Transport in plants and fungi
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Rescooped by Kevin Garcia from MycorWeb Plant-Microbe Interactions
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Glycerol metabolism and transport in yeast and fungi: Established knowledge and ambiguities

There is huge variability among yeasts with regard to their efficiency in utilizing glycerol as the sole source of carbon and energy. Certain species show growth rates with glycerol comparable to those reached with glucose as carbon source; others are virtually unable to utilize glycerol, especially in synthetic medium. Most of our current knowledge regarding glycerol uptake and its catabolic pathways has been gained from studying laboratory strains of the model yeast Saccharomyces cerevisiae. The growth of these strains on glycerol is dependent on the presence of medium supplements such as amino acids and nucleobases. In contrast, there is only fragmentary knowledge about S. cerevisiae isolates able to grow in synthetic glycerol medium without such supplements as well as about growth of non-Saccharomyces yeast species on glycerol. Thus, more research is required to understand why certain strains and species show superior growth performance on glycerol compared to common S. cerevisiae laboratory strains. This minireview summarizes what is known so far about the gene products and pathways involved in glycerol metabolism and transport in yeast and fungi as well as the regulation of these processes.

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Regulation of sugar transporter activity for antibacterial defense in Arabidopsis

Regulation of sugar transporter activity for antibacterial defense in Arabidopsis | Transport in plants and fungi | Scoop.it

Microbial pathogens strategically acquire metabolites from their hosts during infection. Here we show that the host can intervene to prevent such metabolite loss to pathogens. Phosphorylation-dependent regulation of sugar transporter 13 (STP13) is required for antibacterial defense in the plant Arabidopsis thaliana . STP13 physically associates with the flagellin receptor flagellin-sensitive 2 (FLS2) and its co-receptor BRASSINOSTEROID INSENSITIVE 1-associated receptor kinase 1 (BAK1). BAK1 phosphorylates STP13 at threonine 485, which enhances its monosaccharide uptake activity to compete with bacteria for extracellular sugars. Limiting the availability of extracellular sugar deprives bacteria of an energy source and restricts virulence factor delivery. Our results reveal that control of sugar uptake, managed by regulation of a host sugar transporter, is a defense strategy deployed against microbial infection. Competition for sugar thus shapes host-pathogen interactions.

 
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Quantitative modelling of legume root nodule primordium induction by a diffusive signal of epidermal origin that inhibits auxin efflux

Rhizobium nitrogen fixation in legumes takes place in specialized organs called root nodules. The initiation of these symbiotic organs has two important components. First, symbiotic rhizobium bacteria are recognized at the epidermis through specific bacterially secreted lipo-chitooligosaccharides (LCOs). Second, signaling processes culminate in the formation of a local auxin maximum marking the site of cell divisions. Both processes are spatially separated. This separation is most pronounced in legumes forming indeterminate nodules, such as model organism Medicago truncatula, in which the nodule primordium is formed from pericycle to most inner cortical cell layers. We used computer simulations of a simplified root of a legume that can form indeterminate nodules. A diffusive signal that inhibits auxin transport is produced in the epidermis, the site of rhizobium contact. In our model, all cells have the same response characteristics to the diffusive signal. Nevertheless, we observed the fastest and strongest auxin accumulation in the pericycle and inner cortex. The location of these auxin maxima correlates with the first dividing cells of future nodule primordia in M. truncatula. The model also predicts a transient reduction of the vascular auxin concentration rootward of the induction site as is experimentally observed. We use our model to investigate how competition for the vascular auxin source could contribute to the regulation of nodule number and spacing. Our simulations show that the diffusive signal may invoke the strongest auxin accumulation response in the inner root layers, although the signal itself is strongest close to its production site.
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Improving phosphorus use efficiency - a complex trait with emerging opportunities 

