Plant nitrogen assimilation and use efficiency

Nitrogen Assimilation Plays a Role in Balancing the Chloroplastic Glutathione Redox Potential Under High Light Conditions

Nitrate reduction requires reducing equivalents produced by the photosynthetic electron transport chain. Therefore, it has been suggested that nitrate assimilation provides a sink for electrons under high light conditions. We tested this hypothesis by monitoring photosynthetic efficiency and the chloroplastic glutathione redox potential (chl-EGSH) of plant lines with mutated glutamine synthetase 2 (GS2) and ferredoxin-dependent glutamate synthase 1 (GOGAT1). Mutant lines incorporated significantly less isotopically-labelled nitrate into amino acids than wild-type plants, demonstrating impaired nitrogen assimilation. When nitrate assimilation was compromised, photosystem II (PSII) proved more vulnerable to photodamage. The effect of the nitrate assimilation pathway on the chl- EGSH was monitored using the chloroplast-targeted roGFP2 biosensor (chl-roGFP2). Remarkably, while oxidation followed by reduction of chl-roGFP2 was detected in WT plants in response to high light, oxidation values were stable in the mutant lines, suggesting that chl-EGSH relaxation after high light-induced oxidation is achieved by diverting excess electrons to the nitrogen assimilation pathway. Importantly, similar ΦPSII and chl-roGFP2 patterns were observed at elevated CO2, suggesting that mutant phenotypes are not associated with photorespiration activity. Together, these findings indicate that the nitrogen assimilation pathway serves as a sustainable energy dissipation route, ensuring efficient photosynthetic activity and fine-tuning redox metabolism under light-saturated conditions.

Two types of covering crops are beneficial to improve the nitrogen metabolism of Citrus roots

Citrus is the world's largest fruit category, yet it is frequently damaged by weeds during cultivation and management. As a green cultivation measure, covering crops in orchards effectively controls weeds and enhances soil quality. At present, the research on covering crops is mostly focused on soil, but there is still a lack of research on how crops affect citrus trees. This study aims to provide theoretical support for the widespread adoption of the green management practices. The previous research of us found that rattail fescue and vicia villosa had notably enhanced the organic matter and alkali-hydrolyzable nitrogen levels in orchard soils. Consequently, this study treated citrus orchards with sowing rattail fescue and vicia villosa between rows, with manual tillage serving as the control, to investigate the impact of two-year grass cultivation on N metabolism in citrus roots. Results indicated that both types of grass significantly enhanced amino acid metabolism in citrus roots at depths of 0-20 cm, significantly increasing activities of nitrate reductase, nitrite reductase, glutamine synthetase, NADH-glutamate synthetase, and NADPH-glutamate dehydrogenase, as well as expression levels of NR and NiR. Rattail fescue demonstrated superior effects. There was no discernible pattern in amino acid levels at depths of 20-40 cm, with both grass types significantly increasing NR, NADH-GOGAT enzyme activity, and also increasing gene expression levels for NiR, GDH1, and GDH2. Both types of grass significantly promoted N metabolism in citrus roots at depths of 0-20 cm, with rattail fescue outperforming vicia villosa.

Amino acid transporter OsATL13 coordinately regulates rice yield and quality by transporting phenylalanine and methionine

Amino acids are crucial nutrients for growth in crops. In this study, we found an amino acid transporter-like 13 (OsATL13), that coordinately determined rice yield and quality. OsATL13 was primarily expressed in the root and panicle, its protein was localized on plasma membrane, and it principally transported phenylalanine and methionine. Overexpression (OE) of OsATL13 increased the tiller number by 31.4 %, resulting in a 16.18 % increase in grain yield compared to Zhonghua 11 (ZH11). It also decreased amylose content and increased protein content in OsATL13 OE lines compared to ZH11, whereas the OsATL13 mutant exhibited opposite effects. RNA-seq analysis revealed that upregulation of OsATL13 influenced the expression of genes associated with nitrogen and starch metabolism pathways. Notably, exogenous treatment with phenylalanine and methionine promoted axillary buds outgrowth, increased tiller number and rice yield, improved milled and head rice rates, and decreased chalky rice rate. Furthermore, rapid viscosity analysis supported the observation that phenylalanine and methionine treatments influenced rice eating and cooking quality. This research offers new perspectives on the synchronized enhancement of both rice yield and quality with amino acid transporter OsATL13.

The MdWRKY17 positively regulates nitrate uptake by promoting MdNRT2.5 expression under long-term low N stress in apple

Nitrogen (N) supply is critical for apple yield and quality. Improving nitrogen use efficiency (NUE) could reduce fertilizer application for maintaining apple yield at the cost of environmental pollution in infertile soil. The molecular mechanisms underlying nitrate (NO3-) uptake are foundational for breeding high NUE cultivars. The two-month low N treatment mimicking infertile soil dramatically induced the accumulation of transcription factor MdWRKY17 in apple. Overexpression of MdWRKY17 conferred enhanced long-term low nitrogen tolerance in transgenic apple plants and calli, while RNA interference of MdWRKY17 reduced this tolerance. MdNRT2.5 encoding a high-affinity nitrate transporter was identified by chromatin immunoprecipitation sequencing (ChIP-seq) as the direct target of MdWRKY17. This is confirmed by in vitro EMSA and in vivo ChIP-qPCR assay. Notably, overexpression of MdNRT2.5 increased NO3- uptake under long-term N-deficiency conditions. RNA interference of MdNRT2.5 in roots decreased NO3- uptake efficiency of MdWRKY17-OE transgenic apple plants, indicating that MdWRKY17 improves NO3- uptake mainly by activating MdNRT2.5 expression. Our study identified an important MdWRKY17-MdNRT2.5 module in response to long-term low N stress, which will contribute to the molecular breeding of high NUE apple cultivars.

9311 allele of OsNAR2.2 enhances nitrate transport to improve rice yield and nitrogen use efficiency

Improving nitrogen use efficiency (NUE) in rice is a requirement for future sustainable agricultural production. However, key factors and regulatory networks involved in NUE remain unclear. Here, QTL analysis, fine-mapping and functional validation demonstrated that qCR4 encodes a putative high-affinity nitrate transporter-activating protein 2.2 (OsNAR2.2). Located in the endoplasmic reticulum (ER), OsNAR2.2 was confirmed to regulate nitrate transport from root-to-shoot and control panicle number, grain yield and NUE in rice. RNA-seq and RT-qPCR revealed that OsNAR2.2 modulates nitrogen utilization by altering the expressions of some nitrogen metabolism-related genes and auxin signal-related genes. Furthermore, the 9311 allele of OsNAR2.2 significantly enhanced panicle number, grain yield and NUE, which provides a potential target for rice yield and NUE improvement.

Plant Nitrogen Assimilation: A Climate Change Perspective

Of all the essential macronutrients necessary for plant growth and development, nitrogen is required in the greatest amounts. Nitrogen is a key component of important biomolecules like proteins and has high nutritive importance for humans and other animals. Climate change factors, such as increasing levels of carbon dioxide, increasing temperatures, and increasing watering regime, directly or indirectly influence plant nitrogen uptake and assimilation dynamics. The impacts of these stressors can directly threaten our primary source of nitrogen as obtained from the soil by plants. In this review, we discuss how climate change factors can influence nitrogen uptake and assimilation in cultivated plants. We examine the effects of these factors alone and in combination with species of both C3 and C4 plants. Elevated carbon dioxide, e[CO2], causes the dilution of nitrogen in tissues of non-leguminous C3 and C4 plants but can increase nitrogen in legumes. The impact of high-temperature (HT) stress varies depending on whether a species is leguminous or not. Water stress (WS) tends to result in a decrease in nitrogen assimilation. Under some, though not all, conditions, e[CO2] can have a buffering effect against the detrimental impacts of other climate change stressors, having an ameliorating effect on the adverse impacts of HT or WS. Together, HT and WS are seen to cause significant reductions in biomass production and nitrogen uptake in non-leguminous C3 and C4 crops. With a steadily rising population and rapidly changing climate, consideration must be given to the morphological and physiological effects that climate change will have on future crop health and nutritional quality of N.

