Pi Transporter Genes Research Articles

Proteomic Analysis Provides New Insights in Phosphorus Homeostasis Subjected to Pi (Inorganic Phosphate) Starvation in Tomato Plants (Solanum lycopersicum L.).

Phosphorus is a major nutrient acquired by plants via high-affinity inorganic phosphate (Pi) transporters. To determine the adaptation and homeostasis strategy to Pi starvation, we compared the proteome analysis of tomato leaves that were treated with and without Pi (as KH2PO4) for 10 days. Among 600 reproducible proteins on 2-DE gels 46 of them were differentially expressed. These proteins were involved in major metabolic pathways, including photosynthesis, transcriptional/translational regulations, carbohydrate/energy metabolism, protein synthesis, defense response, and other secondary metabolism. The results also showed that the reduction in photosynthetic pigments lowered P content under –Pi treatments. Furthermore, high-affinity Pi transporters (lePT1 and lePT2) expressed in higher amounts under –Pi treatments. Also, the accumulation of Pi transporters was observed highly in the epidermis and palisade parenchyma under +Pi treatments compared to –Pi treatments. Our data suggested that tomato plants developed reactive oxygen species (ROS) scavenging mechanisms to cope with low Pi content, including the up-regulation of proteins mostly involved in important metabolic pathways. Moreover, Pi-starved tomato plants increased their internal Pi utilization efficiency by increasing the Pi transporter genes and their rational localization. These results thus provide imperative information about how tomato plants respond to Pi starvation and its homeostasis.

A novel point mutation promotes growth phase-dependent daptomycin tolerance in Staphylococcus aureus.

Recalcitrance of genetically susceptible bacteria to antibiotic killing is a hallmark of bacterial drug tolerance. This phenomenon is prevalent in biofilms, persisters, and also planktonic cells and is associated with chronic or relapsing infections with pathogens such as Staphylococcus aureus. Here we report the in vitro evolution of an S. aureus strain that exhibits a high degree of nonsusceptibility to daptomycin as a result of cyclic challenges with bactericidal concentrations of the drug. This phenotype was attributed to stationary growth phase-dependent drug tolerance and was clearly distinguished from resistance. The underlying genetic basis was revealed to be an adaptive point mutation in the putative inorganic phosphate (Pi) transporter gene pitA. Drug tolerance caused by this allele, termed pitA6, was abrogated when the upstream gene pitR was inactivated. Enhanced tolerance toward daptomycin, as well as the acyldepsipeptide antibiotic ADEP4 and various combinations of other drugs, was accompanied by elevated intracellular concentrations of Pi and polyphosphate, which may reversibly interfere with critical cellular functions. The evolved strain displayed increased rates of survival within human endothelial cells, demonstrating the correlation of intracellular persistence and drug tolerance. These findings will be useful for further investigations of S. aureus drug tolerance, toward the development of additional antipersister compounds and strategies.

The Phosphate Transporter Gene OsPht1;4 Is Involved in Phosphate Homeostasis in Rice.

A total of 13 phosphate transporters in rice (Oryza sative) have been identified as belonging to the Pht1 family, which mediates inorganic phosphate (Pi) uptake and transport. We report the biological property and physiological role of OsPht1;4 (OsPT4). Overexpressing OsPT4 resulted in significant higher Pi accumulation in roots, straw and brown rice, and suppression of OsPT4 caused decreased Pi concentration in straw and brown rice. Expression of the β-glucuronidase reporter gene driven by the OsPT4 promoter showed that OsPT4 is expressed in roots, leaves, ligules, stamens, and caryopses under sufficient Pi conditions, consistent with the expression profile showing that OsPT4 has high expression in roots and flag leaves. The transcript level of OsPT4 increased significantly both in shoots and roots with a long time Pi starvation. OsPT4 encoded a plasma membrane—localized protein and was able to complement the function of the Pi transporter gene PHO84 in yeast. We concluded that OsPT4 is a functional Pi-influx transporter involved in Pi absorption in rice that might play a role in Pi translocation. This study will enrich our understanding about the physiological function of rice Pht1 family genes.

