Nitrate Regulation Research Articles

NRT2.1 mediates the reciprocal regulation of nitrate and NO/SNO in seedling leaves of Fraxinus mandshurica and Betula platyphylla

Nitric oxide (NO) and S-nitrosothiol (SNO) are signal molecules and the products of nitrogen metabolism. Nitrate (NO3−) is the main nitrogen source, and nitrate transporters (NRTs) are responsible for NO3− absorption or transport. However, the interactive effect between NO3−/NRT and NO/SNO in tree plants remains ambiguous. In the present study, 25 mmol L−1 NO3− and 1 mmol L−1 NO donor sodium nitroprusside (SNP) treatment that was conducted for 24 h enhanced NO/SNO and NO3− metabolism, whereas 2.5 mmol L−1 NO3− and 80 μmol L−1 N6022 (a compound that increases SNO content) treatment reduced them in seedling leaves of Fraxinus mandshurica and Betula platyphylla. Among the nine NRT family members examined, the gene expression level of NRT2.1 had a greater response to NO/SNO and NO3− treatment in the seedling leaves of F. mandshurica and B. platyphylla. Meanwhile, FmNRT2.1 mediated NO and SNO production in seedling leaves of F. mandshurica using Agrobacterium-mediated transient transformation. These findings shed light on the reciprocal regulation between NO3− and NO/SNO in seedlings of F. mandshurica and B. platyphylla, and NRT2.1 may act as a key regulatory hub.

Reviewing impacts of biotic and abiotic stresses on the regulation of phosphate homeostasis in plants.

Adapting to varying phosphate levels in the environment is vital for plant growth. The PHR1phosphate starvation response transcription factor family, along with SPX inhibitors, plays a pivotal role in plant phosphate responses. However, this regulatory hub intricately links with diverse biotic and abiotic signaling pathways, as outlined in this review. Understanding these intricate networks is crucial, not only on a fundamental level but also for practical applications, such as enhancing sustainable agriculture and optimizing fertilizer efficiency. This comprehensive review explores the multifaceted connections between phosphate homeostasis and environmental stressors, including various biotic factors, such as symbiotic mycorrhizal associations and beneficial root-colonizing fungi. The complex coordination between phosphate starvation responses and the immune system are explored, and the relationship between phosphate and nitrate regulation in agriculture are discussed. Overall, this review highlights the complex interactions governing phosphate homeostasis in plants, emphasizing its importance for sustainable agriculture and nutrient management to contribute to environmental conservation.

NRG2 family members of Arabidopsis and maize regulate nitrate signalling and promote nitrogen use efficiency.

Nitrogen (N) is an essential nutrient for plant growth, and most plants absorb it as nitrate. AtNRG2 has been reported to play an important role in nitrate regulation. In this study, we investigated the functions of AtNRG2 family members of Arabidopsis thaliana and maize in nitrate signalling and metabolism. Our results showed that both AtNRG2.10 and AtNRG2.15 regulated nitrate signalling and metabolism. Overexpression of AtNRG2.11 (AtNRG2) could promote plant growth and improve nitrogen use efficiency (NUE). In addition, the maize genome harbors 23 ZmNRG2 members. We detected the expression of these genes treated with nitrate and the expression of four genes was strongly induced with ZmNRG2.7 having the highest levels. Overexpression of ZmNRG2.7 in the atnrg2 mutant could restore the defects of atnrg2, suggesting that ZmNRG2.7 is involved in nitrate signalling and metabolism. Moreover, the overexpression lines of ZmNRG2.7 showed increased biomass and NUE. These findings demonstrate that at least a part of NRG2 family genes in Arabidopsis and maize regulate nitrate signalling and provide a molecular basis for improving the NUE of crops.

Transcriptomic analysis of nitrogen metabolism pathways in Klebsiella aerogenes under nitrogen-rich conditions.

