PHT1;5 Repressed by ANT Mediates Pi Acquisition and Distribution under Low Pi and Salinity in Salt Cress.

Salinity and phosphate (Pi) starvation are the most common abiotic stresses that threaten crop productivity. Salt cress (Eutrema salsugineum) displays good tolerance to both salinity and Pi limitation. Previously, we found several Phosphate Transporter (PHT) genes in salt cress upregulated under salinity. Here, EsPHT1;5 induced by both low Pi (LP) and salinity was further characterized. Overexpression of EsPHT1;5 in salt cress enhanced plant tolerance to LP and salinity, while the knock-down lines exhibited growth retardation. The analysis of phosphorus (P) content and shoot/root ratio of total P in EsPHT1;5-overexpressing salt cress seedlings and the knock-down lines as well as arsenate uptake assays suggested the role of EsPHT1;5 in Pi acquisition and root-shoot translocation under Pi limitation. In addition, overexpression of EsPHT1;5 driven by the native promoter in salt cress enhanced Pi mobilization from rosettes to siliques upon a long-term salt treatment. Particularly, the promoter of EsPHT1;5 outperformed that of AtPHT1;5 in driving gene expression under salinity. We further identified a transcription factor EsANT, which negatively regulated EsPHT1;5 expression and plant tolerance to LP and salinity. Taken together, EsPHT1;5 plays an integral role in Pi acquisition and distribution in plant response to LP and salt stress. Further, EsANT may be involved in the cross-talk between Pi starvation and salinity signaling pathways. This work provides further insight into the mechanism underlying high P use efficiency in salt cress in its natural habitat, and evidence for a link between Pi and salt signaling.

Novel Phosphate Transporter-B PvPTB1;1/1;2 Contribute to Efficient Phosphate Uptake and Arsenic Accumulation in As-Hyperaccumulator Pteris vittata.

Arsenic (As) contamination in soil poses a potential threat to human health via crop uptake. As-hyperaccumulator Pteris vittata serves as a model plant to study As uptake and associated mechanisms. This study focuses on a novel P/AsV transport system mediated by low-affinity phosphate transporter-B 1 family (PTB1) in P. vittata. Here, we identified two plasma-membrane-localized PTB1 genes, PvPTB1;1/1;2, in vascular plants for the first time, which were 4.4-40-fold greater in expression in P. vittata than in other Pteris ferns. Functional complementation of a yeast P-uptake mutant and enhanced P accumulation in transgenic Arabidopsis thaliana confirmed their role in P uptake. Moreover, the expression of PvPTB1;1/1;2 facilitated the transport and accumulation of As in both yeast and A. thaliana shoots, demonstrating a comparable AsV uptake capacity. Microdissection-qPCR analysis and single-cell transcriptome analysis collectively suggest that PvPTB1;1/1;2 are specifically expressed in the epidermal cells of P. vittata roots. PTB1 may play a pivotal role in efficient P recycling during phytate secretion and hydrolysis in P. vittata roots. In summary, the dual P transport mechanisms consisting of high-affinity Pht1 and low-affinity PTB1 may have contributed to the efficient P/As uptake in P. vittata, thereby contributing to efficient phytoremediation for As-contaminated soils.

Insoluble-Phytate Improves Plant Growth and Arsenic Accumulation in As-Hyperaccumulator Pteris vittata: Phytase Activity, Nutrient Uptake, and As-Metabolism.

