Potassium and phosphorus transport and signaling in plants

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.

Genome-wide identification of kiwifruit K+ channel Shaker family members and their response to low-K+ stress

BACKGROUND

'Hongyang' kiwifruit (Actinidia chinensis cv 'Hongyang') is a high-quality variety of A. chinensis with the advantages of high yield, early ripening, and high stress tolerance. Studies have confirmed that the Shaker K+ genes family is involved in plant uptake and distribution of potassium (K+).

RESULTS

Twenty-eight Shaker genes were identified and analyzed from the 'Hongyang' kiwifruit (A. chinensis cv 'Hongyang') genome. Subcellular localization results showed that more than one-third of the AcShaker genes were on the cell membrane. Phylogenetic analysis indicated that the AcShaker genes were divided into six subfamilies (I-VI). Conservative model, gene structure, and structural domain analyses showed that AcShaker genes of the same subfamily have similar sequence features and structure. The promoter cis-elements of the AcShaker genes were classified into hormone-associated cis-elements and environmentally stress-associated cis-elements. The results of chromosomal localization and duplicated gene analysis demonstrated that AcShaker genes were distributed on 18 chromosomes, and segmental duplication was the prime mode of gene duplication in the AcShaker family. GO enrichment analysis manifested that the ion-conducting pathway of the AcShaker family plays a crucial role in regulating plant growth and development and adversity stress. Compared with the transcriptome data of the control group, all AcShaker genes were expressed under low-K+stress, and the expression differences of three genes (AcShaker15, AcShaker17, and AcShaker22) were highly significant. The qRT-PCR results showed a high correlation with the transcriptome data, which indicated that these three differentially expressed genes could regulate low-K+ stress and reduce K+ damage in kiwifruit plants, thus improving the resistance to low-K+ stress. Comparison between the salt stress and control transcriptomic data revealed that the expression of AcShaker11 and AcShaker18 genes was significantly different and lower under salt stress, indicating that both genes could be involved in salt stress resistance in kiwifruit.

CONCLUSION

The results showed that 28 AcShaker genes were identified and all expressed under low K+ stress, among which AcShaker22 was differentially and significantly upregulated. The AcShaker22 gene can be used as a candidate gene to cultivate new varieties of kiwifruit resistant to low K+ and provide a reference for exploring more properties and functions of the AcShaker genes.

Genome-wide transcriptome and gene family analysis reveal candidate genes associated with potassium uptake of maize colonized by arbuscular mycorrhizal fungi

BACKGROUND

Potassium (K) is an essential nutrient for plant growth and development. Maize (Zea mays) is a widely planted crops in the world and requires a huge amount of K fertilizer. Arbuscular mycorrhizal fungi (AMF) are closely related to the K uptake of maize. Genetic improvement of maize K utilization efficiency will require elucidating the molecular mechanisms of maize K uptake through the mycorrhizal pathway. Here, we employed transcriptome and gene family analysis to elucidate the mechanism influencing the K uptake and utilization efficiency of mycorrhizal maize.

METHODS AND RESULTS

The transcriptomes of maize were studied with and without AMF inoculation and under different K conditions. AM symbiosis increased the K concentration and dry weight of maize plants. RNA sequencing revealed that genes associated with the activity of the apoplast and nutrient reservoir were significantly enriched in mycorrhizal roots under low-K conditions but not under high-K conditions. Weighted gene correlation network analysis revealed that three modules were strongly correlated with K content. Twenty-one hub genes enriched in pathways associated with glycerophospholipid metabolism, glycerolipid metabolism, starch and sucrose metabolism, and anthocyanin biosynthesis were further identified. In general, these hub genes were upregulated in AMF-colonized roots under low-K conditions. Additionally, the members of 14 gene families associated with K obtain were identified (ARF: 38, ILK: 4, RBOH: 12, RUPO: 20, MAPKK: 89, CBL: 14, CIPK: 44, CPK: 40, PIN: 10, MYB: 174, NPF: 79, KT: 19, HAK/HKT/KUP: 38, and CPA: 8) from maize. The transcript levels of these genes showed that 92 genes (ARF:6, CBL:5, CIPK:13, CPK:2, HAK/HKT/KUP:7, PIN:2, MYB:26, NPF:16, RBOH:1, MAPKK:12 and RUPO:2) were upregulated with AM symbiosis under low-K conditions.

CONCLUSIONS

This study indicated that AMF increase the resistance of maize to low-K stress by regulating K uptake at the gene transcription level. Our findings provide a genome-level resource for the functional assignment of genes regulated by K treatment and AM symbiosis in K uptake-related gene families in maize. This may contribute to elucidate the molecular mechanisms of maize response to low K stress with AMF inoculation, and provided a theoretical basis for AMF application in the crop field.

Nitrate Starvation Induces Lateral Root Organogenesis in Triticum aestivum via Auxin Signaling

The lateral root (LR) is an essential component of the plant root system, performing important functions for nutrient and water uptake in plants and playing a pivotal role in cereal crop productivity. Nitrate (NO3-) is an essential nutrient for plants. In this study, wheat plants were grown in 1/2 strength Hoagland's solution containing 5 mM NO3- (check; CK), 0.1 mM NO3- (low NO3-; LN), or 0.1 mM NO3- plus 60 mg/L 2,3,5-triiodobenzoic acid (TIBA) (LNT). The results showed that LN increased the LR number significantly at 48 h after treatment compared with CK, while not increasing the root biomass, and LNT significantly decreased the LR number and root biomass. The transcriptomic analysis showed that LN induced the expression of genes related to root IAA synthesis and transport and cell wall remodeling, and it was suppressed in the LNT conditions. A physiological assay revealed that the LN conditions increased the activity of IAA biosynthesis-related enzymes, the concentrations of tryptophan and IAA, and the activity of cell wall remodeling enzymes in the roots, whereas the content of polysaccharides in the LRP cell wall was significantly decreased compared with the control. Fourier-transform infrared spectroscopy and atomic microscopy revealed that the content of cell wall polysaccharides decreased and the cell wall elasticity of LR primordia (LRP) increased under the LN conditions. The effects of LN on IAA synthesis and polar transport, cell wall remodeling, and LR development were abolished when TIBA was applied. Our findings indicate that NO3- starvation may improve auxin homeostasis and the biological properties of the LRP cell wall and thus promote LR initiation, while TIBA addition dampens the effects of LN on auxin signaling, gene expression, physiological processes, and the root architecture.

The plant rhabdovirus viroporin P9 facilitates insect-mediated virus transmission in barley

Potassium (K+) plays crucial roles in both plant development and immunity. However, the function of K+ in plant-virus interactions remains largely unknown. Here, we utilized Barley yellow striate mosaic virus (BYSMV), an insect-transmitted plant cytorhabdovirus, to investigate the interplay between viral infection and plant K+ homeostasis. The BYSMV accessory P9 protein exhibits viroporin activity by enhancing membrane permeability in Escherichia coli. Additionally, P9 increases K+ uptake in yeast (Saccharomyces cerevisiae) cells, which is disrupted by a point mutation of glycine 14 to threonine (P9G14T). Furthermore, BYSMV P9 forms oligomers and targets to both the viral envelope and the plant membrane. Based on the recombinant BYSMV-GFP (BYGFP) virus, a P9-deleted mutant (BYGFPΔP9) was rescued and demonstrated infectivity within individual plant cells of Nicotiana benthamiana and insect vectors. However, BYGFPΔP9 failed to infect barley plants after transmission by insect vectors. Furthermore, infection of barley plants was severely impaired for BYGFP-P9G14T lacking P9 K+ channel activity. In vitro assays demonstrate that K+ facilitates virion disassembly and the release of genome RNA for viral mRNA transcription. Altogether, our results show that the K+ channel activity of viroporins is conserved in plant cytorhabdoviruses and plays crucial roles in insect-mediated virus transmission.

Multi-locus genome-wide association study for phosphorus use efficiency in a tropical maize germplasm

Phosphorus (P) is an essential macronutrient for maize (Zea mays L.) growth and development. Therefore, generating cultivars with upgraded P use efficiency (PUE) represents one of the main strategies to reduce the global agriculture dependence on phosphate fertilizers. In this work, genome-wide association studies (GWAS) were performed to detect quantitative trait nucleotide (QTN) and potential PUE-related candidate genes and associated traits in greenhouse and field trials under contrasting P conditions. The PUE and other agronomy traits of 132 maize inbred lines were assessed in low and normal P supply through the greenhouse and field experiments and Multi-locus GWAS was used to map the associated QTNs. Wide genetic variability was observed among the maize inbred lines under low and normal P supply. In addition, we confirm the complex and quantitative nature of PUE. A total of 306 QTNs were associated with the 24 traits evaluated using different multi-locus GWAS methods. A total of 186 potential candidate genes were identified, mainly involved with transcription regulator, transporter, and transference activity. Further studies are still needed to elucidate the functions and relevance of these genes regarding PUE. Nevertheless, pyramiding the favorable alleles pinpointed in the present study can be considered an efficient strategy for molecular improvement to increase maize PUE.

