Expression Of Pi Transporters Research Articles

Beneficial Bacterium Azospirillum brasilense Induces Morphological, Physiological and Molecular Adaptation to Phosphorus Deficiency in Arabidopsis.

Although most cultivated soils have high levels of total phosphorus (P), the levels of bioavailable inorganic P (Pi) are insufficient. The application of plant-growth-promoting rhizobacteria (PGPR) is an eco-friendly strategy for P utilization; however, PGPR-mediated plant responses that enhance Pi acquisition remain unexplored. Here, we investigated the effect of Azospirillum brasilense on Arabidopsis adaptation to Pi deficiency. Results showed that A. brasilense inoculation alleviated Pi-deficiency-induced growth inhibition and anthocyanin accumulation and increased the total P content in Arabidopsis plants. A comprehensive analysis of root morphology revealed that A. brasilense increased root hair density and length under Pi-limited conditions. We further demonstrated that A. brasilense enhanced the acid phosphatase activity and upregulated the expression of several Pi transporter genes, such as PHOSPHATE1 (PHO1), PHOSPHATE TRANSPORTER 1:(PHT1:1) and PHT1;4. However, A. brasilense did not enhance the growth o total P content in pht1;1, pht1;4 and pht1;1pht1;4 mutants. Moreover, A. brasilense could not increase the P content and PHT1;1 expression in the root hairless mutant rsl4rsl2, because of the occurrence of low-Pi-induced PHT1;1 and PHT1;4 in root hairs. These results indicate that A. brasilense can promote root hair development and enhance acid phosphatase activity and Pi transporter expression levels, consequently improving the Pi absorption capacity and conferring plant tolerance to Pi deficiency.

Monogalactosyl diacylglycerol synthase 3 affects phosphate utilization and acquisition in rice.

Galactolipids are essential to compensate for the loss of phospholipids by 'membrane lipid remodelling' in plants under phosphorus (P) deficiency conditions. Monogalactosyl diacylglycerol (MGDG) synthases catalyse the synthesis of MGDG which is further converted into digalactosyl diacylglycerol (DGDG), later replacing phospholipids in the extraplastidial membranes. However, the roles of these enzymes are not well explored in rice. In this study, the rice MGDG synthase 3 gene (OsMGD3) was identified and functionally characterized. We showed that the plant phosphate (Pi) status and the transcription factor PHOSPHATE STARVATION RESPONSE 2 (OsPHR2) are involved in the transcriptional regulation of OsMGD3. CRISPR/Cas9 knockout and overexpression lines of OsMGD3 were generated to explore its potential role in rice adaptation to Pi deficiency. Compared with the wild type, OsMGD3 knockout lines displayed a reduced Pi acquisition and utilization while overexpression lines showed an enhancement of the same. Further, OsMGD3 showed a predominant role in roots, altering lateral root growth. Our comprehensive lipidomic analysis revealed a role of OsMGD3 in membrane lipid remodelling, in addition to a role in regulating diacylglycerol and phosphatidic acid contents that affected the expression of Pi transporters. Our study highlights the role of OsMGD3 in affecting both internal P utilization and P acquisition in rice.

Increased phosphate absorption in mice lacking NHE3 in intestinal epithelial cells

