Tightening the Phosphorus Cycle through Phosphorus-Efficient Crop Genotypes

Comparative transcriptomes and WGCNA reveal hub genes for spike germination in different quinoa lines

BACKGROUND

Quinoa, as a new food crop, has attracted extensive attention at home and abroad. However, the natural disaster of spike germination seriously threatens the quality and yield of quinoa. Currently, there are limited reports on the molecular mechanisms associated with spike germination in quinoa.

RESULTS

In this study, we utilized transcriptome sequencing technology and successfully obtained 154.51 Gb of high-quality data with a comparison efficiency of more than 88%, which fully demonstrates the extremely high reliability of the sequencing results and lays a solid foundation for subsequent analysis. Using these data, we constructed a weighted gene co-expression network (WGCNA) related to starch, sucrose, α-amylase, and phenolic acid metabolites, and screened six co-expression modules closely related to spike germination traits. Two of the modules associated with physiological indicators were analyzed in depth, and nine core genes were finally predicted. Further functional annotation revealed four key transcription factors involved in the regulation of dormancy and germination processes: gene LOC110698065, gene LOC110696037, gene LOC110736224, and gene LOC110705759, belonging to the bHLH, NF-YA, MYB, and FAR1 gene families, respectively.

CONCLUSIONS

These results provide clues to identify the core genes involved in quinoa spike germination. This will ultimately provide a theoretical basis for breeding new quinoa varieties with resistance.

Improvement of soil nutrient cycling by dominant plants in natural restoration of heavy metal polluted areas

Referring to the natural succession to restore polluted land is one of the most vital assignments to solving the environmental problems. However, there is little understanding of the natural restoration of nutrient biogeochemical cycles in abandoned land with severe metal pollution. To clarify the nutrient cycling process and the influence of organisms on it, we investigated the magnitude of rhizosphere effects on soil nitrogen (N), phosphorus (P) and sulphur (S) cycles in natural restoration of an abandoned metal mine, as well as the roles of plants and microorganisms in the nutrient cycles. Our data revealed that the rhizosphere had higher levels of ammoniation than non-rhizosphere soil at both stages of restoration. In the early stage, the rhizosphere had greater levels of inorganic phosphorus and organophosphorus solubilisation, as well as sulphite oxidation, compared to non-rhizosphere soil. The bacterial composition influenced the N and S cycles, while the fungal composition had the greatest effect on the P cycles. Furthermore, rhizosphere nutrition cycles and microbial communities altered according plant strategy. Overall, the plants that colonize the early stages of natural recovery demonstrate enhanced restoration of nutrient efficiency. These results contribute to further knowledge of nutrient recovery in mining areas, as well as suggestions for selecting remedial microorganisms and plants in metal-polluted environments.

Growing in phosphorus-impoverished habitats in south-western Australia: How general are phosphorus-acquisition and -allocation strategies among Proteaceae, Fabaceae and Myrtaceae species?

Numerous phosphorus (P)-acquisition and -utilisation strategies have evolved in plants growing in severely P-impoverished environments. Although these strategies have been well characterised for certain taxa, like Proteaceae, P-poor habitats are characterised by a high biodiversity, and we know little about how species in other families cope with P scarcity. We compared the P-acquisition and leaf P-allocation strategies of Fabaceae and Myrtaceae with those of Proteaceae growing in the same severely P-impoverished habitat. Myrtaceae and Fabaceae exhibited multiple P-acquisition strategies: P-mining by carboxylates or phosphatases, P uptake facilitated by carboxylate-releasing neighbours, and dependence on the elevated soil P availability after fire. Surprisingly, not all species showed high photosynthetic P-use efficiency (PPUE). Highly P-efficient species showed positive correlations between PPUE and the proportion of metabolite P (enzyme substrates), and negative correlations between PPUE and phospholipids (cellular membranes) and nucleic acid P (mostly ribosomal RNA), while we found no correlations in less P-efficient species. Overall, we found that Myrtaceae and Fabaceae used a wider range of strategies than Proteaceae to cope with P scarcity, at both the rhizosphere and leaf level. This knowledge is pivotal to better understand the mechanisms underlying plant survival in severely nutrient-impoverished biodiverse ecosystems.

Genotypic Variability in Root Morphology in a Diverse Wheat Genotypes Under Drought and Low Phosphorus Stress

Screening genotypes with optimal root traits presents a promising breeding strategy for enhancing adaptability to abiotic stresses and improving resource use efficiency. This study evaluated root traits of 100 winter wheat genotypes under four treatments: control (C), low phosphorus (LP), PEG-induced drought (D), and a combination of LP and drought (DLP), using a semi-hydroponic phenotyping platform. Significant variations in root traits were observed 65 days after transplanting, with over 80% of traits being significantly affected by drought, phosphorus, or their interactions. Biomass and phosphorus content decreased under LP and drought, while root length and diameter in deeper layers increased, especially under drought stress. Combined stress led to the most severe reductions in biomass, P-content, and leaf number. Phosphorus acquisition efficiency was positively correlated with root length but inversely related to stress tolerance. High heritability traits, such as root number, root length, maximum root depth, leaf number, and biomass, hold potential for breeding programs focused on environmental adaptation, resource efficiency, and yield improvement. The substantial genotypic variation in root morphology under stress conditions highlights the potential for breeding stress-resilient wheat genotypes. This finding lays a foundation for wheat-breeding initiatives aimed at developing genotypes better suited to prevailing environmental conditions.

Belowground cascading biotic interactions trigger crop diversity benefits

Crop diversification practices offer numerous synergistic benefits. So far, research has traditionally been confined to exploring isolated, unidirectional single-process interactions among plants, soil, and microorganisms. Here, we present a novel and systematic perspective, unveiling the intricate web of plant-soil-microbiome interactions that trigger cascading effects. Applying the principles of cascading interactions can be an alternative way to overcome soil obstacles such as soil compaction and soil pathogen pressure. Finally, we introduce a research framework comprising the design of diversified cropping systems by including commercial varieties and crops with resource-efficient traits, the exploration of cascading effects, and the innovation of field management. We propose that this provides theoretical and methodological insights that can reveal new mechanisms by which crop diversity increases productivity.

Phenotypic, Physiological, and Gene Expression Analysis for Nitrogen and Phosphorus Use Efficienies in Three Popular Genotypes of Rice (Oryza sativa Indica)

Crop nitrogen (N) and phosphorus (P) use efficiencies (NUE/PUE) are important to minimize wastage and nutrient pollution, but no improved crop for both is currently available. We addressed them together in rice, in the view of its high consumption of NPK fertilizers. We analyzed 46 morphophysiological parameters for the N/P response in three popular indica genotypes, namely, BPT 5204, Panvel 1, and CR Dhan 301 at low, medium, and normal N/P doses. They include 18 vegetative, 15 physiological, and 13 reproductive parameters. The segregation of significantly N/P-responsive parameters correlating with NUE/PUE revealed 21 NUE, 22 PUE, and 12 common parameters. Feature selection analyses revealed the common high-ranking parameters including the photosynthetic rate at the reproductive stage, tiller number, root-shoot ratio, culm thickness, and flag leaf width. The venn selection using the reported NUE/PUE-related candidate genes in rice revealed five genes in common for both, namely OsIAA3, OsEXPA10, OsCYP75B4, OsSultr3;4, and OsFER2, which were associated with three of the common traits for NUE/PUE. Their expression studies using qRT-PCR revealed the opposite regulation in contrasting genotypes for OsSultr3;4 and OsEXPA10 in N-response and for OsFER2 in P-response, indicating their role in contrasting N/P use efficiencies. Overall, CR Dhan 301 has the highest NUE and PUE followed by Panvel 1 and BPT5204 among the studied genotypes.

Genetic improvement of phosphate-limited photosynthesis for high yield in rice

Low phosphate (Pi) availability decreases photosynthesis, with phosphate limitation of photosynthesis occurring particularly during grain filling of cereal crops; however, effective genetic solutions remain to be established. We previously discovered that rice phosphate transporter OsPHO1;2 controls seed (sink) development through Pi reallocation during grain filling. Here, we find that OsPHO1;2 regulates Pi homeostasis and thus photosynthesis in leaves (source). Loss-of-function of OsPHO1;2 decreased Pi levels in leaves, leading to decreased photosynthetic electron transport activity, CO2 assimilation rate, and early occurrence of phosphate-limited photosynthesis. Interestingly, ectopic expression of OsPHO1;2 greatly increased Pi availability, and thereby, increased photosynthetic rate in leaves during grain filling, contributing to increased yield. This was supported by the effect of foliar Pi application. Moreover, analysis of core rice germplasm resources revealed that higher OsPHO1;2 expression was associated with enhanced photosynthesis and yield potential compared to those with lower expression. These findings reveal that phosphate-limitation of photosynthesis can be relieved via a genetic approach, and the OsPHO1;2 gene can be employed to reinforce crop breeding strategies for achieving higher photosynthetic efficiency.