Improving phosphorus use efficiency - a complex trait with emerging opportunities  | Transport in plants and fungi | Scoop.it
Phosphorus (P) is one of the essential nutrients for plants and indispensable for plant growth and development. P deficiency severely limits crop yield and regular fertilizer applications are required to obtain high yields and prevent soil degradation. To access P from the soil, plants have evolved high and low affinity Pi transporters and the ability to induce root architectural changes to forage P. Also, adjustments of numerous cellular processes are triggered by the P starvation response, a tightly regulated process in plants. With the increasing demand for food due to the growing population, demand for P fertilizer is steadily increasing. Given the high costs of fertilizers and in light of the fact that phosphate rock, the source of P fertilizer, is a finite natural resource, there is a need to enhance P fertilizer use efficiency in agricultural systems and develop plants with enhanced Pi uptake and internal P-use efficiency (PUE). In this review we will provide an overview of ongoing relevant research and highlight different approaches towards developing crops with enhanced PUE. In this context, we will summarize our current understanding of root responses to low phosphorus conditions and emphasize the importance of combining PUE with tolerance of other stresses, such as aluminum toxicity. Of the many genes associated with Pi deficiency, this review will focus on those that hold promise or are already at an advanced stage of testing (OsPSTOL1, AVP1, PHO1, OsPHT1;6). Finally, an update is provided on the progress made exploring alternative technologies, such as phosphite fertilizer.
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Interview with Dale Sanders

Interview with Dale Sanders | Transport in plants and fungi | Scoop.it
Dale Sanders is the director and a professor of John Innes Centre, UK. His research focuses on how plant cells respond to changes in their environment and how they store the nutrients they acquire, and especially on how the transport of chemical elements across cell membranes in plants is integrated with cellular signaling and nutritional status.
 
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Transcriptional profiling of arbuscular mycorrhizal roots exposed to high levels of phosphate reveals the repression of cell cycle-related genes and secreted protein genes in Rhizophagus irregularis

The development of arbuscular mycorrhiza (AM) is strongly suppressed under high-phosphate (Pi) conditions. To investigate AM fungal responses during the suppression of AM by high Pi, we performed an RNA-seq analysis of Rhizophagus irregularis colonizing Lotus japonicus roots at different levels of Pi (20, 100, 300, and 500 μM). AM fungal colonization decreased markedly under high-Pi conditions. In total, 163 fungal genes were differentially expressed among the four Pi treatments. Among these genes, a cell cycle-regulatory gene, cyclin-dependent kinase CDK1, and several DNA replication- and mitosis-related genes were repressed under high-Pi conditions. More than 20 genes encoding secreted proteins were also downregulated by high-Pi conditions, including the strigolactone-induced putative secreted protein 1 gene that enhances AM fungal colonization. In contrast, the expression of genes related to aerobic respiration and transport in R. irregularis were largely unaffected. Our data suggest that high Pi suppresses the expression of genes associated with fungal cell cycle progression or that encode secreted proteins that may be required for intercellular hyphal growth and arbuscule formation. However, high Pi has little effect on the transcriptional regulation of the primary metabolism or transport in preformed fungal structures.

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High-level expression of a novel chromoplast phosphate transporter ClPHT4;2 is required for flesh color development in watermelon - Zhang - 2016 - New Phytologist - Wiley Online Library

