Plant-microbe interaction
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J Plant Science: Differential spatio-temporal expression of carotenoid cleavage dioxygenases regulates apocarotenoid fluxes during AM symbiosis

J Plant Science: Differential spatio-temporal expression of carotenoid cleavage dioxygenases regulates apocarotenoid fluxes during AM symbiosis | Plant-microbe interaction | Scoop.it

Apocarotenoids are a class of compounds that play important roles in nature. In recent years, a prominent role for these compounds in arbuscular mycorrhizal (AM) symbiosis has been shown. They are derived from carotenoids by the action of the carotenoid cleavage dioxygenase (CCD) enzyme family. In the present study, using tomato as a model, the spatio-temporal expression pattern of the CCD genes during AM symbiosis establishment and functioning was investigated. In addition, the levels of the apocarotenoids strigolactones (SLs), C13 α-ionol and C14 mycorradicin (C13/C14) derivatives were analyzed. The results suggest an increase in SLs promoted by the presence of the AM fungus at the early stages of the interaction, which correlated with an induction of the SL biosynthesis gene SlCCD7. At later stages, induction of SlCCD7 and SlCCD1 expression in arbusculated cells promoted the production of C13/C14 apocarotenoid derivatives. We show here that the biosynthesis of apocarotenoids during AM symbiosis is finely regulated throughout the entire process at the gene expression level, and that CCD7 constitutes a key player in this regulation. Once the symbiosis is established, apocarotenoid flux would be turned towards the production of C13/C14 derivatives, thus reducing SL biosynthesis and maintaining a functional symbiosis.
López-Ráez JA, Fernández I, García JM, Berrio E, Bonfante P, Walter MH, Pozo MJ
DOI: 10.1016/j.plantsci.2014.10.010

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Les substances naturelles de biocontrôle pour lutter contre les agents pathogènes

Dans le cadre du séminaire "Biocontrôle et expérimentation" organisé par AgroSYS (Montpellier SupAgro), Elsa Ballini nous présente les substances naturelle

Via Agriculture Nouvelle
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Cell Biology: Control of Partner Lifetime in a Plant–Fungus Relationship

Cell Biology: Control of Partner Lifetime in a Plant–Fungus Relationship | Plant-microbe interaction | Scoop.it
Arbuscules are tree-shaped fungal structures inside plant root cells that facilitate the exchange of nutrients delivered by the fungus with carbon sources from the host. To maintain symbiotic efficiency, plant cells can trigger degeneration of underperforming arbuscules. A recent study reveals the first transcription factor, which induces genes encoding hydrolytic enzymes, to mediate arbuscule degeneration.
Gutjahr C, Parniske M
DOI: 10.1016/j.cub.2017.04.020
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PNAS: Live imaging of root–bacteria interactions in a microfluidics setup (2017)

PNAS: Live imaging of root–bacteria interactions in a microfluidics setup (2017) | Plant-microbe interaction | Scoop.it

Plant roots play a dominant role in shaping the rhizosphere, the environment in which interaction with diverse microorganisms occurs. Tracking the dynamics of root–microbe interactions at high spatial resolution is currently limited because of methodological intricacy. Here, we describe a microfluidics-based approach enabling direct imaging of root–bacteria interactions in real time. The microfluidic device, which we termed tracking root interactions system (TRIS), consists of nine independent chambers that can be monitored in parallel. The principal assay reported here monitors behavior of fluorescently labeled Bacillus subtilis as it colonizes the root of Arabidopsis thaliana within the TRIS device. Our results show a distinct chemotactic behavior of B. subtilis toward a particular root segment, which we identify as the root elongation zone, followed by rapid colonization of that same segment over the first 6 h of root–bacteria interaction. Using dual inoculation experiments, we further show active exclusion of Escherichia coli cells from the root surface after B. subtilis colonization, suggesting a possible protection mechanism against root pathogens. Furthermore, we assembled a double-channel TRIS device that allows simultaneous tracking of two root systems in one chamber and performed real-time monitoring of bacterial preference between WT and mutant root genotypes. Thus, the TRIS microfluidics device provides unique insights into the microscale microbial ecology of the complex root microenvironment and is, therefore, likely to enhance the current rate of discoveries in this momentous field of research.


