Overexpression of GmPAP4 Enhances Symbiotic Nitrogen Fixation and Seed Yield in Soybean under Phosphorus-Deficient Condition.

Legume crops establish symbiosis with nitrogen-fixing rhizobia for biological nitrogen fixation (BNF), a process that provides a prominent natural nitrogen source in agroecosystems; and efficient nodulation and nitrogen fixation processes require a large amount of phosphorus (P). Here, a role of GmPAP4, a nodule-localized purple acid phosphatase, in BNF and seed yield was functionally characterized in whole transgenic soybean (Glycine max) plants under a P-limited condition. GmPAP4 was specifically expressed in the infection zones of soybean nodules and its expression was greatly induced in low P stress. Altered expression of GmPAP4 significantly affected soybean nodulation, BNF, and yield under the P-deficient condition. Nodule number, nodule fresh weight, nodule nitrogenase, APase activities, and nodule total P content were significantly increased in GmPAP4 overexpression (OE) lines. Structural characteristics revealed by toluidine blue staining showed that overexpression of GmPAP4 resulted in a larger infection area than wild-type (WT) control. Moreover, the plant biomass and N and P content of shoot and root in GmPAP4 OE lines were also greatly improved, resulting in increased soybean yield in the P-deficient condition. Taken together, our results demonstrated that GmPAP4, a purple acid phosphatase, increased P utilization efficiency in nodules under a P-deficient condition and, subsequently, enhanced symbiotic BNF and seed yield of soybean.

Microbial community interactions determine the mineralization of soil organic phosphorus in subtropical forest ecosystems.

In subtropical forest ecosystems with few phosphorus (P) inputs, P availability and forest productivity depend on soil organic P (Po) mineralization. However, the mechanisms by which the microbial community determines the status and fate of soil Po mineralization remain unclear. In the present study, soils were collected from three typical forest types: secondary natural forest (SNF), mixed planting, and monoculture forest of Chinese fir. The P fractions, Po-mineralization ability, and microbial community in the soils of different forest types were characterized. In addition, we defined Po-mineralizing taxa with the potential to interact with the soil microbial community to regulate Po mineralization. We found that a higher labile P content persisted in SNF and was positively associated with the Po-mineralization capacity of the soil microbial community. In vitro cultures of soil suspensions revealed that soil Po mineralization of three forest types was distinguished by differences in the composition of fungal communities. We further identified broad phylogenetic lineages of Po-mineralizing fungi with a high intensity of positive interactions with the soil microbial community, implying that the facilitation of Po-mineralizing taxa is crucial for soil P availability. Our dilution experiments to weaken microbial interactions revealed that in SNF soil, which had the highest interaction intensity of Po-mineralizing taxa with the community, Po-mineralization capacity was irreversibly lost after dilution, highlighting the importance of microbial diversity protection in forest soils. In summary, this study demonstrates that the interactions of Po-mineralizing microorganisms with the soil microbial community are critical for P availability in subtropical forests.IMPORTANCEIn subtropical forest ecosystems with few phosphorus inputs, phosphorus availability and forest productivity depend on soil organic phosphorus mineralization. However, the mechanisms by which the microbial community interactions determine the mineralization of soil organic phosphorus remain unclear. In the present study, soils were collected from three typical forest types: secondary natural forest, mixed planting, and monoculture forest of Chinese fir. We found that a higher soil labile phosphorus content was positively associated with the organic phosphorus mineralization capacity of the soil microbial community. Soil organic phosphorus mineralization of three forest types was distinguished by the differences in the composition of fungal communities. The positive interactions between organic phosphorus-mineralizing fungi and the rest of the soil microbial community facilitated organic phosphorus mineralization. This study highlights the importance of microbial diversity protection in forest soils and reveals the microbial mechanism of phosphorus availability maintenance in subtropical forest ecosystems.

Transcriptome analysis of axillary buds in low phosphorus stress and functional analysis of TaWRKY74s in wheat.