Phytate, the principal P storage in plant seeds, is also an important organic P in soils, but it is unavailable for plant uptake. However, the As-hyperaccumulator Pteris vittata can effectively utilize soluble Na-phytate, while its ability to utilize insoluble Ca/Fe-phytate is unclear. Here, we investigated phytate uptake and the underlying mechanisms based on the phytase activity, nutrient uptake, and expression of genes involved in As metabolisms. P. vittata plants were cultivated hydroponically in 0.2-strength Hoagland nutrient solution containing 50 µM As and 0.2 mM Na/Ca/Fe-phytate, with 0.2 mM soluble-P as the control. As the sole P source, all three phytates supported P. vittata growth, with its biomass being 3.2-4.1 g plant-1 and Ca/Fe-phytate being 19-29% more effective than Na-phytate. Phytate supplied soluble P to P. vittata probably via phytase hydrolysis, which was supported by 0.4-0.7 nmol P min-1 g-1 root fresh weight day-1 phytase activity in its root exudates, with 29-545 µM phytate-P being released into the growth media. Besides, compared to Na-phytate, Ca/Fe-phytate enhanced the As contents by 102-140% to 657-781 mg kg-1 in P. vittata roots and by 43-86% to 1109-1447 mg kg-1 in the fronds, which was accompanied by 21-108% increase in Ca and Fe uptake. The increased plant As is probably attributed to 1.3-2.6 fold upregulation of P transporters PvPht1;3/4 for root As uptake, and 1.8-4.3 fold upregulation of arsenite antiporters PvACR3/3;1/3;3 for As translocation to and As sequestration into the fronds. This is the first report to show that, besides soluble Na-phytate, P. vittata can also effectively utilize insoluble Ca/Fe-phytate as the sole P source, which sheds light onto improving its application in phytoremediation of As-contaminated sites.

Sorting Nexin1 negatively modulates phosphate uptake by facilitating Phosphate Transporter1;1 degradation in Arabidopsis.

High-affinity phosphate (Pi) transporters (PHTs) PHT1;1 and PHT1;4 are necessary for plant root Pi uptake especially under Pi-deficient conditions, but how their protein stability is modulated remains elusive. Here, we identified a Ttransfer DNA insertion mutant of Sorting Nexin1 (SNX1), which had more Pi content and less anthocyanin accumulation than the wild type under deficient Pi. By contrast, the snx1-2 mutant displayed higher sensitivity to exogenous arsenate in terms of seed germination and root elongation, revealing higher Pi uptake rates. Further study showed that SNX1 could co-localize and interact with PHT1;1 and PHT1;4 in vesicles and at the plasma membrane. Genetic analysis showed that increased Pi content in the snx1-2 mutant under low Pi conditions could be extensively compromised by mutating PHT1;1 in the double mutant snx1-2 pht1;1, revealing that SNX1 is epistatic to PHT1;1. In addition, SNX1 negatively controls PHT1;1 protein stability; therefore, PHT1;1 protein abundance in the plasma membrane was increased in the snx1-2 mutant compared with the wild type under either sufficient or deficient Pi. Together, our study (i) identifies SNX1 as a key modulator of the plant response to low Pi and (ii) unravels its role in the modulation of PHT1;1 protein stability, PHT1;1 accumulation at the plasma membrane, and root Pi uptake.

Phosphate (Pi) stress-responsive transcription factors PdeWRKY6 and PdeWRKY65 regulate the expression of PdePHT1;9 to modulate tissue Pi concentration in poplar.

Phosphorus (P) is an important nutrient for plants. Here, we identify a WRKY transcription factor (TF) in poplar (Populus deltoides × Populus euramericana) (PdeWRKY65) that modulates tissue phosphate (Pi) concentrations in poplar. PdeWRKY65 overexpression (OE) transgenic lines showed reduced shoot Pi concentrations under both low and normal Pi availabilities, while PdeWRKY65 reduced expression (RE) lines showed the opposite phenotype. A gene encoding a Pi transporter (PHT), PdePHT1;9, was identified as the direct downstream target of PdeWRKY65 by RNA sequencing (RNA-Seq). The negative regulation of PdePHT1;9 expression by PdeWRKY65 was confirmed by DNA-protein interaction assays, including yeast one-hybrid (Y1H), electrophoretic mobility shift assay (EMSA), co-expression of the promoters of PdePHT1;9 and PdeWRKY65 in tobacco (Nicotiana benthamiana) leaves, and chromatin immunoprecipitation-quantitative PCR. A second WRKY TF, PdeWRKY6, was subsequently identified and confirmed to positively regulate the expression of PdePHT1;9 by DNA-protein interaction assays. PdePHT1;9 and PdeWRKY6 OE and RE poplar transgenic lines were used to confirm their positive regulation of shoot Pi concentrations, under both normal and low Pi availabilities. No interaction between PdeWRKY6 and PdeWRKY65 was observed at the DNA or protein levels. Collectively, these data suggest that the low Pi-responsive TFs PdeWRKY6 and PdeWRKY65 independently regulate the expression of PHT1;9 to modulate tissue Pi concentrations in poplar.

