Transport in plants and fungi
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IJMS | Free Full-Text | Pumpkin CmHKT1;1 Controls Shoot Na+ Accumulation via Limiting Na+ Transport from Rootstock to Scion in Grafted Cucumber

IJMS | Free Full-Text | Pumpkin CmHKT1;1 Controls Shoot Na+ Accumulation via Limiting Na+ Transport from Rootstock to Scion in Grafted Cucumber | Transport in plants and fungi | Scoop.it
Soil salinity adversely affects the growth and yield of crops, including cucumber, one of the most important vegetables in the world. Grafting with salt-tolerant pumpkin as the rootstock effectively improves the growth of cucumber under different salt conditions by limiting Na+ transport from the pumpkin rootstock to the cucumber scion. High-affinity potassium transporters (HKTs) are crucial for the long distance transport of Na+ in plants, but the function of pumpkin HKTs in this process of grafted cucumber plants remains unclear. In this work, we have characterized CmHKT1;1 as a member of the HKT gene family in Cucurbita moschata and observed an obvious upregulation of CmHKT1;1 in roots under NaCl stress conditions. Heterologous expression analyses in yeast mutants indicated that CmHKT1;1 is a Na+-selective transporter. The transient expression in tobacco epidermal cells and in situ hybridization showed CmHKT1;1 localization at plasma membrane, and preferential expression in root stele. Moreover, ectopic expression of CmHKT1;1 in cucumber decreased the Na+ accumulation in the plants shoots. Finally, the CmHKT1;1 transgenic line as the rootstock decreased the Na+ content in the wild type shoots. These findings suggest that CmHKT1;1 plays a key role in the salt tolerance of grafted cucumber by limiting Na+ transport from the rootstock to the scion and can further be useful for engineering salt tolerance in cucurbit crops.
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AP2 transcription factor CBX1 with a specific function in symbiotic exchange of nutrients in mycorrhizal Lotus japonicus

AP2 transcription factor CBX1 with a specific function in symbiotic exchange of nutrients in mycorrhizal Lotus japonicus | Transport in plants and fungi | Scoop.it

Arbuscular mycorrhizal (AM) fungi promote phosphorus uptake into host plants in exchange for organic carbon. Physiological tracer experiments showed that up to 100% of acquired phosphate can be delivered to plants via the mycorrhizal phosphate uptake pathway (MPU). Previous studies revealed that the CTTC cis -regulatory element (CRE) is required for promoter activation of mycorrhiza-specific phosphate transporter and H+-ATPase genes. However, the precise transcriptional mechanism directly controlling MPU is unknown. Here, we show that CBX1 binds CTTC and AW-box CREs and coregulates mycorrhizal phosphate transporter and H+-ATPase genes. Interestingly, genes involved in lipid biosynthesis are also regulated by CBX1 through binding to AW box, including RAM2 . Our work suggests a common regulatory mechanism underlying complex trait control of symbiotic exchange of nutrients.

 
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Early senescence in older leaves of low nitrate-grown Atxdh1 uncovers a role for purine catabolism in N supply

Early senescence in older leaves of low nitrate-grown Atxdh1 uncovers a role for purine catabolism in N supply | Transport in plants and fungi | Scoop.it
The nitrogen (N)-rich ureides allantoin and allantoate, which are products of purine catabolism, play a role in N delivery in Leguminosae. Here, we examined their role as a N source in non-legume plants using Arabidopsis (Arabidopsis thaliana) plants mutated in XANTHINE DEHYDROGENASE1 (AtXDH1), a catalytic bottleneck in purine catabolism. Older leaves of the Atxdh1 mutant exhibited early senescence, lower soluble protein and lower organic-N levels as compared to wild-type (WT) older leaves when grown with 1 mM nitrate but were comparable to WT under 5 mM nitrate. Similar nitrate-dependent senescence phenotypes were evident in the older leaves of allantoinase (Ataln) and allantoate amidohydrolase (Ataah) mutants, which are also impaired in purine catabolism. Under low nitrate conditions, xanthine accumulated in older leaves of Atxdh1, whereas allantoin accumulated in both older and younger leaves of Ataln but not in WT leaves, indicating remobilization of xanthine-degraded products from older to younger leaves. Supporting this notion, ureide transporter expression was enhanced in older leaves of WT in low nitrate as compared to high nitrate conditions. Elevated transcripts and proteins of AtXDH and AtAAH were detected in low nitrate-grown WT, indicating regulation at protein and transcript levels. The higher nitrate reductase activity in Atxdh1 leaves compared to WT leaves indicated a need for nitrate assimilation products. Together, the results indicate that the absence of remobilized purine-degraded N from older leaves of Atxdh1 caused senescence symptoms, a result of higher chloroplastic protein degradation in older leaves of low nitrate grown plants.
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Nutrient-related Long-Distance Signals: common players and possible crosstalk | Plant and Cell Physiology | Oxford Academic

