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Phosphate (Pi) starvation response (PHR) transcription factors play key roles in plant Pi homeostasis maintenance. They are negatively regulated by stand-alone SPX proteins, cellular receptors for inositol pyrophosphate (PP-InsP) nutrient messengers. How PP-InsP-bound SPX interacts with PHRs is poorly understood. Here, we report crystal structures of the rice SPX2/InsP6/PHR2 complex and of the PHR2 DNA binding (MYB) domain in complex with target DNA at resolutions of 3.1 Å and 2.7 Å, respectively. In the SPX2/InsP6/PHR2 complex, the signalling-active SPX2 assembles into a domain-swapped dimer conformation and binds two copies of PHR2, targeting both its coiled-coil (CC) oligomerisation domain and MYB domain. Our results reveal that the SPX2 senses PP-InsPs to inactivate PHR2 by establishing severe steric clashes with the PHR2 MYB domain, preventing DNA binding, and by disrupting oligomerisation of the PHR2 CC domain, attenuating promoter binding. Our findings rationalize how PP-InsPs activate SPX receptor proteins to target PHR family transcription factors. SPX receptors regulate plant phosphate response via PHR transcription factors. Here, based on crystal structure analysis of rice PHR2 complexes, the authors propose that SPX2 regulates PHR2 by preventing DNA binding and oligomerisation of the PHR2 CC domain. [ABSTRACT FROM AUTHOR]

Summary: Phosphorus (P) is an essential element for plant growth and development. Vacuoles play a fundamental role in the storage and remobilization of P in plants, while our understanding of the evolutionary mechanisms of creating and reusing P stores are limited. Besides, we also know very little about the coordination of intercellular P translocation, neither the inorganic phosphate (Pi) signaling nor the Pi transport patterns. Here we summarize recent advances in understanding the core elements involved in cellular and/or subcellular P homeostasis and signaling in unicellular green algae and multicellular land plants. We also propose further work that might help to uncover the high‐resolution intracellular and intercellular landscape of Pi distribution and signaling in plants. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is an essential nutrient for plant growth and development. Phosphate transporters (PHTs) are trans -membrane proteins that mediate the uptake and translocation of phosphate (Pi) in green plants. The PHT family including PHT1, PHT2, PHT3 and PHT4 subfamilies are well-studied in land plants; however, PHT genes in green algae are poorly documented and not comprehensively identified. Here, we analyzed the PHTs in a model green alga Chlamydomonas reinhardtii and found 25 putative PHT genes, which can be divided into four subfamilies. The subfamilies of CrPTA, CrPTB, CrPHT3, and CrPHT4 contain four, eleven, one, and nine genes, respectively. The structure, chromosomal distribution, subcellular localization, duplication, phylogenies, and motifs of these genes were systematically analyzed in silico. Expression profile analysis showed that CrPHT genes displayed differential expression patterns under P starvation condition. The expression levels of CrPTA1 and CrPTA3 were down-regulated, while the expression of most CrPTB genes was up-regulated under P starvation, which may be controlled by CrPSR1. The transcript abundance of most CrPHT3 and CrPHT4 genes was not significantly affected by P starvation except CrPHT4-3 , CrPHT4-4 , and CrPHT4-6. Our results provided basic information for understanding the evolution and features of the PHT family in green algae. [ABSTRACT FROM AUTHOR]

An R2R3 MYB transcription factor, OsMYB2P-1, was identified from microarray data by monitoring file expression profile of rice (Oryza sativa ssp. japonica) seedlings exposed to phosphate (Pi)-deficient medium. Expression of OsMYB2P-1 was induced by Pi starvation. OsMYB2P-1 was localized in the nuclei and exhibited transcriptional activation activity. Over expression of OsMYB2P-1 in Arabidopsis (Arabidopsis thaliana) and rice enhanced tolerance to Pi starvation, while suppression of OsMYB2P-1 by RNA interference in rice rendered the transgenic rice more sensitive to Pi deficiency. Furthermore, primary roots of OsMYB2P-1-overexpressing plants were shorter than those in wild-type plants under Pi-sufficient conditions, while primary roots and adventitious roots of OsMYB2P-1-over expressing plants were longer than those of wild-type plants under Pi-deficient conditions. These results suggest that OsMYB2P-1 may also be associated with the regulation of root system architecture. Over expression of OsMYB2P-1 led to greater expression of Pi-responsive genes such as Oryza sativa UDP-sulfoquinovose synthase, OsIPS1, OsPAP1O, OsmiR399a, and OsmiR399j. In contrast, over expression of OsMYB2P-1 suppressed the expression of OsPHO2 under both Pi-sufficient and Pi-deficient conditions. Moreover, expression of OsPT2, which encodes a low-affinity Pi transporter, was up-regulated in OsMYB2P-1- over expressing plants under Pi-sufficient conditions, whereas expression of the high-affinity Pi transporters OsPT6, OsPT8, and OsPT1O was up-regulated by over expression of OsMYB2P-1 under Pi-deficient conditions, suggesting that OsMYB2P-1 may act as a Pi-dependent regulator in controlling the expression of Pi transporters. These findings demonstrate that OsMYB2P-1 is a novel R2R3 MYB transcriptional factor associated with Pi starvation signaling in rice. [ABSTRACT FROM AUTHOR]