Getting to the roots of N, P, and K uptake.

The soil contributes to the main pool of essential mineral nutrients for plants. These mineral nutrients are critical elements for the building blocks of plant biomolecules, play fundamental roles in cell processes, and act in various enzymatic reactions. The roots are the main entry point for mineral nutrients used within the plant to grow, develop, and produce seeds. In this regard, a suite of plant nutrient transport systems, sensors, and signaling proteins function in acquiring mineral nutrients through the roots. Mineral nutrients from chemical fertilizers, composed mainly of nitrogen, phosphorus, and potassium (NPK), are added to agricultural land to maximize crop yields, worldwide. However, improving nutrient uptake and use within crops is critical for economically and environmentally sustainable agriculture. Therefore, we review the molecular basis for N, P, and K nutrient uptake into the roots. Remarkably, plants are responsive to heterogeneous nutrient distribution and align root growth and nutrient uptake with nutrient-rich patches. We highlight the relationship between nutrient distribution in the growth environment and root system architecture. We discuss the exchange of information between the root and shoot systems through the xylem and phloem, which coordinates nutrient uptake with photosynthesis. The size and structure of the root system, along with the abundance and activity of nutrient transporters, largely determine the nutrient acquisition rate. Lastly, we discuss connections between N, P, and K uptake and signaling.

Oligopeptide/Histidine Transporter PHT1 and PHT2 - Function, Regulation, and Pathophysiological Implications Specifically in Immunoregulation.

The oligopeptide/histidine transporters PHT1 and PHT2, two mammalian solute carrier family 15A proteins, mediate the transmembrane transport of histidine and some di/tripeptides via proton gradient. PHT1 and PHT2 are distributed in a variety of tissues but are preferentially expressed in immune cells and localize to the lysosome-related organelles. Studies have reported the relationships between PHT1/PHT2 and immune diseases. PHT1 and PHT2 participate in the regulation of lysosomal homeostasis and lysosome-associated signaling pathways through their transport and nontransport functions, playing important roles in inflammatory diseases. In this review, we summarize recent research on PHT1 and PHT2, aiming to provide reference for their further biological research and as targets for drug design.

Proton-Coupled Oligopeptide Transport (Slc15) in the Brain: Past and Future Research.

This mini-review describes the role of the solute carrier (SLC)15 family of proton-coupled oligopeptide transporters (POTs) and particularly Pept2 (Slc15A2) and PhT1 (Slc15A4) in the brain. That family transports endogenous di- and tripeptides and peptidomimetics but also a number of drugs. The review focuses on the pioneering work of David E. Smith in the field in identifying the impact of PepT2 at the choroid plexus (the blood-CSF barrier) as well as PepT2 and PhT1 in brain parenchymal cells. It also discusses recent findings and future directions in relation to brain POTs including cellular and subcellular localization, regulatory pathways, transporter structure, species differences and disease states.

Integrating genome-wide association studies with selective sweep reveals genetic loci associated with tolerance to low phosphate availability in Brassica napus.

Oilseed rape (Brassica napus L.; B. napus) is an important oil crop worldwide. However, the genetic mechanisms of B. napus adaptations to low phosphate (P) stress are largely unknown. In this study, a genome-wide association study (GWAS) identified 68 SNPs significantly associated with seed yield (SY) under low P (LP) availability, and 7 SNPs significantly associated with phosphorus efficiency coefficient (PEC) in two trials. Among these SNPs, two, chrC07__39807169 and chrC09__14194798, were co-detected in two trials, and BnaC07.ARF9 and BnaC09.PHT1;2 were identified as candidate genes of them, respectively, by combining GWAS with quantitative reverse-transcription PCR (qRT-PCR). There were significant differences in the gene expression level of BnaC07.ARF9 and BnaC09.PHT1;2 between P-efficient and -inefficiency varieties at LP. SY_LP had a significant positive correlation with the gene expression level of both BnaC07.ARF9 and BnaC09.PHT1;2. BnaC07.ARF9 and BnaA01.PHR1 could directly bind the promoters of BnaA01.PHR1 and BnaC09.PHT1;2, respectively. Selective sweep analysis was conducted between ancient and derived B. napus, and detected 1280 putative selective signals. Within the selected region, a large number of genes related to P uptake, transport, and utilization were detected, such as purple acid phosphatase (PAP) family genes and phosphate transporter (PHT) family genes. These findings provide novel insights into the molecular targets for breeding P efficiency varieties in B. napus. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-023-01399-9.

