Genome-wide identification of nitrate transporter 2 (NRT2) gene family and functional analysis of MeNRT2.2 in cassava (Manihot esculenta Crantz)

Melatonin confers tolerance to nitrogen deficiency through regulating MdHY5 in apple plants

Nitrogen (N) is an essential nutrient for crop growth and development, significantly influencing both yield and quality. Melatonin (MT), a known enhancer of abiotic stress tolerance, has been extensively studied. However, its relationship with nutrient stress, particularly N deficiency, and the underlying regulatory mechanisms of MT on N absorption remain unclear. In this study, exogenous MT treatment was found to improve the tolerance of apple plants to N deficiency. Apple plants overexpressing the MT biosynthetic gene N-acetylserotonin methyltransferase 9 (MdASMT9) were used to further investigate the effects of endogenous MT on low-N stress. Overexpression of MdASMT9 improved the light harvesting and heat transfer capability of apple plants, thereby mitigating the detrimental effects of N deficiency on the photosynthetic system. Proteomic and physiological data analyses indicated that MdASMT9 overexpression enhanced the trichloroacetic acid cycle and positively modulated amino acid metabolism to counteract N-deficiency stress. Additionally, both exogenous and endogenous MT promoted the transcription of MdHY5, which in turn bound to the MdNRT2.1 and MdNRT2.4 promoters and activated their expression. Notably, MT-mediated promotion of MdNRT2.1 and MdNRT2.4 expression through regulating MdHY5, ultimately enhancing N absorption. Taken together, these findings shed light on the association between MdASMT9-mediated MT biosynthesis and N absorption in apple plants under N-deficiency conditions.

PsNRT2.3 interacts with PsNAR to promote high-affinity nitrate uptake in pea (Pisum sativum L.)

Nitrate, the primary form of nitrogen absorbed by plants, supplies essential compounds for plant growth and development. Peas are frequently used as rotation crops to improve and stabilize soil fertility. However, the determinants of nitrate uptake and transport in peas remain largely unclear, primarily due to the pea genome's complexity and size. In this study, we utilized the complete genomic information of peas to identify three PsNRT2 family genes within the pea genome. We conducted a comprehensive examination of their protein conserved domains, physicochemical properties, gene structure, and phylogenetic evolution, revealing PsNRT2.3 as the potential key gene for high-affinity nitrate transport in peas. Subcellular localization studies indicated that PsNRT2.3 resides on the plasma membrane. Using hairy root transformation, we noted the predominant expression of PsNRT2.3 in the root stele, which is inducible by nitrate. Our experiments involving overexpression and silencing methods further confirmed that PsNRT2.3 plays a key role in enhancing nitrate uptake in peas. Additionally, our work showed that PsNAR could interact with PsNRT2.3, modulating pea nitrate uptake. After silencing PsNAR, even with the normal expression of PsNRT2.3, the ability of peas to absorb nitrate was significantly reduced. In conclusion, this study identifies the high-affinity nitrate transport gene PsNRT2.3 in peas and clarifies its critical role and regulatory network in nitrate transport, contributing to a new understanding of nitrate utilization in peas.

Functional characterization of the GhNRT2.1e gene reveals its significant role in improving nitrogen use efficiency in Gossypium hirsutum

Background

Nitrate is the primary type of nitrogen available to plants, which is absorbed and transported by nitrate transporter 2 (NRT2) at low nitrate conditions.

Methods

Genome-wide identification of NRT2 genes in G. hirsutum was performed. Gene expression patterns were revealed using RNA-seq and qRT-PCR. Gene functions were characterized using overexpression in A. thaliana and silencing in G. hirsutum. Protein interactions were verified by yeast two-hybrid and luciferase complementation imaging (LCI) assays.

Results

We identified 14, 14, seven, and seven NRT2 proteins in G. hirsutum, G. barbadense, G. raimondii, and G. arboreum. Most NRT2 proteins were predicted in the plasma membrane. The NRT2 genes were classified into four distinct groups through evolutionary relationships, with members of the same group similar in conserved motifs and gene structure. The promoter regions of NRT2 genes included many elements related to growth regulation, phytohormones, and abiotic stresses. Tissue expression pattern results revealed that most GhNRT2 genes were specifically expressed in roots. Under low nitrate conditions, GhNRT2 genes exhibited different expression levels, with GhNRT2.1e being the most up-regulated. Arabidopsis plants overexpressing GhNRT2.1e exhibited increased biomass, nitrogen and nitrate accumulation, nitrogen uptake and utilization efficiency, nitrogen-metabolizing enzyme activity, and amino acid content under low nitrate conditions. In addition, GhNRT2.1e-silenced plants exhibited suppressed nitrate uptake and accumulation, hampered plant growth, affected nitrogen metabolism processes, and reduced tolerance to low nitrate. The results showed that GhNRT2.1e could promote nitrate uptake and transport under low nitrate conditions, thus effectively increasing nitrogen use efficiency (NUE). We found that GhNRT2.1e interacts with GhNAR2.1 by yeast two-hybrid and LCI assays.

