A chloroplast phosphate transporter, PHT2;1, influences allocation of phosphate within the plant and phosphate-starvation responses

Sulfur and phosphorus transporters in plants: Integrating mechanisms for optimized nutrient supply

In recent years, advancements in molecular techniques have considerably deepened the understanding of mechanisms governing sulfur and phosphorus metabolism and transport in plants. These macronutrients play essential roles in regulating plant growth, development, and stress responses. Plants absorb sulfur and phosphorus through their roots in the form of inorganic sulfate (SO42-) and phosphate (H2PO4- or HPO42-or PO42-) ions through specialized sulfate (SULTR) and phosphate (PHT) transporter families, respectively. The molecular characterization and regulatory control of these transporter genes, along with insights into their cellular localization, offer promising strategies for improving nutrient use efficiency in crops. Additionally, plants have evolved intricate signalling networks that integrate nutrient sensing, uptake, and homeostasis, with feedback mechanisms to regulate transporter activity in response to nutrient deficiencies. This review provides a comprehensive analysis of the molecular mechanisms underlying distribution, functional dynamics, and regulatory pathways for sulfur and phosphorus transporters in plants. It also highlights their crucial role in plant adaptation to environmental stresses, emphasizing their integration with stress signalling networks. Furthermore, the critical role of phytohormones in coordinating sulfur and phosphorus homeostasis to enhance abiotic stress tolerance is critically described.

Genome-wide analysis of PHT gene family and their role in LP and salt stress in sweet potato

Phosphate transporters (PHTs), which are essential for phosphate (Pi) uptake, translocation, and utilization, play crucial roles in regulating plant growth and development. Despite extensive characterization of PHTs in many plant species, their function in sweet potato remains unclear. Here, we conducted a genome-wide investigation, and identified 27 PHTs in cultivated hexaploid sweet potato (Ipomoea batatas L.), which are divided into five clusters (IbPHT1-IbPHT5). Phylogenetic analysis and collinearity analysis showed that sweet potato shares a closer homological evolutionary relationship with dicotyledonous (Arabidopsis) species compared with the monocotyledonous (rice). Promoter analysis revealed that the MYB (myeloblastosis) cis-element is the most abundant among all cis-elements found in the promoters of IbPHTs. RNA-seq analysis in different tissues and under low phosphate (LP) stress revealed that IbPHT1;3, IbPHT1;4, IbPHT1;5 and IbPHT3;3 were the most highly expressed genes in sweet potato. IbPHT1; 5, which located on plasma membrane, was functionally characterized and involved in Pi uptake and transport in transgenic Arabidopsis and yeast. Besides, the Pi uptake and transcriptome analysis assay showed that salt stress inhibits Pi uptake and expression of most members in PHT1 subfamily (at least 50%). This suggested that PHTs may play crucial roles in salt stress response in sweet potato. This study provides new insights for understanding the function of IbPHTs, which are candidate for improving phosphorus use efficiency and abiotic stress tolerance in cultivated sweet potato.

Phosphorus and sulphur crosstalk in cereals: Unraveling the molecular interplay, agronomic impacts on yield and heavy metal tolerance

Phosphorus (P) and sulphur (S) are essential macronutrients for crop growth, playing critical roles in physiological and biochemical processes throughout the plant life cycle, as well as in mitigating heavy metal and metalloid toxicity. Therefore, the coordinated use of P and S is crucial for optimizing crop growth and reducing the accumulation of heavy metals and metalloids in plants. While P and S signaling pathways are often studied independently, our understanding of their interactions remains limited. A series of recent studies have revealed key components regulating P-S interactions in cereal crops such as rice, maize and wheat, providing new insights into the network that integrates the signaling pathways of P and S. However, the interaction between P and S in molecular regulatory pathways, crop yield improvement, and resistance to heavy metal stress has not yet been systematically summarized or hypothesized. Here, we summarize the latest advances in P-S interactions and propose potential working mechanisms that integrate these P-S interactive regulatory pathways in cereal crops. Furthermore, we discuss the regulatory mechanisms of P-S interactions in cereal crops that still need to be uncovered in the future.

Genome-Wide Identification and Expression Assessment for the Phosphate Transporter 2 Gene Family Within Sweet Potato Under Phosphorus Deficiency Stress

Hainan's unique climate significantly contributes to soil acidification, causing phosphorus fixation into insoluble compounds, leading to phosphorus deficiency and reduced yield in sweet potatoes. The Phosphate Transporter 2 (PHT2) family, a group of trans-membrane phosphate transporters, is crucial for phosphate transport, distribution, and homeostasis regulation. Two PHT2 genes, IbPHT2-1 and IbPHT2-2, were first identified in sweet potato, and a phylogenetic analysis of 46 species showed high conservation of the IbPHT2 gene family throughout plant evolution. Tissue-specific expression patterns of IbPHT2 genes were determined in four sweet potato varieties using transcriptome analysis and RT-qPCR. The results demonstrated that IbPHT2 was predominantly expressed in shoots, mature leaves, stems, and fibrous roots. Under phosphorus deficiency stress, IbPHT2-2 expression was upregulated in shoots, mature leaves, and fibrous roots, with higher expression in mature leaves compared to IbPHT2-1. This observation suggests that, in the context of phosphorus deficiency stress, IbPHT2-2 assumes a more pivotal function in the response mechanism. The expression levels of IbPHT2-2 presented a negative relationship with fresh leaf weight (FLW) as well as fibrous root number per plant (FRNPP) and fibrous root weight per plant (FRWPP) based on correlation analysis. The restrictive function of IbPHT2-2 became impaired by phosphorus deficiency, which resulted in inhibited leaf and root development of sweet potato. The findings of this study provide preliminary evidence that IbPHT2-2 is a key gene involved in the response to phosphorus deficiency stress, influencing phosphorus absorption and distribution in sweet potato. This research contributes to our understanding of the molecular mechanisms underlying phosphorus utilization in sweet potato and may inform future strategies for improving phosphorus use efficiency in this important crop.

Diurnal Rhythmicity in the Rhizosphere Microbiome-Mechanistic Insights and Significance for Rhizosphere Function

The rhizosphere is a key interface between plants, microbes and the soil which influences plant health and nutrition and modulates terrestrial biogeochemical cycling. Recent research has shown that the rhizosphere environment is far more dynamic than previously recognised, with evidence emerging for diurnal rhythmicity in rhizosphere chemistry and microbial community composition. This rhythmicity is in part linked to the host plant's circadian rhythm, although some heterotrophic rhizosphere bacteria and fungi may also possess intrinsic rhythmicity. We review the evidence for diurnal rhythmicity in rhizosphere microbial communities and its link to the plant circadian clock. Factors which may drive microbial rhythmicity are discussed, including diurnal change in root exudate flux and composition, rhizosphere physico-chemical properties and plant immunity. Microbial processes which could contribute to community rhythmicity are considered, including self-sustained microbial rhythms, bacterial movement into and out of the rhizosphere, and microbe-microbe interactions. We also consider evidence that changes in microbial composition mediated by the plant circadian clock may affect microbial function and its significance for plant health and broader soil biogeochemical cycling processes. We identify key knowledge gaps and approaches which could help to resolve the spatial and temporal variation and functional significance of rhizosphere microbial rhythmicity. This includes unravelling the factors which determine the oscillation of microbial activity, growth and death, and cross-talk with the host over diurnal time frames. We conclude that diurnal rhythmicity is an inherent characteristic of the rhizosphere and that temporal factors should be considered and reported in rhizosphere studies.

Unravelling OsPHT2;1 function in Chloroplast Phosphorus Homeostasis and Photosynthetic Efficiency under Low Phosphorus Stress in Rice

Phosphorus (P) deficiency is a critical factor limiting crop productivity, primarily due to its detrimental effects on photosynthesis and dry matter accumulation. In this study, we investigate the role of the rice gene OsPHT2;1 in mediating chloroplast P homeostasis and its subsequent impact on photosynthetic function under low P conditions. Stomatal conductance is typically positively correlated with net photosynthetic rates; however, P deficiency disrupts this relationship, leading to reduced stomatal opening and diminished photosynthetic efficiency. Our findings show that the OsPHT2;1 mutation leads to a decrease in the plastoquinone (PQ) pool size. This change is associated with altered stomatal conductance and modifications in electron transport dynamics, including an increase in the transmembrane proton gradient and a shift from linear to cyclic electron transport. This disruption significantly impairs the transport of photosynthetic products, particularly triose phosphates, essential for sucrose synthesis in the cytoplasm. Additionally, the reduced PQ pool influences the expression of key genes involved in photostability, highlighting the interplay between P homeostasis and photosynthetic regulation. By elucidating the mechanisms underlying OsPHT2;1's role in chloroplast function, our research underscores its significance in optimizing rice adaptation to low P environments, thereby enhancing crop resilience and productivity.

