low-P Stress Research Articles

Genetic diversity, relationships among traits and selection of tropical maize inbred lines for low-P tolerance based on root and shoot traits at seedling stage.

The tropical maize breeding for low-P tolerance and good performance under low-P stress environments can be achieved through selection based on root morphology traits at seedling stage. Here, we assessed the genotypic variation and genetic diversity of a panel of 151 tropical maize inbred lines for root and shoot seedling traits, investigated the relationship among traits and selected a set of promising inbred lines for low-P tolerance and performance. We evaluated the inbred lines at seedling stage in a greenhouse experiment under two conditions: applied P (AP) and non-applied P (NAP). A mixed model approach was used to estimate variance components and predict the genotypic values of each inbred line. The genetic diversity among inbred lines based on root and shoot traits was assessed, and correlations were estimated between tested traits under AP and NAP. Our panel of inbred lines showed huge genetic variability for all traits and presented large genetic diversity under both P conditions. Variance components due to the inbred line × P condition interaction were also highly significant (P < 0.01) for all traits. Root dry weight (RDW) was positively associated with stalk dimeter (SD), shoot dry weight (SDW) and root length, volume, and area under both P conditions. Also, the SD and SDW were associated with most root traits under AP. Based on low-P tolerance and performance indices, we selected a set of top 20 inbred lines to be used in our maize breeding program. We therefore concluded that there is a significant genetic diversity in the tropical maize inbred lines which have the genetic potential to be use in association mapping studies and also to develop improved low-P tolerant and P-efficient hybrids and maize breeding populations for low-P stress environments.

The soybean NUCLEAR FACTOR-Y C4 and α-EXPANSIN 7 module influences phosphorus uptake by regulating root morphology

Abstract Soybean (Glycine max) is a globally important crop; however, its productivity is severely impacted by phosphorus (P) deficiency. Understanding the transcriptional regulation of low P (LP) response mechanisms is essential for enhancing soybean P use efficiency. In this study, we found that the Nuclear Factor-Y (NF-Y) transcription factor GmNF-YC4, in addition to its previously discovered role in regulating flowering time, possesses other functions in modulating root morphology and P uptake. Knockout of GmNF-YC4 notably boosted root proliferation and P uptake while also influencing the expression of genes related to LP stress. GmNF-YC4 acts as a specific DNA-binding transcriptional repressor, modulating the expression of the soybean α-EXPANSIN 7 (GmEXPA7) gene, which encodes a cell-wall-loosening factor, through direct binding to its promoter region. Further investigation revealed that GmEXPA7 expression is predominantly root-specific and induced by LP. Moreover, overexpression of GmEXPA7 in soybean hairy roots enhanced LP tolerance by stimulating root growth and P uptake. We further screened and obtained more potential target genes of GmNF-YC4 via DNA affinity purification sequencing, including those related to LP stress. These findings underscore the pivotal role of the GmNF-YC4-GmEXPA7 module as a key regulator in mitigating LP stress in soybeans.

Effects of Low-Phosphorus Stress on Use of Leaf Intracellular Water and Nutrients, Photosynthesis, and Growth of Brassica napus L.

Phosphorus (P) deficiency is one of the main reasons limiting plant production of Brassica napus L. Exploring the dynamics of leaf intracellular substances and the correlations with photosynthesis and growth helps to understand the response mechanisms of B. napus L. to P deficiency. This study conducted experiments on B. napus L. plants by measuring the leaf electrophysiological parameters, leaf structure, elastic modulus (Em), photosynthesis, and growth indices under different P treatment conditions. The dynamics of leaf intracellular water and nutrients of B. napus L. were calculated and analyzed by using the electrophysiological parameters, and the plant tolerance threshold to low-P stress was discovered. The results indicated that the status of the leaf intracellular water and nutrients remained stable when the P concentration was not lower than 0.250 mmol·L−1, but maximized the photosynthesis and growth at a P level of 0.250 mmol·L−1. The 0.125 mmol·L−1 P concentration significantly decreased the mesophyll cell volume, and the palisade–sponge ratio and tightness degree of leaf tissue structure were remarkably increased. This led to an increase in cell elastic modulus, and significantly improved the water retention capacity of leaf cells. At the same time, the intracellular water use efficiency and total nutrient transport capacity of leaves remained stable. As a result, the photosynthesis and growth of plants were maintained at the same level as that of the control group. However, photosynthesis and growth were clearly inhibited with a further decrease in P concentration. Therefore, 0.125 mmol·L−1 was the tolerance threshold of B. napus L. to low P. With the help of electrophysiological information, the effects of the dynamics of intracellular substances on photosynthesis and growth of B. napus L. under low-P stress can be investigated, and the plant’s adaptive response can be revealed. However, the findings of the current hydroponic study are not directly applicable to field conditions with naturally P-deficient soils.