The acceleration of the nitrogen cycle and the nitrogen excess observed in some coastal waters has increased interest into understanding the biochemical and molecular basis of nitrogen metabolism in various microorganisms. To investigate nitrogen metabolism of a novel heterotrophic nitrification and aerobic denitrification bacterium Klebsiella aerogenes strain (B23) under nitrogen-rich conditions, we conducted physiological and transcriptomic high-throughput sequencing analyses on strain B23 cultured on potassium nitrate-free or potassium nitrate-rich media. Overall, K. aerogenes B23 assimilated 82.47% of the nitrate present into cellular nitrogen. Further, 1,195 differentially expressed genes were observed between K. aerogenes B23 cultured on potassium nitrate-free media and those cultured on potassium nitrate-rich media. Gene annotation and metabolic pathway analysis of the transcriptome were performed using a series of bioinformatics tools, including Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, and Non-Redundant Protein Database annotation. Accordingly, the nitrogen metabolism pathway of K. aerogenes B23 was analyzed; overall, 39 genes were determined to be involved in this pathway. Differential expression analysis of the genes involved in the nitrogen metabolism pathway demonstrated that, compared to the control, FNR, NarK/14945, fdx, gshA, proB, proA, gapA, argH, artQ, artJ, artM, ArgR, GAT1, prmB, pyrG, glnS, and Ca1 were significantly upregulated in the nitrogen-treated K. aerogenes B23; these genes have been established to be involved in the regulation of nitrate, arginine, glutamate, and ammonia assimilation. Further, norV, norR, and narI were also upregulated in nitrogen-treated K. aerogenes B23; these genes are involved in the regulation of NO metabolism. These differential expression results are important for understanding the regulation process of key nitrogen metabolism enzyme genes in K. aerogenes B23. Therefore, this study establishes a solid foundation for further research into the expression regulation patterns of nitrogen metabolism-associated genes in K. aerogenes B23 under nitrogen-rich conditions; moreover, this research provides essential insight into how K. aerogenes B23 utilizes nutritional elements.

The Arabidopsis eIF4E1 regulates NRT1.1-mediated nitrate signaling at both translational and transcriptional levels.

Identifying new nitrate regulatory genes and illustrating their mechanisms in modulating nitrate signaling are of great significance for achieving the high yield and nitrogen use efficiency (NUE) of crops. Here, we screened a mutant with defects in nitrate response and mapped the mutation to the gene eIF4E1 in Arabidopsis. Our results showed that eIF4E1 regulated nitrate signaling and metabolism. Ribo-seq and polysome profiling analysis revealed that eIF4E1 modulated the amount of some nitrogen (N)-related mRNAs being translated, especially the mRNA of NRT1.1 was reduced in the eif4e1 mutant. RNA-Seq results enriched some N-related genes, supporting that eIF4E1 is involved in nitrate regulation. The genetic analysis indicated that eIF4E1 worked upstream of NRT1.1 in nitrate signaling. In addition, an eIF4E1-interacting protein GEMIN2 was identified and found to be involved in nitrate signaling. Further investigation showed that overexpression of eIF4E1 promoted plant growth and enhanced yield and NUE. These results demonstrate that eIF4E1 regulates nitrate signaling by modulating NRT1.1 at both translational and transcriptional levels, laying the foundation for future research on the regulation of mineral nutrition at the translational level.

Regulation of soil water and nitrate by optimizing nitrogen fertilization and the addition of manure based on precipitation: An 8-year field record

Optimizing fertilization strategies to improve water utilization efficiency and obtain higher crop yields and low nitrate leaching is essential for balancing food security and environmental risks in the rain-fed area of the Loess Plateau. The eight consecutive years (2014–2022) field experiment followed a split-plot design, and the experimental factors were nitrogen application rate (N0, N75, N150, N225, and N300) and manure application rate (M0 and M1). In general, (1) the relationships between nitrogen application rate and grain yield (GY), crop N uptake and water utilization efficiency (WUE) followed a quadratic curve. Compared with chemical fertilizer alone (NPK), chemical fertilizer plus manure (MNPK) significantly increased the annual average grain yield by 28.5%, 18.3%, 8.9%, 6.9% and 4.2% at the N application rate of N0, N75, N150, N225 and N300. (2) The nitrate accumulation (SNA) in the same soil layer increased with the nitrogen application rate. The residue nitrate will increase dramatically when the N application rate exceeds 150 kg ha-1. The peaks of SNA gradually moved to the deeper layer with increasing years of fertilization. The total soil nitrate accumulation (TSNA) of NPK was significantly higher than that of MNPK in dry and normal years, but the opposite was true in wet years. The total soil water storage (TSWS) decreased and then increased with the N application rate, and the annual average TSWS of the MNPK treatments was 3.9% less than that of the NPK treatments. (3) The addition of manure significantly increased the annual average moisture storage rate (MSR) during the fallow season by 4.6%. The GY in dry and normal years was more dependent on MSR than that in wet years. In terms of the long-term effects, the MSR contributes more to GY than growing season precipitation (GSP), and the high MSR caused by manure application reduced TSNA and TSWS by promoting crop growth. The results showed that M1N150 could obtain a high grain yield while maintaining low nitrate residue. Taken together, this study emphasized the importance of optimizing nitrogen fertilizer management and cattle manure application in combination with precipitation types to ensure food production and reduce negative environmental effects in the rain-fed area of the Loess Plateau in China.