High-level expression of a novel chromoplast phosphate transporter ClPHT4;2 is required for flesh color development in watermelon - Zhang - 2016 - New Phytologist - Wiley Online Library | Transport in plants and fungi | Scoop.it
Chromoplast development plays a crucial role in controlling carotenoid content in watermelon flesh. Modern cultivated watermelons with colorful flesh are believed to originate from pale-colored and no-sweet progenitors. But the molecular basis of flesh color formation and regulation is poorly understood. More chromoplasts and released carotenoid globules were observed in the red-fleshed fruit of the 97103 cultivar than in the pale-colored fruits of the PI296341-FR line. Transcriptome profiles of these two materials identified Cla017962, predicted as ClPHT4;2, was dramatically up-regulated during flesh color formation. High ClPHT4;2 expression levels were closely correlated with increased flesh carotenoid contents among 198 representative watermelon accessions. Down-regulation of ClPHT4;2 expression in transgenic watermelons reduced the fruit carotenoid accumulation. ClPHT4;2 as a function of chromoplast-localized phosophate transporter was tested by heterologous expression into a yeast phosphate-uptake-defective mutant, western blotting, subcellular localization, and immunogold electron microscopy analysis. Two transcription factors, ClbZIP1 and ClbZIP2, were identified, which responded to ABA and sugar signaling to regulate ClPHT4;2 transcription only in cultivated watermelon species. Our findings suggest that elevated ClPHT4;2 gene expression is necessary for carotenoid accumulation, and may help to characterize the co-development of flesh color and sweetness during watermelon development and domestication.
 
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The transportome of mycorrhizal systems - Molecular Mycorrhizal Symbiosis 

Mycorrhizal colonization of plant roots increases the sink strength and creates an additional sugar demand for the plant. Nutrient uptake from soil and exchanges between fungal and plant partners forming mycorrhizal symbioses present a mean feature among the beneficial effects of these mutualistic relationships. In the mycorrhizal associations, in return for mineral nutrient provisioning, the plant provides sugar photosynthates to the heterotrophic symbiont. This trade is regulated by both plant and fungal transport components, as for instance the long-distance transport of sucrose from leaves towards mycorrhizal roots and subsequent cellular transfer of monosaccharides at the symbiotic interface. This chapter provides recent knowledge concerning mycorrhizal nutrient exchanges and the involved molecular players in membrane transport of the ecto- and endomycorrhizal partners. It summarizes transport of sugars from plants towards mycorrhizal fungi. The chapter reviews uptake and exchange of main nutrients such as nitrogen, phosphate, sulfate, potassium, and water by the symbiotic partners.
 
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Wiley: Molecular Mycorrhizal Symbiosis - Francis Martin

Wiley: Molecular Mycorrhizal Symbiosis - Francis Martin | Transport in plants and fungi | Scoop.it
Recent years have seen extensive research in the molecular underpinnings of symbiotic plant-fungal interactions. Molecular Mycorrhizal Symbiosis is a timely collection of work that will bridge the gap between molecular biology, fungal genomics, and ecology. A more profound understanding of mycorrhizal symbiosis will have broad-ranging impacts on the fields of plant biology, mycology, crop science, and ecology. Molecular Mycorrhizal Symbiosis will open with introductory chapters on the biology, structure and phylogeny of the major types of mycorrhizal symbioses. Chapters then review different molecular mechanisms driving the development and functioning of mycorrhizal systems and molecular analysis of mycorrhizal populations and communities. The book closes with chapters that provide an overall synthesis of field and provide perspectives for future research. Authoritative and timely, Molecular Mycorrhizal Symbiosis, will be an essential reference from those working in plant and fungal biology.
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Cell-type specific H+-ATPase activity enables root K+ retention and mediates acclimation to salinity

While the importance of cell-type specificity in plant adaptive responses is widely accepted, only a limited number of studies have addressed this issue at the functional level. We have combined electrophysiological, imaging, and biochemical techniques to reveal physiological mechanisms conferring higher sensitivity of apical root cells to salinity in barley. We show that salinity application to the root apex arrests root growth in a highly tissue- and treatment-specific manner. Although salinity-induced transient net Na+ uptake was about 4-fold higher in the root apex compared with the mature zone, mature root cells accumulated more cytosolic and vacuolar Na+ suggesting that higher sensitivity of apical cells to salt is not related to either enhanced Na+ exclusion or sequestration inside the root. Rather, the above differential sensitivity between the two zones originates from a 10-fold difference in K+ efflux between the mature zone and the apical region (much poorer in the root apex) of the root. Major factors contributing to this poor K+ retention ability are: (1) an intrinsically lower H+-ATPase activity in the root apex; (2) greater salt-induced membrane depolarization and (3) a higher ROS production under NaCl and a larger density of ROS-activated cation currents in the apex. Salinity treatment increased (2 to 5 fold) the content of 10 (out of 25 detected) amino acids in the root apex but not in the mature zone and changed the organic acid and sugar contents. The causal link between observed changes in the root metabolic profile and regulation of transporters activity is discussed.
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Modelling the influence of ectomycorrhizal decomposition on plant nutrition and soil carbon sequestration in boreal forest ecosystems