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.

Vascular bundle cell-specific expression of a phosphate transporter improves phosphate use efficiency of transgenic Arabidopsis without detrimental effects

Constitutive overexpression of phosphate (Pi) transporter family 1 often results in the accumulation of toxic levels of Pi, which causes growth retardation in plants. In contrast, we had previously reported that root epidermis-specific overexpression of the phosphate transporter TaPT2 in Arabidopsis leads to improved growth and Pi use efficiency. In the present study, we used promoters AtHKT1;1 and SKOR, which are predominantly expressed in the vascular bundle tissues, to overexpress TaPT2. Transgenic lines exhibited increased shoot growth compared to wild type plants under normal- and low-Pi conditions, along with elevated root Pi and total P content, and higher xylem sap Pi concentration, specifically under low-Pi conditions. This was attributed to moderate Pi accumulation in the xylem parenchyma cells, enhancing the Pi uploading capacity to the xylem. SKOR-TaPT2, however, did not complement pho1 mutant, which was defective in uploading Pi to the xylem. The transcriptional levels of VPT1 and VPT3, which are responsible for transporting excess Pi into a vacuole, were upregulated in SKOR promoter lines under normal-Pi conditions. Our results suggested that root vascular bundle-specific expression of TaPT2 is another promising strategy for increasing biomass production, Pi uptake, and Pi use efficiency while preventing growth retardation in transgenic plants.

Genome-wide association study reveals genetic basis and candidate genes for chlorophyll content of leaves in maize (Zea mays L.)

The chlorophyll content (CC) directly affects photosynthesis, growth, and yield. However, the genetic basis of CC is still unclear in maize (Zea mays L.). Here, we conducted a genome-wide association study using mixed linear model for CC of the fifth leaves at seedling stage (CCFSS) and the ear leaves at filling stage (CCEFS) for 334 maize inbred lines. The heritability estimates for CCFSS and CCEFS, obtained via variance components analysis using the lme4 package in R, were 70.84% and 78.99%, respectively, indicating that the CC of leaves is primarily controlled by genetic factors. A total of 15 CC-related SNPs and 177 candidate genes were identified with a p-value < 4.49 × 10-5, which explained 4.98-7.59% of the phenotypic variation. Lines with more favorable gene variants showed higher CC. Meanwhile, Gene Ontology (GO) analysis implied that these candidate genes were probably related to chlorophyll biosynthesis. In addition, gene-based association analyses revealed that six variants in GRMZM2G037152, GRMZM5G816561, GRMZM2G324462, and GRMZM2G064657 genes were significantly (p-value < 0.01) correlated with CC, of which GRMZM2G064657 (encodes a phosphate transporter protein) and GRMZM5G816561 (encodes a cytochrome P450 protein) were specifically highly expressed in leaves tissues. Interestingly, these candidate genes were previously reported to involve in the regulation of the contents of chlorophyll in plants or Chlamydomonas. These results may contribute to the understanding of genetic basis and molecular mechanisms of maize CC and the selection of maize varieties with improved CC.

Silencing Osa-miR827 via CRISPR/Cas9 protects rice against the blast fungus Magnaporthe oryzae

MicroRNAs (miRNAs) are short, non-coding RNAs that regulate gene expression at the post-transcriptional level. In plants, miRNAs participate in diverse developmental processes and adaptive responses to biotic and abiotic stress. MiR827 has long been recognized to be involved in plant responses to phosphate starvation. In rice, the miR827 regulates the expression of OsSPX-MFS1 and OsSPX-MFS2, these genes encoding vacuolar phosphate transporters. In this study, we demonstrated that miR827 plays a role in resistance to infection by the fungus Magnaporthe oryzae in rice. We show that MIR827 overexpression enhances susceptibility to infection by M. oryzae which is associated to a weaker induction of defense gene expression during pathogen infection. Conversely, CRISPR/Cas9-induced mutations in the MIR827 gene completely abolish miR827 production and confer resistance to M. oryzae infection. This resistance is accompanied by a reduction of leaf Pi content compared to wild-type plants, whereas Pi levels increase in leaves of the blast-susceptible miR827 overexpressor plants. In wild-type plants, miR827 accumulation in leaves decreases during the biotrophic phase of the infection process. Taken together, our data indicates that silencing MIR827 confers resistance to M. oryzae infection in rice while further supporting interconnections between Pi signaling and immune signaling in plants. Unravelling the role of miR827 during M. oryzae infection provides knowledge to improve blast resistance in rice by CRISPR/Cas9-editing of MIR827.

Genetically manipulated chloroplast stromal phosphate levels alter photosynthetic efficiency

The concentration of inorganic phosphate (Pi) in the chloroplast stroma must be maintained within narrow limits to sustain photosynthesis and to direct the partitioning of fixed carbon. However, it is unknown if these limits or the underlying contributions of different chloroplastic Pi transporters vary throughout the photoperiod or between chloroplasts in different leaf tissues. To address these questions, we applied live Pi imaging to Arabidopsis (Arabidopsis thaliana) wild-type plants and 2 loss-of-function transporter mutants: triose phosphate/phosphate translocator (tpt), phosphate transporter 2;1 (pht2;1), and tpt pht2;1. Our analyses revealed that stromal Pi varies spatially and temporally, and that TPT and PHT2;1 contribute to Pi import with overlapping tissue specificities. Further, the series of progressively diminished steady-state stromal Pi levels in these mutants provided the means to examine the effects of Pi on photosynthetic efficiency without imposing nutritional deprivation. ΦPSII and nonphotochemical quenching (NPQ) correlated with stromal Pi levels. However, the proton efflux activity of the ATP synthase (gH+) and the thylakoid proton motive force (pmf) were unaltered under growth conditions, but were suppressed transiently after a dark to light transition with return to wild-type levels within 2 min. These results argue against a simple substrate-level limitation of ATP synthase by depletion of stromal Pi, favoring more integrated regulatory models, which include rapid acclimation of thylakoid ATP synthase activity to reduced Pi levels.

Single-cell RNA sequencing reveals dynamics of gene expression for 2D elongation and 3D growth in Physcomitrium patens

The transition from two-dimensional (2D) to 3D growth likely facilitated plants to colonize land, but its heterogeneity is not well understood. In this study, we utilized single-cell RNA sequencing to analyze the moss Physcomitrium patens, whose morphogenesis involves a transition from 2D to 3D growth. We profiled over 17,000 single cells covering all major vegetative tissues, including 2D filaments (chloronema and caulonema) and 3D structures (bud and gametophore). Pseudotime analyses revealed larger numbers of candidate genes that determine cell fates for 2D tip elongation or 3D bud differentiation. Using weighted gene co-expression network analysis, we identified a module that connects β-type carbonic anhydrases (βCAs) with auxin. We further validated the cellular expression patterns of βCAs and demonstrated their roles in 3D gametophore development. Overall, our study provides insights into cellular heterogeneity in a moss and identifies molecular signatures that underpin the 2D-to-3D growth transition at single-cell resolution.

ATP regeneration by ATPases for in vitro biotransformation

Adenosine triphosphate (ATP) regeneration is a significant step in both living cells and in vitro biotransformation (ivBT). Rotary motor ATP synthases (ATPases), which regenerate ATP in living cells, have been widely assembled in biomimetic structures for in vitro ATP synthesis. In this review, we present a comprehensive overview of ATPases, including the working principle, orientation and distribution density properties of ATPases, as well as the assembly strategies and applications of ATPase-based ATP regeneration modules. The original sources of ATPases for in vitro ATP regeneration include chromatophores, chloroplasts, mitochondria, and inverted Escherichia coli (E. coli) vesicles, which are readily accessible but unstable. Although significant advances have been made in the assembly methods for ATPase-artificial membranes in recent decades, it remains challenging to replicate the high density and orientation of ATPases observed in vivo using in vitro assembly methods. The use of bioproton pumps or chemicals for constructing proton motive forces (PMF) enables the versatility and potential of ATPase-based ATP regeneration modules. Additionally, overall robustness can be achieved via membrane component selection, such as polymers offering great mechanical stability, or by constructing a solid supporting matrix through layer-by-layer assembly techniques. Finally, the prospects of ATPase-based ATP regeneration modules can be expected with the technological development of ATPases and artificial membranes.

