Plant phosphate nutrition
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Mol Plant: An Arabidopsis ABC transporter mediates phosphate deficiency-induced remodeling of root architecture by modulating iron homeostasis in roots

The remodeling of root architecture is a major developmental response of plants to phosphate (Pi) deficiency and is thought to enhance a plant's ability to forage Pi in topsoil. The underlying mechanism controlling this response, however, is poorly understood. In this work, we identified an Arabidopsis mutant, hps10 (hypersensitive to Pi starvation 10), that is morphologically normal under Pi sufficiency but shows increased inhibition of primary root growth and enhanced production of lateral roots under Pi deficiency. hps10 is a previously identified allele (als3-3) of the ALUMINUM SENSITIVE3 (ALS3) gene, which is involved in plant tolerance to aluminum toxicity. Our results show that ALS3 and its interacting protein AtSTAR1 form an ABC transporter complex in tonoplasts. This protein complex mediates a highly electrogenic transport in Xenopus oocytes. Under Pi deficiency, als3 accumulates higher levels of Fe3+ in its roots than the wild type. In Arabidopsis, LPR1 (LOW PHOSPHATE ROOT1) and LPR2 encode ferroxidase, which when mutated reduces Fe3+ accumulation in roots and causes root growth to be insensitive to Pi deficiency. Here, we provide compelling evidence that ALS3 acts with LPR1/2 to regulate Pi deficiency-induced remodeling of root architecture by modulating Fe homeostasis in roots. Dong J, Piñeros MA, Li X, Yang H, Liu Y, Muphy AS, Kochian LV, Liu D. DOI: 10.1016/j.molp.2016.11.001
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Plant Biotechnology Journal: A phosphate starvation-driven bidirectional promoter as a potential tool for crop improvement and in vitro plant biotechnology

Plant Biotechnology Journal: A phosphate starvation-driven bidirectional promoter as a potential tool for crop improvement and in vitro plant biotechnology | Plant phosphate nutrition | Scoop.it
Phosphate (Pi) deficient soils are a major limitant factor for crop production in many regions in the world. Despite that plants have innovated several developmental and biochemical strategies to deal with this stress, there are still massive extensions of land which combine several abiotic stresses, including phosphate starvation, that limit their use for plant growth and food production. In several plant species a genetic program underlies the biochemical and developmental responses of the organism to cope with low phosphate (Pi) availability. Both protein- and miRNA–coding genes involved in the adaptative response are transcriptionally activated upon Pi starvation. Several of the responsive genes have been identified as transcriptional targets of PHR1, a transcription factor that binds a conserved cis-element called PHR1 Binding Site (P1BS). Our group has previously described and characterized a minimal genetic arrangement that includes two P1BS elements, as a phosphate-responsive enhancer (EZ2). Here we report the engineering and successful use of a phosphate-dependent bidirectional promoter, which has been designed and constructed based on the palindromic sequences of the two P1BS elements present in EZ2. This bidirectional promoter has a potential use in both plant in vitro approaches and in the generation of improved crops adapted to Pi starvation and other abiotic stresses.
Oropeza-Aburto A, Cruz-Ramírez A, Mora-Macías J and Herrera-Estrella L
DOI: 10.1111/pbi.12653
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Plant Physiol: The Chloroplast Protease AMOS1/EGY1 affects Phosphate Homeostasis under Phostphate Stress

Plastid intramembrane proteases in Arabidopsis thaliana are involved in jasmonic acid biosynthesis, chloroplast development, and flower morphology. Here we show that Ammonium-Overly-Sensitive 1 (AMOS1), a member of the family of plastid intramembrane proteases, plays an important role in the maintenance of phosphate (P) homeostasis under P stress. Loss of function of AMOS1 revealed a striking resistance to P starvation. amos1 plants displayed retarded root growth and reduced P accumulation in the root compared to wild type (Col-0: WT) under P-replete control conditions, but remained unaffected by P starvation, displaying comparable P accumulation and root growth under P-deficient conditions. Further analysis revealed that, under P-deficient conditions, cell-wall pectin of amos1 released more P than that of WT, in an ethylene-dependent manner. Using an abscisic acid (ABA)-insensitive mutant, deficient in the ethylene-dependent transcription factor ABI4, abi4, and applying ABA exogenously, ABA was found to function downstream of AMOS1 and ethylene in the maintenance of P homeostasis under P stress. Our findings uncover the role of AMOS1 in the maintenance of P homeostasis in response to P deficiency through ABA-antagonized ethylene signaling. Yu F, Zhu X, Li G, Kronzucker HJ, Shi W DOI: http:/​/​dx.​doi.​org/​10.​1104/​pp.​16.​00786
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BMC Plant Biology: BOTRYTIS-INDUCED KINASE1, a plasma membrane-localized receptor-like protein kinase, is a negative regulator of phosphate homeostasis in Arabidopsis thaliana.