Moderate Nitrogen Application Synergistically Improved Yield and Quality of Nanjing Series japonica Rice Varieties with Good Taste

Nanjing series japonica rice varieties developed by the Institute of Food Crops, Jiangsu Academy of Agricultural Sciences in China have the characteristics of an excellent taste quality, high yield, and good resistance. They are widely promoted and applied in the lower reaches of the Yangtze River in China's japonica rice planting areas. In response to the problem of the lack of coordination between nitrogen fertilizer management measures and variety characteristics in production, which makes it difficult to synergistically improve yield and quality, this study adopted a split-plot experimental design to study the effect of nitrogen fertilizer application on yield and rice quality of Nanjing series japonica rice varieties. In 2021, four nitrogen application rates of 0 (N1), 150 (N2), 300 (N3), and 450 (N4) kg hm-2 (all pure nitrogen) were set up, and in 2022, four treatments of 120 (N1), 180 (N2), 240 (N3), and 300 (N4) kg hm-2 were set up, all with nitrogen application rate as the main plot factor and variety as the sub-plot factor. The results showed that the differences between the different nitrogen fertilizer treatments were significant at the 5% or 1% level, except for the milled rice rate, head rice rate, peak viscosity, setback viscosity, and paste temperature in 2021 and panicle number, grain number per panicle, all Rapid Visco-analyzer (RVA) characteristic values, and amylose content in 2022. With an increase in the nitrogen application rate, the number of panicles, grain number per panicle, and yield increased. Either the rates of brown rice, milled rice, or head rice and chalky grains or chalkiness showed an increase trend. The peak viscosity, hot viscosity, final viscosity, and breakdown viscosity decreased, while the setback viscosity increased. For the quality of cooked rice, the hardness increased, appearance, viscosity, and balance decreased, protein content increased, and taste value decreased. The interaction between nitrogen application rate and variety was significant at p < 0.05 or p < 0.01 only for yield components, processing quality, and rice protein content in 2021 and for eating and cooking quality, appearance quality, and peak viscosity in 2022. Other traits were not significant. The comprehensive results from two years of experiments showed that, under the conditions of this experiment, a nitrogen application rate of 240-300 kg hm-2 could improve the quality of rice in the Nanjing series varieties while maintaining a high yield. The results of this experiment have a guiding significance for the high-yield and high-quality cultivation of excellent-tasting Nanjing series japonica rice.

Phenotype Assessment and Putative Mechanisms of Ammonium Toxicity to Plants

Ammonium (NH4+) and nitrate (NO3-) are the primary inorganic nitrogen (N) sources that exert influence on plant growth and development. Nevertheless, when NH4+ constitutes the sole or dominant N source, it can inhibit plant growth, a process also known as ammonium toxicity. Over multiple decades, researchers have shown increasing interest in the primary causes, mechanisms, and detoxification strategies of ammonium toxicity. Despite this progress, the current investigations into the mechanisms of ammonium toxicity remain equivocal. This review initially presents a comprehensive assessment of phenotypes induced by ammonium toxicity. Additionally, this review also recapitulates the existing mechanisms of ammonium toxicity, such as ion imbalance, disruption of the phytohormones homeostasis, ROS (reactive oxygen species) burst, energy expenditure, and rhizosphere acidification. We conclude that alterations in carbon-nitrogen (C-N) metabolism induced by high NH4+ may be one of the main reasons for ammonium toxicity and that SnRK1 (Sucrose non-fermenting 1-related kinase) might be involved in this process. The insights proffered in this review will facilitate the exploration of NH4+ tolerance mechanisms and the development of NH4+-tolerant crops in agricultural industries.

Navigating nitrogen sustainability with microbiome-associated phenotypes

Crop microbiomes promote plant health through various mechanisms, including nutrient provisioning. However, agriculture neglected the importance of these microbiome-associated phenotypes (MAPs) in conventional management approaches originating from the Green Revolution. Green Revolution innovations, such as nitrogen fertilizers and high-yielding germplasm, supported an increase in global crop yields. Yet these advances also led to many environmental issues, including disruptions in microbially mediated nitrogen transformations that have reduced reliance on microbiomes for sustainable nitrogen acquisition. Overcoming the challenges introduced by the Green Revolution requires a shift toward ecologically informed agronomic strategies that incorporate MAPs into breeding and management decisions. Agriculture in the Anthropocene needs to mindfully manage crop microbiomes to decouple agrochemical inputs from profitable yields, minimizing the environmental repercussions of modern agriculture.

BcAMT1;2 interacts with BcLBD41 and BcMAMYB transcription factors during nitrogen metabolism in flowering Chinese cabbage

Chinese cabbage is an important vegetable in southern China. Excessive nitrogen fertilizer application can lead to the accumulation of nitrate in edible organs, which affects food value. Hence, the cultivation of varieties with high nitrogen utilization efficiency (NUE) and low nitrate accumulation is essential for molecular breeding. In flowering Chinese cabbage, Ammonium transporter 1;2 (AMT1;2,XM_009113156.2) significantly promotes plant growth, while reducing the nitrate content and ultimately improving the nutritional value of the crop; however, the exact underlying regulatory mechanisms remain unclear. Here, we aimed to investigate the response pattern of BcAMT1;2 to nitrogen (N) deficiency and mixed ammonium-nitrate nutrition and the potential roles played by its interacting proteins, Lateral organ boundaries domain 41 (LBD41,XM_009120072.3) and Membrane-anchored MYB (MAMYB,XM_009103351.3), in N metabolism. We found that transient silencing and overexpression of BcAMT1;2 regulated the absorption and accumulation of ammonium (NH4+) and nitrate (NO3-) in flowering Chinese cabbage. BcLBD41 may directly induce BcAMT1;2 expression, thereby regulating NH4+ accumulation in flowering Chinese cabbages. The expression of BcLBD41 and BcAMT1;2 were downregulated during N-deficiency and upregulated after NH4+ supply restoration. Overexpression of BcLBD41 in Arabidopsis improved root and shoot growth under both LA (low-ammonium; 0.25 mM NH4+) and A/Ni (ammonium [NH4+]: nitrate [NO3-]; 0.25 mM:0.75 mM) conditions by facilitating the expression of AtAMT1;2 in transgenic plants, leading to enhanced NH4+ uptake and accumulation. The BcMAMYB protein serves as a transmembrane protein and has a strong interaction with the BcAMT1;2 protein, as well as inducing the expression of the BcAMT1;2 promoter. In the OE-BcMAMYB strain, the expression of both BcMAMYB and BcAMT1;2 were repressed under N-deficiency conditions, whereas after silencing BcMAMYB, the expression of BcAMT1;2 was not induced by ammonium. Our findings contribute to a more profound understanding of the regulatory mechanisms responsible for nitrogen absorption and accumulation in relation to BcAMT1;2.

Ferredoxin-mediated mechanism for efficient nitrogen utilization in maize

Nitrogen (N) is an essential macronutrient for plant development and, ultimately, yield. Identifying the genetic components and mechanisms underlying N use efficiency in maize (Zea mays L.) is thus of great importance. Nitrate (NO3-) is the preferred inorganic N source in maize. Here we performed a genome-wide association study of shoot NO3- accumulation in maize seedlings grown under low-NO3- conditions, identifying the ferredoxin family gene ZmFd4 as a major contributor to this trait. ZmFd4 interacts and co-localizes with nitrite reductases (ZmNiRs) in chloroplasts to promote their enzymatic activity. Furthermore, ZmFd4 forms a high-affinity heterodimer with its closest paralogue, ZmFd9, in a NO3--sensitive manner. Although ZmFd4 exerts similar biochemical functions as ZmFd9, ZmFd4 and ZmFd9 interaction limits their ability to associate with ZmNiRs and stimulate their activity. Knockout lines for ZmFd4 with decreased NO3- contents exhibit more efficient NO3- assimilation, and field experiments show consistently improved N utilization and grain yield under N-deficient conditions. Our work thus provides molecular and mechanistic insights into the natural variation in N utilization, instrumental for genetic improvement of yield in maize and, potentially, in other crops.

Genome-Wide Association Study Identifies the Serine/Threonine Kinase ClSIK1 for Low Nitrogen Tolerance in Watermelon Species

Plants have evolved multiple complex mechanisms enabling them to adapt to low nitrogen (LN) stress via increased nitrogen use efficiency (NUE) as nitrogen deficiency in soil is a major factor limiting plant growth and development. However, the adaptive process and evolutionary roles of LN tolerance-related genes in plants remain largely unknown. In this study, we resequenced 191 watermelon accessions and examined their phenotypic differences related to LN tolerance. A major gene ClSIK1 encoding a serine/threonine protein kinase involved in the response to LN stress was identified on chromosome 11 using genome-wide association study and RNA-Seq analysis. According to a functional analysis, ClSIK1 overexpression can increase the root area, total biomass, NUE and LN tolerance by manipulating multiple nitrogen-metabolized genes. Interestingly, the desirable LN-tolerant haplotype ClSIK1HapC was detected in only one wild relative (Citrullus mucosospermus) and likely gradually lost during watermelon domestication and improvement. This study clarified the regulatory effects of ClSIK1 on NUE and adaptations to LN stress, which also identifying valuable haplotypes-resolved gene variants for molecular design breeding of 'green' watermelon varieties highly tolerant to LN stress.