Local and distal effects of arbuscular mycorrhizal colonization on direct pathway Pi uptake and root growth in Medicago truncatula.

Two pathways exist for plant Pi uptake from soil: via root epidermal cells (direct pathway) or via associations with arbuscular mycorrhizal (AM) fungi, and the two pathways interact in a complex manner. This study investigated distal and local effects of AM colonization on direct root Pi uptake and root growth, at different soil P levels. Medicago truncatula was grown at three soil P levels in split-pots with or without AM fungal inoculation and where one root half grew into soil labelled with (33)P. Plant genotypes included the A17 wild type and the mtpt4 mutant. The mtpt4 mutant, colonized by AM fungi, but with no functional mycorrhizal pathway for Pi uptake, was included to better understand effects of AM colonization per se. Colonization by AM fungi decreased expression of direct Pi transporter genes locally, but not distally in the wild type. In mtpt4 mutant plants, direct Pi transporter genes and the Pi starvation-induced gene Mt4 were more highly expressed than in wild-type roots. In wild-type plants, less Pi was taken up via the direct pathway by non-colonized roots when the other root half was colonized by AM fungi, compared with non-mycorrhizal plants. Colonization by AM fungi strongly influenced root growth locally and distally, and direct root Pi uptake activity locally, but had only a weak influence on distal direct pathway activity. The responses to AM colonization in the mtpt4 mutant suggested that in the wild type, the increased P concentration of colonized roots was a major factor driving the effects of AM colonization on direct root Pi uptake.

Impact of arbuscular mycorrhizal fungi (AMF) on cucumber growth and phosphorus uptake under cold stress.

Symbiosis with root-associated arbuscular mycorrhizal fungi (AMF) can improve plant phosphorus (P) uptake and alleviate environmental stresses. It could be also an effective mean to promote plant performance under low temperatures. The combined effects of arbuscular mycorrhiza and low temperature (15°C/10°C day/night) on cucumber seedlings were investigated in the present study. Root colonisation by AMF, succinate dehydrogenase and alkaline phosphatase activity in the intraradical fungal structures, plant growth parameters, and expression profiles of four cucumber phosphate (Pi) transporters, the fungal Pi transporter GintPT and alkaline phosphatase GintALP were determined. Cold stress reduced plant growth and mycorrhizal colonisation. Inoculation improved cucumber growth under ambient temperatures, whereas under cold stress only root biomass was significantly increased by inoculation. AMF supplied P to the host plant under ambient temperatures and cold stress, as evidenced by the higher P content of mycorrhizal plants compared with non-mycorrhizal plants. Thus, the cold-stressed cucumber seedlings still benefited from mycorrhiza, although the benefit was less than that under ambient temperatures. In accordance with this, a cucumber Pi transporter gene belonging to the Pht1 gene family was strongly induced by mycorrhiza at ambient temperature and to a lesser extent under cold stress. The other three Pi transporters tested from different families were most highly expressed in cold-stressed mycorrhizal plants, suggesting a complex interactive effect of mycorrhiza and cold stress on internal P cycling in cucumber plants.

Liming of anthropogenically acidified soil promotes phosphorus acquisition in the rhizosphere of wheat