A viral protein competitively bound to rice CIPK23 inhibits potassium absorption and facilitates virus systemic infection in rice

Potassium (K+) plays a crucial role as a macronutrient in the growth and development of plants. Studies have definitely determined the vital roles of K+ in response to pathogen invasion. Our previous investigations revealed that rice plants infected with rice grassy stunt virus (RGSV) displayed a reduction in K+ content, but the mechanism by which RGSV infection subverts K+ uptake remains unknown. In this study, we found that overexpression of RGSV P1, a specific viral protein encoded by viral RNA1, results in enhanced sensitivity to low K+ stress and exhibits a significantly lower rate of K+ influx compared to wild-type rice plants. Further investigation revealed that RGSV P1 interacts with OsCIPK23, an upstream regulator of Shaker K+ channel OsAKT1. Moreover, we found that the P1 protein recruits the OsCIPK23 to the Cajal bodies (CBs). In vivo assays demonstrated that the P1 protein competitively binds to OsCIPK23 with both OsCBL1 and OsAKT1. In the nucleus, the P1 protein enhances the binding of OsCIPK23 to OsCoilin, a homologue of the signature protein of CBs in Arabidopsis, and facilitates their trafficking through these CB structures. Genetic analysis indicates that mutant in oscipk23 suppresses RGSV systemic infection. Conversely, osakt1 mutants exhibited increased sensitivity to RGSV infection. These findings suggest that RGSV P1 hinders the absorption of K+ in rice plants by recruiting the OsCIPK23 to the CB structures. This process potentially promotes virus systemic infection but comes at the expense of inhibiting OsAKT1 activity.

Nutritional management and physiological responses of Atriplex nummularia Lindl. on the improvement of phytoextraction in salt-affected soil

Soil salinity is a significant abiotic stress and poses risks to environmental sustainability. Thus, the improvement of the time for recovering the salt-affect soil is crucial for the phytoextraction process using halophytes plants, especially regarding on nutritional management. We evaluated the responses of Atriplex nummularia Lindl. to nitrogen (N) and phosphorus (P) under different salinity levels. The treatments comprised doses of N (N1 = 80 kg ha-1) and P (P1 = 60 kg ha-1): (1) without N and P (N0P0) (control); (2) with N and without P (N1P0); (3) without N and with P (N0P1); and (4) with N and P (N1P1) and five levels of electrical conductivity from irrigation water: 0.08, 1.7, 4.8, 8.6, and 12.5 dS m-1. The. We evaluated dry biomass of leaves, stems, and roots 93 days after transplantation. We also assessed the leaf and osmotic water potential, the osmotic adjustment, and the nutrient contents (N, P, Na, and K). N application increased 22.3, 17.8, and 32.8% the leaf biomass, stem biomass, and osmotic adjustment, respectively; and consequently, boosts Na extraction in 27.8%. Thus, the time of the phytoextraction process can be improved with N fertilizer at a rate of 80 kg ha-1.

Mechanisms of vacuolar phosphate efflux supporting soybean root hair growth in response to phosphate deficiency

Phosphorus is an essential macronutrient for plant growth and development. In response to phosphate (Pi) deficiency, plants rapidly produce a substitutive amount of root hairs; however, the mechanisms underlying Pi supply for root hair growth remain unclear. Here, we observed that soybean (Glycine max) plants maintain a consistent level of Pi within root hairs even under external Pi deficiency. We therefore investigated the role of vacuole-stored Pi, a major Pi reservoir in plant cells, in supporting root hair growth under Pi-deficient conditions. Our findings indicated that two vacuolar Pi efflux (VPE) transporters, GmVPE1 and GmVPE2, remobilize vacuolar stored Pi to sustain cytosolic Pi content in root hair cells. Genetic analysis showed that double mutants of GmVPE1 and GmVPE2 exhibited reduced root hair growth under low Pi conditions. Moreover, GmVPE1 and GmVPE2 were highly expressed in root hairs, with their expression levels significantly upregulated by low Pi treatment. Further analysis revealed that GmRSL2 (ROOT HAIR DEFECTIVE 6-like 2), a transcription factor involved in root hair morphogenesis, directly binds to the promoter regions of GmVPE1 and GmVPE2, and promotes their expressions under low Pi conditions. Additionally, mutants lacking both GmRSL2 and its homolog GmRSL3 exhibited impaired root hair growth under low Pi stress, which was rescued by overexpressing either GmVPE1 or GmVPE2. Taken together, our study has identified a module comprising vacuolar Pi exporters and transcription factors responsible for remobilizing vacuolar Pi to support root hair growth in response to Pi deficiency in soybean.

SPX family response to low phosphorus stress and the involvement of ZmSPX1 in phosphorus homeostasis in maize

Phosphorus (P) is a crucial macronutrient for plant growth and development, and low-Pi stress poses a significant limitation to maize production. While the role of the SPX domain in encoding proteins involved in phosphate (Pi) homeostasis and signaling transduction has been extensively studied in other model plants, the molecular and functional characteristics of the SPX gene family members in maize remain largely unexplored. In this study, we identified six SPX members, and the phylogenetic analysis of ZmSPXs revealed a close relationship with SPX genes in rice. The promoter regions of ZmSPXs were abundant in biotic and abiotic stress-related elements, particularly associated with various hormone signaling pathways, indicating potential intersections between Pi signaling and hormone signaling pathways. Additionally, ZmSPXs displayed tissue-specific expression patterns, with significant and differential induction in anthers and roots, and were localized to the nucleus and cytoplasm. The interaction between ZmSPXs and ZmPHRs was established via yeast two-hybrid assays. Furthermore, overexpression of ZmSPX1 enhanced root sensitivity to Pi deficiency and high-Pi conditions in Arabidopsis thaliana. Phenotypic identification of the maize transgenic lines demonstrated the negative regulatory effect on the P concentration of stems and leaves as well as yield. Notably, polymorphic sites including 34 single-nucleotide polymorphisms (SNPs) and seven insertions/deletions (InDels) in ZmSPX1 were significantly associated with 16 traits of low-Pi tolerance index. Furthermore, significant sites were classified into five haplotypes, and haplotype5 can enhance biomass production by promoting root development. Taken together, our results suggested that ZmSPX family members possibly play a pivotal role in Pi stress signaling in plants by interacting with ZmPHRs. Significantly, ZmSPX1 was involved in the Pi-deficiency response verified in transgenic Arabidopsis and can affect the Pi concentration of maize tissues and yield. This work lays the groundwork for deeper exploration of the maize SPX family and could inform the development of maize varieties with improved Pi efficiency.

GLABRA 2 regulates ETHYLENE OVERPRODUCER 1 accumulation during nutrient deficiency-induced root hair growth

Root hairs (RHs), extensive structures of root epidermal cells, are important for plant nutrient acquisition, soil anchorage, and environmental interactions. Excessive production of the phytohormone ethylene (ET) leads to substantial root hair growth, manifested as tolerance to plant nutrient deficiencies. However, the molecular basis of ET production during root hair growth in response to nutrient starvation remains unknown. Herein, we found that a critical transcription factor, GLABRA 2 (GL2), inhibits ET production during root hair growth in Arabidopsis (Arabidopsis thaliana). GL2 directly binds to the promoter of the gene encoding ET OVERPRODUCER 1 (ETO1), one of the most important ET-production-regulation factors, in vitro and in vivo, and then regulates the accumulation and function of ETO1 in root hair growth. The GL2-regulated-ETO1 module is required for promoting root hair growth under nitrogen, phosphorus, or potassium deficiency. Genome-wide analysis revealed numerous genes, such as ROOT HAIR DEFECTIVE 6-LIKE 4, ETHYLENE-INSENSITIVE 3-LIKE 2, ROOT HAIR SPECIFIC 13, are involved in the GL2-regulated-ETO1 module. Our work reveals a key transcription mechanism in the control of ET production during root hair growth under three major nutrient deficiencies.

Genome-wide association studies dissect low-phosphorus stress response genes underling field and seedling traits in maize

Phosphorus (P) is an essential element for plant growth, and its deficiency can cause decreased crop yield. This study systematically evaluated the low-phosphate (Pi) response traits in a large population at maturity and seedling stages, and explored candidate genes and their interrelationships with specific traits. The results revealed a greater sensitivity of seedling maize to low-Pi stress compared to that at maturity stage. The phenotypic response patterns to low-Pi stress at different stages were independent. Chlorophyll content was found to be a potential indicator for screening low-Pi-tolerant materials in the field. A total of 2900 and 1446 significantly associated genes at the maturity and seedling stages were identified, respectively. Among these genes, 972 were uniquely associated with maturity traits, while 330 were specifically detected at the seedling stage under low-Pi stress. Moreover, 768 and 733 genes were specifically associated with index values (low-Pi trait/normal-Pi trait) at maturity and seedling stage, respectively. Genetic network diagrams showed that the low-Pi response gene Zm00001d022226 was specifically associated with multiple primary P-related traits under low-Pi conditions. A total of 963 out of 2966 genes specifically associated with traits under low-Pi conditions or index values were found to be induced by low-Pi stress. Notably, ZmSPX4.1 and ZmSPX2 were sharply up-regulated in response to low-Pi stress across different lines or tissues. These findings advance our understanding of maize's response to low-Pi stress at different developmental stages, shedding light on the genes and pathways implicated in this response.