Phospholipase-mediated phosphate recycling during plant leaf senescence

BACKGROUND

Phosphorus is a macronutrient necessary for plant growth and development and its availability and efficient use affect crop yields. Leaves are the largest tissue that uses phosphorus in plants, and membrane phospholipids are the main source of cellular phosphorus usage.

RESULTS

Here we identify a key process for plant cellular phosphorus recycling mediated by membrane phospholipid hydrolysis during leaf senescence. Our results indicate that over 90% of lipid phosphorus, accounting for more than one-third of total cellular phosphorus, is recycled from senescent leaves before falling off the plants. Nonspecific phospholipase C4 (NPC4) and phospholipase Dζ2 (PLDζ2) are highly induced during leaf senescence, and knockouts of PLDζ2 and NPC4 decrease the loss of membrane phospholipids and delay leaf senescence. Conversely, overexpression of PLDζ2 and NPC4 accelerates the loss of phospholipids and leaf senescence, promoting phosphorus remobilization from senescent leaves to young tissues and plant growth. We also show that this phosphorus recycling process in senescent leaves mediated by membrane phospholipid hydrolysis is conserved in plants.

CONCLUSIONS

These results indicate that PLDζ2- and NPC4-mediated membrane phospholipid hydrolysis promotes phosphorus remobilization from senescent leaves to growing tissues and that the phospholipid hydrolysis-mediated phosphorus recycling improves phosphorus use efficiency in plants.

Selenium-Mediated Shaping of Citrus Rhizobiome for Promotion in Root Growth and Soil Phosphorus Activation

Selenium (Se) has been widely reported to affect plant growth, nutrient cycling, and the rhizobiome. However, how Se shapes the rhizobiome and interacts with plants remains largely elusive. Pot and hydroponic experiments were employed to elucidate the regulatory mechanism of Se in the citrus rhizobiome. Compared to the control, soil Se application significantly increased the root biomass (34.7%) and markedly reduced rhizosphere HCl-P, H2O-P, NaHCO3-IP, and residual-P of citrus, which were related to the variation of citrus rhizobiome. Se primarily enriched Proteobacteria and Actinobacteria as well as the phosphorus (P) functional genes phod and pqqc. Further study revealed that Se altered the metabolite profile of root exudate, particularly enhancing the abundance of l-cyclopentylglycine, cycloleucine, l-proline, l-pipecolic acid, and inositol, which played a key role in reshaping the citrus rhizobiome. These metabolites could serve as both nutrient sources and signaling molecules, thus supporting the growth or chemotaxis of the functional microbes. These bacterial taxa have the potential to solubilize P or stimulate plant growth. These findings provide a novel mechanistic understanding of the intriguing interactions between Se, root exudate, and rhizosphere microbiomes, and demonstrate the potential for utilizing Se to regulate rhizobiome function and enhance soil P utilization in citrus cultivation.

Physiological and molecular responses in phosphorus-hyperaccumulating Polygonum species to high phosphorus exposure

Phosphorus (P)-hyperaccumulators for phytoextraction from P-polluted areas generally show rapid growth and accumulate large amounts of P without any toxicity symptom, which depends on a range of physiological processes and gene expression patterns that have never been explored. We investigated growth, leaf element concentrations, P fractions, photosynthetic traits, and leaf metabolome and transcriptome response in amphibious P-hyperaccumulators, Polygonum hydropiper and P. lapathifolium, to high-P exposure (5 mmol L-1), with 0.05 mmol L-1 as the control. Under high-P exposure, both species demonstrated good growth, allocating more P to metabolite P and inorganic P (Pi) accompanied by high potassium and calcium. The expression of a cluster of unigenes associated with photosynthesis was maintained or increased in P. lapathifolium, explaining the increase in net photosynthetic rate and the rapid growth under high-P exposure. Metabolites of trehalose metabolism, including trehalose 6-phosphate and trehalose, were sharply increased in both species by the high-P exposure, in line with the enhanced expression of associated unigenes, indicating that trehalose metabolic pathway was closely related to high-P tolerance. These findings elucidated the physiological and molecular responses involved in the photosynthesis and trehalose metabolism in P-hyperaccumulators to high-P exposure, and provides potential regulatory pathways to improve the P-phytoextraction capability.

Evolution of the SPX gene family and its role in the response mechanism to low phosphorus stress in self-rooted apple stock

BACKGROUND

Phosphorus plays a key role in plant adaptation to adversity and plays a positive role in the yield and quality formation of apples. Genes of the SPX domain-containing family are widely involved in the regulation of phosphorus signalling networks. However, the mechanisms controlling phosphorus deficiency are not completely understood in self-rooted apple stock.

RESULTS

In this study, 26 members of the apple SPX gene family were identified by genome-wide analysis, and further divided into four subfamilies (SPX, SPX-MFS, SPX-EXS, and SPX-RING) based on their structural features. The chromosome distribution and gene duplications of MdSPXs were also examined. The promoter regions of MdSPXs were enriched for multiple biotic/abiotic stresses, hormone responses and typical P1BS-related elements. Analysis of the expression levels of 26 MdSPXs showed that some members were remarkably induced when subjected to low phosphate (Pi) stress, and in particular MdSPX2, MdSPX3, and MdPHO1.5 exhibited an intense response to low Pi stress. MdSPX2 and MdSPX3 showed significantly divergent expression levels in low Pi sensitive and insensitive apple species. Protein interaction networks were predicted for 26 MdSPX proteins. The interaction of MdPHR1 with MdSPX2, MdSPX3, MdSPX4, and MdSPX6 was demonstrated by yeast two-hybrid assay, suggesting that these proteins might be involved in the Pi-signaling pathway by interacting with MdPHR1.

CONCLUSION

This research improved the understanding of the apple SPX gene family and contribute to future biological studies of MdSPX genes in self-rooted apple stock.

Comparative functional analyses of PHR1, PHL1, and PHL4 transcription factors in regulating Arabidopsis responses to phosphate starvation

To cope with phosphate (Pi) starvation, plants trigger an array of adaptive responses to sustain their growth and development. These responses are largely controlled at transcriptional levels. In Arabidopsis (Arabidopsis thaliana), PHOSPHATE RESPONSE 1 (PHR1) is a key regulator of plant physiological and transcriptional responses to Pi starvation. PHR1 belongs to a MYB-CC-type transcription factor family which contains 15 members. In this PHR1 family, PHR1/PHR1-like 1(PHL1) and PHL2/PHL3 form two distinct modules in regulating plant development and transcriptional responses to Pi starvation. PHL4 is the most closely related member to PHR1. Previously, using the phr1phl4 mutant, we showed that PHL4 is also involved in regulating plant Pi responses. However, the precise roles of PHL1 and PHL4 in regulating plant Pi responses and their functional relationships with PHR1 have not been clearly defined. In this work, we further used the phl1phl4 and phr1phl1phl4 mutants to perform comparative phenotypic and transcriptomic analyses with phr1, phr1phl1, and phr1phl4. The results showed that both PHL1 and PHL4 act redundantly and equally with PHR1 to regulate leaf senescence, Pi starvation induced-inhibition of primary root growth, and accumulation of anthocyanins in shoots. Unlike PHR1 and PHL1, however, the role of PHL4 in maintaining Pi homeostasis is negligible. In regulating transcriptional responses to Pi starvation at genomic levels, both PHL1 and PHL4 play minor roles when acts alone, however, they act synergistically with PHR1. In regulating Pi starvation-responsive genes, PHL4 also function less than PHL1 in terms of the number of the genes it regulates and the magnitude of gene transcription it affects. Furthermore, no synergistic interaction was found between PHL1 and PHL4 in regulating plant response to Pi starvation. Therefore, our results clarified the roles of PHL1 and PHL4 in regulating plant responses to Pi starvation. In addition, this work revealed a new function of these three transcription factors in regulating flowering time.

Unraveling plant-microbe interactions: can integrated omics approaches offer concrete answers?

