An Integrative Systems Perspective on Plant Phosphate Research

Plants Under Stress: Exploring Physiological and Molecular Responses to Nitrogen and Phosphorus Deficiency

Nitrogen (N) and phosphorus (P) are essential mineral macronutrients critical for plant structure and function. Both contribute to processes ranging from cellular integrity to signal transduction. Since plants require these nutrients in high concentrations, replenishing them in soil often involves chemical fertilizers. However, the main source of P, rock phosphate, is non-renewable and in decline. N, second only to carbon, oxygen, and hydrogen in plant requirements, is vital for synthesizing proteins, nucleic acids, and plant pigments. Although N is available to plants through biological fixation or fertilizer application, the frequent application of N is not a sustainable solution due to environmental concerns like groundwater contamination and eutrophication. Plants have developed sophisticated mechanisms to adapt to nutrient deficiencies, such as changes in root architecture, local signaling, and long-distance signaling through the phloem. A dual deficiency of N and P is common in the field. In addition to individual N and P deficiency responses, this review also highlights some of the most recent discoveries in the responses of plants to the combined N and P deficiencies. Understanding the molecular and physiological responses in plants to mineral deficiency will help implement strategies to produce plants with high mineral use efficiency, leading to the reduced application of fertilizers, decreased mineral runoff, and improved environment.

Transcriptomic Analysis Reveals the Response Mechanisms of Bell Pepper (Capsicum annuum) to Phosphorus Deficiency

Phosphorus (P) is an important nutritional element needed by plants. Roots obtain P as inorganic phosphate (Pi), mostly in H2PO-4 form. It is vital for plants to have a sufficient supply of Pi since it participates in important processes like photosynthesis, energy transfer, and protein activation, among others. The physicochemical properties and the organic material usually make Pi bioavailability in soil low, causing crops and undomesticated plants to experience variations in accessibility or even a persistent phosphate limitation. In this study, transcriptome data from pepper roots under low-Pi stress was analyzed in order to identify Pi starvation-responsive genes and their relationship with metabolic pathways and functions. Transcriptome data were obtained from pepper roots with Pi deficiency by RNASeq and analyzed with bioinformatic tools. A total of 97 differentially expressed genes (DEGs) were identified; Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment revealed that metabolic pathways, such as porphyrin and chlorophyll metabolism, were down-regulated, and galactose and fatty acid metabolism were up-regulated. The results indicate that bell pepper follows diverse processes related to low Pi tolerance regulation, such as the remobilization of internal Pi, alternative metabolic pathways to generate energy, and regulators of root development.

Prospects of genetics and breeding for low-phosphate tolerance: an integrated approach from soil to cell

Improving phosphorus (P) crop nutrition has emerged as a key factor toward achieving a more resilient and sustainable agriculture. P is an essential nutrient for plant development and reproduction, and phosphate (Pi)-based fertilizers represent one of the pillars that sustain food production systems. To meet the global food demand, the challenge for modern agriculture is to increase food production and improve food quality in a sustainable way by significantly optimizing Pi fertilizer use efficiency. The development of genetically improved crops with higher Pi uptake and Pi-use efficiency and higher adaptability to environments with low-Pi availability will play a crucial role toward this end. In this review, we summarize the current understanding of Pi nutrition and the regulation of Pi-starvation responses in plants, and provide new perspectives on how to harness the ample repertoire of genetic mechanisms behind these adaptive responses for crop improvement. We discuss on the potential of implementing more integrative, versatile, and effective strategies by incorporating systems biology approaches and tools such as genome editing and synthetic biology. These strategies will be invaluable for producing high-yielding crops that require reduced Pi fertilizer inputs and to develop a more sustainable global agriculture.

An assessment of biochar as a potential amendment to enhance plant nutrient uptake

In a desperate attempt to find organic alternatives to synthetic fertilizers, agricultural scientists are increasingly using biochar as a soil amendment. Using chemical fertilizers results in enormous financial burdens and chronic health problems for plants and soils. Global concerns have also increased over the prolonged consumption of foods grown with artificial fertilizers and growth promotors. This adversely affects the environment and the welfare of humans, animals, and other living organisms. This way, organic biofertilizers have established a sustainable farming system. In such a context, biochar is gaining much attention among scientists as it may improve the overall performance of plants; in particular, crops have been optimistically cultivated with the addition of various sources. Field experiments have been conducted with multiple plant-based biochars and animal manure-based biochar. Plants receive different essential nutrients from biochar due to their physicochemical properties. Despite extensive research on biochar's effects on plant growth, yield, and development, it is still unknown how biochar promotes such benefits. Plant performance is affected by many factors in response to biochar amendment, but biochar's effect on nutrient uptake is not widely investigated. We attempted this review by examining how biochar affects nutrient uptake in various crop plants based on its amendment, nutrient composition, and physicochemical and biological properties. A greater understanding and optimization of biochar-plant nutrient interactions will be possible due to this study.