Effect of various phosphorus levels on the extraction of Cd, the transformation of P, and phosphorus-related gene during the phytoremediation of Cd contaminated soil

Phytoremediation has emerged as a common technique for remediating Cd pollution in farmland soil. Moreover, phosphorus, an essential element for plants, can alter the pectin content of plant cell walls and facilitate the accumulation of Cd in plant tissues, thereby enhancing phytoremediation efficiency. Therefore, pot experiments were conducted in order to investigate the effect of phosphorus levels on Cd extraction, phosphorus transformation and phosphorus-related genes during phytoremediation. The results revealed that an optimal application of suitable phosphate fertilizers elevated the soil's pH and electrical conductivity (EC), facilitated the conversion of soil from insoluble phosphorus into available forms, augmented the release of pertinent enzyme activity, and induced the expression of phosphorus cycling-related genes. These enhancements in soil conditions significantly promoted the growth of ryegrass. When applying phosphorus at a rate of 600 mg/kg, ryegrass exhibited plant height, dry weight, and chlorophyll relative content that were 1.27, 1.26, and 1.18 times higher than those in the control group (P0), while the Cd content was 1.12 times greater than that of P0. The potentially toxic elements decline ratio and bioconcentration factor were 42.86% and 1.17 times higher than those of P0, respectively. Consequently, ryegrass demonstrated the highest Cd removal efficiency under these conditions. Results from redundancy analysis (RDA) revealed a significant correlation among pH, total phosphorus, heavy metal content, phosphorus forms, soil enzyme activity, and phosphorus-related genes. In conclusion, this study suggests applying an optimal amount of suitable phosphate fertilizers can enhance restoration efficiency, leading to a reduction in soil Cd content and ultimately improving the safety of crop production in farmlands.

Carbon nanosol promotes plant growth and broad-spectrum resistance

Carbon nanosol (CNS) is a carbon-based nanomaterial capable of promoting plant growth while the underlying mechanism involved in this process remains unknown. This study demonstrates that CNS promotes rice seedling growth under restricted concentrations. Macroelement transporter mutants were investigated to further investigate the CNS-mediated promotion of rice seedling growth. The genetic and physiological findings revealed that nitrate transporter 1.1B (NRT1.1B) and ammonium transporter 1 (AMT1) mutants inhibited the CNS-induced growth development of rice seedlings, whereas potassium transporter (AKT1) and phosphate transporter 8 (PT8) did not exhibit any inhibitory effects. Further investigations demonstrated the inhibition of CNS-mediated growth promotion via glutamine synthetase 1;1 (gs1;1) mutants. Additionally, the administration of CNS resulted in enhanced accumulation of chlorophyll in plants, and the promotion of CNS-induced growth was inhibited by yellow-green leaf 8 (YGL8) mutants and the chlorophyll biosynthetic gene divinyl reductase (DVR) mutants. According to these findings, the CNS promotes plant growth by stimulating chlorophyll biosynthesis. Furthermore, the presence of CNS enhanced the ability of rice to withstand blast, sheath blight (ShB), and bacterial blight. The nrt1.1b, amt1, dvr, and ygl8 mutants did not exhibit a broad spectrum effect. The positive regulation of broad-spectrum resistance in rice by GS1;1 suggests the requirement of N assimilation for CNS-mediated broad-spectrum resistance. In addition, an in vitro assay demonstrated that CNS inhibits the growth of pathogens responsible for blast, ShB, and bacterial blight, namely Magnaporthe oryzae, Rhizoctonia solani AG1-IA, and Xanthomonas oryzae pv. Oryzae, respectively. CNS application may also induce broad-spectrum resistance against bacterial and fungal pathogens, indicating that in addition to its antifungal and antibacterial properties, CNS application may also stimulate N assimilation. Collectively, the results indicate that CNS may be a potential nano-therapeutic agent for improved plant growth promotion while also providing broad-spectrum resistance.

Exploring the phosphorus-starch content balance mechanisms in maize grains using GWAS population and transcriptome data

Examining the connection between P and starch-related signals can help elucidate the balance between nutrients and yield. This study utilized 307 diverse maize inbred lines to conduct multi-year and multi-plot trials, aiming to explore the relationship among P content, starch content, and 100-kernel weight (HKW) of mature grains. A significant negative correlation was found between P content and both starch content and HKW, while starch content showed a positive correlation with HKW. The starch granules in grains with high-P and low-starch content (HPLS) were significantly smaller compared to grains with low-P high-starch content (LPHS). Additionally, mian04185-4 (HPLS) exhibited irregular and loosely packed starch granules. A significant decrease in ZmPHOs genes expression was detected in the HPLS line ZNC442 as compared to the LPHS line SCML0849, while no expression difference was observed in AGPase encoding genes between these two lines. The down-regulated genes in ZNC442 grains were enriched in nucleotide sugar and fatty acid anabolic pathways, while up-regulated genes were enriched in the ABC transporters pathway. An accelerated breakdown of fat as the P content increased was also observed. This implied that HPLS was resulted from elevated lipid decomposition and inadequate carbon sources. The GWAS analysis identified 514 significantly associated genes, out of which 248 were differentially expressed. Zm00001d052392 was found to be significantly associated with P content/HKW, exhibiting high expression in SCML0849 but almost no expression in ZNC442. Overall, these findings suggested new approaches for achieving a P-yield balance through the manipulation of lipid metabolic pathways in grains.

Comparative transcriptomic and physiological analyses unravel wheat source root adaptation to phosphorous deficiency

Phosphorus (P) is a crucial macronutrient for plant growth and development. Basic metabolic processes regulate growth; however, the molecular detail of these pathways under low phosphorous (LP) in wheat is still unclear. This study aims to elucidate the varied regulatory pathways responses to LP stress in wheat genotypes. Phenotypic, physiological, and transcriptome analyses were conducted on Fielder (P efficient) and Ardito (P inefficient) wheat genotypes after four days of normal phosphorous (NP) and LP stress. In response to LP, Fielder outperformed Ardito, displaying higher chlorophyll content-SPAD values (13%), plant height (45%), stem diameter (12%), shoot dry weight (42%), and root biomass (75%). Root structure analysis revealed that Fielder had greater total root length (50%), surface area (56%), volume (15%), and diameter (4%) than Ardito under LP. These findings highlight Fielder's superior performance and adaptation to LP stress. Transcriptome analysis of wheat genotype roots identified 3029 differentially expressed genes (DEGs) in Fielder and 1430 in Ardito, highlighting LP-induced changes. Key DEGs include acid phosphatases (PAPs), phosphate transporters (PHT1 and PHO1), SPX, and transcription factors (MYB, bHLH, and WRKY). KEGG enrichment analysis revealed key pathways like plant hormones signal transduction, biosynthesis of secondary metabolites, and carbohydrate biosynthesis metabolism. This study unveils crucial genes and the intricate regulatory process in wheat's response to LP stress, offering genetic insights for enhancing plant P utilization efficiency.

WRKY33 negatively regulates anthocyanin biosynthesis and cooperates with PHR1 to mediate acclimation to phosphate starvation

Anthocyanin accumulation is acknowledged as a phenotypic indicator of phosphate (Pi) starvation. However, negative regulators of this process and their molecular mechanisms remain largely unexplored. In this study, we demonstrate that WRKY33 acts as a negative regulator of phosphorus-status-dependent anthocyanin biosynthesis. WRKY33 regulates the expression of the gene encoding dihydroflavonol 4-reductase (DFR), a rate-limiting enzyme in anthocyanin production, both directly and indirectly. WRKY33 binds directly to the DFR promoter to repress its expression and also interferes with the MBW complex through interacting with PAP1 to indirectly influence DFR transcriptional activation. Under -Pi conditions, PHR1 interacts with WRKY33, and the protein level of WRKY33 decreases; the repression of DFR expression by WRKY33 is thus attenuated, leading to anthocyanin accumulation in Arabidopsis. Further genetic and biochemical assays suggest that PHR1 is also involved in regulating factors that affect WRKY33 protein turnover. Taken together, our findings reveal that Pi starvation represses WRKY33, a repressor of anthocyanin biosynthesis, to finely tune anthocyanin biosynthesis. This "double-negative logic" regulation of phosphorus-status-dependent anthocyanin biosynthesis is required for the maintenance of plant metabolic homeostasis during acclimation to Pi starvation.