Advances in high throughput omics techniques provide avenues to decipher plant microbiomes. However, there is limited information on how integrated informatics can help provide deeper insights into plant-microbe interactions in a concerted way. Integrating multi-omics datasets can transform our understanding of the plant microbiome from unspecified genetic influences on interacting species to specific gene-by-gene interactions. Here, we highlight recent progress and emerging strategies in crop microbiome omics research and review key aspects of how the integration of host and microbial omics-based datasets can be used to provide a comprehensive outline of complex crop-microbe interactions. We describe how these technological advances have helped unravel crucial plant and microbial genes and pathways that control beneficial, pathogenic, and commensal plant-microbe interactions. We identify crucial knowledge gaps and synthesize current limitations in our understanding of crop microbiome omics approaches. We highlight recent studies in which multi-omics-based approaches have led to improved models of crop microbial community structure and function. Finally, we recommend holistic approaches in integrating host and microbial omics datasets to achieve precision and efficiency in data analysis, which is crucial for biotic and abiotic stress control and in understanding the contribution of the microbiota in shaping plant fitness.

ZmARF1 positively regulates low phosphorus stress tolerance via modulating lateral root development in maize

Phosphorus (P) deficiency is one of the most critical factors for plant growth and productivity, including its inhibition of lateral root initiation. Auxin response factors (ARFs) play crucial roles in root development via auxin signaling mediated by genetic pathways. In this study, we found that the transcription factor ZmARF1 was associated with low inorganic phosphate (Pi) stress-related traits in maize. This superior root morphology and greater phosphate stress tolerance could be ascribed to the overexpression of ZmARF1. The knock out mutant zmarf1 had shorter primary roots, fewer root tip number, and lower root volume and surface area. Transcriptomic data indicate that ZmLBD1, a direct downstream target gene, is involved in lateral root development, which enhances phosphate starvation tolerance. A transcriptional activation assay revealed that ZmARF1 specifically binds to the GC-box motif in the promoter of ZmLBD1 and activates its expression. Moreover, ZmARF1 positively regulates the expression of ZmPHR1, ZmPHT1;2, and ZmPHO2, which are key transporters of Pi in maize. We propose that ZmARF1 promotes the transcription of ZmLBD1 to modulate lateral root development and Pi-starvation induced (PSI) genes to regulate phosphate mobilization and homeostasis under phosphorus starvation. In addition, ZmERF2 specifically binds to the ABRE motif of the promoter of ZmARF1 and represses its expression. Collectively, the findings of this study revealed that ZmARF1 is a pivotal factor that modulates root development and confers low-Pi stress tolerance through the transcriptional regulation of the biological function of ZmLBD1 and the expression of key Pi transport proteins.

Direct observations of nanoscale brushite dissolution by the concentration-dependent adsorption of phosphate or phytate

With the development of agricultural intensification, phosphorus (P) accumulation in croplands and sediments has resulted in the increasingly widespread interaction between inorganic and organic P species, which has been, previously, underestimated or even ignored. We quantified the nanoscale dissolution kinetics of sparingly soluble brushite (CaHPO4·2H2O, DCPD) over a broad range of phosphate and/or phytate concentrations by using in situ atomic force microscopy (AFM). Compared to water, we found that low concentrations of phosphate (1-1000 µM) or phytate (1-100 µM) inhibited brushite dissolution by slowing single step retraction. However, with increasing phosphate or phytate concentrations to 10 mM, there was a reverse effect of dissolution promotion at brushite-water interfaces. In situ observations of the coupled dissolution-reprecipitation showed that phosphate precipitated more readily than phytate on brushite surfaces, with the formation of amorphous calcium phosphate (ACP). For a fundamental understanding, zeta potential and in situ Raman spectroscopy (RS) revealed that the concentration-dependent dissolution is attributed to the reverse of outer-sphere to inner-sphere adsorption with increasing phosphate or phytate concentrations. In addition, the mineralization of phytate with outer-sphere adsorption by phytase was higher than that with inner-spere adsorption, and the presence of phytate delayed ACP phase transformation to hydroxylapatite (HAP). These in situ observations and analyses may fill the knowledge gaps of interaction between inorganic and organic P species in P-rich terrestrial and aquatic environments, thereby implicating their biogeochemical cycling and the associated availability.

Keystone taxa of phoD-harboring bacteria mediate alkaline phosphatase activity during biochar remediation of Cd-contaminated soil

Phosphorus (P)-modified biochar can efficiently remediate cadmium (Cd)-contaminated soil. However, the mechanisms of responses of alkaline phosphatase (ALP) and phoD-harboring microorganisms, which are notably sensitive to Cd and P, are not clear during the remediation process. In this study, apple (Malus domestica) tree branches were co-pyrolyzed with tripotassium phosphate (K3PO4) to prepare P-modified biochar, which was used to remediate Cd-soil contaminated soil collected near a mine site. The effect of P-modified biochar on the composition of the phoD-harboring microbial community and its mechanism of interacting with ALP were analyzed. The results showed that the application of P-modified biochar to Cd-contaminated soil promoted the co-precipitation of Cd and phosphate and reduced the content of bioavailable Cd by 69.77 %. P-modified biochar improved the complexity and stability of the soil phoD-harboring microbial community. Furthermore, this study clarified that ALP activity was not completely regulated by the abundance of phoD, but Priestia and Massilia that contain phoD genes dominated the activity of ALP in rhizosphere and bulk soils, respectively. It is notable that bioavailable Cd significantly stimulated Priestia, Massilia, and ALP activity. These findings provide a theoretical basis for the application of P-modified biochar to the remediation of soil contaminated with Cd with respect to P functional microorganisms.

Comparative physiological and transcriptomic analysis of two salt-tolerant soybean germplasms response to low phosphorus stress: role of phosphorus uptake and antioxidant capacity

BACKGROUND

Phosphorus (P) and salt stress are common abiotic stressors that limit crop growth and development, but the response mechanism of soybean to low phosphorus (LP) and salt (S) combined stress remains unclear.

RESULTS

In this study, two soybean germplasms with similar salt tolerance but contrasting P-efficiency, A74 (salt-tolerant and P-efficient) and A6 (salt-tolerant and P-inefficient), were selected as materials. By combining physiochemical and transcriptional analysis, we aimed to elucidate the mechanism by which soybean maintains high P-efficiency under salt stress. In total, 14,075 differentially expressed genes were identified through pairwise comparison. PageMan analysis subsequently revealed several significantly enriched categories in the LP vs. control (CK) or low phosphorus + salt (LPS) vs. S comparative combination when compared to A6, in the case of A74. These categories included genes involved in mitochondrial electron transport, secondary metabolism, stress, misc, transcription factors and transport. Additionally, weighted correlation network analysis identified two modules that were highly correlated with acid phosphatase and antioxidant enzyme activity. Citrate synthase gene (CS), acyl-coenzyme A oxidase4 gene (ACX), cytokinin dehydrogenase 7 gene (CKXs), and two-component response regulator ARR2 gene (ARR2) were identified as the most central hub genes in these two modules.

CONCLUSION

In summary, we have pinpointed the gene categories responsible for the LP response variations between the two salt-tolerant germplasms, which are mainly related to antioxidant, and P uptake process. Further, the discovery of the hub genes layed the foundation for further exploration of the molecular mechanism of salt-tolerant and P-efficient in soybean.

Phosphorus-based nanomaterials as a potential phosphate fertilizer for sustainable agricultural development

Phosphorus-based nanomaterials (PNMs) have been reported to have substantial promise for promoting plant growth, improving plant tolerance mechanisms, and increasing resistance to pathogenic organisms. Recent scientific investigation has demonstrated that utilizing PNMs can enhance plant physiological growth, photosynthetic pigments, antioxidant system, metabolism, nutrient absorption, rhizosphere secretion, and soil nutrients activation. Previous research on PNMs mostly concentrated on calcium phosphate, zeolite, and chitosan, with little systematic summarization, demanding a thorough evaluation of PNMs' broader uses. In our current review article, we address the knowledge gap by classifying PNMs according to green synthesis methods and the valence state of phosphorus while elucidating the underlying mechanisms through which these PNMs facilitate plant growth. In addition, we also targeted some strategies to improve the bioavailability of PNMs, offering valuable insights for the future design and safe implementation of PNMs in agricultural practices.