We studied the effect of liming and P fertilization of extremely acid soil (accidently acidified by sulfidic mining waste) on P availability and the subsequent adaptive responses of wheat roots. The wheat plants were grown in rhizoboxes allowing precise sampling of rhizosphere and bulk soil for sequential extraction of P fractions and determination of exchangeable Al. Root exudates were collected by pieces of paper for electrophoresis and subjected to HPLC analysis. Expression of organic anions and Pi transporter genes was analyzed by a real-time quantitative PCR. The concomitant application of lime with P fertilization increased the concentrations of plant-available P fractions in both rhizosphere and bulk compartments. The applied soil amendments strongly affected plant growth, biomass partitioning and shoot P accumulation. Liming enhanced root exudation of citrate in P unfertilized plants, while the high malate efflux was maintained until both P deficiency and Al toxicity were eliminated by the amendments. We showed the importance of liming for recovering of P acquisition potential of wheat roots, which can be strongly impaired in acid soils. Our results clearly demonstrated that P-deficient roots not subjected to Al stress in the limed soil can maintain high efflux of malate and even increase efflux of citrate along with the enhanced expression of related anion transporters (TaMATE1 and TaALMT1).

MiR444a has multiple functions in the rice nitrate‐signaling pathway

Nitrate (NO3-) is a key signaling molecule in plant metabolism and development, in addition to its role as a nutrient. It has been shown previously in Arabidopsis that ANR1, a MADS-box transcription factor, is a major component in the NO3--signaling pathway that triggers lateral root growth and that miR444, which is specific to monocots, targets four genes that are homologous to ANR1 in rice. Here, we show that miR444a plays multiple roles in the rice NO3--signaling pathway - not only in root development, but also involving nitrate accumulation and even Pi -starvation responses. miR444a overexpression resulted in reduced rice lateral root elongation, but promoted rice primary and adventitious root growth, in a nitrate-dependent manner. In addition, overexpression of miR444a improved nitrate accumulation and expression of nitrate transporter genes under high nitrate concentration conditions, but reduced the remobilization of nitrate from old leaves to young leaves thus affecting the plant's ability to adapt to nitrogen-limitating conditions. Intriguingly, we found that Pi starvation strongly induced miR444 accumulation in rice roots and that overexpression of miR444a altered Pi -starvation-induced root architecture and enhanced Pi accumulation and expression of three Pi transporter genes. We further provide evidence that miR444a is involved in the interaction between the NO3--signaling and Pi -signaling pathways in rice. Taken together, our observations demonstrated that miR444a plays multiple roles in the rice NO3--signaling pathway in nitrate-dependent root growth, nitrate accumulation and phosphate-starvation responses.

Opening the black box: outcomes of interactions between arbuscular mycorrhizal (AM) and non‐host genotypes of Medicago depend on fungal identity, interplay between P uptake pathways and external P supply

We investigated the physiology that underlies the influence of arbuscular mycorrhizal (AM) colonization on outcomes of interactions between plants. We grew Medicago truncatula A17 and its AM-defective mutant dmi1 in intragenotypic (two plants per pot of the same genotype, x2) or intergenotypic (one plant of each genotype, 1 + 1) combinations, inoculated or not with Rhizophagus irregularis (formerly Glomus intraradices) or Gigaspora margarita. We measured plant growth, colonization, contributions of AM and direct P uptake pathways using (32)P, and expression of plant Pi transporter genes at two levels of P supply. A17 (x2) responded positively to inoculation only at low P. The response was enhanced with 1 + 1 even at high P where colonization in A17 was reduced. With R. irregularis P uptake by the AM pathway was unaffected by P supply, whereas with G. margarita, the AM pathway was lower at high P, and direct uptake higher. Gene expression varied and was unrelated to P uptake through the two pathways. There was no evidence of plant control of P uptake via R. irregularis at high P but there was via G. margarita. Importantly, growth responses of plant genotypes grown alone did not predict outcomes of intergenotypic interactions.