BACKGROUND: Wheat is one of the main grain crops in the world, and the tiller number is a key factor affecting the yield of wheat. Phosphorus is an essential element for tiller development in wheat. However, due to decreasing phosphorus content in soil, there has been increasing use of phosphorus fertilizer, while imposing risk of soil and water pollution. Hence, it is important to identify low phosphorus tolerance genes and utilize them for stress resistance breeding in wheat. RESULTS: We subjected the wheat variety Kenong 199 (KN199) to low phosphorus stress and observed a reduced tiller number. Using transcriptome analysis, we identified 1651 upregulated genes and 827 downregulated of genes after low phosphorus stress. The differentially expressed genes were found to be enriched in the enzyme activity regulation related to phosphorus, hormone signal transduction, and ion transmembrane transport. Furthermore, the transcription factor analysis revealed that TaWRKY74s were important for low phosphorus tolerance. TaWRKY74s have three alleles: TaWRKY74-A, TaWRKY74-B, and TaWRKY74-D, and they all belong to the WRKY family with conserved WRKYGQK motifs. These proteins were found to be located in the nucleus, and they were expressed in axillary meristem, shoot apical meristem(SAM), young leaves, leaf primordium, and spikelet primordium. The evolutionary tree showed that TaWRKY74s were closely related to OsWRKY74s in rice. Moreover, TaWRKY74s-RNAi transgenic plants displayed significantly fewer tillers compared to wild-type plants under normal conditions. Additionally, the tiller numebr of the RNAi transgenic plants was also significantly lower than that of the wild-type plants under low-phosphorus stress, and increased the decrease amplitude. This suggestd that TaWRKY74s are related to phosphorus response and can affect the tiller number of wheat. CONCLUSIONS: The results of this research showed that TaWRKY74s were key genes in wheat response to low phosphorus stress, which might regulate wheat tiller number through abscisic acid (ABA) and auxin signal transduction pathways. This research lays the foundation for further investigating the mechanism of TaWRKY74s in the low phosphorus environments and is significant for wheat stress resistance breeding.

Integrated Analysis of Metabolome and Transcriptome Reveals Insights for Low Phosphorus Tolerance in Wheat Seedling.

Low phosphorus (LP) stress leads to a significant reduction in wheat yield, primarily in the reduction of biomass, the number of tillers and spike grains, the delay in heading and flowering, and the inhibition of starch synthesis and grouting. However, the differences in regulatory pathway responses to low phosphorus stress among different wheat genotypes are still largely unknown. In this study, metabolome and transcriptome analyses of G28 (LP-tolerant) and L143 (LP-sensitive) wheat varieties after 72 h of normal phosphorus (CK) and LP stress were performed. A total of 181 and 163 differentially accumulated metabolites (DAMs) were detected for G28CK vs. G28LP and L143CK vs. L143LP, respectively. Notably, the expression of pilocarpine (C07474) in G28CK vs. G28LP was significantly downregulated 4.77-fold, while the expression of neochlorogenic acid (C17147) in L143CK vs. L143LP was significantly upregulated 2.34-fold. A total of 4023 differentially expressed genes (DEGs) were acquired between G28 and L143, of which 1120 DEGs were considered as the core DEGs of LP tolerance of wheat after LP treatment. The integration of metabolomics and transcriptomic data further revealed that the LP tolerance of wheat was closely related to 15 metabolites and 18 key genes in the sugar and amino acid metabolism pathway. The oxidative phosphorylation pathway was enriched to four ATPases, two cytochrome c reductase genes, and fumaric acid under LP treatment. Moreover, PHT1;1, TFs (ARFA, WRKY40, MYB4, MYB85), and IAA20 genes were related to the Pi starvation stress of wheat roots. Therefore, the differences in LP tolerance of different wheat varieties were related to energy metabolism, amino acid metabolism, phytohormones, and PHT proteins, and precisely regulated by the levels of various molecular pathways to adapt to Pi starvation stress. Taken together, this study may help to reveal the complex regulatory process of wheat adaptation to Pi starvation and provide new genetic clues for further study on improving plant Pi utilization efficiency.