Dissecting the Roles of Phosphorus Use Efficiency, Organic Acid Anions, and Aluminum-Responsive Genes under Aluminum Toxicity and Phosphorus Deficiency in Ryegrass Plants.

Aluminum (Al) toxicity and phosphorus (P) deficiency are widely recognized as major constraints to agricultural productivity in acidic soils. Under this scenario, the development of ryegrass plants with enhanced P use efficiency and Al resistance is a promising approach by which to maintain pasture production. In this study, we assessed the contribution of growth traits, P efficiency, organic acid anion (OA) exudation, and the expression of Al-responsive genes in improving tolerance to concurrent low-P and Al stress in ryegrass (Lolium perenne L.). Ryegrass plants were hydroponically grown under optimal (0.1 mM) or low-P (0.01 mM) conditions for 21 days, and further supplied with Al (0 and 0.2 mM) for 3 h, 24 h and 7 days. Accordingly, higher Al accumulation in the roots and lower Al translocation to the shoots were found in ryegrass exposed to both stresses. Aluminum toxicity and P limitation did not change the OA exudation pattern exhibited by roots. However, an improvement in the root growth traits and P accumulation was found, suggesting an enhancement in Al tolerance and P efficiency under combined Al and low-P stress. Al-responsive genes were highly upregulated by Al stress and P limitation, and also closely related to P utilization efficiency. Overall, our results provide evidence of the specific strategies used by ryegrass to co-adapt to multiple stresses in acid soils.

Harnessing Phosphorous (P) Fertilizer-Insensitive Bacteria to Enhance Rhizosphere P Bioavailability in Legumes.

Phosphorous (P) is widely used in agriculture; yet, P fertilizers are a nonrenewable resource. Thus, mechanisms to improve soil P bioavailability need to be found. Legumes are efficient in P acquisition and, therefore, could be used to develop new technologies to improve soil P bioavailability. Here, we studied different species and varieties of legumes and their rhizosphere microbiome responses to low-P stress. Some varieties of common beans, cowpeas, and peas displayed a similar biomass with and without P fertilization. The rhizosphere microbiome of those varieties grown without P was composed of unique microbes displaying different levels of P solubilization and mineralization. When those varieties were amended with P, some of the microbes involved in P solubilization and mineralization decreased in abundance, but other microbes were insensitive to P fertilization. The microbes that decreased in abundance upon P fertilization belonged to groups that are commonly used as biofertilizers such as Pseudomonas and Azospirillum. The microbes that were not affected by P fertilization constitute unique species involved in P mineralization such as Arenimonas daejeonensis, Hyphomicrobium hollandicum, Paenibacillus oenotherae, and Microlunatus speluncae. These P-insensitive microbes could be used to optimize P utilization and drive future sustainable agricultural practices to reduce human dependency on a nonrenewable resource.

Integrated transcriptome and metabolome analysis reveals the divergent evolution of low-P tolerance in cultivated and Tibetan wild barley

Most arable lands in the world are quite low in available phosphorus (P), becoming an important factor restricting crop yield. However, the genotypic difference of low-P tolerance in barley is rarely understood at molecular level. In this study, low-P responses of three barley genotypes were explored by physiological, transcriptomic and metabolomic analysis. The results showed that low-P-tolerant genotypes Zaoaibai (cultivar) and X130 (Tibetan wild accession) showed less growth inhibition compared to low-P-sensitive Salooni2 under low-P stress. Omics analysis showed that many genes involved in Pi acquisition and transport were more upregulated in Zaoaibai, which had relatively higher concentrations of shoot P and glucose-6-phosphate, indicating that enhancement of P acquisition, P translocation and P availability contributed to low-P tolerance in Zaoaibai. On the other hand, the genes and metabolites involved in biosynthesis of Pi-free lipids were highly expressed and more abundant in X130, suggesting that remodeling of membrane lipids by replacing phospholipids with Pi-free lipids is an important strategy for X130 in its adaptation to low-P stress. The divergent evolution of low-P tolerance in Zaoaibai and X130 could be driven by diverse ecological factors in Eastern China (low soil P) and Tibet Plateau (high soil P and low temperature), respectively.