The kidneys play a major role in maintaining phosphate (Pi) homeostasis. Patients in later stages of CKD develop hyperphosphatemia. One novel treatment option is tenapanor, an intestinal‐specific NHE3 inhibitor. To gain mechanistic insight into the role of intestinal NHE3 in Pi homeostasis, we studied tamoxifen (Tam) ‐inducible intestinal epithelial cell‐specific NHE3 knockout (NHE3IEC‐KO) mice with the hypothesis that their phenotype should reflect inhibitory effects of tenapanor on intestinal Pi uptake. Mice were challenged by high dietary Pi, and hormones as well as plasma Pi were determined. The in vivo effects of tenapanor were studied via 33P uptake from the intestine. Pi transport was measured ex vivo in everted gut sacs (EGS) and brush border membrane vesicles (BBMV). Intestinal and renal protein expression of Pi transporters were determined. No differences were found between genotypes in terms of Pi homeostasis before Tam. Two weeks after Tam, NHE3IEC‐KO mice had similar Pi homeostasis, but a ~25% reduction in FGF23 compared with control mice on standard diet. Two‐fold greater intestinal Npt2b expression in NHE3IEC‐KO mice (P<0.05) was associated with significantly enhanced Pi uptake in EGS and BBMV. One hour after acute oral Pi loading (0.5 mol/L NaH2PO4), plasma Pi levels increased to a significantly greater extent in NHE3IEC‐KO compared to control mice (2.0±0.2 vs 1.1±0.1 mmol L‐1, P<0.05). Tenapanor treatment caused ~67% lower 33P uptake (P<0.05) after 5 minutes compared with vehicle‐treated control mice. At later time points, tenapanor‐treated control mice showed an increase in intestinal Pi uptake, reaching a maximum of 33P in plasma after 60 minutes. In response to high dietary Pi, plasma Pi slightly but significantly decreased (‐0.25±0.1 mmol/L, P<0.05) in control mice, possibly the consequence of the combination of significantly elevated PTH and FGF23. In contrast to control mice, high dietary Pi significantly increased plasma Pi in NHE3IEC‐KO mice (0.5±0.1 mmol/L, P<0.05), which was associated with significantly increased plasma PTH levels (P<0.05). FGF23 levels also increased to a significantly greater extent in NHE3IEC‐KO vs control mice (552±66 vs 244±14 pg/mL, P<0.05). This was associated with ~2.25‐fold greater Npt2b expression (P<0.05). Fifty percent lower renal Npt2c expression (P<0.05) and a trend for lower Npt2a expression (~25%) were unable to correct for higher plasma Pi. In summary, intestinal NHE3 significantly contributes to Pi homeostasis. In contrast to effects described for tenapanor on Pi homeostasis, NHE3IEC‐KO mice show higher, rather than lower, intestinal Pi uptake.

OsCKX2 regulates phosphate deficiency tolerance by modulating cytokinin in rice

Cytokinin oxidase/dehydrogenases (CKXs) are key enzymes that degrade cytokinins (CTKs) and play an essential role in plant growth and development. The present study analyzed the phenotypic and physiological characteristics of OsCKX2 overexpressing (OE) and knockout (KO) rice plants after exposure to phosphate (Pi) deficiency and the transcriptome and metabolome to investigate the function of OsCKX2 in response to Pi deficiency. OsCKX2 KO plants demonstrated higher endogenous CTK levels than wild-type (WT) under Pi deficiency. Further analysis indicated more robust tolerance of OsCKX2 KO plants to Pi deficiency, which exhibited higher phosphorus concentration, larger shoot biomass, and lesser leaf yellowing under Pi deficiency; whereas the opposite was observed for OsCKX2 OE plants. Transcriptome and metabolome analyses revealed that overexpression of OsCKX2 downregulated the transcriptional levels of genes related to Pi transporters, membrane lipid metabolism, and glycolysis, and reduced the consumption of metabolites in membrane lipid metabolism and glycolysis. On the contrary, knockout of OsCKX2 upregulated the expression of Pi transporters, and increased the consumption of metabolites in membrane lipid metabolism and glycolysis. These results indicated that OsCKX2 impacted Pi uptake, recycling, and plant growth via Pi transporters, phospholipid hydrolysis, and glycolysis under Pi deficiency. Overall, OsCKX2 negatively regulated Pi deficiency tolerance by modulating CTKs in rice.