Leaf phosphorus allocation to chemical fractions and its seasonal variation in south-western Australia is a species-dependent trait

South-western Australia is a global biodiversity hotspot and has some of the oldest and most phosphorus (P)-impoverished soils in the world. Proteaceae is one of the dominant P-efficient plant families there, but it is unknown how leaf P concentrations and foliar P allocation of Proteaceae and coexisting dominant plant families vary between seasons and habitats. To investigate this, we selected 18 species from Proteaceae, Myrtaceae and Fabaceae, six from each family, in two habitats from Alison Baird Reserve (32°1'19''S 15°58'52''E) in Western Australia. Total leaf P and nitrogen (N) concentrations, leaf mass per area, photosynthetic rate, pre-dawn leaf water potential and foliar P fractions were determined for each species both at the end of summer (March 2019 and early April 2020) and at the end of winter (September 2019). Soil P availability was also determined for each site. This is the very first study that focused on seasonal changes of foliar P fractions from different P-impoverished environments in three plant families. However, contrary to our expectation, we found little evidence for convergence of foliar P allocation within family, season or habitat. Each species exhibited a specific species-dependent pattern of foliar P allocation, and many species showed differences between seasons. Native plants in south-western Australia converged on a high photosynthetic P-use efficiency, but each species showed its own unique way associated with that outcome.

Non-specific phospholipase C4 hydrolyzes phosphosphingolipids and phosphoglycerolipids and promotes rapeseed growth and yield

Phosphorus is a major nutrient vital for plant growth and development, with a substantial amount of cellular phosphorus being used for the biosynthesis of membrane phospholipids. Here, we report that NON-SPECIFIC PHOSPHOLIPASE C4 (NPC4) in rapeseed (Brassica napus) releases phosphate from phospholipids to promote growth and seed yield, as plants with altered NPC4 levels showed significant changes in seed production under different phosphate conditions. Clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated nuclease 9 (Cas9)-mediated knockout of BnaNPC4 led to elevated accumulation of phospholipids and decreased growth, whereas overexpression (OE) of BnaNPC4 resulted in lower phospholipid contents and increased plant growth and seed production. We demonstrate that BnaNPC4 hydrolyzes phosphosphingolipids and phosphoglycerolipids in vitro, and plants with altered BnaNPC4 function displayed changes in their sphingolipid and glycerolipid contents in roots, with a greater change in glycerolipids than sphingolipids in leaves, particularly under phosphate deficiency conditions. In addition, BnaNPC4-OE plants led to the upregulation of genes involved in lipid metabolism, phosphate release, and phosphate transport and an increase in free inorganic phosphate in leaves. These results indicate that BnaNPC4 hydrolyzes phosphosphingolipids and phosphoglycerolipids in rapeseed to enhance phosphate release from membrane phospholipids and promote growth and seed production.

Potential of root acid phosphatase activity to reduce phosphorus fertilization in maize cultivated in Brazil

It is urgent to mitigate the environmental impacts resulting from agriculture, especially in highly biodiverse and threatened areas, as the Brazilian Cerrado. We aim to investigate whether root acid phosphatase activity is alternative plant strategies for nutrient acquisition in maize genotypes cultivated under fertilized and unfertilized conditions in Brazil, potentially contributing to reducing the use of phosphate fertilizers needed for production. Three experiments were performed: the first was conducted in a glasshouse, with 17 experimental maize inbred lines and two phosphorus (P) treatments; the second in the field, with three maize inbred lines and two treatments, one without fertilization and another with NPK fertilization; and the third was also carried out in the field, with 13 commercial hybrids, grown either under NK or under NPK treatment. Plant variables were measured and tested for the response to fertilization, differences amongst genotypes and response to root acid phosphatase activity. The activity of root acid phosphatase was modulated by the availability of P and nitrogen (N) in the soil and promoted grain filling of commercial hybrids in soils with low P availability. These results demonstrate that it is possible to select genotypes that are more adapted to low soil P availability aiming at organic production, or to use genotypes that have high phosphatase activity under P fertilization to reduce the amount of added P needed for maize production in Brazil.

Resilient and sustainable production of peanut (Arachis hypogaea) in phosphorus-limited environment by using exogenous gamma-aminobutyric acid to sustain photosynthesis

Globally, many low to medium yielding peanut fields have the potential for further yield improvement. Low phosphorus (P) limitation is one of the significant factors curtailing Arachis hypogaea productivity in many regions. In order to demonstrate the effects of gamma-aminobutyric acid (GABA) on peanuts growing under P deficiency, we used a pot-based experiment to examine the effects of exogenous GABA on alleviating P deficiency-induced physiological changes and growth inhibition in peanuts. The key physiological parameters examined were foliar gas exchange, photochemical efficiency, proton motive force, reactive oxygen species (ROS), and adenosine triphosphate (ATP) synthase activity of peanuts under cultivation with low P (LP, 0.5 mM P) and control conditions. During low P, the cyclic electron flow (CEF) maintained the high proton gradient (∆pH) induced by low ATP synthetic activity. Applying GABA during low P conditions stimulated CEF and reduced the concomitant ROS generation and thereby protecting the foliar photosystem II (PSII) from photoinhibition. Specifically, GABA enhanced the rate of electronic transmission of PSII (ETRII) by pausing the photoprotection mechanisms including non-photochemical quenching (NPQ) and ∆pH regulation. Thus, GABA was shown to be effective in restoring peanut growth when encountering P deficiency. Exogenous GABA alleviated two symptoms (increased root-shoot ratio and photoinhibition) of P-deficient peanuts. This is possibly the first report of using exogenous GABA to restore photosynthesis and growth under low P availability. Therefore, foliar applications of GABA could be a simple, safe and effective approach to overcome low yield imposed by limited P resources (low P in soils or P-fertilizers are unavailable) for sustainable peanut cultivation and especially in low to medium yielding fields.

Ideotype breeding for crop adaptation to low phosphorus availability on extensive organic farms

Organic farming in extensive production regions, such as the Canadian prairies have a particularly difficult challenge of replenishing soil reserves of phosphorus (P). Organic grains are exported off the farm while resupply of lost P is difficult due to limited availability of animal manures and low solubility of rock organic fertilizers. As a result, many organic farms on the prairies are deficient in plant-available P, leading to productivity breakdown. A portion of the solution may involve crop genetic improvement. A hypothetical 'catch and release' wheat ideotype for organic production systems is proposed to (i) enhance P uptake and use efficiency but (ii) translocate less P from the vegetative biomass into the grain. Root traits that would improve P uptake efficiency from less-available P pools under organic production are explored. The need to understand and classify 'phosphorus use efficiency' using appropriate indices for organic production is considered, as well as the appropriate efficiency indices for use if genetically selecting for the proposed ideotype. The implications for low seed P and high vegetative P are considered from a crop physiology, environmental, and human nutrition standpoint; considerations that are imperative for future feasibility of the ideotype.

Involvement of the 4-coumarate:coenzyme A ligase 4CL4 in rice phosphorus acquisition and rhizosphere microbe recruitment via root growth enlargement

MAIN CONCLUSION

The 4-coumarate:coenzyme A ligase 4CL4 is involved in enhancing rice P acquisition and use in acid soil by enlarging root growth and boosting functional rhizosphere microbe recruitment. Rice (Oryza sativa L.) cannot easily acquire phosphorus (P) from acid soil, where root growth is inhibited and soil P is fixed. The combination of roots and rhizosphere microbiota is critical for plant P acquisition and soil P mobilization, but the associated molecular mechanism in rice is unclear. 4CL4/RAL1 encodes a 4-coumarate:coenzyme A ligase related to lignin biosynthesis in rice, and its dysfunction results in a small rice root system. In this study, soil culture and hydroponic experiments were conducted to examine the role of RAL1 in regulating rice P acquisition, fertilizer P use, and rhizosphere microbes in acid soil. Disruption of RAL1 markedly decreased root growth. Mutant rice plants exhibited decreased shoot growth, shoot P accumulation, and fertilizer P use efficiency when grown in soil-but not under hydroponic conditions, where all P is soluble and available for plants. Mutant ral1 and wild-type rice rhizospheres had distinct bacterial and fungal community structures, and wild-type rice recruited some genotype-specific microbial taxa associated with P solubilization. Our results highlight the function of 4CL4/RAL1 in enhancing rice P acquisition and use in acid soil, namely by enlarging root growth and boosting functional rhizosphere microbe recruitment. These findings can inform breeding strategies to improve P use efficiency through host genetic manipulation of root growth and rhizosphere microbiota.