The small peptide CEP1 and the NIN-like protein NLP1 regulate NRT2.1 to mediate root nodule formation across nitrate concentrations.

Legumes acquire fixed nitrogen (N) from the soil and through endosymbiotic association with diazotrophic bacteria. However, establishing and maintaining N2-fixing nodules are expensive for the host plant, relative to taking up N from the soil. Therefore, plants suppress symbiosis when N is plentiful and enhance symbiosis when N is sparse. Here, we show that the nitrate transporter MtNRT2.1 is required for optimal nodule establishment in Medicago truncatula under low-nitrate conditions and the repression of nodulation under high-nitrate conditions. The NIN-like protein (NLP) MtNLP1 is required for MtNRT2.1 expression and regulation of nitrate uptake/transport under low- and high-nitrate conditions. Under low nitrate, the gene encoding the C-terminally encoded peptide (CEP) MtCEP1 was more highly expressed, and the exogenous application of MtCEP1 systemically promoted MtNRT2.1 expression in a compact root architecture 2 (MtCRA2)-dependent manner. The enhancement of nodulation by MtCEP1 and nitrate uptake were both impaired in the Mtnrt2.1 mutant under low nitrate. Our study demonstrates that nitrate uptake by MtNRT2.1 differentially affects nodulation at low- and high-nitrate conditions through the actions of MtCEP1 and MtNLP1.

Integrated physiological and weighted gene co-expression network analysis reveals the hub genes engaged in nitrate-regulated alleviation of ammonium toxicity at the seedling stage in wheat (Triticum aestivum L.).

Wheat has a specific preference for NO3 - and shows toxicity symptoms under high NH4 + concentrations. Increasing the nitrate supply may alleviate ammonium stress. Nevertheless, the mechanisms underlying the nitrate regulation of wheat root growth to alleviate ammonium toxicity remain unclear. In this study, we integrated physiological and weighted gene co-expression network analysis (WGCNA) to identify the hub genes involved in nitrate alleviation of ammonium toxicity at the wheat seedling stage. Five NH4 +/NO3 - ratio treatments, including 100/0 (Na), 75/25 (Nr1), 50/50 (Nr2), 25/75 (Nr3), and 0/100 (Nn) were tested in this study. The results showed that sole ammonium treatment (Na) increased the lateral root number but reduced root biomass. Increasing the nitrate supply significantly increased the root biomass. Increasing nitrate levels decreased abscisic acid (ABA) content and increased auxin (IAA) content. Furthermore, we identified two modules (blue and turquoise) using transcriptome data that were significantly related to root physiological growth indicators. TraesCS6A02G178000 and TraesCS2B02G056300 were identified as hub genes in the two modules which coded for plastidic ATP/ADP-transporter and WRKY62 transcription factors, respectively. Additionally, network analysis showed that in the blue module, TraesCS6A02G178000 interacts with downregulated genes that coded for indolin-2-one monooxygenase, SRG1, DETOXIFICATION, and wall-associated receptor kinase. In the turquoise module, TraesCS2B02G056300 was highly related to the genes that encoded ERD4, ERF109, CIGR2, and WD40 proteins, and transcription factors including WRKY24, WRKY22, MYB30, and JAMYB, which were all upregulated by increasing nitrate supply. These studies suggest that increasing the nitrate supply could improve root growth and alleviate ammonium toxicity through physiological and molecular regulation networks, including ROS, hormonal crosstalk, and transcription factors.

The Arabidopsis protein farnesylation era1 mutant displays an altered hormonal-dependent nitrate regulation of root architecture

The Arabidopsis protein farnesylation era1 mutant displays an altered hormonal-dependent nitrate regulation of root architecture

Photobiomodulation at 830 nm Reduced Nitrite Production by Peripheral Blood Mononuclear Cells Isolated from Multiple Sclerosis Subjects.