Phosphorus uptake, transport, and signaling in woody and model plants

Phosphorus (P), a critical macronutrient for plant growth and reproduction, is primarily acquired and translocated in the form of inorganic phosphate (Pi) by roots. Pi deficiency is widespread in many natural ecosystems, including forest plantations, due to its slow movement and easy fixation in soils. Plants have evolved complex and delicate regulation mechanisms on molecular and physiological levels to cope with Pi deficiency. Over the past two decades, extensive research has been performed to decipher the underlying molecular mechanisms that regulate the Pi starvation responses (PSR) in plants. This review highlights the prospects of Pi uptake, transport, and signaling in woody plants based on the backbone of model and crop plants. In addition, this review also highlights the interactions between phosphorus and other mineral nutrients such as Nitrogen (N) and Iron (Fe). Finally, this review discusses the challenges and potential future directions of Pi research in woody plants, including characterizing the woody-specific regulatory mechanisms of Pi signaling and evaluating the regulatory roles of Pi on woody-specific traits such as wood formation and ultimately generating high Phosphorus Use Efficiency (PUE) woody plants.

Microbe-dependent and independent nitrogen and phosphate acquisition and regulation in plants

Nitrogen (N) and phosphorus (P) are the most important macronutrients required for plant growth and development. To cope with the limited and uneven distribution of N and P in complicated soil environments, plants have evolved intricate molecular strategies to improve nutrient acquisition that involve adaptive root development, production of root exudates, and the assistance of microbes. Recently, great advances have been made in understanding the regulation of N and P uptake and utilization and how plants balance the direct uptake of nutrients from the soil with the nutrient acquisition from beneficial microbes such as arbuscular mycorrhiza. Here, we summarize the major advances in these areas and highlight plant responses to changes in nutrient availability in the external environment through local and systemic signals.

Milestones in understanding transport, sensing, and signaling of the plant nutrient phosphorus

As an essential nutrient element, phosphorus (P) is primarily acquired and translocated as inorganic phosphate (Pi) by plant roots. Pi is often sequestered in the soil and becomes limited for plant growth. Plants have developed a sophisticated array of adaptive responses, termed P starvation responses, to cope with P deficiency by improving its external acquisition and internal utilization. Over the past 2 to 3 decades, remarkable progress has been made toward understanding how plants sense and respond to changing environmental P. This review provides an overview of the molecular mechanisms that regulate or coordinate P starvation responses, emphasizing P transport, sensing, and signaling. We present the major players and regulators responsible for Pi uptake and translocation. We then introduce how P is perceived at the root tip, how systemic P signaling is operated, and the mechanisms by which the intracellular P status is sensed and conveyed. Additionally, the recent exciting findings about the influence of P on plant-microbe interactions are highlighted. Finally, the challenges and prospects concerning the interplay between P and other nutrients and strategies to enhance P utilization efficiency are discussed. Insights obtained from this knowledge may guide future research endeavors in sustainable agriculture.

Light controls mesophyll-specific post-transcriptional splicing of photoregulatory genes by AtPRMT5

Light plays a central role in plant growth and development, providing an energy source and governing various aspects of plant morphology. Previous study showed that many polyadenylated full-length RNA molecules within the nucleus contain unspliced introns (post-transcriptionally spliced introns, PTS introns), which may play a role in rapidly responding to changes in environmental signals. However, the mechanism underlying post-transcriptional regulation during initial light exposure of young, etiolated seedlings remains elusive. In this study, we used FLEP-seq2, a Nanopore-based sequencing technique, to analyze nuclear RNAs in Arabidopsis (Arabidopsis thaliana) seedlings under different light conditions and found numerous light-responsive PTS introns. We also used single-nucleus RNA sequencing (snRNA-seq) to profile transcripts in single nucleus and investigate the distribution of light-responsive PTS introns across distinct cell types. We established that light-induced PTS introns are predominant in mesophyll cells during seedling de-etiolation following exposure of etiolated seedlings to light. We further demonstrated the involvement of the splicing-related factor A. thaliana PROTEIN ARGININE METHYLTRANSFERASE 5 (AtPRMT5), working in concert with the E3 ubiquitin ligase CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), a critical repressor of light signaling pathways. We showed that these two proteins orchestrate light-induced PTS events in mesophyll cells and facilitate chloroplast development, photosynthesis, and morphogenesis in response to ever-changing light conditions. These findings provide crucial insights into the intricate mechanisms underlying plant acclimation to light at the cell-type level.

Phosphate accumulation in rice leaves promotes fungal pathogenicity and represses host immune responses during pathogen infection

Rice is one of the most important crops in the world and a staple food for more than half of the world's population. At present, the blast disease caused by the fungus Magnaporthe oryzae poses a severe threat to food security through reduction of rice yields worldwide. High phosphate fertilization has previously been shown to increase blast susceptibility. At present, however, our knowledge on the mechanisms underpinning phosphate-induced susceptibility to M. oryzae infection in rice is limited. In this work, we conducted live cell imaging on rice sheaths inoculated with a M. oryzae strain expressing two fluorescently-tagged M. oryzae effectors. We show that growing rice under high phosphate fertilization, and subsequent accumulation of phosphate in leaf sheaths, promotes invasive growth of M. oryzae. Consistent with this, stronger expression of M. oryzae effectors and Pathogenicity Mitogen-activated Protein Kinase (PMK1) occurs in leaf sheaths of rice plants grown under high a phosphate regime. Down-regulation of fungal genes encoding suppressors of plant cell death and up-regulation of plant cell death-inducing effectors also occurs in sheaths of phosphate over-accumulating rice plants. Treatment with high Pi causes alterations in the expression of fungal phosphate transporter genes potentially contributing to pathogen virulence. From the perspective of the plant, Pi accumulation in leaf sheaths prevents H2O2 accumulation early during M. oryzae infection which was associated to a weaker activation of Respiratory Burst Oxidase Homologs (RBOHs) genes involved in reactive oxygen species (ROS) production. Further, a weaker activation of defense-related genes occurs during infection in rice plants over-accumulating phosphate. From these results, it can be concluded that phosphate fertilization has an effect on the two interacting partners, pathogen and host. Phosphate-mediated stimulation of fungal effector genes (e.g., potentiation of fungal pathogenicity) in combination with repression of pathogen-inducible immune responses (e.g., ROS accumulation, defense gene expression) explains higher colonization by M. oryzae in rice tissues accumulating phosphate. Phosphate content can therefore be considered as an important factor in determining the outcome of the rice/M. oryzae interaction. As fertilizers and pesticides are commonly used in rice cultivation to maintain optimal yield and to prevent losses caused by pathogens, a better understanding of how phosphate impacts blast susceptibility is crucial for developing strategies to rationally optimize fertilizer and pesticide use in rice production.

The transporter PHO84/NtPT1 is a target of aluminum to affect phosphorus absorption in Saccharomyces cerevisiae and Nicotiana tabacum L

The molecular mechanism of aluminum toxicity in biological systems is not completely understood. Saccharomyces cerevisiae is one of the most used model organisms in the study of environmental metal toxicity. Using an unbiased metallomic approach in yeast, we found that aluminum treatment caused phosphorus deprivation, and the lack of phosphorus increased as the pH of the environment decreased compared to the control strain. By screening the phosphate signaling and response pathway (PHO pathway) in yeast with the synthetic lethality of a new phosphorus-restricted aluminum-sensitive gene, we observed that pho84Δ mutation conferred severe growth defect to aluminum under low-phosphorus conditions, and the addition of phosphate alleviated this sensitivity. Subsequently, the data showed that PHO84 determined the intracellular aluminum-induced phosphorus deficiency, and the expression of PHO84 was positively correlated with aluminum stress, which was mediated by phosphorus through the coordinated regulation of PHO4/PHO2. Moreover, aluminum reduced phosphorus absorption and inhibited tobacco plant growth in acidic media. In addition, the high-affinity phosphate transporter NtPT1 in tobacco exhibited similar effects to PHO84, and overexpression of NtPT1 conferred aluminum resistance in yeast cells. Taken together, positive feedback regulation of the PHO pathway centered on the high-affinity phosphate transporters is a highly conservative mechanism in response to aluminum toxicity. The results may provide a basis for aluminum-resistant microorganisms or plant engineering and acidic soil treatment.

