Nitrogen Transporter Genes Research Articles

Optimal nitrogen source for the recovery of phycoerythrin in discolored Rhodomonas sp.

Rhodomonas species are of interest as excellent aquaculture feed because of their ideal biochemical composition, especially their high protein content, resulting from the presence of intracellular phycoerythrin (PE). One of the most crucial issue with this species as a feed source is PE degradation under ambient nitrogen starvation, which leads to unpredictable growth defects and reduced nutritional value associated with cell discoloration. The aim of this study was to propose an optimal nitrogen source for the recovery of intracellular PE in discolored Rhodomonas sp. We supplied three different nitrogen sources, i.e., nitrate, ammonium, and urea, to PE-degraded cells and monitored changes in PE content and the expression of related genes. Supplementation with each nitrogen source increased cell density, with nitrate exhibiting the highest specific growth rate of 0.30 ± 0.02 day−1. The maximum PE content in each nitrogen group at 48 h after N supplementation was about 3.8 pg cell−1 with no major difference between groups. In contrast, the highest relative PE recovery rate of 5.73 ± 0.18-fold and the highest PE productivities of 0.32 ± 0.01 μg mL−1 h−1 were obtained in the nitrate group. Nitrogen transporter genes, including RhNrt2, RhAmt1, and RhDur3, were upregulated under nitrogen-starvation conditions, demonstrating the ability of this species to utilize each of the tested nitrogen sources. Furthermore, RhCpeb, which serves as a molecular indicator of PE biosynthesis, was significantly upregulated in all nitrogen-supplemented groups, with the strongest and fastest increase in expression in the nitrate group, emphasizing the potential of nitrate as the most favorable nitrogen source for PE recovery in this species. Our findings pave the way for informed strategies for the stable management and production of Rhodomonas species as high-protein feed in aquaculture.

EXPRESSION OF NITROGEN TRANSPORTER GENES IN LEAVES OF WHEAT (Triticum aestivum L.) AND FIELD PERFORMANCES UNDER ORGANIC CONDITIONS

This study aimed to investigate the expression patterns of nitrogen transporter genes in wheat (Triticum aestivum L.) grown in organic farming systems. Expression profiling of these genes will provide valuable insights into the molecular mechanisms involved in nitrogen uptake and transport in wheat plants. In addition, the agronomic responses of the wheat genotypes were evaluated under organic conditions. This will help in the creation of genotypes that support effective nitrogen use in organic farming systems. The study showed that the nitrate transporter gene family member TaNRT2.1 exhibited the highest expression level. The Alada cultivar performed well in terms of yield under field conditions and showed the highest expression levels of TaNRT2.1, NRT2.1, and TaGS1. The 6DZT-03-01 genotype had the highest expression levels of NPF6.3 and AMT2.1. Alada, YE-4, and YE-31 were identified as the most suitable genotypes for organic farming. Several genes, including TaNRT2.1, were more highly expressed in the high-yielding genotype, Alada, than in the other genotypes. This suggested that nitrate and ammonium transporters play an important role in determining how different genotypes of wheat take in nitrogen. Further research is needed to understand the complex mechanisms that contribute to genotypic variation in nitrogen uptake in wheat. To fully understand the genetic basis of nitrogen uptake in wheat and to develop ways to improve nutrient management in organic farming systems, the expression levels of other genes involved in nitrogen metabolism should also be examined. Keywords: Bread wheat, Yield, Gene expression, Nitrogen transporter genes, qRT-PCR

Heat stress memory differentially regulates the expression of nitrogen transporter genes in the filamentous red alga 'Bangia' sp. ESS1.

To withstand high temperatures that would be lethal to a plant in the naïve state, land plants must establish heat stress memory. The acquisition of heat stress tolerance via heat stress memory in algae has only been observed in the red alga 'Bangia' sp. ESS1. In this study, we further evaluated the intrinsic ability of this alga to establish heat stress memory by monitoring hydrogen peroxide (H2O2) production and examining the relationship between heat stress memory and the expression of genes encoding nitrogen transporters, since heat stress generally reduces nitrogen absorption. Next, genes encoding nitrogen transporters were selected from our unpublished transcriptome data of 'Bangia' sp. ESS1. We observed a reduction in H2O2 content when heat stress memory was established in the alga. In addition, six ammonium transporter genes, a single-copy nitrate transporter gene and two urea transporter genes were identified. Two of these nitrogen transporter genes were induced by heat stress but not by heat stress memory, two genes showed heat stress memory-dependent expression, and one gene was induced by both treatments. Heat stress memory therefore differentially regulated the expression of the nitrogen transporter genes by reducing heat stress-inducible gene expression and inducing heat stress memory-dependent gene expression. These findings point to the functional diversity of nitrogen transporter genes, which play different roles under various heat stress conditions. The characteristic effects of heat stress memory on the expression of individual nitrogen transporter genes might represent an indispensable strategy for reducing the threshold of sensitivity to recurrent high-temperature conditions and for maintaining nitrogen absorption under such conditions in 'Bangia' sp. ESS1.