Genetic and molecular mechanisms underlying nitrogen use efficiency in maize

Nitrogen (N) is vital for crop growth and yield, impacting food quality. However, excessive use of N fertilizers leads to high agricultural costs and environmental challenges. This review offers a thorough synthesis of the genetic and molecular regulation of N uptake, assimilation, and remobilization in maize, emphasizing the role of key genes and metabolic pathways in enhancing N use efficiency (NUE). We summarize the genetic regulators of N transports for nitrate (NO3-) and ammonium (NH4+) that contribute to efficient N uptake and transportation. We further discuss the molecular mechanisms by which root system development adapts to N distribution and how N influences root system development and growth. Given the advancements in high-throughput microbiome studies, we delve into the impact of rhizosphere microorganisms on NUE and the complex plant-microbe interactions that regulate maize NUE. Additionally, we conclude with intricate regulatory mechanisms of N assimilation and remobilization in maize, involving key enzymes, transcription factors, and amino acid transporters. We also scrutinize the known N signaling perception and transduction mechanisms in maize. This review underscores the challenges in improving maize NUE and advocates for an integrative research approach that leverages genetic diversity and synthetic biology, paving the way for sustainable agriculture.

Time-course transcriptomic analysis reveals transcription factors involved in modulating nitrogen sensibility in maize

Nitrogen (N) serves both as a vital macronutrient and a signaling molecule for plants. Unveiling key regulators involved in N metabolism helps dissect the mechanisms underlying N metabolism, which is essential for developing maize with high N use efficiency. Two maize lines, B73 and Ki11, show differential chlorate and low-N tolerance. Time-course transcriptomic analysis reveals that the expression of N utilization genes (NUGs) in B73 and Ki11 have distinct responsive patterns to nitrate variation. By the coexpression networks, significant differences in the number of N response modules and regulatory networks of transcription factors (TFs) are revealed between B73 and Ki11. There are 23 unique TFs in B73 and 41 unique TFs in Ki11. MADS26 is a unique TF in the B73 N response network, with different expression levels and N response patterns in B73 and Ki11. Overexpression of MADS26 enhances the sensitivity to chlorate and the utilization of nitrate in maize, at least partially explaining the differential chlorate tolerance and low-N sensitivity between B73 and Ki11. The findings in this work provide unique insights and promising candidates for maize breeding to reduce unnecessary N overuse.

Grafting improves nitrogen efficiency and stabilizes yield and quality of cucumber by enhancing the NO3 - uptake

Grafting can promote the growth and nitrogen use efficiency (NUE) of cucumber seedlings under reduced nitrogen (N) application, however, its underlying mechanisms and effects on mature plants remain unknown. For this purpose, self-grafted and rootstock-grafted cucumber plants were treated with two N levels (7 and 4 mM) throughout the entire growth period. The long-term reduced-N treatment significantly limited the growth, root morphology, nitrate (NO3 -) uptake, NUE traits, photosynthesis, phenylalanine ammonia-lyase (PAL) activity, yield, and fruit quality of self-grafted plants but had no influence on rootstock-grafted plants, it even improved their NUE traits, total phenolic and flavonoid contents, and PAL activity. Furthermore, the expression of the NRT1.2, NRT1.5, NRT2.2, and NRT2.5 genes were significantly down-regulated in self-grafted plant roots, while they and the transcription factors NLP6 and LBD38 were up-regulated in rootstock-grafted plant roots under reduced-N environments. Correlation analysis showed that plant growth, root surface area, N-accumulation, N-uptake efficiency (NUpE), NUE, photosynthesis, PAL activity, yield, and fruit quality were all positively correlated with each other; meanwhile, the root morphology, NRT1.2 and NRT2.1 gene expression were all positively correlated with NUpE and NUE. The results demonstrate that under reduced-N application, rootstock grafting can enhance NO3 - uptake and N accumulation to improve the NUE of cucumber plants and resist reduced-N environment through secondary metabolism, maintaining growth, photosynthesis, yield, and fruit quality without adverse effects. The up-regulation of NRT genes and related transcription factors regulates the NO3 - uptake in rootstock-grafted plants. Rootstock grafting will be beneficial for fertilizer conservation and efficient cucumber production. yield and fruit quality.

Genetic variation underlying nitrogen-deficiency tolerance in Gossypium hirsutum during the seedling stage

As over-fertilization leads to environmental concerns, selecting high yield cotton cultivars with a high nitrogen use efficiency (NUE) has become crucially important. However, the genetic effects underlying NUE traits remain unclear. In this study, a genome-wide association study (GWAS) was performed using 2.65 million high-quality single-nucleotide polymorphisms (SNPs) based on three NUE related traits at the seedling stage of 419 core accessions in four environments. A total of 21 novel loci were detected, of which, the novel peak on D10 chromosome was consistently detected for multiple traits and selected to analyze. We further identified and validated a novel candidate gene GhERF4 by RNA-seq, RT-qPCR, virus-induced gene silencing (VIGS) and overexpression methods, and the results suggest that GhERF4 plays a negative role in the regulation of N-deficiency tolerance. The identified SNPs and candidate genes provide new insights into understanding the molecular mechanism and breeding varieties in N-efficient tolerance.

The Ammonium Transporter SpAMT1;2 Contributes to Nitrogen Utilisation and Cadmium Accumulation in the Hyperaccumulator Sedum Plumbizincicola

Sedum plumbizincicola (Sp) is a cadmium (Cd) hyperaccumulator found specifically in abandoned ancient mines where N is regularly deficient while Cd presents in excess. How Sp got adapted to this unique habitat remains unknown. Here, we reported relative abundant presence of NH4 + in mine areas for Sp, and the isolation and functional characterisation of a putative NH4 + transporter gene AMT1;2, which is highly expressed in Sp roots and encodes a pH-dependent dual affinity ammonium uptake transporter. Compared to SaAMT1;2, the homologous gene in the nonhyperaccumulating control Sedum alfredii (Sa), SpAMT1;2 expression is much higher and not inhibited by Cd. Only eight amino acid sequence polymorphisms were observed between SpAMT1;2 and SaAMT1;2, and the in-vitro NH4 + uptake activity and subcellular localisation are identical between them with or without Cd stress. Moreover, in contrast in Sa, NH4 + uptake in Sp is not inhibited by Cd, and NH4 + at ambient level promotes Cd accumulation. These data suggest that SpAMT1;2 is likely an essential gene contributing to nitrogen nutrition and the interaction between NH4 +and Cd uptake in Sp, which might represent a novel N utilisation pathway evolved in mines for the hyperaccumulator Sp.

Can foliar application of soluble monoammonium phosphate effectively alleviate herbicide-induced oxidative stress in key crops?

Phosphorus (P) and nitrogen (N) directly impact final crop productivity by playing essential roles in photosynthesis, ATP formation, carbon assimilation, cell division, and transport. Compared with nutrient application to soil, the nutrients are applied directly to leaves provides a faster response because the nutrients enter plant metabolism more quickly. Foliar fertilization with nutritional supplements can intend to increase crop yields, and little is known about its ability to reduce oxidative stress. This study evaluated the effects of foliar fertilization on crop recovery from phytotoxicity induced by herbicide exposure. Phytotoxicity was induced in soybean, maize, and cotton plants by applying the herbicide carfentrazone-ethyl (at V3, V3 and V4 growth stages, respectively), which induces the accumulation of reactive oxygen species in the cytoplasm, leading to membrane rupture and the appearance of chlorotic spots on leaves. Phytotoxicity induction was followed by the foliar application of monoammonium phosphate (MAP) as a source of N and P. Leaf nutrient content, gas exchange performance, pigment content, photosynthetic enzyme activity, antioxidant metabolism, oxidative stress, proline content, metabolite content, and biometric parameters were evaluated. MAP supplementation increased chlorophyll content, and RuBisCO activity by up to 20.5% (maize) and 16.2% (cotton), respectively, resulting in higher net photosynthetic rates (26.3%; cotton), stomatal conductance (45.7%; cotton), water use efficiency (35.6%; cotton), and carboxylation efficiency (45%; cotton). The activities of antioxidant enzymes also increased, and the concentrations of oxidative stress indicators decreased (H2O2: 33.7% and MDA: 28.3%; soybean). Furthermore, the productivity of all three crops increased, suggesting that foliar application of MAP is an efficient strategy for attenuating phytotoxicity symptoms in crops.

OsNLP3 and OsPHR2 orchestrate direct and mycorrhizal pathways for nitrate uptake by regulating NAR2.1-NRT2s complexes in rice

Nitrogen (N) is the most important essential nutrient required by plants. Most land plants have evolved two N uptake pathways, a direct root pathway and a symbiotic pathway, via association with arbuscular mycorrhizal (AM) fungi. However, the interaction between the two pathways is ambiguous. Here, we report that OsNAR2.1-OsNRT2s, the nitrate (NO3-) transporter complexes with crucial roles in direct NO3- uptake, are also recruited for symbiotic NO3- uptake. OsNAR2.1 and OsNRT2.1/2.2 are coregulated by NIN-like protein 3 (OsNLP3), a key regulator in NO3- signaling, and OsPHR2, a major regulator of phosphate starvation responses. More importantly, AM symbiosis induces expression of OsNAR2.1-OsNRT2s, OsNLP3, and OsSPX4, encoding an intracellular Pi sensor, in arbuscular-containing cells, but weakens their expression in the epidermis. OsNAR2.1 and OsNLP3 can activate both mycorrhizal NO3- uptake and mycorrhization efficiency. Overall, we demonstrate that OsNLP3 and OsPHR2 orchestrate the direct and mycorrhizal NO3- uptake pathways by regulating the NAR2.1-NRT2s complexes in rice.