Impact of arsenic on phosphate solubilization, acquisition and poly-phosphate accumulation in endophytic fungus Serendipita indica

Symbiotic interactions play a crucial role in the phosphate (Pi) nutrient status of the host plant and offer resilience during biotic and abiotic stresses. Despite a competitive behavior of arsenic (AsV) with Pi, Serendipita indica association promotes plant growth by reducing arsenic bioavailability in the rhizosphere. Reduced arsenic availability is due to the adsorption, accumulation, and precipitation of arsenic in the fungus. The present investigation focused on the fitness and performance of Pi acquisition and utilization in S. indica for growth and metabolism under arsenic stress. The fungus accumulates a massive amount of arsenic up to 2459.3 ppm at a tolerable limit of arsenic supply (1 mM) with a bioaccumulation factor (BAF) 32. Arsenic induces Pi transporter expression to stimulate the arsenic acquisition in the fungus. At the same time, Pi accumulation was also enhanced by 112.2 times higher than the control with an increase in poly-P (polyphosphate) content (6.69 times) of the cell. This result suggests arsenic does not hamper poly-P storage in the cell but shows a marked delocalization of stored poly-P from the vacuoles. Furthermore, an enhanced exopolyphosphatase activity and poly-P storage during arsenic stress suggest induction of cellular machinery for the utilization of Pi is required to deal with arsenic toxicity and competition. However, at high arsenic supply (2.5 and 5 mM), 14.55 and 22.07 times reduced Pi utilization, respectively, was observed during the Pi uptake by the fungus. The reduction of Pi uptake reduces the cell growth and biomass due to competition between arsenic and phosphate. The study suggests no negative impact of arsenic on the Pi acquisition, storage, and metabolism in symbiotic fungus, S. indica, under environmental arsenic contamination.

Enhanced phosphate absorption in intestinal epithelial cell-specific NHE3 knockout mice.

AimsThe kidneys play a major role in maintaining Pi homeostasis. Patients in later stages of CKD develop hyperphosphatemia. One novel treatment option is tenapanor, an intestinal‐specific NHE3 inhibitor. To gain mechanistic insight into the role of intestinal NHE3 in Pi homeostasis, we studied tamoxifen‐inducible intestinal epithelial cell‐specific NHE3 knockout (NHE3IEC‐KO) mice.MethodsMice underwent dietary Pi challenges, and hormones as well as urinary/plasma Pi were determined. Intestinal 33P uptake studies were conducted in vivo to compare the effects of tenapanor and NHE3IEC‐KO. Ex vivo Pi transport was measured in everted gut sacs and brush border membrane vesicles. Intestinal and renal protein expression of Pi transporters were determined.ResultsOn the control diet, NHE3IEC‐KO mice had similar Pi homeostasis, but a ~25% reduction in FGF23 compared with control mice. Everted gut sacs and brush border membrane vesicles showed enhanced Pi uptake associated with increased Npt2b expression in NHE3IEC‐KO mice. Acute oral Pi loading resulted in higher plasma Pi in NHE3IEC‐KO mice. Tenapanor inhibited intestinal 33P uptake acutely but then led to hyper‐absorption at later time points compared to vehicle. In response to high dietary Pi, plasma Pi and FGF23 increased to higher levels in NHE3IEC‐KO mice which was associated with greater Npt2b expression. Reduced renal Npt2c and a trend for reduced Npt2a expression were unable to correct for higher plasma Pi.ConclusionIntestinal NHE3 has a significant contribution to Pi homeostasis. In contrast to effects described for tenapanor on Pi homeostasis, NHE3IEC‐KO mice show enhanced, rather than reduced, intestinal Pi uptake.