Discussion

Our research lays the foundation to increase NUE and cultivate new cotton varieties with efficient nitrogen use.

Genome-wide identification, expression profiling, and functional analysis of ammonium transporter 2 (AMT2) gene family in cassava (Manihot esculenta crantz)

Background: Nitrogen (N), absorbed primarily as ammonium (NH₄ ⁺) from soil by plant, is a necessary macronutrient in plant growth and development. Ammonium transporter (AMT) plays a vital role in the absorption and transport of ammonium (NH₄ ⁺). Cassava (Manihot esculenta Crantz) has a strong adaptability to nitrogen deprivation. However, little is known about the functions of ammonium transporter AMT2 in cassava. Methods: The cassava AMT2-type genes were identified and their characteristics were analyzed using bioinformatic techniques. The spatial expression patterns were analyzed based on the public RNA-seq data and their expression profiles under low ammonium treatment were studied using Real-time quantitative PCR (RT-qPCR) method. The cassava AMT2 genes were transformed into yeast mutant strain TM31019b by PEG/LiAc method to investigate their functions. Results: Seven AMT2-type genes (MeAMT2.1-2.7) were identified in cassava and they were distributed on 6 chromosomes and included two segmental duplication events (MeAMT2.2/MeAMT2.4 and MeAMT2.3/MeAMT2.5). Based on their amino acid sequences, seven MeAMT2 were further divided into four subgroups, and each subgroup contained similar motif constitution and protein structure. Synteny analysis showed that two and four MeAMT2 genes in cassava were collinear with those in the Arabidopsis and soybean genomes, respectively. Sixteen types of cis-elements were identified in the MeAMT2 promoters, and they were related to light-, hormone-, stress-, and plant growth and development-responsive elements, respectively. Most of the MeAMT2 genes displayed tissue-specific expression patterns according to the RNA-seq data, of them, three MeAMT2 (MeAMT2.3, MeAMT2.5, and MeATM2.6) expressions were up-regulated under ammonium deficiency. Complementation experiments showed that yeast mutant strain TM31019b transformed with MeAMT2.3, MeAMT2.5, or MeATM2.6 grew better than untransgenic yeast cells under ammonium deficiency, suggesting that MeAMT2.3, MeAMT2.5, and MeATM2.6 might be the main contributors in response to ammonium deficiency in cassava. Conclusion: This study provides a basis for further study of nitrogen efficient utilization in cassava.

Genome-Wide Identification and Expression Analysis of AMT and NRT Gene Family in Pecan (Carya illinoinensis) Seedlings Revealed a Preference for NH4+-N

Nitrogen (N) is a major limiting factor for plant growth and crop production. The use of N fertilizer in forestry production is increasing each year, but the loss is substantial. Mastering the regulatory mechanisms of N uptake and transport is a key way to improve plant nitrogen use efficiency (NUE). However, this has rarely been studied in pecans. In this study, 10 AMT and 69 NRT gene family members were identified and systematically analyzed from the whole pecan genome using a bioinformatics approach, and the expression patterns of AMT and NRT genes and the uptake characteristics of NH₄⁺ and NO₃⁻ in pecan were analyzed by aeroponic cultivation at varying NH₄⁺/NO₃⁻ ratios (0/0, 0/100,25/75, 50/50, 75/25,100/0 as CK, T1, T2, T3, T4, and T5). The results showed that gene duplication was the main reason for the amplification of the AMT and NRT gene families in pecan, both of which experienced purifying selection. Based on qRT-PCR results, CiAMTs were primarily expressed in roots, and CiNRTs were majorly expressed in leaves, which were consistent with the distribution of pecan NH₄⁺ and NO₃⁻ concentrations in the organs. The expression levels of CiAMTs and CiNRTs were mainly significantly upregulated under N deficiency and T4 treatment. Meanwhile, T4 treatment significantly increased the NH₄⁺, NO₃⁻, and NO₂⁻ concentrations as well as the Vmax and Km values of NH₄⁺ and NO₃⁻ in pecans, and Vmax/Km indicated that pecan seedlings preferred to absorb NH₄⁺. In summary, considering the single N source of T5, we suggested that the NH₄⁺/NO₃⁻ ratio of 75:25 was more beneficial to improve the NUE of pecan, thus increasing pecan yield, which provides a theoretical basis for promoting the scale development of pecan and provides a basis for further identification of the functions of AMT and NRT genes in the N uptake and transport process of pecan.