Via IPM Lab, Kamoun Lab @ TSL, Stéphane Hacquard, Francis Martin
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Plant Phys: Phosphate Treatment Strongly Inhibits New Arbuscule Development But Not the Maintenance of Arbuscule in Mycorrhizal Rice Roots

Plant Phys: Phosphate Treatment Strongly Inhibits New Arbuscule Development But Not the Maintenance of Arbuscule in Mycorrhizal Rice Roots | Plant-microbe interaction | Scoop.it
Phosphorus (P) is a crucial nutrient for plant growth, but its availability to roots is limited in soil. Arbuscular mycorrhizal (AM) symbiosis is a promising strategy for improving plant P acquisition. However, P fertilizer reduces fungal colonization (P inhibition) and compromises mycorrhizal P uptake, warranting studies on the mechanistic basis of P inhibition. In this study, early morphological changes in P inhibition were identified in rice (Oryza sativa) using fungal cell wall staining and live-cell imaging of plant membranes that were associated with arbuscule life cycles. Arbuscule density decreased, and aberrant hyphal branching was observed in roots at 5 h after P treatment. Although new arbuscule development was severely inhibited, preformed arbuscules remained intact and longevity remained constant. P inhibition was accelerated in the rice pt11-1 mutant, which lacks P uptake from arbuscule branches, suggesting that mature arbuscules are stabilized by the symbiotic P transporter under high P condition. Moreover, P treatment led to increases in the number of vesicles, in which lipid droplets accumulated and then decreased within a few days. The development of new arbuscules resumed within by 2 d. Our data established that P strongly and temporarily inhibits new arbuscule development, but not intraradical accommodation of AM fungi.
Kobae Y, Ohmori Y, Saito C, Yano K, Ohtomo R, Fujiwara T
DOI: ​10.​1104/​pp.​16.​00127 dit the content
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MPMI: Haustorium Formation in Medicago truncatula Roots Infected by Phytophthora palmivora Does Not Involve the Common Endosymbiotic Program Shared by Arbuscular Mycorrhizal Fungi and Rhizobia

MPMI: Haustorium Formation in Medicago truncatula Roots Infected by Phytophthora palmivora Does Not Involve the Common Endosymbiotic Program Shared by Arbuscular Mycorrhizal Fungi and Rhizobia | Plant-microbe interaction | Scoop.it
In biotrophic plant-microbe interactions, microbes infect living plant cells, in which they are hosted in a novel membrane compartment, the host-microbe interface. To create a host-microbe interface, arbuscular mycorrhizal (AM) fungi and rhizobia make use of the same endosymbiotic program. It is a long-standing hypothesis that pathogens make use of plant proteins that are dedicated to mutualistic symbiosis to infect plants and form haustoria. In this report, we developed a Phytophthora palmivora pathosystem to study haustorium formation in Medicago truncatula roots. We show that P. palmivora does not require host genes that are essential for symbiotic infection and host-microbe interface formation to infect Medicago roots and form haustoria. Based on these findings, we conclude that P. palmivora does not hijack the ancient intracellular accommodation program used by symbiotic microbes to form a biotrophic host-microbe interface.
Huisman R, Bouwmeester K, Brattinga M, Govers F, Bisseling T, Limpens E.
DOI: 10.1094/MPMI-06-15-0130-R
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Trends in Plant Science: Beneficial Microbes Affect Endogenous Mechanisms Controlling Root Development

Trends in Plant Science: Beneficial Microbes Affect Endogenous Mechanisms Controlling Root Development | Plant-microbe interaction | Scoop.it

Plants have incredible developmental plasticity, enabling them to respond to a wide range of environmental conditions. Among these conditions is the presence of plant growth-promoting rhizobacteria (PGPR) in the soil. Recent studies show that PGPR affect Arabidopsis thaliana root growth and development by modulating cell division and differentiation in the primary root and influencing lateral root development. These effects lead to dramatic changes in root system architecture that significantly impact aboveground plant growth. Thus, PGPR may promote shoot growth via their effect on root developmental programs. This review focuses on contextualizing root developmental changes elicited by PGPR in light of our understanding of plant–microbe interactions and root developmental biology.

Trends
- Interaction between plant roots and the beneficial bacteria within their rhizosphere shapes the bacteria community composition, and enhances plant growth and plant pathogen defense.
- Plant growth-promoting rhizobacteria (PGPR) affect cell division and differentiation leading to changes in root system architecture, which contributes to enhanced shoot growth. These modifications are established by changing plant endogenous signaling pathways.
- While several PGPR can produce phytohormones, many effects on plant developmental pathways are exerted by other molecules.
- Several fungi have the same effects on root system architecture as PGPR, indicating that growth-promoting mechanisms might be conserved across kingdoms.