Exogenous Melatonin Enhances the Low Phosphorus Tolerance of Barley Roots of Different Genotypes

Melatonin (N-acetyl-5-methoxytryptamine) plays an important role in plant growth and development, and in the response to various abiotic stresses. However, its role in the responses of barley to low phosphorus (LP) stress remains largely unknown. In the present study, we investigated the root phenotypes and metabolic patterns of LP-tolerant (GN121) and LP-sensitive (GN42) barley genotypes under normal P, LP, and LP with exogenous melatonin (30 μM) conditions. We found that melatonin improved barley tolerance to LP mainly by increasing root length. Untargeted metabolomic analysis showed that metabolites such as carboxylic acids and derivatives, fatty acyls, organooxygen compounds, benzene and substituted derivatives were involved in the LP stress response of barley roots, while melatonin mainly regulated indoles and derivatives, organooxygen compounds, and glycerophospholipids to alleviate LP stress. Interestingly, exogenous melatonin showed different metabolic patterns in different genotypes of barley in response to LP stress. In GN42, exogenous melatonin mainly promotes hormone-mediated root growth and increases antioxidant capacity to cope with LP damage, while in GN121, it mainly promotes the P remobilization to supplement phosphate in roots. Our study revealed the protective mechanisms of exogenous MT in alleviating LP stress of different genotypes of barley, which can be used in the production of phosphorus-deficient crops.

Engineering microalgae for water phosphorus recovery to close the phosphorus cycle

As a finite and non-renewable resource, phosphorus (P) is essential to all life and crucial for crop growth and food production. The boosted agricultural use and associated loss of P to the aquatic environment are increasing environmental pollution, harming ecosystems, and threatening future global food security. Thus, recovering and reusing P from water bodies is urgently needed to close the P cycle. As a natural, eco-friendly, and sustainable reclamation strategy, microalgae-based biological P recovery is considered a promising solution. However, the low P-accumulation capacity and P-removal efficiency of algal bioreactors restrict its application. Herein, it is demonstrated that manipulating genes involved in cellular P accumulation and signalling could triple the Chlamydomonas P-storage capacity to ~7% of dry biomass, which is the highest P concentration in plants to date. Furthermore, the engineered algae could recover P from wastewater almost three times faster than the unengineered one, which could be directly used as a P fertilizer. Thus, engineering genes involved in cellular P accumulation and signalling in microalgae could be a promising strategy to enhance P uptake and accumulation, which have the potential to accelerate the application of algae for P recovery from the water body and closing the P cycle.

Allelic Variation in GmPAP14 Alters Gene Expression to Affect Acid Phosphatase Activity in Soybean

Improvement in acid phosphatase (APase) activity is considered as an important approach to enhance phosphorus (P) utilization in crops. Here, GmPAP14 was significantly induced by low P (LP), and its transcription level in ZH15 (P efficient soybean) was higher than in NMH (P inefficient soybean) under LP conditions. Further analyses demonstrated that there were several variations in gDNA (G-GmPAP14Z and G-GmPAP14N) and the promoters (P-GmPAP14Z and P-GmPAP14N) of GmPAP14, which might bring about differential transcriptional levels of GmPAP14 in ZH15 and NMH. Histochemical staining measurements revealed that a stronger GUS signal was present in transgenic Arabidopsis with P-GmPAP14Z under LP and normal P (NP) conditions compared with the P-GmPAP14N plant. Functional research demonstrated that transgenic Arabidopsis with G-GmPAP14Z had a higher level of GmPAP14 expression than the G-GmPAP14N plant. Meanwhile, higher APase activity was also observed in the G-GmPAP14Z plant, which led to increases in shoot weight and P content. Additionally, validation of variation in 68 soybean accessions showed that varieties with Del36 displayed higher APase activities than the del36 plant. Thus, these results uncovered that allelic variation in GmPAP14 predominantly altered gene expression to influence APase activity, which provided a possible direction for research of this gene in plants.

PHOSPHATE RESPONSE 1 family members act distinctly to regulate transcriptional responses to phosphate starvation

To sustain growth when facing phosphate (Pi) starvation, plants trigger an array of adaptive responses that are largely controlled at transcriptional levels. In Arabidopsis (Arabidopsis thaliana), the four transcription factors of the PHOSPHATE RESPONSE 1 (PHR1) family, PHR1 and its homologs PHR1-like 1 (PHL1), PHL2, and PHL3 form the central regulatory system that controls the expression of Pi starvation-responsive (PSR) genes. However, how each of these four proteins function in regulating the transcription of PSR genes remains largely unknown. In this work, we performed comparative phenotypic and transcriptomic analyses using Arabidopsis mutants with various combinations of mutations in these four genes. The results showed that PHR1/PHL1 and PHL2/PHL3 do not physically interact with each other and function as two distinct modules in regulating plant development and transcriptional responses to Pi starvation. In the PHR1/PHL1 module, PHR1 plays a dominant role, whereas, in the PHL2/PHL3 module, PHL2 and PHL3 contribute similarly to the regulation of PSR gene transcription. By analyzing their common and specific targets, we showed that these PHR proteins could function as both positive and negative regulators of PSR gene expression depending on their targets. Some interactions between PHR1 and PHL2/PHL3 in regulating PSR gene expression were also observed. In addition, we identified a large set of defense-related genes whose expression is not affected in wild-type plants but is altered in the mutant plants under Pi starvation. These results increase our understanding of the molecular mechanism underlying plant transcriptional responses to Pi starvation.

Deciphering Interactions between Phosphorus Status and Toxic Metal Exposure in Plants and Rhizospheres to Improve Crops Reared on Acid Soil

Acid soils are characterized by deficiencies in essential nutrient elements, oftentimes phosphorus (P), along with toxicities of metal elements, such as aluminum (Al), manganese (Mn), and cadmium (Cd), each of which significantly limits crop production. In recent years, impressive progress has been made in revealing mechanisms underlying tolerance to high concentrations of Al, Mn, and Cd. Phosphorus is an essential nutrient element that can alleviate exposure to potentially toxic levels of Al, Mn, and Cd. In this review, recent advances in elucidating the genes responsible for the uptake, translocation, and redistribution of Al, Mn, and Cd in plants are first summarized, as are descriptions of the mechanisms conferring resistance to these toxicities. Then, literature highlights information on interactions of P nutrition with Al, Mn, and Cd toxicities, particularly possible mechanisms driving P alleviation of these toxicities, along with potential applications for crop improvement on acid soils. The roles of plant phosphate (Pi) signaling and associated gene regulatory networks relevant for coping with Al, Mn, and Cd toxicities, are also discussed. To develop varieties adapted to acid soils, future work needs to further decipher involved signaling pathways and key regulatory elements, including roles fulfilled by intracellular Pi signaling. The development of new strategies for remediation of acid soils should integrate the mechanisms of these interactions between limiting factors in acid soils.

Phosphorus acquisition strategies of wheat are related to biochar types added in cadmium-contaminated soil: Evidence from soil zymography and root morphology

Biochar application for the remediation of cadmium (Cd)-contaminated soils may result in a relative deficiency of phosphorus (P) due to the disruption of soil nutrient balance. However, the P acquisition strategies of plants in such situation are still unclear. In this study, analyses on soil zymography and root morphology were combined for the first time to investigate the effects of pristine and P-modified biochars from apple tree branches on the P acquisition strategies of wheat under Cd stress. The results show that the application of pristine biochar exacerbated the soil's relative P deficiency. Wheat was forced to improve foraging for P by forming longer and thinner roots (average diameter 0.284 mm) as well as releasing more phosphatase to promote P mobilization in the soil. Moreover, bioavailable Cd affected the P acquisition strategies of wheat through stimulating the release of phosphatase from roots. The P-modified biochar maintained high levels of Olsen-P (>100 mg kg^-1) in the soil over time by slow release, avoiding the creation of relative P deficiency in the soil; and increased the average root diameter (0.338 mm) and growth performance index, which promoted shoot growth (length and biomass). Furthermore, the P-modified biochar reduced DTPA-extracted Cd concentration in soils by 79.8 % (pristine biochar by 26.9 %), and decreased the Cd translocation factor from root to shoot as well as Cd concentration in the shoots. Therefore, P-modified biochar has a great potential to regulate the soil element balance (carbon, nitrogen, and P), promote wheat growth, and remediate the Cd-contaminated soil.

Genome-wide identification, evolution, and expression analysis of carbonic anhydrases genes in soybean (Glycine max)

Carbonic anhydrases (CAs), as zinc metalloenzymes, are ubiquitous in nature and play essential roles in diverse biological processes. Although CAs have been broadly explored and studied, comprehensive characteristics of CA gene family members in the soybean (Glycine max) are still lacking. A total of 35 CA genes (GmCAs) were identified; they distributed on sixteen chromosomes of the soybean genome and can be divided into three subfamilies (α-type, β-type, and γ-type). Bioinformatics analysis showed that the specific GmCA gene subfamily or clade exhibited similar characteristics and that segmental duplications took the major role in generating new GmCAs. Furthermore, the synteny and evolutionary constraints analyses of CAs among soybean and distinct species provided more detailed evidence for GmCA gene family evolution. Cis-element analysis of promoter indicated that GmCAs may be responsive to abiotic stress and regulate photosynthesis. Moreover, the expression patterns of GmCAs varied in different tissues at diverse developmental stages in soybean. Additionally, we found that eight representative GmCAs may be involved in the response of soybean to low phosphorus stress. The systematic investigation of the GmCA gene family in this study will provide a valuable basis for further functional research on soybean CA genes.