Inorganic phosphate (Pi) is an essential nutrient for plants, and the low bioavailability of Pi in soils is often a limitation to growth and development. Consequently, plants have evolved a range of regulatory mechanisms to adapt to phosphorus‐starvation in order to optimise uptake and assimilation of Pi. Recently, significant progress has been made in elucidating these mechanisms. The coordinated expression of a large number of genes is important for many of these adaptations. Several global expression studies using microarray analysis have been conducted in Arabidopsis thaliana. These studies provide a valuable basis for the identification of new regulatory genes and promoter elements to further the understanding of Pi‐dependent gene regulation. With focus on the Arabidopsis transcriptome, we extract common findings that point to new groups of putative regulators, including the NAC, MYB, ethylene response factor/APETALA2, zinc‐finger, WRKY and CCAAT‐binding families. With a number of new discoveries of regulatory elements, a complex regulatory network is emerging. Some regulatory elements, e.g. the transcription factor PHR1 and the microRNA (miRNA) miR399 and associated factors are well documented, yet not fully understood, whereas other suggested components need further characterisation. Here, we evaluate the contribution of the regulatory elements to the P‐responses and present a model comprising factors directly or indirectly involved in transcriptional regulation and the role of miRNAs as regulators and long‐distance signals. A striking feature is a series of feedback loops and parallel mechanisms that can modify and attenuate responses. We suggest that these mechanisms are instrumental in providing an accurate response and in keeping P‐homeostasis. [ABSTRACT FROM AUTHOR]

Background: Phosphorus (P) is often a limiting mineral nutrient for plant growth. Many soils worldwide are deficient in soluble inorganic phosphate (Pi), the form of P most readily absorbed and utilized by plants. A network of elaborate developmental and biochemical adaptations has evolved in plants to enhance Pi acquisition and avoid starvation. [ABSTRACT FROM PUBLISHER]

An appropriate cellular phosphate (Pi) concentration is indispensable for essential physiological and biochemical processes. To maintain cellular Pi homeostasis, plants have developed a series of adaptive responses to facilitate external Pi acquisition and to limit Pi consumption and to adjust Pi recycling internally when the Pi supply is inadequate. Over the past decade, significant progress has been made toward understanding such regulation at the molecular level. In this review, the focus is on the molecular regulators that mediate cellular Pi concentrations. The regulators are introduced and organized according to their original identification procedures, by the forward genetic approach of mutant screening or by reverse genetic analysis. These genes are involved in Pi uptake, allocation or remobilization or are upstream regulators, such as transcriptional factors or signalling molecules. In the future, integration of current knowledge and exploration of new technology is expected to offer new insights into molecular mechanisms that maintain Pi homeostasis. [ABSTRACT FROM PUBLISHER]

Maize (Zea mays) is the most widely cultivated crop around the world; however, it is commonly affected by phosphate (Pi) deficiency in many regions, particularly in acid and alkaline soils of developing countries. To cope with Pi deficiency, plants have evolved a large number of developmental and biochemical adaptations; however, for maize, the underlying molecular basis of these responses is still unknown. In this work, the transcriptional response of maize roots to Pi starvation at 1, 3, 6, and 10 d after the onset of Pi deprivation was assessed. The investigation revealed a total of 1179 Pi-responsive genes, of which 820 and 363 genes were found to be either up- or down-regulated, respectively, by 2-fold or more. Pi-responsive genes were found to be involved in various metabolic, signal transduction, and developmental gene networks. A large set of transcription factors, which may be potential targets for crop breeding, was identified. In addition, gene expression profiles and changes in specific metabolites were also correlated. The results show that several dicotyledonous plant responses to Pi starvation are conserved in maize, but that some genetic responses appear to be more specific and that Pi deficiency leads to a shift in the recycling of internal Pi in maize roots. Ultimately, this work provides a more comprehensive view of Pi-responses in a model for economically important cereals and also sets a framework to produce Pi-specific maize microarrays to study the changes in global gene expression between Pi-efficient and Pi-inefficient maize genotypes. [ABSTRACT FROM PUBLISHER]