Modelling the influence of ectomycorrhizal decomposition on plant nutrition and soil carbon sequestration in boreal forest ecosystems | Transport in plants and fungi | Scoop.it
Tree growth in boreal forests is limited by nitrogen (N) availability. Most boreal forest trees form symbiotic associations with ectomycorrhizal (ECM) fungi, which improve the uptake of inorganic N and also have the capacity to decompose soil organic matter (SOM) and to mobilize organic N (‘ECM decomposition’). To study the effects of ‘ECM decomposition’ on ecosystem carbon (C) and N balances, we performed a sensitivity analysis on a model of C and N flows between plants, SOM, saprotrophs, ECM fungi, and inorganic N stores. The analysis indicates that C and N balances were sensitive to model parameters regulating ECM biomass and decomposition. Under low N availability, the optimal C allocation to ECM fungi, above which the symbiosis switches from mutualism to parasitism, increases with increasing relative involvement of ECM fungi in SOM decomposition. Under low N conditions, increased ECM organic N mining promotes tree growth but decreases soil C storage, leading to a negative correlation between C stores above- and below-ground. The interplay between plant production and soil C storage is sensitive to the partitioning of decomposition between ECM fungi and saprotrophs. Better understanding of interactions between functional guilds of soil fungi may significantly improve predictions of ecosystem responses to environmental change.

Via Francis Martin
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A proteomic atlas of the legume Medicago truncatula and its nitrogen-fixing endosymbiont Sinorhizobium meliloti

A proteomic atlas of the legume Medicago truncatula and its nitrogen-fixing endosymbiont Sinorhizobium meliloti | Transport in plants and fungi | Scoop.it

Legumes are essential components of agricultural systems because they enrich the soil in nitrogen and require little environmentally deleterious fertilizers. A complex symbiotic association between legumes and nitrogen-fixing soil bacteria called rhizobia culminates in the development of root nodules, where rhizobia fix atmospheric nitrogen and transfer it to their plant host. Here we describe a quantitative proteomic atlas of the model legume Medicago truncatula and its rhizobial symbiont Sinorhizobium meliloti, which includes more than 23,000 proteins, 20,000 phosphorylation sites, and 700 lysine acetylation sites. Our analysis provides insight into mechanisms regulating symbiosis. We identify a calmodulin-binding protein as a key regulator in the host and assign putative roles and targets to host factors (bioactive peptides) that control gene expression in the symbiont. Further mining of this proteomic resource may enable engineering of crops and their microbial partners to increase agricultural productivity and sustainability.

 

Via Jean-Michel Ané
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Jean-Michel Ané's curator insight, October 17, 11:13 AM

Our big proteomics paper is out!

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Below-ground frontiers in trait-based plant ecology - Laliberté - 2016 - New Phytologist 

Below-ground frontiers in trait-based plant ecology - Laliberté - 2016 - New Phytologist  | Transport in plants and fungi | Scoop.it
Trait-based approaches have led to significant advances in plant ecology, but are currently biased toward above-ground traits. It is becoming clear that a stronger emphasis on below-ground traits is needed to better predict future changes in plant biodiversity and their consequences for ecosystem functioning. Here I propose six ‘below-ground frontiers’ in trait-based plant ecology, with an emphasis on traits governing soil nutrient acquisition: redefining fine roots; quantifying root trait dimensionality; integrating mycorrhizas; broadening the suite of root traits; determining linkages between root traits and abiotic and biotic factors; and understanding ecosystem-level consequences of root traits. Focusing research efforts along these frontiers should help to fulfil the promise of trait-based ecology: enhanced predictive capacity across ecological scales.
 