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.

Transcriptomics Insights into Phosphorus Stress Response of Myriophyllum aquaticum.

Through excellent absorption and transformation, the macrophyte Myriophyllum (M.) aquaticum can considerably remove phosphorus from wastewater. The results of changes in growth rate, chlorophyll content, and roots number and length showed that M. aquaticum could cope better with high phosphorus stress compared with low phosphorus stress. Transcriptome and differentially expressed genes (DEGs) analyses revealed that, when exposed to phosphorus stresses at various concentrations, the roots were more active than the leaves, with more DEGs regulated. M. aquaticum also showed different gene expression and pathway regulatory patterns when exposed to low phosphorus and high phosphorus stresses. M. aquaticum's capacity to cope with phosphorus stress was maybe due to its improved ability to regulate metabolic pathways such as photosynthesis, oxidative stress reduction, phosphorus metabolism, signal transduction, secondary metabolites biosynthesis, and energy metabolism. In general, M. aquaticum has a complex and interconnected regulatory network that deals efficiently with phosphorus stress to varying degrees. This is the first time that the mechanisms of M. aquaticum in sustaining phosphorus stress have been fully examined at the transcriptome level using high-throughput sequencing analysis, which may indicate the direction of follow-up research and have some guiding value for its future applications.

Overexpression of the autophagy-related gene SiATG8a from foxtail millet (Setaria italica L.) in transgenic wheat confers tolerance to phosphorus starvation.

In plants, autophagy plays an important role in regulating intracellular degradation and amino acid recycling in response to nutrient starvation, senescence, and other environmental stresses. Foxtail millet (Setaria italica) shows strong resistance to various abiotic stresses; however, current understanding of the regulation network of abiotic stress resistance in foxtail millet remains limited. In this study, we aimed to determine the autophagy-related gene SiATG8a in foxtail millet. We found that SiATG8a was mainly expressed in the stem and was induced by low-phosphorus (LP) stress. Overexpression of SiATG8a in wheat (Triticum aestivum) significantly increased the grain yield and spike number per m2 under LP treatment compared to those in the WT varieties S366 and S4056. There was no significant difference in the grain P content between SiATG8a-overexpressing wheat and WT wheat under normal phosphorus (NP) and LP treatments. However, the phosphorus (P) content in the roots, stems, and leaves of transgenic plants was significantly higher than that in WT plants under NP and LP conditions. Furthermore, the expression of P transporter genes, such as TaPHR1, TaPHR3, TaIPS1, and TaPT9, in SiATG8a-transgenic wheat was higher than that in WT under LP. Collectively, overexpression of SiATG8a increases the P content of roots, stems, and leaves of transgenic wheat under LP conditions by modulating the expression of P-related transporter gene, which may result in increased grain yield; thus, SiATG8a is a candidate gene for generating transgenic wheat with improved tolerance to LP stress in the field.

Biochemical and proteomic insights revealed selenium priming induced phosphorus stress tolerance in common bean (Phaseolus vulgaris L.).