Improved chloroplast Pi allocation helps sustain electron transfer to enhance photosynthetic low-phosphorus tolerance of wheat

Phosphorus (P) deficit limits high wheat (Triticum aestivum L.) yields. Breeding low-P-tolerant cultivars is vital for sustainable agriculture and food security, but the low-P adaptation mechanisms are largely not understood. Two wheat cultivars, ND2419 (low-P-tolerant) and ZM366 (low-P-sensitive) were used in this study. They were grown under hydroponic conditions with low-P (0.015 mM) or normal-P (1 mM). Low-P suppressed biomass accumulation and net photosynthetic rate (A) in both cultivars, whereas ND2419 was relatively less suppressed. Intercellular CO2 concentration did not decrease with the decline of stomatal conductance. Additionally, maximum electron transfer rate (Jmax) decreased sooner than maximum carboxylation rate (Vcmax). Results indicate that impeded electron transfer is directly responsible for decreased A. Under low-P, ND2419 exhibited greater PSII functionality (potential activity (Fv/Fo), maximum quantum efficiency (Fv/Fm), photochemical quenching (qL) and non-photochemical quenching (NPQ) required for electron transfer than ZM366, resulting more ATP for Rubisco activation. Furthermore, ND2419 maintained higher chloroplast Pi concentrations by enhancing chloroplast Pi allocation, compared with ZM366. Overall, the low-P-tolerant cultivar sustained electron transfer under low-P by enhancing chloroplast Pi allocation, allowing more ATP synthesis for Rubisco activation, ultimately presenting stronger photosynthesis capacities. The improved chloroplasts Pi allocation may provide new insights into improve low-P tolerance.

Effects of Soybean Phosphate Transporter Gene GmPHT2 on Pi Transport and Plant Growth under Limited Pi Supply Condition

Phosphorus is an essential macronutrient for plant growth and development, but phosphate resources are limited and rapidly depleting due to massive global agricultural demand. This study identified two genes in the phosphate transporter 2 (PHT2) family of soybean by bioinformatics. The expression patterns of two genes by qRT-PCR at leaves and all were induced by low-phosphate stress. After low-phosphate stress, GmPHT2;2 expression was significantly higher than GmPHT2;1, and the same trend was observed throughout the reproductive period. The result of heterologous expression of GmPHT2 in Arabidopsis knockout mutants of atpht2;1 shows that chloroplasts and whole-plant phosphorus content were significantly higher in plants complementation of GmPHT2;2 than in plants complementation of GmPHT2;1. This suggests that GmPHT2;2 may play a more important role in plant phosphorus metabolic homeostasis during low-phosphate stress than GmPHT2;1. In the yeast backfill assay, both genes were able to backfill the ability of the defective yeast to utilize phosphorus. GmPHT2 expression was up-regulated by a low-temperature treatment at 4 °C, implying that GmPHT2;1 may play a role in soybean response to low-temperature stress, in addition to being involved in phosphorus transport processes. GmPHT2;1 and GmPHT2;2 exhibit a cyclic pattern of circadian variation in response to light, with the same pattern of gene expression changes under red, blue, and white light conditions. GmPHT2 protein was found in the chloroplast, according to subcellular localization analysis. We conclude that GmPHT2 is a typical phosphate transporter gene that can improve plant acquisition efficiency.

Genome-Wide Analysis of the PHT Gene Family and Its Response to Mycorrhizal Symbiosis in Tomatoes under Phosphate Starvation Conditions

Phosphate is one of the essential mineral nutrients. Phosphate transporter genes (PHTs) play an important role in Pi acquisition and homeostasis in tomato plants. However, basic biological information on PHT genes and their responses of symbiosis with arbuscular mycorrhizal in the genome remains largely unknown. We analyzed the physiological changes and PHT gene expression in tomatoes (Micro-Tom) inoculated with arbuscular mycorrhizal (AM) fungi (Funneliformis mosseae) under different phosphate conditions (P1: 0 µM, P2: 25 µM, and P3: 200 µM Pi). Twenty-three PHT genes were identified in the tomato genomics database. Protein sequence alignment further divided the 23 PHT genes into three groups, with similar classifications of exons and introns. Good colonization of plants was observed under low phosphate conditions (25 µM Pi), and Pi stress and AM fungi significantly affected P and N accumulation and root morphological plasticity. Moreover, gene expression data showed that genes in the SlPHT1 (SlPT3, SlPT4, and SlPT5) gene family were upregulated by Funneliformis mosseae under all conditions, which indicated that these gene levels were significantly increased with AM fungi inoculation. None of the analyzed SlPHT genes in the SlPH2, SlPHT3, SlPHT4, and SlPHO gene families were changed at any Pi concentration. Our results indicate that inoculation with AM fungi mainly altered the expression of the PHT1 gene family. These results will lay a foundation for better understanding the molecular mechanisms of inorganic phosphate transport under AM fungi inoculation.

Integrated IBD Analysis, GWAS Analysis and Transcriptome Analysis to Identify the Candidate Genes for White Spot Disease in Maize

Foundation parents (FPs) play an irreplaceable role in maize breeding practices. Maize white spot (MWS) is an important disease in Southwest China that always seriously reduces production. However, knowledge about the genetic mechanism of MWS resistance is limited. In this paper, a panel of 143 elite lines were collected and genotyped by using the MaizeSNP50 chip with approximately 60,000 single nucleotide polymorphisms (SNPs) and evaluated for resistance to MWS among 3 environments, and a genome-wide association study (GWAS) and transcriptome analysis were integrated to reveal the function of the identity-by-descent (IBD) segments for MWS. The results showed that (1) 225 IBD segments were identified only in the FP QB512, 192 were found only in the FP QR273 and 197 were found only in the FP HCL645. (2) The GWAS results showed that 15 common quantitative trait nucleotides (QTNs) were associated with MWS. Interestingly, SYN10137 and PZA00131.14 were in the IBD segments of QB512, and the SYN10137-PZA00131.14 region existed in more than 58% of QR273's descendants. (3) By integrating the GWAS and transcriptome analysis, Zm00001d031875 was found to located in the region of SYN10137-PZA00131.14. These results provide some new insights for the detection of MWS's genetic variation mechanisms.

NtNCED3 regulates responses to phosphate deficiency and drought stress in Nicotiana tabacum

Plants are sessile and encounter to abiotic environmental stressors, such as nutrient deficiency and drought stress. Identifying stress tolerance genes and their mechanisms is vital to ensuring plant survival. In this study, we characterized NCED3 in the tobacco plant Nicotiana tabacum, a key enzyme in the biosynthesis of abscisic acid that is widely involved in abiotic stress responses, using overexpression and RNA interference knockdown. Overexpression of NtNCED3 promoted primary root development, leading to increased dry weight, root-to-shoot ratio, photosynthetic capacity, and acid phosphatase activity, coinciding with highly increased phosphate uptake capability under low phosphate conditions. Under both drought and extreme phosphate deficiency conditions, the phosphate starvation response preceded the drought stress response. However, under high phosphate conditions, the drought stress phenotype emerged before the symptoms of phosphate deficiency. Plants overexpressing NtNCED3 grew better than the wild-type and NtNCED3 knockdown plants, with more developed root systems and higher biomass, phosphorus content, and hormone content. This study provides evidence that NtNCED3 enzyme participates in plant responses to phosphate deficiency and drought stress in N. tabacum, and NtNCED3 may serve as a potentially valuable gene for genetic modification of plant tolerance to both drought stress and phosphate starvation.

Root epidermis-specific expression of a phosphate transporter TaPT2 enhances the growth of transgenic Arabidopsis under Pi-replete and Pi-depleted conditions

Although attempts to improve the phosphate (Pi) uptake and use efficiency by constitutively overexpressing phosphate transporters have resulted in enhanced Pi or total phosphorous contents, growth promotion by Pi acquisition was observed in only a few cases. This study examined the effect of the tissue-specific overexpression of phosphate transporter on Pi acquisition and plant growth. We cloned cDNA for a wheat phosphate transporter, TaPT2, using PCR and confirmed its Pi transport activity in Arabidopsis suspension cells. The overexpression of TaPT2 by the Arabidopsis Shaker family inward rectifying potassium channel 1 (AKT1) promoter, dominantly expressed in root epidermal cells, resulted in increased root and shoot growth of transgenic Arabidopsis under Pi-replete and Pi-depleted conditions. However, their Pi and total P contents did not increase. The overexpression of TaPT2 by the constitutive promoter, actin8 (ACT8), increased shoot total P contents in transgenic plants, but did not promote their growth. These results suggested that enhanced Pi uptake in root epidermal cells is suitable as a driving force for Pi transport from roots to shoots, improving subsequent Pi use in shoots. Thus, the root epidermal cell-specific expression of TaPT2 may be a simple and promising strategy for enhancing plant Pi uptake and efficiency.