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The role of nutrients in drought-induced tree mortality and recovery - Gessler - 2016 - New Phytologist - Wiley Online Library

The role of nutrients in drought-induced tree mortality and recovery - Gessler - 2016 - New Phytologist - Wiley Online Library | Transport in plants and fungi | Scoop.it
Global forests are experiencing rising temperatures and more severe droughts, with consistently dire forecasts for negative future impacts. Current research on the physiological mechanisms underlying drought impacts is focused on the water- and carbon-associated mechanisms. The role of nutrients is notably missing from this research agenda. Here, we investigate what role, if any, forest nutrition plays for survival and recovery of forests during and after drought. High nutrient availability may play a detrimental role in drought survival due to preferential biomass allocation aboveground that (1) predispose plants to hydraulic constraints limiting photosynthesis and promoting hydraulic failure, (2) increases carbon costs during periods of carbon starvation, and (3) promote biotic attack due to low tissue carbon: nitrogen (C : N). When nutrient uptake occurs during drought, high nutrient availability can increase water use efficiency thus minimizing negative feedbacks between carbon and nutrient balance. Nutrients are released after drought ceases, which might promote faster recovery but the temporal dynamics of microbial immobilization and nutrient leaching have a significant impact on nutrient availability. We provide a framework for understanding nutrient impacts on drought survival that allows a more complete analysis of forest ecosystem responses.
 
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Auxin transport in the evolution of branching forms

Auxin transport in the evolution of branching forms | Transport in plants and fungi | Scoop.it
Branching is one of the most striking aspects of land plant architecture, affecting resource acquisition and yield. Polar auxin transport by PIN proteins is a primary determinant of flowering plant branching patterns regulating both branch initiation and branch outgrowth. Several lines of experimental evidence suggest that PIN-mediated polar auxin transport is a conserved regulator of branching in vascular plant sporophytes. However, the mechanisms of branching and auxin transport and relationships between the two are not well known outside the flowering plants, and the paradigm for PIN-regulated branching in flowering plants does not fit bryophyte gametophytes. The evidence reviewed here suggests that divergent auxin transport routes contributed to the diversification of branching forms in distinct land plant lineages.

Via Pierre-Marc Delaux
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An Arabidopsis ABC transporter mediates phosphate deficiency-induced remodeling of root architecture by modulating iron homeostasis in roots 

The remodeling of root architecture is a major developmental response of plants to phosphate (Pi) deficiency and is thought to enhance a plant’s ability to forage Pi in topsoil. The underlying mechanism controlling this response, however, is poorly understood. In this work, we identified an Arabidopsis mutant, hps10 (hypersensitive to Pi starvation 10), that is morphologically normal under Pi sufficiency but shows increased inhibition of primary root growth and enhanced production of lateral roots under Pi deficiency. hps10 is a previously identified allele (als3-3) of the ALUMINUM SENSITIVE3 (ALS3) gene, which is involved in plant tolerance to aluminum toxicity. Our results show that ALS3 and its interacting protein AtSTAR1 form an ABC transporter complex in tonoplasts. This protein complex mediates a highly electrogenic transport in Xenopus oocytes. Under Pi deficiency, als3 accumulates higher levels of Fe3+ in its roots than the wild type. In Arabidopsis, LPR1 (LOW PHOSPHATE ROOT1) and LPR2 encode ferroxidase, which when mutated reduces Fe3+ accumulation in roots and causes root growth to be insensitive to Pi deficiency. Here, we provide compelling evidence that ALS3 acts with LPR1/2 to regulate Pi deficiency-induced remodeling of root architecture by modulating Fe homeostasis in roots.
 