Inositol hexakisphosphate kinases 1 and 2 (IP6K1/2) are involved in renal control of phosphate homeostasis

Phosphate (Pi) is an indispensable component of living organisms. In the body, Pi homeostasis is tightly regulated by four main tissues: intestine, kidney, bone and parathyroid glands. There are multiple complex mechanisms underlying the regulation of serum Pi including hormones and transporters. Although plenty of studies have analysed Pi regulation, the mechanism with which Pi levels are sensed by mammalian cells remains elusive. Molecular mechanisms of Pi-sensing have been elucidated in detail in yeast and bacteria. However, most of the Pi-sensing proteins identified in yeast and bacteria are encoded by genes that are not conserved in mammals. As a major exception, inositol polyphosphates—which respond to changes in ambient Pi in yeast and, in turn, regulate the expression of Pi transporters—are also found in mammals. Here, we addressed the role of inositol polyphosphates and their biogenic enzymes, the IP6Ks (especially IP6K1 and 2), in cellular Pi sensing in mammals. Human and mouse kidneys express the IP6K1 and IP6K2 isoforms. Likewise, Opossum Kidney (OK) cells, a model for renal proximal tubules express IP6K1 and 2. Pharmacological inhibition of IP6K1/2 or CRISPR/Cas9 mediated knockout in OK cells downregulates Pi transporter mRNA, particularly NaPi-IIa/c. Ip6k1-/-2-/- KO cells also exhibited decreased Pi uptake (by 70%) and an abrogated adaptation to ambient Pi. To study the role of IP6K1 and 2 in vivo, we generated renal tubule-specific inducible ip6k1-/-2-/- KO mice: the mice had strongly reduced expression of renal Pi transporters, at the protein and mRNA levels, and lower serum Pi (by 20%) together with the transcriptional downregulation of many other transporters. Serum intact fibroblast growth factor 23—a principal phosphaturic hormone—was also substantially reduced (10-fold) in these mice. Our data indicate that the deletion of IP6K1 and 2 decreases transcription of renal Pi transporters both in vivo and in vitro, and that Ip6k1-/-2-/- cells are unable to adapt to ambient Pi. Therefore, IP6K1 and 2 play a critical role in renal Pi metabolism and, potentially, sensing.

PhoPR Contributes to Staphylococcus aureus Growth during Phosphate Starvation and Pathogenesis in an Environment-Specific Manner.

Microbial pathogens must obtain all essential nutrients, including phosphate, from the host. To optimize phosphate acquisition in diverse and dynamic environments, such as mammalian tissues, many bacteria use the PhoPR two-component system. Despite the necessity of this system for virulence in several species, PhoPR has not been studied in the major human pathogen Staphylococcus aureus To illuminate its role in staphylococcal physiology, we initially assessed whether PhoPR controls the expression of the three inorganic phosphate (Pi) importers (PstSCAB, NptA, and PitA) in S. aureus This analysis revealed that PhoPR is required for the expression of pstSCAB and nptA and can modulate pitA expression. Consistent with a role in phosphate homeostasis, PhoPR-mediated regulation of the transporters is influenced by phosphate availability. Further investigations revealed that PhoPR is necessary for growth under Pi-limiting conditions, and in some environments, its primary role is to induce the expression of pstSCAB or nptA Interestingly, in other environments, PhoPR is necessary for growth independent of Pi transporter expression, indicating that additional PhoPR-regulated factors promote S. aureus adaptation to low-Pi conditions. Together, these data suggest that PhoPR differentially contributes to growth in an environment-specific manner. In a systemic infection model, a mutant of S. aureus lacking PhoPR is highly attenuated. Further investigation revealed that PhoPR-regulated factors, in addition to Pi transporters, are critical for staphylococcal pathogenesis. Cumulatively, these findings point to an important role for PhoPR in orchestrating Pi acquisition as well as transporter-independent mechanisms that contribute to S. aureus virulence.

Role of phosphate sensing in bone and mineral metabolism.