Duckweed: a starch-hyperaccumulating plant under cultivation with a combination of nutrient limitation and elevated CO2

Introduction

The increasing global demand for starch has created an urgent need to identify more efficient and sustainable production methods. However, traditional starch sources, such as crop-based options, experience significant bottlenecks due to limitations in land use, water consumption, and the impacts of climate change. Therefore, there is a pressing need to explore and develop new sources of starch.

Methods

We develop a novel duckweed cultivation technology that combines nutrients limitation and CO2 supplementation to achieve very high starch content. In this study, we integrated whole-genome sequencing, epigenomics, transcriptomics, enzyme activity, and composition variation to elucidate the mechanisms of efficient starch accumulation in duckweed in terms of starch accumulation and carbon partitioning, regulation of the expression of genes in the starch metabolic pathway, and sucrose biosynthesis and transportation.

Results and discussion

Although Landoltia punctata exhibits dramatic gene family contraction, its starch content and productivity reached 72.2% (dry basis) and 10.4 g m-2 d-1, respectively, in 10 days, equivalent to a yield of 38.0 t ha-1 y-1, under nutrient limitation treatment with elevated CO2 levels. We also examined the mechanism of high starch accumulation in duckweed. This phenomenon is associated with the regulation of DNA methylation and transcription factors as well as the significantly upregulated transcription levels and the increased activities of key enzymes involved in starch biosynthesis. Moreover, while nitrogen redistribution was increased, sucrose biosynthesis and transportation and lignocellulose biosynthesis were reduced. These alterations led to a reduction in lignocellulose and protein contents and ultimately an increase in the accumulation of starch in the chloroplasts.

Conclusion

This work demonstrates the potential of duckweed as a highly efficient starch producer.

Overexpression of AspAT alleviates the inhibitory effects of ammonium on root development in Populus tomentosa

Ammonium toxicity, resulting from prolonged use of ammonium as the sole nitrogen source, can lead to physiological and morphological disorders, ultimately stunting plant growth. Enhancing ammonium assimilation efficiency has been extensively explored as a strategy to mitigate ammonium toxicity. However, the role of AspAT, a key enzyme in nitrogen assimilation, remains underexplored. This study investigates the function of AspAT in alleviating ammonium toxicity and uncovers the underlying physiological mechanisms. The results show that two Populus AspAT genes, AspAT13 and AspAT15, exhibit the highest expression levels in roots and are induced by exogenous ammonium. Overexpression of AspAT13 and AspAT15 in transgenic plants results in increased root biomass. In these plants, the activities of key nitrogen assimilation enzymes (GS and GOGAT) are significantly enhanced, along with increases in soluble protein, soluble sugar, and free amino acid contents. Additionally, the activities of antioxidant enzymes, such as SOD and CAT, are elevated, and ammonium content in the roots is significantly reduced. Moreover, the levels of hormones, including IAA, ACC, IBA, and BR, are significantly increased in the roots of transgenic plants. Our findings suggest that AspAT13 and AspAT15 play essential roles in mitigating ammonium toxicity, a process closely linked to enhanced nitrogen assimilation, antioxidant systems, and the regulation of auxin and brassinosteroid (BR) signaling.

Multivariate Analysis of Root Architecture, Morpho-Physiological, and Biochemical Traits Reveals Higher Nitrogen Use Efficiency Heterosis in Maize Hybrids During Early Vegetative Growth

Maize (Zea mays L.) is a globally significant crop with high economic and nutritional importance. Its productivity, however, relies heavily on nitrogen (N) inputs, often resulting in low nitrogen use efficiency (NUE). Enhancing NUE necessitates a comprehensive understanding of the biochemical and physiological mechanisms driving N uptake and utilization. The study evaluated the NUE heterosis of 7 inbred lines and their 12 hybrids under low and high N conditions during early vegetative growth. Significant genotypic variations across traits were analyzed using analysis of variance, principal component analysis, correlation, regression, and structural equation modeling. The key contributors to genetic variation included shoot dry weight, N accumulation, and NUE. Hybrids demonstrated enhanced root architecture, superior enzymatic activities of nitrate reductase (NR) and glutamine synthetase (GS), and improved morphological traits, photosynthetic efficiency, and N accumulation, resulting in greater biomass production, N accumulation, and NUE compared to inbred lines. Among hybrids, Zheng58 × PH4CV exhibited the highest NUE, driven by efficient N uptake, robust enzymatic activity, and substantial N accumulation. Nitrogen uptake efficiency (NUpE) correlated strongly with root traits such as activity (r = 0.80 ***), length (r = 0.73 ***), surface area (r = 0.67 ***), GS activity (r = 0.84 ***), and dry weight (r = 0.92). Similarly, nitrogen utilization efficiency (NutE) was positively correlated with shoot NR activity (r = 0.90 ***), shoot GS activity (r = 0.56 ***), leaf area (r = 0.73 ***), shoot dry weight (r = 0.82 ***), and shoot N accumulation (r = 0.55 ***), particularly under high N conditions. Based on key traits such as shoot dry weight, N accumulation, and NUE, hybrids Zheng58 × PH4CV, 444 × PH4CV, 444 × MO17, and B73 × MO17 emerged as N-efficient genotypes, confirmed by contrasting root systems, enhanced N metabolism, and superior NUE. These findings reveal the pivotal roles of root architecture and N metabolism in optimizing NUE, emphasizing the biochemical and physiological traits crucial for developing highly N-efficient maize hybrids.

Integrative analyses of morpho-physiological, biochemical, and transcriptomic reveal the seedling growth response of Pinus yunnanensis to nitrogen and phosphorus fertilization

Appropriate nitrogen (N) and phosphorus (P) fertilization is critical for plant growth and production. Pinus yunnanensis, a silvicultural tree in southwestern China, faces economic and ecological limitations due to nutrient deficiency in the soils in its distribution areas. The slow growth of this species during the seedling stage exacerbates these problems. Therefore, it is important to realize the regulating effects of N and P proportioning fertilization on seedling growth to enhance nutrient-use efficiency. In this study, variations in morphological, physiological, and biochemical characteristics of seedlings were analyzed under nine treatments of NP proportioning in an open nursery using a regression design. Growth in height and basal diameter increased and showed an approximate tendency in all treatments. The maximum biomass accumulation was observed at 480 d after treatment in roots of T5 (14.714 g) (application N 0.4 g·per-1 and P 3 g·per-1), stems of T5 (12.654 g), leaves of T9 (24.261 g) (application N 0.8 g·per-1 and P 6 g·per-1), aboveground parts of T9 (35.402 g) and individuals of T5 (49 g). The total chlorophyll content peaked in the leaves at 120 d and was correlated with the peak levels of N, P, and K in leaves. The content and reserves of nutrient elements in the organs of seedlings subjected to NP proportioning were significantly higher than those in unfertilized seedlings. Analysis of nutrient utilization efficiency revealed that T5 demonstrated superior seedling growth performance. Appropriate fertilization dosage of N and P for P. yunnanensis seedlings in this study was 0.32 g·per-1-0.58 g·per-1 and 3.02 g·per-1-4.95 g·per-1 respectively, using path analysis and regression equation. Transcriptomic sequencing revealed that there were 2,301 DEGs between T5 and T1 (control), which were involved in the uptake and assimilation of nutrients, biosynthesis of phytohormones and secondary metabolites, and photosynthesis. Additionally, the abundance of genes involved in cell division and proliferation, cellulose biosynthesis, and cell wall extension were dramatically upregulated, which potentially correlated with enhanced seedling growth. In conclusion, this study provides comprehensive information on the response of seedlings to varying proportions of N and P and may promote the growth of P. yunnanensis seedlings by optimizing the proportion of N and P in fertilizers.

Divergent Patterns of Metabolite Expression in Red Seaweeds (Devaleraea mollis and Palmaria hecatensis) Following Nitrate and Ammonium Supplementation

This study explores species-specific metabolic responses to different nitrogen-rich formulations in Devaleraea mollis and Palmaria hecatensis, highlighting distinct adaptive strategies. We evaluated the effects of Von Stosch Enrichment (VSE, nitrate-only), F/2 (nitrate-only), and Jack's Special (JS, nitrate and ammonium) on metabolic profiles. D. mollis exhibited elevated energy storage and growth-related metabolites, with JS enhancing creatine production for energy storage and regeneration, alongside increased DNA/RNA synthesis and cell division activity. This suggests D. mollis prioritizes rapid growth and energy demands, supporting broader ecological adaptability. Conversely, P. hecatensis showed higher expression of metabolites linked to amino acid metabolism and protein synthesis, indicating a focus on efficient nitrogen use for protein production, likely advantageous in low-light, high-turbidity conditions. Nitrogen sources significantly influence amino acid metabolism, with JS promoting broader amino acid production and VSE and F/2 stimulating specific metabolites. These species-specific metabolic patterns underscore the flexibility of D. mollis in energy use versus adaptations of P. hecatensis to protein synthesis pathways. These findings highlight species-specific nutrient formulations as essential for optimizing seaweed growth and metabolic traits in aquaculture.