Roles of plastid-located phosphate transporters in carotenoid accumulation

Enhanced carotenoid accumulation in plants is crucial for the nutritional and health demands of the human body since these beneficial substances are acquired through dietary intake. Plastids are the major organelles to accumulate carotenoids in plants and it is reported that manipulation of a single plastid phosphate transporter gene enhances carotenoid accumulation. Amongst all phosphate transport proteins including phosphate transporters (PHTs), plastidial phosphate translocators (pPTs), PHOSPHATE1 (PHO1), vacuolar phosphate efflux transporter (VPE), and Sulfate transporter [SULTR]-like phosphorus distribution transporter (SPDT) in plants, plastidic PHTs (PHT2 & PHT4) are found as the only clade that is plastid located, and manipulation of which affects carotenoid accumulation. Manipulation of a single chromoplast PHT (PHT4;2) enhances carotenoid accumulation, whereas manipulation of a single chloroplast PHT has no impact on carotenoid accumulation. The underlying mechanism is mainly attributed to their different effects on plastid orthophosphate (Pi) concentration. PHT4;2 is the only chromoplast Pi efflux transporter, and manipulating this single chromoplast PHT significantly regulates chromoplast Pi concentration. This variation subsequently modulates the carotenoid accumulation by affecting the supply of glyceraldehyde 3-phosphate, a substrate for carotenoid biosynthesis, by modulating the transcript abundances of carotenoid biosynthesis limited enzyme genes, and by regulating chromoplast biogenesis (facilitating carotenoid storage). However, at least five orthophosphate influx PHTs are identified in the chloroplast, and manipulating one of the five does not substantially modulate the chloroplast Pi concentration in a long term due to their functional redundancy. This stable chloroplast Pi concentration upon one chloroplast PHT absence, therefore, is unable to modulate Pi-involved carotenoid accumulation processes and finally does affect carotenoid accumulation in photosynthetic tissues. Despite these advances, several cases including the precise location of plastid PHTs, the phosphate transport direction mediated by these plastid PHTs, the plastid PHTs participating in carotenoid accumulation signal pathway, the potential roles of these plastid PHTs in leaf carotenoid accumulation, and the roles of these plastid PHTs in other secondary metabolites are waiting for further research. The clarification of the above-mentioned cases is beneficial for breeding high-carotenoid accumulation plants (either in photosynthetic or non-photosynthetic edible parts of plants) through the gene engineering of these transporters.

Adaptive strategies of plants to conserve internal phosphorus under P deficient condition to improve P utilization efficiency

Phosphorus (P) is one of the limiting factors for plant growth and productivity due to its slow diffusion and immobilization in the soil which necessitates application of phosphatic fertilizers to meet the crop demand and obtain maximum yields. However, plants have evolved mechanisms to adapt to low P stress conditions either by increasing acquisition (alteration of belowground processes) or by internal inorganic P (Pi) utilization (cellular Pi homeostasis) or both. In this review, we have discussed the adaptive strategies that conserve the use of P and maintain cellular Pi homeostasis in the cytoplasm. These strategies involve modification in membrane lipid composition, flavanol/anthocyanin level, scavenging and reutilization of Pi adsorbed in cell wall pectin, remobilization of Pi during senescence by enzymes like RNases and purple acid phosphatases, alternative mitochondrial electron transport, and glycolytic pathways. The remobilization of Pi from senescing tissues and its internal redistribution to various cellular organelles is mediated by various Pi transporters. Although much efforts have been made to enhance P acquisition efficiency, an understanding of the physiological mechanisms conserving internal Pi and their manipulation would be useful for plants that can utilize P more efficiently to produce optimum growth per unit P uptake.

A Coccidia-Specific Phosphate Transporter Is Essential for the Growth of Toxoplasma gondii Parasites

Toxoplasma gondii is an obligate intracellular parasite that acquires all necessary nutrients from the hosts, but the exact nutrient acquisition mechanisms are poorly understood. Here, we identified three putative phosphate transporters in T. gondii. TgPiT and TgPT2 are mainly on the plasma membrane, whereas TgmPT is localized to the mitochondrion. TgPiT and TgmPT are widely present and conserved in apicomplexan parasites that include Plasmodium and Eimeria species. Nonetheless, they are dispensable for the growth and virulence of Toxoplasma. TgPT2, on the other hand, is restricted to coccidia parasites and is essential for Toxoplasma survival. TgPT2 depletion led to reduced motility and invasion, as well as growth arrest of the parasites both in vitro and in vivo. Both TgPiT and TgPT2 have phosphate transport activities and contribute to parasites' inorganic phosphate (Pi) absorption. Interestingly, the Pi importing activity of Toxoplasma parasites could be competitively inhibited by ATP and AMP. Furthermore, direct uptake of 32P-ATP was also observed, indicating the parasites' ability to scavenge host ATP. Nonetheless, ATP/AMP import is not mediated by TgPiT or TgPT2, suggesting additional mechanisms. Together, these results show the complex pathways of phosphate transport in Toxoplasma, and TgPT2 is a potential target for antitoxoplasmic intervention design due to its essential role in parasite growth. IMPORTANCE To grow and survive within host cells, Toxoplasma must scavenge necessary nutrients from hosts to support its parasitism. Transporters located in the plasma membrane of the parasites play critical roles in nutrient acquisition. Toxoplasma encodes a large number of transporters, but so far, only a few have been characterized. In this study, we identified two phosphate transporters, TgPiT and TgPT2, to localize to the plasma membrane of Toxoplasma. Although both TgPiT and TgPT2 possess phosphate transport activities, only the novel transporter TgPT2 was essential for parasite growth, both in vitro and in vivo. In addition, TgPT2 and its orthologs are only present in coccidia parasites. As such, TgPT2 represents a potential target for drug design against toxoplasmosis. In addition, our data indicated that Toxoplasma can take up ATP and AMP from the environment, providing new insights into the energy metabolism of Toxoplasma.

Loss-of-function of NITROGEN LIMITATION ADAPTATION confers disease resistance in Arabidopsis by modulating hormone signaling and camalexin content

Phosphorus is an important macronutrient required for plant growth and development. It is absorbed by the roots in the form of inorganic phosphate (Pi). Under Pi limiting conditions, plants activate the Phosphate Starvation Response (PSR) system to enhance Pi acquisition. The NITROGEN LIMITATION ADAPTION (NLA) gene is a component of the Arabidopsis PSR, and its expression is post-transcriptionally regulated by miR827. We show that loss-of-function of NLA and MIR827 overexpression increases Pi level and enhances resistance to infection by the fungal pathogen Plectosphaerella cucumerina in Arabidopsis. Upon pathogen infection, high Pi plants (e.g. nla plants and wild type plants grown under high Pi supply) showed enhanced callose deposition. High Pi plants also exhibited superinduction of camalexin biosynthesis genes which is consistent with increased levels of camalexin during pathogen infection. Pathogen infection and treatment with fungal elicitors, triggered up-regulation of MIR827 and down-regulation of NLA expression. Under non-infection conditions, the nla plants showed increased levels of SA and JA compared with wild type plants, their levels further increasing upon pathogen infection. Overall, the outcomes of this study suggest that NLA plays a role in Arabidopsis immunity, while supporting convergence between Pi signaling and immune signaling in Arabidopsis.

The Roles of Phosphorus and Nitrogen Nutrient Transporters in the Arbuscular Mycorrhizal Symbiosis

More than 80% of land plant species can form symbioses with arbuscular mycorrhizal (AM) fungi, and nutrient transfer to plants is largely mediated through this partnership. Over the last few years, great progress has been made in deciphering the molecular mechanisms underlying the AM-mediated modulation of nutrient uptake progress, and a growing number of fungal and plant genes responsible for the uptake of nutrients from soil or transfer across the fungal-root interface have been identified. In this review, we outline the current concepts of nutrient exchanges within this symbiosis (mechanisms and regulation) and focus on P and N transfer from the fungal partner to the host plant, with a highlight on a possible interplay between P and N nutrient exchanges. Transporters belonging to the plant or AM fungi can synergistically process the transmembrane transport of soil nutrients to the symbiotic interface for further plant acquisition. Although much progress has been made to elucidate the complex mechanism for the integrated roles of nutrient transfers in AM symbiosis, questions still remain to be answered; for example, P and N transporters are less studied in different species of AM fungi; the involvement of AM fungi in plant N uptake is not as clearly defined as that of P; coordinated utilization of N and P is unknown; transporters of cultivated plants inoculated with AM fungi and transcriptomic and metabolomic networks at both the soil-fungi interface and fungi-plant interface have been insufficiently studied. These findings open new perspectives for fundamental research and application of AM fungi in agriculture.

Plant growth stimulation by high CO2 depends on phosphorus homeostasis in chloroplasts

Elevated atmospheric CO₂ enhances photosynthetic rate,¹ thereby increasing biomass production in plants. Nevertheless, high CO₂ reduces the accumulation of essential nutrients² such as phosphorus (P),³ which are required for photosynthetic processes and plant growth. How plants ensure enhanced growth despite meager P status remains enigmatic. In this study, we utilize genome-wide association analysis in Arabidopsis thaliana to identify a P transporter, PHT4;3, which mediates the reduction of P in chloroplasts at high CO₂. Decreasing chloroplastic P fine-tunes the accumulation of a sugar-P metabolite, phytic acid, to support plant growth. Furthermore, we demonstrate that this adaptive mechanism is conserved in rice. Our results establish a mechanistic framework for sustainable food production against the backdrop of soaring CO₂ levels across the world.