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Structural features of the aromatic/arginine constriction in the aquaglyceroporin GintAQPF2 are responsible for glycerol impermeability in arbuscular mycorrhizal symbiosis

Structural features of the aromatic/arginine constriction in the aquaglyceroporin GintAQPF2 are responsible for glycerol impermeability in arbuscular mycorrhizal symbiosis | Transport in plants and fungi | Scoop.it
Carbon transport in arbuscular mycorrhizal (AM) symbiosis is of fundamental importance. However, the role of glycerol transport in AM symbiosis has not yet been resolved. Glycerol transport across the cell membrane is mediated by aquaglyceroporins (AQGPs), whereas our previous study revealed that it was disfavoured by GintAQPF2, an AQGP from AM fungi (AMF). Here, we analysed the function of two amino acid residues in the aromatic/arginine (ar/R) constriction known as the major selectivity filter in AQGPs. Replacement of phenylalanine-94 (Phe-94) by alanine (Ala) enlarged the diameter of the ar/R constriction and resulted in an increased intracellular glycerol accumulation and thus survival rate of yeast cells at high glycerol levels, while individual or joint replacement of Phe-94 and Ala-234 by tryptophan and glycine induced a closed state of GintAQPF2, suggesting that the potential double gates (Phe94-Phe243 and arginine-249) of the ar/R constriction also likely determined solute permeability. To figure out whether GintAQPF2 functions were relevant to the establishment of AM symbiosis, genomic analyses of four representative fungi with different lifestyles were performed. We found that glycerol facilitators existed in the facultative fungi (the ectomycorrhizal fungus Laccaria bicolor and hemibiotrophic pathogen Magnaporthe oryzae), but not in the obligatory fungi (the AMF Rhizophagus irregularis and necrotrophic pathogen Fusarium verticillioides), revealing a conserved pattern of glycerol transport in symbionts and pathogens. Our results suggested that glycerol blocks due to the special structural features of the ar/R constriction in the only AMF AQGP could potentially play a role in the establishment of AM symbiosis.


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VAMP721 conformations unmask an extended motif for K+ channel binding and gating control

VAMP721 conformations unmask an extended motif for K+ channel binding and gating control | Transport in plants and fungi | Scoop.it
SNARE proteins play a major role in membrane fusion and contribute to cell expansion, signalling and polar growth in plants. The SNARE SYP121 of Arabidopsis that facilitates vesicle fusion at the plasma membrane also binds with, and regulates K+ channels already present at plasma membrane to affect K+ uptake and K+-dependent growth. Here we report that its cognate partner VAMP721 binds to the KAT1 K+ channel via two sites on the protein, only one of which contributes to channel gating control. Binding to the VAMP721 SNARE domain suppressed channel gating. By contrast, interaction with the N-terminal longin domain conferred specificity on VAMP721 binding without influencing gating. Channel binding was defined by a linear motif within the longin domain. The SNARE domain is thought to wrap around this structure when not assembled with SYP121 in SNARE complex. Fluorescence lifetime analysis showed that mutations within this motif, which suppressed channel binding and its effects on gating, also altered the conformational displacement between the VAMP721 SNARE and longin domains. Thus, channel binding depends on a coordination between the two binding sites on VAMP721, consistent with the K+ channels as nucleation points for SNARE complex assembly and initial channel binding of VAMP721.
 
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A framework for lateral membrane trafficking and polar tethering of the PEN3 ATP-binding cassette transporter