Soil Fertility Clock-Crop Rotation as a Paradigm in Nitrogen Fertilizer Productivity Control

The Soil Fertility Clock (SFC) concept is based on the assumption that the critical content (range) of essential nutrients in the soil is adapted to the requirements of the most sensitive plant in the cropping sequence (CS). This provides a key way to effectively control the productivity of fertilizer nitrogen (Nf). The production goals of a farm are set for the maximum crop yield, which is defined by the environmental conditions of the production process. This target can be achieved, provided that the efficiency of Nf approaches 1.0. Nitrogen (in fact, nitrate) is the determining yield-forming factor, but only when it is balanced with the supply of other nutrients (nitrogen-supporting nutrients; N-SNs). The condition for achieving this level of Nf efficiency is the effectiveness of other production factors, including N-SNs, which should be set at ≤1.0. A key source of N-SNs for a plant is the soil zone occupied by the roots. N-SNs should be applied in order to restore their content in the topsoil to the level required by the most sensitive crop in a given CS. Other plants in the CS provide the timeframe for active controlling the distance of the N-SNs from their critical range.

Effects of Fermented Seaweed Fertilizer Treatment on Paddy Amino Acid Content and Rhizosphere Microbiome Community

Seaweed has often been reported on for it potential bioresources for fertilizers to improve crop productivity and reduce the use of chemical fertilizers (CF). However, little is known about the nutritional status of the crop grown with the implementation of seaweed fertilizers (SF). In this study, the amino acid content of rice produced by SF implementation was evaluated. Furthermore, the rhizosphere bacterial community was also investigated. The paddy seedlings were divided into five groups, control (C0), chemical fertilizer (CF), seaweed fertilizer (SF), chemical and seaweed fertilizer combination 25:75 (CFSF1), and chemical and fertilizer combination 50:50 (CFSF2). The CFSF2 group shown significantly better growth characteristics compared to other groups. Based on the concentration of macronutrients (N, P, K) in paddy leaf, CFSF2 also shown the best results. This also correlates with the abundant amino acid composition in CFSF2 in almost all tested amino acids, namely, serine, phenylalanine, isoleucine, valine, glycine, tyrosine, proline, threonine, histidine, and arginine. Interestingly, beneficial bacteria Rhizobiales were significantly higher in CFSF2-treated soil (58%) compared to CF (29%). Another important group, Vicinamibacterales, was also significantly higher in CFSF2 (58%) compared to CF (7%). Hence, these potentially contributed to the high rice amino acid content and yield in the CFSF2-treated paddy. However, further field-scale studies are needed to confirm the bioindustrial application of seaweed in agricultural systems.

Dissection of Crop Metabolome Responses to Nitrogen, Phosphorus, Potassium, and Other Nutrient Deficiencies

Crop growth and yield often face sophisticated environmental stresses, especially the low availability of mineral nutrients in soils, such as deficiencies of nitrogen, phosphorus, potassium, and others. Thus, it is of great importance to understand the mechanisms of crop response to mineral nutrient deficiencies, as a basis to contribute to genetic improvement and breeding of crop varieties with high nutrient efficiency for sustainable agriculture. With the advent of large-scale omics approaches, the metabolome based on mass spectrometry has been employed as a powerful and useful technique to dissect the biochemical, molecular, and genetic bases of metabolisms in many crops. Numerous metabolites have been demonstrated to play essential roles in plant growth and cellular stress response to nutrient limitations. Therefore, the purpose of this review was to summarize the recent advances in the dissection of crop metabolism responses to deficiencies of mineral nutrients, as well as the underlying adaptive mechanisms. This review is intended to provide insights into and perspectives on developing crop varieties with high nutrient efficiency through metabolite-based crop improvement.