Integrated multi-omics reveals the molecular mechanisms underlying efficient phosphorus use under phosphate deficiency in elephant grass (Pennisetum purpureum)

Phosphorus (P) is an essential macronutrient element for plant growth, and deficiency of inorganic phosphate (Pi) limits plant growth and yield. Elephant grass (Pennisetum purpureum) is an important fodder crop cultivated widely in tropical and subtropical areas throughout the world. However, the mechanisms underlying efficient P use in elephant grass under Pi deficiency remain poorly understood. In this study, the physiological and molecular responses of elephant grass leaves and roots to Pi deficiency were investigated. The results showed that dry weight, total P concentration, and P content decreased in Pi-deprived plants, but that acid phosphatase activity and P utilization efficiency (PUE) were higher than in Pi-sufficient plants. Regarding Pi starvation-responsive (PSR) genes, transcriptomics showed that 59 unigenes involved in Pi acquisition and transport (especially 18 purple acid phosphatase and 27 phosphate transporter 1 unigenes) and 51 phospholipase unigenes involved in phospholipids degradation or Pi-free lipids biosynthesis, as well as 47 core unigenes involved in the synthesis of phenylpropanoids and flavonoids, were significantly up-regulated by Pi deprivation in leaves or roots. Furthermore, 43 unigenes related to Pi-independent- or inorganic pyrophosphate (PPi)-dependent bypass reactions were markedly up-regulated in Pi-deficient leaves, especially five UDP-glucose pyrophosphorylase and 15 phosphoenolpyruvate carboxylase unigenes. Consistent with PSR unigene expression changes, metabolomics revealed that Pi deficiency significantly increased metabolites of Pi-free lipids, phenylpropanoids, and flavonoids in leaves and roots, but decreased phospholipid metabolites. This study reveals the mechanisms underlying the responses to Pi starvation in elephant grass leaves and roots, which provides candidate unigenes involved in efficient P use and theoretical references for the development of P-efficient elephant grass varieties.

Genome wide association studies for acid phosphatase activity at varying phosphorous levels in Brassica juncea L

Acid phosphatases (Apases) are an important group of enzymes that hydrolyze soil and plant phosphoesters and anhydrides to release Pi (inorganic phosphate) for plant acquisition. Their activity is strongly correlated to the phosphorus use efficiency (PUE) of plants. Indian mustard (Brassica juncea L. Czern & Coss) is a major oilseed crop that also provides protein for the animal feed industry. It exhibits low PUE. Understanding the genetics of PUE and its component traits, especially Apase activity, will help to reduce Pi fertilizer application in the crop. In the present study, we evaluated 280 genotypes of the diversity fixed foundation set of Indian mustard for Apase activity in the root (RApase) and leaf (LApase) tissues at three- low (5µM), normal (250µM) and high (1mM) Pi levels in a hydroponic system. Substantial effects of genotype and Pi level were observed for Apase activity in both tissues of the evaluated lines. Low Pi stress induced higher mean RApase and LApase activities. However, mean LApase activity was relatively more than mean RApase at all three Pi levels. JM06016, IM70 and Kranti were identified as promising genotypes with higher LApase activity and increased R/S at low Pi. Genome-wide association study revealed 10 and 4 genomic regions associated with RApase and LApase, respectively. Annotation of genomic regions in the vicinity of peak associated SNPs allowed prediction of 15 candidates, including genes encoding different family members of the acid phosphatase such as PAP10 (purple acid phosphatase 10), PAP16, PNP (polynucleotide phosphorylase) and AT5G51260 (HAD superfamily gene, subfamily IIIB acid phosphatase) genes. Our studies provide an understanding of molecular mechanism of the Apase response of B. juncea at varying Pi levels. The identified SNPs and candidate genes will support marker-assisted breeding program for improving PUE in Indian mustard. This will redeem the crop with enhanced productivity under restricted Pi reserves and degrading agro-environments.

Interception of fertile soil phosphorus leaching with immobilization materials: Recent progresses, opportunities and challenges

The non-point source pollution induced by phosphorus (P) leaching from fertile soils is accelerating the eutrophication phenomena in aqueous ecosystems. Herein, to alleviate and intercept the P leaching from the fertile soils, diverse P immobilization materials (PIM) which can transform labile P into stable P via a range of physicochemical and biological interactions have been adopted and received increasing research interest. However, the remediation mechanisms of different PIMs were complex and vary with soil properties and PIM application methods. In this review, the P fraction and mobility characteristics of different fertile soils were first introduced. Then, three kinds of PIM including inorganic materials (e.g., clay minerals and red mud), organic materials (e.g., polyacrylamide), and composites (e.g., modified biochar) applied in soil P leaching interception were concluded. The key factors (i.e., soil pH, soil texture, organic matter content and variable soil moisture) influencing PIM performance and potential PIMs used for reducing soil P leaching were also introduced. Current review can favor for proposing more suitable and insightful strategies to regulate the fertile soil P and achieve the dual goals of improving the crop land quality and yield, and preventing agricultural non-point source pollution.

Evaluation for phosphorus accumulation and removal capability of nine species in the Polygonaceae to excavate amphibious superstars used for phosphorus-phytoextraction

Reducing excessive phosphorus (P) from both soils and eutrophic waters is attractive to achieve environmental P balance, and P-phytoextraction by amphibious plants with great biomass and P uptake is an amazing method, as already reported for P-accumulating plant, Polygonum hydropiper. However, it is still unknown how widespread high P tolerance and great P accumulation is among species in the Polygonaceae, and if there are new amphibious superstars used for P-phytoextraction. We used six Polygonum species and three non-Polygonum species to compare P accumulation and removal capability in hydroponics and soils with different P treatments. In high P hydroponics, all species showed superiority in growth and P accumulation without P toxicity, except for F. multiflora. In high P soils, all species showed much better growth performance with green leaves at 8 weeks, with shoot biomass being 3.60-29.49 g plant^-1. At 8 weeks, Polygonum species displayed obviously higher shoot P accumulation (31.32-152.37 mg plant^-1), P extraction ratio (3.16%-15.36%), maximum potential P removal (13.89-67.59 kg ha^-1), and much lower plant effective number (7-32) than non-Polygonum species under high P soils. Besides, P. lapathifolium, P. divaricatum and P. orientale ranked the top three in growth with P concentration more than 10 mg g^-1 dry weight in hydroponics and showed dominant advantage in P accumulation and P removal from high P soils. Through the cluster analysis, P. lapathifolium was always separated into a class, and P. divaricatum and P. orientale more likely clustered together. It is therefore that P. lapathifolium, P. divaricatum and P. orientale are tolerant to high P and attractive in P accumulation and P removal from high P waters and soils, and thus can be used as new amphibious superstars for P-phytoextraction, particularly P. lapathifolium.

Genetic variation in morphological traits in cotton and their roles in increasing phosphorus-use-efficiency in response to low phosphorus availability

Phosphorus (P) is an essential macronutrient required for fundamental processes in plants. Trait plasticity is crucial for plant adaptation to environmental change. Variations in traits underlie diverse phosphorus (P) acquisition strategies among plants. Nevertheless, how the intraspecific plasticity and integration of morphological traits contribute to Phosphorus-Use-Efficiency (PUE) in cotton is unknown. In this study, 25 morphological traits were evaluated in 384 cotton genotypes grown with low P (LP, 10μmol. L^-1) and normal nutrition (CK, 500μmol. L^-1) to assess the genetic variability of morphological traits and their relationship to phosphorus use efficiency. Results revealed a large genetic variation in mostly morphological traits under low P. Significant enhancement in root traits and phosphorus efficiency-related traits like PUE was observed at LP as compared to CK conditions. In response to low P availability, cotton genotypes showed large plasticity in shoot and total dry biomass, phosphorus, and nitrogen efficiency-related traits (i.e., phosphorus/nitrogen use efficiency, phosphorus/nitrogen uptake efficiency), and most root traits, but a limited response in root dry biomass, taproot length, root surface area, root volume, and SPAD value. In addition, significant correlations were observed between PUtE (phosphorus uptake efficiency), NUE (nitrogen use efficiency), TDB (total dry biomass), and RTD (root tissue density) with PUE under both P supply level and phosphorus stress index, which may be a key indicator for improving PUE under LP conditions. Most root traits are most affected by genotypes than nutrition level. Conserved PUE is more affected by the nutrition level than the genotype effect. Principal component analysis depicted the comprehensive indicators under two P supply conditions were mainly reflected in root-related traits and morphological indicators such as dry matter biomass. These results indicate that interspecific variations exist within these cotton genotypes and traits. Our study provides suggestions for future research to enhance the ability of the earth system model to predict how crops respond to environmental interference and provide target quality for cotton breeding in phosphorus-deficient areas.