BACKGROUND: Plants have evolved complex coordinated regulatory networks to cope with deficiency of phosphate (Pi) in their growth environment; however, the detailed molecular mechanisms that regulate Pi sensing and signaling pathways are not fully understood yet. We report here that the involvement of Arabidopsis BIK1, a plasma membrane-localized receptor-like protein kinase that plays critical role in immunity, in Pi starvation response. RESULTS: qRT-PCR analysis revealed that expression of BIK1 was induced by Pi starvation and GUS staining indicated that the BIK1 promoter activity was detected in root, stem and leaf tissues of plants grown in Pi starvation condition, demonstrating that BIK1 is responsive to Pi starvation stress. The bik1 plants accumulated higher Pi content in root and leaf tissues and exhibited altered root architecture such as shorter primary roots, longer and more root hairs and lateral roots, as compared with those in the wild type plants, when grown under Pi sufficient and deficient conditions. Increased anthocyanin content and acid phosphatase activity, reduced accumulation of reactive oxygen species and downregulated expression of Pi starvation-induced genes including PHR1, WRKY75, AT4, PHT1;2 and PHT1;4 were observed in bik1 plants grown under Pi deficient condition. Furthermore, the expression of PHO2 was downregulated while the expression of miRNA399a and miRNA399d, which target to PHO2, was upregulated in bik1 plants, compared to the wild type plants, when grown under Pi deficient condition. CONCLUSION: Our results demonstrate that BIK1 is a Pi starvation-responsive gene that functions as a negative regulator of Pi homeostasis in Arabidopsis. Zhang H, Huang L, Hong Y, Song F DOI: 10.1186/s12870-016-0841-1
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Plant Phys: The THO/TREX complex active in mRNA export suppresses root-associated acid phosphatase activity induced by phosphate starvation

Induction and secretion of acid phosphatases (APases) is an adaptive response that plants use to cope with phosphate (Pi) deficiency in their environment. The molecular mechanism that regulates this response, however, is poorly understood. In this work, we identified an Arabidopsis mutant, hps8, that exhibits enhanced APase activity on its root surface (also called root-associated APase activity). Our molecular and genetic analyses indicate that this altered Pi response results from a mutation in the AtTHO1 gene that encodes a subunit of the THO/TREX protein complex. The mutation in another subunit of this complex, AtTHO3, also enhances root-associated APase activity under Pi starvation. In Arabidopsis, the THO/TREX complex functions in mRNA export and miRNA biogenesis. When treated with Ag+, an inhibitor of ethylene perception, the enhanced root-associated APase activity in hps8 is largely reversed. hpr1-5 is another mutant allele of AtTHO1 and shows similar phenotypes as hps8. ein2 is completely insensitive to ethylene. In the hpr1-5ein2 double mutant, the enhanced root-associated APase activity is also greatly suppressed. These results indicate that the THO/TREX complex in Arabidopsis negatively regulates root-associated APase activity induced by Pi starvation by inhibiting ethylene signaling. In addition, we found that the miRNA399-PHO2 pathway is also involved in the regulation of root-associated APase activity induced by Pi starvation. These results provide insight into the molecular mechanism underlying the adaptive response of plants to Pi starvation.
Tao S, Zhang Y, Wang X, Xu L, Fang X, Lu ZJ, Liu D.
pii: pp.00680.2016
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J Exp Bot: Phytohormone regulation of root growth triggered by P deficiency or Al toxicity

Phosphorus (P) deficiency and aluminum (Al) toxicity often coexist and limit plant growth on acid soils. It has been well documented that both P deficiency and Al toxicity alter root growth, including inhibition of primary roots and promotion of lateral roots. This suggests that plants adapt to both stresses through a common regulation pathway. Although an expanding set of results shows that phytohormones play vital roles in controlling root responses to Pi starvation and Al toxicity, it remains largely unknown whether P and Al coordinately regulate root growth through interacting phytohormone biosynthesis and signal transduction pathways. This review provides a summary of recent results concerning the influences of P deficiency and Al toxicity on root growth through the action of phytohormones, most notably auxin and ethylene. The objective is to facilitate increasing insights into complex responses of plants to adverse factors common on acid soils, which can spur development of ‘smart’ cultivars with better root growth and higher yield on these globally distributed marginal soils.
Lili Sun, Jiang Tian, Haiyan Zhang, Hong Liao
DOI: 10.1093/jxb/erw188
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Plant, Cell & Environment: Strigolactones are required for nitric oxide to induce root elongation in response to nitrogen and phosphate deficiencies in rice