PHR1 involved in the regulation of low phosphate-induced leaf senescence by modulating phosphorus homeostasis in Arabidopsis.

Phosphorus (P) is a crucial macronutrient for plant growth, development, and reproduction. The effects of low P (LP)stress on leaf senescence and the role of PHR1in LP-induced leaf senescence are still unknown. Here, we report that PHR1 plays a crucial role in LP-induced leaf senescence, showing delayed leaf senescence in phr1 mutant and accelerated leaf senescence in 35S:PHR1 transgenic Arabidopsis under LP stress. The transcriptional profiles indicate that 763 differentially expressed SAGs (DE-SAGs)were upregulated and 134 DE-SAGswere downregulated by LP stress. Of the 405 DE-SAGsregulated by PHR1, 27 DE-SAGswere involved in P metabolism and transport. PHR1 could bind to the promoters of six DE-SAGs(RNS1, PAP17, SAG113, NPC5, PLDζ2, and Pht1;5), and modulate them in LP-induced senescing leaves. The analysis of RNA content, phospholipase activity, acid phosphatase activity, total P and phosphate content also revealed that PHR1 promotes P liberation from senescing leaves and transport to young tissues under LP stress. Our results indicated that PHR1 is one of the crucial modulators for P recycling and redistribution under LP stress, and the drastic decline of P level is at least one of the causes of early senescence in P-deficient leaves.

Polyphosphate promotes oxidation resistance of ppk-expressing transgenic rice in low phosphorus culture

Phosphorus (P) plays a crucial role in plant growth. Insufficient availability of inorganic phosphate (Pi) can significantly impact crop yields. To address this, we previously developed transgenic rice expressing the low polyphosphate kinase gene (ppk) - known as ETRS - to enhance the efficiency of P resource utilization. Previous studies have shown that ETRS thrives and presents high yields in the low P culture. ETRS and wild-type rice (WT) were cultivated to the heading stage at 15 μM of P in the low P (LP) culture and 300 μM of P in the normal culture (CK) to identify the molecular pathways behind low P tolerance. Our findings revealed that polyphosphate (polyP) significantly enhanced the growth performance of ETRS in the LP culture. This enhanced tolerance can be attributed to polyP's capacity to mitigate oxidative damage induced by LP. This was evidenced by the reduction in levels of superoxide radicals, hydrogen peroxide, and malondialdehyde. PolyP also improved the antioxidant capacity of ETRS under LP stress by regulating enzymatic antioxidants viz., superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), as well as non-enzymatic antioxidants such as ascorbate (AsA) and glutathione (GSH). In addition, transcriptomics analysis suggested that polyP synthesis positively promoted the expressions of SOD, POD, and CAT related genes and played an active role in regulating the expression of AsA-GSH cycle system related genes in ETRS in the LP culture. These results strongly support the notion that polyP within ETRS mitigates oxidative damage through enhancement of the antioxidant system, ultimately bolstering tolerance to LP conditions.

Maize Genotypes Sensitive and Tolerant to Low Phosphorus Levels Exhibit Different Transcriptome Profiles under Talaromyces purpurogenus Symbiosis and Low-Phosphorous Stress.

Talaromyces purpurogenus, an endophytic fungus, exhibits beneficial effects on plants during plant-fungus interactions. However, the molecular mechanisms underlying plants' responses to T. purpurogenus under low-phosphorous (P) stress are not fully understood. In this study, we investigated the transcriptomic changes in maize with low-P-sensitive (31778) and -tolerant (CCM454) genotypes under low-P stress and its symbiotic interaction with T. purpurogenus. Its colonization enhanced plant growth and facilitated P uptake, particularly in 31778. Transcriptome sequencing revealed that 135 DEGs from CCM454 and 389 from 31778 were identified, and that only 6 DEGs were common. This suggested that CCM454 and 31778 exhibited distinct molecular responses to T. purpurogenus inoculation. GO and KEGG analysis revealed that DEGs in 31778 were associated with nicotianamine biosynthesis, organic acid metabolic process, inorganic anion transport, biosynthesis of various secondary metabolites and nitrogen metabolism. In CCM454, DEGs were associated with anthocyanin biosynthesis, diterpenoid biosynthesis and metabolic process. After T. purpurogenus inoculation, the genes associated with phosphate transporter, phosphatase, peroxidase and high-affinity nitrate transporter were upregulated in 31778, whereas AP2-EREBP-transcription factors were detected at significantly higher levels in CCM454. This study provided insights on the molecular mechanisms underlying plant-endophytic fungus symbiosis and low-P stress in maize with low-P-sensitive and -tolerant genotypes.