Inorganic phosphate (Pi) is essential for signal transduction and cell metabolism, and is also an essential structural component of the extracellular matrix of the skeleton. Pi is sensed in bacteria and yeast at the plasma membrane, which activates intracellular signal transduction to control the expression of Pi transporters and other genes that control intracellular Pi levels. In multicellular organisms, Pi homeostasis must be maintained in the organism and at the cellular level, requiring an endocrine and metabolic Pi-sensing mechanism, about which little is currently known. This Review will discuss the metabolic effects of Pi, which are mediated by Pi transporters, inositol pyrophosphates and SYG1-Pho81-XPR1 (SPX)-domain proteins to maintain cellular phosphate homeostasis in the musculoskeletal system. In addition, we will discuss how Pi is sensed by the human body to regulate the production of fibroblast growth factor 23 (FGF23), parathyroid hormone and calcitriol to maintain serum levels of Pi in a narrow range. New findings on the crosstalk between iron and Pi homeostasis in the regulation of FGF23 expression will also be outlined. Mutations in components of these metabolic and endocrine phosphate sensors result in genetic disorders of phosphate homeostasis, cardiomyopathy and familial basal ganglial calcifications, highlighting the importance of this newly emerging area of research.

Organ–specific hormonal cross-talk in phosphate deficiency

Plant interactions with the environment, including nutrient sensing and acquisition, are regulated by plant hormones. Responses to phosphate (Pi) deficiency are governed by strigolactones, in cross-talk with other hormones. Reaction of Arabidopsis thaliana plants to Pi deficiency has been characterized in shoot apices, leaves and roots at hormonal and selected transcript levels. Pi starvation was associated with elevation of abscisic acid and jasmonic acid in all followed organs, as well as of salicylic acid in roots. Stimulation of strigolactone signaling pathway was indicated by suppressed expression of strigolactone repressors SMXL6 and SMXL8. Simultaneously, Pi deficiency downregulated the levels of gibberellin GA4 and the most physiologically active cytokinin, trans-zeatin, in all studied organs, increasing less active cis-zeatin in roots. Data imply suppression of the plastid cytokinin biosynthetic pathway and promotion of the cytoplasmic one. Strigolactone function has been characterized comparing the effect of 5 μM synthetic strigolactone GR24 at Pi deficiency and full Pi supply (100 μM). GR24 promoted Pi uptake, including expression of Pi transporters PHT1;4 and PHT1;7. GR24 in Pi presence generally mimicked the impact of Pi deficiency in roots, with exception of jasmonic acid and salicylic acid, which were in full Pi medium, i.e. under conditions optimal for growth, decreased. Pi availability strongly affected expression of selected genes in apices, the major differences being found in the expression of Pi-transporters, auxin- and strigolactone-related genes. The data show highly organ-specific effects of Pi deficiency and decisive role of strigolactones, not only in roots but also in apices.

Individual versus Combinatorial Effects of Silicon, Phosphate, and Iron Deficiency on the Growth of Lowland and Upland Rice Varieties.

Mineral nutrient homeostasis is essential for plant growth and development. Recent research has demonstrated that the occurrence of interactions among the mechanisms regulating the homeostasis of different nutrients in plants is a general rule rather than an exception. Therefore, it is important to understand how plants regulate the homeostasis of these elements and how multiple mineral nutrient signals are wired to influence plant growth. Silicon (Si) is not directly involved in plant metabolism but it is an essential element for a high and sustainable production of crops, especially rice, because of its high content in the total shoot dry weight. Although some mechanisms underlying the role of Si in plants responses to both abiotic and biotic stresses have been proposed, the involvement of Si in regulating plant growth in conditions where the availability of essential macro- and micronutrients changes remains poorly investigated. In this study, the existence of an interaction between Si, phosphate (Pi), and iron (Fe) availability was examined in lowland (Suphanburi 1, SPR1) and upland (Kum Hom Chiang Mai University, KH CMU) rice varieties. The effect of Si and/or Fe deficiency on plant growth, Pi accumulation, Pi transporter expression (OsPHO1;2), and Pi root-to-shoot translocation in these two rice varieties grown under individual or combinatorial nutrient stress conditions were determined. The phenotypic, physiological, and molecular data of this study revealed an interesting tripartite Pi-Fe-Si homeostasis interaction that influences plant growth in contrasting manners in the two rice varieties. These results not only reveal the involvement of Si in modulating rice growth through an interaction with essential micro- and macronutrients, but, more importantly, they opens new research avenues to uncover the molecular basis of Pi-Fe-Si signaling crosstalk in plants.