The response of the root system architecture to nutrient deficiencies is critical for sustainable agriculture. Nitric oxide (NO) is considered a key regulator of root growth, although the mechanisms remain unknown. Phenotypic, cellular and genetic analyses were undertaken in rice to explore the role of NO in regulating root growth and strigolactone (SL) signalling under nitrogen-deficient and phosphate-deficient conditions (LN and LP). LN-induced and LP-induced seminal root elongation paralleled NO production in root tips. NO played an important role in a shared pathway of LN-induced and LP-induced root elongation via increased meristem activity. Interestingly, no responses of root elongation were observed in SL d mutants compared with wild-type plants, although similar NO accumulation was induced by sodium nitroprusside (SNP) application. Application of abamine (the SL inhibitor) reduced seminal root length and pCYCB1;1::GUS expression induced by SNP application in wild type; furthermore, comparison with wild type showed lower SL-signalling genes in nia2 mutants under control and LN treatments and similar under SNP application. Western blot analysis revealed that NO, similar to SL, triggered proteasome-mediated degradation of D53 protein levels. Therefore, we presented a novel signalling pathway in which NO-activated seminal root elongation under LN and LP conditions, with the involvement of SLs. Sun H, Bi Y, Tao J, Huang S, Hou M, Xue R, Liang Z, Gu P, Yoneyama K, Xie X, Shen Q, Xu G, Zhang Y. DOI: 10.1111/pce.12709
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Nature: Scientific reports : The development of a phosphite-mediated fertilization and weed control system for rice

Nature: Scientific reports : The development of a phosphite-mediated fertilization and weed control system for rice | Plant phosphate nutrition | Scoop.it

Fertilizers and herbicides are two vital components of modern agriculture. The imminent danger of phosphate reserve depletion and multiple herbicide tolerance casts doubt on agricultural sustainability in the future. Phosphite, a reduced form of phosphorus, has been proposed as an alternative fertilizer and herbicide that would address the above problems to a considerable extent. To assess the suitability of a phosphite-based fertilization and weed control system for rice, we engineered rice plants with a codon-optimized ptxD gene from Pseudomonas stutzeri. Ectopic expression of this gene led to improved root growth, physiology and overall phenotype in addition to normal yield in transgenic plants in the presence of phosphite. Phosphite functioned as a translocative, non-selective, pre- and post-emergent herbicide. Phosphite use as a dual fertilizer and herbicide may mitigate the overuse of phosphorus fertilizers and reduce eutrophication and the development of herbicide resistance, which in turn will improve the sustainability of agriculture.

Manna M, Achary VM, Islam T, Agrawal PK, Reddy MK

DOI:10.1038/srep24941

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Science: Control of eukaryotic phosphate homeostasis by inositol polyphosphate sensor domains

Science: Control of eukaryotic phosphate homeostasis by inositol polyphosphate sensor domains | Plant phosphate nutrition | Scoop.it
Phosphorus is a macronutrient taken up by cells as inorganic phosphate (Pi). How cells sense cellular Pi levels is poorly characterized. Here we report that SPX domains, which are found in eukaryotic phosphate transporters, signaling proteins and inorganic polyphosphate polymerases, provide a basic binding surface for inositol polyphosphate signaling molecules (InsPs), whose concentrations change in response to Pi availability. Substitutions of critical binding surface residues impair InsP binding in vitro, inorganic polyphosphate synthesis in yeast and Pi transport in Arabidopsis. In plants, InsPs trigger the association of SPX proteins with transcription factors to regulate Pi starvation responses. We propose that InsPs communicate cytosolic Pi levels to SPX domains and enable them to interact with a multitude of proteins to regulate Pi uptake, transport and storage in fungi, plants and animals. Wild R, Gerasimaite R, Jung JY, Truffault V, Pavlovic I, Schmidt A, Saiardi A, Jessen HJ, Poirier Y, Hothorn M, Mayer A. DOI: 10.1126/science.aad9858
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elife: A novel role for the root cap in phosphate uptake and homeostasis

elife: A novel role for the root cap in phosphate uptake and homeostasis | Plant phosphate nutrition | Scoop.it

The root cap has a fundamental role in sensing environmental cues as well as regulating root growth via altered meristem activity. Despite this well-established role in the control of developmental processes in roots, the root cap’s function in nutrition remains obscure. Here, we uncover its role in phosphate nutrition by targeted cellular inactivation or phosphate transport complementation in Arabidopsis, using a transactivation strategy with an innovative high-resolution real-time 33P imaging technique. Remarkably, the diminutive size of the root cap cells at the root-to-soil exchange surface accounts for a significant amount of the total seedling phosphate uptake (approximately 20%). This level of Pi absorption is sufficient for shoot biomass production (up to a 180% gain in soil), as well as repression of Pi starvation-induced genes. These results extend our understanding of this important tissue from its previously described roles in environmental perception to novel functions in mineral nutrition and homeostasis control.

Kanno S, Arrighi JF, Chiarenza S, Bayle V, Berthomé R, Péret B, Javot H, Delannoy E, Marin E, Nakanishi TM, Thibaud MC, Nussaume L.

DOI: 10.7554/eLife.14577.