Identifying Lettuce Accessions for Efficient Use of Phosphorus in Hydroponics

Lettuce (Lactuca sativa L.) is the most common leafy vegetable produced hydroponically in the United States. Although hydroponic systems are advantageous due to lower pest and disease pressure, and reduced water and nutrient requirements, the increasing prices of fertilizers, including phosphorus (P), still influences the profitability of hydroponic production of lettuce. Characterizing lettuce germplasm capable of producing high yield using less P inputs may help reduce fertilizer use, production costs, and P loads in wastewater. In this study, 12 lettuce accessions were grown in four experiments in a nutrient film technique system. In the first two experiments, the treatments consisted of two P concentrations (3.1 and 31 mg·L−1). Lettuce cultivated with 3.1 mg·L−1 of P had variable shoot and root biomass, root–shoot ratio, P uptake efficiency, and P utilization efficiency, indicating the existence of genetic variation. Five accessions (‘Little Gem’, 60183, ‘Valmaine’, BG19-0539, and ‘Green Lightning’) were considered efficient to P because produced similar shoot biomass with the low and high P treatments. In the third and fourth experiments, the treatments consisted of two P sources (monosodium phosphate (NaH2PO4) and tricalcium phosphate [TCP; Ca3(PO4)2]. Initially, extra 5 mM of calcium (Ca) was added to the TCP solution to reduce the TCP solubility and, hence, P bioavailability to plants. All accessions produced similar shoot and root weight with both treatments, indicating that the TCP treatment did not cause low-P stress to the plants. After, the extra Ca concentration added to TCP was increased to 10 mM, resulting in low-P stress and a significant reduction in shoot weight of all accessions. Despite the severe P stress, ‘Little Gem’ and 60183 were among the accessions with the least shoot weight reduction in the TCP treatment. Variability was observed in root biomass root–shoot ratio among accessions under the TCP treatment, suggesting that lettuce accessions responded differently to P stress conditions. The genetic variation for P use efficiency (PUE) and PUE-related traits in lettuce grown hydroponically suggests the feasibility of breeding new lettuce cultivars from elite lettuce germplasm adapted to low P availability in hydroponics.

Genetic variation in BnGRP1 contributes to low phosphorus tolerance in Brassica napus.

Lack of phosphorus (P) is a major environmental factor affecting rapeseed (Brassica napus. L) root growth and development. For breeding purposes, it is crucial to identify the molecular mechanisms of root system architecture (RSA) traits underlying low P tolerance in rapeseed. The natural variations in the glycine-rich protein gene, BnGRP1, were analyzed in the natural population of 400 rapeseed cultivars under low P stress through genome-wide association study (GWAS) and transcriptome analyses. Based on 11 SNP mutations in BnGRP1 sequence, ten types of haplotypes (Hap) were formed. Compared with the other types, the cultivar of BnGRP1Hap1 type in the panel demonstrated the longest root length and heaviest root weight. BnGRP1Hap1 overexpression in rapeseed depicted the ability to enhance its resistance in response to low P tolerance. CRISPR/Cas9-derived BnGRP1Hap4 knockout mutations in rapeseed can lead to sensitivity to low P stress. Furthermore, BnGRP1Hap1 influences the expression of phosphate transporter 1 (PHT1) genes associated with P absorption. Overall, the findings of this study highlight new mechanisms of GRP1 genes in enhancing low P tolerance in rapeseed.

Transcriptome analysis provides insights into the response of Lotus corniculatus roots to low-phosphorus stress.