Two-Phase Conceptual Framework of Phosphatase Activity and Phosphorus Bioavailability

The activity of extracellular phosphatases is a dynamic process controlled by both plant roots and microorganisms, which is responsible for the mineralization of soil phosphorus (P). Plants regulate the availability of soil P through the release of root mucilage and the exudation of low-molecular weight organic acids (LMWOAs). Mucilage increases soil hydraulic conductivity as well as pore connectivity, both of which are associated with increased phosphatase activity. The LMWOAs, in turn, stimulate the mineralization of soil P through their synergistic effects of acidification, chelation, and exchange reactions. This article reviews the catalytic properties of extracellular phosphatases and their interactions with the rhizosphere interfaces. We observed a biphasic effect of root metabolic products on extracellular phosphatases, which notably altered their catalytic mechanism. In accordance with the proposed conceptual framework, soil P is acquired by both plants and microorganisms in a coupled manner that is characterized by the exudation of their metabolic products. Due to inactive or reduced root exudation, plants recycle P through adsorption on the soil matrix, thereby reducing the rhizosphere phosphatase activity. The two-phase conceptual framework might assist in understanding P-acquisition (substrate turnover) and P-restoration (phosphatase adsorption by soil) in various terrestrial ecosystems.

Are cysteine, glutathione and phytochelatins responses of Myriophyllum alterniflorum to copper and arsenic stress affected by trophic conditions?

The aim of this article is to study the impact of both copper (Cu²⁺) and arsenic (As (V)) at 100 µg/L, with each element being combined with trophic conditions at the level of glutathione, cysteine and phytochelatins in the aquatic macrophyte Myriophyllum alterniflorum, whose potential for bioindication and phytoremediation of metal/metalloid pollution has already been demonstrated. To achieve this goal, a synthetic medium, of a composition similar to the water found in the Vienne River in France's Limousin Region and modified for eutrophic or oligotrophic conditions, is prepared. The analysis of cysteine, glutathione and phytochelatins is performed at 0, 3, 7, 14 and 21 days. Our results indicate that the eutrophic medium without contaminant only induces a significant increase in the glutathione level when compared to the oligotrophic medium. However, the joint presence of As (V) and Cu is able to increase the synthesis of cysteine, glutathione and phytochelatins (PC2 and PC3) under both eutrophic and oligotrophic conditions, with a significant increase in the eutrophic medium compared to the oligotrophic one. Phytochelatins (PC2 and PC3) are induced after as little as 3 days of exposure to copper and arsenic under both trophic conditions. Copper induces the synthesis of more PC3 than PC2, unlike arsenic. Our results confirm the potential use of phytochelatins as a specific biochemical biomarker for metal/metalloid stress. In conclusion, the eutrophic condition combined with copper or arsenic does change the response of Myriophyllum alterniflorum by enhancing its antioxidative defense. Thus, M. alterniflorum phytochelatins represent a potential dedicated biomarker to monitor water quality in terms of metal/metalloid stress regardless of the trophic level.

Mechanisms Underlying Soybean Response to Phosphorus Deficiency through Integration of Omics Analysis

Low phosphorus (P) availability limits soybean growth and yield. A set of potential strategies for plant responses to P deficiency have been elucidated in the past decades, especially in model plants such as Arabidopsis thaliana and rice (Oryza sativa). Recently, substantial efforts focus on the mechanisms underlying P deficiency improvement in legume crops, especially in soybeans (Glycine max). This review summarizes recent advances in the morphological, metabolic, and molecular responses of soybean to phosphate (Pi) starvation through the combined analysis of transcriptomics, proteomics, and metabolomics. Furthermore, we highlight the functions of the key factors controlling root growth and P homeostasis, base on which, a P signaling network in soybean was subsequently presumed. This review also discusses current barriers and depicts perspectives in engineering soybean cultivars with high P efficiency.

Integrative analysis of the metabolome and transcriptome reveal the phosphate deficiency response pathways of alfalfa