Assessing inorganic nitrogen transport in marine phytoplankton assemblages through the 15N-tracer technique and metatranscriptomics

The availability of inorganic nitrogen is considered one of the limiting factors for primary production in the ocean. However, different phytoplankton possess unique strategies to take up and assimilate nitrate and ammonium to cope with environmental changes. To investigate the nitrogen uptake characteristics of different size-fractionated phytoplankton in natural assemblages, 3 research cruises were conducted in the southern East China Sea in 2018 and 2019. The nitrogen uptake characteristics of 2 size-fractionated natural assemblages, microphytoplankton (20-200 µm) and pico-nanophytoplankton (<20 µm), were measured using the 15N-tracer technique. At most of the stations, significantly higher potential maximum uptake rates of ammonium than of nitrate were detected in the pico-nanophytoplankton, indicating that small phytoplankton possess a relatively superior capacity to take up ammonium. By contrast, comparing the potential maximum uptake rate for nitrate between microphytoplankton and pico-nanophytoplankton showed that microphytoplankton exhibit a higher capacity for nitrate uptake as a nitrogen source compared to pico-nanophytoplankton. However, repressed uptake rates of ammonium and nitrate in microphytoplankton were sometimes found at the coastal station even when ambient nitrate concentrations remained high. Metatranscriptomic analysis of nitrogen transporter genes in microphytoplankton suggests that most diatoms utilize regenerated ammonium before nitrate to maintain their populations at the end of blooms. Metatranscriptomic approaches identify the transcriptional responses of dominant diatoms to explain how diatoms regulate their nitrogen transporter genes to cope with environmental changes in natural assemblages.

The Relationship between Ectomycorrhizal Fungi, Nitrogen Deposition, and Pinus massoniana Seedling Nitrogen Transporter Gene Expression and Nitrogen Uptake Kinetics.

Analyzing the molecular and physiological processes that govern the uptake and transport of nitrogen (N) in plants is central to efforts to fully understand the optimization of plant N use and the changes in the N-use efficiency in relation to changes in atmospheric N deposition changes. Here, a field experiment was conducted using the ectomycorrhizal fungi (EMF), Pisolithus tinctorius (Pt) and Suillus grevillei (Sg). The effects of N deposition were investigated using concentrations of 0 kg·N·hm-2a-1 (N0), a normal N deposition of 30 kg·N·hm-2a-1 (N30), a moderate N deposition of 60 kg·N·hm-2a-1 (N60), and a severe N deposition of 90 kg·N·hm-2a-1 (N90), with the goal of examining how these factors impacted root activity, root absorbing area, NH4+ and NO3- uptake kinetics, and the expression of ammonium and nitrate transporter genes in Pinus massoniana seedlings under different levels of N deposition. These data revealed that EMF inoculation led to increased root dry weight, activity, and absorbing area. The NH4+ and NO3- uptake kinetics in seedlings conformed to the Michaelis-Menten equation, and uptake rates declined with increasing levels of N addition, with NH4+ uptake rates remaining higher than NO3- uptake rates for all tested concentrations. EMF inoculation was associated with higher Vmax values than were observed for non-mycorrhizal plants. Nitrogen addition resulted in the upregulation of genes in the AMT1 family and the downregulation of genes in the NRT family. EMF inoculation under the N60 and N90 treatment conditions resulted in the increased expression of each of both these gene families. NH4+ and NO3- uptake kinetics were also positively correlated with associated transporter gene expression in P. massoniana roots. Together, these data offer a theoretical foundation for EMF inoculation under conditions of increased N deposition associated with climate change in an effort to improve N absorption and transport rates through the regulation of key nitrogen transporter genes, thereby enhancing N utilization efficiency and promoting plant growth. Synopsis: EMF could enhance the efficiency of N utilization and promote the growth of Pinus massoniana under conditions of increased N deposition.

Orange Leafhopper Cicadulina bipunctata Feeding Induces Gall Formation Nitrogen Dependently and Regulates Gibberellin Signaling.