Potassium transporter OsHAK17 may contribute to saline-alkaline tolerant mechanisms in rice (Oryza sativa)

Rice production is seriously affected by saline-alkaline stress worldwide. To elucidate the saline-alkaline tolerance mechanisms in a novel tolerant rice variety, Shwe Nang Gyi (SNG), we investigated ion accumulation in SNG and Koshihikari (KSH), which is a saline-alkaline sensitive rice variety, and the candidates for saline-alkaline inducible genes in SNG using RNA-seq. SNG had superior ion accumulation capacity, such as K and Zn, compared to KSH. In contrast, SNG accumulated the same level of Na content in its leaf blades as KSH despite the higher dry weight of the SNG leaf blades. We further found that the expression of numerous genes, including several K+ transporter/high-affinity K+ transporter/K+ uptake protein/K+ transporter (HAK/KUP/KT) family members, were upregulated in SNG, and that OsHAK17 and OsHAK21 expression levels in the roots were significantly higher in SNG than in KSH. Moreover, yeast complementation analysis revealed that OsHAK17 was involved in K+ uptake under high-Na conditions. These results suggested that SNG has an effective K+ acquisition system supported by OsHAK17 functioning in saline-alkaline environments.

The MYB-CC Transcription Factor PHOSPHATE STARVATION RESPONSE-LIKE 7 (PHL7) Functions in Phosphate Homeostasis and Affects Salt Stress Tolerance in Rice

Inorganic phosphate (Pi) homeostasis plays an important role in plant growth and abiotic stress tolerance. Several MYB-CC transcription factors involved in Pi homeostasis have been identified in rice (Oryza sativa). PHOSPHATE STARVATION RESPONSE-LIKE 7 (PHL7) is a class II MYC-CC protein, in which the MYC-CC domain is located at the N terminus. In this study, we established that OsPHL7 is localized to the nucleus and that the encoding gene is induced by Pi deficiency. The Pi-responsive genes and Pi transporter genes are positively regulated by OsPHL7. The overexpression of OsPHL7 enhanced the tolerance of rice plants to Pi starvation, whereas the RNA interference-based knockdown of this gene resulted in increased sensitivity to Pi deficiency. Transgenic rice plants overexpressing OsPHL7 produced more roots than wild-type plants under both Pi-sufficient and Pi-deficient conditions and accumulated more Pi in the shoots and roots. In addition, the overexpression of OsPHL7 enhanced rice tolerance to salt stress. Together, these results demonstrate that OsPHL7 is involved in the maintenance of Pi homeostasis and enhances tolerance to Pi deficiency and salt stress in rice.

Comparative transcriptome analysis reveals the adaptive mechanisms of halophyte Suaeda dendroides encountering high saline environment

Suaeda dendroides, a succulent euhalophyte of the Chenopodiaceae family, intermittently spread around northern Xinjiang, China, has the ability to grow and develop in saline and alkali environments. The objective of this study was therefore to investigate the underlying molecular mechanisms of S. dendroides response to high salt conditions. 27 sequencing libraries prepared from low salt (200 mM NaCl) and high salt (800 mM NaCl) treated plants at 5 different stages were sequenced using Illumina Hiseq 2000. A total of 133,107 unigenes were obtained, of which 4,758 were DEGs. The number of DEGs in the high salt group (3,189) was more than the low salt treatment group (733) compared with the control. GO and KEGG analysis of the DEGs at different time points of the high salt treatment group showed that the genes related to cell wall biosynthesis and modification, plant hormone signal transduction, ion homeostasis, organic osmolyte accumulation, and reactive oxygen species (ROS) detoxification were significantly expressed, which indicated that these could be the main mechanisms of S. dendroides acclimate to high salt stress. The study provides a new perspective for understanding the molecular mechanisms of halophytes adapting to high salinity. It also provides a basis for future investigations of key salt-responsive genes in S. dendroides.

Effect of a Zinc Phosphate Shell on the Uptake and Translocation of Foliarly Applied ZnO Nanoparticles in Pepper Plants (Capsicum annuum)

Here, isotopically labeled 68ZnO NPs (ZnO NPs) and 68ZnO NPs with a thin 68Zn3(PO4)2 shell (ZnO_Ph NPs) were foliarly applied (40 μg Zn) to pepper plants (Capsicum annuum) to determine the effect of surface chemistry of ZnO NPs on the Zn uptake and systemic translocation to plant organs over 6 weeks. Despite similar dissolution of both Zn-based NPs after 3 weeks, the Zn3(PO4)2 shell on ZnO_Ph NPs (48 ± 12 nm; -18.1 ± 0.6 mV) enabled a leaf uptake of 2.31 ± 0.34 μg of Zn, which is 2.7 times higher than the 0.86 ± 0.18 μg of Zn observed for ZnO NPs (26 ± 8 nm; 14.6 ± 0.4 mV). Further, ZnO_Ph NPs led to higher Zn mobility and phloem loading, while Zn from ZnO NPs was stored in the epidermal tissues, possibly through cell wall immobilization as a storage strategy. These differences led to higher translocation of Zn from the ZnO_Ph NPs within all plant compartments. ZnO_Ph NPs were also more persistent as NPs in the exposed leaf and in the plant stem over time. As a result, the treatment of ZnO_Ph NPs induced significantly higher Zn transport to the fruit than ZnO NPs. As determined by spICP-TOFMS, Zn in the fruit was not in the NP form. These results suggest that the Zn3(PO4)2 shell on ZnO NPs can help promote the transport of Zn to pepper fruits when foliarly applied. This work provides insight into the role of Zn3(PO4)2 on the surface of ZnO NPs in foliar uptake and in planta biodistribution for improving Zn delivery to edible plant parts and ultimately improving the Zn content in food for human consumption.

Morpho-physiological, Genomic, and Transcriptional Diversities in Response to Potassium Deficiency in Rapeseed (Brassica napus L.) Genotypes

Variations in the resistance to potassium (K) deficiency among rapeseed genotypes emphasize complicated regulatory mechanisms. In this study, a low-K-sensitivity accession (L49) responded to K deficiency with smaller biomasses, severe leaf chlorosis, weaker photosynthesis ability, and deformed stomata morphology compared to a low-K resistant accession (H280). H280 accumulated more K+ than L49 under low K. Whole-genome resequencing (WGS) revealed a total of 5,538,622 single nucleotide polymorphisms (SNPs) and 859,184 insertions/deletions (InDels) between H280 and L49. RNA-seq identified more differentially expressed K+ transporter genes with higher expression in H280 than in L49 under K deficiency. Based on the K+ profiles, differential expression profiling, weighted gene coexpression network analysis, and WGS data between H280 and L49, BnaC4.AKT1 was proposed to be mainly responsible for root K absorption-mediated low K resistance. BnaC4.AKT1 was expressed preferentially in the roots and localized on the plasma membrane. An SNP and an InDel found in the promoter region of BnaC4.AKT1 were proposed to be responsible for its differential expression between rapeseed genotypes. This study identified a gene resource for improving low-K resistance. It also facilitates an integrated knowledge of the differential physiological and transcriptional responses to K deficiency in rapeseed genotypes.

Telomere-to-telomere genome of the allotetraploid legume Sesbania cannabina reveals transposon-driven subgenome divergence and mechanisms of alkaline stress tolerance

Alkaline soils pose an increasing problem for agriculture worldwide, but using stress-tolerant plants as green manure can improve marginal land. Here, we show that the legume Sesbania cannabina is very tolerant to alkaline conditions and, when used as a green manure, substantially improves alkaline soil. To understand genome evolution and the mechanisms of stress tolerance in this allotetraploid legume, we generated the first telomere-to-telomere genome assembly of S. cannabina spanning ∼2,087 Mb. The assembly included all centromeric regions, which contain centromeric satellite repeats, and complete chromosome ends with telomeric characteristics. Further genome analysis distinguished A and B subgenomes, which diverged approximately 7.9 million years ago. Comparative genomic analysis revealed that the chromosome homoeologs underwent large-scale inversion events (>10 Mb) and a significant, transposon-driven size expansion of the chromosome 5A homoeolog. We further identified four specific alkali-induced phosphate transporter genes in S. cannabina; these may function in alkali tolerance by relieving the deficiency in available phosphorus in alkaline soil. Our work highlights the significance of S. cannabina as a green tool to improve marginal lands and sheds light on subgenome evolution and adaptation to alkaline soils.

Can nutrients act as signals under abiotic stress?

Plant cells are in constant communication to coordinate development processes and environmental reactions. Under stressful conditions, such communication allows the plant cells to adjust their activities and development. This is due to intercellular signaling events which involve several components. In plant development, cell-to-cell signaling is ensured by mobile signals hormones, hydrogen peroxide (H2O2), nitric oxide (NO), or hydrogen sulfide (H2S), as well as several transcription factors and small RNAs. Mineral nutrients, including macro and microelements, are determinant factors for plant growth and development and are, currently, recognized as potential signal molecules. This review aims to highlight the role of nutrients, particularly calcium, potassium, magnesium, nitrogen, phosphorus, and iron as signaling components with special attention to the mechanism of response against stress conditions.