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Cell: Root Endophyte Colletotrichum tofieldiae Confers Plant Fitness Benefits that Are Phosphate Status Dependent

Cell: Root Endophyte Colletotrichum tofieldiae Confers Plant Fitness Benefits that Are Phosphate Status Dependent | Plant phosphate nutrition | Scoop.it
Highlights
•Colletotrichum tofieldiae (Ct) is a fungal root endophyte of Arabidopsis
•Ct transfers the macronutrient phosphorus to Arabidopsis shoots •Ct-mediated plant growth promotion needs an intact phosphate starvation response
•A branch of the plant innate immune system is essential for beneficial Ct activities
Summary
A staggering diversity of endophytic fungi associate with healthy plants in nature, but it is usually unclear whether these represent stochastic encounters or provide host fitness benefits. Although most characterized species of the fungal genus Colletotrichum are destructive pathogens, we show here that C. tofieldiae (Ct) is an endemic endophyte in natural Arabidopsis thaliana populations in central Spain. Colonization by Ct initiates in roots but can also spread systemically into shoots. Ct transfers the macronutrient phosphorus to shoots, promotes plant growth, and increases fertility only under phosphorus-deficient conditions, a nutrient status that might have facilitated the transition from pathogenic to beneficial lifestyles. The host’s phosphate starvation response (PSR) system controls Ct root colonization and is needed for plant growth promotion (PGP). PGP also requires PEN2-dependent indole glucosinolate metabolism, a component of innate immune responses, indicating a functional link between innate immunity and the PSR system during beneficial interactions with Ct.
Kei Hiruma K, Gerlach N, Sacristán S, Nakano RT, Hacquard S, Kracher B, Neumann U, Ramírez D, Bucher M, O’Connell RJ, Schulze-Lefert P.
DOI: http://dx.doi.org/10.1016/j.cell.2016.02.028
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Cell: Adaptation of Root Function by Nutrient-Induced Plasticity of Endodermal Differentiation

Cell: Adaptation of Root Function by Nutrient-Induced Plasticity of Endodermal Differentiation | Plant phosphate nutrition | Scoop.it

Highlights
•The endodermis, a plant epithelium, later coats itself with hydrophobic suberin
•Suberization can be enhanced or reversed, depending on nutrient availabilities
•This stress-hormone-regulated plasticity allows adaptive regulation of root function
Summary
Plant roots forage the soil for minerals whose concentrations can be orders of magnitude away from those required for plant cell function. Selective uptake in multicellular organisms critically requires epithelia with extracellular diffusion barriers. In plants, such a barrier is provided by the endodermis and its Casparian strips—cell wall impregnations analogous to animal tight and adherens junctions. Interestingly, the endodermis undergoes secondary differentiation, becoming coated with hydrophobic suberin, presumably switching from an actively absorbing to a protective epithelium. Here, we show that suberization responds to a wide range of nutrient stresses, mediated by the stress hormones abscisic acid and ethylene. We reveal a striking ability of the root to not only regulate synthesis of suberin, but also selectively degrade it in response to ethylene. Finally, we demonstrate that changes in suberization constitute physiologically relevant, adaptive responses, pointing to a pivotal role of the endodermal membrane in nutrient homeostasis.
Barberon M,Vermeer JEM, De Bellis D, Wang P, Naseer S, Andersen TG, Humbe BM, Nawrath C, Takano J, Salt DE, GeldnerN.
DOI:10.1016/j.cell.2015.12.021

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Frontiers | The Role of Ethylene in Plant Adaptations for Phosphate Acquisition in Soils – A Review

Frontiers | The Role of Ethylene in Plant Adaptations for Phosphate Acquisition in Soils – A Review | Plant phosphate nutrition | Scoop.it

Although a role of ethylene in the regulation of senescence and plant stress responses in general has a long history, a possible involvement in the regulation of adaptive responses to nutrient deficiencies has been mainly investigated since the last two decades. In the case of plant responses to phosphate (Pi) starvation, ethylene was identified as a modulator of adaptive responses in root growth and morphology. The molecular base of these adaptations has been elucidated in supplementation studies with ethylene precursors and antagonists, as well as analysis of mutants and transgenic plants with modified ethylene biosynthesis and responsiveness, using mainly Arabidopsis thaliana as a model plant. However, increasing evidence suggests that apart from root growth responses, ethylene may be involved in various additional plant adaptations to Pi limitation including Pi mobilization in the rhizosphere, Pi uptake and internal Pi recycling. The ethylene-mediated responses are frequently characterized by high genotypic variability and may partially share common pathways in different nutrient limitations.
Neumann G
DOI: 10.3389/fpls.2015.01224

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Plant J: Improving phosphorus use efficiency - a complex trait with emerging opportunities