Background: Multiple sclerosis (MS) is a neurodegenerative condition characterized by high concentration of nitric oxide leading to the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS), a condition known as nitrosative stress. ROS and RNS produce the inhibition of the mitochondrial electron transport chain leading to mitochondrial dysfunction, reduction of adenosine triphosphate, and death of neurons, producing severe and irreversible damage in the central nervous system of people with MS (PwMS). Current drug treatments for MS focus on the regulation of immune response in acute stages of disease, but they do not regulate nitrosative stress which is present in the acute and chronic stages of disease. Previously, our laboratory showed that photobiomodulation (PBM) on experimental autoimmune encephalomyelitis mice, the animal model of MS, reduced clinical severity of disease, gene expression of inducible nitric oxide synthase (iNOS), and the levels of nitrite in in vivo and in vitro experiments. Objective: We evaluated the effect of PBM on the regulation of nitrosative stress in PwMS. Methods: PBM was applied on peripheral blood mononuclear cells (PBMCs) obtained from PwMS to evaluate PBM on the regulation of nitrate as a marker of nitrosative stress. Results: PBM at 830 nm (10 J/cm2 at 72 h) reduced the levels of nitrite and this reduction was in relationship with the increase of interleukin-10 and the reduction of interferon-γ produced by the PBMCs regardless of the severity of disease present in the participants. Conclusions: PBM at 830 nm can potentially be used to reduce nitrosative stress at any point of disease in PwMS.

Comparison of Phytochemicals, Antioxidant, and Antimicrobial Activities of in Vitro Propagated and Wild Grown Potentilla Nepalensis, an Endemic Medicinal Plant from North Western Himalayas

ABSTRACT A reliable protocol for in vitro propagation of Potentilla nepalensis was developed and the phytochemical, antioxidant, and antimicrobial effects of in vitro propagated and wild grown P. nepalensis plants were compared. Leaves of P. nepalensis used as explants were cultured on conventional Murashige and Skoog (MS) medium supplemented with different concentrations and combinations of plant growth regulators. Optimum sterilization conditions were achieved by using 0.04% Bavistin for 10 min, 0.04% sodium hypochlorite for 1 min, and 0.04% mercuric chloride for 1 min and the optimum media composition for callus generation was MS minerals containing ammonium nitrate (165 mg L−1), calcium chloride (44 mg L−1), and growth regulators IBA (20 mg L−1), and BAP (4 mg L−1). The phenolic and flavonoid content were higher in wild grown plant (TPC-21.21 ± 0.54 mg g−1 GAE; TFC-4.24 ± 0.17 mg g−1RE) compared to in vitro propagated P. nepalensis (TPC-3.55889 ± 0.72 mg g−1 GAE; TFC-0.33 ± 0.07 mg g−1 RE). Although the antioxidant activity was high in wild grown plant (IC50-235 ± 92.120 µg mL−1) than in vitro propagated (IC50-682.989 ± 57.118 µg mL−1), the antimicrobial properties for bacterial and fungal pathogens were similar.

Nitrate-responsive transcriptome analysis reveals additional genes/processes and associated traits viz. height, tillering, heading date, stomatal density and yield in japonica rice.

Our transcriptomic analysis expanded the repertoire of nitrate-responsive genes/processes in rice and revealed their phenotypic association with root/shoot, stomata, tiller, panicle/flowering and yield, with agronomic implications for nitrogen use efficiency. Nitrogen use efficiency (NUE) is a multigenic quantitative trait, involving many N-responsive genes/processes that are yet to be fully characterized. Microarray analysis of early nitrate response in excised leaves of japonica rice revealed 6688 differentially expressed genes (DEGs), including 2640 hitherto unreported across multiple functional categories. They include transporters, enzymes involved in primary/secondary metabolism, transcription factors (TFs), EF-hand containing calcium binding proteins, hormone metabolism/signaling and methytransferases. Some DEGs belonged to hitherto unreported processes viz. alcohol, lipid and trehalose metabolism, mitochondrial membrane organization, protein targeting and stomatal opening. 1158 DEGs were associated with growth physiology and grain yield or phenotypic traits for NUE. We identified seven DEGs for shoot apical meristem, 66 for leaf/culm/root, 31 for tiller, 70 for heading date/inflorescence/spikelet/panicle, 144 for seed and 78 for yield. RT-qPCR validated nitrate regulation of 31 DEGs belonging to various important functional categories/traits. Physiological validation of N-dose responsive changes in plant development revealed that relative to 1.5mM, 15mM nitrate significantly increased stomatal density, stomatal conductance and transpiration rate. Further, root/shoot growth, number of tillers and grain yield declined and panicle emergence/heading date delayed, despite increased photosynthetic rate. We report the binding sites of diverse classes of TFs such as WRKY, MYB, HMG etc., in the 1kb up-stream regions of 6676 nitrate-responsive DEGs indicating their role in regulating nitrate response/NUE. Together, these findings expand the repertoire of genes and processes involved in genomewide nitrate response in rice and reveal their physiological, phenotypic and agronomic implications for NUE.