Understanding the mechanisms underlying the responses to inorganic phosphate (Pi) deficiency in alfalfa will help enhance Pi acquisition efficiency and the sustainable use of phosphorous resources. Integrated global metabolomic and transcriptomic analyses of mid-vegetative alfalfa seedlings under 12-day Pi deficiency were conducted. Limited seedling growth were found, including 13.24%, 16.85% and 33.36% decreases in height, root length and photosynthesis, and a 24.10% increase in root-to-shoot ratio on day 12. A total of 322 and 448 differentially abundant metabolites and 1199 and 1061 differentially expressed genes were identified in roots and shoots. Increased (>3.68-fold) inorganic phosphate transporter 1;4 and SPX proteins levels in the roots (>2.15-fold) and shoots (>2.50-fold) were related to Pi absorption and translocation. The levels of phospholipids and Pi-binding carbohydrates and nucleosides were decreased, while those of phosphatases and pyrophosphatases in whole seedlings were induced under reduced Pi. In addition, nitrogen assimilation was affected by inhibiting high-affinity nitrate transporters (NRT2.1 and NRT3.1), and nitrate reductase. Increased delphinidin-3-glucoside might contribute to the gray-green leaves induced by Pi limitation. Stress-induced MYB, WRKY and ERF transcription factors were identified. The responses of alfalfa to Pi deficiency were summarized as local systemic signaling pathways, including root growth, stress-related responses consisting of enzymatic and nonenzymatic systems, and hormone signaling and systemic signaling pathways including Pi recycling and Pi sensing in the whole plant, as well as Pi recovery, and nitrate and metal absorption in the roots. This study provides important information on the molecular mechanism of the response to Pi deficiency in alfalfa.

TaPHT1;9-4B and its transcriptional regulator TaMYB4-7D contribute to phosphate uptake and plant growth in bread wheat

Efficient phosphate (Pi) uptake and utilisation are essential for promoting crop yield. However, the underlying molecular mechanism is still poorly understood in complex crop species such as hexaploid wheat. Here we report that TaPHT1;9-4B and its transcriptional regulator TaMYB4-7D function in Pi acquisition, translocation and plant growth in bread wheat. TaPHT1;9-4B, a high-affinity Pi transporter highly upregulated in roots by Pi deficiency, was identified using quantitative proteomics. Disruption of TaPHT1;9-4B function by BSMV-VIGS or CRISPR editing impaired wheat tolerance to Pi deprivation, whereas transgenic expression of TaPHT1;9-4B in rice improved Pi uptake and plant growth. Using yeast-one-hybrid assay, we isolated TaMYB4-7D, a R2R3 MYB transcription factor that could activate TaPHT1;9-4B expression by binding to its promoter. Silencing TaMYB4-7D decreased TaPHT1;9-4B expression, Pi uptake and plant growth. Four promoter haplotypes were identified for TaPHT1;9-4B, with Hap3 showing significant positive associations with TaPHT1;9-4B transcript level, growth performance and phosphorus (P) content in wheat plants. A functional marker was therefore developed for tagging Hap3. Collectively, our data shed new light on the molecular mechanism controlling Pi acquisition and utilisation in bread wheat. TaPHT1;9-4B and TaMYB4-7D may aid further research towards the development of P efficient crop cultivars.

Multiple origins of Indian dwarf wheat by mutations targeting the TREE domain of a GSK3-like kinase for drought tolerance, phosphate uptake, and grain quality

Multiple origins of Indian dwarf wheat were due to two mutations targeting the same TREE domain of a GSK3-like kinase, and these mutations confer to enhanced drought tolerance and increased phosphate and nitrogen accumulation for adaptation to the dry climate of Indian and Pakistan. Indian dwarf wheat, featured by the short stature, erect leaves, dense spikes, and small, spherical grains, was a staple crop in India and Pakistan from the Bronze Age until the early 1900s. These morphological features are controlled by a single locus Sphaerococcum 1 (S1), but the genetic identity of the locus and molecular mechanisms underlying the selection of this wheat type are unknown. In this study, we showed that the origin of Indian dwarf wheat was due to two independent missense mutations targeting the conserved TREE domain of a GSK3-like kinase, which is homologous to the Arabidopsis BIN2 protein, a negative regulator in brassinosteroid signaling. The S1 protein is involved in brassinosteroid signaling by physical interaction with the wheat BES1/BZR1 proteins. The dwarf alleles are insensitive to brassinosteroid, upregulates brassinosteroid biosynthetic genes, significantly enhanced drought tolerance, facilitated phosphate accumulation, and increased high molecular weight glutenins. It is the enhanced drought tolerance and accumulation of nitrogen and phosphate that contributed to the adaptation of such a small-grain form of wheat to the dry climate of India and Pakistan. Thus, our research not only identified the genetic events underlying the origin of the Indian dwarf wheat, but also revealed the function of brassinosteroid in the regulation of drought tolerance, phosphate homeostasis, and grain quality.