Orange leafhopper Cicadulina bipunctata feeding induces wallaby ear symptoms, namely growth suppression and gall formation characterized by severe swelling of leaf veins, on various Poaceae, thereby leading to low crop yields. Here, we investigated the development of wallaby ear symptoms on rice seedlings due to C. bipunctata feeding. After confirming that C. bipunctata feeding induces growth suppression and gall formation on rice seedlings, we further demonstrated that gall formation score decreased with decreasing levels of nitrogen in the medium and that C. bipunctata feeding induces the expression levels of nitrogen transporter genes. These gene expression changes may participate in the nutrient accumulation observed in galled tissues and in gall formation. In addition, these expression changes should induce growth promotion but the inhibition of gibberellin signaling by C. bipunctata feeding might be the reason why growth is suppressed. Treatment with plant growth regulators did not affect gall formation, suggesting the existence of a complex gall formation mechanism by C. bipunctata feeding.

Effect of Seedling Nitrogen Condition on Subsequent Vegetative Growth Stages and Its Relationship to the Expression of Nitrogen Transporter Genes in Rice.

Nitrogen (N) deficiency is one of the most common problems in soils, limiting crop growth and production. However, the effects of N limitation in seedlings on vegetative growth remain poorly understood. Here, we show that N limitation in rice seedlings restricted vegetative growth but not yield. Aboveground parts were affected mainly during the period of tillering, but belowground parts were sensitive throughout vegetative growth, especially during panicle development. At the tillering stage, N-limited plants had a significantly lower N content in shoots, but not in roots. On the other hand, N content in roots during the panicle development stage was significantly lower in N-limited plants. This distinct response was driven by significant changes in expression of N transporter genes during growth. Under N limitation, N translocation from roots to shoots was greatly sped up by systemic expression of N transporter genes to obtain balanced growth. N limitation during the seedling stage did not reduce any yield components. We conclude that the N condition during the seedling stage affects physiological responses such as N translocation through the expression of N transporter genes.

Low temperature causes discoloration by repressing growth and nitrogen transporter gene expression in the edible red alga Pyropia yezoensis

The reduced availability of nitrogen sources in seawater leads to discoloration of the edible red seaweed Pyropia yezoensis and induces the expression of genes encoding ammonium, nitrate and urea transporters. In the present study, we demonstrate that low temperatures can also cause discoloration of this economically important seaweed. Thus, we addressed regulatory mechanisms of cold-inducible discoloration. When P. yezoensis thalli were incubated at 0, 5 and 10°C, the thalli exhibited retarded growth and discoloration, along with reduced phycoerythrin contents. Fertilization with nitrogen sources did not recover this discoloration at 0°C, suggesting that defects in nitrogen absorption cause low temperature-induced discoloration. The expression levels of many nitrogen transporter genes were reduced at low temperature. We propose that low temperature-mediated repression of ammonium, nitrate and urea transporter gene expression promotes the reduced absorption of nitrogen sources in P. yezoensis, thereby leading to discoloration. This process is different from the well-known mechanism underlying discoloration in P. yezoensis under nitrogen-deficient conditions at normal culture temperature.

Tissue and nitrogen-linked expression profiles of ammonium and nitrate transporters in maize

BackgroundIn order to grow, plants rely on soil nutrients which can vary both spatially and temporally depending on the environment, the soil type or the microbial activity. An essential nutrient is nitrogen, which is mainly accessible as nitrate and ammonium. Many studies have investigated transport genes for these ions in Arabidopsis thaliana and recently in crop species, including Maize, Rice and Barley. However, in most crop species, an understanding of the participants in nitrate and ammonium transport across the soil plant continuum remains undefined.ResultsWe have mapped a non-exhaustive set of putative nitrate and ammonium transporters in maize. The selected transporters were defined based on previous studies comparing nitrate transport pathways conserved between Arabidopsis and Zea mays (Plett D et. al, PLOS ONE 5:e15289, 2010). We also selected genes from published studies (Gu R et. al, Plant and Cell Physiology, 54:1515-1524, 2013, Garnett T et. al, New Phytol 198:82-94, 2013, Garnett T et. al, Frontiers in Plant Sci 6, 2015, Dechorgnat J et. al, Front Plant Sci 9:531, 2018). To analyse these genes, the plants were grown in a semi-hydroponic system to carefully control nitrogen delivery and then harvested at both vegetative and reproductive stages. The expression patterns of 26 putative nitrogen transporters were then tested. Six putative genes were found not expressed in our conditions. Transcripts of 20 other genes were detected at both the vegetative and reproductive stages of maize development. We observed the expression of nitrogen transporters in all organs tested: roots, young leaves, old leaves, silks, cobs, tassels and husk leaves. We also followed the gene expression response to nitrogen starvation and resupply and uncovered mainly three expression patterns: (i) genes unresponsiveness to nitrogen supply; (ii) genes showing an increase of expression after nitrogen starvation; (iii) genes showing a decrease of expression after nitrogen starvation.ConclusionsThese data allowed the mapping of putative nitrogen transporters in maize at both the vegetative and reproductive stages of development. No growth-dependent expression was seen in our conditions. We found that nitrogen transporter genes were expressed in all the organs tested and in many cases were regulated by the availability of nitrogen supplied to the plant. The gene expression patterns in relation to organ specificity and nitrogen availability denote a speciality of nitrate and ammonium transporter genes and their probable function depending on the plant organ and the environment.