Phosphorus (P) is one of the essential nutrients for plants and indispensable for plant growth and development. P deficiency severely limits crop yield and regular fertilizer applications are required to obtain high yields and prevent soil degradation. To access P from the soil, plants have evolved high and low affinity Pi transporters and the ability to induce root architectural changes to forage P. Also, adjustments of numerous cellular processes are triggered by the P starvation response, a tightly regulated process in plants. With the increasing demand for food due to the growing population, demand for P fertilizer is steadily increasing. Given the high costs of fertilizers and in light of the fact that phosphate rock, the source of P fertilizer, is a finite natural resource, there is a need to enhance P fertilizer use efficiency in agricultural systems and develop plants with enhanced Pi uptake and internal P-use efficiency (PUE). In this review we will provide an overview of ongoing relevant research and highlight different approaches towards developing crops with enhanced PUE. In this context, we will summarize our current understanding of root responses to low phosphorus conditions and emphasize the importance of combining PUE with tolerance of other stresses, such as aluminum toxicity. Of the many genes associated with Pi deficiency, this review will focus on those that hold promise or are already at an advanced stage of testing (OsPSTOL1, AVP1, PHO1, OsPHT1;6). Finally, an update is provided on the progress made exploring alternative technologies, such as phosphite fertilizer. This article is protected by copyright. All rights reserved. Heuer S, Gaxiola R, Schilling R, Herrera-Estrella L, López-Arredondo D, Wissuwa M, Delhaize E, Rouached H. DOI: 10.1111/tpj.13423

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BMC Genomics: Systematic characterization of novel lncRNAs responding to phosphate starvation in Arabidopsis thaliana


Background Previously, several long non-coding RNAs (lncRNAs) were characterized as regulators in phosphate (Pi) starvation responses. However, systematic studies of novel lncRNAs involved in the Pi starvation signaling pathways have not been reported. Results Here, we used a genome-wide sequencing and bioinformatics approach to identify both poly(A) + and poly(A)– lncRNAs that responded to Pi starvation in Arabidopsis thaliana. We sequenced shoot and root transcriptomes of the Arabidopsis seedlings grown under Pi-sufficient and Pi-deficient conditions, and predicted 1212 novel lncRNAs, of which 78 were poly(A)– lncRNAs. By employing strand-specific RNA libraries, we discovered many novel antisense lncRNAs for the first time. We further defined 309 lncRNAs that were differentially expressed between P+ and P– conditions in either shoots or roots. Through Gene Ontology enrichment of the associated protein-coding genes (co-expressed or close on the genome), we found that many lncRNAs were adjacent or co-expressed with the genes involved in several Pi starvation related processes, including cell wall organization and photosynthesis. In total, we identified 104 potential lncRNA targets of PHR1, a key regulator for transcriptional response to Pi starvation. Moreover, we identified 16 candidate lncRNAs as potential targets of miR399, another key regulator of plant Pi homeostasis. Conclusions Altogether, our data provide a rich resource of candidate lncRNAs involved in the Pi starvation regulatory network. Yuan J, Zhang Y, Dong J, Sun Y, Lim BL, Liu D, Lu ZJ. DOI: 10.1186/s12864-016-2929-2


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Sci Rep: Genome-wide DNA polymorphisms in low Phosphate tolerant and sensitive rice genotypes

Sci Rep: Genome-wide DNA polymorphisms in low Phosphate tolerant and sensitive rice genotypes | Plant phosphate nutrition | Scoop.it

Soil Phosphorus (P) deficiency is one of the major challenges to rice crop world-wide. Modern rice genotypes are highly P-responsive and rely on high input of P fertilizers. However, low P tolerant traditional cultivars and landraces have genetic potential to sustain well under low P. Identification of high resolution DNA polymorphisms (SNPs and InDels) in such contrasting genotypes is largely missing for low P response at gene levels. Here, we report high quality DNA polymorphisms in low P sensitive genotype, PB1 and tolerant traditional genotype, Dular. We performed whole genome resequencing using Illumina NGS platform and identified a total of 5,157,939 sequence variants in PB1 and Dular with reference to Nipponbare genome. We have identified approximately 2.3 million and 2.9 million high quality polymorphisms in PB1 and Dular, respectively, with an average read depth of ≥24X. We further mapped several DNA polymorphisms (non-synonymous and regulatory variants) having potential functional significance to key Phosphate Starvation Responsive (PSR) and root architecture genes in Dular and Kasalath using a compiled list of low P responsive genes. These identified variants can serve as a useful source of genetic variability for improving low P tolerance and root architecture of high yielding modern genotypes. Mehra P, Pandey BK, Giri J DOI: 10.1038/srep1309

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PLOS Genetic: The Molecular Mechanism of Ethylene-Mediated Root Hair Development Induced by Phosphate Starvation