Nutrient-related Long-Distance Signals: common players and possible crosstalk | Plant and Cell Physiology | Oxford Academic | Transport in plants and fungi | Scoop.it
Nutrient fluctuations are more a rule rather than an exception in the life of sessile organisms such as plants. Despite this constraint that adds up to abiotic and biotic stresses, plants are able to accomplish their life cycle thanks to an efficient signaling network that reciprocally control nutrient acquisition and use with growth and development. The majority of nutrients are acquired by the root system where multiple local signaling that rely on nutrient sensing systems are implemented to direct root growth toward soil resources. Moreover, long-distance signaling plays an essential role in integrating nutrient availability at the whole plant level and adjusting nutrient acquisition to plant growth requirements. By studying the signaling network for single mineral nutrients, several long-distance signals traveling between roots and shoots and taking a diversity of forms have been identified and are summarized here. However, the nutritional environment is multifactorial, adding a tremendous complexity for our understanding of the nutrient signaling network as a unique system. For instance, long-distance signals are expected to in part support this nutrient crosstalk but the mechanisms are is still largely unknown. Therefore, the involvement of possible long-distance signals as conveyers of nutrient crosstalk is discussed here together with approaches and strategies that are now considered to build a picture from the nutrient-signaling puzzle.
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Foxtail millet SiHAK1 excites extreme high-affinity K+ uptake to maintain K+ homeostasis under low K+ or salt stress

Foxtail millet SiHAK1 excites extreme high-affinity K+ uptake to maintain K+ homeostasis under low K+ or salt stress | Transport in plants and fungi | Scoop.it
Crop genomes have shown the richness of K+ transporters in HAK/KUP/KT (High Affinity K+/K+ Uptake Proteins/K+ Transporter) family, and much progress have been achieved toward understanding the diverse roles of K+ uptake and translocation, and abiotic stresses resistance in this family. The HAK/KUP/KT family has increasingly been recognized to be at a pivotal status in the mediation of K+ translocation and long-term transport; however, our understanding of the molecular mechanisms remains limited. Foxtail millet is an ideal plant for studying long-distance potassium (K) transport because of its small diploid genome and better adaptability to arid lands. Here, we identified 29 putative HAK/KUP/KT proteins from the Setaria italica genome database. These genes were distributed in seven chromosomes of foxtail millet and divided into five clusters. SiHAK1 exhibited widespread expression in various tissues and significant up-regulation in the shoots under low K condition. SiHAK1 was localized in the cell membrane and low K elicited SiHAK1-meidated high-affinity K+ uptake activity in Cy162 yeast cells and Arabidopsis athak5 mutants. The transport activity of SiHAK1 was coordinately modulated by external K+ supply and internal K+ content in the cell under low K and high salt environment. Our findings reveal the K uptake mechanisms of SiHAK1 and indicated that it may be involved in the mediation of K homeostasis in S. italica under K+-deficiency and salt stress.
 
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Effects of two contrasted arbuscular mycorrhizal fungal isolates on nutrient uptake by Sorghum bicolor under drought 

Effects of two contrasted arbuscular mycorrhizal fungal isolates on nutrient uptake by Sorghum bicolor under drought  | Transport in plants and fungi | Scoop.it
Drought is a limiting factor for crop production, especially in arid and semi-arid climates. In this study, Sorghum bicolor plants were inoculated, or not, with Rhizophagus irregularis, an arbuscular mycorrhizal (AM) strain typical for temperate climates, or Rhizophagus arabicus, a strain endemic to hyper-arid ecosystems. Plants were grown under well-watered or drought conditions in compartmented microcosms. Transpiration rates, plant growth, and nutrient uptake (using 15N as a tracer) were determined to assess the impact of drought stress on sorghum plants in AM symbiosis. Although AM colonization did not affect the bulk biomass of host plants, R. arabicus improved their transpiration efficiency and drought tolerance more than R. irregularis. Moreover, R. arabicus was able to extract more 15N from the soil under both water regimes, and AM-driven enhancement of the nitrogen and phosphorus content of sorghum, especially when water was limiting, was greater for R. arabicus-inoculated plants than for R. irregularis-inoculated plants. Our work demonstrates close links between AM hyphal phosphorus and nitrogen transport and uptake by AM plants for both AM fungal species. It also underscores that, under the drought stress conditions we applied, R. arabicus transfers significantly more nitrogen to sorghum than R. irregularis.
 