A novel plant–fungus symbiosis benefits the host without forming mycorrhizal structures

• Most terrestrial plants form mutually beneficial symbioses with specific soil-borne fungi known as mycorrhiza. In a typical mycorrhizal association, fungal hyphae colonize plant roots, explore the soil beyond the rhizosphere and provide host plants with nutrients that might be chemically or physically inaccessible to root systems. • Here, we combined nutritional, radioisotopic ((33)P) and genetic approaches to describe a plant growth promoting symbiosis between the basidiomycete fungus Austroboletus occidentalis and jarrah (Eucalyptus marginata), which has quite different characteristics. • We show that the fungal partner does not colonize plant roots; hyphae are localized to the rhizosphere soil and vicinity and consequently do not transfer nutrients located beyond the rhizosphere. Transcript profiling of two high-affinity phosphate (Pi) transporter genes (EmPHT1;1 and EmPHT1;2) and hyphal-mediated (33)Pi uptake suggest that the Pi uptake shifts from an epidermal to a hyphal pathway in ectomycorrhizal plants (Scleroderma sp.), similar to arbuscular mycorrhizal symbioses, whereas A. occidentalis benefits its host indirectly. The enhanced rhizosphere carboxylates are linked to growth and nutritional benefits in the novel symbiosis. • This work is a starting point for detailed mechanistic studies on other basidiomycete-woody plant relationships, where a continuum between heterotrophic rhizosphere fungi and plant beneficial symbioses is likely to exist.

Functional properties and expression quantitative trait loci for phosphate transporter GmPT1 in soybean

Phosphate (Pi) remobilization within a plant is critical for plant survival under Pi-limiting conditions. In this paper, a soybean Pi transporter gene, GmPT1, was characterized. A marked induction of GmPT1 transcript was observed in young leaves, mature leaves and lateral roots during long-term Pi starvation. Transgenic tobacco plants containing the GmPT1 gene were obtained using an Agrobacterium-mediated transformation system. Compared with wild-type plants, transgenic plants showed significant increases in phosphorus-use efficiency (PUE), photosystem II (PSII) function, total dry weight and seed weight under Pi-deficient conditions. GmPT1 expression levels and PUE were determined in a soybean recombinant inbred line population during a pot experiment that was conducted to measure chlorophyll fluorescence parameters, photosynthetic rate (PN ) and seed yield. Correlation analysis revealed that GmPT1 expression levels had significantly positive correlations with seed yield, PUE, PN and the quantum yield of PSII primary photochemistry (ΦPSII ). Expression quantitative trait loci (eQTL) mapping for GmPT1 revealed two eQTLs, one of which coincided with both the physical location of GmPT1 and a QTL associated with seed yield. These results suggest that GmPT1 plays a role in Pi remobilization, and it may be possible to improve soybean seed yields under Pi-limiting conditions by modulating GmPT1 expression levels.

Phosphate deficiency signaling pathway is a target of arsenate and phosphate transporter OsPT1 is involved in As accumulation in shoots of rice

Arsenate [As(V)] is toxic to organisms, and phosphate (Pi) transporter can mediate As(V) uptake due to their similarity in chemical structure. In the rice (Oriza sativa L.) genome, 13 Pi transporter genes (OsPTs) are present. Their response to As(V) and contribution to As(V) accumulation are unknown. We determined absolute mRNA amount of OsPTs in rice seedlings and OsPT1, OsPT2, OsPT4, and OsPT8 were quantified by real-time polymerase chain reaction (PCR). OsPT2, OsPT4, and OsPT8 were highly induced by Pi deficiency, while OsPT1 was not. In accordance with Pi deficiency response, OsPT2, OsPT4, and OsPT8 induction by Pi deficiency were severely suppressed by As(V). Those data suggest that As(V) affects Pi deficiency signaling in rice. To examine the As(V) transport activity of OsPT1 in planta, we obtained T-DNA mutant of OsPT1 (ospt1). The transcript expression level of OsPT1 in ospt1 was reduced by 70% in shoots and 50% in roots compared to those in the wild-type (WT), and arsenic (As) concentrations in shoots were reduced by 60% compared to WT. We further overexpressed OsPT1-GFP in rice. Overexpression lines showed higher As accumulation in shoots compared to wild-type. OsPT1-GFP is localized to plasma membrane. These results indicate that OsPT1 is involved in As(V) uptake from soil or apoplast.