Verbon EH & Liberman LM
DOI: 10.1016/j.tplants.2016.01.013

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Appressorium-mediated penetration of Magnaporthe oryzae and Colletotrichum orbiculare into surface-cross-linked agar media

Appressorium-mediated penetration of Magnaporthe oryzae and Colletotrichum orbiculare into surface-cross-linked agar media | Plant-microbe interaction | Scoop.it

Many phytopathogenic fungi form appressoria on some artificial substances. However, it is difficult to induce appressorium-mediated penetration into artificial substances. In the present study, novel artificial agar media were developed to investigate the in vitro penetration process of phytopathogenic fungi. The media contained sodium carboxymethyl cellulose or sodium alginate, and the surfaces were subjected to ionic cross-linking using trivalent metal ions. The hemibiotrophic phytopathogenic fungi, rice blast fungus and cucurbit anthracnose fungus, formed appressoria and penetrated into the surface cross-linked artificial agar media from the base of appressoria. These artificial media appeared to induce fungal infection behaviour that occurred on host plants.
Tanaka E
DOI: 10.1093/femsle/fnv066

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Plant Physiology: Hyphal Branching during Arbuscule Development Requires Reduced Arbuscular Mycorrhiza

Plant Physiology: Hyphal Branching during Arbuscule Development Requires Reduced Arbuscular Mycorrhiza | Plant-microbe interaction | Scoop.it

During arbuscular mycorrhizal symbiosis, arbuscule development in the root cortical cell and simultaneous deposition of the plant periarbuscular membrane generate the interface for symbiotic nutrient exchange. The transcriptional changes that accompany arbuscule development are extensive and well documented. By contrast, the transcriptional regulators that control these programs are largely unknown. Here, we provide a detailed characterization of an insertion allele of Medicago truncatula Reduced Arbuscular Mycorrhiza1 (RAM1), ram1-3, which reveals that RAM1 is not necessary to enable hyphopodium formation or hyphal entry into the root but is essential to support arbuscule branching. In ram1-3, arbuscules consist only of the arbuscule trunk and in some cases, a few initial thick hyphal branches. ram1-3 is also insensitive to phosphate-mediated regulation of the symbiosis. Transcript analysis of ram1-3 and ectopic expression of RAM1 indicate that RAM1 regulates expression of EXO70I and Stunted Arbuscule, two genes whose loss of function impacts arbuscule branching. Furthermore, RAM1 regulates expression of a transcription factor Required for Arbuscule Development (RAD1). RAD1 is also required for arbuscular mycorrhizal symbiosis, and rad1 mutants show reduced colonization. RAM1 itself is induced in colonized root cortical cells, and expression of RAM1 and RAD1 is modulated by DELLAs. Thus, the data suggest that DELLAs regulate arbuscule development through modulation of RAM1 and RAD1 and that the precise transcriptional control essential to place proteins in the periarbuscular membrane is controlled, at least in part, by RAM1.
Park HJ, Floss DS, Levesque-Tremblay V, Bravo A , Harrison MJ
DOI: 10.1104/pp.15.01155

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Frontiers: Fungal association and utilization of phosphate by plants: success, limitations, and future prospects

Phosphorus (P) is a major macronutrient for plant health and development. The available form of P is generally low in the rhizosphere even in fertile soils. A major proportion of applied phosphate (Pi) fertilizers in the soil become fixed into insoluble, unavailable forms, which restricts crop production throughout the world. Roots possess two distinct modes of P uptake from the soil, direct and indirect uptake. The direct uptake of P is facilitated by the plant’s own Pi transporters while indirect uptake occurs via mycorrhizal symbiosis, where the host plant obtains P primarily from the fungal partner, while the fungus benefits from plant-derived reduced carbon. So far, only one Pi transporter has been characterized from the mycorrhizal fungus Glomus versiforme. As arbuscular mycorrhizal fungi cannot be cultured axenically, their Pi transporter network is difficult to exploite for large scale sustainable agriculture. Alternatively, the root-colonizing endophytic fungus Piriformospora indica can grow axenically and provides strong growth-promoting activity during its symbiosis with a broad spectrum of plants. P. indica contains a high affinity Pi transporter (PiPT) involved in improving Pi nutrition levels in the host plant under P limiting conditions. As P. indica can be manipulated genetically, it opens new vistas to be used in P deficient fields.
Johri AK, Oelmüller R, Dua M, Yadav V, Kumar M, Tuteja N, Varma A, Bonfante P, Persson BL, Stroud RM
DOI: 10.3389/fmicb.2015.00984

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BMC lant Biol: The strigolactone biosynthesis gene DWARF27 is co-opted in rhizobium symbiosis

BMC lant Biol: The strigolactone biosynthesis gene DWARF27 is co-opted in rhizobium symbiosis | Plant-microbe interaction | Scoop.it