Expression of Phosphate Transporters during Dental Mineralization

The importance of phosphate (Pi) as an essential component of hydroxyapatite crystals suggests a key role for membrane proteins controlling Pi uptake during mineralization in the tooth. To clarify the involvement of the currently known Pi transporters (Slc17a1, Slc34a1, Slc34a2, Slc34a3, Slc20a1, Slc20a2, and Xpr1) during tooth development and mineralization, we determined their spatiotemporal expression in murine tooth germs from embryonic day 14.5 to postnatal day 15 and in human dental samples from Nolla stages 6 to 9. Using real-time polymerase chain reaction, in situ hybridization, immunohistochemistry, and X-gal staining, we showed that the expression of Slc17a1, Slc34a1, and Slc34a3 in tooth germs from C57BL/6 mice were very low. In contrast, Slc34a2, Slc20a1, Slc20a2, and Xpr1 were highly expressed, mostly during the postnatal stages. The expression of Slc20a2 was 2- to 10-fold higher than the other transporters. Comparable results were obtained in human tooth germs. In mice, Slc34a2 and Slc20a1 were predominantly expressed in ameloblasts but not odontoblasts, while Slc20a2 was detected neither in ameloblasts nor in odontoblasts. Rather, Slc20a2 was highly expressed in the stratum intermedium and the subodontoblastic cell layer. Although Slc20a2 knockout mice did not show enamel defects, mutant mice showed a disrupted dentin mineralization, displaying unmerged calcospherites at the mineralization front. This latter phenotypical finding raises the possibility that Slc20a2 may play an indirect role in regulating the extracellular Pi availability for mineralizing cells rather than a direct role in mediating Pi transport through mineralizing plasma cell membranes. By documenting the spatiotemporal expression of Pi transporters in the tooth, our data support the possibility that the currently known Pi transporters may be dispensable for the initiation of dental mineralization and may rather be involved later during the tooth mineralization scheme.

Silicon increases phosphorus (P) uptake by wheat under low P acid soil conditions

Although silicon (Si) is known to improve plant growth under low phosphorus (P) conditions, the in planta mechanisms responsible for this effect are still unknown. Here, we investigated the role of Si on P uptake along with the expression of Pi transporters in wheat (Triticum aestivum L.) grown in low P acid soil in comparison with P fertilization and liming. A combined approach was performed including analyses of rhizosphere soil, tissue P content, the expression of the root Pi transporter genes (TaPHT1.1 and TaPHT1.2), and the root exudation of citrate and malate. Supply of Si in a form of Na2SiO3 increased shoot P concentration to an adequate level in the range of P-fertilized plants. Silicon ameliorated low soil pH and high Al3+ comparable to the effect of liming. The in planta effect of Si on up-regulating the expression of TaPHT1.1 and TaPHT1.2 was several fold higher and consequently P uptake doubled compared to both P fertilization and liming. In addition, Si directly stimulated root Pi acquisition by prominently increasing both malate and citrate exudation rate. Application of Si increased root exudation of organic acids that mobilize Pi in the rhizosphere and up-regulated Pi transporters in wheat roots.

Heat Stress Affects Pi-related Genes Expression and Inorganic Phosphate Deposition/Accumulation in Barley