Systematic Identification and Expression Analysis of the Sorghum Pht1 Gene Family Reveals Several New Members Encoding High-Affinity Phosphate Transporters.

Sorghum (Sorghum bicolor) is known to have a more robust capability of phosphorus uptake than many other cereal plants, which could be attributed to its phosphate transporter 1 (Pht1) that has a high phosphorus affinity. There are eleven SbPht1 genes in the sorghum genome, nine of which are expressed in sorghum roots or shoots in response to phosphorus deficiency (low-P). The molecular features of these nine genes were investigated by gene expression analysis, subcellular localization, and a yeast mutant complementation growth assay. They were found to be induced in response to low-P stress in root or shoot. All these SbPht1 proteins were found to be localized on the cell membrane, and SbPht1;8 was also detected in the endoplasmic reticulum. These SbPht1s were able to complement the yeast mutant EY917 that lacks all the functional phosphate transporters, and, among them, SbPht1;5, SbPht1;6 and SbPht1;8 could partially complement the yeast mutant strain EY917 in low-P conditions. Overall, these findings demonstrate that SbPht1;5, SbPht1;6, and SbPht1;8 are high-affinity phosphate transporters. SbPht1;5, in particular, is specifically involved in phosphorus uptake in the roots, whilst SbPht1;6 and SbPht1;8 are key players in both P uptake and P transport in response to low-P stress in sorghum.

Identification of SLC15A4/PHT1 Gene Products Upregulation Marking the Intestinal Epithelial Monolayer of Ulcerative Colitis Patients.

SLC15A4/PHT1 is an endolysosome-resident carrier of oligopeptides and histidine recently come into view as a key path marker of immune/autoimmune/inflammatory pathways in immune cells. Yet, its emerging role in inflammatory processes directly targeting the gastrointestinal epithelial layer, as in the multifactorial pathophysiology of inflammatory bowel disease (IBD), is poorly investigated. Here, the first identification of SLC15A4/PHT1 gene products in human colonic epithelium of ulcerative colitis (UC) patients is reported, showing protein primarily localized in intracellular vesicle-like compartments. Qualitative and quantitative immunohistochemical analyses of colon biopsies revealed overexpression of SLC15A4/PHT1 protein product in the epithelial layer of UC patients. Results were successfully mirrored in vitro, in spontaneously differentiated enterocyte-like monolayers of Caco-2 cells specifically exposed to DSS (dextran sodium sulphate) to mimic IBD inflammatory onsets. SLC15A4/PHT1 expression and cellular localization were characterized confirming its (dys)regulation traits in inflamed vs. healthy epithelia, strongly hinting the hypothesis of SLC15A4/PHT1 increased function associated with epithelial inflammation in IBD patients.

Environmental Control of Phosphorus Acquisition: A Piece of the Molecular Framework Underlying Nutritional Homeostasis.

Homeostasis of phosphorus (P), an essential macronutrient, is vital for plant growth under diverse environmental conditions. Although plants acquire P from the soil as inorganic phosphate (Pi), its availability is generally limited. Therefore, plants employ mechanisms involving various Pi transporters that facilitate efficient Pi uptake against a steep concentration gradient across the plant-soil interface. Among the different types of Pi transporters in plants, some members of the PHOSPHATE TRANSPORTER 1 (PHT1) family, present in the plasma membrane of root epidermal cells and root hairs, are chiefly responsible for Pi uptake from the rhizosphere. Therefore, accurate regulation of PHT1 expression is crucial for the maintenance of P homeostasis. Previous investigations positioned the Pi-dependent posttranslational regulation of PHOSPHATE STARVATION RESPONSE 1 (PHR1) transcription factor activity at the center of the regulatory mechanism controlling PHT1 expression and P homeostasis; however, recent studies indicate that several other factors also regulate the expression of PHT1 to modulate P acquisition and sustain P homeostasis against environmental fluctuations. Together with PHR1, several transcription factors that mediate the availability of other nutrients (such as nitrogen and zinc), light, and stress signals form an intricate transcriptional network to maintain P homeostasis under highly diverse environments. In this review, we summarize this intricate transcriptional network for the maintenance of P homeostasis under different environmental conditions, with a main focus on the mechanisms identified in Arabidopsis.