Assessment of Water Quality Regulation Functions in Southwestern Europe Watersheds

Estimation at large scale of the water quality regulation services is still lacking. It is essential to develop methodological approaches to quantify nutrient-related functions’ distribution. The present study aims to quantify nitrate-related ecological functions through nitrate net balance (NNB), nitrate removal (NR), and nitrate production (NP). This study explores the spatiotemporal dynamics of these indicators in South-Western Europe (SUDOE, 216 subsystems over 81 basins) at a monthly scale from 2000 to 2010. We use the Soil and Water Assessment Tool model to simulate nutrient transfer at the subsystem scale (~3000 km2) and calculate ecological functions. The modeled NNB is validated at the subsystem scale by comparing with NNB predicted at the water body scale (~60 km2) over the Garonne watershed (France). Hot spots of NR are located in the south of SUDOE, characterized by a warmer and dryer climate, whereas NP hot spots are located in the most anthropized streams. The mean NNB (the balance between NP and NR) at the subsystem scale for the SUDOE territory reaches −3.5 and −2.8 gN m−2 day−1 during the most active seasons. The results highlight drivers influencing NR such as streamflow, river slope, and hydrological alteration. Getting an overview of where and when these nitrate regulation functions (NP and NR) occur is essential for socio-ecosystem sustainability and this study highlights its sensitivity to anthropogenic stressors.

Regulation of Nitrate (NO3) Transporters and Glutamate Synthase-Encoding Genes under Drought Stress in Arabidopsis: The Regulatory Role of AtbZIP62 Transcription Factor.

Nitrogen (N) is an essential macronutrient, which contributes substantially to the growth and development of plants. In the soil, nitrate (NO3) is the predominant form of N available to the plant and its acquisition by the plant involves several NO3 transporters; however, the mechanism underlying their involvement in the adaptive response under abiotic stress is poorly understood. Initially, we performed an in silico analysis to identify potential binding sites for the basic leucine zipper 62 transcription factor (AtbZIP62 TF) in the promoter of the target genes, and constructed their protein–protein interaction networks. Rather than AtbZIP62, results revealed the presence of cis-regulatory elements specific to two other bZIP TFs, AtbZIP18 and 69. A recent report showed that AtbZIP62 TF negatively regulated AtbZIP18 and AtbZIP69. Therefore, we investigated the transcriptional regulation of AtNPF6.2/NRT1.4 (low-affinity NO3 transporter), AtNPF6.3/NRT1.1 (dual-affinity NO3 transporter), AtNRT2.1 and AtNRT2.2 (high-affinity NO3 transporters), and AtGLU1 and AtGLU2 (both encoding glutamate synthase) in response to drought stress in Col-0. From the perspective of exploring the transcriptional interplay of the target genes with AtbZIP62 TF, we measured their expression by qPCR in the atbzip62 (lacking the AtbZIP62 gene) under the same conditions. Our recent study revealed that AtbZIP62 TF positively regulates the expression of AtPYD1 (Pyrimidine 1, a key gene of the de novo pyrimidine biosynthesis pathway know to share a common substrate with the N metabolic pathway). For this reason, we included the atpyd1-2 mutant in the study. Our findings revealed that the expression of AtNPF6.2/NRT1.4, AtNPF6.3/NRT1.1 and AtNRT2.2 was similarly regulated in atzbip62 and atpyd1-2 but differentially regulated between the mutant lines and Col-0. Meanwhile, the expression pattern of AtNRT2.1 in atbzip62 was similar to that observed in Col-0 but was suppressed in atpyd1-2. The breakthrough is that AtNRT2.2 had the highest expression level in Col-0, while being suppressed in atbzip62 and atpyd1-2. Furthermore, the transcript accumulation of AtGLU1 and AtGLU2 showed differential regulation patterns between Col-0 and atbzip62, and atpyd1-2. Therefore, results suggest that of all tested NO3 transporters, AtNRT2.2 is thought to play a preponderant role in contributing to NO3 transport events under the regulatory influence of AtbZIP62 TF in response to drought stress.