BACKGROUND:
Strigolactones are a class of plant hormones whose biosynthesis is activated in response to phosphate starvation. This involves several enzymes, including the carotenoid cleavage dioxygenases 7 (CCD7) and CCD8 and the carotenoid isomerase DWARF27 (D27). D27 expression is known to be responsive to phosphate starvation. In Medicago truncatula and rice (Oryza sativa) this transcriptional response requires the GRAS-type proteins NSP1 and NSP2; both proteins are essential for rhizobium induced root nodule formation in legumes. In line with this, we questioned whether MtNSP1-MtNSP2 dependent MtD27 regulation is co-opted in rhizobium symbiosis.
RESULTS:
We provide evidence that MtD27 is involved in strigolactone biosynthesis in M. truncatula roots upon phosphate stress. Spatiotemporal expression studies revealed that this gene is also highly expressed in nodule primordia and subsequently becomes restricted to the meristem and distal infection zone of a mature nodules. A similar expression pattern was found for MtCCD7 and MtCCD8. Rhizobium lipo-chitooligosaccharide (LCO) application experiments revealed that of these genes MtD27 is most responsive in an MtNSP1 and MtNSP2 dependent manner. Symbiotic expression of MtD27 requires components of the symbiosis signaling pathway; including MtDMI1, MtDMI2, MtDMI3/MtCCaMK and in part MtERN1. This in contrast to MtD27 expression upon phosphate starvation, which only requires MtNSP1 and MtNSP2.
CONCLUSION:
Our data show that the phosphate-starvation responsive strigolactone biosynthesis gene MtD27 is also rapidly induced by rhizobium LCO signals in an MtNSP1 and MtNSP2-dependent manner. Additionally, we show that MtD27 is co-expressed with MtCCD7 and MtCCD8 in nodule primordia and in the infection zone of mature nodules.
van Zeijl A, Liu W, Xiao TT, Kohlen W, Yang WC, Bisseling T, Geurts R.
DOI: 10.1186/s12870-015-0651-x

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Planta: The Medicago truncatula MtRbohE gene is activated in arbusculated cells and is involved in root cortex colonization

Our study demonstrated that the NAPDH oxidase gene MtRbohE is expressed in arbusculated cells and plays a role in arbuscule development. Plant NADPH oxidases, known as respiratory burst oxidase homologs (RBOH), belong to a multigenic family that plays an important role in the regulation of plant development and responses to biotic and abiotic stresses. In this study, we monitored the expression profiles of five Rboh genes (MtRbohA, MtRbohB, MtRbohE, MtRbohG, MtRbohF) in the roots of the model species Medicago truncatula upon colonization by arbuscular mycorrhizal fungi. A complementary cellular and molecular approach was used to monitor changes in mRNA abundance and localize transcripts in different cell types from mycorrhizal roots. Rboh transcript levels did not drastically change in total RNA extractions from whole mycorrhizal and non-mycorrhizal roots. Nevertheless, the analysis of laser microdissected cells and Agrobacterium rhizogenes-transformed roots expressing a GUS transcriptional fusion construct highlighted the MtRbohE expression in arbuscule-containing cells. Furthermore, the down regulation of MtRbohE by an RNAi approach generated an altered colonization pattern in the root cortex, when compared to control roots, with fewer arbuscules and multiple penetration attempts. Altogether our data indicate a transient up-regulation of MtRbohE expression in cortical cells colonized by arbuscules and suggest a role for MtRbohE in arbuscule accommodation within cortical cells.
Belmondo S, Calcagno C, Genre A, Puppo A, Pauly N, Lanfranco L.
DOI: 10.1007/s00425-015-2407-0

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Frontiers: Host and non-host roots in rice: cellular and molecular approaches reveal differential responses to arbuscular mycorrhizal fungi

Oryza sativa, a model plant for Arbuscular Mycorrhizal (AM) symbiosis, has both host and non-host roots. Large lateral (LLR) and fine lateral (FLR) roots display opposite responses: LLR support AM colonization, but FLR do not. Our research aimed to study the molecular, morphological and physiological aspects related to the non-host behavior of FLR. RNA-seq analysis revealed that LLR and FLR displayed divergent expression profiles, including changes in many metabolic pathways. Compared with LLR, FLR showed down-regulation of genes instrumental for AM establishment and gibberellin signaling, and a higher expression of nutrient transporters. Consistent with the transcriptomic data, FLR had higher phosphorus content. Light and electron microscopy demonstrated that, surprisingly, in the Selenio cultivar, FLR have a two-layered cortex, which is theoretically compatible with AM colonization. According to RNA-seq, a gibberellin inhibitor treatment increased anticlinal divisions leading to a higher number of cortex cells in FLR. We propose that some of the differentially regulated genes that lead to the anatomical and physiological properties of the two root types also function as genetic factors regulating fungal colonization. The rice root apparatus offers a unique tool to study AM symbiosis, allowing direct comparisons of host and non-host roots in the same individual plant.
Fiorilli V, Vallino M, Biselli C, Faccio A, Bagnaresi P, Bonfante P.
DOI: 10.3389/fpls.2015.00636

 

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Plant, Cell & Environment: Arbuscular mycorrhizal symbiosis induces strigolactone biosynthesis under drought and improves drought tolerance in lettuce and tomato