A lack of soil phosphorus (P) is a principal factor restricting the normal growth of Lotus corniculatus in the karst area of Guizhou Province, China, but the response mechanism of L. corniculatus under low-phosphorus stress remains unclear. Therefore, we treated two selected L. corniculatus lines (low-P-intolerant line 08518 and low-P-tolerant line 01549) from 13 L. corniculatus lines with normal phosphorus (0.5 mmol/L KH2PO4, NP) and low phosphorus (0.005 mmol/L KH2PO4, LP) concentrations to study changes in morphological, physiological and transcriptome data under low-phosphorus stress. The low-P-tolerant line 01549 exhibited better performance under low-phosphorus stress. Compared with the NP treatment, all root morphological indicators of the low-P-tolerant line 01549 increased, and those of the low-P-intolerant line 08518 decreased under low-P stress. Compared with the NP treatment, acid phosphatase (ACP), catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) activities, and the malondialdehyde (MDA), soluble sugar (SS), soluble protein (SP) and proline (Pro) contents of the two L. corniculatus lines increased under low-P stress. A transcriptome analysis of L. corniculatus showed that a total of 656 and 2243 differentially expressed genes (DEGs) were identified in line 01549 and line 08518, respectively. Meanwhile, the main pathways, such as carbohydrate metabolism, acid phosphatases, phosphate transporters and biosynthesis of secondary metabolites, as well as related genes were also screened by performing a KEGG enrichment analysis. The findings provide an essential point of reference for studying the physiological and molecular mechanism of the response to low-P stress in L. corniculatus.

GmEIL4 enhances soybean (Glycine max) phosphorus efficiency by improving root system development.

Phosphorus (P) deficiency seriously affects plant growth and development and ultimately limits the quality and yield of crops. Here, a new P efficiency-related major quantitative trait locusgene, GmEIL4 (encoding an ethylene-insensitive 3-like 1 protein), was cloned at qP2, which was identified by linkage analysis and genome-wide association studyacross four environments. Overexpressing GmEIL4 significantly improved the P uptake efficiency by increasing the number, length and surface area of lateral roots of hairy roots in transgenic soybeans, while interfering with GmEIL4 resulted in poor root phenotypic characteristics compared with the control plants under low P conditions. Interestingly, we found that GmEIL4 interacted with EIN3-binding F box protein 1 (GmEBF1), which may regulate the root response to low P stress. We conclude that the expression of GmEIL4 was induced by low-P stress and that overexpressing GmEIL4 improved P accumulation by regulating root elongation and architecture. Analysis of allele variation of GmEIL4 in 894 soybean accessions suggested that GmEIL4 is undergoing artificial selection during soybean evolution, which will benefit soybean production. Together, this study further elucidates how plants respond to low P stress by modifying root structure and provides insight into the great potential of GmEIL4 in crop P-efficient breeding.

Systematic Identification and Expression Analysis of the Sorghum Pht1 Gene Family Reveals Several New Members Encoding High-Affinity Phosphate Transporters.

Sorghum (Sorghum bicolor) is known to have a more robust capability of phosphorus uptake than many other cereal plants, which could be attributed to its phosphate transporter 1 (Pht1) that has a high phosphorus affinity. There are eleven SbPht1 genes in the sorghum genome, nine of which are expressed in sorghum roots or shoots in response to phosphorus deficiency (low-P). The molecular features of these nine genes were investigated by gene expression analysis, subcellular localization, and a yeast mutant complementation growth assay. They were found to be induced in response to low-P stress in root or shoot. All these SbPht1 proteins were found to be localized on the cell membrane, and SbPht1;8 was also detected in the endoplasmic reticulum. These SbPht1s were able to complement the yeast mutant EY917 that lacks all the functional phosphate transporters, and, among them, SbPht1;5, SbPht1;6 and SbPht1;8 could partially complement the yeast mutant strain EY917 in low-P conditions. Overall, these findings demonstrate that SbPht1;5, SbPht1;6, and SbPht1;8 are high-affinity phosphate transporters. SbPht1;5, in particular, is specifically involved in phosphorus uptake in the roots, whilst SbPht1;6 and SbPht1;8 are key players in both P uptake and P transport in response to low-P stress in sorghum.

Long-term fertilization has different impacts on bacterial communities and phosphorus forms in sugarcane rhizosphere and bulk soils under low-P stress.