Phosphorus (P) in plants is taken from soil as an inorganic phosphate (Pi) and is one of the most important macroelements in growth and development. Plants actively react to Pi starvation by the induced expression of Pi transporters, MIR399, MIR827, and miR399 molecular sponge – IPS1 genes and by the decreased expression of the ubiquitin-conjugating enzyme E2 (PHOSPHATE2 – PHO2) and Pi sensing and transport SPX-MFS genes. The PHO2 protein is involved in the degradation of Pi transporters PHT1;1 (from soil to roots) and PHO1 (from roots to shoots). The decreased expression of PHO2 leads to Pi accumulation in shoots. In contrast, the pho1 mutant shows a decreased level of Pi concentration in shoots. Finally, Pi starvation leads to decreased Pi concentration in all plant tissues. Little is known about plant Pi homeostasis in other abiotic stress conditions. We found that, during the first hour of heat stress, Pi accumulated in barley shoots but not in the roots, and transcriptomic data analysis as well as RT-qPCR led us to propose an explanation for this phenomenon. Pi transport inhibition from soil to roots is balanced by lower Pi efflux from roots to shoots directed by the PHO1 transporter. In shoots, the PHO2 mRNA level is decreased, leading to an increased Pi level. We concluded that Pi homeostasis in barley during heat stress is maintained by dynamic changes in Pi-related genes expression.

Interaction between carbon metabolism and phosphate accumulation is revealed by a mutation of a cellulose synthase-like protein, CSLF6.

Phosphorus is an essential macronutrient for plant growth and development. However, the network that affects phosphate (Pi) accumulation in crops is not well established. It is reported here that OsCSLF6, a member of the cellulose synthase-like family (CSLF), which is found only in grasses, is involved in Pi accumulation. The oscslf6 mutants (oscslf6-1 and oscslf6-2) display Pi toxic symptoms and increased Pi accumulation in both roots and shoots under the Pi-sufficient condition, which correlate with the induced expression of Pi transporters in the knockout mutants. Consistent with the over-accumulation of Pi, a significant decrease in primary root length, adventitious root length, and adventitious root number were observed in the oscslf6 mutants when compared with the wild type (WT) under Pi-sufficient conditions. In addition, the sucrose (Suc) level was increased in the oscslf6 mutants and the expression of sucrose synthases (OsSUS4/5) and sucrose transporters (OsSUT1/2/4/OsSweet14) genes were also induced in the shoots of oscslf6 mutants, suggesting that OsCSLF6 may play a role in affecting Pi accumulation by affecting the level of carbon metabolism.

Plant phosphorus acquisition in a common mycorrhizal network: regulation of phosphate transporter genes of the Pht1 family in sorghum and flax.

In a preceding microcosm study, we found huge differences in phosphorus (P) acquisition in sorghum (Sorghum bicolor) and flax (Linum usitatissimum) sharing a common mycorrhizal network (CMN). Is the transcriptional regulation of arbuscular mycorrhizal (AM)-induced inorganic orthophosphate (Pi) transporters responsible for these differences? We characterized and analyzed the expression of Pi transporters of the Pht1 family in both plant species, and identified two new AM-inducible Pi transporters in flax. Mycorrhizal Pi acquisition was strongly affected by the combination of plant and AM fungal species. A corresponding change in the expression of two AM-inducible Pht1 transporters was noticed in both plants (SbPT9, SbPT10, LuPT5 and LuPT8), but the effect was very weak. Overall, the expression level of these genes did not explain why flax took up more Pi from the CMN than did sorghum. The post-transcriptional regulation of the transporters and their biochemical properties may be more important for their function than the fine-tuning of their gene expression.

Exposure of barley plants to low Pi leads to rapid changes in root respiration that correlate with specific alterations in amino acid substrates.

The majority of inorganic phosphate (Pi ) stress studies in plants have focused on the response after growth has been retarded. Evidence from transcript analysis, however, shows that a Pi -stress specific response is initiated within minutes of transfer to low Pi and in crop plants precedes the expression of Pi transporters and depletion of vacuolar Pi reserves by days. In order to investigate the physiological and metabolic events during early exposure to low Pi in grain crops, we monitored the response of whole barley plants during the first hours following Pi withdrawal. Lowering the concentration of Pi led to rapid changes in root respiration and leaf gas exchange throughout the early phase of the light course. Combining amino and organic acid analysis with (15) N labelling we show a root-specific effect on nitrogen metabolism linked to specific substrates of respiration as soon as 1h following Pi withdrawal; this explains the respiratory responses observed and was confirmed by stimulation of respiration by exogenous addition of these respiratory substrates to roots. The rapid adjustment of substrates for respiration in roots during short-term Pi -stress is highlighted and this could help guide roots towards Pi -rich soil patches without compromising biomass accumulation of the plant.