Arbuscular mycorrhizal fungi enhanced the growth, phosphorus uptake and Pht expression of olive (Olea europaea L.) plantlets

Olive (Olea europaea L.) is a highly mycotrophic species that has been introduced and cultivated in China for half a century. The arbuscular mycorrhizal fungi (AMF) is extremely valuable as a kind of biofertilizer to promote the health and vigor of olive plants. However, it is still unclear how native AMF impact growth and mineral nutrients, especially phosphorus absorption in the area where olive trees were introduced in China. In the present study, through a pot experiment, the effects of native AMF on the growth, phosphorus uptake and expression levels of four phosphate transporter genes (Pht) of olive plantlets were characterized. We found that (1) typical AMF colonization was observed within the roots of inoculated olive plantlets, and the growth of plantlets was significantly promoted; (2) some indigenous consortia (AMF1 and AMF2) notably promoted the absorption of phosphorus, fertilizers significantly increased the foliar content of nitrogen, and both AMF inoculation and fertilization had no significant effect on the uptake of potassium; and (3) AMF inoculation enhanced the expression of phosphate transporter genes in inoculated olive roots. This work demonstrates the effectiveness of native AMF on the cultivation of robust olive plantlets and highlights the role of AMF in increasing phosphorus uptake. There is great potential in using native AMF consortia as inoculants for the production of healthy and robust olive plantlets.

scCloudMine: A cloud-based app for visualization, comparison, and exploration of single-cell transcriptomic data

scCloudMine is a cloud-based application for visualization, comparison, and exploration of single-cell transcriptome data. It does not require an on-site, high-power computing server, installation, or associated expertise and expense. Users upload their own or publicly available scRNA-seq datasets after pre-processing for visualization using a web browser. The data can be viewed in two color modes-Cluster, representing cell identity, and Values, showing levels of expression-and data can be queried using keywords or gene identification number(s). Using the app to compare studies, we determined that some genes frequently used as cell-type markers are in fact study specific. The apparent cell-specific expression of PHO1;H3 differed between GFP-tagging and scRNA-seq studies. Some phosphate transporter genes were induced by protoplasting, but they retained cell specificity, suggesting that cell-specific responses to stress (i.e., protoplasting) can occur. Examination of the cell specificity of hormone response genes revealed that 132 hormone-responsive genes display restricted expression and that the jasmonate response gene TIFY8 is expressed in endodermal cells, in contrast to previous reports. It also appears that JAZ repressors have cell-type-specific functions. These features identified using scCloudMine highlight the need for resources to enable biological researchers to compare their datasets of interest under a variety of parameters. scCloudMine enables researchers to form new hypotheses and perform comparative studies and allows for the easy re-use of data from this emerging technology by a wide variety of users who may not have access or funding for high-performance on-site computing and support.

Narrowing down molecular targets for improving phosphorus-use efficiency in maize (Zea mays L.)

Conventional agricultural practices rely heavily on chemical fertilizers to boost production. Among the fertilizers, phosphatic fertilizers are copiously used to ameliorate low-phosphate availability in the soil. However, phosphorus-use efficiency (PUE) for major cereals, including maize, is less than 30%; resulting in more than half of the applied phosphate being lost to the environment. Rock phosphate reserves are finite and predicted to exhaust in near future with the current rate of consumption. Thus, the dependence of modern agriculture on phosphatic fertilizers poses major food security and sustainability challenges. Strategies to optimize and improve PUE, like genetic interventions to develop high PUE cultivars, could have a major impact in this area. Here, we present the current understanding and recent advances in the biological phenomenon of phosphate uptake, translocation, and adaptive responses of plants under phosphate deficiency, with special reference to maize. Maize is one of the most important cereal crops that is cultivated globally under diverse agro-climatic conditions. It is an industrial, feed and food crop with multifarious uses and a fast-rising global demand and consumption. The interesting aspects of diversity in the root system architecture traits, the interplay between signaling pathways contributing to PUE, and an in-depth discussion on promising candidate genes for improving PUE in maize are elaborated.

OsCKX2 regulates phosphate deficiency tolerance by modulating cytokinin in rice

Cytokinin oxidase/dehydrogenases (CKXs) are key enzymes that degrade cytokinins (CTKs) and play an essential role in plant growth and development. The present study analyzed the phenotypic and physiological characteristics of OsCKX2 overexpressing (OE) and knockout (KO) rice plants after exposure to phosphate (Pi) deficiency and the transcriptome and metabolome to investigate the function of OsCKX2 in response to Pi deficiency. OsCKX2 KO plants demonstrated higher endogenous CTK levels than wild-type (WT) under Pi deficiency. Further analysis indicated more robust tolerance of OsCKX2 KO plants to Pi deficiency, which exhibited higher phosphorus concentration, larger shoot biomass, and lesser leaf yellowing under Pi deficiency; whereas the opposite was observed for OsCKX2 OE plants. Transcriptome and metabolome analyses revealed that overexpression of OsCKX2 downregulated the transcriptional levels of genes related to Pi transporters, membrane lipid metabolism, and glycolysis, and reduced the consumption of metabolites in membrane lipid metabolism and glycolysis. On the contrary, knockout of OsCKX2 upregulated the expression of Pi transporters, and increased the consumption of metabolites in membrane lipid metabolism and glycolysis. These results indicated that OsCKX2 impacted Pi uptake, recycling, and plant growth via Pi transporters, phospholipid hydrolysis, and glycolysis under Pi deficiency. Overall, OsCKX2 negatively regulated Pi deficiency tolerance by modulating CTKs in rice.

Zinc Transporter ZmLAZ1-4 Modulates Zinc Homeostasis on Plasma and Vacuolar Membrane in Maize

Zinc is an essential micronutrient for plant growth and development, and functions as a cofactor for hundreds of transcription factors and enzymes in numerous biological processes. Zinc deficiency is common abiotic stress resulting in yield loss and quality deterioration of crops, but zinc excess causes toxicity for biological systems. In plants, zinc homeostasis is tightly modulated by zinc transporters and binding compounds that uptake/release, transport, localize, and store zinc, as well as their upstream regulators. Lazarus 1 (LAZ1), a member of DUF300 protein family, functions as transmembrane organic solute transporter in vertebrates. However, the function of LAZ1 in plants is still obscure. In the present study, the ZmLAZ1-4 protein was confirmed to bind to zinc ions by bioinformatic prediction and thermal shift assay. Heterologous expression of ZmLAZ1-4 in the zinc-sensitive yeast mutant, Arabidopsis, and maize significantly facilitated the accumulation of Zn2+ in transgenic lines, respectively. The result of subcellular localization exhibited that ZmLAZ1-4 was localized on the plasma and vacuolar membrane, as well as chloroplast. Moreover, the ZmLAZ1-4 gene was negatively co-expressed with ZmBES1/BZR1-11 gene through co-expression and real-time quantitative PCR analysis. The results of yeast one-hybrid and dual-luciferase assay suggested that ZmBES1/BZR1-11 could bind to ZmLAZ1-4 promoter to inhibit its transcription. All results indicated that ZmLAZ1-4 was a novel zinc transporter on plasma and vacuolar membrane, and transported zinc under negative regulation of the ZmBES1/BZR1-11 transcription factor. The study provides insights into further underlying the mechanism of ZmLAZ1-4 regulating zinc homeostasis.

Analysis of miRNAs responsive to long-term calcium deficiency in tef (Eragrostis tef (Zucc.) Trotter)

MicroRNAs (miRNAs) play an important role in growth, development, stress resilience, and epigenetic modifications of plants. However, the effect of calcium (Ca²⁺) deficiency on miRNA expression in the orphan crop tef (Eragrostis tef) remains unknown. In this study, we analyzed expression of miRNAs in roots and shoots of tef in response to Ca²⁺ treatment. miRNA-seq followed by bioinformatic analysis allowed us to identify a large number of small RNAs (sRNAs) ranging from 17 to 35 nt in length. A total of 1380 miRNAs were identified in tef experiencing long-term Ca²⁺ deficiency while 1495 miRNAs were detected in control plants. Among the miRNAs identified in this study, 161 miRNAs were similar with those previously characterized in other plant species and 348 miRNAs were novel, while the remaining miRNAs were uncharacterized. Putative target genes and their functions were predicted for all the known and novel miRNAs that we identified. Based on gene ontology (GO) analysis, the predicted target genes are known to have various biological and molecular functions including calcium uptake and transport. Pairwise comparison of differentially expressed miRNAs revealed that some miRNAs were specifically enriched in roots or shoots of low Ca²⁺-treated plants. Further characterization of the miRNAs and their targets identified in this study may help in understanding Ca²⁺ deficiency responses in tef and related orphan crops.