BACKGROUND: Mineral stress is one of the dominating abiotic stresses, which leads to decrease in crop production. Selenium (Se) seed priming is a recent approach to mitigate the plant's mineral deficiency stress. Although not an essential element, Se has beneficial effects on the plants in terms of growth, quality, yield and plant defense system thus, enhancing plant tolerance to mineral deficiency. METHODS AND RESULTS: The present research was accomplished to find out the effect of Se priming on common bean plant (SFB-1 variety) under phosphorus (P) stress. The seeds were grown invitro on four different MGRL media which are normal MGRL media as control with non-Se primed seeds (Se- P+), non -Se primed seeds grown on P deficient MGRL media (Se- P-), Se primed seeds grown on normal MGRL media (Se+P+) and Se primed seeds grown on P deficient MGRL media (Se+P -). The various morphological and biochemical parameters such as proline content, total sugar content, polyphenols and expression of proteins were analyzed under P stress. The results showed that Se priming has significantly (p ≤ 0.05) affected the morphological as well as biochemical parameters under normal and P stress conditions. The morphological parameters-length, weight, number of nodes and leaves of Se+P+, Se+P- root and shoot tissue showed significant increase as compared to Se-P+, Se-P-. Similarly various biochemical parameters such as total chlorophyll content, proline, total sugar content and polyphenols of Se+P+, Se+P- increased significantly as compared to Se-P+, Se-P-. The differential protein expression in both Se+P+, Se+P- and Se-P+, Se-P- plants were determined using MALDI-MS/MS. The differentially expressed proteins in Se+P+, Se+P- plants were identified as caffeic acid-3-O-methyltransferase (COMT) and SecA protein (a subunit of Protein Translocan transporter), and are found responsible for lignin synthesis in root cell walls and ATP dependent movement of thylakoid proteins across the membranes in shoot respectively. The differential expression of proteins in plant tissues, validated morphological and biochemical responses such as maintaining membrane integrity, enhanced modifications in cellular metabolism, improved polyphenol activities and expression of defensive proteins against mineral deficiency. CONCLUSIONS: The study provided an understanding of Se application as a potential approach increasing tolerance and yield in crop plants against mineral deficiency.

Transcription Factor IAA27 Positively Regulates P Uptake through Promoted Adventitious Root Development in Apple Plants.

Phosphate (P) deficiency severely limits the growth and production of plants. Adventitious root development plays an essential role in responding to low phosphorus stress for apple plants. However, the molecular mechanisms regulating adventitious root growth and development in response to low phosphorus stress have remained elusive. In this study, a mutation (C-T) in the coding region of the apple AUXIN/INDOLE-3-ACETIC ACID 27 (IAA27) gene was identified. MdIAA27T-overexpressing transgenic apple improved the tolerance to phosphorus deficiency, which grew longer and denser adventitious roots and presented higher phosphorous content than the control plants under low phosphorus conditions, while the overexpression of MdIAA27C displayed the opposite trend. Moreover, the heterologous overexpression of MdIAA27 in tobacco yielded the same results, supporting the aforementioned findings. In vitro and in vivo assays showed that MdIAA27 directly interacted with AUXIN RESPONSE FACTOR (ARF8), ARF26 and ARF27, which regulated Small Auxin-Up RNA 76 (MdSAUR76) and lateral organ boundaries domain 16 (MdLBD16) transcription. The mutation in IAA27 resulted in altered interaction modes, which in turn promoted the release of positive ARFs to upregulate SAUR76 and LBD16 expression in low phosphorus conditions. Altogether, our studies provide insights into how the allelic variation of IAA27 affects adventitious root development in response to low phosphorus stress.

The purple acid phosphatase GmPAP17 predominantly enhances phosphorus use efficiency in soybean.

Purple acid phosphatase (PAP) is an important plant acid phosphatase, which can secrete to the rhizosphere to decompose organophosphorus, promote phosphorus use efficiency, plant growth and development. However, little is known about the functions of intracellular PAP in plants, especially for soybean. Our previous study integrating QTL mapping and transcriptome analysis identified an promising low phosphorus (LP)-induced gene GmPAP17. Here, we determined that GmPAP17 was mainly expressed in roots and had a strong response to LP stress. Furthermore, and the relative expression in the root of LP tolerant genotypes NN94-156 was significantly greater than that of LP sensitive genotype Bogao after LP stress treatment. The overexpression of GmPAP17 significantly enhanced both acid phosphatase activity and growth performance of hairy roots under LP stress condition, it was vice versa for RNAi interference of GmPAP17, indicating that GmPAP17 plays an important role in P use efficiency. Moreover, yeast two-hybrid and bimolecular fluorescence complementation analysis showed that GmRAP2.2 was involved in the regulation network of GmPAP17. Taken together, our results suggest that GmPAP17 is a novel plant PAP that functions in the adaptation of soybean to LP stress, possibly through its involvement in P recycling in plants.