The application of phosphorus (P) fertilizer effectively improves soil P availability, but it also affects soil microbial communities. However, the responses of soil bacterial communities and P forms to long-term P fertilization, and the relationships of bacterial communities with soil P forms remain unclear in P-deficient field. In this study, the impacts of different P fertilization treatments (chemical nitrogen and potassium (NK); chemical N, P and K (NPK); and NPK plus straw (NPKS)) on the bacterial communities and P forms in sugarcane rhizosphere (RS) and bulk soils (BS) were evaluated. Compared with the NK, the NPK and NPKS treatments significantly (P<0.05) increased the yield and quality characters of sugarcane, especially under NPKS. Additionally, P fertilization significantly increased the available P (AP), soluble inorganic P (Pi) and retained Pi in both the RS and BS, but they significantly increased the Chao1 and Shannon index only in the BS; and almost all these indices were significantly higher in the RS than in the BS. The bacterial community compositions were also significantly altered by P fertilization, with major changes in the RS and minor changes in the BS. The bacterial genera that were enriched in the sugarcane rhizosphere mainly included Bradyrhizobium, Rhodanobacter, Pseudolabrys, Conexibacter, and Burkholderia-Caballeronia-Paraburkholderia, some of which potentially promote the plant growth. Compared to NK, functional groups involved in the cycling of carbon, N, and sulfur significantly increased or decreased with fertilizer P application. Moreover, the relative abundances of many bacterial species were significantly correlated with the soil P forms. In conclusion, long-term P fertilization altered bacterial structure and functions in P-deficient sugarcane soil, which could help the soil P cycling and suppling. The results provide useful information to stimulate the power of the microbes by fertilization measures to improve soil nutrients and crop production.

Genome-wide association analysis discovered new loci and candidate genes associated with low-phosphorus tolerance based on shoot mineral elements concentrations in soybean.

Phosphorus (P) deficiency is one of the major limitations for soybean production. Moreover, it has been well reported P and other mineral elements function interdependently or antagonistically to control nutrients homeostasis in plants. Thus, it is urgently needed to understand the genetic mechanism of the accumulation of mineral elements in response to low-P stress. In this study, to identify single nucleotide polymorphisms (SNPs) and candidate genes controlling the accumulation of mineral elements suffering low-P stress in seedling stage of soybean plants, we measured concentrations of mineral elements, including P, Zn, Fe, Mn, Mg and Ca, in shoots of 211 soybean accessions under normal phosphorus (+P) and low phosphorus (-P) conditions in two hydroponic experiments. And genome-wide association study (GWAS) using high density NJAU 355K SoySNP array and concentrations of five of these mineral elements except P was performed. A total of 36 SNPs distributed on 13 chromosomes were identified to be significantly associated with low-P tolerance, and nine SNPs on chromosome 10 formed a SNP cluster. Meanwhile, the candidate gene GmFeB1 was found to serve as a negative regulator element involved in soybean P metabolism and the haplotype1 (Hap1) of GmFeB1 showed significantly higher shoot Fe concentration under -P condition than that of Hap2. In summary, we uncover 36 SNPs significantly associated with shoot mineral elements concentrations under different P conditions and a soybean low-P related gene GmFeB1, which will provide additional genetic information for soybean low-P tolerance and new gene resources for P-efficient soybean varieties breeding.

Study on the Relationship of Root Morphology and Phosphorus Absorption Efficiency With Phosphorus Uptake Capacity in 235 Peanut (Arachis hypogaea L.) Germplasms

Peanut (Arachis hypogaea L.) is a significant oil and protein crop. Its yields greatly depend on the availability of phosphorus (P). Root morphology and P absorption efficiency are important factors affecting the P uptake capacity, but their relationships in peanuts are rarely reported. Here, we report the effect of root morphology and P absorption efficiency on the P uptake capacity in peanuts using 235 germplasms. In this work, we use the P uptake rate per plant to reflect the P uptake capacity. The P uptake capacity was significantly increased after low-P treatment and showed great differences among the germplasms. The germplasms with higher P absorption efficiency and a well-developed root system have higher P uptake capacity. Under both P conditions, the P absorption efficiency plays more important roles than root morphology in P uptake capacity, and the P uptake rate per unit root dry weight and the P uptake rate per unit root surface area contributed the most. Root morphology contributes more to the P uptake capacity under low-P treatment than under sufficient-P conditions, and root surface area contributed the most. Forty-eight germplasms with higher P uptake capacity were screened, and they had three different uptake strategies under low-P treatment. These findings indicated that low-P stress induces root growth and improves the P absorption efficiency of peanuts to ensure the plant gets enough P; provides new insights into the relationship between the P uptake capacity, P absorption efficiency, and root morphology; and furnishes important evaluation indexes for high P-efficient germplasm selection.