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Bob Reeves's curator insight, July 18, 8:29 AM
More evidence that Nature supports diversity of species (below grade) for a very good reason. We linear thinkers love the idea of a single Silver Bullet mycorrhizal species as a kind of magical inoculate - but Nature creates and supports species diversity for a compelling (if not complicating) reason; it is essential for success.
Joe Finn's curator insight, August 7, 6:00 PM
The power of the fungi below our feet in drought. Complicated stuff but we are learning more about fungi as a natural farmer.
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Symbiotic Tripartism in the Model Plant Family of Legumes and Soil Sustainability

Symbiotic Tripartism in the Model Plant Family of Legumes and Soil Sustainability | Transport in plants and fungi | Scoop.it
The demands of feeding a world population are expected to double by 2050. This is because 2.5 billion will be added to the urban population alone. This massive undertaking has posed many challenges toward agricultural productivity and increase in food quality, quantity, and production of protein-rich crops, but on the other hand, modern aggressive agricultural practices have rendered the current acreage of arable land and soil unsustainable to meet the demands of sustainable cropping systems. However, the beneficial role of legumes in cropping systems such as symbiotic nitrogen fixation, intercropping, and rotation of legumes with cereals offers credible potential for providing economically sustainable advantages for farming. The inherent capacity of legumes to form symbiotic associations with biological nitrogen-fixing (BNF) rhizobia and phosphorus-acquiring arbuscular mycorrhizal fungi (AMF), i.e., symbiotic tripartism, further advocates the use of legumes as cover crops, increasing soil fertility, rhizospheric processes, and sustainable (food/oil) crop production. Furthermore, it is estimated that BNF of legumes contribute to five to seven times less greenhouse gas (GHG) emissions per unit area compared to other crops, in addition to estimates of total global BNF of 122 T gN/year (=million tons of N), while AMF play a critical role in global carbon cycle, with estimates of the amount of total C fixed to be up to 20% which is c. 5 T PgC/year (=billion tons of C). In view of this importance of symbiotic tripartism in natural and managed ecosystems, this chapter emphasizes the genetic and symbiotic feature(s) of legumes in large-scale community and global food security programs and soil sustainability and management.


Via Jean-Michel Ané
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The PILNCR1-miR399 regulatory module is important for low-phosphate tolerance in maize

The PILNCR1-miR399 regulatory module is important for low-phosphate tolerance in maize | Transport in plants and fungi | Scoop.it
The regulation of adaptive responses to phosphorus (P) deficiency by the microRNA399 (miR399)/PHOSPHATE2 (PHO2) pathway has been well studied in Arabidopsis thaliana but not in maize (Zea mays). Here, we show that miR399 transcripts are strongly induced in maize by phosphate (Pi) deficiency. Transgenic maize plants that over-expressed MIR399b accumulated excessive amounts of P in their shoots and displayed typical Pi-toxicity phenotypes. We re-annotated ZmPHO2 with an additional 1165 bp of the 5'-untranslated region. miR399-guided post-transcriptional repression of ZmPHO2 was mainly observed in the P-efficient lines. We identified Pi-deficiency-induced long non-coding RNA 1 (PILNCR1) from our strand-specific RNA libraries. Transient expression assays in Nicotiana benthamiana and maize leaf protoplasts demonstrated that PILNCR1 inhibits ZmmiR399-guided cleavage of ZmPHO2. The abundance of PILNCR1 was significantly higher in P-inefficient lines than in P-efficient lines, which is consistent with the abundance of ZmmiR399 transcripts. These results indicate that the interaction between PILNCR1 and miR399 is important for tolerance to low Pi in maize.
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MtMOT1.2 is responsible for molybdate supply to Medicago truncatula nodules 

Symbiotic nitrogen fixation in legume root nodules requires a steady supply of molybdenum for synthesis of the iron‐molybdenum cofactor of nitrogenase. This nutrient has to be provided by the host plant from the soil, crossing several symplastically disconnected compartments through molybdate transporters, including members of the MOT1 family. MtMOT1.2 is a Medicago truncatula MOT1 family member located in the endodermal cells in roots and nodules. Immunolocalization of a tagged MtMOT1.2 indicates that it is associated to the plasma membrane and to intracellular membrane systems, where it would be transporting molybdate towards the cytosol, as indicated in yeast transport assays. Loss‐of‐function mot1.2‐1 mutant showed reduced growth compared to wild‐type plants when nitrogen fixation was required, but not when nitrogen was provided as nitrate. While no effect on molybdenum‐dependent nitrate reductase activity was observed, nitrogenase activity was severely affected, explaining the observed difference of growth depending on nitrogen source. This phenotype was the result of molybdate not reaching the nitrogen‐fixing nodules, since genetic complementation with a wild‐type MtMOT1.2 gene or molybdate‐fortification of the nutrient solution, both restored wild‐type levels of growth and nitrogenase activity. These results support a model in which MtMOT1.2 would mediate molybdate delivery by the vasculature into the nodules.
 