PLOS Genetic: The Molecular Mechanism of Ethylene-Mediated Root Hair Development Induced by Phosphate Starvation | Plant phosphate nutrition | Scoop.it
Enhanced root hair production, which increases the root surface area for nutrient uptake, is a typical adaptive response of plants to phosphate (Pi) starvation. Although previous studies have shown that ethylene plays an important role in root hair development induced by Pi starvation, the underlying molecular mechanism is not understood. In this work, we characterized an Arabidopsis mutant, hps5, that displays constitutive ethylene responses and increased sensitivity to Pi starvation due to a mutation in the ethylene receptor ERS1. hps5 accumulates high levels of EIN3 protein, a key transcription factor involved in the ethylene signaling pathway, under both Pi sufficiency and deficiency. Pi starvation also increases the accumulation of EIN3 protein. Combined molecular, genetic, and genomic analyses identified a group of genes that affect root hair development by regulating cell wall modifications. The expression of these genes is induced by Pi starvation and is enhanced in the EIN3-overexpressing line. In contrast, the induction of these genes by Pi starvation is suppressed in ein3 and ein3eil1 mutants. EIN3 protein can directly bind to the promoter of these genes, some of which are also the immediate targets of RSL4, a key transcription factor that regulates root hair development. Based on these results, we propose that under normal growth conditions, the level of ethylene is low in root cells; a group of key transcription factors, including RSL4 and its homologs, trigger the transcription of their target genes to promote root hair development; Pi starvation increases the levels of the protein EIN3, which directly binds to the promoters of the genes targeted by RSL4 and its homologs and further increase their transcription, resulting in the enhanced production of root hairs. This model not only explains how ethylene mediates root hair responses to Pi starvation, but may provide a general mechanism for how ethylene regulates root hair development under both stress and non-stress conditions.
Song L, Yu H, Dong J, Che X, Jiao Y, Liu D.
DOI: 10.1371/journal.pgen.1006194. eCollection 2016.
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Plant Phys: Phosphate Treatment Strongly Inhibits New Arbuscule Development But Not the Maintenance of Arbuscule in Mycorrhizal Rice Roots

Plant Phys: Phosphate Treatment Strongly Inhibits New Arbuscule Development But Not the Maintenance of Arbuscule in Mycorrhizal Rice Roots | Plant phosphate nutrition | Scoop.it
Phosphorus (P) is a crucial nutrient for plant growth, but its availability to roots is limited in soil. Arbuscular mycorrhizal (AM) symbiosis is a promising strategy for improving plant P acquisition. However, P fertilizer reduces fungal colonization (P inhibition) and compromises mycorrhizal P uptake, warranting studies on the mechanistic basis of P inhibition. In this study, early morphological changes in P inhibition were identified in rice (Oryza sativa) using fungal cell wall staining and live-cell imaging of plant membranes that were associated with arbuscule life cycles. Arbuscule density decreased, and aberrant hyphal branching was observed in roots at 5 h after P treatment. Although new arbuscule development was severely inhibited, preformed arbuscules remained intact and longevity remained constant. P inhibition was accelerated in the rice pt11-1 mutant, which lacks P uptake from arbuscule branches, suggesting that mature arbuscules are stabilized by the symbiotic P transporter under high P condition. Moreover, P treatment led to increases in the number of vesicles, in which lipid droplets accumulated and then decreased within a few days. The development of new arbuscules resumed within by 2 d. Our data established that P strongly and temporarily inhibits new arbuscule development, but not intraradical accommodation of AM fungi. Kobae Y, Ohmori Y, Saito C, Yano K, Ohtomo R, Fujiwara T DOI: ​10.​1104/​pp.​16.​00127
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Plant Phys: Phosphate-dependent root system architecture responses to salt stress

Nutrient availability and salinity of the soil affect growth and development of plant roots. Here, we describe how phosphate availability affects root system architecture (RSA) of Arabidopsis and how phosphate levels modulate responses of the root to salt stress. Phosphate (Pi) starvation reduced main root length and increased the number of lateral roots of Arabidopsis Col-0 seedlings. In combination with salt, low Pi dampened the inhibiting effect of mild salt stress (75mM) on all measured RSA components. At higher NaCl concentrations, the Pi deprivation response prevailed over the salt stress only for lateral root elongation. The Pi deprivation response of lateral roots appeared to be oppositely affected by abscisic acid (ABA) signaling compared to the salt stress response. Natural variation in the response to the combination treatment of salt and Pi starvation within 330 Arabidopsis accessions could be grouped into four response patterns. When exposed to double stress, in general lateral roots prioritized responses to salt, while the effect on main root traits was additive. Interestingly, these patterns were not identical for all accessions studied and multiple strategies to integrate the signals from Pi deprivation and salinity were identified. By Genome Wide Association Mapping (GWAS) 13 genomic loci were identified as putative factors integrating responses to salt stress and Pi starvation. From our experiments, we conclude that Pi starvation interferes with salt responses mainly at the level of lateral roots and that large natural variation exists in the available genetic repertoire of accessions to handle the combination of stresses. Kawa D, Julkowska M, Montero Sommerfeld H, Horst AT, Haring MA, Testerink C. DOI: 10.​1104/​pp.​16.​00712
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BMC Plant Biology: Comparative expression profiling reveals a role of the root apoplast in local phosphate response.