Nutrient Loading Fosters Seagrass Productivity Under Ocean Acidification

The effects of climate change are likely to be dependent on local settings. Nonetheless, the compounded effects of global and regional stressors remain poorly understood. Here, we used CO2 vents to assess how the effects of ocean acidification on the seagrass, Posidonia oceanica, and the associated epiphytic community can be modified by enhanced nutrient loading. P. oceanica at ambient and low pH sites was exposed to three nutrient levels for 16 months. The response of P. oceanica to experimental conditions was assessed by combining analyses of gene expression, plant growth, photosynthetic pigments and epiphyte loading. At low pH, nutrient addition fostered plant growth and the synthesis of photosynthetic pigments. Overexpression of nitrogen transporter genes following nutrient additions at low pH suggests enhanced nutrient uptake by the plant. In addition, enhanced nutrient levels reduced the expression of selected antioxidant genes in plants exposed to low pH and increased epiphyte cover at both ambient and low pH. Our results show that the effects of ocean acidification on P. oceanica depend upon local nutrient concentration. More generally, our findings suggest that taking into account local environmental settings will be crucial to advance our understanding of the effects of global stressors on marine systems.

Influence of nutrient signals and carbon allocation on the expression of phosphate and nitrogen transporter genes in winter wheat (Triticum aestivum L.) roots colonized by arbuscular mycorrhizal fungi.

Arbuscular mycorrhizal (AM) colonization of plant roots causes the down-regulation of expression of phosphate (Pi) or nitrogen (N) transporter genes involved in direct nutrient uptake pathways. The mechanism of this effect remains unknown. In the present study, we sought to determine whether the expression of Pi or N transporter genes in roots of winter wheat colonized by AM fungus responded to (1) Pi or N nutrient signals transferred from the AM extra-radical hyphae, or (2) carbon allocation changes in the AM association. A three-compartment culture system, comprising a root compartment (RC), a root and AM hyphae compartment (RHC), and an AM hyphae compartment (HC), was used to test whether the expression of Pi or N transporter genes responded to nutrients (Pi, NH4+ and NO3-) added only to the HC. Different AM inoculation density treatments (roots were inoculated with 0, 20, 50 and 200 g AM inoculum) and light regime treatments (6 hours light and 18 hours light) were established to test the effects of carbon allocation on the expression of Pi or N transporter genes in wheat roots. The expression of two Pi transporter genes (TaPT4 and TaPHT1.2), five nitrate transporter genes (TaNRT1.1, TaNRT1.2, TaNRT2.1, TaNRT2.2, and TaNRT2.3), and an ammonium transporter gene (TaAMT1.2) was quantified using real-time polymerase chain reaction. The expression of TaPT4, TaNRT2.2, and TaAMT1.2 was down-regulated by AM colonization only when roots of host plants received Pi or N nutrient signals. However, the expression of TaPHT1.2, TaNRT2.1, and TaNRT2.3 was down-regulated by AM colonization, regardless of whether there was nutrient transfer from AM hyphae. The expression of TaNRT1.2 was also down-regulated by AM colonization even when there was no nutrient transfer from AM hyphae. The present study showed that an increase in carbon consumption by the AM fungi did not necessarily result in greater down-regulation of expression of Pi or N transporter genes.