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HcTOK1 participates in the maintenance of K+ homeostasis in the ectomycorrhizal fungus Hebeloma cylindrosporum, which is essential for the symbiotic K+ nutrition of Pinus pinaster 

Most land plants rely on root symbioses to complement or improve their mineral nutrition. Recent researches have put forward that mycorrhizal fungi efficiently absorb and transfer potassium (K+) from the soil to host plant roots, but the molecular mechanisms involved are not completely elucidated yet. We have recently revealed that K+ is likely released from the fungal Hartig net to the plant by TOK channels in the ectomycorrhizal model Hebeloma cylindrosporum – Pinus pinaster. H. cylindrosporum harbours three TOK members. Herein, we report that one of them, HcTOK1, has similar features than the yeast ScTOK1. Moreover, we propose a role for this channel in the transport of K+ from the medium to ectomycorrhizal roots under K+ starvation.
 
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Calcium transport across plant membranes: mechanisms and functions 

Calcium transport across plant membranes: mechanisms and functions  | Transport in plants and fungi | Scoop.it
Calcium is an essential structural, metabolic and signalling element. The physiological functions of Ca2+ are enabled by its orchestrated transport across cell membranes, mediated by Ca2+‐permeable ion channels, Ca2+‐ATPases and Ca2+/H+ exchangers. Bioinformatics analysis has not determined any Ca2+‐selective filters in plant ion channels, but electrophysiological tests do reveal Ca2+ conductances in plant membranes. The biophysical characteristics of plant Ca2+ conductances have been studied in detail and were recently complemented by molecular genetic approaches. Plant Ca2+ conductances are mediated by several families of ion channels, including cyclic nucleotide‐gated channels (CNGCs), ionotropic glutamate receptors, two‐pore channel 1 (TPC1), annexins and several types of mechanosensitive channels. Key Ca2+‐mediated reactions (e.g. sensing of temperature, gravity, touch and hormones, and cell elongation and guard cell closure) have now been associated with the activities of specific subunits from these families. Structural studies have demonstrated a unique selectivity filter in TPC1, which is passable for hydrated divalent cations. The hypothesis of a ROS‐Ca2+ hub is discussed, linking Ca2+ transport to ROS generation. CNGC inactivation by cytosolic Ca2+, leading to the termination of Ca2+ signals, is now mechanistically explained. The structure–function relationships of Ca2+‐ATPases and Ca2+/H+ exchangers, and their regulation and physiological roles are analysed.
 
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Nutrient demand and fungal access to resources control the carbon allocation to the symbiotic partners in tripartite interactions of Medicago truncatula - Kafle 

Legumes form tripartite interactions with arbuscular mycorrhizal (AM) fungi and rhizobia, and both root symbionts exchange nutrients against carbon from their host. The carbon costs of these interactions are substantial, but our current understanding of how the host controls its carbon allocation to individual root symbionts is limited. We examined nutrient uptake and carbon allocation in tripartite interactions of Medicago truncatula under different nutrient supply conditions, and when the fungal partner had access to nitrogen, and followed the gene expression of several plant transporters of the SUT and SWEET family. Tripartite interactions led to synergistic growth responses and stimulated the phosphate and nitrogen uptake of the plant. Plant nutrient demand but also fungal access to nutrients played an important role for the carbon transport to different root symbionts, and the plant allocated more carbon to rhizobia under nitrogen demand, but more carbon to the fungal partner when nitrogen was available. These changes in carbon allocation were consistent with changes in the SUT and SWEET expression. Our study provides important insights into how the host plant controls its carbon allocation under different nutrient supply conditions and changes its carbon allocation to different root symbionts to maximize its symbiotic benefits.
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Responses to Systemic Nitrogen Signaling in Arabidopsis Roots Involve trans-Zeatin in Shoots

Responses to Systemic Nitrogen Signaling in Arabidopsis Roots Involve trans-Zeatin in Shoots | Transport in plants and fungi | Scoop.it