[Screening and identification of key enzyme genes for steroidal saponin biosynthesis in Dioscorea zingiberensis under low phosphorus stress].

To investigate the responses of key enzymes involved in steroidal saponin biosynthesis of Dioscorea zingiberensis to low phosphorus stress, we designed three treatments of severe phosphorus stress, moderate phosphorus stress, and normal phosphorus level. The D. zingiberensis plants were collected at the early, middle, and late stages of treatment. The content of total steroidal saponins in different tissues of D. zingiberensis was determined by spectrophotometry for the identification of the critical stage in response to low phosphorus stress. BGI 500 sequencing platform was employed to obtain the transcript information of D. zingiberensis samples at the critical stage of low phosphorus stress, and then a transcriptome library was constructed. The correlation between the expression of genes involved in steroidal saponin biosynthesis and the content of total steroidal saponins was analyzed for the screening of the key enzyme genes in response to low phosphorus stress. Further, the expression patterns of these genes were analyzed by real-time fluorescence PCR(qRT-PCR). The content of total steroidal saponins in D. zingiberensis had obvious tissue specificity under low phosphorus stress, and the early stage of stress was particularly important for D. zingiberensis to respond to low phosphorus stress. A total of 101 593 unigenes were obtained by transcriptome sequencing, of which 77.35% were annotated in NT, NR, SwissProt, KOG, GO, and KEGG. A total of 256 transcripts of known key enzyme genes in the biosynthetic pathway of steroidal saponins were identified. The expression levels of 69 transcripts encoding 18 catalytic enzymes were significantly correlated with the content of total steroidal saponins. The qRT-PCR results showed that several key enzyme genes presented different expression patterns in four tissues under low phosphorus stress. The results indicated that the content of total steroidal saponins and the expression of key enzyme genes regulating steroidal saponin biosynthesis in D. zingensis changed under low phosphorus stress. This study provides the biological information for elucidating the molecular mechanism of steroidal saponin biosynthesis in D. zingensis exposed to low phosphorus stress.

Identification, Structural, and Expression Analyses of SPX Genes in Giant Duckweed (Spirodela polyrhiza) Reveals Its Role in Response to Low Phosphorus and Nitrogen Stresses.

SPX genes play important roles in the coordinated utilization of nitrogen (N) and phosphorus (P) in plants. However, a genome-wide analysis of the SPX family is still lacking. In this study, the gene structure and phylogenetic relationship of 160 SPX genes were systematically analyzed at the genome-wide level. Results revealed that SPX genes were highly conserved in plants. All SPX genes contained the conserved SPX domain containing motifs 2, 3, 4, and 8. The 160 SPX genes were divided into five clades and the SPX genes within the same clade shared a similar motif composition. P1BS cis-elements showed a high frequency in the promoter region of SPXs, indicating that SPX genes could interact with the P signal center regulatory gene Phosphate Starvation Response1 (PHR1) in response to low P stress. Other cis-elements were also involved in plant development and biotic/abiotic stress, suggesting the functional diversity of SPXs. Further studies were conducted on the interaction network of three SpSPXs, revealing that these genes could interact with important components of the P signaling network. The expression profiles showed that SpSPXs responded sensitively to N and P deficiency stresses, thus playing a key regulatory function in P and N metabolism. Furthermore, the expression of SpSPXs under P and N deficiency stresses could be affected by environmental factors such as ABA treatment, osmotic, and LT stresses. Our study suggested that SpSPXs could be good candidates for enhancing the uptake ability of Spirodela polyrhiza for P nutrients in wastewater. These findings could broaden the understanding of the evolution and biological function of the SPX family and offer a foundation to further investigate this family in plants.

Phosphorus homeostasis: acquisition, sensing, and long-distance signaling in plants.