Genetically controlling VACUOLAR PHOSPHATE TRANSPORTER 1 contributes to low-phosphorus seeds in Arabidopsis

Phosphorus (P) is an indispensable nutrient for seed germination, but the seeds always store excessive P over demand. High-P seeds of feeding crops lead to environmental and nutrition issues, because phytic acid (PA), the major form of P in seeds, cannot be digested by mono-gastric animals. Therefore, reduction of P level in seeds has become an imperative task in agriculture. Our study here suggested that both VPT1 and VPT3, two vacuolar phosphate transporters responsible for vacuolar Pi sequestration, were downregulated in leaves during the flowering stage, which led to less Pi accumulated in leaves and more Pi allocated to reproductive organs, and thus high-P containing seeds. To reduce the total P content in seeds, we genetically regulated VPT1 during the flowering stage and found that overexpression of VPT1 in leaves could reduce P content in seeds without affecting the production and seed vigor. Therefore, our finding provides a potential strategy to reduce the P level of the seeds to prevent the nutrition over-accumulation pollution.

TORC pathway intersects with a calcium sensor kinase network to regulate potassium sensing in Arabidopsis

Potassium (K) is an essential macronutrient for plant growth, and its availability in the soil varies widely, requiring plants to respond and adapt to the changing K nutrient status. We show here that plant growth rate is closely correlated with K status in the medium, and this K-dependent growth is mediated by the highly conserved nutrient sensor, target of rapamycin (TOR). Further study connected the TOR complex (TORC) pathway with a low-K response signaling network consisting of calcineurin B-like proteins (CBL) and CBL-interacting kinases (CIPK). Under high K conditions, TORC is rapidly activated and shut down the CBL-CIPK low-K response pathway through regulatory-associated protein of TOR (RAPTOR)-CIPK interaction. In contrast, low-K status activates CBL-CIPK modules that in turn inhibit TORC by phosphorylating RAPTOR, leading to dissociation and thus inactivation of the TORC. The reciprocal regulation of the TORC and CBL-CIPK modules orchestrates plant response and adaptation to K nutrient status in the environment.

Environmental Stimuli and Phytohormones in Anthocyanin Biosynthesis: A Comprehensive Review

Anthocyanin accumulation in plants plays important roles in plant growth and development, as well as the response to environmental stresses. Anthocyanins have antioxidant properties and play an important role in maintaining the reactive oxygen species (ROS) homeostasis in plant cells. Furthermore, anthocyanins also act as a "sunscreen", reducing the damage caused by ultraviolet radiation under high-light conditions. The biosynthesis of anthocyanin in plants is mainly regulated by an MYB-bHLH-WD40 (MBW) complex. In recent years, many new regulators in different signals involved in anthocyanin biosynthesis were identified. This review focuses on the regulation network mediated by different environmental factors (such as light, salinity, drought, and cold stresses) and phytohormones (such as jasmonate, abscisic acid, salicylic acid, ethylene, brassinosteroid, strigolactone, cytokinin, and auxin). We also discuss the potential application value of anthocyanin in agriculture, horticulture, and the food industry.

Calcium signaling in plant mineral nutrition: From uptake to transport

Plant mineral nutrition is essential for crop yields and human health. However, the uneven distribution of mineral elements over time and space leads to a lack or excess of available mineral elements in plants. Among the essential nutrients, calcium (Ca2+) stands out as a prominent second messenger that plays crucial roles in response to extracellular stimuli in all eukaryotes. Distinct Ca2+ signatures with unique parameters are induced by different stresses and deciphered by various Ca2+ sensors. Recent research on the participation of Ca2+ signaling in regulation of mineral elements has made great progress. In this review, we focus on the impact of Ca2+ signaling on plant mineral uptake and detoxification. Specifically, we emphasize the significance of Ca2+ signaling for regulation of plant mineral nutrition and delve into key points and novel avenues for future investigations, aiming to offer new insights into plant ion homeostasis.

Genome-Wide Identification and Characterization of the HAK Gene Family in Quinoa (Chenopodium quinoa Willd.) and Their Expression Profiles under Saline and Alkaline Conditions

The high-affinity K+ transporter (HAK) family, the most prominent potassium transporter family in plants, which involves K+ transport, plays crucial roles in plant responses to abiotic stresses. However, the HAK gene family remains to be characterized in quinoa (Chenopodium quinoa Willd.). We explored HAKs in quinoa, identifying 30 members (CqHAK1-CqHAK30) in four clusters phylogenetically. Uneven distribution was observed across 18 chromosomes. Furthermore, we investigated the proteins' evolutionary relationships, physicochemical properties, conserved domains and motifs, gene structure, and cis-regulatory elements of the CqHAKs family members. Transcription data analysis showed that CqHAKs have diverse expression patterns among different tissues and in response to abiotic stresses, including drought, heat, low phosphorus, and salt. The expressional changes of CqHAKs in roots were more sensitive in response to abiotic stress than that in shoot apices. Quantitative RT-PCR analysis revealed that under high saline condition, CqHAK1, CqHAK13, CqHAK19, and CqHAK20 were dramatically induced in leaves; under alkaline condition, CqHAK1, CqHAK13, CqHAK19, and CqHAK20 were dramatically induced in leaves, and CqHAK6, CqHAK9, CqHAK13, CqHAK23, and CqHAK29 were significantly induced in roots. Our results establish a foundation for further investigation of the functions of HAKs in quinoa. It is the first study to identify the HAK gene family in quinoa, which provides potential targets for further functional study and contributes to improving the salt and alkali tolerance in quinoa.

Deep learning-enabled discovery and characterization of HKT genes in Spartina alterniflora

Spartina alterniflora is a halophyte that can survive in high-salinity environments, and it is phylogenetically close to important cereal crops, such as maize and rice. It is of scientific interest to understand why S. alterniflora can live under such extremely stressful conditions. The molecular mechanism underlying its high-saline tolerance is still largely unknown. Here we investigated the possibility that high-affinity K+ transporters (HKTs), which function in salt tolerance and maintenance of ion homeostasis in plants, are responsible for salt tolerance in S. alterniflora. To overcome the imprecision and unstable of the gene screening method caused by the conventional sequence alignment, we used a deep learning method, DeepGOPlus, to automatically extract sequence and protein characteristics from our newly assemble S. alterniflora genome to identify SaHKTs. Results showed that a total of 16 HKT genes were identified. The number of S. alterniflora HKTs (SaHKTs) is larger than that in all other investigated plant species except wheat. Phylogenetically related SaHKT members had similar gene structures, conserved protein domains and cis-elements. Expression profiling showed that most SaHKT genes are expressed in specific tissues and are differentially expressed under salt stress. Yeast complementation expression analysis showed that type I members SaHKT1;2, SaHKT1;3 and SaHKT1;8 and type II members SaHKT2;1, SaHKT2;3 and SaHKT2;4 had low-affinity K+ uptake ability and that type II members showed stronger K+ affinity than rice and Arabidopsis HKTs, as well as most SaHKTs showed preference for Na+ transport. We believe the deep learning-based methods are powerful approaches to uncovering new functional genes, and the SaHKT genes identified are important resources for breeding new varieties of salt-tolerant crops.

Melatonin enhances KCl salinity tolerance by maintaining K+ homeostasis in Malus hupehensis

Large amounts of potash fertilizer are often applied to apple (Malus domestica) orchards to enhance fruit quality and yields, but this treatment aggravates KCl-based salinity stress. Melatonin (MT) is involved in a variety of abiotic stress responses in plants. However, its role in KCl stress tolerance is still unknown. In the present study, we determined that an appropriate concentration (100 μm) of MT significantly alleviated KCl stress in Malus hupehensis by enhancing K+ efflux out of cells and compartmentalizing K+ in vacuoles. Transcriptome deep-sequencing analysis identified the core transcription factor gene MdWRKY53, whose expression responded to both KCl and MT treatment. Overexpressing MdWRKY53 enhanced KCl tolerance in transgenic apple plants by increasing K+ efflux and K+ compartmentalization. Subsequently, we characterized the transporter genes MdGORK1 and MdNHX2 as downstream targets of MdWRKY53 by ChIP-seq. MdGORK1 localized to the plasma membrane and enhanced K+ efflux to increase KCl tolerance in transgenic apple plants. Moreover, overexpressing MdNHX2 enhanced the KCl tolerance of transgenic apple plants/callus by compartmentalizing K+ into the vacuole. RT-qPCR and LUC activity analyses indicated that MdWRKY53 binds to the promoters of MdGORK1 and MdNHX2 and induces their transcription. Taken together, our findings reveal that the MT-WRKY53-GORK1/NHX2-K+ module regulates K+ homeostasis to enhance KCl stress tolerance in apple. These findings shed light on the molecular mechanism of apple response to KCl-based salinity stress and lay the foundation for the practical application of MT in salt stress.