Plants face temporal and spatial variation in nitrogen (N) availability. This includes heterogeneity in soil nitrate (NO3-) content. To overcome these constraints, plants modify their gene expression and physiological processes to optimize N acquisition. This plasticity relies on a complex long-distance root-shoot-root signaling network that remains poorly understood. We previously showed that cytokinin (CK) biosynthesis is required to trigger systemic N signaling. Here, we performed split-root experiments and used a combination of CK-related mutant analyses, hormone profiling, transcriptomic analysis, NO3- uptake assays, and root growth measurements to gain insight into systemic N signaling in Arabidopsis thaliana. By comparing wild-type plants and mutants affected in CK biosynthesis and ABCG14-dependent root-to-shoot translocation of CK, we revealed an important role for active trans-Zeatin (tZ) in systemic N signaling. Both rapid sentinel gene regulation and long-term functional acclimation to heterogeneous NO3- supply, including NO3- transport and root growth regulation, are likely mediated by the integration of tZ content in shoots. Furthermore, shoot transcriptome profiling revealed that glutamate/glutamine metabolism is likely a target of tZ root-to-shoot translocation, prompting an interesting hypothesis regarding shoot-to-root communication. Finally, this study highlights tZ-independent pathways regulating gene expression in shoots as well as NO3- uptake activity in response to total N-deprivation.

 
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Glutamate triggers long-distance, calcium-based plant defense signaling

Glutamate triggers long-distance, calcium-based plant defense signaling | Transport in plants and fungi | Scoop.it

Animals require rapid, long-range molecular signaling networks to integrate sensing and response throughout their bodies. The amino acid glutamate acts as an excitatory neurotransmitter in the vertebrate central nervous system, facilitating long-range information exchange via activation of glutamate receptor channels. Similarly, plants sense local signals, such as herbivore attack, and transmit this information throughout the plant body to rapidly activate defense responses in undamaged parts. Here we show that glutamate is a wound signal in plants. Ion channels of the GLUTAMATE RECEPTOR–LIKE family act as sensors that convert this signal into an increase in intracellular calcium ion concentration that propagates to distant organs, where defense responses are then induced.

 
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The combination of K+ deficiency with other environmental stresses: what is the outcome? - Nieves‐Cordones - - Physiologia Plantarum

Potassium (K+) is a macronutrient known for its high mobility and positive charge which allows efficient and fast control of the electrical balance and osmotic potential in plant cells. Such features allow K+ to remarkably contribute to plant stress adaptation. Some agricultural lands are deficient in K+, imposing a stress that reduces crop yield and makes fertilization a common practice. However, individual stress conditions in the field are rare and crops usually face a combination of different stresses. Since plant response to a stress combination cannot always be deduced from individual stress action, it is necessary to gain insights into the specific mechanisms that connect K+ homeostasis with other stress effects to improve plant performance in the context of climate change. Surprisingly, plant responses to environmental stresses under a K+‐limiting scenario are poorly understood. In the present review, we summarize current knowledge and find substantial gaps regarding specific outcomes of K+ deficiency in addition to other environmental stresses. With this regard, combined nutrient deficiencies of K+ and other macronutrients are covered in the first part of the review and interactions arising from K+‐deficiency with salinity, drought, and biotic factors in the second part. Information available so far suggests a prominent role of potassium and nitrate transport systems and their regulatory proteins in the response of plants to several stress combinations. Thus, such molecular pathway, which locates at the crossroad between K+ homeostasis and environmental stresses, could be considered as biotechnological targets in future studies.
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Piriformospora indica improves salinity stress tolerance in Zea mays L. plants by regulating Na+ and K+ loading in root and allocating K+ in shoot

Piriformospora indica is known as a fungus that can easily colonize a wide range of plants and enhance host’s growth and tolerance to abiotic stresses, including salinity. The mechanistic basis behind this phenomenon remains poorly understood. This work was aimed to fill in this gap and reveal mechanisms enhancing salinity tolerance in maize roots colonised by P. indica. A range of agronomic and physiological characteristics were compared between inoculated and non-inoculated maize plants under 0/100/200 mM NaCl conditions. The impact of P. indica inoculation or root’s cytosolic K+ retention ability were also assessed using micro-electrode ion flux estimation technique. The results showed that inoculated plants had higher biomass, higher stomatal conductance, lower K+ efflux from roots and higher potassium content in shoots than non-inoculated plants under salt stress. Collectively, the results indicated that the beneficial effects of inoculation on plant performance under saline conditions were mainly attributed to the improved stomata operation associated with higher rate of K delivery into the shoots.