Plant, Cell & Environment: Arbuscular mycorrhizal symbiosis induces strigolactone biosynthesis under drought and improves drought tolerance in lettuce and tomato | Plant-microbe interaction | Scoop.it

Arbuscular mycorrhizal (AM) symbiosis alleviates drought stress in plants. However the intimate mechanisms involved, as well as its effect on the production of signalling molecules associated to the host plant-AM fungus interaction remains largely unknown. In the present work, the effects of drought on lettuce and tomato plant performance and hormone levels were investigated in non-AM and AM plants. Three different water regimes were applied and their effects analysed over time. AM plants showed an improved growth rate and efficiency of photosystem II than non-AM plants under drought from very early stages of plant colonization. The levels of the phytohormone abscisic acid, as well as the expression of the corresponding marker genes, were influenced by drought stress in non-AM and AM plants. The levels of strigolactones and the expression of corresponding marker genes were affected by both AM symbiosis and drought. The results suggest that AM symbiosis alleviates drought stress by altering the hormonal profiles and affecting plant physiology in the host plant. In addition, a correlation between AM root colonization, strigolactone levels and drought severity is shown, suggesting that under these unfavourable conditions plants might increase strigolactone production in order to promote symbiosis establishment to cope with the stress.
Ruiz-Lozano JM, Aroca R, Zamarreño ÁM, Molina S, Andreo-Jiménez B, Porcel R,  García-Mina JM, Ruyter-Spira C, López-Ráez JA
DOI: 10.1111/pce.12631

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PNAS: Pulses of Ca2+ coordinate actin assembly and exocytosis for stepwise cell extension

PNAS: Pulses of Ca2+ coordinate actin assembly and exocytosis for stepwise cell extension | Plant-microbe interaction | Scoop.it
The day–night rhythm in living organisms controls many processes, which then oscillate in a circadian manner. In addition, there are many processes that appear continuous but the underlying mechanisms oscillate with distinct periods. For example, eukaryotic cells grow by extending their cell periphery in pulses rather than by continuous extension. Here we investigate the molecular basis for such oscillatory growth by using the unique tip growth system of filamentous fungi, where actin assembly, exocytosis, and growth rate were observed simultaneously. We provide evidence that temporally controlled actin assembly and exocytosis are coordinated by pulsed Ca2+ influxes, resulting in stepwise cell extension. This mechanism allows the cells to respond more quickly to both internal and environmental cues, including chemical and mechanical stimuli.
Takeshitaa N, Evangelinos M, Zhoud L, Serizawa T, Somera-Fajardo RA, Lu L, Takaya N, Nienhaus GU, Fischer R
DOi: 10.1073/pnas.1700204114
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Science: Fatty acids in arbuscular mycorrhizal fungi are synthesized by the host plant

Science: Fatty acids in arbuscular mycorrhizal fungi are synthesized by the host plant | Plant-microbe interaction | Scoop.it
Plants form beneficial associations with arbuscular mycorrhizal fungi, which facilitate nutrient acquisition from the soil. In return, the fungi receive organic carbon from the plants. The transcription factor RAM1 (REQUIRED FOR ARBUSCULAR MYCORRHIZATION 1) is crucial for this symbiosis, and we demonstrate that it is required and sufficient for the induction of a lipid biosynthetic pathway that is expressed in plant cells accommodating fungal arbuscules. Lipids are transferred from the plant to mycorrhizal fungi, which are fatty acid auxotrophs, and this lipid export requires the glycerol-3-phosphate acyltransferase RAM2, a direct target of RAM1. Our work shows that in addition to sugars, lipids are a major source of organic carbon delivered to the fungus, and this is necessary for the production of fungal lipids.
Luginbuehl LH, Menard GN, Kurup S, Van Erp H, Radhakrishnan GV, Breakspear A, Oldroyd GED, Eastmond PJ
DOI: 10.1126/science.aan0081
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LRSV/LIPM/iMMM2017 - "3rd international Molecular Mycorrhiza Meeting"

LRSV/LIPM/iMMM2017 - "3rd international Molecular Mycorrhiza Meeting" | Plant-microbe interaction | Scoop.it
After Munich (2012) and Cambridge (2015), the next "international molecular mycorrhiza meeting" will take place in Toulouse. July, 26-28 2017.
www.immm2017.com

Via Marie Aizpuru
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Marie Aizpuru's curator insight, August 2, 2016 4:46 AM
Une adresse www.immm2017.com - Un fil twitter @iMMM_2017
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Cell: Root Endophyte Colletotrichum tofieldiae Confers Plant Fitness Benefits that Are Phosphate Status Dependent