Effects of Scion Variety on the Phosphorus Efficiency of Grafted Camellia oleifera Seedlings

Grafting provides a way to improve tolerance to low phosphorus (P) stress for plants, and has been extensively applied in commercial cultivars grafted onto appropriate rootstocks. However, little literature is available concerning the scion-mediated effect on P efficiency in grafted plants. In this study, three different Camellia oleifera Abel. scion cultivars (G8, G83-1, and W2) were grafted onto the same rootstock (W2) under controls (0.5 mM) and low-P (0 mM) availability for eight months. The results showed that the scions significantly affected root-to-shoot weight ratios, the root morphology with a diameter larger than 1 mm, P accumulation, and the P utilization efficiency (PUE) of the root. A higher increase in the root-to-shoot weight ratio under the low-P supply was observed in the G83-1/W2 (26.15%) than in the G8/W2 (0%) and the W2/W2 (5.32%). Root PUE of the scion G8, G83-1, and W2 was improved by up to 113.73%, 45.46%, and 20.97% under the low-P supply. Moreover, G8/W2 exhibited higher shoot P accumulation and the highest root PUE under the low-P supply, indicating a high capability to tolerate P deficiency by maximizing the cost-effectiveness of P remobilization to photosynthetic organs. This suggested the vigorous variety of G8 could be a promising scion to improve grafted C. oleifera tolerance to low-P stress. Our results would have important implications for exploration and identification of a superior scion variety to enhance the ability of resistance concerning P deficiency stress in C. oleifera.

Tampk2b, a Member of the Mapk Family in T. Aestivum, Enhances Plant Low-Pi Stress Tolerance Through Modulating Physiological Processes Associated with Low-P Stress Defensiveness

Tampk2b, a Member of the Mapk Family in T. Aestivum, Enhances Plant Low-Pi Stress Tolerance Through Modulating Physiological Processes Associated with Low-P Stress Defensiveness

Physiological responses and transcriptomic changes reveal the mechanisms underlying adaptation of Stylosanthes guianensis to phosphorus deficiency

BackgroundPhosphorus (P) is an essential macronutrient for plant growth that participates in a series of biological processes. Thus, P deficiency limits crop growth and yield. Although Stylosanthes guianensis (stylo) is an important tropical legume that displays adaptation to low phosphate (Pi) availability, its adaptive mechanisms remain largely unknown.ResultsIn this study, differences in low-P stress tolerance were investigated using two stylo cultivars (‘RY2’ and ‘RY5’) that were grown in hydroponics. Results showed that cultivar RY2 was better adapted to Pi starvation than RY5, as reflected by lower values of relative decrease rates of growth parameters than RY5 at low-P stress, especially for the reduction of shoot and root dry weight. Furthermore, RY2 exhibited higher P acquisition efficiency than RY5 under the same P treatment, although P utilization efficiency was similar between the two cultivars. In addition, better root growth performance and higher leaf and root APase activities were observed with RY2 compared to RY5. Subsequent RNA-seq analysis revealed 8,348 genes that were differentially expressed under P deficient and sufficient conditions in RY2 roots, with many Pi starvation regulated genes associated with P metabolic process, protein modification process, transport and other metabolic processes. A group of differentially expressed genes (DEGs) involved in Pi uptake and Pi homeostasis were identified, such as genes encoding Pi transporter (PT), purple acid phosphatase (PAP), and multidrug and toxin extrusion (MATE). Furthermore, a variety of genes related to transcription factors and regulators involved in Pi signaling, including genes belonging to the PHOSPHATE STARVATION RESPONSE 1-like (PHR1), WRKY and the SYG1/PHO81/XPR1 (SPX) domain, were also regulated by P deficiency in stylo roots.ConclusionsThis study reveals the possible mechanisms underlying the adaptation of stylo to P deficiency. The low-P tolerance in stylo is probably manifested through regulation of root growth, Pi acquisition and cellular Pi homeostasis as well as Pi signaling pathway. The identified genes involved in low-P tolerance can be potentially used to design the breeding strategy for developing P-efficient stylo cultivars to grow on acid soils in the tropics.