Integrated transcriptomics and metabolomics analyses provide new insights into cassava in response to nitrogen deficiency

Nitrogen deficiency is a key constraint on crop yield. Cassava, the world's sixth-largest food crop and a crucial source of feed and industrial materials, can thrive in marginal soils, yet its yield is still significantly affected by limited nitrogen availability. Investigating cassava's response mechanisms to nitrogen scarcity is therefore essential for advancing molecular breeding and identifying nitrogen-efficient varieties. This research undertook a comprehensive analysis of cassava seedlings' physiological, gene expression, and metabolite responses under low nitrogen stress. Findings revealed that nitrogen deficiency drastically suppressed seedling growth, significantly reduced nitrate and ammonium transport to aerial parts, and led to a marked increase in carbohydrate, reactive oxygen species, and ammonium ion levels in the leaves. Transcriptomic and metabolomic analyses further demonstrated notable alterations in genes and metabolites linked to carbon and nitrogen metabolism, flavonoid biosynthesis, and the purine metabolic pathway. Additionally, several transcription factors associated with cassava flavonoid biosynthesis under nitrogen-deficient conditions were identified. Overall, this study offers fresh insights and valuable genetic resources for unraveling cassava's adaptive mechanisms to nitrogen deprivation.

Novel insights into strigolactone perception

A recent study conducted by Hu et al. has provided novel insights into the perception of strigolactone (SL). These findings offer a comprehensive understanding of activation, termination, and regulation mechanisms involved in SL perception, all of which are crucial for the adaptation of plant architecture to fluctuations in nitrogen availability.

Global Crop-Specific Fertilization Dataset from 1961-2019

As global fertilizer application rates increase, high-quality datasets are paramount for comprehensive analyses to support informed decision-making and policy formulation in crucial areas such as food security or climate change. This study aims to fill existing data gaps by employing two machine learning models, eXtreme Gradient Boosting and HistGradientBoosting algorithms to produce precise country-level predictions of nitrogen (N), phosphorus pentoxide (P2O5), and potassium oxide (K2O) application rates. Subsequently, we created a comprehensive dataset of 5-arcmin resolution maps depicting the application rates of each fertilizer for 13 major crop groups from 1961 to 2019. The predictions were validated by both comparing with existing databases and by assessing the drivers of fertilizer application rates using the model's SHapley Additive exPlanations. This extensive dataset is poised to be a valuable resource for assessing fertilization trends, identifying the socioeconomic, agricultural, and environmental drivers of fertilizer application rates, and serving as an input for various applications, including environmental modeling, causal analysis, fertilizer price predictions, and forecasting.

Odyssey of environmental and microbial interventions in maize crop improvement

Maize (Zea mays) is India's third-largest grain crop, serving as a primary food source for at least 30% of the population and sustaining 900 million impoverished people globally. The growing human population has led to an increasing demand for maize grains. However, maize cultivation faces significant challenges due to a variety of environmental factors, including both biotic and abiotic stresses. Abiotic stresses such as salinity, extreme temperatures, and drought, along with biotic factors like bacterial, fungal, and viral infections, have drastically reduced maize production and grain quality worldwide. The interaction between these stresses is complex; for instance, abiotic stress can heighten a plant's susceptibility to pathogens, while an overabundance of pests can exacerbate the plant's response to environmental stress. Given the complexity of these interactions, comprehensive studies are crucial for understanding how the simultaneous presence of biotic and abiotic stresses affects crop productivity. Despite the importance of this issue, there is a lack of comprehensive data on how these stress combinations impact maize in key agricultural regions. This review focuses on developing abiotic stress-tolerant maize varieties, which will be essential for maintaining crop yields in the future. One promising approach involves the use of Plant Growth-Promoting Rhizobacteria (PGPR), soil bacteria that colonize the rhizosphere and interact with plant tissues. Scientists are increasingly exploring microbial strategies to enhance maize's resistance to both biotic and abiotic stresses. Throughout the cultivation process, insect pests and microorganisms pose significant threats to maize, diminishing both the quantity and quality of the grain. Among the various factors causing maize degradation, insects are the most prevalent, followed by fungal infections. The review also delves into the latest advancements in applying beneficial rhizobacteria across different agroecosystems, highlighting current trends and offering insights into future developments under both normal and stress conditions.

Partial replacement by ammonium nutrition enhances Brassica napus growth by promoting root development, photosynthesis, and nitrogen metabolism

Nitrogen (N) is crucial for plant growth, available primarily as nitrate (NO3-) and ammonium (NH4+). However, its presence in soil is often limited, necessitating strategies to augment N availability. This study delves into the enigmatic interplay between NO3- and NH4+ in fostering the growth of Brassica napus, an important oil crop worldwide. Here, we examined the growth responses of 49 B. napus varieties to five NH4+:NO3- ratios (12:0, 9:3, 3:9, 1:11, 0:12). In general, the biomass of 49 rapeseed varieties increased with the decrease of NH4+ to NO3- ratios in the growth environment. However, different varieties may respond diversely to the mixed N sources, or sole NO3- or NH4+ condition. For some cultivars, the mixed N supply significantly enhanced the plant growth compared with the sole NO3- conditions. Thus, we further investigate the morphological, physiological and molecular response of rapeseed to the mixed N source condition using sole NO3- as a control. The results show that partial replacement by ammonium nutrition in the environment can promote rapeseed root development, net photosynthetic rate and NO3- reduction compared to NO3--only conditions. Using transcriptome analysis, we found a total of 399 and 465 genes which were differentially expressed in root and shoot under A1N11 compared to A0N12 treatments, respectively. Genes involved in photosynthesis, N uptake and assimilation were upregulated by mixed N supplies. These findings highlight that the mixed N supply primarily stimulates B. napus growth by enhancing root development, photosynthesis and N metabolism in the shoot. Such insights are crucial for optimizing N form selection in B. napus to enhance plant performance and N use efficiency.

A novel transcription factor CsSNACA2 plays a pivotal role within nitrogen assimilation in tea plants

Tea (Camellia sinensis) is a globally renowned economic crop, with organs such as leaves and buds utilized for consumption. As a perennial foliage crop, tea plants have high-nitrogen consumption and demand but exhibit relatively low nitrogen use efficiency. Exploring the genetic factors involved in nitrogen assimilation in tea plants could lead to improvements in both tea yield and quality. Here, we first conducted transcriptome sequencing on two tissues (roots and young leaves) under two different nitrate levels (0.2 and 2.5 mm KNO3) and at six time points (0, 15, and 45 min; 2 and 6 h and 2 days). Differential gene expression patterns were observed for several genes that exhibited altered expression at 2 h. Clustering and enrichment analyses, along with co-expression network construction, provided evidence for the crucial involvement of CsSNACA2 in nitrogen assimilation. CsSNACA2 overexpression elicited pronounced phenotypic changes in nitrogen-deficient plants. Furthermore, CsSNACA2 suppressed the expression of CsNR (encoding nitrate reductase) and CsCLCa (encoding aNO 3 - /H+ exchanger). Moreover, CsSNACA2 served as a downstream target of CsSPL6.1. In addition, we characterized Csi-miR156e and Csi-miR156k, which directly cleave CsSPL6.1. This study identified a transcription factor module participating in nitrogen assimilation in tea plants, providing a genetic foundation for future innovations in tea cultivar improvement. These results broaden our understanding of the genetic mechanisms governing nitrogen assimilation in dicotyledonous plants.

Identification and Characterization of Key Genes for Nitrogen Utilization from Saccharum spontaneum Sub-Genome in Modern Sugarcane Cultivar

Sugarcane (Saccharum spp.) is globally considered an important crop for sugar and biofuel production. During sugarcane production, the heavy reliance on chemical nitrogen fertilizer has resulted in low nitrogen use efficiency (NUE) and high loss. Up until now, there has been extensive research on the transcriptomic dynamics during sugarcane response to low nitrogen (LN) stress. However, the specific contribution of S. spontaneum to the NUE of modern sugarcane remains unclear. In the present study, the comparative transcriptome analysis of two contrasting sugarcane cultivars in response to nitrogen deficiency was performed via the combination of genomes of S. spontaneum and S. officinarum. Sub-genome analysis indicated that S. spontaneum supports the high NUE of modern sugarcane by providing genes related to nitrogen and carbohydrate metabolism, photosynthesis, and amino acid metabolism. Additionally, the key genes involved in nitrogen metabolism from the S. spontaneum were successfully identified through weighted gene co-expression network analyses (WGCNA), and a high-affinity nitrate transporter named ScNRT2.3 was subsequently cloned. Heterogeneous expression of the ScNRT2.3, a cell membrane-localized protein, could enhance the growth of Arabidopsis under low nitrate conditions. Furthermore, a conserved protein module known as NAR2.1/NRT2.3 was shown to regulate the response to LN stress in sugarcane roots through molecular interaction. This work helps to clarify the contribution of S. spontaneum to the NUE in modern sugarcane, and the function of the ScNRT2.3 in sugarcane.