Cell: Root Endophyte Colletotrichum tofieldiae Confers Plant Fitness Benefits that Are Phosphate Status Dependent | Plant-microbe interaction | Scoop.it
Highlights
•Colletotrichum tofieldiae (Ct) is a fungal root endophyte of Arabidopsis
•Ct transfers the macronutrient phosphorus to Arabidopsis shoots •Ct-mediated plant growth promotion needs an intact phosphate starvation response
•A branch of the plant innate immune system is essential for beneficial Ct activities
Summary
A staggering diversity of endophytic fungi associate with healthy plants in nature, but it is usually unclear whether these represent stochastic encounters or provide host fitness benefits. Although most characterized species of the fungal genus Colletotrichum are destructive pathogens, we show here that C. tofieldiae (Ct) is an endemic endophyte in natural Arabidopsis thaliana populations in central Spain. Colonization by Ct initiates in roots but can also spread systemically into shoots. Ct transfers the macronutrient phosphorus to shoots, promotes plant growth, and increases fertility only under phosphorus-deficient conditions, a nutrient status that might have facilitated the transition from pathogenic to beneficial lifestyles. The host’s phosphate starvation response (PSR) system controls Ct root colonization and is needed for plant growth promotion (PGP). PGP also requires PEN2-dependent indole glucosinolate metabolism, a component of innate immune responses, indicating a functional link between innate immunity and the PSR system during beneficial interactions with Ct.
Kei Hiruma K, Gerlach N, Sacristán S, Nakano RT, Hacquard S, Kracher B, Neumann U, Ramírez D, Bucher M, O’Connell RJ, Schulze-Lefert P.
DOI: http://dx.doi.org/10.1016/j.cell.2016.02.028
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MPMI: Noncoding RNAs, Emerging Regulators in Root Endosymbioses

MPMI: Noncoding RNAs, Emerging Regulators in Root Endosymbioses | Plant-microbe interaction | Scoop.it

Endosymbiosis interactions allow plants to grow in nutrient-deficient soil environments. The arbuscular mycorrhizal (AM) symbiosis is an ancestral interaction between land plants and fungi, whereas nitrogen-fixing symbioses are highly specific for certain plants, notably major crop legumes. The signaling pathways triggered by specific lipochitooligosaccharide molecules involved in these interactions have common components that also overlap with plant root development. These pathways include receptor-like kinases, transcription factors (TFs), and various intermediate signaling effectors, including noncoding (nc)RNAs. These latter molecules have emerged as major regulators of gene expression and small ncRNAs, composed of micro (mi)RNAs and small interfering (si)RNAs, are known to control gene expression at transcriptional (chromatin) or posttranscriptional levels. In this review, we describe exciting recent data connecting variants of conserved si/miRNAs with the regulation of TFs, such as NSP2, NFY-A1, auxin-response factors, and AP2-like proteins, known to be involved in symbiosis. The link between hormonal regulations and these si- and miRNA-TF nodes is proposed in a model in which different feedback loops or regulations controlling endosymbiosis signaling are integrated. The diversity and emerging regulatory networks of young legume miRNAs are also highlighted.
Lelandais-Brière C, Moreau J, Hartmann C, Crespi M
DOI: 10.1094/MPMI-10-15-0240-FI

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BMC Genomics: The effector candidate repertoire of the arbuscular mycorrhizal fungus Rhizophagus clarus

Abstract
Background
Arbuscular mycorrhizal fungi (AMF) form an ecologically important symbiosis with more than two thirds of studied land plants. Recent studies of plant-pathogen interactions showed that effector proteins play a key role in host colonization by controlling the plant immune system. We hypothesise that also for symbiotic-plant interactions the secreted effectome of the fungus is a major component of communication and the conservation level of effector proteins between AMF species may be indicative whether they play a fundamental role.
Results
In this study, we used a bioinformatics pipeline to predict and compare the effector candidate repertoire of the two AMF species, Rhizophagus irregularis and Rhizophagus clarus. Our in silico pipeline revealed a list of 220 R. irregularis candidate effector genes that create a valuable information source to elucidate the mechanism of plant infection and colonization by fungi during AMF symbiotic interaction. While most of the candidate effectors show no homologies to known domains or proteins, the candidates with homologies point to potential roles in signal transduction, cell wall modification or transcription regulation. A remarkable aspect of our work is presence of a large portion of the effector proteins involved in symbiosis, which are not unique to each fungi or plant species, but shared along the Glomeromycota phylum. For 95 % of R. irregularis candidates we found homologs in a R. clarus genome draft generated by Illumina high-throughput sequencing. Interestingly, 9 % of the predicted effectors are at least as conserved between the two Rhizophagus species as proteins with housekeeping functions (similarity > 90 %). Therefore, we state that this group of highly conserved effector proteins between AMF species may play a fundamental role during fungus-plant interaction.
Conclusions
We hypothesise that in symbiotic interactions the secreted effectome of the fungus might be an important component of communication. Identification and functional characterization of the primary AMF effectors that regulate symbiotic development will help in understanding the mechanisms of fungus-plant interaction.
Sędzielewska Toro K and Brachmann A
DOI: 10.1186/s12864-016-2422-y