Phosphorus (P), an essential nutrient required by plants often becomes the limiting factor for plant growth and development. Plants employ various mechanisms to sense the continuously changing P content in the soil. Transcription factors, such as SHORT ROOT (SHR), AUXIN RESPONSE FACTOR19 (ARF19), and ETHYLENE-INSENSITIVE3 (EIN3) regulate the growth of primary roots, root hairs, and lateral roots under low P. Crop improvement strategies under low P depend either on improving P acquisition efficiency or increasing P utilization. The various phosphate transporters (PTs) are involved in the uptake and transport of P from the soil to various plant cellular organelles. A plethora of regulatory elements including transcription factors, microRNAs and several proteins play a critical role in the regulation of coordinated cellular P homeostasis. Among these, the well-established P starvation signaling pathway comprising of central transcriptional factor phosphate starvation response (PHR), microRNA399 (miR399) as a long-distance signal molecule, and PHOSPHATE 2 (PHO2), an E2 ubiquitin conjugase is crucial in the regulation of phosphorus starvation responsive genes. Under PHR control, several classes of PHTs, microRNAs, and proteins modulate root architecture, and metabolic processes to enable plants to adapt to low P. Even though sucrose and inositol phosphates are known to influence the phosphorus starvation response genes, the exact mechanism of regulation is still unclear. In this review, a basic understanding of P homeostasis under low P in plants and all the above aspects are discussed.

Identification of Phosphorus Stress Related Proteins in the Seedlings of Dongxiang Wild Rice (Oryza Rufipogon Griff.) Using Label-Free Quantitative Proteomic Analysis.

Phosphorus (P) deficiency tolerance in rice is a complex character controlled by polygenes. Through proteomics analysis, we could find more low P tolerance related proteins in unique P-deficiency tolerance germplasm Dongxiang wild rice (Oryza Rufipogon, DXWR), which will provide the basis for the research of its regulation mechanism. In this study, a proteomic approach as well as joint analysis with transcriptome data were conducted to identify potential unique low P response genes in DXWR during seedlings. The results showed that 3589 significant differential accumulation proteins were identified between the low P and the normal P treated root samples of DXWR. The degree of change was more than 1.5 times, including 60 up-regulated and 15 downregulated proteins, 24 of which also detected expression changes of more than 1.5-fold in the transcriptome data. Through quantitative trait locus (QTLs) matching analysis, seven genes corresponding to the significantly different expression proteins identified in this study were found to be uncharacterized and distributed in the QTLs interval related to low P tolerance, two of which (LOC_Os12g09620 and LOC_Os03g40670) were detected at both transcriptome and proteome levels. Based on the comprehensive analysis, it was found that DXWR could increase the expression of purple acid phosphatases (PAPs), membrane location of P transporters (PTs), rhizosphere area, and alternative splicing, and it could decrease reactive oxygen species (ROS) activity to deal with low P stress. This study would provide some useful insights in cloning the P-deficiency tolerance genes from wild rice, as well as elucidating the molecular mechanism of low P resistance in DXWR.

A phosphorus-limitation induced, functionally conserved DUF506 protein is a repressor of root hair elongation in plants.

Root hairs (RHs) function in nutrient and water acquisition, root metabolite exudation, soil anchorage and plant-microbe interactions. Longer or more abundant RHs are potential breeding traits for developing crops that are more resource-use efficient and can improve soil health. While many genes are known to promote RH elongation, relatively little is known about genes and mechanisms that constrain RH growth. Here we demonstrate that a DOMAIN OF UNKNOWN FUNCTION 506 (DUF506) protein, AT3G25240, negatively regulates Arabidopsis thaliana RH growth. The AT3G25240 gene is strongly and specifically induced during phosphorus (P)-limitation. Mutants of this gene, which we call REPRESSOR OF EXCESSIVE ROOT HAIR ELONGATION 1 (RXR1), have much longer RHs, higher phosphate content and seedling biomass, while overexpression of the gene exhibits opposite phenotypes. Co-immunoprecipitation, pull-down and bimolecular fluorescence complementation (BiFC) analyses reveal that RXR1 physically interacts with a RabD2c GTPase in nucleus, and a rabd2c mutant phenocopies the rxr1 mutant. Furthermore, N-terminal variable region of RXR1 is crucial for inhibiting RH growth. Overexpression of a Brachypodium distachyon RXR1 homolog results in repression of RH elongation in Brachypodium. Taken together, our results reveal a novel DUF506-GTPase module with a prominent role in repression of plant RH elongation especially under P stress.