Inorganic phosphate uptake in Trypanosoma cruzi is coupled to K+ cycling and to active Na+ extrusion

BackgroundOrthophosphate (Pi) is a central compound in the metabolism of all organisms, including parasites. There are no reports regarding the mechanisms of Pi acquisition by Trypanosoma cruzi. Methods32Pi influx was measured in T. cruzi epimastigotes. The expression of Pi transporter genes and the coupling of the uptake to Na+, H+ and K+ fluxes were also investigated. The transport capacities of different evolutive forms were compared. ResultsEpimastigotes grew significantly more slowly in 2mM than in 50mM Pi. Influx of Pi into parasites grown under low Pi conditions took place in the absence and presence of Na+. We found that the parasites express TcPho84, a H+:Pi-symporter, and TcPho89, a Na+:Pi-symporter. Both Pi influx mechanisms showed Michaelis–Menten kinetics, with a one-order of magnitude higher affinity for the Na+-dependent system. Collapsing the membrane potential with carbonylcyanide-p-trifluoromethoxyphenylhydrazone strongly impaired the influx of Pi. Valinomycin (K+ ionophore) or SCH28028 (inhibitor of (H++K+)ATPase) significantly inhibited Pi uptake, indicating that an inwardly-directed H+ gradient energizes uphill Pi entry and that K+ recycling plays a key role in Pi influx. Furosemide, an inhibitor of the ouabain-insensitive Na+-ATPase, decreased only the Na+-dependent Pi uptake, indicating that this Na+ pump generates the Na+ gradient utilized by the symporter. Trypomastigote forms take up Pi inefficiently. ConclusionsPi starvation stimulates membrane potential-sensitive Pi uptake through different pathways coupled to Na+ or H+/K+ fluxes. General significanceThis study unravels the mechanisms of Pi acquisition by T. cruzi, a key process in epimastigote development and differentiation to trypomastigote forms.

The cis‐acting CTTC–P1BS module is indicative for gene function of LjVTI12, a Qb‐SNARE protein gene that is required for arbuscule formation in Lotus japonicus

The majority of land plants live in symbiosis with arbuscular mycorrhizal fungi from the phylum Glomeromycota. This symbiosis improves acquisition of phosphorus (P) by the host plant in exchange for carbohydrates, especially under low-P availability. The symbiosome, constituted by root cortex cells accommodating arbuscular mycorrhizal fungal hyphae, is the site at which bi-directional exchange of nutrients and metabolites takes place. Uptake of orthophosphate (Pi) in the symbiosome is facilitated by mycorrhiza-specific plant Pi transporters. Modifications of the potato Pi transporter 3 (StPT3) promoter were analysed in transgenic mycorrhizal roots, and it was found that the CTTC cis-regulatory element is necessary and sufficient for a transcriptional response to fungal colonization under low-Pi conditions. Phylogenetic footprinting also revealed binary combination of the CTTC element with the Pi starvation response-associated PHR1-binding site (P1BS) in the promoters of several mycorrhiza-specific Pi transporter genes. Scanning of the Lotus japonicus genome for gene promoters containing both cis-regulatory elements revealed a strong over-representation of genes involved in transport processes. One of these, LjVTI12, encoding a member of the SNARE family of proteins involved in membrane transport, exhibited enhanced transcript levels in Lotus roots colonized with the arbuscular mycorrhizal fungus Glomus intraradices. Down-regulation of LjVTI12 by RNA interference resulted in a mycorrhiza-specific phenotype characterized by distorted arbuscule morphology. The results highlight cooperative cis-regulation which integrates mycorrhiza and Pi starvation signaling with vesicle trafficking in symbiosome development.