New Developments in CKD-MBD. Molecular mechanisms of intestinal and renal phosphate transport

Intestinal inorganic phosphate (Pi) absorption and renal Pi reabsorption are regulated by parathyroid hormone, fibroblast growth factor 23, or 1,25-dihydroxyvitamin D, which modulate the expression of Pi transporters. Identification, functional characterization and analysis of knockout mice of Pi transporters contributed to clarify the role of each transporter in Pi homeostasis. Furthermore, the molecular mechanisms will lead to the development of new pharmaceutical research approaches.

Auxin secretion by Bacillus amyloliquefaciens FZB42 both stimulates root exudation and limits phosphorus uptake in Triticum aestivium.

BackgroundThe use of auxin-producing rhizosphere bacteria as agricultural products promises increased root production and therefore greater phosphate (Pi) uptake. Whilst such bacteria promote root production in vitro, the nature of the bacteria-plant interaction in live soil, particularly concerning any effects on nutrient uptake, are not known. This study uses Bacillus amyloliquefaciens FZB42, an auxin-producing rhizobacterium, as a dressing on Triticum aestivum seeds. It then examines the effects on root production, Pi uptake, Pi-related gene expression and organic carbon (C) exudation.ResultsSeed treatment with B. amyloliquefaciens FZB42 increased root production at low environmental Pi concentrations, but significantly repressed root Pi uptake. This coincided with an auxin-mediated reduction in expression of the Pi transporters TaPHT1.8 and TaPHT1.10. Applied exogenous auxin also triggered an increase in root C exudation. At high external Pi concentrations, root production was promoted by B. amyloliquefaciens FZB42, but Pi uptake was unaffected.ConclusionsWe conclude that, alongside promoting root production, auxin biosynthesis by B. amyloliquefaciens FZB42 both re-models Pi transporter expression and elevates organic C exudation. This shows the potential importance of rhizobacterial-derived auxin following colonisation of root surfaces, and the nature of this bacteria-plant interaction in soil.

Adaptive responses of calcium and phosphate homeostasis in goats to low nitrogen intake: renal aspects

In a previous study, in goats, we showed that apart from variations in dietary calcium (Ca) and phosphorus intake, also low dietary nitrogen (N) intake altered plasma concentrations of hormones, which regulate Ca and phosphate (Pi ) homeostasis. These hormonal responses in goats were in accordance with findings in monogastric animals and humans with low protein intake. In the aforementioned studies, alterations of electrolyte transport in the kidneys were also observed. However, whether renal electrolyte transport in goats is also involved in the adaptation of Ca and Pi homeostasis to low N intake remains unknown. Thus, the aim of the present study was to investigate whether in addition to the hormonal changes, as observed in our former study, renal Ca transport and renal Pi transport were also altered by low N intake in goats. Therefore, in kidney samples from the goats used in our former study, the protein expression of Ca and Pi transporters and of related regulatory proteins was examined. Furthermore, the uptake of Pi into isolated brush border membrane vesicles (BBMV) was detected. The results showed that the protein amount of the renal sodium-dependent Pi transporter NaPi IIa was elevated, and concomitantly, protein expression of its upstream regulators, the parathyroid hormone receptor and the extracellular signal-regulated kinases 1 and 2 was decreased. However, Pi uptake into renal BBMV was not enhanced. Furthermore, protein expression of the renal Ca channel, the transient receptor potential cation channel subfamily V member 5 (TRPV5) and of the vitamin D receptor was not influenced by dietary N reduction. We conclude that regulation of renal Pi transporter expression in goats is involved in the adaptation of electrolyte homeostasis to low N intake.