Sustainable Cannabis Nutrition: Elevated root-zone phosphorus significantly increases leachate P and does not improve yield or quality

Phosphorus (P) is an essential but often over-applied nutrient in agricultural systems. Because of its detrimental environmental effects, P fertilization is well studied in crop production. Controlled environment agriculture allows for precise control of root-zone P and has the potential to improve sustainability over field agriculture. Medical Cannabis is uniquely cultivated for the unfertilized female inflorescence and mineral nutrition can affect the yield and chemical composition of these flowers. P typically accumulates in seeds, but its partitioning in unfertilized Cannabis flowers is not well studied. Here we report the effect of increasing P (25, 50, and 75 mg P per L) in continuous liquid fertilizer on flower yield, cannabinoid concentration, leachate P, nutrient partitioning, and phosphorus use efficiency (PUE) of a high-CBD Cannabis variety. There was no significant effect of P concentration on flower yield or cannabinoid concentration, but there were significant differences in leachate P, nutrient partitioning, and PUE. Leachate P increased 12-fold in response to the 3-fold increase in P input. The P concentration in the unfertilized flowers increased to more than 1%, but this did not increase yield or quality. The fraction of P in the flowers increased from 25 to 65% and PUE increased from 31 to 80% as the as the P input decreased from 75 to 25 mg per L. Avoiding excessive P fertilization can decrease the environmental impact of Cannabis cultivation.

New Insights into the Phosphorus Acquisition Capacity of Chilean Lowland Quinoa Roots Grown under Low Phosphorus Availability

Reducing phosphate fertilizer inputs while increasing food nutritional quality has been posited as a major challenge to decrease human undernourishment and ensure food security. In this context, quinoa has emerged as a promising crop due to its ability to tolerate different stress conditions and grow in marginal soils with low nutrient content, in addition to the exceptional nutritional quality of its grains. However, there is scarce information about the phosphorus acquisition capacity of quinoa roots. This work aimed to provide new insights into P acquisition and functional root traits, such as root biomass, rhizosphere pH, carboxylate exudation, and acid phosphatase activity of thirty quinoa genotypes grown under P limiting conditions (7 mg P kg^-1). Significant genotypic variation was observed among genotypes, with average P accumulation ranging from 1.2 to 11.8 mg. The shoot biomass production varied more than 14 times among genotypes and was correlated with the P accumulation on shoots (r = 0.91). Despite showing high variability in root traits, only root biomass production highly correlated with P acquisition (r = 0.77), suggesting that root growth/morphology rather than the measured biochemical activity possesses a critical role in the P nutrition of quinoa.

The spatio-temporal change in soil P and P-solubilizing bacteria under clover mulching in apple orchards of Loess Plateau

Cover crop is an effective practice for improving soil quality and increase soil nutrients. However, the spatio-temporal change of soil phosphorus (P) components and P-solubilizing microorganisms in the process of grass succession is not evident. Here, we studied the variation of soil P components and P-solubilizing bacteria at 0-60 cm soil layer under clean tillage (CT) and white clover (WC, Trifolium repens L.) grown for 5, 9, and 14 years in an apple test station on the Loess Plateau, China. This study suggested that clover cover could effectively increase the total P, available P (AP), microbial P, organic P (Po), and inorganic P (Al-P, Ca₂-P, Ca₈-P and Fe-P) in topsoil (0-20 cm) and AP, Po and inorganic P at 20-40 cm soil layer to improve the soil P bioavailability. The effects of WC living mulch on the soil P forms were more significant with the increase in grass growing years, but this effect was difficult to extend to deep soil. In addition, the WC treatments were beneficial to the growth of P-solubilizing microorganisms in surface soil and improved the alkaline phosphatase activity at 0-40 cm soil layer, mainly including Bacillus, Bradyrhizobium, Nocardioides, Sphingomonas and Streptomyces. This study provided a perspective on the dynamic changes of soil P forms and P-solubilizing microorganisms and under long-term cover crop.

Wheat heat shock factor TaHsfA2d contributes to plant responses to phosphate deficiency

Phosphate (Pi) availability has become a major constraint limiting crop growth and production. Heat shock factors (Hsfs) play important roles in mediating plant resistance to various environmental stresses, including heat, drought and salinity. However, whether members of the Hsf family are involved in the transcriptional regulation of plant responses to Pi insufficiency has not been reported. Here, we identified that TaHsfA2d, a member of the heat shock factor family, was strongly repressed by Pi deficiency. Overexpressing TaHsfA2d-4A in Arabidopsis results in significantly enhanced sensitivity to Pi deficiency, evidenced by increased anthocyanin content, decreased proliferation and elongation of lateral roots, and reduced Pi uptake. Furthermore, RNA-seq analyses showed that TaHsfA2d-4A functions through up-regulation of a number of genes involved in stress responses and flavonoid biosynthesis. Collectively, these results provide evidence that TaHsfA2d participates in the regulation of Pi deficiency stress, and that TaHsfA2d could serve as a valuable gene for genetic modification of crop tolerance to Pi starvation.

Involvement of PtPHR1 in phosphates starvation-induced alkaloid biosynthesis in Pinellia ternata (Thunb.) Breit

Nowadays, because of the great benefit to human health, more and more efforts have been made to increase the production of alkaloids in Pinellia ternata (Thunb.) Breit. Phosphate (Pi) plays a critical role in plant growth and development, as well as secondary metabolism. However, its effect and regulation mechanism of Pi signaling on alkaloid biosynthesis call for further exploration. Here, we reported that Pi starvation could induce alkaloid accumulation in P. ternata. We cloned a cDNA sequence encoding PtPHR1 from P. ternata, which was further identified by nuclear localization, transcription activity, and binding ability to the PHR1-binding sequence. We found that the transformation of PtPHR1 into the Arabidopsis phr1 mutant (designated as PtPHR1OE/phr1) led to the rescue of the phenotype of the phr1 mutant to that of the wild-type, including the expression level of Pi starvation-induced genes and anthocyanin accumulation. The combination of these biochemical and genetic experiments indicated that PtPHR1 was intended to have a role similar to that of AtPHR1 in Pi signaling and metabolic responses. Interestingly, we found that Pi starvation also induced the production of benzoic acid, an intermediate in the biosynthetic pathway of phenylpropylamino alkaloids. Furthermore, this induction effect was impaired in the phr1 mutant but partly recovered in PtPHR1OE/phr1 plants. Together, our data suggest that Pi starvation promoted benzoic acid-derived alkaloid biosynthesis in P. ternata under the control of PtPHR1. Our finding that PtPHR1 is involved in the regulation of Pi signaling on alkaloid biosynthesis shows a direct link between the Pi nutrient supply and secondary metabolism.

Legacies at work: plant-soil-microbiome interactions underpinning agricultural sustainability

Agricultural intensification has had long-lasting negative legacies largely because of excessive inputs of agrochemicals (e.g., fertilizers) and simplification of cropping systems (e.g., continuous monocropping). Conventional agricultural management focuses on suppressing these negative legacies. However, there is now increasing attention for creating positive above- and belowground legacies through selecting crop species/genotypes, optimizing temporal and spatial crop combinations, improving nutrient inputs, developing intelligent fertilizers, and applying soil or microbiome inoculations. This can lead to enhanced yields and reduced pest and disease pressure in cropping systems, and can also mitigate greenhouse gas emissions and enhance carbon sequestration in soils. Strengthening positive legacies requires a deeper understanding of plant-soil-microbiome interactions and innovative crop, input, and soil management which can help to achieve agricultural sustainability.