The interplay between P uptake pathways in mycorrhizal peas: a combined physiological and gene‐silencing approach

Arbuscular mycorrhizal fungi (AMF) have a key role in plant phosphate (Pi) uptake by their efficient capture of soil phosphorus (P) that is transferred to the plant via Pi transporters in the root cortical cells. The activity of this mycorrhizal Pi uptake pathway is often associated with downregulation of Pi transporter genes in the direct Pi uptake pathway. As the total Pi taken up by the plant is determined by the combined activity of mycorrhizal and direct pathways, it is important to understand the interplay between these, in particular the actual activity of the pathways. To study this interplay we modulated the delivery of Pi via the mycorrhizal pathway in Pisum sativum by two means: (1) Partial downregulation by virus-induced gene silencing of PsPT4, a putative Pi transporter gene in the mycorrhizal pathway. This resulted in decreased fungal development in roots and soil and led to reduced plant Pi uptake. (2) Changing the percentage of AMF-colonized root length by using non-, half-mycorrhizal or full-mycorrhizal split-root systems. The combination of split roots, use of ³²P and ³³P isotopes and partial silencing of PsPT4 enabled us to show that the expression of PsPT1, a putative Pi transporter gene in the direct pathway, was negatively correlated with increasing mycorrhizal uptake capacity of the plant, both locally and systemically. However, transcript changes in PsPT1 were not translated into corresponding, systemic changes in actual direct Pi uptake. Our results suggest that AMF have a limited long-distance impact on the direct pathway.

Arbuscular mycorrhizal fungi differ in their ability to regulate the expression of phosphate transporters in maize (Zea mays L.)

Previous studies have found that some phosphate (Pi) starvation inducible transporter genes are downregulated and arbuscular mycorrhizal (AM) inducible Pi transporter genes are upregulated in maize roots associated with the fungus Glomus intraradices. However, little is known about the functional diversity of different AM fungal species in influencing the expression of Pi transporters in maize roots. Here, we studied the expression of two Pi transporter genes ZEAma:Pht1;3 (Pi starvation inducible) and ZEAma:Pht1;6 (AM inducible) in maize root colonized by different AM fungal inoculants. Non-mycorrhizal maize, maize colonized by Glomus deserticola (CA113), Glomus intraradices (IA506), Glomus mosseae (CA201), Gigaspora gigantea (MN922A) and the co-inoculation of all four species were established. The expression patterns of the two genes were quantified using real-time, reverse transcription polymerase chain reaction. The expression level of ZEAma:Pht1;6 was 26-135 times higher in AM plants than in non-mycorrhizal maize roots, whereas the expression level of ZEAma:Pht1;3 was five to 44 times lower in AM plants than in non-mycorrhizal plants. Expression of the two genes differed with inoculation treatment, and increasing the diversity of AM fungi in maize roots led to greater expression of ZEAma:Pht1;6 as well as Pi uptake in shoots. The expression of ZEAma:Pht1;6 was significantly positively correlated with AM colonization rate, concentration of AM biomarkers in maize roots, Pi uptake and dry weight of shoot, but negatively correlated with the expression of ZEAma:Pht1;3. Addition of Pi fertilizer at a low concentration significantly increased the expression of ZEAma:Pht1;6 but had no effect on the expression of ZEAma:Pht1;3.

Mycorrhizal phosphate uptake pathway in maize: vital for growth and cob development on nutrient poor agricultural and greenhouse soils.