Enhanced soil P immobilization and microbial biomass P by application of biochar modified with eggshell

Phosphate fertilizers have been excessively applied in agricultural production, bringing the risk of phosphorus (P) loss to nearby river systems and low utilization efficiency. In this study, eggshell-modified biochars prepared by pyrolysis of eggshell and corn straw or pomelo peel were applied to soil for enhancing P immobilization and utilization. The structure and properties of modified biochars before and after P adsorption were analyzed using the Brunauer-Emmett-Teller (BET) nitrogen adsorption method, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM). The eggshell-modified biochar performed an excellent adsorption performance for P (up to 200 mg/g), which was well described by the Langmuir model (R2 > 0.969), showing monolayer chemical adsorption with homogenous surface. The Ca(OH)2 appeared on the surface of eggshell modified biochars and changed to Ca5(PO4)3(OH) and CaHPO4(H2O)2 after P adsorption. The release of immobilized P by modified biochar increased with decreased pH. In addition, pot experiments of soybean indicated that the combined application of modified biochar and P fertilizer significantly increased the content of microbial biomass P in soil, raising from 4.18 mg/kg (control group) to 51.6-61.8 mg/kg (treatment group), and plants height increased by 13.8-26.7%. Column leaching experiments showed that P concentration in the leachate decreased by 97.9% with the modified biochar application. This research provides a new perspective that the eggshell-modified biochar could serve as a potential soil amendment for enhancing P immobilization and utilization.

Plant growth promoting activities of Pseudomonas sp. and Enterobacter sp. isolated from the rhizosphere of Vachellia gummifera in Morocco

The Moroccan endemic Vachellia gummifera grows wild under extreme desert conditions. This plant could be used as an alternative fodder for goats, and camels, in order to protect the Argan forests against overgrazing in Central and Southwestern Moroccan semiarid areas. With the aim to improve the V. gummifera population's density in semiarid areas, we proposed its inoculation with performing plant growth-promoting bacteria. Hence, 500 bacteria were isolated from the plant rhizosphere. From these, 291 isolates were retained for plant growth-promoting (PGP) activities assessment. A total of 44 isolates showed the best phosphates solubilization potential, as well as siderophore and auxin production. The combination of REP-PCR (repetitive extragenic palindromic-polymerase chain reaction) fingerprinting, PGP activities, and phenotypic properties, allowed the selection of three strains for the inoculation experiments. The three selected strains' 16S rRNA sequencing showed that they are members of the Enterobacter and Pseudomonas genera. The inoculation with three strains had diverse effects on V. gummifera growth parameters. All single and combined inoculations improved the plant shoot weight by more than 200%, and the root length by up to 139%, while some combinations further improved protein and chlorophyll content, thereby improving the plant's forage value. The three selected strains constitute an effective inoculum for use in the arid and semiarid zones of southern Morocco.

Imazethapyr disrupts plant phosphorus homeostasis and acquisition strategies

The deficiency of essential mineral nutrients caused by xenobiotics often results in plant mortality or an inability to complete its life cycle. Imazethapyr, a widely utilized imidazolinone herbicide, has a long-lasting presence in the soil-plant system and can induce toxicity in non-target plants. However, the effects of imazethapyr on mineral nutrient homeostasis remain poorly comprehended. In this study, Arabidopsis seedlings exposed to concentrations of 4 and 10 μg/L imazethapyr showed noticeable reductions in shoot development and displayed a distinct dark purple color, which is commonly associated with phosphorus (P) deficiency in crops. Additionally, the total P content in both the shoots and roots of Arabidopsis significantly decreased following imazethapyr treatment when compared to the control groups. Through the complementary use of physiological and molecular analyses, we discovered that imazethapyr hinders the abundance and functionality of inorganic phosphorus (Pi) transporters and acid phosphatase. Furthermore, imazethapyr impairs the plant's Pi-deficiency adaptation strategies, such as inhibiting Pi transporter activities and impeding root hair development, which ultimately exacerbate P starvation. These results provide compelling evidence that residues of imazethapyr have the potential to disrupt plant P homeostasis and acquisition strategies. These findings offer valuable insights for risk assessment and highlight the need to reconsider the indiscriminate use of imazethapyr, particularly under specific scenarios such as nutrient deficiency.

Modulation of potassium transport to increase abiotic stress tolerance in plants

Potassium is the major cation responsible for the maintenance of the ionic environment in plant cells. Stable potassium homeostasis is indispensable for virtually all cellular functions, and, concomitantly, viability. Plants must cope with environmental changes such as salt or drought that can alter ionic homeostasis. Potassium fluxes are required to regulate the essential process of transpiration, so a constraint on potassium transport may also affect the plant's response to heat, cold, or oxidative stress. Sequencing data and functional analyses have defined the potassium channels and transporters present in the genomes of different species, so we know most of the proteins directly participating in potassium homeostasis. The still unanswered questions are how these proteins are regulated and the nature of potential cross-talk with other signaling pathways controlling growth, development, and stress responses. As we gain knowledge regarding the molecular mechanisms underlying regulation of potassium homeostasis in plants, we can take advantage of this information to increase the efficiency of potassium transport and generate plants with enhanced tolerance to abiotic stress through genetic engineering or new breeding techniques. Here, we review current knowledge of how modifying genes related to potassium homeostasis in plants affect abiotic stress tolerance at the whole plant level.

Sailing in complex nutrient signaling networks: Where I am, where to go, and how to go?

To ensure survival and promote growth, sessile plants have developed intricate internal signaling networks tailored in diverse cells and organs with both shared and specialized functions that respond to various internal and external cues. A fascinating question arises: how can a plant cell or organ diagnose the spatial and temporal information it is experiencing to know "where I am," and then is able to make the accurate specific responses to decide "where to go" and "how to go," despite the absence of neuronal systems found in mammals. Drawing inspiration from recent comprehensive investigations into diverse nutrient signaling pathways in plants, this review focuses on the interactive nutrient signaling networks mediated by various nutrient sensors and transducers. We assess and illustrate examples of how cells and organs exhibit specific responses to changing spatial and temporal information within these interactive plant nutrient networks. In addition, we elucidate the underlying mechanisms by which plants employ posttranslational modification codes to integrate different upstream nutrient signals, thereby conferring response specificities to the signaling hub proteins. Furthermore, we discuss recent breakthrough studies that demonstrate the potential of modulating nutrient sensing and signaling as promising strategies to enhance crop yield, even with reduced fertilizer application.

Rice potassium transporter OsHAK18 mediates phloem K+ loading and redistribution

High-affinity K+ transporters/K+ uptake permeases/K+ transporters (HAK/KUP/KT) are important pathways mediating K+ transport across cell membranes, which function in maintaining K+ homeostasis during plant growth and stress response. An increasing number of studies have shown that HAK/KUP/KT transporters play crucial roles in root K+ uptake and root-to-shoot translocation. However, whether HAK/KUP/KT transporters also function in phloem K+ translocation remain unclear. In this study, we revealed that a phloem-localized rice HAK/KUP/KT transporter, OsHAK18, mediated cell K+ uptake when expressed in yeast, Escherichia coli and Arabidopsis. It was localized at the plasma membrane. Disruption of OsHAK18 rendered rice seedlings insensitive to low-K+ (LK) stress. After LK stress, some WT leaves showed severe wilting and chlorosis, whereas the corresponding leaves of oshak18 mutant lines (a Tos17 insertion line and two CRISPR lines) remained green and unwilted. Compared with WT, the oshak18 mutants accumulated more K+ in shoots but less K+ in roots after LK stress, leading to a higher shoot/root ratio of K+ per plant. Disruption of OsHAK18 does not affect root K+ uptake and K+ level in xylem sap, but it significantly decreases phloem K+ concentration and inhibits root-to-shoot-to-root K+ (Rb+ ) translocation in split-root assay. These results reveal that OsHAK18 mediates phloem K+ loading and redistribution, whose disruption is in favor of shoot K+ retention under LK stress. Our findings expand the understanding of HAK/KUP/KT transporters' functions and provide a promising strategy for improving rice tolerance to K+ deficiency.

Cloning and functional characterization of FtWRKY29, a low phosphorus stress-inducible transcription factor in Tartary buckwheat

The regulation of the expression of genes related to abiotic stress in plants is significantly influenced by the binding of the transcription factor (TF) WRKY to the W-box elements in their promoters. The findings of this study have confirmed that the ability of Tartary buckwheat (Fagopyrum tataricum Gaertn.) to tolerate phosphorus (P) deficiency is regulated by FtWRKY29, which is classified as a member of group II of the WRKY family. The roots predominantly exhibited an enhanced expression of FtWRKY29, which was significantly upregulated in response to low-P-induced stress. The W-box motif was bound to by FtWRKY29 which enhanced the transcription of genes and was localized to the nucleus. The overexpression of FtWRKY29 in Arabidopsis thaliana produced transgenic lines that exhibited phenotypes typical of diminished sensitivity to low-P-induced stress by promoting root growth, increasing P-uptake, and regulating the accumulation of anthocyanin. The low-P-responsive genes, PHT1;1, PHT1;4, and PHO1 were significantly up-regulated in these lines. In addition, the overexpression of FtWRKY29 restored the P-absorption ability of the wrky75 mutant to a certain extent. Moreover, the binding of FtWRKY29 to the promoter of PHT1;1 activated its expression in tobacco. It was also observed that FtWRKY29 interacts with AtMPK3, AtMPK6, FtMPK3, and FtMPK7. This study provides preliminary evidence that FtWRKY29 improved the tolerance of transgenic A. thaliana plants to low-P-induced stress and deepened the understanding of the regulatory mechanism behind the same in Tartary buckwheat.