Transcriptional, metabolic, physiological and developmental responses of switchgrass to phosphorus limitation

Knowing how switchgrass (Panicum virgatum L.) responds and adapts to phosphorus (P)-limitation will aid efforts to optimize P acquisition and use in this species for sustainable biomass production. This integrative study investigated the impacts of mild, moderate, and severe P-stress on genome transcription and whole-plant metabolism, physiology and development in switchgrass. P-limitation reduced overall plant growth, increased root/shoot ratio, increased root branching at moderate P-stress, and decreased root diameter with increased density and length of root hairs at severe P-stress. RNA-seq analysis revealed thousands of genes that were differentially expressed under moderate and severe P-stress in roots and/or shoots compared to P-replete plants, with many stress-induced genes involved in transcriptional and other forms of regulation, primary and secondary metabolism, transport, and other processes involved in P-acquisition and homeostasis. Amongst the latter were multiple miRNA399 genes and putative targets of these. Metabolite profiling showed that levels of most sugars and sugar alcohols decreased with increasing P stress, while organic and amino acids increased under mild and moderate P-stress in shoots and roots, although this trend reversed under severe P-stress, especially in shoots.

Influence of Ethylene Signaling in the Crosstalk Between Fe, S, and P Deficiency Responses in Arabidopsis thaliana

To cope with P, S, or Fe deficiency, dicot plants, like Arabidopsis, develop several responses (mainly in their roots) aimed to facilitate the mobilization and uptake of the deficient nutrient. Within these responses are the modification of root morphology, an increased number of transporters, augmented synthesis-release of nutrient solubilizing compounds and the enhancement of some enzymatic activities, like ferric reductase activity (FRA) or phosphatase activity (PA). Once a nutrient has been acquired in enough quantity, these responses should be switched off to minimize energy costs and toxicity. This implies that they are tightly regulated. Although the responses to each deficiency are induced in a rather specific manner, crosstalk between them is frequent and in such a way that P, S, or Fe deficiency can induce responses related to the other two nutrients. The regulation of the responses is not totally known but some hormones and signaling substances have been involved, either as activators [ethylene (ET), auxin, nitric oxide (NO)], or repressors [cytokinins (CKs)]. The plant hormone ET is involved in the regulation of responses to P, S, or Fe deficiency, and this could partly explain the crosstalk between them. In spite of these crosslinks, it can be hypothesized that, to confer the maximum specificity to the responses of each deficiency, ET should act in conjunction with other signals and/or through different transduction pathways. To study this latter possibility, several responses to P, S, or Fe deficiency have been studied in the Arabidopis wild-type cultivar (WT) Columbia and in some of its ethylene signaling mutants (ctr1, ein2-1, ein3eil1) subjected to the three deficiencies. Results show that key elements of the ET transduction pathway, like CTR1, EIN2, and EIN3/EIL1, can play a role in the crosstalk among nutrient deficiency responses.

A genome-wide association study reveals the quantitative trait locus and candidate genes that regulate phosphate efficiency in a Vietnamese rice collection

The crucial role of phosphate (Pi) for plant alongside the expected depletion of non-renewable phosphate rock have created an urgent need for phosphate-efficient rice varieties. In this study, 157 greenhouse-grown Vietnamese rice landraces were treated under Pi-deficient conditions to discover the genotypic variation among biochemical traits, including relative efficiency of phosphorus use (REP), relative root to shoot weight ratio (RRSR), relative physiological phosphate use efficiency (RPPUE), and relative phosphate uptake efficiency (RPUpE). Plants were grown in Yoshida nutrient media with either a full (320 μM) or a low Pi supply (10 μM) over six weeks. This genome-wide association study led to the discovery of 31 significant single nucleotide polymorphisms, 18 quantitative trait loci (QTLs), and 85 candidate genes. A common QTL named qRPUUE9.16 was found among the three investigated traits. Some interesting candidate genes, such as PLASMA MEMBRANE PROTEIN1 (OsPM1), CALMODULIN-RELATED CALCIUM SENSOR PROTEIN 15 (OsCML15), phosphatases 2C (PP2C), STRESS-ACTIVATED PROTEIN KINASE (OsSAPK2), and GLYCEROPHOSPHORYL DIESTER PHOSPHODIESTERASES (GDPD13), were found strongly correlated to the Pi starvation. RNA sequencing transcriptomes revealed that 45 out of 85 candidate genes were significantly regulated under Pi starvation. Furthermore, nearly two-thirds of genotypes did not possess the OsPsTOL1 gene; however, no significant difference was observed in response to Pi deficiency between genotypes with or without this gene, suggesting that other QTLs in rice may resist Pi starvation. These results provide new information on the genetics of nutrient use efficiency in rice and may potentially assist with developing more phosphate-efficient rice plants.