Phosphorus removal and recovery: state of the science and challenges

Phosphorus is one of the main nutrients required for all life. Phosphorus as phosphate form plays an important role in different cellular processes. Entrance of phosphorus in the environment leads to serious ecological problems including water quality problems and soil pollution. Furthermore, it may cause eutrophication as well as harmful algae blooms (HABs) in aquatic environments. Several physical, chemical, and biological methods have been presented for phosphorus removal and recovery. In this review, there is an overview of phosphorus role in nature provided, available removal processes are discussed, and each of them is explained in detail. Chemical precipitation, ion exchange, membrane separation, and adsorption can be listed as the most used methods. Identifying advantages of these technologies will allow the performance of phosphorus removal systems to be updated, optimized, evaluate the treatment cost and benefits, and support select directions for further action. Two main applications of biochar and nanoscale materials are recommended.

A natural uORF variant confers phosphorus acquisition diversity in soybean

Phosphorus (P) is an essential element for all organisms. Because P fertilizers are a non-renewable resource and high fixation in soils, sustainable agriculture requires researchers to improve crop P acquisition efficiency. Here, we report a strong association signal at a locus of CPU1 (component of phosphorus uptake 1), from a genome-wide association study of P acquisition efficiency in a soybean core collection grown in the field. A SEC12-like gene, GmPHF1, is identified as the causal gene for CPU1. GmPHF1 facilitates the ER (endoplasmic reticulum) exit of the phosphate transporter, GmPT4, to the plasma membrane of root epidermal cells. A common SNP in an upstream open reading frame (uORF) of GmPHF1, which alters the abundance of GmPHF1 in a tissue-specific manner, contributes to P acquisition diversity in soybean. A natural genetic variation conditions diversity in soybean P acquisition, which can be used to develop P-efficient soybean genotypes.

Combining analyses of metabolite profiles and phosphorus fractions to explore high phosphorus utilization efficiency in maize

Phosphorus (P) limitation is a significant factor restricting crop production in agricultural systems, and enhancing the internal P utilization efficiency (PUE) of crops plays an important role in ensuring sustainable P use in agriculture. To better understand how P is remobilized to affect crop growth, we first screened P-efficient (B73 and GEMS50) and P-inefficient (Liao5114) maize genotypes at the same shoot P content, and then analyzed P pools and performed non-targeted metabolomic analyses to explore changes in cellular P fractions and metabolites in maize genotypes with contrasting PUE. We show that lipid P and nucleic acid P concentrations were significantly lower in lower leaves of P-efficient genotypes, and these P pools were remobilized to a major extent in P-efficient genotypes. Broad metabolic alterations were evident in leaves of P-efficient maize genotypes, particularly affecting products of phospholipid turnover and phosphorylated compounds, and the shikimate biosynthesis pathway. Taken together, our results suggest that P-efficient genotypes have a high capacity to remobilize lipid P and nucleic acid P and promote the shikimate pathway towards efficient P utilization in maize.

Plant phosphorus acquisition links to phosphorus transformation in the rhizospheres of soybean and rice grown under CO2 and temperature co-elevation

Climate change is likely to influence the reservoir of soil phosphorus (P) as plants adaptably respond to climate change in the perspective of P acquisition capability via root proliferation and mediating biochemical properties in the rhizosphere to access various soil P fractions. It is particularly important in cropping soils where P fertilizer plus soil P is required to synchronize crop P demand for the production sustainability under climate change. However, few studies have examined the effect of CO2 and temperature co-elevation on plant P acquisition, P fractions and relevant functional genes in the rhizosphere of different crops. Thus, the present study investigated the effect of elevated CO2 and warming on P uptake of soybean and rice grown in Mollisols, and soil P fractions and relevant biochemical properties and microbial functions in the rhizosphere with or without P application. Open-top chambers were used to achieve elevated CO2 of 700 ppm combined with warming (+ 2 °C above ambient temperature). CO2 and temperature co-elevation increased P uptake in soybean by 23% and 28% under the no-P and P application treatments, respectively; and in rice, by 34% and 13%, respectively. CO2 and temperature co-elevation depleted organic P in the rhizosphere of soybean, but increased in the rhizosphere of rice. The phosphatase activity negatively correlated with organic P in the highland soil while positively in the paddy soil. The P mineralization likely occurs in soybean-grown soils under climate change, while the P immobilization in paddy soils. CO2 and temperature co-elevation increased the copy numbers of P functional genes including phoD, phoC, pstS and phnX, in soils with P application. These results indicate that the P application would be requested to satisfy the increased P demand in soybean under climate change, but not in rice in paddy soils where soil P availability is sufficient. Therefore, elevated CO2 and temperature facilitated the crop P uptake via biochemical and microbial pathways, and P functional genes played an essential role in the conversion of P.

Phosphorus Acquisition and Utilization in Plants

Tremendous progress has been made on molecular aspects of plant phosphorus (P) nutrition, often without heeding information provided by soil scientists, ecophysiologists, and crop physiologists. This review suggests ways to integrate information from different disciplines. When soil P availability is very low, P-mobilizing strategies are more effective than mycorrhizal strategies. Soil parameters largely determine how much P roots can acquire from P-impoverished soil, and kinetic properties of P transporters are less important. Changes in the expression of P transporters avoid P toxicity. Plants vary widely in photosynthetic P-use efficiency, photosynthesis per unit leaf P. The challenge is to discover what the trade-offs are of different patterns of investment in P fractions. Less investment may save P, but are costs incurred? Are these costs acceptable for crops? These questions can be resolved only by the concerted action of scientists working at both molecular and physiological levels, rather than pursuing these problems independently.

The Dynamics of Phosphorus Uptake and Remobilization during the Grain Development Period in Durum Wheat Plants

Post-anthesis phosphorus (P) uptake and the remobilization of the previously acquired P are the principal sources of grain P nutrition in wheat. However, how the acquired P reaches the grains and its partitioning at the whole plant level remain poorly understood. Here, the temporal dynamics of the newly acquired P in durum wheat organs and its allocation to grain were examined using pulse-chase 32P-labeling experiments at 5 and 14 days after anthesis. Durum wheat plants were grown hydroponically under high and low P supplies. Each labeling experiment lasted for 24 h. Plants were harvested 24, 48, and 96 h after labeling. Low and high P treatments significantly affected the allocation of the newly acquired P at the whole plant level. Three days (96 h) after the first 32P-labeling, 8% and 4% of the newly acquired P from exogenous solution were allocated to grains, 73% and 55% to the remainder aboveground organs, and 19% and 41% to the roots at low and high P supplies, respectively. Three days after the second labeling, the corresponding values were 48% and 20% in grains, 44% and 53% in the remainder aboveground organs, and 8% and 27% in roots at low and high P supplies, respectively. These results reveal that the dynamics of P allocation to grain was faster in plants grown under low P supply than under high supply. However, the obtained results also indicate that the origin of P accumulated in durum wheat grains was mainly from P remobilization with little contribution from post-anthesis P uptake. The present study emphasizes the role of vegetative organs as temporary storage of P taken up during the grain filling period before its final allocation to grains.

The rice phosphate transporter OsPHT1;7 plays a dual role in phosphorus redistribution and anther development

Inorganic phosphate (Pi) is the predominant form of phosphorus (P) readily accessible to plants, and Pi Transporter 1 (PHT1) genes are the major contributors to root Pi uptake. However, the mechanisms underlying the transport and recycling of Pi within plants, which are vital for optimizing P use efficiency, remain elusive. Here, we characterized a functionally unknown rice (Oryza sativa) PHT1 member barely expressed in roots, OsPHT1;7. Yeast complementation and Xenopus laevis oocyte assay demonstrated that OsPHT1;7 could mediate Pi transport. Reverse-transcription quantitative polymerase chain reaction and histochemical analyses showed that OsPHT1;7 was preferentially expressed in source leaves and nodes. A further fine-localization analysis by immunostaining showed that OsPHT1;7 expression was restricted in the vascular bundle (VB) sheath and phloem of source leaves as well as in the phloem of regular/diffuse- and enlarged-VBs of nodes. In accordance with this expression pattern, mutation of OsPHT1;7 led to increased and decreased P distribution in source (old leaves) and sink organs (new leaves/panicles), respectively, indicating that OsPHT1;7 is involved in P redistribution. Furthermore, OsPHT1;7 showed an overwhelmingly higher transcript abundance in anthers than other PHT1 members, and ospht1;7 mutants were impaired in P accumulation in anthers but not in pistils or husks. Moreover, the germination of pollen grains was significantly inhibited upon OsPHT1;7 mutation, leading to a >80% decrease in seed-setting rate and grain yield. Taken together, our results provide evidence that OsPHT1;7 is a crucial Pi transporter for Pi transport and recycling within rice plants, stimulating both vegetative and reproductive growth.

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.