[Response of root morphogenesis of medicinal plants to low phosphorus stress and molecular mechanism].

The content of available phosphorus in soil is generally low worldwide. Phosphorus, one of the necessary macroelements for plant growth and development, plays an important role in cell structure, material composition and energy metabolism, and signal transduction in plants. Phosphate transporter(PHT) genes are important for plant growth and development, root morphogenesis, secondary metabolism, hormone response, and phosphorus balance. Most of the active components in medicinal plants are secondary metabolites. Thus, it is essential to reveal the relationship between the regulation of phosphorus and the accumulation of active components in medicinal plants, especially the effect of phosphorus starvation on root morphogenesis of root medicinal materials and its coupling with hormone response. With advancement of molecular biology, scholars gradually emphasize the mechanism of PHT regulating the secondary metabolism of medicinal plants. This study summarized the strategies of plants to adapt to low phosphorus environment, such as changing root morphogenesis, inhibiting taproot growth, forming cluster root and changing physiological metabolism, PHT, its regulatory network, phenotypic biological characteristics and key genes in medicinal plants related to phosphorus starvation, and the response mechanism. The findings are expected to lay a basis for the cultivation of medicinal plants with high quality, excellent shape, and high price.

Identification of SPX family genes in the maize genome and their expression under different phosphate regimes.

Many studies have revealed that SPX (SYG1/Pho81/XPR1) family genes play a key role in signal transduction related to phosphorus (P) deficiency in plants. Here, we identified 33 SPX gene family members in maize through genome-wide analysis and classified them into 4 subfamilies according to SPX structural characteristics (SPX, SPX-MFS, SPX-EXS and SPX-RING). The promoter regions of ZmSPXs are rich in biotic/abiotic-related stress elements. The quantitative real-time PCR analysis of 33 ZmSPXs revealed that all members except for ZmSPX3 of the SPX subfamily were significantly induced under P-deficient conditions, especially ZmSPX4.1 and ZmSPX4.2, which showed strong responses to low P stress and exhibited remarkably different expression patterns in low Pi sensitive and insensitive cultivars of maize. These results suggested that the SPX subfamily might play pivotal roles in P stress sensing and response. Experimental observations of subcellular localization in maize protoplasts indicated the following results, implying multiple roles in cell metabolism: ZmSPX2, ZmSPX5 and ZmSPX6 localized in the nucleus; ZmSPX1 and ZmSPX3 localized in the nucleus and cytoplasm; and ZmSPX4.2 localized in the chloroplast. A Y2H assay suggested that ZmPHR1 could interact with ZmSPX3, ZmSPX4.2, ZmSPX5, and ZmSPX6, indicating the involvement of these proteins in the P stress response in a ZmPHR1-mediated manner.

Replenishment of urban landscape ponds with reclaimed water: Spatiotemporal variations of water quality and mechanism of algal inhibition with alum sludge.