Arbuscular mycorrhizal fungi (AMF) form a mutually beneficial symbiosis with plant roots providing predominantly phosphorus in the form of orthophosphate (Pi) in exchange for plant carbohydrates on low P soils. The goal of this work was to generate molecular-genetic evidence in support of a major impact of the mycorrhizal Pi uptake (MPU) pathway on the productivity of the major crop plant maize under field and controlled conditions. Here we show, that a loss-of-function mutation in the mycorrhiza-specific Pi transporter gene Pht1;6 correlates with a dramatic reduction of above-ground biomass and cob production in agro-ecosystems with low P soils. In parallel mutant pht1;6 plants exhibited an altered fingerprint of chemical elements in shoots dependent on soil P availability. In controlled environments mycorrhiza development was impaired in mutant plants when grown alone. The presence of neighboring mycorrhizal nurse plants enhanced the reduced mycorrhiza formation in pht1;6 roots. Uptake of 33P-labeled orthophosphate via the MPU pathway was strongly impaired in colonized mutant plants. Moreover, repression of the MPU pathway resulted in a redirection of Pi to neighboring plants. In line with previous results, our data highlight the relevance of the MPU pathway in Pi allocation within plant communities and in particular the role of Pht1;6 for the establishment of symbiotic Pi uptake and for maize productivity and nutritional value in low-input agricultural systems. In a first attempt to identify cellular pathways which are affected by Pht1;6 activity, gene expression profiling via RNA-Seq was performed and revealed a set of maize genes involved in cellular signaling which exhibited differential regulation in mycorrhizal pht1;6 and control plants. The RNA data provided support for the hypothesis that fungal supply of Pi and/or Pi transport across Pht1;6 affects cell wall biosynthesis and hormone metabolism in colonized root cells.

Phosphorus supply level affects the regulation of phosphorus uptake by different arbuscular mycorrhizal fungal species in a highly P-efficient backcross maize line

Arbuscular mycorrhizal (AM) fungi are known to facilitate effective acquisition of phosphorus (P) by host plants in low P soils. However, the contribution of mycorrhizal traits to high P-use efficiency in modern-bred maize genotypes is still not clear. In the present study one backcross maize inbred line 224 (bred for high P-use efficiency) was used as the host plant associated with AM fungal species (Rhizophagus irregularis or Glomus mosseae) grown at a range of soil P treatments (10, 20, 30, 40, 50, 100 mg P kg–1, Experiment 1) or foliar P applications (0, 0.025%, 0.5% m/v, Experiment 2). The experiments were to test the hypothesis whether the change point of the mycorrhizal growth and P responsiveness of 224, as well as the expression of ZEAma;Pht1;6 was at or near the optimal P supply level. In addition, different AM inoculants might differ in regulating P uptake of the host. Our results indicated that inbred line 224 was highly responsive to mycorrhizal inoculation. In Experiment 1, root colonisation rate, hyphal length density and alkaline phosphatase increased with the increase of soil P supply level. However, the mycorrhizal growth response (MGR) and P accumulation in shoot (MPR) were greatly affected by soil P supply level and varied between the two fungal species. Maize plants exhibited higher MGR and MPR at lower P supply when inoculated with R. irregularis, and at intermediate P supply when inoculated with G. mosseae. In Experiment 2, shoot P uptake was significantly increased by foliar P supply and inoculation, whereas shoot growth was significantly affected by P supply and the interaction. The expression of the AM-inducible Pi transporter gene ZEAma;Pht1;6 was neither significantly affected by soil (except at 100 mg P kg–1, Experiment 1) or foliar P supply level, nor by fungal species. Root P uptake efficiency (RPUE) was generally greatly increased by mycorrhizal colonisation at all P supply levels in both experiments, and significant correlations were observed between mycorrhizal variables and RPUE in Experiment 1. Our results indicate that the formation of mycorrhizal association could increase RPUE and thus may be partly attributed to high P-use efficiency of inbred line 224. The different responsiveness of mycorrhizal fungi to soil-available P implies the importance for the development of precision strategies to optimise the potential function of AM fungi under different P fertilisation management regime in agricultural soils.

Functional Characterization of 14 Pht1 Family Genes in Yeast and Their Expressions in Response to Nutrient Starvation in Soybean