Nitrogen input reduces the physical defense of rice plant against planthopper, Nilaparvata lugens (Hemiptera: Delphacidae)

Nitrogen has important effects on plant growth and defense. Although studies on the alternation in plant chemical defense by nitrogen fertilization have been extensively reported, how it affects physical defense is poorly understood. Two rice (Oryza sativa L.) (Poales: Poaceae) varieties (LDQ7 and YLY1) were applied with varying nitrogen regimes (0.90 and 180 kg ha-1) to study their physical defense against the brown planthopper (BPH) Nilaparvata lugens (Hemiptera: Delphacidae) in this study. Results of the electrical penetration graph showed that BPH searching and penetrating duration time was shortened with increasing nitrogen application. Also, the tubercle papicle of rice leaves decreased with increasing nitrogen application, while rice leaves' surface structure and waxy composition changed with increasing nitrogen application. In field experiments, BPH populations increased with the application of nitrogen fertilizer. These findings suggest that nitrogen input can affect plant-insect interactions by reducing the physical defense of plants, which provides new ideas for the organic combinations of yield increase and pest control in rice fields.

Functional and Molecular Characterization of Plant Nitrate Transporters Belonging to NPF (NRT1/PTR) 6 Subfamily

Plant nitrate transporters in the NPF (NRT1) family are characterized by multifunctionality and their involvement in a number of physiological processes. The proteins in this family have been identified in many monocotyledonous and dicotyledonous species: a bioinformatic analysis predicts from 20 to 139 members in the plant genomes sequenced so far, including mosses. Plant NPFs are phylogenetically related to proton-coupled oligopeptide transporters, which are evolutionally conserved in all kingdoms of life apart from Archaea. The phylogenetic analysis of the plant NPF family is based on the amino acid sequences present in databases; an analysis identified a separate NPF6 clade (subfamily) with the first plant nitrate transporters studied at the molecular level. The available information proves that proteins of the NPF6 clade play key roles not only in the supply of nitrate and its allocation within different parts of plants but also in the transport of chloride, amino acids, ammonium, and plant hormones such as auxins and ABA. Moreover, members of the NPF6 family participate in the perception of nitrate and ammonium, signaling, plant responses to different abiotic stresses, and the development of tolerance to these stresses and contribute to the structure of the root-soil microbiome composition. The available information allows us to conclude that NPF6 genes are among the promising targets for engineering/editing to increase the productivity of crops and their tolerance to stresses. The present review summarizes the available published data and our own results on members of the NPF6 clade of nitrate transporters, especially under salinity; we outline their molecular, structural, and functional characteristics and suggest potential lines for future research.

"Ca. Nitrosocosmicus" members are the dominant archaea associated with plant rhizospheres

Archaea catalyzing the first step of nitrification in the rhizosphere possibly have an influence on plant growth and development. In this study, we found a distinct archaeal community, dominated by ammonia-oxidizing archaea (AOA), associated with the root system of pepper (Capsicum anuum L.) and ginseng plants (Panax ginseng C.A. Mey.) compared to bulk soil not penetrated by roots. While the abundance of total AOA decreased in the rhizosphere soils, AOA related to "Candidatus Nitrosocosmicus," which harbor gene encoding manganese catalase (MnKat) in contrast to most other AOA, dominated the AOA community in the rhizosphere soils. For both plant species, the ratio of copy numbers of the AOA MnKat gene to the amoA gene (encoding the ammonia monooxygenase subunit A) was significantly higher in the rhizospheres than in bulk soils. In contrast to MnKat-negative strains from other AOA clades, the catalase activity of a representative isolate of "Ca. Nitrosocosmicus" was demonstrated. Members of this clade were enriched in H2O2-amended bulk soils, and constitutive expression of their MnKat gene was observed in both bulk and rhizosphere soils. Due to their abundance, "Ca. Nitrosocosmicus" members can be considered important players mediating the nitrification process in rhizospheres. The dominance of this MnKat-containing AOA in rhizospheres of agriculturally important plants hints at a previously overlooked AOA-plant interaction.

IMPORTANCE

Ammonia-oxidizing archaea (AOA) are widespread in terrestrial environments and outnumber other ammonia oxidizers in the rhizosphere, possibly exerting an influence on plant growth and development. However, little is known about the selection forces that shape their composition, functions, survival, and proliferation strategies in the rhizosphere. Here, we observed a distinct AOA community on root systems of two different plant species compared to bulk soil. Our results show that the "Ca. Nitrosocosmicus" clade, which possesses functional MnKat genes unlike most other AOA, dominated the rhizosphere soils. Moreover, members of this clade were enriched in H2O2-amended bulk soil, which mimics the ROS stress in root systems. While research on AOA-plant interactions in the rhizosphere is still in its infancy, these findings suggest that "Ca. Nitrosocosmicus" may be an important clade of AOA with potential AOA-plant interaction.

Investigation of hybrid Freeman maple resistance to Chrysobothris flatheaded borers (Coleoptera: Buprestidae)

Red maples (Acer rubrum L.; Sapindales: Sapindaceae) are common shade trees well known for their stunning autumn foliage and fast growth. They are a popular choice for landscapes, parks, and public places across the United States. Flatheaded borer species in the genus Chrysobothris (Coleoptera: Buprestidae) are some of the most damaging insects in red maple production, with attacks being most common on stressed and newly transplanted trees. In nurseries, red maples routinely experience flatheaded borer attacks, while the Freeman maple hybrid 'Autumn Blaze' has been reported as potentially resistant to flatheaded borers. In this study, traits of three borer susceptible red maple cultivars ('Brandywine', 'Sun Valley', and 'October Glory') were compared against a potentially resistant Freeman maple hybrid cultivar for baseline differences as well as differences under the stress of a foliar herbicide application Scythe (pelargonic acid 57%). Morphological, physiological, and biochemical traits of the red maple cultivars were evaluated and contrasted with the hybrid to identify traits related with borer resistance. Under normal conditions, the hybrid maple exhibited faster growth, greater concentrations of sulfur, and lower concentrations of zinc and flavonoids in leaf tissues compared to red maples. The herbicide stress treatment resulted in greater nitrogen and sulfur concentrations in hybrid foliage, but less chlorophyll, flavonoid, and zinc concentrations compared to the red maple cultivars. Field trials validated borer preference for red maples over the hybrid. Traits associated with the hybrid warrant additional study if an understanding of the causal relationship with borer resistance is to be achieved.

Electrocatalytic nitrate reduction using iron single atoms for sustainable ammonium supplies to increase rice yield

Increasing food production and ensuring drinking water safety have always been a focus of attention, especially for people in underdeveloped regions of the world. Traditional excessive fertilizer applications have increased crop yield but also caused groundwater nitrate pollution. Agricultural irrigating water is an important reservoir for nitrogen (N) (e.g., nitrate) accumulation after fertilization. Ammonium (NH4+-N) is a more readily absorbed N form by rice than nitrate (NO3--N). In this study, we proposed a strategy using iron single-atom catalysts (Fe-SAC) to selectively reduce NO3--N to NH4+-N from the real paddy field irrigating water to provide sustainable NH4+-N supplies for rice uptakes, thereby highlighting decreasing N fertilizer applications and mitigating NO3--N pollution. Then, we constructed a solar-energy-driven electrochemical reactor for NO3--N reduction, with the Fe single atom as the core catalyst, and achieved an average NH4+-N selectivity of 80.2 ± 2.6% with no additional energy input. Sustainable NH4+-N supplies resulted in a 30.4 % increase in the 100-grain weight of the cultivated rice and a 50% decrease of fertilizer application than those of the fertilization group in the pot experiment, which were one of the best values ever reported. Furthermore, the 15N isotope tracing results indicated a N use efficiency (NUE) from 15NO3--N of 71.2 ± 3.2%. Sustainable NH4+-N supplies played a key role in promoting rice root development which contributed to the high NUE. Our study shares unique insights in increasing grain yield, reducing fertilizer applications, and preventing nitrate leaching into groundwater.

Jasmonate signaling modulates root growth by suppressing iron accumulation during ammonium stress

Plants adapt to changing environmental conditions by adjusting their growth physiology. Nitrate (NO3-) and ammonium (NH4+) are the major inorganic nitrogen forms for plant uptake. However, high NH4+ inhibits plant growth, and roots undergo striking changes, such as inhibition of cell expansion and division, leading to reduced root elongation. In this work, we show that high NH4+ modulates nitrogen metabolism and root developmental physiology by inhibiting iron (Fe)-dependent Jasmonate (JA) signaling and response in Arabidopsis (Arabidopsis thaliana). Transcriptomic data suggested that NH4+ availability regulates Fe and JA-responsive genes. High NH4+ levels led to enhanced root Fe accumulation, which impaired nitrogen balance and growth by suppressing JA biosynthesis and signaling response. Integrating pharmacological, physiological, and genetic experiments revealed the involvement of NH4+ and Fe-derived responses in regulating root growth and nitrogen metabolism through modulation of the JA pathway during NH4+ stress. The JA signaling transcription factor MYC2 directly bound the promoter of the NITRATE TRANSPORTER 1.1 (NRT1.1) and repressed it to optimize the NH4+/Fe-JA balance for plant adaptation during NH4+ stress. Our findings illustrate the intricate balance between nutrient and hormone-derived signaling pathways that appear essential for optimizing plant growth by adjusting physiological and metabolic responses during NH4+/Fe stress.