 

 

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New Phytol: Common and divergent shoot–root signalling in legume symbioses

- The role of shoot–root signals in the control of nodulation and arbuscular mycorrhizal (AM) development were examined in the divergent legume species pea and blue lupin. These species were chosen as pea can host both symbionts, whereas lupin can nodulate but has lost the ability to form AM.
- Intergeneric grafts between lupin and pea enabled examination of key long-distance signals in these symbioses. The role of strigolactones, auxin and elements of the autoregulation of nodulation (AON) pathway were investigated. Grafting studies were combined with loss-of-function mutants to monitor symbioses (nodulation, AM) and hormone effects (levels, gene expression and application studies).
- Lupin shoots suppress AM colonization in pea roots, in part by downregulating strigolactone exudation involving reduced expression of the strigolactone biosynthesis gene PsCCD8. By contrast, lupin shoots enhance pea nodulation, independently of strigolactones, possibly due to a partial incompatibility in AON shoot–root signalling between pea and lupin.
- This study highlights that nodulation and AM symbioses can be regulated independently and this may be due to long-distance signals, a phenomenon we were able to uncover by working with divergent legumes. We also identify a role for strigolactone exudation in determining the status of non-AM hosts.
Foo E, Heynen EMH, Reid JB
DOI: 10.1111/nph.13779View/save citation

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Mycorrhiza: Different levels of hyphal self-incompatibility modulate interconnectedness of mycorrhizal networks in three arbuscular mycorrhizal fungi within the Glomeraceae

Mycorrhiza: Different levels of hyphal self-incompatibility modulate interconnectedness of mycorrhizal networks in three arbuscular mycorrhizal fungi within the Glomeraceae | Plant-microbe interaction | Scoop.it

Arbuscular mycorrhizal fungi (AMF) live in symbiosis with most plant species and produce underground extraradical hyphal networks functional in the uptake and translocation of mineral nutrients from the soil to host plants. This work investigated whether fungal genotype can affect patterns of interconnections and structural traits of extraradical mycelium (ERM), by comparing three Glomeraceae species growing in symbiosis with five plant hosts. An isolate of Funneliformis coronatus consistently showed low ability to form interconnected ERM and self-incompatibility that represented up to 21 % of hyphal contacts. The frequency of post-fusion self-incompatible interactions, never detected before in AMF extraradical networks, was 8.9 %. In F. coronatus ERM, the percentage of hyphal contacts leading to perfect hyphal fusions was 1.2–7.7, while it ranged from 25.8–48 to 35.6–53.6 in Rhizophagus intraradices and Funneliformis mosseae, respectively. Low interconnectedness of F. coronatus ERM resulted also from a very high number of non-interacting contacts (83.2 %). Such findings show that AMF genotypes in Glomeraceae can differ significantly in anastomosis behaviour and that ERM interconnectedness is modulated by the fungal symbiont, as F. coronatus consistently formed poorly interconnected networks when growing in symbiosis with five different host plants and in the asymbiotic stage. Structural traits, such as extent, density and hyphal self-compatibility/incompatibility, may represent key factors for the differential performance of AMF, by affecting fungal absorbing surface and foraging ability and thus nutrient flow from soil to host roots.

Pepe A, Giovannetti M, Sbrana C

DOi: 10.1007/s00572-015-0671-2


Via Jean-Michel Ané
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New Phytol: Chitinase-resistant hydrophilic symbiotic factors secreted by Frankia activate both Ca2+ spiking and NIN gene expression in the actinorhizal plant Casuarina glauca

New Phytol: Chitinase-resistant hydrophilic symbiotic factors secreted by Frankia activate both Ca2+ spiking and NIN gene expression in the actinorhizal plant Casuarina glauca | Plant-microbe interaction | Scoop.it

    Although it is now well-established that decorated lipo-chitooligosaccharide Nod factors are the key rhizobial signals which initiate infection/nodulation in host legume species, the identity of the equivalent microbial signaling molecules in the Frankia/actinorhizal association remains elusive.
    With the objective of identifying Frankia symbiotic factors we present a novel approach based on both molecular and cellular pre-infection reporters expressed in the model actinorhizal species Casuarina glauca.
    By introducing the nuclear-localized cameleon Nup-YC2.1 into Casuarina glauca we show that cell-free culture supernatants of the compatible Frankia CcI3 strain are able to elicit sustained high frequency Ca2+ spiking in host root hairs. Furthermore, an excellent correlation exists between the triggering of nuclear Ca2+ spiking and the transcriptional activation of the ProCgNIN:GFP reporter as a function of the Frankia strain tested. These two pre-infection symbiotic responses have been used in combination to show that the signal molecules present in the Frankia CcI3 supernatant are hydrophilic, of low molecular weight and resistant to chitinase degradation.
    In conclusion, the biologically active symbiotic signals secreted by Frankia appear to be chemically distinct from the currently known chitin-based rhizobial/arbuscular mycorrhizal signaling molecules. Convenient bioassays in Casuarina glauca are now available for their full characterization.
Chabaud M, Gherbi H, Pirolles E, Vaissayre V, Fournier J, Moukouanga D, Franche C, Bogusz D, Tisa LS, Barker DG, Svistoonoff S
DOI: 10.1111/nph.13732

