of Rhizosphere Bacterial Communities over Consecutive Seasons

Successional Trajectories of Rhizosphere Bacterial Communities over Consecutive Seasons | Plant-Microbe Symbiosis | Scoop.it


It is well known that rhizosphere microbiomes differ from those of surrounding soil, and yet we know little about how these root-associated microbial communities change through the growing season and between seasons. We analyzed the response of soil bacteria to roots of the common annual grass Avena fatua over two growing seasons using high-throughput sequencing of 16S rRNA genes. Over the two periods of growth, the rhizosphere bacterial communities followed consistent successional patterns as plants grew, although the starting communities were distinct. Succession in the rhizosphere was characterized by a significant decrease in both taxonomic and phylogenetic diversity relative to background soil communities, driven by reductions in both richness and evenness of the bacterial communities. Plant roots selectively stimulated the relative abundance of Alphaproteobacteria, Betaproteobacteria, and Bacteroidetes but reduced the abundance of Acidobacteria, Actinobacteria, and Firmicutes. Taxa that increased in relative abundance in the rhizosphere soil displayed phylogenetic clustering, suggesting some conservation and an evolutionary basis for the response of complex soil bacterial communities to the presence of plant roots. The reproducibility of rhizosphere succession and the apparent phylogenetic conservation of rhizosphere competence traits suggest adaptation of the indigenous bacterial community to this common grass over the many decades of its presence.

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Changes in plastid proteome and structure in arbuscular mycorrhizal roots display a nutrient starvation signature

During arbuscular mycorrhizal symbiosis, arbuscule-containing root cortex cells display a proliferation of plastids, a feature usually ascribed to an increased plant anabolism despite the lack of studies focusing on purified root plastids. In this study, we investigated mycorrhiza-induced changes in plastidic pathways by performing a label-free comparative subcellular quantitative proteomic analysis targeted on plastid-enriched fractions isolated from Medicago truncatula roots, coupled to a cytological analysis of plastid structure. We identified 490 root plastid protein candidates, among which 79 changed in abundance upon mycorrhization, as inferred from spectral counting. According to cross-species sequence homology searches, the mycorrhiza-responsive proteome was enriched in proteins experimentally localized in thylakoids, whereas it was depleted of proteins ascribed predominantly to amyloplasts. Consistently, the analysis of plastid morphology using transmission electron microscopy indicated that starch depletion associated with the proliferation of membrane-free and tubular membrane-containing plastids was a feature specific to arbusculated cells. The loss of enzymes involved in carbon/nitrogen assimilation and provision of reducing power, coupled to macromolecule degradation events in the plastid-enriched fraction of mycorrhizal roots that paralleled lack of starch accumulation in arbusculated cells, lead us to propose that arbuscule functioning elicits a nutrient starvation and an oxidative stress signature that may prime arbuscule breakdown.
Jean-Michel Ané's insight:

Very interesting!

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Rescooped by Jean-Michel Ané from Nature et Biodiversité en Ville
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Cette bande dessinée pourrait bien sauver les sols

Cette bande dessinée pourrait bien sauver les sols | Plant-Microbe Symbiosis | Scoop.it
Alors qu’ils sont à la base de notre alimentation et de notre santé, les sols ne bénéficient d’aucune réglementation. Pour les protéger, plus de 400 associations se sont réunies pour la mise en place d’une législation européenne.

Via La Bièvre - SMBVB
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La Bièvre - SMBVB's curator insight, December 11, 2016 12:42 PM
Les sols nous sont indispensables et pourtant nous les maltraitons sans en avoir conscience. Le sol est fragile, s'est constitué sur des millénaires et est détruit d'un coup de pelle mécanique ou à force de labours profonds qui en détruisent la structure. Il faut les préserver et cette sensibilisation doit aussi concerner la ville. En laissant de la place à la nature, en allant vers l'agriculture urbaine de plein sol, nous pouvons essayer de stopper ce mouvement d'artificialisation. Pour vous convaincre de l'intérêt des sols, vous pouvez lire cette BD.