Expression of phosphate starvation inducible genes was studied during recovery from phosphate starvation of Arabidopsis thaliana. Genes analysed were ACP5 (encoding an acid phosphatase), RNS1 (encoding an RNase), At4 and IPS1 (both of unknown function), Pht1;7 and Pht2;1 (encoding phosphate transporters). Plants grown at limiting phosphate exhibited reduced growth rate and accumulated anthocyanins, soluble sugars, and starch. Re-supply of phosphate resulted in dramatic uptake of phosphate, increased growth rate and decreased levels of anthocyanins, soluble sugars, and starch in leaf tissue. In both shoots and roots re-supplied with Pi, transcript levels decreased rapidly, and first changes were observed within 30 min. These alterations in gene expression occurred before the content of carbohydrates decreased, indicating that transcriptional regulation was due to phosphate sensing, and not a secondary effect of carbon accumulation. The data reveal different response rates for individual genes and demonstrate that roots and shoots can differ with respect to both timing and genes responding. In general, the changes in transcriptional activity in roots preceded the changes in shoots. Furthermore, transcriptional regulation was observed in isolated roots and shoots. This implies that roots do not strictly require a signal from the shoot, and vice versa, in order to respond to phosphate starvation. [ABSTRACT FROM AUTHOR]

Plants have evolved an array of responses that adapt their growth to conditions of limited phosphate (Pi) supply. These involve biochemical and developmental changes that improve Pi acquisition and recycling, and protect against the stress of Pi starvation. The induction of these responses requires a sophisticated regulatory system that integrates information on external and internal plant Pi status and the details of this regulatory system are only just beginning to be elucidated. In this review, the current knowledge of this regulatory system is summarized, the hallmark of which is the central role of transcription factor PHR1 in the co‐ordinated regulation of many phosphate‐starvation‐responsive genes. The role of hormonal signalling is also described, including auxins, ethylene and, particularly, cytokinins in the regulation of Pi‐starvation responses. [ABSTRACT FROM PUBLISHER]

We previously isolated 31 cDNAs corresponding to pdi [inorganic phosphate (Pi) deficiency-inducible] genes through the differential screening of a cDNA library constructed from the mycelium of Pholiota nameko strain N2 cultured in Pi-depleted medium. Among the cDNAs, pdi251, pdi263 and pdi315 were analyzed here. The deduced amino acid sequences of pdi251, pdi263 and pdi315 showed high similarity to fungal hydrophobins and genes corresponding to these cDNAs encoding P. nameko hydrophobins were designated pnh1, pnh2 and pnh3, respectively. PNH1, PNH2 and PNH3 had a conserved spacing of eight cysteine residues in hydrophobins and a hydropathy pattern characteristic of class I hydrophobins. Phylogenetic analysis showed that PNH1, PNH2 and PNH3 were phylogenetically similar and significantly related to the hydrophobin POH1 specifically expressed in fruiting bodies of Pleurotus ostreatus. Northern blot analysis indicated that, under conditions of Pi deficiency, pnh2 and pnh3 were also induced in strains N4 and N301. [ABSTRACT FROM AUTHOR]

The effect of Pi on the properties of phosphoenolpyruvate carboxylase (PEPC) from Amaranthus hypochondriacus, a NAD‐ME type C4 plant, was studied in leaf extracts as well as with purified protein. Efforts were also made to modulate the Pi status of the leaf by feeding leaves with either Pi or mannose. Inclusion of 30 mM Pi during the assay enhanced the enzyme activity in leaf extracts or of purified protein by >2‐fold. The effect of Pi on the enzyme purified from dark‐adapted leaves was more pronounced than that from light‐adapted ones. The Ki for malate increased >2.3‐fold and >1.9‐fold by Pi in the enzyme purified from dark‐adapted leaves and light‐adapted leaves, respectively. Pi also induced an almost 50–60% increase in Km for PEP or Ka for glucose‐6‐phosphate. Feeding the leaves with Pi also increased the activity of PEPC in leaf extracts, while decreasing the malate sensitivity of the enzyme. On the other hand, Pi sequestering by mannose marginally decreased the activity, while markedly suppressing the light activation, of PEPC. There was no change in phosphorylation of PEPC in leaves of A. hypochondriacus due to the feeding of 30 mM Pi. However, feeding with mannose decreased the light‐enhanced phosphorylation of PEPC. The marked decrease in malate sensitivity of PEPC with no change in phosphorylation state indicates that the changes induced by Pi are independent of the phosphorylation of PEPC. It is suggested here that Pi is an important factor in regulating PEPC in vivo and could also be used as a tool to analyse the properties of PEPC. [ABSTRACT FROM PUBLISHER]