BackgroundPhosphorus (P) is essential for plant growth and development. Phosphate (Pi) transporter genes in the Pht1 family play important roles in Pi uptake and translocation in plants. Although Pht1 family genes have been well studied in model plants, little is known about their functions in soybean, an important legume crop worldwide.Principal FindingsWe identified and isolated a complete set of 14 Pi transporter genes (GmPT1-14) in the soybean genome and categorized them into two subfamilies based on phylogenetic analysis. Then, an experiment to elucidate Pi transport activity of the GmPTs was carried out using a yeast mutant defective in high-affinity Pi transport. Results showed that 12 of the 14 GmPTs were able to complement Pi uptake of the yeast mutant with Km values ranging from 25.7 to 116.3 µM, demonstrating that most of the GmPTs are high-affinity Pi transporters. Further results from qRT-PCR showed that the expressions of the 14 GmPTs differed not only in response to P availability in different tissues, but also to other nutrient stresses, including N, K and Fe deficiency, suggesting that besides functioning in Pi uptake and translocation, GmPTs might be involved in synergistic regulation of mineral nutrient homeostasis in soybean.ConclusionsThe comprehensive analysis of Pi transporter function in yeast and expression responses to nutrition starvation of Pht1 family genes in soybean revealed their involvement in other nutrient homeostasis besides P, which could help to better understand the regulation network among ion homeostasis in plants.

Differential regulation of Pht1 phosphate transporters from trifoliate orange (Poncirus trifoliata L. Raf) seedlings

Phosphate (P) deficiency decreases the yield and quality of citrus fruits. Citrus seedlings acquire P from their environment either directly, via the roots, or indirectly, via a symbiotic interaction with arbuscular mycorrhizal fungi (AMF). To clarify the effects of different arbuscular mycorrhizal fungi on the growth of trifoliate orange (Poncirus trifoliata L. Raf) under inorganic phosphorus (Pi) starvation, AM colonization, trifoliate orange weight, phosphate (P) concentration, P uptake and the expressions of trifoliate orange Pht1 inorganic P (Pi) transporter genes were analyzed in five Glomus species treated roots under high and low Pi concentrations. The results showed that among five Glomus species, the suitable fungus type for the growth of trifoliate orange seedlings varied with soil Pi concentration. Seven Pht1 phosphate transporter genes which were cloned based on citrus genome were regulated by both soil Pi concentration and AMF colonization. Pi starvation triggered the up-regulation of most members of the Pht1 family except PtaPT6 which showed steady expression in all P treatments. Although only PtaPT4 was phylogenetically associated with the AM-inducible Pht1 subfamily I, the expressions of both PtaPT4 and PtaPT5 showed a striking up-regulation by AMF colonization. Meanwhile, PtaPT1, PtaPT2, PtaPT3 and PtaPT7 were down-regulated in mycorrhizal roots.

The high-affinity phosphate transporter GmPT5 regulates phosphate transport to nodules and nodulation in soybean.

Legume biological nitrogen (N) fixation is the most important N source in agroecosystems, but it is also a process requiring a considerable amount of phosphorus (P). Therefore, developing legume varieties with effective N(2) fixation under P-limited conditions could have profound significance for improving agricultural sustainability. We show here that inoculation with effective rhizobial strains enhanced soybean (Glycine max) N(2) fixation and P nutrition in the field as well as in hydroponics. Furthermore, we identified and characterized a nodule high-affinity phosphate (Pi) transporter gene, GmPT5, whose expression was elevated in response to low P. Yeast heterologous expression verified that GmPT5 was indeed a high-affinity Pi transporter. Localization of GmPT5 expression based on β-glucuronidase staining in soybean composite plants with transgenic roots and nodules showed that GmPT5 expression occurred principally in the junction area between roots and young nodules and in the nodule vascular bundles for juvenile and mature nodules, implying that GmPT5 might function in transporting Pi from the root vascular system into nodules. Overexpression or knockdown of GmPT5 in transgenic composite soybean plants altered nodulation and plant growth performance, which was partially dependent on P supply. Through both in situ and in vitro (33)P uptake assays using transgenic soybean roots and nodules, we demonstrated that GmPT5 mainly functions in transporting Pi from roots to nodules, especially under P-limited conditions. We conclude that the high-affinity Pi transporter, GmPT5, controls Pi entry from roots to nodules, is critical for maintaining Pi homeostasis in nodules, and subsequently regulates soybean nodulation and growth performance.