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Plasma-membrane-type aquaporins from marine diatoms function as CO2/NH3 channels and provide photoprotection

Plasma-membrane-type aquaporins from marine diatoms function as CO2/NH3 channels and provide photoprotection | Transport in plants and fungi | Scoop.it
Aquaporins (AQPs) are ubiquitous water channels that facilitate transport of many small molecules and may play multiple vital roles in aquatic environments. In particular, mechanisms to maintain transmembrane fluxes of important small molecules have yet to be studied in marine photoautotrophic organisms. Here, we report the occurrence of multiple AQPs with differential cellular localizations in marine diatoms, an important group of oceanic primary producers. The AQPs play a role in mediating the permeability of membranes to CO2 and NH3. In silico surveys revealed the presence of five AQP orthologs in the pennate diatom Phaeodactylum tricornutum and two in the centric diatom Thalassiosira pseudonana. GFP fusions of putative AQPs displayed clear localization to the plasma membrane (PM) (PtAGP1, PtAQP2), the chloroplast endoplasmic reticulum (CER) (PtAGP1, PtAQP3), and the tonoplast (PtAQP5) in P. tricornutum. In T. pseudonana, GFP-AQP fusion proteins were found on the vacuole membrane (TpAQP1) and CER (TpAQP2). Transcript levels of both PtAQP1 and PtAQP2 were highly induced by ammonia, while only PtAQP2 was induced by high (1%) CO2. Constitutive over-expression of GFP-tagged PtAQP1 and PtAQP2 significantly increased CO2 and NH3 permeability in P. tricornutum, strongly indicating that these AQPs function in regulating CO2/NH3 permeability in the PM and/or CER. Cells carrying GFP-tagged PtAQP1 and PtAQP2 had higher non-photochemical quenching (NPQ) under high light relative to that of wild-type cells, suggesting that these AQPs are involved in photoprotection. These AQPs may facilitate the efflux of NH3, preventing the uncoupling effect of high intracellular ammonia concentrations.
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AnnAt1 and AnnAt2 function in post-phloem sugar transport in root tips to affect primary root growth 

AnnAt1 and AnnAt2 function in post-phloem sugar transport in root tips to affect primary root growth  | Transport in plants and fungi | Scoop.it

Annexins are a multigene family of calcium-dependent membrane-binding proteins that play important roles in plant cell signalling. Annexins are multifunctional proteins and their function in plants is not comprehensively understood. Arabidopsis thaliana annexins AnnAt1 and AnnAt2 are 64% identical in their primary structure, and both are highly expressed in seedlings. Here, we showed that annAt-mutant seedlings grown in the absence of sugar show decreased primary root growth and altered columella cells in root caps; however, these mutant defects are rescued by sucrose, glucose or fructose. In seedlings grown without sugar, significant up-regulation of photosynthetic gene expression and chlorophyll accumulation was found in annAt-mutant cotyledons compared to that in wild-type, which indicates potential sugar starvation in the roots of annAt-mutant seedlings. Unexpectedly, the overall sugar content of annAt-mutant primary roots was significantly higher than that of wild-type roots when grown without sugar. To examine the diffusion of sugar along the entire root to the root tip, we examined the unloading pattern of carboxyfluorescein dye and found that post-phloem sugar transport was impaired in annAt-mutant root tips compared to that in wild-type. Increased levels of ROS and callose were detected in the root tips of annAt-mutant seedlings grown without sucrose, the latter of which would restrict plasmodesmal sugar transport to root tips. Our results indicate that AnnAt1 and AnnAt2 play an important role in post-phloem sugar transport to the root tip, which in turn indirectly influences photosynthetic rates in cotyledons. This study expands our understanding of the function of annexins in plants.

 
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OsATX1 Interacts with Heavy Metal P1B-type ATPases and Affects Copper Transport and Distribution

OsATX1 Interacts with Heavy Metal P1B-type ATPases and Affects Copper Transport and Distribution | Transport in plants and fungi | Scoop.it
Copper (Cu) is an essential micronutrient for plant growth. However, the molecular mechanisms underlying Cu trafficking and distribution to different organs in rice are poorly understood. Here, we report the function and role of Antioxidant Protein1 (OsATX1), a Cu chaperone in rice (Oryza sativa). Knocking out OsATX1 resulted in increased Cu concentrations in roots, whereas OsATX1 overexpression reduced root Cu concentrations but increased Cu accumulation in the shoots. At the reproductive stage, the concentrations of Cu in developing tissues, including panicles, upper nodes and internodes, younger leaf blades, and leaf sheaths of the main tiller, were significantly increased in OsATX1-overexpressing plants and decreased in osatx1 mutants compared to that in wild type. The osatx1 mutants also showed a higher Cu concentration in older leaves. Yeast two-hybrid and bimolecular fluorescence complementation assays showed that OsATX1 interacts with the rice heavy metal P1B-ATPases HMA4, HMA5, HMA6, and HMA9. These results suggest that OsATX1 may function to deliver Cu to heavy metal P1B-ATPases for Cu trafficking and distribution in order to maintain Cu homeostasis in different rice tissues. In addition, heterologous expression of OsATX1 in the yeast (Saccharomyces cerevisiae) cadmium (Cd)-sensitive mutant Δycf1 increased the tolerance to Cu and Cd by decreasing their respective concentrations in the transformed yeast cells. Taken together, our results indicate that OsATX1 plays an important role in facilitating root-to-shoot Cu translocation and the redistribution of Cu from old leaves to developing tissues and seeds in rice.
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Towards identification of the substrates of ATP-binding cassette transporters