Genome-Wide Identification of NLP Gene Families and Haplotype Analysis of SiNLP2 in Foxtail Millet (Setaria italica)

Nitrogen is a critical factor in plant growth, development, and crop yield. NODULE-INCEPTION-like proteins (NLPs), which are plant-specific transcription factors, function as nitrate sensors and play a vital role in the nitrogen response of plants. However, the genome-wide identification of the NLP gene family, the elucidation of the underlying molecular mechanism governing nitrogen response, and haplotype mining remain elusive in millet. In this study, we identified seven members of the NLP gene family in the millet genome and systematically analyzed their physicochemical properties. Evolutionary tree analysis indicated that SiNLP members can be classified into three subgroups, with NLP members from the same species preferentially grouped together within each subgroup. Analysis of gene structure characteristics revealed that all SiNLP members contained 10 conserved motifs, as well as the RWP-RK and PB1 domains, indicating that these motifs and domains have been relatively conserved throughout evolution. Additionally, we identified a significant abundance of response elements related to hormones, stress, growth, and development within the promoter regions of SiNLP members, suggesting that these members are involved in regulating diverse physiological processes in millet. Transcriptome data under low-nitrogen conditions showed significant differences in the expression profiles of SiNLP2 and SiNLP4 compared to the other members. RNA-seq and qRT-PCR results demonstrated that SiNLP2 significantly responds to low-nitrogen stress. Notably, we found that SiNLP2 is involved in nitrogen pathways by regulating the expression of the SiNAR2.1A, SiNAR2.1B, SiNRT1.1, and SiNR2 genes. More importantly, we identified an elite haplotype, Hap2, of SiNLP2, which is gradually being utilized in the breeding process. Our study established a foundation for a comprehensive understanding of the SiNLP gene family and provided gene resources for variety improvement and marker-assisted selection breeding.

Increasing nitrogen use efficiency in agronomically important plants: An insight into gene characteristics on a genome-wide scale in barley

Nitrogen (N) is a critical element for plant growth and development. Hence, improving nitrogen use efficiency (NUE) is vital for reducing costs and the environmental impact of agricultural practices. Understanding the genetic control of N metabolism is crucial to improve NUE, especially in agronomically important plants, such as barley (Hordeum vulgare). Using bioinformatics and functional genomics tools, we identified and characterized sixteen barley nitrogen metabolism-related gene families (HvNMGs) on a genome-wide scale, analysing gene features and evolution. These genes, located on six of seven barley chromosomes, are highly conserved in plants (including barley, rice, and Arabidopsis), as shown by phylogenetic analysis. We further explored the evolutionary relationships of NMGs through a genome-to-genome synteny analysis, which indicated higher conservation of NMGs between barley and other monocots, suggesting that these orthologous pairs predate species divergence. Protein-protein interaction analyses revealed that all of the HvNMGs show interactions, mainly with each other. The H. vulgare miRNAs target sites (hvu-miR) prediction identified six hvu-miR in 4 HvNMGs (HvGABA-T2, HvALDH10-1, HvALDH10-2 and HvARGAH), indicating their potential involvement in stress responses. The expression patterns analysis of publicly available RNA-seq data revealed that HvNMGs are expressed in all developmental stages of barley, and they respond to different stress conditions, indicating their essential role in plant growth, development and stress response. The organ-specific expression analysis, conducted using qPCR, of HvNMGs revealed higher expression of HvNiR and HvNRs in the leaf and significantly higher expression of HvARGAH and HvALDH10 in the spike than in other tissues, showing that some of the genes may be particularly important in some tissues than others. This data provides a foundation for understanding HvNMG function and could be used to improve barley yield by enhancing NUE - an important goal for both crop productivity and environmental sustainability.

Effects of Water and Nitrogen Regulation on Soil Environment and Crop Growth in a Lycium barbarum||Alfalfa System

The increasing scarcity of water and soil resources, combined with inefficient water and fertilizer management, poses significant challenges to agriculture in arid regions. This study aimed to determine an optimal water and nitrogen regulation model to alleviate water shortages and improve agricultural productivity and quality. In this study, a two-year experiment was conducted to investigate the effects of varying irrigation and nitrogen levels on the soil environment and crop growth in a Lycium barbarum||alfalfa system (LB||AS). The experiment involved four moisture gradients and four nitrogen application levels (using urea as the nitrogen source). The results indicated that soil moisture decreased during crop development, followed by a slow increase, with significant variation across soil depths. Soil temperature peaked during the fruiting stage of Lycium barbarum in July, decreasing significantly with soil depth. Higher temperatures were recorded in N0 under the same irrigation level and in W3 under the same nitrogen level. Soil organic carbon (SOC) levels increased by 16.24% in W3N0 and by 18.05% in W2N1, compared to W0N3. Easily oxidizable organic carbon (EOC) and soluble organic carbon (DOC) levels exhibited significant variations depending on irrigation and nitrogen treatments. Irrigation and nitrogen had a stronger individual impact on alfalfa height and stem thickness than their combined effects. Water and nitrogen regulation significantly influenced Lycium barbarum yield, its 100-fruit weight, and economic efficiency (p < 0.05). The W0N2 treatment produced the highest yield (3238 kg·ha-1), exceeding other treatments by up to 29.52%. In conclusion, the optimal water-nitrogen regulation model for the LB||AS system is full irrigation (75-85% θfc) with a nitrogen application rate of 300 kg·ha-1. These findings offer critical insights for improving water and nitrogen management strategies in arid regions.

Coordination of Carbon and Nitrogen Metabolism Through Well-Timed Mid-Stage Nitrogen Compensation in Japonica Super Rice

The carbon and nitrogen (N) metabolism of rice under different mid-stage N compensation timings is unclear. Two Japonica super rice cultivars were examined under four N compensation timings (N1-N3: N compensation at mid-tillering, panicle initiation, and spikelet differentiation. N0: no N compensation) and CK with no N application. Mid-stage N compensation increased the N concentrations of various tissues, and N2 showed the highest plant N uptake at both the heading stage, maturity, and the grain filling period. Among the treatments, N2 showed the highest N utilization efficiency. With delayed compensation timing, there was a gradual decrease in soluble sugar and starch concentrations in each tissue, accompanied by a decline in the non-structural carbohydrate (NSC) concentration. Specifically, N2 treatment exhibited the highest NSC accumulation and the remobilized NSC reserve, but NSCs per spikelet decreased with delayed compensation timing. The highest yield was also obtained with N2, exhibiting a 4.5% increase compared to the N0 treatment, primarily due to an improvement in spikelets per panicle. Conclusively, N compensation at the panicle initiation stage is a reasonable N management strategy that can coordinate the improvement of carbon and N metabolism, enhance N accumulation with efficient utilization and NSC accumulation, and ultimately increase the yield.

Bioinformatics and Expression Analyses of the TaATLa Gene Subfamily in Wheat (Triticum aestivum L.)

Amino acids are the main form of nitrogen in plants, and their transport across cell membranes relies on amino acid transporters (AATs). Among the plant AATs, the TaATLa subfamily comprises 18 members, yet the bioinformatics characteristics and functions of TaATLa genes in common wheat remain poorly understood due to their complex genomes. This study performed genomic analyses of TaATLas. These analyses included chromosome distributions, evolutionary relationships, collinearity, gene structures, and expression patterns. An analysis of cis-acting elements and predicted miRNA-TaATLas regulatory networks suggests that TaATLas are regulated by light, hormones, and stress signals. Functional assays revealed that TaATLa6 transports glutamine (Gln), glutamate (Glu), and aspartate (Asp) in yeast. In contrast, TaATLa4 specifically transports Gln and Asp. Furthermore, TaATLas exhibits diverse gene expression patterns, with TaATLa4-7D enhancing yeast heat tolerance in a heterologous expression system, indicating its potential role in adapting to environmental stress by regulating amino acid transport and distribution. This study sheds light on the functional roles of TaATLa genes, with implications for improving nitrogen use in wheat and other crop species.