The outermost cell layer of plants, the epidermis, and its outer (lateral) membrane domain facing the environment are continuously challenged by biotic and abiotic stresses. Therefore, the epidermis and the outer membrane domain provide important selective and protective barriers. However, only a small number of specifically outer membrane-localized proteins are known. Similarly, molecular mechanisms underlying the trafficking and the polar placement of outer membrane domain proteins require further exploration. Here, we demonstrate that ACTIN7 (ACT7) mediates trafficking of the PENETRATION3 (PEN3) outer membrane protein from the trans-Golgi network (TGN) to the plasma membrane in the root epidermis of Arabidopsis thaliana and that actin function contributes to PEN3 endocytic recycling. In contrast to such generic ACT7-dependent trafficking from the TGN, the EXOCYST84b (EXO84b) tethering factor mediates PEN3 outer membrane polarity. Moreover, precise EXO84b placement at the outer membrane domain itself requires ACT7 function. Hence, our results uncover spatially and mechanistically distinct requirements for ACT7 function during outer lateral membrane cargo trafficking and polarity establishment. They further identify an exocyst tethering complex mediator of outer lateral membrane cargo polarity.
 
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Unearthing the roots of ectomycorrhizal symbioses : Nature Reviews Microbiology

Unearthing the roots of ectomycorrhizal symbioses : Nature Reviews Microbiology | Transport in plants and fungi | Scoop.it
During the diversification of Fungi and the rise of conifer-dominated and angiosperm- dominated forests, mutualistic symbioses developed between certain trees and ectomycorrhizal fungi that enabled these trees to colonize boreal and temperate regions. The evolutionary success of these symbioses is evident from phylogenomic analyses that suggest that ectomycorrhizal fungi have arisen in approximately 60 independent saprotrophic lineages, which has led to the wide range of ectomycorrhizal associations that exist today. In this Review, we discuss recent genomic studies that have revealed the adaptations that seem to be fundamental to the convergent evolution of ectomycorrhizal fungi, including the loss of some metabolic functions and the acquisition of effectors that facilitate mutualistic interactions with host plants. Finally, we consider how these insights can be integrated into a model of the development of ectomycorrhizal symbioses.

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Bob Reeves's curator insight, November 5, 8:05 PM
Ectomycorrhizal fungi evolved after the primordial plant symbionts: endomycorrhizae. And their arrival paved the way for the dominance of the conifers and hardwood trees in today's temperate forests. They remain a linchpin mutualist organism supporting these ecosystems today.  
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AtSWEET13 and AtSWEET14 regulate gibberellin-mediated physiological processes

AtSWEET13 and AtSWEET14 regulate gibberellin-mediated physiological processes | Transport in plants and fungi | Scoop.it
Transmembrane transport of plant hormones is required for plant growth and development. Despite reports of a number of proteins that can transport the plant hormone gibberellin (GA), the mechanistic basis for GA transport and the identities of the transporters involved remain incomplete. Here, we provide evidence that Arabidopsis SWEET proteins, AtSWEET13 and AtSWEET14, which are members of a family that had previously been linked to sugar transport, are able to mediate cellular GA uptake when expressed in yeast and oocytes. A double sweet13 sweet14 mutant has a defect in anther dehiscence and this phenotype can be reversed by exogenous GA treatment. In addition, sweet13 sweet14 exhibits altered long distant transport of exogenously applied GA and altered responses to GA during germination and seedling stages. These results suggest that AtSWEET13 and AtSWEET14 may be involved in modulating GA response in Arabidopsis.
 
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Fine-tuned regulation of the K+/H+ antiporter KEA3 is required to optimize photosynthesis during induction - Wang - The Plant Journal - Wiley Online Library

Fine-tuned regulation of the K+/H+ antiporter KEA3 is required to optimize photosynthesis during induction - Wang - The Plant Journal - Wiley Online Library | Transport in plants and fungi | Scoop.it
KEA3 is a thylakoid membrane localized K+/H+ antiporter and regulates photosynthesis by modulating two components of proton motive force (pmf), the proton gradient (∆pH) and the electric potential (∆ψ). We identified a mutant allele of KEA3, disturbed proton gradient regulation (dpgr) based on its reduced non-photochemical quenching (NPQ) in artificial (CO2-free with low O2) air. This phenotype was enhanced in the mutant backgrounds of PSI cyclic electron transport (pgr5 and crr2-1). In ambient air, reduced NPQ was observed during induction of photosynthesis in dpgr, the phenotype that was enhanced after overnight dark adaptation. In contrast, the knockout allele of kea3-1 exhibited high NPQ phenotype during steady-state in ambient air. Consistent with this kea3-1 phenotype in ambient air, the membrane topology of KEA3 indicated a proton efflux from the thylakoid lumen to the stroma. The dpgr heterozygotes showed a semidominant and dominant phenotype in artificial and ambient air, respectively. In dpgr, the protein level of KEA3 was unaffected but the downregulation of its activity was likely disturbed. Our findings suggest that a fine regulation of KEA3 activity is necessary for optimizing photosynthesis.
 