Transcriptome analysis for understanding the mechanism of dark septate endophyte S16 in promoting the growth and nitrate uptake of sweet cherry

Sweet cherry is one of the most popular fresh fruits in the world. Previously, we isolated a soilborne dark septate endophyte (DSE) strain, S16, which promoted the growth of Gisela 5 sweet cherry rootstock. However, little is known about the molecular mechanism of the effect of S16 on the growth of sweet cherry. In this study, the physiological parameters and transcript profiles of sweet cherry roots were analyzed under S16 treatment compared with a control to elucidate the molecular mechanisms of the effect of this strain on sweet cherry growth. After inoculation with S16, sweet cherry seedlings exhibited more vigorous growth. Moreover, we identified 4249 differentially expressed genes (DEGs) between S16-treated plants and the control. Many of the DEGs are involved in pathways related to plant growth, such as cellular metabolic and plant hormone pathways. Additionally, some genes involved in nitrate regulation were also enriched; and these genes may be involved in the regulation of nitrate uptake in plants. Physiological index detection demonstrated that S16 could improve the nitrate assimilation of sweet cherry via NO3− transporters. This RNA-seq dataset provides comprehensive insight into the transcriptomic landscape to reveal the molecular mechanisms whereby the DSE influences the growth of sweet cherry.

Barley transcription factor HvNLP2 mediates nitrate signaling and affects nitrogen use efficiency.

Plants have evolved complex mechanisms to adapt to the changing nitrogen levels in the environment. In Arabidopsis, more than a dozen nitrate signaling regulatory genes have been characterized, including the NODULE INCEPTION-LIKE PROTEIN (AtNLP) genes, which play essential roles in nitrate signaling. However, whether NLP genes in the Triticeae crops are involved in nitrate regulation and nitrogen use efficiency (NUE) remains unknown. Here, we isolated a barley (Hordeum vulgare L.) mutant, hvnlp2-1, from a TILLING (Targeting Local Lesions IN Genomes) population and constructed two RNAi lines, hvnlp2-2 and hvnlp2-3, to study the function of HvNLP2. The expression of the nitrate-responsive genes was substantially inhibited after nitrate treatment in the hvnlp2 mutants, indicating that HvNLP2 controls nitrate signaling. Nitrate content was significantly higher in the hvnlp2 mutants, which may result from the decreased assimilation of nitrogen caused by reduced nitrate reductase activity and expression of nitrate assimilatory genes. HvNLP2 is localized to the nucleus in the presence of nitrate. Further investigation showed that HvNLP2 binds to and activates the nitrate-responsive cis-elements. Moreover, hvnlp2 exhibited reduced biomass, seed yield, and NUE. Therefore, HvNLP2 controls nitrate signaling and plays an important role in NUE.

Evolution of N-balance with qualitative expert evaluation approach

Pollution of rivers by nitrate is a major issue. Many land use units are considered as net nitrate producers when the input dominates the uptake (e.g. agricultural areas), or in the opposite, net consumers (e.g. wetlands), but the role of their spatial organization and temporal dynamics together across the watershed is unclear. Here, we used a Nitrate-related Ecological Functions (NEF) concept, together with an expert-based analysis in a Geographical Information System, to investigate the role of two opposite landscape types in the nitrate regulation across the Garonne river watershed (France). At any point in a watershed, there is nitrate production (NP) and nitrate removal (NR). The nitrate net balance (NNB) between NP and NR functions can be neutral (NB, Neutral Balance) when nitrate fluxes balance over space and time. The first landscape type, called Actual, was obtained using a set of 7 actual environmental variables, as land cover types, soil organic matter content and wetlands presence. The second landscape type, called Natural, described a non-anthropized landscape, using the same layer types as the Actual landscape. Potentials in NP and NR for each class in each map layer were rated by a set of experts according to their scientific knowledge. NP, NR and by difference, NNB maps were obtained, overlaid and compared to provide an evaluation of the potential for each landscape. In both landscapes, NNB were largely balanced (Actual=48% and Natural=67%). In the Actual landscape, NNB were secondly dominated by an imbalance toward NP (43%) and in the Natural landscape secondly imbalanced toward NR (32%). We constructed 'maps of disagreement' between both landscapes to provide a spatially explicit assessment of NNB evolution caused by changing land cover. We found that 67% of the agricultural areas and 60% of the artificial areas of the watershed had been subjected to a loss of nitrate ecological functions from Natural to Actual landscapes. Some management practices able to modify these factors may improve ecological functions and diminish the NEF disagreement of the watershed.