Balancing Growth and Defense: Nanoselenium and Melatonin in Tea (Camellia sinensis) Protection against Glufosinate

Current crop stress resistance research suggests that the prominent stimulants nanoselenium (NSe) and melatonin (MT) might improve tea safety, quality, and stress resistance induced by the widely used nonselective herbicide glufosinate (GLU). Their biofortification effects on tea growth, antioxidant activity, and secondary metabolism pathways response to GLU remain unclear. Here, NSe, MT, and their combination NSe-MT effectively reduced 26.6-50.9% GLU and its metabolites in tea seedlings, balanced the photosystem, enhanced antioxidant defenses, and optimized reactive oxygen species scavenging mechanisms. Further, GLU-induced inhibition of glutamine synthetase (11.2-34.0%), ammonium toxicity (55.0-64.7%), and nitrogen metabolism disorders were alleviated. Stimulants exhibited different preferences in the accumulation of l-theanine (8.4-47%), gamma-aminobutyric acid (10.3-41.7%), and catechins (13.1-73.1%, excluding ECG), thereby influencing tea quality. Transcriptomic and metabolomic analyses validated that NSe-MT had a more pronounced impact on tender tea leaves than individual stimulant treatments. All stimulants reduced GLU-induced excessive jasmonic acid (29.8-50.5%) production and signaling responses, revealing their significance in crop physiological activities under herbicide or nitrogen stress. The reduction in aromatic amino acids helped mitigate GLU's interference with phenylpropanoid biosynthesis, leading to inhibited lignin production but enhanced nutritional flavonoid levels, such as catechins. NSe and NSe-MT demonstrated promising potential as herbicide safeners. These findings provided insights into GLU detoxification mechanisms in other nontarget crops as well.

EARLY NODULIN93 acts via cytochrome c oxidase to alter respiratory ATP production and root growth in plants

EARLY NODULIN 93 (ENOD93) has been genetically associated with biological nitrogen fixation in legumes and nitrogen use efficiency in cereals, but its precise function is unknown. We show that hidden Markov models define ENOD93 as a homolog of the N-terminal domain of RESPIRATORY SUPERCOMPLEX FACTOR 2 (RCF2). RCF2 regulates cytochrome oxidase (CIV), influencing the generation of a mitochondrial proton motive force in yeast (Saccharomyces cerevisiae). Knockout of ENOD93 in Arabidopsis (Arabidopsis thaliana) causes a short root phenotype and early flowering. ENOD93 is associated with a protein complex the size of CIV in mitochondria, but neither CIV abundance nor its activity changed in ruptured organelles of enod93. However, a progressive loss of ADP-dependent respiration rate was observed in intact enod93 mitochondria, which could be recovered in complemented lines. Mitochondrial membrane potential was higher in enod93 in a CIV-dependent manner, but ATP synthesis and ADP depletion rates progressively decreased. The respiration rate of whole enod93 seedlings was elevated, and root ADP content was nearly double that in wild type without a change in ATP content. We propose that ENOD93 and HYPOXIA-INDUCED GENE DOMAIN 2 (HIGD2) are the functional equivalent of yeast RCF2 but have remained undiscovered in many eukaryotic lineages because they are encoded by 2 distinct genes.

TaNAR2.1 and TaNAR2.2 differ in influencing nitrogen uptake and growth of wheat (Triticum aestivum L.)

NAR2 (Nitrate assimilation related protein) is a protein chaperone involved in transporting nitrate across membranes. However, the expression pattern and function of NAR2 genes in wheat are still largely unknown. Here, we cloned two TaNAR2 genes (TaNAR2.1 and TaNAR2.2). To assess and compare the functional differences of TaNAR2.1 and TaNAR2.2, we analyzed the subcellular localization and expression pattern of the two genes in wheat under low nitrogen (LN) and high nitrogen (HN) conditions, as well as the nitrate influx and root system architecture of TaNAR2.1 and TaNAR2.2 overexpression wheat under LN and HN. Additionally, we investigated the effects of TaNAR2.1 and TaNAR2.2 overexpression on the growth phenotype, nitrogen uptake and yield of wheat throughout the growth period. There are significant differences in the expression patterns and functions of TaNAR2.1 and TaNAR2.2. TaNAR2.1 is located in the cytoplasm, nucleus and the plasma membrane, whereas TaNAR2.2 is a cytoplasm-specific protein. TaNAR2.1 appears to exhibit larger changes in expression levels and a higher capacity for nitrate influx than TaNAR2.2 under external nitrate supply. Overexpression of TaNAR2.1 significantly improves grain nitrogen use efficiency and increases grain yield, whereas overexpression of TaNAR2.2 enhances vegetative and reproductive growth of wheat roots. These findings indicate that TaNAR2.1 plays a crucial role in wheat nitrogen accumulation and yield, while TaNAR2.2 is pivotal for wheat root growth.

Recovery of ecosystems pollution by contaminants of potential concern using phytoremediation techniques

Phytoremediation is a technology that uses plants to break down, remove, and immobilize contaminants in surface water, shallow groundwater, and sediment to achieve cost savings compared with conventional treatments. This study describes a marshy land on an explosives manufacturing site in India that consistently reported elevated concentrations of nitrates, nitrites, ammonia, perchlorate, and lead (contaminants of potential concern-CoPC). The study also illustrates the potential for addressing the human health and environmental risks associated with the explosives manufacturing industrsy in India using innovative, sustainable, and carbon-neutral techniques. This work focuses on reconstructed marshy lands, desedimentation, microwatershed management, and phytoremediation using Phragmites and Vetiveria species (also known as vetiver) to reduce contaminants in surface water and groundwater, improve stormwater management and carbon capture, and increase natural capital like biodiversity. The results obtained during the trial indicate that the selected indigenous species are effective and can be used to remediate sediment and shallow groundwater for many CoPC in tropical climates. Integr Environ Assess Manag 2024;20:1987-2002. © 2024 SETAC.

The Arabidopsis thaliana ecotype Ct-1 achieves higher salt tolerance relative to Col-0 via higher tissue retention of K+ and NO3. JOURNAL OF PLANT PHYSIOLOGY 2024;302:154321. [PMID: 39116627 DOI: 10.1016/j.jplph.2024.154321] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Agriculture is vital for global food security, and irrigation is essential for improving crop yields. However, irrigation can pose challenges such as mineral scarcity and salt accumulation in the soil, which negatively impact plant growth and crop productivity. While numerous studies have focused on enhancing plant tolerance to high salinity, research targeting various ecotypes of Arabidopsis thaliana has been relatively limited. In this study, we aimed to identify salt-tolerant ecotypes among the diverse wild types of Arabidopsis thaliana and elucidate their characteristics at the molecular level. As a result, we found that Catania-1 (Ct-1), one of the ecotypes of Arabidopsis, exhibits greater salt tolerance compared to Col-0. Specifically, Ct-1 exhibited less damage from reactive oxygen species (ROS) than Col-0, despite not accumulating antioxidants like anthocyanins. Additionally, Ct-1 accumulated more potassium ions (K+) in its shoots and roots than Col-0 under high salinity, which is crucial for water balance and preventing dehydration. In contrast, Ct-1 plants were observed to accumulate slightly lower levels of Na+ than Col-0 in both root and shoot tissues, regardless of salt treatment. These findings suggest that Ct-1 plants achieve high salinity resistance not by extruding more Na+ than Col-0, but rather by absorbing more K+ or releasing less K+. Ct-1 exhibited higher nitrate (NO3-) levels than Col-0 under high salinity conditions, which is associated with enhanced retention of K+ ions. Additionally, genes involved in NO3- transport and uptake, such as NRT1.5 and NPF2.3, showed higher transcript levels in Ct-1 compared to Col-0 when exposed to high salinity. However, Ct-1 did not demonstrate significantly greater resistance to osmotic stress compared to Col-0. These findings suggest that enhancing plant tolerance to salt stress could involve targeting the cellular processes responsible for regulating the transport of NO3- and K+. Overall, our study sheds light on the mechanisms of plant salinity tolerance, emphasizing the importance of K+ and NO3- transport in crop improvement and food security in regions facing salinity stress.

Advantages of compost tea: Promotion of nitrogen influx into the fruit and improvement of fruit nitrogen metabolism in tomato

The use of compost tea is important to improve food safety. However, the effect of compost tea on N uptake and partitioning in tomato is unclear. In this study, we measured temporal and spatial changes in nitrogen content, enzyme activities, and expression levels of nitrogen transporters genes in different organs of tomato treated with five nutrient solutions. The results showed that the expression levels of ammonium transporter protein genes (AMT1s) increased and that of a nitrogen transporters gene (NRT2.1) decreased under treatment with compost tea, which promoted NH4+ transport to the fruit and reduced nutrient wastage compared with the response to chemical fertilizers. In addition, the lowermost leaves on the stem showed reduced nitrate content, faster metabolism, and decreased chlorophyll a content, but fruit yield was not increased, in compost tea-treated plants. These changes were dependent on the expression level of the glutamine synthetase gene (GS1.1), which was increased in leaves and decreased in fruit. Compost tea influenced the expression of critical genes in the fruits and leaves, and improved the competitiveness of sexual reproductive growth as a sink for nitrogen. However, the benefits of compost tea were reduced when it was mixed chemical fertilizers. This research establishes a theoretical framework for optimization of organic vegetable cultivation and promoting the widespread production of organic crops.