Enhancement patterns of potassium on nitrogen transport and functional genes in cotton vary with nitrogen levels

The application of potassium (K) in conjunction with nitrogen (N) has been shown to enhance N use efficiency. However, there is still a need for further understanding of the optimal ratios and molecular regulatory mechanisms, particularly in soil-cotton systems. Here, a field trial was conducted, involving varying rates of N and K, alongside pot and hydroponic experiments. The objective was to assess the impact of N-K interaction on the absorption, transport and distribution of N in cotton. The results showed that K supply at 90 and 240 kg ha-1 had a beneficial impact on N uptake and distribution to both seed and lint, resulting in the highest N use efficiency ranging from 22% to 62% and yield improvements from 20% to 123%. The increase in stem and root diameters, rather than the quantify of xylem vessels and phloem sieve tubes, facilitated the uptake and transport of N due to the provision of K. At the molecular level, K supply upregulated the expression levels of genes encoding GhNRT2.1 transporter and GhSLAH3 channel in cotton roots to promote N uptake and GhNRT1.5/NPF7.3 genes to transport N to shoot under low-N conditions. However, under high-N conditions, K supply induced anion channel genes (GhSLAH4) of roots to promote N uptake and genes encoding GhNRT1.5/NPF7.3 and GhNRT1.8/NPF7.2 transporters to facilitate NO3- unloading from xylem to mesophyll cell in high-N plants. Furthermore, K supply resulted in the upregulation of gene expression for GhGS2 in leaves, while simultaneously downregulating the expression of GhNADH-GOGAT, GhGDH1 and GhGDH3 genes in high-N roots. The enzyme activities of nitrite reductase and glutamine synthetase increased and glutamate dehydrogenase decreased, but the concentration of NO3- and soluble protein exhibited a significant increase and free amino acid decreased in the shoots subsequent to K supply.

Calcium signaling-mediated transcriptional reprogramming during abiotic stress response in plants

Calcium (Ca2+) is a second messenger in plants growth and development, as well as in stress responses. The transient elevation in cytosolic Ca2+ concentration have been reported to be involved in plants response to abiotic and biotic stresses. In plants, Ca2+-induced transcriptional changes trigger molecular mechanisms by which plants adapt and respond to environment stresses. The mechanism for transcription regulation by Ca2+ could be either rapid in which Ca2+ signals directly cause the related response through the gene transcript and protein activities, or involved amplification of Ca2+ signals by up-regulation the expression of Ca2+ responsive genes, and then increase the transmission of Ca2+ signals. Ca2+ regulates the expression of genes by directly binding to the transcription factors (TFs), or indirectly through its sensors like calmodulin, calcium-dependent protein kinases (CDPK) and calcineurin B-like protein (CBL). In recent years, significant progress has been made in understanding the role of Ca2+-mediated transcriptional regulation in different processes in plants. In this review, we have provided a comprehensive overview of Ca2+-mediated transcriptional regulation in plants in response to abiotic stresses including nutrition deficiency, temperature stresses (like heat and cold), dehydration stress, osmotic stress, hypoxic, salt stress, acid rain, and heavy metal stress.

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.

Effects of foliar-sprayed potassium dihydrogen phosphate on accumulation of flavonoids in Cabernet Sauvignon (Vitis vinifera L.)

BACKGROUND

In current vineyards, potassium dihydrogen phosphate (KH₂ PO₄ ) is a common foliar fertilizer with the lowest salt index. It is employed to improve the transportation and distribution of grape photosynthetic products, but the mechanism of its effect on fruit flavonoid synthesis is unclear.

RESULTS

This study investigated the effects of foliar spraying of KH₂ PO₄ at different developmental stages (1 week before veraison; the end of veraison (EV)) on flavonoid metabolites and related gene expression of 'Cabernet Sauvignon' grape for two consecutive vintages. High-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry technology was used to identify 6 flavan-3-ols, 11 flavonols, and 16 anthocyanins. KH₂ PO₄ influenced anthocyanins content, especially when applied at the EV stage, the content of anthocyanins was significantly higher than that of the control. Further, quantitative polymerase chain reaction analysis showed that KH₂ PO₄ treatment applied at the EV stage can increase the expression of anthocyanin synthesis genes and accelerate anthocyanin synthesis. In particular, the expression of VviGST in EV treatment was significantly higher than that of the control during the development process.

CONCLUSION

These findings have enhanced our understanding of the effect of KH₂ PO₄ treatment on grape flavonoids. Among them, EV treatment can significantly increase anthocyanins content. © 2023 Society of Chemical Industry.

Multi-omics strategies uncover the molecular mechanisms of nitrogen, phosphorus and potassium deficiency responses in Brassica napus

BACKGROUND

Nitrogen (N), phosphorus (P) and potassium (K) are critical macronutrients in crops, such that deficiency in any of N, P or K has substantial effects on crop growth. However, the specific commonalities of plant responses to different macronutrient deficiencies remain largely unknown.

METHODS

Here, we assessed the phenotypic and physiological performances along with whole transcriptome and metabolomic profiles of rapeseed seedlings exposed to N, P and K deficiency stresses.

RESULTS

Quantities of reactive oxygen species were significantly increased by all macronutrient deficiencies. N and K deficiencies resulted in more severe root development responses than P deficiency, as well as greater chlorophyll content reduction in leaves (associated with disrupted chloroplast structure). Transcriptome and metabolome analyses validated the macronutrient-specific responses, with more pronounced effects of N and P deficiencies on mRNAs, microRNAs (miRNAs), circular RNAs (circRNAs) and metabolites relative to K deficiency. Tissue-specific responses also occurred, with greater effects of macronutrient deficiencies on roots compared with shoots. We further uncovered a set of common responders with simultaneous roles in all three macronutrient deficiencies, including 112 mRNAs and 10 miRNAs involved in hormonal signaling, ion transport and oxidative stress in the root, and 33 mRNAs and 6 miRNAs with roles in abiotic stress response and photosynthesis in the shoot. 27 and seven common miRNA-mRNA pairs with role in miRNA-mediated regulation of oxidoreduction processes and ion transmembrane transport were identified in all three macronutrient deficiencies. No circRNA was responsive to three macronutrient deficiency stresses, but two common circRNAs were identified for two macronutrient deficiencies. Combined analysis of circRNAs, miRNAs and mRNAs suggested that two circRNAs act as decoys for miR156 and participate in oxidoreduction processes and transmembrane transport in both N- and P-deprived roots. Simultaneously, dramatic alterations of metabolites also occurred. Associations of RNAs with metabolites were observed, and suggested potential positive regulatory roles for tricarboxylic acids, azoles, carbohydrates, sterols and auxins, and negative regulatory roles for aromatic and aspartate amino acids, glucosamine-containing compounds, cinnamic acid, and nicotianamine in plant adaptation to macronutrient deficiency.

CONCLUSIONS

Our findings revealed strategies to rescue rapeseed from macronutrient deficiency stress, including reducing the expression of non-essential genes and activating or enhancing the expression of anti-stress genes, aided by plant hormones, ion transporters and stress responders. The common responders to different macronutrient deficiencies identified could be targeted to enhance nutrient use efficiency in rapeseed.

Calcium signalling components underlying NPK homeostasis: potential avenues for exploration

Plants require the major macronutrients, nitrogen (N), phosphorus (P) and potassium (K) for normal growth and development. Their deficiency in soil directly affects vital cellular processes, particularly root growth and architecture. Their perception, uptake and assimilation are regulated by complex signalling pathways. To overcome nutrient deficiencies, plants have developed certain response mechanisms that determine developmental and physiological adaptations. The signal transduction pathways underlying these responses involve a complex interplay of components such as nutrient transporters, transcription factors and others. In addition to their involvement in cross-talk with intracellular calcium signalling pathways, these components are also engaged in NPK sensing and homeostasis. The NPK sensing and homeostatic mechanisms hold the key to identify and understand the crucial players in nutrient regulatory networks in plants under both abiotic and biotic stresses. In this review, we discuss calcium signalling components/pathways underlying plant responses to NPK sensing, with a focus on the sensors, transporters and transcription factors involved in their respective signalling and homeostasis.

Arbuscular mycorrhizal fungi enhance phosphate uptake and alter bacterial communities in maize rhizosphere soil

Arbuscular mycorrhizal fungi (AMF) can symbiose with many plants and improve nutrient uptake for their host plant. Rhizosphere microorganisms have been pointed to play important roles in helping AMF to mobilize soil insoluble nutrients, especially phosphorus. Whether the change in phosphate transport under AMF colonization will affect rhizosphere microorganisms is still unknown. Here, we evaluated the links of interactions among AMF and the rhizosphere bacterial community of maize (Zea mays L.) by using a maize mycorrhizal defective mutant. Loss of mycorrhizal symbiosis function reduced the phosphorus concentration, biomass, and shoot length of maize colonized by AMF. Using 16S rRNA gene amplicon high-throughput sequencing, we found that the mutant material shifted the bacterial community in the rhizosphere under AMF colonization. Further functional prediction based on amplicon sequencing indicated that rhizosphere bacteria involved in sulfur reduction were recruited by the AMF colonized mutant but reduced in the AMF- colonized wild type. These bacteria harbored much abundance of sulfur metabolism-related genes and negatively correlated with biomass and phosphorus concentrations of maize. Collectively, this study shows that AMF symbiosis recruited rhizosphere bacterial communities to improve soil phosphate mobilization, which may also play a potential role in regulating sulfur uptake. This study provides a theoretical basis for improving crop adaptation to nutrient deficiency through soil microbial management practices.