Towards identification of the substrates of ATP-binding cassette transporters | Transport in plants and fungi | Scoop.it
Most ATP-binding cassette (ABC) proteins function in transmembrane transport and plant genomes encode a large number of ABC transporters compared to animal or fungal genome s. These transporters have been classified into eight subfamilies according to their topology and phylogenetic relationships. Transgenic plants and mutants with altered ABC transporter expression or function have contributed to deciphering the physiological roles of these proteins, such as in plant development, response to biotic and abiotic stress, or detoxification activities within the cell. In agreement with the diversity of these functions, a large range of substrates (e.g., hormones, primary and secondary metabolites) has been identified. We review in detail transporters for which substrates have been unambiguously identified. However, some cases are far from clear because some ABC transporters have the ability to transport several structurally unrelated substrates or because identification of their substrates was performed indirectly without any flux measurement. Various heterologous or homologous expression systems have been used to better characterize the transport activity and other biochemical properties of ABC transporters, opening the way to addressing new issues such as particular structural features of plant ABC transporters, bi-directionality of transport, or the role of post-translational modifications.
 
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Reducing Water Availability Impacts the Development of the Arbuscular Mycorrhizal Fungus Rhizophagus irregularis MUCL 41833 and Its Ability to Take Up and Transport Phosphorus Under in Vitro Condit...

Reducing Water Availability Impacts the Development of the Arbuscular Mycorrhizal Fungus Rhizophagus irregularis MUCL 41833 and Its Ability to Take Up and Transport Phosphorus Under in Vitro Condit... | Transport in plants and fungi | Scoop.it
Climate change scenarios predict a higher variability in rainfall and an increased risk of water deficits during summers for the coming decades. For this reason, arbuscular mycorrhizal fungi (AMF) and their mitigating effects on drought stress in plants are increasingly considered in crop management. However, the impact of a decrease in water availability on the development of AMF and their ability to take up and transport inorganic phosphorus (Pi) to their hosts remain poorly explored. Here, Medicago truncatula plantlets were grown in association with Rhizophagus irregularis MUCL 41833 in bi-compartmented Petri plates. The system consisted in associating the plant and AMF in a root compartment (RC), allowing only the hyphae to extend in a root-free hyphal compartment (HC). Water availability in the HC was then lowered by increasing the concentration of polyethylene glycol-8000 (PEG-8000) from 0 to 10, 25, and 50 g L-1 (corresponding to a slight decrease in water potential of -0.024, -0.025, -0.030, and -0.056 Mpa, respectively). Hyphal growth, spore production and germination were severely impaired at the lowest water availability. The dynamics of Pi uptake by the AMF was also impacted, although total Pi uptake evaluated after 24 h stayed unchanged. The percentage of metabolically active extraradical hyphae remained above 70%. Finally, at the lowest water availability, a higher P concentration was observed in the shoots of M. truncatula. At reduced water availability, the extraradical mycelium (ERM) development was impacted, potentially limiting its capacity to explore a higher volume of soil. Pi uptake was slowed down but not prevented. The sensitivity of R. irregularis MUCL 41833 to a, even small, decrease in water availability contrasted with several studies reporting tolerance of AMF to drought. This suggests a species or strain-dependent effect and support the necessity to compare the impact of water availability on morpho-anatomy, nutrient uptake and transport capacities of other, potentially more drought-tolerant (e.g., isolated from dry environments) AMF.


Via Jean-Michel Ané
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The Hebeloma cylindrosporum HcPT2 Pi transporter plays a key role in ectomycorrhizal symbiosis - Becquer - New Phytologist  

The Hebeloma cylindrosporum HcPT2 Pi transporter plays a key role in ectomycorrhizal symbiosis - Becquer - New Phytologist   | Transport in plants and fungi | Scoop.it
Through a mutualistic relationship with woody plant roots, ectomycorrhizal fungi provide growth‐limiting nutrients, including inorganic phosphate (Pi), to their host. Reciprocal trades occur at the Hartig net, which is the symbiotic interface of ectomycorrhizas where the two partners are symplasmically isolated. Fungal Pi must be exported to the symbiotic interface, but the proteins facilitating this transfer are unknown. In the present study, we combined transcriptomic, microscopy, whole plant physiology, X‐ray fluorescence mapping, 32P labeling and fungal genetic approaches to unravel the role of HcPT2, a fungal Pi transporter, during the Hebeloma cylindrosporum–Pinus pinaster ectomycorrhizal association. We localized HcPT2 in the extra‐radical hyphae and the Hartig net and demonstrated its determinant role for both the establishment of ectomycorrhizas and Pi allocation towards P. pinaster. We showed that the host plant induces HcPT2 expression and that the artificial overexpression of HcPT2 is sufficient to significantly enhance Pi export towards the central cylinder. Together, our results reveal that HcPT2 plays an important role in ectomycorrhizal symbiosis, affecting both Pi influx in the mycelium and efflux towards roots under the control of P. pinaster.
 