Strigolactones and Auxin Cooperate to Regulate Maize Root Development and Response to Nitrate.

In maize, nitrate regulates root development thanks to the coordinated action of many players. In this study, the involvement of strigolactones (SLs) and auxin as putative components of the nitrate regulation of lateral root (LR) was investigated. To this aim, the endogenous SL content of maize root in response to nitrate was assessed by liquid chromatography with tandem mass Spectrometry (LC-MS/MS) and measurements of LR density in the presence of analogues or inhibitors of auxin and SLs were performed. Furthermore, an untargeted RNA-sequencing (RNA-seq)-based approach was used to better characterize the participation of auxin and SLs to the transcriptional signature of maize root response to nitrate. Our results suggested that N deprivation induces zealactone and carlactonoic acid biosynthesis in root, to a higher extent if compared to P-deprived roots. Moreover, data on LR density led to hypothesize that the induction of LR development early occurring upon nitrate supply involves the inhibition of SL biosynthesis, but that the downstream target of SL shutdown, besides auxin, also includes additional unknown players. Furthermore, RNA-seq results provided a set of putative markers for the auxin- or SL-dependent action of nitrate, meanwhile also allowing to identify novel components of the molecular regulation of maize root response to nitrate. Globally, the existence of at least four different pathways was hypothesized: one dependent on auxin, a second one mediated by SLs, a third deriving from the SL-auxin interplay, and a last one attributable to nitrate itself through further downstream signals. Further work will be necessary to better assess the reliability of the model proposed.

Novel Aspects of Nitrate Regulation in Arabidopsis.

Nitrogen (N) is one of the most essential macronutrients for plant growth and development. Nitrate (NO3–), the major form of N that plants uptake from the soil, acts as an important signaling molecule in addition to its nutritional function. Over the past decade, significant progress has been made in identifying new components involved in NO3– regulation and starting to unravel the NO3– regulatory network. Great reviews have been made recently by scientists on the key regulators in NO3– signaling, NO3– effects on plant development, and its crosstalk with phosphorus (P), potassium (K), hormones, and calcium signaling. However, several novel aspects of NO3– regulation have not been previously reviewed in detail. Here, we mainly focused on the recent advances of post-transcriptional regulation and non-coding RNA (ncRNAs) in NO3– signaling, and NO3– regulation on leaf senescence and the circadian clock. It will help us to extend the general picture of NO3– regulation and provide a basis for further exploration of NO3– regulatory network.

Sensing of O2 and nitrate by bacteria: alternative strategies for transcriptional regulation of nitrate respiration by O2 and nitrate.

Many bacteria are able to use O2 and nitrate as alternative electron acceptors for respiration. Strategies for regulation in response to O2 and nitrate can vary considerably. In the paradigmatic system of E. coli (and γ-proteobacteria), regulation by O2 and nitrate is established by the O2 -sensor FNR and the two-component system NarX-NarL (for nitrate regulation). Expression of narGHJI is regulated by the binding of FNR and NarL to the promoter. A similar strategy by individual regulation in response to O2 and nitrate is verified in many genera by the use of various types of regulators. Otherwise, in the soil bacteria Bacillus subtilis (Firmicutes) and Streptomyces (Actinobacteria), nitrate respiration is subject to anaerobic induction, without direct nitrate induction. In contrast, the NreA-NreB-NreC two-component system of Staphylococcus (Firmicutes) performs joint sensing of O2 and nitrate by interacting O2 and nitrate sensors. The O2 -sensor NreB phosphorylates the response regulator NreC to activate narGHJI expression. NreC-P transmits the signal for anaerobiosis to the promoter. The nitrate sensor NreA modulates NreB function by converting NreB in the absence of nitrate from the kinase to a phosphatase that dephosphorylates NreC-P. Thus, widely different strategies for coordinating the response to O2 and nitrate have evolved in bacteria.