BMC Plant Biology: Comparative expression profiling reveals a role of the root apoplast in local phosphate response. | Plant phosphate nutrition | Scoop.it
BACKGROUND: Plant adaptation to limited phosphate availability comprises a wide range of responses to conserve and remobilize internal phosphate sources and to enhance phosphate acquisition. Vigorous restructuring of root system architecture provides a developmental strategy for topsoil exploration and phosphate scavenging. Changes in external phosphate availability are locally sensed at root tips and adjust root growth by modulating cell expansion and cell division. The functionally interacting Arabidopsis genes, LOW PHOSPHATE RESPONSE 1 and 2 (LPR1/LPR2) and PHOSPHATE DEFICIENCY RESPONSE 2 (PDR2), are key components of root phosphate sensing. We recently demonstrated that the LOW PHOSPHATE RESPONSE 1 - PHOSPHATE DEFICIENCY RESPONSE 2 (LPR1-PDR2) module mediates apoplastic deposition of ferric iron (Fe(3+)) in the growing root tip during phosphate limitation. Iron deposition coincides with sites of reactive oxygen species generation and triggers cell wall thickening and callose accumulation, which interfere with cell-to-cell communication and inhibit root growth.
RESULTS: We took advantage of the opposite phosphate-conditional root phenotype of the phosphate deficiency response 2 mutant (hypersensitive) and low phosphate response 1 and 2 double mutant (insensitive) to investigate the phosphate dependent regulation of gene and protein expression in roots using genome-wide transcriptome and proteome analysis. We observed an overrepresentation of genes and proteins that are involved in the regulation of iron homeostasis, cell wall remodeling and reactive oxygen species formation, and we highlight a number of candidate genes with a potential function in root adaptation to limited phosphate availability. Our experiments reveal that FERRIC REDUCTASE DEFECTIVE 3 mediated, apoplastic iron redistribution, but not intracellular iron uptake and iron storage, triggers phosphate-dependent root growth modulation. We further highlight expressional changes of several cell wall-modifying enzymes and provide evidence for adjustment of the pectin network at sites of iron accumulation in the root.
CONCLUSION: Our study reveals new aspects of the elaborate interplay between phosphate starvation responses and changes in iron homeostasis. The results emphasize the importance of apoplastic iron redistribution to mediate phosphate-dependent root growth adjustment and suggest an important role for citrate in phosphate-dependent apoplastic iron transport. We further demonstrate that root growth modulation correlates with an altered expression of cell wall modifying enzymes and changes in the pectin network of the phosphate-deprived root tip, supporting the hypothesis that pectins are involved in iron binding and/or phosphate mobilization.
Hoehenwarter W, Mönchgesang S, Neumann S, Majovsky P, Abel S, Müller J. DOI: 10.1186/s12870-016-0790-8
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Nature, scientific reports: AtOPR3 specifically inhibits primary root growth in Arabidopsis under phosphate deficiency

Nature, scientific reports: AtOPR3 specifically inhibits primary root growth in Arabidopsis under phosphate deficiency | Plant phosphate nutrition | Scoop.it

The primary root plays essential roles in root development, nutrient absorption, and root architectural establishment. Primary root growth is generally suppressed by phosphate (P) deficiency in A. thaliana; however, the underlying molecular mechanisms are largely elusive to date. We found that AtOPR3 specifically inhibited primary root growth under P deficiency via suppressing root tip growth at the transcriptional level, revealing an important novel function of AtOPR3 in regulating primary root response to the nutrient stress. Importantly, AtOPR3 functioned to down-regulate primary root growth under P limitation mostly by its own, rather than depending on the Jasmonic acid signaling pathway. Further, AtOPR3 interacted with ethylene and gibberellin signaling pathways to regulate primary root growth upon P deficiency. In addition, the AtOPR3’s function in inhibiting primary root growth upon P limitation was also partially dependent on auxin polar transport. Together, our studies provide new insights into how AtOPR3, together with hormone signaling interactions, modulates primary root growth in coping with the environmental stress in Arabidopsis.

Zheng H, Pan X, Deng Y, Wu H, Liu P, Li X

DOI:10.1038/srep24778

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Nature Plant: Vascular-mediated signalling involved in early phosphate stress response in plants

Nature Plant: Vascular-mediated signalling involved in early phosphate stress response in plants | Plant phosphate nutrition | Scoop.it

Depletion of finite global rock phosphate (Pi) reserves will impose major limitations on future agricultural productivity and food security. Hence, modern breeding programmes seek to develop Pi-efficient crops with sustainable yields under reduced Pi fertilizer inputs. In this regard, although the long-term responses of plants to Pi stress are well documented, the early signalling events have yet to be elucidated. Here, we show plant tissue-specific responses to early Pi stress at the transcription level and a predominant role of the plant vascular system in this process. Specifically, imposition of Pi stress induces rapid and major changes in the mRNA population in the phloem translocation stream, and grafting studies have revealed that many hundreds of phloem-mobile mRNAs are delivered to specific sink tissues. We propose that the shoot vascular system acts as the site of root-derived Pi stress perception, and the phloem serves to deliver a cascade of signals to various sinks, presumably to coordinate whole-plant Pi homeostasis.