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Frontiers | MtMTP2-facilitated zinc transport into intracellular compartments is essential for nodule development in Medicago truncatula 

Zinc (Zn) is an essential nutrient for plants that is involved in almost every biological process. This includes symbiotic nitrogen fixation, a process carried out by endosymbiotic bacteria (rhizobia) living within differentiated plant cells of legume root nodules. Zn transport in nodules involves delivery from the root, via the vasculature, release into the apoplast and uptake into nodule cells. Once in the cytosol, Zn can be used directly by cytosolic proteins or delivered into organelles, including symbiosomes of infected cells, by zinc efflux transporters. Medicago truncatula MtMTP2 (Medtr4g064893) is a nodule-induced Zn-efflux protein that was localized to an intracellular compartment in root epidermal and endodermal cells, as well as in nodule cells. Although the MtMTP2 gene is expressed in roots, shoots, and nodules, mtp2 mutants exhibited growth defects only under symbiotic, nitrogen-fixing conditions. Loss of MtMTP2 function resulted in altered nodule development, defects in bacteroid differentiation, and severe reduction of nitrogenase activity. The results presented here support a role of MtMTP2 in intracellular compartmentation of Zn, which is required for effective symbiotic nitrogen fixation in M. truncatula.
 
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Nitrogen and phosphate metabolism in ectomycorrhizas - Nehls & Plassard 

Nitrogen and phosphate metabolism in ectomycorrhizas - Nehls & Plassard  | Transport in plants and fungi | Scoop.it
Nutrient homeostasis is essential for fungal cells and thus tightly adapted to the local demand in a mycelium with hyphal specialization. Based on selected ectomycorrhizal (ECM) fungal models, we outlined current concepts of nitrogen and phosphate nutrition and their limitations, and included knowledge from Baker's yeast when major gaps had to be filled. We covered the entire pathway from nutrient mobilization, import and local storage, distribution within the mycelium and export at the plant–fungus interface. Even when nutrient import and assimilation were broad issues for ECM fungi, we focused mainly on nitrate and organic phosphorus uptake, as other nitrogen/phosphorus (N/P) sources have been covered by recent reviews. Vacuolar N/P storage and mobilization represented another focus point of this review. Vacuoles are integrated into cellular homeostasis and central for an ECM mycelium at two locations: soil‐growing hyphae and hyphae of the plant–fungus interface. Vacuoles are also involved in long‐distance transport. We further discussed potential mechanisms of bidirectional long‐distance nutrient transport (distances from millimetres to metres). A final focus of the review was N/P export at the plant–fungus interface, where we compared potential efflux mechanisms and pathways, and discussed their prerequisites.
 
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Contrasting nutrient‐disease relationships: Potassium gradients in barley leaves have opposite effects on two fungal pathogens with different sensitivities to jasmonic acid 

Understanding the interactions between mineral nutrition and disease is essential for crop management. Our previous studies with Arabidopsis thaliana demonstrated that potassium (K) deprivation induced the biosynthesis of jasmonate (JA) and increased the plant's resistance to herbivorous insects. Here we addressed the question how tissue K affects the development of fungal pathogens and whether sensitivity of the pathogens to JA could play a role for the K‐disease relationship in barley (Hordeum vulgare cv. Optic). We report that K‐deprived barley plants showed increased leaf concentrations of JA and other oxylipins. Furthermore, a natural tip‐to base K‐concentrations gradient within leaves of K‐sufficient plants was quantitatively mirrored by the transcript levels of JA‐responsive genes. The local leaf tissue K concentrations affected the development of two economically important fungi in opposite ways, showing a positive correlation with powdery mildew (Blumeria graminis) and a negative correlation with leaf scald (Rhynchosporium commune) disease symptoms. B. graminis induced a JA‐response in the plant and was sensitive to methyl‐JA treatment while R. commune initiated no JA‐response and was JA‐insensitive. Our study challenges the view that high K generally improves plant health and suggests that JA‐sensitivity of pathogens could be an important factor determining the exact K‐disease relationship.
 
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