Expression of nitrogen transporter genes in roots of winter wheat (Triticum aestivum L.) in response to soil drought with contrasting nitrogen supplies

The expression of nitrate and ammonium transporter genes in the roots of winter wheat in response to drought stress is largely unknown. A greenhouse experiment was established to study the expression of five putative nitrate transporter (NRT) genes (TaNRT2.1, TaNRT2.2, TaNRT2.3, TaNRT1.1, TaNRT1.2) and three ammonium transporter (AMT) genes (TaAMT1.1, TaAMT1.2, TaAMT2.1) in the roots of winter wheat in response to soil drought under conditions of limited nitrogen (N) (no N added) and adequate N (addition of 0.3 g N kg–1 soil). Two wheat genotypes with low and high N-uptake efficiencies were used, and water-stress treatments were applied at the vegetative and reproductive growth stages of wheat. Expression of all of the genes was quantified using real-time reverse transcription PCR. The results indicated that wheat plants growing in the N-adequate soil were more sensitive to drought stress than those growing in the N-limited soil. The response of the expression of the NRT and AMT genes to soil drought largely depends on N application, wheat genotype and growth stage. The expression of the two low-affinity NRT genes (i.e. TaNRT1.1 and TaNRT1.2) in the N-inefficient genotype XY6 was mainly induced by drought stress, but the expression of the two genes in the N-efficient genotype XY107 was repressed by drought stress. The expression of the high-affinity NRT gene TaNRT2.1 was repressed by drought stress, but the expression of the other two high-affinity NRT genes, TaNRT2.2 and TaNRT2.3, was induced or repressed by soil drought depending on N application and growth stage. The expression of the genes TaAMT1.1 and TaAMT2.1 was mainly repressed by drought stress, whereas the expression of the gene TaAMT1.2 was induced by drought stress. The expression of TaNRT2.1 in XY107 was significantly higher than in XY6.

Systemic and local regulation of phosphate and nitrogen transporter genes by arbuscular mycorrhizal fungi in roots of winter wheat (Triticum aestivum L.)

Previous studies have reported that the expression of phosphate (Pi) or nitrogen (N) transporter genes in roots of plants could be regulated by arbuscular mycorrhizal (AM) fungi, but little is known whether the regulation is systemic or not. The present study investigated the systemic and local regulation of multiple phosphate and nitrogen transporter genes by four AM fungal species belonging to four genera in the roots of winter wheat. A split-root culture system with AM inoculated (MR) and non-inoculated root compartments (NR) was used to investigate the systemic or local responses of phosphate and nitrogen transporter genes to colonization by four AM fungi in the roots of wheat. The expression of four Pi transporter, five nitrate transporter, and three ammonium transporter genes was quantified using real-time PCR. Of the four AM fungi tested, all locally increased expression of the AM-inducible Pi transporter genes, and most locally decreased expression of a Pi-starvation inducible Pi transporter gene. The addition of N in soil increased the expression of either Pi starvation inducible Pi transporters or AM inducible Pi transporters. Inoculation with AM fungi either had no effect, or could locally or systemically down-regulate expression of nitrogen transporter genes depending on gene type and AM fungal species.

Stimulation of nodulation inMedicago truncatulaby low concentrations of ammonium: quantitative reverse transcription PCR analysis of selected genes

Although mineral nitrogen generally has negative effects on nodulation in legume-rhizobia symbioses, low concentrations of ammonium stimulate nodulation in some legumes. In this study, the effects of ammonium and nitrate on growth, nodulation and expression of 2 nitrogen transport and 12 putative nodulation-related genes of the model symbiosis of Medicago truncatula - Sinorhizobium meliloti are investigated. After 3 weeks of hydroponic growth, whole-plant nodulation was enhanced in all the ammonium treatments and up to three-fold in the 0.5 mM treatment compared with the zero-nitrogen control. Specific nodulation (nodules g(-1) root dry weight) was greatly stimulated in the 0.1 and 0.5 mM NH4+ treatments, to a lower extent in the 0.1 mM NO3- treatment, and inhibited in all other treatments. Expression of the 14 selected genes was observed at 0, 6, 12 and 24 h after exposure to rhizobia and nitrogen. Expression of nitrogen transporter genes increased significantly, but responses of the three genes putatively associated with symbiosis signaling/nodule initiation were mixed. There were infrequent responses of genes coding for an ABA-activated protein kinase or a gibberellin-regulated protein, but an ethylene-responsive element-binding factor showed increased expression in various treatments and sampling times. Three auxin-responsive genes and three cytokinin-responsive genes showed varied responses to ammonium and nitrate. This study indicates that low concentrations of ammonium stimulate nodulation in M. truncatula, but the data were inconclusive in verifying the hypothesis that a relatively high ratio of cytokinin to auxin in roots may be an underlying mechanism in this stimulation of nodulation.