Insights to improve the plant nutrient transport by CRISPR/Cas system

We need to improve food production to feed the ever growing world population especially in a changing climate. Nutrient deficiency in soils is one of the primary bottlenecks affecting the crop production both in developed and developing countries. Farmers are forced to apply synthetic fertilizers to improve the crop production to meet the demand. Understanding the mechanism of nutrient transport is helpful to improve the nutrient-use efficiency of crops and promote the sustainable agriculture. Many transporters involved in the acquisition, export and redistribution of nutrients in plants are characterized. In these studies, heterologous systems like yeast and Xenopus were most frequently used to study the transport function of plant nutrient transporters. CRIPSR/Cas system introduced recently has taken central stage for efficient genome editing in diverse organisms including plants. In this review, we discuss the key nutrient transporters involved in the acquisition and redistribution of nutrients from soil. We draw insights on the possible application CRISPR/Cas system for improving the nutrient transport in plants by engineering key residues of nutrient transporters, transcriptional regulation of nutrient transport signals, engineering motifs in promoters and transcription factors. CRISPR-based engineering of plant nutrient transport not only helps to study the process in native plants with conserved regulatory system but also aid to develop non-transgenic crops with better nutrient use-efficiency. This will reduce the application of synthetic fertilizers and promote the sustainable agriculture strengthening the food and nutrient security.

Phosphate-induced resistance to pathogen infection in Arabidopsis

In nature, plants are concurrently exposed to a number of abiotic and biotic stresses. Our understanding of convergence points between responses to combined biotic/abiotic stress pathways remains, however, rudimentary. Here we show that MIR399 overexpression, loss-of-function of PHOSPHATE2 (PHO2), or treatment with high phosphate (Pi) levels is accompanied by an increase in Pi content and accumulation of reactive oxygen species (ROS) in Arabidopsis thaliana. High Pi plants (e.g., miR399 overexpressors, pho2 mutants, and plants grown under high Pi supply) exhibited resistance to infection by necrotrophic and hemibiotrophic fungal pathogens. In the absence of pathogen infection, the expression levels of genes in the salicylic acid (SA)- and jasmonic acid (JA)-dependent signaling pathways were higher in high Pi plants compared to wild-type plants grown under control conditions, which is consistent with increased levels of SA and JA in non-infected high Pi plants. During infection, an opposite regulation in the two branches of the JA pathway (ERF1/PDF1.2 and MYC2/VSP2) occurs in high Pi plants. Thus, while pathogen infection induces PDF1.2 expression in miR399 OE and pho2 plants, VSP2 expression is downregulated by pathogen infection in these plants. This study supports the notion that Pi accumulation promotes resistance to infection by fungal pathogens in Arabidopsis, while providing a basis to better understand interactions between Pi signaling and hormonal signaling pathways for modulation of plant immune responses.

Understanding the Adaptive Mechanisms of Plants to Enhance Phosphorus Use Efficiency on Podzolic Soils in Boreal Agroecosystems

Being a macronutrient, phosphorus (P) is the backbone to complete the growth cycle of plants. However, because of low mobility and high fixation, P becomes the least available nutrient in podzolic soils; hence, enhancing phosphorus use efficiency (PUE) can play an important role in different cropping systems/crop production practices to meet ever-increasing demands in food, fiber, and fuel. Additionally, the rapidly decreasing mineral phosphate rocks/stocks forced to explore alternative resources and methods to enhance PUE either through improved seed P reserves and their remobilization, P acquisition efficiency (PAE), or plant's internal P utilization efficiency (IPUE) or both for sustainable P management strategies. The objective of this review article is to explore and document important domains to enhance PUE in crop plants grown on Podzol in a boreal agroecosystem. We have discussed P availabilities in podzolic soils, root architecture and morphology, root exudates, phosphate transporters and their role in P uptake, different contributors to enhance PAE and IPUE, and strategies to improve plant PUE in crops grown on podzolic soils deficient in P and acidic in nature.

The Genetic Basis of Phosphorus Utilization Efficiency in Plants Provide New Insight into Woody Perennial Plants Improvement

Soil nutrient restrictions are the main environmental conditions limiting plant growth, development, yield, and quality. Phosphorus (P), an essential macronutrient, is one of the most significant factors that vastly restrains the growth and development of plants. Although the total P is rich in soil, its bio-available concentration is still unable to meet the requirements of plants. To maintain P homeostasis, plants have developed lots of intricate responsive and acclimatory mechanisms at different levels, which contribute to administering the acquisition of inorganic phosphate (Pi), translocation, remobilization, and recycling of Pi. In recent years, significant advances have been made in the exploration of the utilization of P in annual plants, while the research progress in woody perennial plants is still vague. In the meanwhile, compared to annual plants, relevant reviews about P utilization in woody perennial plants are scarce. Therefore, based on the importance of P in the growth and development of plants, we briefly reviewed the latest advances on the genetic and molecular mechanisms of plants to uphold P homeostasis, P sensing, and signaling, ion transporting and metabolic regulation, and proposed the possible sustainable management strategies to fasten the P cycle in modern agriculture and new directions for future studies.

Tailored Bioactive Compost from Agri-Waste Improves the Growth and Yield of Chili Pepper and Tomato

An extensive use of chemical fertilizers has posed a serious impact on food and environmental quality and sustainability. As the organic and biofertilizers can satisfactorily fulfill the crop’s nutritional requirement, the plants require less chemical fertilizer application; hence, the food is low in chemical residues and environment is less polluted. The agriculture crop residues, being a rich source of nutrients, can be used to feed the soil and crops after composting and is a practicable approach to sustainable waste management and organic agriculture instead of open-field burning of crop residues. This study demonstrates a feasible strategy to convert the wheat and rice plant residues into composted organic fertilizer and subsequent enrichment with plant-beneficial bacteria. The bioactive compost was then tested in a series of in vitro and in vivo experiments for validating its role in growing organic vegetables. The compost was enriched with a blend of micronutrients, such as zinc, magnesium, and iron, and a multi-trait bacterial consortium AAP (Azospirillum, Arthrobacter, and Pseudomonas spp.). The bacterial consortium AAP showed survival up to 180 days post-inoculation while maintaining their PGP traits. Field emission scanning electron microscopic analysis and fluorescence in situ hybridization (FISH) of bioactive compost further elaborated the morphology and confirmed the PGPR survival and distribution. Plant inoculation of this bioactive compost showed significant improvement in the growth and yield of chilies and tomato without any additional chemical fertilizer yielding a high value to cost ratio. An increase of ≈35% in chlorophyll contents, ≈25% in biomass, and ≈75% in yield was observed in chilies and tomatoes. The increase in N was 18.7 and 25%, while in P contents were 18.5 and 19% in chilies and tomatoes, respectively. The application of bioactive compost significantly stimulated the bacterial population as well as the phosphatase and dehydrogenase activities of soil. These results suggest that bioactive compost can serve as a source of bioorganic fertilizer to get maximum benefits regarding vegetable yield, soil quality, and fertilizer saving with the anticipated application for other food crops. It is a possible win-win situation for environmental sustainability and food security.

Chloroplast pH Homeostasis for the Regulation of Photosynthesis

The pH of various chloroplast compartments, such as the thylakoid lumen and stroma, is light-dependent. Light illumination induces electron transfer in the photosynthetic apparatus, coupled with proton translocation across the thylakoid membranes, resulting in acidification and alkalization of the thylakoid lumen and stroma, respectively. Luminal acidification is crucial for inducing regulatory mechanisms that protect photosystems against photodamage caused by the overproduction of reactive oxygen species (ROS). Stromal alkalization activates enzymes involved in the Calvin-Benson-Bassham (CBB) cycle. Moreover, proton translocation across the thylakoid membranes generates a proton gradient (ΔpH) and an electric potential (ΔΨ), both of which comprise the proton motive force (pmf) that drives ATP synthase. Then, the synthesized ATP is consumed in the CBB cycle and other chloroplast metabolic pathways. In the dark, the pH of both the chloroplast stroma and thylakoid lumen becomes neutral. Despite extensive studies of the above-mentioned processes, the molecular mechanisms of how chloroplast pH can be maintained at proper levels during the light phase for efficient activation of photosynthesis and other metabolic pathways and return to neutral levels during the dark phase remain largely unclear, especially in terms of the precise control of stromal pH. The transient increase and decrease in chloroplast pH upon dark-to-light and light-to-dark transitions have been considered as signals for controlling other biological processes in plant cells. Forward and reverse genetic screening approaches recently identified new plastid proteins involved in controlling ΔpH and ΔΨ across the thylakoid membranes and chloroplast proton/ion homeostasis. These proteins have been conserved during the evolution of oxygenic phototrophs and include putative photosynthetic protein complexes, proton transporters, and/or their regulators. Herein, we summarize the recently identified protein players that control chloroplast pH and influence photosynthetic efficiency in plants.