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Water transport and energy - Fricke - Plant, Cell & Environment - Wiley Online Library

Water transport and energy - Fricke - Plant, Cell & Environment - Wiley Online Library | Transport in plants and fungi | Scoop.it
Water transport in plants occurs along various paths and is driven by gradients in its free energy. It is generally considered that the mode of transport, being either diffusion or bulk flow, is a passive process, though energy may be required to sustain the forces driving water flow. This review aims at putting water flow at the various organisational levels (cell, organ, plant) in the context of the energy that is required to maintain these flows. In addition, the question is addressed (i) whether water can be transported against a difference in its chemical free energy, ‘water potential’ (Ψ), through, directly or indirectly, active processes; and (ii) whether the energy released when water is flowing down a gradient in its energy, for example during day-time transpiration and cell expansive growth, is significant compared to the energy budget of plant and cell. The overall aim of review is not so much to provide a definite ‘Yes’ and ‘No’ to these questions, but rather to stimulate discussion and raise awareness that water transport in plants has its real, associated, energy costs and potential energy gains.
 
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The host plant Pinus pinaster exerts specific effects on phosphate efflux and polyphosphate metabolism of the ectomycorrhizal fungus Hebeloma cylindrosporum: a radiotracer, cytological staining and...

Ectomycorrhizal (ECM) association can improve plant phosphorus (P) nutrition. Polyphosphates (polyP), synthesized in distant fungal cells after P uptake may contribute to P supply from the fungus to the host plant if they are hydrolyzed to phosphate in ECM roots then transferred to the host plant when required. In this study, we addressed this hypothesis for the ECM fungus Hebeloma cylindrosporum grown in vitro and incubated without plant or with host (Pinus pinaster) and non-host (Zea mays) plants, using an experimental system simulating the symbiotic interface. We used 32P labelling to quantify P accumulation and P efflux and in vivo and in vitro NMR spectroscopy and cytological staining to follow the fate of fungal polyP. Phosphate supply triggered a massive P accumulation as newly synthesized long-chain polyP in H. cylindrosporum if previously grown under P-deficient conditions. P efflux from H. cylindrosporum towards the roots was stimulated by both host and non-host plants. However, the host plant enhanced 32P release compared to the non-host plant and specifically increased the proportion of short-chain polyP in the interacting mycelia. These results support the existence of specific host-plant effects on fungal P metabolism able to provide P in the apoplast of ectomycorrhizal roots.
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Commentary: "Comparative Analysis of Secretomes from Ectomycorrhizal Fungi with an Emphasis on Small-Secreted Proteins" | Frontiers in Microbiology 

Ectomycorrhizal (ECM) symbioses are major components of boreal and temperate forest ecosystems (Clemmensen et al., 2013; Smith and Read, 2008). Although well studied for several decades, very little is known about the molecular players involved in the establishment and maintenance of ECM symbioses (Garcia et al., 2015). Identifying the symbiont secretome is a promising way to dissect the fungal contribution to the mutualistic molecular dialog. Pellegrin et al. (2015) compared for the first time the predicted secretome of 49 soil-borne ECM, saprotrophic and pathogenic fungi, revealing shared and specific features between species, and providing a better understanding of the ECM lifestyle evolution.
 
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