GTPase ROP6 negatively modulates phosphate deficiency through inhibition of PHT1;1 and PHT1;4 in Arabidopsis thaliana.

Phosphorus, an essential macroelement for plant growth and development, is a major limiting factor for sustainable crop yield. The Rho of plant (ROP) GTPase is involved in regulating multiple signal transduction processes in plants, but potentially including the phosphate deficiency signaling pathway remains unknown. Here, we identified that the rop6 mutant exhibited a dramatic tolerant phenotype under Pi-deficient conditions, with higher phosphate accumulation and lower anthocyanin content. In contrast, the rop6 mutant was more sensitive to arsenate (As(V)) toxicity, the analog of Pi. Immunoblot analysis displayed that the ROP6 protein was rapidly degraded through ubiquitin/26S proteasome pathway under Pi-deficient conditions. In addition, pull-down assay using GST-RIC1 demonstrated that the ROP6 activity was decreased obviously under Pi-deficient conditions. Strikingly, protein-protein interaction and two-voltage clamping assays demonstrated that ROP6 physically interacted with and inhibited the key phosphate uptake transporters PHT1;1 and PHT1;4 in vitro and in vivo. Moreover, genetic analysis showed that ROP6 functioned upstream of PHT1;1 and PHT1;4. Thus, we conclude that GTPase ROP6 modulates the uptake of phosphate by inhibiting the activities of PHT1;1 and PHT1;4 in Arabidopsis.

Biotechnological mechanism for improving plant remobilization of phosphorus during leaf senescence.

Phosphorus enrichment of aquatic ecosystems through diffuse source pollution is an ongoing issue worldwide. A potential solution lies in the use of fast-growing, multipurpose feedstocks, such as trees, to limit the flow of phosphorus into riparian areas through luxury consumption. However, the perennial nature of trees and their use of leaves as storage organs for excess phosphorus may reduce the effectiveness of contaminant removal during periods of leaf abscission. In an attempt to improve phosphorus remobilization during autumnal senescence, transgenic hybrid poplar P39 (Populus alba × Populus grandidentata) and Arabidopsis thaliana harbouring a constitutively expressed low-affinity potato phosphate transporter (35S::StPht1-1) were generated using Agrobacterium-mediated transformation. For both species, the highest expressing 35S::StPht1-1 lines were grown alongside wild-type plants and subjected to increasing phosphate applications. StPht1-1 expression in A. thaliana led to a reduction in biomass when grown under high-phosphate conditions and had no effect on phosphate remobilization during senescence. In contrast, StPht1-1 constitutive expression in P39 resulted in increased leaf phosphate content in the highest expressing transgenic line and minimal to no effect on P resorption efficiency. Surprisingly, sulphate resorption showed the greatest improvement in all three transgenic poplar lines, displaying a 31%-37% increase in resorption efficiency. These results highlight the complexity of nutrient resorption mechanisms in plants.

Genome-Wide Identification and Expression Profile Analysis of the PHT1 Gene Family in Gossypium hirsutum and Its Two Close Relatives of Subgenome Donor Species.