Comparing the Effects of N and P Deficiency on Physiology and Growth for Fast- and Slow-Growing Provenances of Fraxinus mandshurica

With the continuous increase in atmospheric carbon dioxide emissions, nitrogen (N) and phosphorus (P) as mineral elements increasingly restrict plant growth. To explore the effect of deficiency of P and N on growth and physiology, Fraxinus mandshurica (hereafter “F. mandshurica”) Rupr. annual seedlings of Wuchang (WC) provenance with fast growth and Dailing (DL) provenance with slow growth were treated with complete nutrition or starvation of N (N-), P (P-) or both elements (NP-). Although P- and N- increased the use efficiency of P (PUE) and N (NUE), respectively, they reduced the leaf area, chlorophyll content and activities of N assimilation enzymes (NR, GS, GOGAT), which decreased the dry weight and P or N amount. The free amino acid content and activities of Phosphoenolpyruvate carboxylase (PEPC) and acid phosphatase enzymes were reduced by N-. The transcript levels of NRT2.1, NRT2.4, NRT2.5, NRT2.7, AVT1, AAP3, NIA2, PHT1-3, PHT1-4 and PHT2-1 in roots were increased, but those of NRT2.1, NRT2.4, NRT2.5, PHT1-3, PHT1-4, PHT2-1 and AAP3 in leaves were reduced by P-. WC was significantly greater than DL under P- in dry weight, C amount, N amount, leaf area, PUE, NUE, which related to greater chlorophyll content, PEPC enzyme activity, N assimilation enzyme activities, and transcript levels of N and P transporter genes in roots and foliage, indicating a greater ability of WC to absorb, transport and utilize N and P under P-. WC was also greater than DL under N- in terms of the above indicators except the transcript levels of N and P assimilation genes, but most of the indicators did not reach a significant level, indicating that WC might be more tolerant to N- than DL, which requires further verification. In summary, WC was identified as a P-efficient provenance, as the growth rate was greater for the genetic type with high than low tolerance to P-.

Intracellular phosphate sensing and regulation of phosphate transport systems in plants

Recent research on the regulation of cellular phosphate (Pi) homeostasis in eukaryotes has collectively made substantial advances in elucidating inositol pyrophosphates (PP-InsP) as Pi signaling molecules that are perceived by the SPX (Syg1, Pho81, and Xpr1) domains residing in multiple proteins involved in Pi transport and signaling. The PP-InsP-SPX signaling module is evolutionarily conserved across eukaryotes and has been elaborately adopted in plant Pi transport and signaling systems. In this review, we have integrated these advances with prior established knowledge of Pi and PP-InsP metabolism, intracellular Pi sensing, and transcriptional responses according to the dynamics of cellular Pi status in plants. Anticipated challenges and pending questions as well as prospects are also discussed.

The effect of silicon supply on photosynthesis and carbohydrate metabolism in two wheat (Triticum aestivum L.) cultivars contrasting in response to phosphorus nutrition

Phosphorus (P) deficiency affects agricultural systems by limiting crop quality and yield. Studies have suggested that silicon (Si) improves P uptake in plants grown under P deficiency. However, the effects of Si on photosynthesis and carbohydrate metabolism under P stress remain unclear. We performed a hydroponic study using two wheat cultivars with contrasting sensitivity to P deficiency (Púrpura, sensitive; Fritz, semi-tolerant) that were exposed to P (0, 0.01, or 0.1 mM) and Si (0 or 2 mM), and we evaluated the photosynthetic performance and metabolic alterations. In plants from the sensitive cultivar undergoing P deficiency, Si application increased sucrose levels, starch breakdown and length of shoots, and also improved plant dry weight. In Fritz (the semi-tolerant cultivar), Si exposure reduced P concentration, and increased shoot length and P use efficiency (PUE) under P shortage. Interestingly, Si application altered cell wall composition, which was associated with higher mesophyll conductance and net CO₂ assimilation in Fritz plants grown under P stress. Together, our results indicate that under P deficiency, Si nutrition positively affects photosynthesis and carbohydrate levels in a genotype-dependent manner. Furthermore, these results suggest that Si plays an important role in maintaining high photosynthetic rates in wheat plants undergoing P deficiency.

The use of phosphonates in agriculture. Chemical, biological properties and legislative issues

The Phosphorus (III) derivatives, named Phosphonates, include congeners with properties as fungicides that are effective in controlling Oomycetes. Examples are organic compounds like Fosetyl-Al [Aluminium tris-(ethylphosphonate)] and salts formed with the anion of phosphonic acid [(OH)₂HPO] and Potassium, Sodium and Ammonium cations. According to IUPAC, the correct nomenclature for these compounds is "phosphonates", but in common language and scientific literature they are often named "phosphites", creating ambiguity. The European legislation restricts the use of phosphonates, with the ban for application in organic agriculture. However, phosphonate residues were detected in some organic products due to their addition to fertilizers allowed in organic agriculture. The legitimacy of this addition is controversial, as it is not evident if phosphonates have also a nutritional role in addition to their fungicidal properties. The new European Directive EU 1009/2019 resolves the problem by banning the phosphonates addition to fertilizers and placing a limit of 0.5% by mass for unintentional addition. However, an official method is not available for phosphonates determination in fertilizers and approval by the European Committee for Standardization (CEN) is necessary in a short time. This review presents an overview about the chemical, biological, analytical and legislative aspects of phosphonates and aims at providing: clarity on the correct nomenclature to avoid misunderstandings; the evaluation of phosphonates properties with the absence of a nutritional role, justifying the ban on adding to fertilizers; a summary of analytical techniques that could be considered by CEN to complete the analytical background for the agricultural use of phosphonates.

Transcriptome Analysis of Zygophyllum xanthoxylum Adaptation Strategies to Phosphate Stress

Soil phosphate (Pi) deficiency is a global issue and a major constraint on plant growth. Plants typically acclimatize to low Pi by enhancing their P utilization and/or P acquisition efficiencies; however, different species have variable preferred strategies. RNA sequencing analysis was performed on the shoots and roots of Zygophyllum xanthoxylum, under 1 day and 10 days of Pi stress, to investigate their adaptation strategies to P deprivation. A total of 364,614 unigenes and 9,270 differentially expressed genes (DEGs) were obtained via transcriptome sequencing. An analysis of the DEGs revealed that under the 10D treatment, anthocyanin synthesis genes were upregulated under Pi stress, whereas gibberellin, ethylene, and cytokinins synthesis genes were upregulated, and abscisic acid synthesis genes were downregulated. Genes related to organic acid synthesis, encoding for purple acid phosphatases (APase) and nucleases (RNase) were upregulated under the 1D and 10D treatments, respectively. Furthermore, genes associated with Pi transport were induced by Pi stress. Zygophyllum xanthoxylum has special P adaptation strategies, the variation trends of genes involved in external P mobilization and acquisition, which were different from that of most other species; however, the expression levels of organophosphorus mobilization related genes, such as APases and RNases, were significantly increased. Meanwhile, PHT2s and TPTs, which distributed Pi to effective sites (e.g., chloroplast), played critical roles in the maintenance of photosynthesis. We speculated that these were economic and energy saving strategies, and there are critical adaptive mechanisms that Z. xanthoxylum employs to cope with deficits in Pi.

Phosphate Uptake and Transport in Plants: An Elaborate Regulatory System

Phosphorus (P) is an essential macronutrient for plant growth and development. Low inorganic phosphate (Pi) availability is a limiting factor for plant growth and yield. To cope with a complex and changing environment, plants have evolved elaborate mechanisms for regulating Pi uptake and use. Recently, the molecular mechanisms of plant Pi signaling have become clearer. Plants absorb Pi from the soil through their roots and transfer Pi to various organs or tissues through phosphate transporters, which are precisely controlled at the transcript and protein levels. Here, we summarize recent progress on the molecular regulatory mechanism of phosphate transporters in Arabidopsis and rice, including the characterization of functional transporters, regulation of transcript levels, protein localization and turnover of phosphate transporters. A more in-depth understanding of plant adaptation to a changing Pi environment will facilitate the genetic improvement of plant P efficiency.