Zhang Z, Zheng Y, Ham BK, Chen J, Yoshida A, Kochian LV, Fei Z, Lucas WJ

DOI:10.1038/nplants.2016.33

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Nature Com: Identification of plant vacuolar transporters mediating phosphate storage

Nature Com: Identification of plant vacuolar transporters mediating phosphate storage | Plant phosphate nutrition | Scoop.it

Plant vacuoles serve as the primary intracellular compartments for inorganic phosphate (Pi) storage. Passage of Pi across vacuolar membranes plays a critical role in buffering the cytoplasmic Pi level against fluctuations of external Pi and metabolic activities. Here we demonstrate that the SPX-MFS proteins, designated as PHOSPHATE TRANSPORTER 5 family (PHT5), also named Vacuolar Phosphate Transporter (VPT), function as vacuolar Pi transporters. Based on 31P-magnetic resonance spectroscopy analysis, Arabidopsis pht5;1 loss-of-function mutants accumulate less Pi and exhibit a lower vacuolar-to-cytoplasmic Pi ratio than controls. Conversely, overexpression of PHT5 leads to massive Pi sequestration into vacuoles and altered regulation of Pi starvation-responsive genes. Furthermore, we show that heterologous expression of the rice homologue OsSPX-MFS1 mediates Pi influx to yeast vacuoles. Our findings show that a group of Pi transporters in vacuolar membranes regulate cytoplasmic Pi homeostasis and are required for fitness and plant growth. TY Liu, TK Huang, SY Yang, YT Hong, SM Huang, FN Wang, SF Chiang, SY Tsai, WC Lu & TJ Chiou DOI:10.1038/ncomms11095

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Planta: Expression of MAX2 under SCARECROW promoter enhances the strigolactone/MAX2 dependent response of Arabidopsis roots to low-phosphate conditions

Planta: Expression of MAX2 under SCARECROW promoter enhances the strigolactone/MAX2 dependent response of Arabidopsis roots to low-phosphate conditions | Plant phosphate nutrition | Scoop.it
MAX2/strigolactone signaling in the endodermis and/or quiescent center of the root is partially sufficient to exert changes in F-actin density and cellular trafficking in the root epidermis, and alter gene expression during plant response to low Pi conditions. Strigolactones (SLs) are a new group of plant hormones that regulate different developmental processes in the plant via MAX2, an F-box protein that interacts with their receptor. SLs and MAX2 are necessary for the marked increase in root-hair (RH) density in seedlings under conditions of phosphate (Pi) deprivation. This marked elevation was associated with an active reduction in actin-filament density and endosomal movement in root epidermal cells. Also, expression of MAX2 under the SCARECROW (SCR) promoter was sufficient to confer SL sensitivity in roots, suggesting that SL signaling pathways act through a root-specific, yet non-cell-autonomous regulatory mode of action. Here we show evidence for a non-cell autonomous signaling of SL/MAX2, originating from the root endodermis, and necessary for seedling response to conditions of Pi deprivation. SCR-derived expression of MAX2 in max2-1 mutant background promoted the root low Pi response, whereas supplementation of the synthetic SL GR24 to these SCR:MAX2 expressing lines further enhanced this response. Moreover, the SCR:MAX2 expression led to changes in actin density and endosome movement in epidermal cells and in TIR1 and PHO2 gene expression. These results demonstrate that MAX2 signaling in the endodermis and/or quiescent center is partially sufficient to exert changes in F-actin density and cellular trafficking in the epidermis, and alter gene expression under low Pi conditions.
Madmon O, Mazuz M, Kumari P, Dam A, Ion A, Mayzlish-Gati E, Belausov E, Wininger S, Abu-Abied M, McErlean CS, Bromhead LJ, Perl-Treves R, Prandi C, Kapulnik K, Koltai H.
DOI: 10.​1007/​s00425-016-2477-7
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Scientific reports: Functional analysis of long intergenic non-coding RNAs in phosphate-starved rice using competing endogenous RNA network

Long intergenic non-coding RNAs (lincRNAs) may play widespread roles in gene regulation and other biological processes, however, a systematic examination of the functions of lincRNAs in the biological responses of rice to phosphate (Pi) starvation has not been performed. Here, we used a computational method to predict the functions of lincRNAs in Pi-starved rice. Overall, 3,170 lincRNA loci were identified using RNA sequencing data from the roots and shoots of control and Pi-starved rice. A competing endogenous RNA (ceRNA) network was constructed for each tissue by considering the competing relationships between lincRNAs and genes, and the correlations between the expression levels of RNAs in ceRNA pairs. Enrichment analyses showed that most of the communities in the networks were related to the biological processes of Pi starvation. The lincRNAs in the two tissues were individually functionally annotated based on the ceRNA networks, and the differentially expressed lincRNAs were biologically meaningful. For example, XLOC_026030 was upregulated from 3 days after Pi starvation, and its functional annotation was ‘cellular response to Pi starvation’. In conclusion, we systematically annotated lincRNAs in rice and identified those involved in the biological response to Pi starvation.
DOI:10.1038/srep20715

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