Phosphate transporter (PHT) is responsible for plant phosphorus (P) absorption and transport. PHT1 is a component of the high-affinity phosphate transporter system and plays pivotal roles in P absorption under P starvation conditions. However, in cotton, the number and identity of PHT1 genes that are crucial for P absorption from soil remain unclear. Here, genome-wide identification detected twelve PHT1 genes in Gossypium hirsutum and seven and eight PHT1 genes in two close relatives of the G. hirsutum genome-G. arboreum and G. raimondii, respectively. In addition, under low-phosphate treatment, the expressions of GaPHT1;3, GaPHT1;4, and GaPHT1;5 in roots were upregulated after 3 h of induction, and GhPHT1;3-At, GhPHT1;4-At, GhPHT1;5-At, GhPHT1;3-Dt, GhPHT1;4-Dt, and GhPHT1;5-Dt in the roots began to respond after 1 h of induction. Homologous pairs-GaPHT1;4 and GhPHT1;4-At; GaPHT1;5 and GhPHT1;5-At; GrPHT1;4 and GhPHT1;4-Dt, with GhPHT1;5-Dt and GhPHT1;5-At being syntenic-were all highly expressed in the roots under normal conditions. Among the genes highly expressed in the roots, GhPHT1;4-At, GhPHT1;5-At, GhPHT1;4-Dt and GhPHT1;5-Dt were continuously upregulated by P starvation. Therefore, it is concluded that these four genes might be key genes for P uptake in cotton roots. The results of this study provide insights into the mechanisms of P absorption and transport in cotton.

Phosphate supply influenced the growth, yield and expression of PHT1 family phosphate transporters in seven millets.

MAIN CONCLUSION: Phosphate starvation altered the root morphology and phosphate uptake with the induction of PHT1 family transporter genes in root and shoot tissues of seven millets. Millets are nutrient-rich cereals majorly cultivated in Asia and Africa. Foxtail millet (FoxM), pearl millet (PeaM), finger millet (FinM), kodo millet (KodM), little millet (LitM), proso millet (ProM), and barnyard millet (BarM) were examined for the influence of external phosphorous (P) supply on phenotypic traits, P uptake, yield, and PHosphate Transporter1 (PHT1) family gene expression. Millet seedlings grown under low Pi condition (LPC) produced significantly lower mean values for all traits except for lateral root length (LRL) and lateral root number (LRN) which were increased under LPC. Under LPC, seed weight (SW) also reduced by > 75% and had significantly lower levels of total P (TP) and Pi contents in leaf and root tissues. Expression dynamics of 12 PHT1 family (PHT1;1-1;12) transporters genes were analyzed in 7 millets. PHT1;2 has been found to be a constitutive transporter gene in all millets. Under LPC, root tissues showed the overexpression of PHT1;2, 1;3, 1;4 and 1;9 in FoxM, PHT1;1, 1;2, 1;3, 1;4, 1;8 and 1;10 in PeaM, PHT1;2 and 1;3 in FinM and ProM and PHT1;3, 1;6 and 1;11 in BarM. In leaf, LPC induced the expression of PHT1;3, 1;4 and 1;6 in FoxM, PHT1;2, 1;3, 1;4 and 1;8 in PeaM, PHT1;2, 1;3 and 1;4 in FinM and KodM, PHT1;2 in LitM and PHT1;4 in ProM and BarnM. This comprehensive study on the influence of P in phenotype, physiology, and molecular responses may help to improve the P uptake and its use efficiency of millets in future.

Expression analysis and functional characterization of two PHT1 family phosphate transporters in ryegrass.

MAIN CONCLUSION: The phosphate transporters LpPHT1;1 and LpPHT1;4 have different roles in phosphate uptake and translocation in ryegrass under P stress condition. The phosphate transporter 1 (PHT1) family are integral membrane proteins that operate in phosphate uptake, distribution and remobilization within plants. In this study, we report on the functional characterization and expression of two PHT1 family members from ryegrass plants (Lolium perenne L.) and determine their roles in the specificity of Pi transport. The expression level of LpPHT1;4 was strongly influenced by phosphorus (P) status, being higher under P-starvation condition. In contrast, the expression level of LpPHT1;1 was not correlated with P supply. Yeast mutant complementation assays showed that LpPHT1;4 can complement the growth defect of the yeast mutant Δpho84 under Pi-deficient conditions, whereas the yeast mutant expressing LpPHT1;1 was not able to restore growth. Phylogenetic and molecular analyses indicated high sequence similarity to previously identified PHT1s from other species in the Poaceae. These results suggest that LpPHT1;1 may function as a low-affinity Pi transporter, whereas LpPHT1;4 could acts as a high-affinity Pi transporter to maintain Pi homeostasis under stress conditions in ryegrass plants. This study will form the basis for the long-term goal of improving the phosphate use efficiency of ryegrass plants.