Membrane-spanning transport proteins are responsible for the selective passage of most mineral nutrients and metabolites across cellular and intracellular membranes. This review's focus is on summarising the current state of research covering the molecular regulation and biochemical mechanisms involved in the transport of phosphorus, an often growth-limiting nutrient, in vascular plants. Physiological data illustrating the tight control of Pi homeostasis on the cellular as well as on the organism's level are discussed together with the recent results on molecular transport mechanisms. [ABSTRACT FROM AUTHOR]

Phosphate (Pi) plays a central role as reactant and effector molecule in plant cell metabolism. However, Pi is the least accessible macronutrient in many ecosystems and its low availability often limits plant growth. Plants have evolved an array of molecular and morphological adaptations to cope with Pi limitation, which include dramatic changes in gene expression and root development to facilitate Pi acquisition and recycling. Although physiological responses to Pi starvation have been increasingly studied and understood, the initial molecular events that monitor and transmit information on external and internal Pi status remain to be elucidated in plants. This review summarizes molecular and developmental Pi starvation responses of higher plants and the evidence for coordinated regulation of gene expression, followed by a discussion of the potential involvement of plant hormones in Pi sensing and of molecular genetic approaches to elucidate plant signalling of low Pi availability. Complementary genetic strategies in Arabidopsis thaliana have been developed that are expected to identify components of plant signal transduction pathways involved in Pi sensing. Innovative screening methods utilize reporter gene constructs, conditional growth on organophosphates and the inhibitory properties of the Pi analogue phosphite, which hold the promise for significant advances in our understanding of the complex mechanisms by which plants regulate Pi-starvation responses. [ABSTRACT FROM AUTHOR]

The effects of inorganic phosphate (Pi) deficiency on the expression of the UDP-glucose pyrophosphorylase (UGPase) gene (Ugp), involved in sucrose synthesis/metabolism, and on carbohydrate status were investigated in different tissues of Arabidopsis thaliana (L.) Heynh. For leaves, a decrease in internal Pi status caused by growth of plants on a medium lacking Pi (-P conditions) led to an increase in the overall content of glucose and starch, but had little effect on sucrose content. The Pi deficiency also led to an increased carbohydrate content in stems/flowers, but not in roots. The expression of Ugp was upregulated in both leaves and roots, but not in stems/flowers. The effects of Pi status on Ugp expression were confirmed using leaves of both pho1-2 and pho2-1 mutants of Arabidopsis (Pi-deficient and Pi-accumulating, respectively) and by feeding the leaves with d-mannose, which acts as a sink for Pi. The Pi-status-dependent changes in Ugp expression followed the same patterns as those of ApS, a gene encoding the small subunit of ADP-glucose pyrophosphorylase, a key enzyme of starch synthesis. The changes in Ugp mRNA levels, depending on internal Pi status, were generally correlated with changes in UGPase protein content and enzymatic activity. This was demonstrated both for wild-type plants grown under Pi-deficiency and for Pi mutants. The data suggest that, under Pi-deficiency, UGPase represents a transcriptionally regulated step in sucrose synthesis/metabolism, involved in homeostatic mechanisms readjusting the nutritional status of a plant under Pi-stress conditions. [ABSTRACT FROM AUTHOR]

Background: MYB-CC transcription factors (TFs) genes have been demonstrated to be involved in the response to inorganic phosphate (Pi) starvation and regulate some Pi-starvation-inducible genes. However, their role in drought stress has not been investigated in bread wheat. In this study, the TaMYBsm3 genes, including TaMYBsm3-A, TaMYBsm3-B, and TaMYBsm3-D, encoding MYB-CC TF proteins in bread wheat, were isolated to investigate the possible molecular mechanisms related to drought-tolerance in plants. Results: TaMYBsm3-A, TaMYBsm3-B, and TaMYBsm3-D were mapped on chromosomes 6A, 6B, and 6D in wheat, respectively. TaMYBsm3 genes belonged to MYB-CC TFs, containing a conserved MYB DNA-binding domain and a conserved coiled–coil domain. TaMYBsm3-D was localized in the nucleus, and the N-terminal region was a transcriptional activation domain. TaMYBsm3 genes were ubiquitously expressed in different tissues of wheat, and especially highly expressed in the stamen and pistil. Under drought stress, transgenic plants exhibited milder wilting symptoms, higher germination rates, higher proline content, and lower MDA content comparing with the wild type plants. P5CS1, DREB2A, and RD29A had significantly higher expression in transgenic plants than in wild type plants. Conclusion: TaMYBsm3-A, TaMYBsm3-B, and TaMYBsm3-D were associated with enhanced drought tolerance in bread wheat. Overexpression of TaMYBsm3-D increases the drought tolerance of transgenic Arabidopsis through up-regulating P5CS1, DREB2A, and RD29A. [ABSTRACT FROM AUTHOR]