Algal blooms caused by high concentrations of nutrients (especially phosphorus) limit the use of recycled water (RW) for replenishing landscape ponds in the context of global water scarcity. Previous studies have demonstrated that alum sludge is a low cost phosphorus sorption medium, which could potentially be applied in constructed wetlands and sewage treatment plants. However, whether alum sludge can be used for algae inhibition in reclaimed water urban landscape ponds (RWULPs) should be explored. In this study, phosphorus removal and algae inhibition by alum sludge were investigated in a RWULP in China. The results highlight that there is a serious risk of algal blooms in RWULPs. The algal density was found to be 1.58 × 105 cell·mL-1, which is 6.84 times higher than that of the surface water ponds. The algal blooms presented a Cyanophyta-Chlorophyta-Bacillariophyta-type, and the dominant algae species were Microcystis flos-aquae (Wittr.) Kirchner, Chlorella vulgaris, and Scenedesmus quadricauda. Moreover, the removal rate of phosphorus by alum sludge was as high as 98% and eventually leads to phosphorus stress, which has an important effect on algae growth and algae inhibition rate of 80%. In addition, the proportion of phosphorus and nitrogen in the adsorbed alum sludge increased by 3.12% and 0.32%, respectively, and Al3+ was reduced by only 2.18%. Alum sludge is a potential inhibitor of algae in RWULPs that does not negatively impact the environment. These results are of great importance in algal bloom control of RWULPs and may help alleviate the problem of urban water resource scarcity.

Metabolite alteration in response to low phosphorus stress in developing tomato fruits.

Alteration of fruit quality caused by environmental stress is a common but largely unresolved issue for plant cultivation and breeding practices. Phosphorus (P) deficiency may interfere with a variety of metabolic processes whose intermediate products are correlated with important fruit quality traits. However, how low P stress affects fruit quality has not been investigated in detail. In this study, we assessed the contents of major metabolites associated with tomato fruit quality under two low P treatments that started at the seedling or flowering stage. The major pigments and the key organic acids related to fruit sourness were differentially over-accumulated as fruit ripened under two low P treatments compared to those under the control treatment, while the total content of soluble sugars contributing to fruit sweetness was substantially reduced under both treatments. These changes were largely attributed to the alteration of enzyme activities in the relevant metabolic pathways. In particular, we found that low P stress from different developmental stages had differential effects on the activation of γ-aminobutyric acid shunt that were likely responsible for the preferential accumulation of different organic acids in tomato fruits. Our study suggested that low P stress strongly affected tomato fruit quality and the effects appeared to be variable under different regimes of low P conditions.

Strength and size of phosphorus-rich patches determine the foraging strategy of Neyraudia reynaudiana.

BACKGROUND: Under natural conditions, soil nutrients are heterogeneously distributed, and plants have developed adaptation strategies to efficiently forage patchily distributed nutrient. Most previous studies examined either patch strength or patch size separately and focused mainly on root morphological plasticity (increased root proliferation in nutrient-rich patch), thus the effects of both patch strength and size on morphological and physiological plasticity are not well understood. In this study, we examined the foraging strategy of Neyraudia reynaudiana (Kunth) Keng ex Hithc, a pioneer grass colonizing degraded sites, with respect to patch strength and size in heterogeneously distributed phosphorus (P), and how foraging patchily distributed P affects total plant biomass production. Plants were grown in sand-culture pots divided into ½, », 1/6 compartments and full size and supplied with 0 + 0/30, 0 + 7.5/30 and 7.5 + 0/30 mg P/kg dry soil as KH2PO4 or 0 + 15/15, 0 + 18.5/ 18.5, 7.5 + 15/15 mg kg - 1 in the homogenous treatment. The first amount was the P concentration in the central region, and that the second amount was the P concentration in the outer parts of the pot. RESULTS: After 3 months of growth under experimental conditions, significantly (p < 0.05) high root elongation, root surface area, root volume and average root diameter was observed in large patches with high patch strength. Roots absorbed significantly more P in P-replete than P-deficient patches. Whole plant biomass production was significantly higher in larger patches with high patch strength than small patches and homogeneous P distribution. CONCLUSION: The result demonstrates that root morphological and physiological plasticity are important adaptive strategies for foraging patchily distributed P and the former is largely determined by patch strength and size. The results also establish that foraging patchily distributed P resulted in increased total plant biomass production compared to homogeneous P distribution.