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PNAS: Algal ancestor of land plants was preadapted for symbiosis

Colonization of land by plants was a major transition on Earth, but the developmental and genetic innovations required for this transition remain unknown. Physiological studies and the fossil record strongly suggest that the ability of the first land plants to form symbiotic associations with beneficial fungi was one of these critical innovations. In angiosperms, genes required for the perception and transduction of diffusible fungal signals for root colonization and for nutrient exchange have been characterized. However, the origin of these genes and their potential correlation with land colonization remain elusive. A comprehensive phylogenetic analysis of 259 transcriptomes and 10 green algal and basal land plant genomes, coupled with the characterization of the evolutionary path leading to the appearance of a key regulator, a calcium- and calmodulin-dependent protein kinase, showed that the symbiotic signaling pathway predated the first land plants. In contrast, downstream genes required for root colonization and their specific expression pattern probably appeared subsequent to the colonization of land. We conclude that the most recent common ancestor of extant land plants and green algae was preadapted for symbiotic associations. Subsequent improvement of this precursor stage in early land plants through rounds of gene duplication led to the acquisition of additional pathways and the ability to form a fully functional arbuscular mycorrhizal symbiosis.
Delaux PM, Radhakrishnan GV, Jayaraman D, Cheema J, Malbreil M, Volkening JD, Sekimoto H, Nishiyama T, Melkonian M, Pokorny L, Rothfels CJ, Sederoff HW, Stevenson DW, Surek B, Zhang Y, Sussman MR, Dunand C, Morris RJ, Roux C, Wong GK, Oldroyd GE, Ané JM.
DOI: 10.1073/pnas.1515426112

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Effect of volatiles versus exudates released by germinating spores of Gigaspora margarita on lateral root formation

Effect of volatiles versus exudates released by germinating spores of Gigaspora margarita on lateral root formation | Plant-microbe interaction | Scoop.it

Highlights
• Exudates or volatiles produced by AM fungi stimulate lateral root formation (LRF).
• Volatiles emitted by AM fungi stimulate LRF in a SYM- and host-independent way.
• Exudates produced by AM fungi stimulate LRF in a SYM- and host-dependent way.
• Strigolactones may participate in the volatile-induced changes.
Sun XG, Bonfante P, Tang M
DOI: 10.1016/j.plaphy.2015.09.010

 

 

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Plant J: Full-length de novo assembly of RNA-seq data in pea (Pisum sativum L.) provides a gene expression atlas and gives insights into root nodulation in this species

Next-generation sequencing technologies allow an almost exhaustive survey of the transcriptome even in species with no available genome sequence. To produce a Unigene set representing most of the expressed genes of pea, 20 cDNA libraries produced from various plant tissues harvested at different developmental stages on plants grown in contrasted N-nutritive conditions were sequenced. Around one billion reads and 100 Gb of sequence were de novo assembled. Following several steps of redundancy reduction, 46,099 contigs with N50 length of 1,667 nt were identified. They constitute the 'Cameor' pea Unigene set. The high depth of sequencing allowed the identification of rare transcripts and detected expression for ca. 80% of contigs in each library. The Unigene set is now available on a website (http ://bios.dijon. inra .fr/FATAL/cgi/pscam .cgi) that allows (i) searching the pea orthologs of candidate genes based on gene sequences from other species, or based on annotation, (ii) determining transcript expression patterns using different metrics, (iii) identifying uncharacterized genes with interesting patterns of expression, and (iv) comparing gene ontology pathways between tissues. This resource has allowed identification of the pea orthologues of major nodulation genes characterized in recent years in model species, as a major step towards deciphering unresolved pea nodulation phenotypes. Besides a remarkable conservation of the early transcriptome nodulation apparatus between pea and Medicago truncatula, some specific features were highlighted. The resource provides a reference for the pea exome and will facilitate transcriptome and proteome approaches as well as SNP discovery in pea.

Alves-Carvalho S, Aubert G, Carrère S, Cruaud C, Brochot AL, Jacquin F, Klein A, Martin C, Boucherot K, Kreplak J, da Silva C, Moreau S, Gamas P, Wincker P, Gouzy J, Burstin J.
DOI: 10.1111/tpj.12967

 

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