Semi-Mechanistic Population Pharmacokinetic Modeling of L-Histidine Disposition and Brain Uptake in Wildtype and Pht1 Null Mice.

PURPOSE: To develop a semi-mechanistic population pharmacokinetic (PK) model to quantitate the disposition kinetics of L-histidine, a peptide-histidine transporter 1 (PHT1) substrate, in the plasma, cerebrospinal fluid and brain parenchyma of wildtype (WT) and Pht1 knockout (KO) mice. METHODS: L-[14C]Hisidine (L-His) was administrated to WT and KO mice via tail vein injection, after which plasma, cerebrospinal fluid (CSF) and brain parenchyma samples were collected. A PK model was developed using non-linear mixed effects modeling (NONMEM). The disposition of L-His between the plasma, brain, and CSF was described by a combination of PHT1-mediated uptake, CSF bulk flow and first-order micro-rate constants. RESULTS: The PK profile of L-His was best described by a four-compartment model. A more rapid uptake of L-His in brain parenchyma was observed in WT mice due to PHT1-mediated uptake, a process characterized by a Michaelis-Menten component (Vmax = 0.051 nmoL/min and Km = 34.94 µM). CONCLUSIONS: A semi-mechanistic population PK model was successfully developed, for the first time, to quantitatively characterize the disposition kinetics of L-His in brain under in vivo conditions. This model may prove a useful tool in predicting the uptake of L-His, and possibly other PHT1 peptide/mimetic substrates, for drug delivery to the brain.

Transcriptional induction of two phosphate transporter 1 genes and enhanced root branching in grape plants inoculated with Funneliformis mosseae.

We investigated the effects of the arbuscular mycorrhizal fungus (AMF) Funneliformis mosseae on the growth and root architecture of plantlets of the grape rootstock 41B MGt under hydroponic conditions, and analyzed the concomitant expression of putative mycorrhizal-specific phosphate transporter 1 (PHT1) genes. In vitro propagated plantlets were acclimatized to ex vitro culture before AMF inoculation and grown under low phosphate (Pi) nutrition conditions during 6 weeks. Grape roots could be efficiently colonized by F. mosseae in this culture system, as shown by high mycorrhization frequency and intensity. The presence of many arbuscules in the cortex was coupled with high-level expression of two PHT1 genes in grape roots. These two very similar genes, named VvPht1-1 and VvPht1-2, present P1BS and MYCS regulatory motifs in their promoter, consistent with a specific role in the mycorrhizal pathway of Pi uptake. Although AMF inoculation significantly increased shoot growth, no effect on root biomass was observed. However, inoculated grapes exhibited an enhanced branched root system compared with non-inoculated controls, with a twofold higher number of tips and a higher proportion of fine roots usually involved in nutrient uptake from the soil. Taken together, these results suggest that root colonization by F. mosseae improved grape growth by favoring the uptake of Pi from the substrate via VvPht1-1 and VvPht1-2 high-level expression.

Phosphorus acquisition efficiency in arbuscular mycorrhizal maize is correlated with the abundance of root-external hyphae and the accumulation of transcripts encoding PHT1 phosphate transporters.

Plant interactions with arbuscular mycorrhizal fungi have long attracted interest for their potential to promote more efficient use of mineral resources in agriculture. Their use, however, remains limited by a lack of understanding of the processes that determine the outcome of the symbiosis. In this study, the impact of host genotype on growth response to mycorrhizal inoculation was investigated in a panel of diverse maize lines. A panel of 30 maize lines was evaluated with and without inoculation with arbuscular mycorrhizal fungi. The line Oh43 was identified to show superior response and, along with five other reference lines, was characterized in greater detail in a split-compartment system, using 33 P to quantify mycorrhizal phosphorus uptake. Changes in relative growth indicated variation in host capacity to profit from the symbiosis. Shoot phosphate content, abundance of root-internal and -external fungal structures, mycorrhizal phosphorus uptake, and accumulation of transcripts encoding plant PHT1 family phosphate transporters varied among lines. Superior response in Oh43 is correlated with extensive development of root-external hyphae, accumulation of specific Pht1 transcripts and high phosphorus uptake by mycorrhizal plants. The data indicate that host genetic factors influence fungal growth strategy with an impact on plant performance.