The Sapria himalayana genome provides new insights into the lifestyle of endoparasitic plants

BACKGROUND

Sapria himalayana (Rafflesiaceae) is an endoparasitic plant characterized by a greatly reduced vegetative body and giant flowers; however, the mechanisms underlying its special lifestyle and greatly altered plant form remain unknown. To illustrate the evolution and adaptation of S. himalayasna, we report its de novo assembled genome and key insights into the molecular basis of its floral development, flowering time, fatty acid biosynthesis, and defense responses.

RESULTS

The genome of S. himalayana is ~ 1.92 Gb with 13,670 protein-coding genes, indicating remarkable gene loss (~ 54%), especially genes involved in photosynthesis, plant body, nutrients, and defense response. Genes specifying floral organ identity and controlling organ size were identified in S. himalayana and Rafflesia cantleyi, and showed analogous spatiotemporal expression patterns in both plant species. Although the plastid genome had been lost, plastids likely biosynthesize essential fatty acids and amino acids (aromatic amino acids and lysine). A set of credible and functional horizontal gene transfer (HGT) events (involving genes and mRNAs) were identified in the nuclear and mitochondrial genomes of S. himalayana, most of which were under purifying selection. Convergent HGTs in Cuscuta, Orobanchaceae, and S. himalayana were mainly expressed at the parasite-host interface. Together, these results suggest that HGTs act as a bridge between the parasite and host, assisting the parasite in acquiring nutrients from the host.

CONCLUSIONS

Our results provide new insights into the flower development process and endoparasitic lifestyle of Rafflesiaceae plants. The amount of gene loss in S. himalayana is consistent with the degree of reduction in its body plan. HGT events are common among endoparasites and play an important role in their lifestyle adaptation.

QTL Mapping and Candidate Gene Identifying for N, P, and K Use Efficiency at the Maturity Stages in Wheat

Nitrogen (N), phosphorus (P), and potassium (K) are the three most important mineral nutrients for crop growth and development. We previously constructed a genetic map of unigenes (UG-Map) based on their physical positions using a RIL population derived from the cross of "TN18 × LM6" (TL-RILs). In this study, a total of 18 traits related to mineral use efficiency (MUE) of N/P/K were investigated under three growing seasons using TL-RILs. A total of 54 stable QTLs were detected, distributed across 19 chromosomes except for 3A and 5B. There were 50 QTLs associated with only one trait, and the other four QTLs were associated with two traits. A total of 73 candidate genes for stable QTLs were identified. Of these, 50 candidate genes were annotated in Chinese Spring (CS) RefSeq v1.1. The average number of candidate genes per QTL was 1.35, with 45 QTLs containing only one candidate gene and nine QTLs containing two or more candidate genes. The candidate gene TraesCS6D02G132100 (TaPTR gene) for QGnc-6D-3306 belongs to the NPF (NRT1/PTR) gene family. We speculate that the TaPTR gene should regulate the GNC trait.

Genome-wide identification of Brassicaceae histone modification genes and their responses to abiotic stresses in allotetraploid rapeseed

BACKGROUND

Histone modification is an important epigenetic regulatory mechanism and essential for stress adaptation in plants. However, systematic analysis of histone modification genes (HMs) in Brassicaceae species is lacking, and their roles in response to abiotic stress have not yet been identified.

RESULTS

In this study, we identified 102 AtHMs, 280 BnaHMs, 251 BcHMs, 251 BjHMs, 144 BnHMs, 155 BoHMs, 137 BrHMs, 122 CrHMs, and 356 CsHMs in nine Brassicaceae species, respectively. Their chromosomal locations, protein/gene structures, phylogenetic trees, and syntenies were determined. Specific domains were identified in several Brassicaceae HMs, indicating an association with diverse functions. Syntenic analysis showed that the expansion of Brassicaceae HMs may be due to segmental and whole-genome duplications. Nine key BnaHMs in allotetraploid rapeseed may be responsible for ammonium, salt, boron, cadmium, nitrate, and potassium stress based on co-expression network analysis. According to weighted gene co-expression network analysis (WGCNA), 12 BnaHMs were associated with stress adaptation. Among the above genes, BnaPRMT11 simultaneously responded to four different stresses based on differential expression analysis, while BnaSDG46, BnaHDT10, and BnaHDA1 participated in five stresses. BnaSDG46 was also involved in four different stresses based on WGCNA, while BnaSDG10 and BnaJMJ58 were differentially expressed in response to six different stresses. In summary, six candidate genes for stress resistance (BnaPRMT11, BnaSDG46, BnaSDG10, BnaJMJ58, BnaHDT10, and BnaHDA1) were identified.

CONCLUSIONS

Taken together, these findings help clarify the biological roles of Brassicaceae HMs. The identified candidate genes provide an important reference for the potential development of stress-tolerant oilseed plants.

Effects of Spraying KH2PO4 on Flag Leaf Physiological Characteristics and Grain Yield and Quality under Heat Stress during the Filling Period in Winter Wheat

As one of the most important wheat-producing areas in China, wheat is prone to heat stress during the grain filling period in the Huang-Huai-Hai Plain (3HP), which lowers yields and degrades the grain quality of wheat. To assess the effects of spraying potassium dihydrogen phosphate (KH₂PO₄) on the physiological traits in flag leaves and grain yield (GY) and quality under heat stress during the filling period, we conducted a two-year field experiment in the winter wheat growing seasons of 2020-2022. In this study, spraying water combined with heat stress (HT), 0.3% KH₂PO₄ (KDP), and 0.3% KH₂PO₄ combined with heat stress (PHT) were designed, and spraying water alone was used as a control (CK). The dates for the spraying were the third and eleventh day after anthesis, and a plastic film shed was used to impose heat stress on the wheat plants during the grain filling period. The results showed that spraying KH₂PO₄ significantly improved the chlorophyll content and net photosynthesis rate (Pn) in flag leaves compared with the non-sprayed treatments. Compared with CK, the Pn in HT decreased by 8.97% after heat stress, while Pn in PHT decreased by 7.44% compared to that of KDP. The activities of superoxide dismutase, catalase, and peroxidase in flag leaves were significantly reduced when the wheat was subjected to heat stress, while malonaldehyde content increased, and the enzyme activities were significantly enhanced when KH₂PO₄ was sprayed. Heat stress significantly decreased the contribution rate of dry matter accumulation (DM) after anthesis of wheat to grain (CRAA), whereas spraying KH₂PO₄ significantly increased the CRAA and harvest index. At maturity, the DM in CK was significantly higher than that in HT, KDP was significantly higher than PHT, and KDP had the highest DM. Compared with CK, the GY in KDP significantly increased by 9.85% over the two years, while the GY in HT decreased by 11.44% compared with that of CK, and the GY in PHT decreased by 6.31% compared to that of KDP. Spraying KH₂PO₄ after anthesis primarily helped GY by maintaining a high thousand grain weight to lessen the negative effects of heat stress on wheat. Moreover, heat stress significantly reduced protein concentration, wet gluten content, dough development time, and hardness index in grains of mature, while spraying KH₂PO₄ maintained a sufficient grain quality under the conditions of achieving higher yields. Overall, spraying KH₂PO₄ after anthesis could enhance the heat stress resistance of wheat and maintain the photosynthetic capacity of flag leaves, ensuring the dry matter production and reducing the negative effects on grain yield and quality in the 3HP.

Aspergillus aculeatus enhances nutrient uptake and forage quality in bermudagrass by increasing phosphorus and potassium availability

Introduction

Potassium and phosphorus are essential macronutrients for plant growth and development. However, most P and K exist in insoluble forms, which are difficult for plants to directly absorb and utilize, thereby resulting in growth retardation of plants under P or K deficiency stress. The Aspergillus aculeatus fungus has growth-promoting characteristics and the ability to dissolve P and K.

Methods

Here, to investigate the physiological effects of A. aculeatus on bermudagrass under P or K deficiency, A. aculeatus and bermudagrass were used as experimental materials.

Results and discussion

The results showed that A. aculeatus could promote tolerance to P or K deficiency stress in bermudagrass, decrease the rate of leaf death, and increase the contents of crude fat as well as crude protein. In addition, A. aculeatus significantly enhanced the chlorophyll a+b and carotenoid contents. Moreover, under P or K deficiency stress, bermudagrass inoculated with A. aculeatus showed higher N, P, and K contents than non-inoculated plants. Furthermore, exogenous A. aculeatus markedly decreased the H2O2 level and CAT and POD activities. Based on our results, A. aculeatus could effectively improve the forage quality of bermudagrass and alleviate the negative effects of P or K deficiency stress, thereby playing a positive economic role in the forage industry.