Genome-wide identification and characterization of high-affinity nitrate transporter 2 (NRT2) gene family in tomato (Solanum lycopersicum) and their transcriptional responses to drought and salinity stresses

The high-affinity nitrate transporter 2 (NRT2) proteins play vital roles in both nitrate (NO₃^-) uptake and translocation in plants. Although the gene families coding the NRT2 proteins have been identified and functionally characterized in many plant species, the systematic identification of NRT2 gene family members has not previously been reported in tomato (Solanum lycopersicum). Moreover, little is known about their expression profiles in response to different environmental stresses. The present study sought to identify the NRT2 gene family members within the tomato genome, and then to characterize them in detail by means of bioinformatics, physiological and expression analyses. Four novel NRT2 genes were identified in the tomato genome, all of which contained the same domain belonging to the major facilitator superfamily (PF07690). The co-expression network of the SlNRT2 genes revealed that they were co-expressed with several other genes in a number of different molecular pathways, including the transport, photosynthesis, fatty acid metabolism and amino acid catabolism pathways. Several phosphorylation sites were predicted in the NRT2 proteins. The SlNRT2 genes interact with many other genes that perform various functions in many crucial pathways within the tomato genome. The sequence variations observed at the gene and protein levels indicate the dynamic regulation of the SlNRT2 gene family members in relation to cell metabolism, particularly with regard to the nitrogen assimilation pathway. The responses of the SlNRT2 genes to drought and salinity stresses are diverse, and they are neither stress- nor tissue-specific. The findings of this study should provide a useful scientific basis for future studies concerning the roles of the NRT2 gene family in plants.

Recent Advances in Agronomic and Physio-Molecular Approaches for Improving Nitrogen Use Efficiency in Crop Plants

The efficiency with which plants use nutrients to create biomass and/or grain is determined by the interaction of environmental and plant intrinsic factors. The major macronutrients, especially nitrogen (N), limit plant growth and development (1.5-2% of dry biomass) and have a direct impact on global food supply, fertilizer demand, and concern with environmental health. In the present time, the global consumption of N fertilizer is nearly 120 MT (million tons), and the N efficiency ranges from 25 to 50% of applied N. The dynamic range of ideal internal N concentrations is extremely large, necessitating stringent management to ensure that its requirements are met across various categories of developmental and environmental situations. Furthermore, approximately 60 percent of arable land is mineral deficient and/or mineral toxic around the world. The use of chemical fertilizers adds to the cost of production for the farmers and also increases environmental pollution. Therefore, the present study focused on the advancement in fertilizer approaches, comprising the use of biochar, zeolite, and customized nano and bio-fertilizers which had shown to be effective in improving nitrogen use efficiency (NUE) with lower soil degradation. Consequently, adopting precision farming, crop modeling, and the use of remote sensing technologies such as chlorophyll meters, leaf color charts, etc. assist in reducing the application of N fertilizer. This study also discussed the role of crucial plant attributes such as root structure architecture in improving the uptake and transport of N efficiency. The crosstalk of N with other soil nutrients plays a crucial role in nutrient homeostasis, which is also discussed thoroughly in this analysis. At the end, this review highlights the more efficient and accurate molecular strategies and techniques such as N transporters, transgenes, and omics, which are opening up intriguing possibilities for the detailed investigation of the molecular components that contribute to nitrogen utilization efficiency, thus expanding our knowledge of plant nutrition for future global food security.

Genome-Wide Characterization of High-Affinity Nitrate Transporter 2 (NRT2) Gene Family in Brassica napus

Nitrate transporter 2 (NRT2) plays an essential role in Nitrogen (N) uptake, transport, utilization, and stress resistance. In this study, the NRT2 gene family in two sequenced Brassica napus ecotypes were identified, including 31 genes in ‘Zhongshuang11’ (BnaZSNRT2s) and 19 in ‘Darmor-bzh’ (BnaDarNRT2s). The candidate genes were divided into three groups (Group I−III) based on phylogenetic analyses, supported by a conserved intron-exon structure in each group. Collinearity analysis revealed that the large expansion of BnaZSNRT2s attributed to allopolyploidization of ancestors Brassica rapa and Brassica oleracea, and small-scale duplication events in B. napus. Transcription factor (TF) binding site prediction, cis-element analysis, and microRNA prediction suggested that the expressions of BnaZSNRT2s are regulated by multiple factors, and the regulatory pattern is relatively conserved in each group and is tightly connected between groups. Expression assay showed the diverse and differentiated spatial-temporal expression profiles of BnaZSNRT2s in Group I, but conserved patterns were observed in Group II/III; and the low nitrogen (LN) stress up-regulated expression profiles were presented in Group I−III, based on RNA-seq data. RT-qPCR analyses confirmed that BnaZSNRT2.5A-1 and BnaZSNRT2.5C-1 in Group II were highly up-regulated under LN stress in B. napus roots. Our results offer valid information and candidates for further functional BnaZSNRT2s studies.

Global Analysis of the WOX Transcription Factor Gene Family in Populus × xiaohei T. S. Hwang et Liang Reveals Their Stress−Responsive Patterns

The WUSCHEL−related homeobox (WOX) family is a group of plant−specific transcription factors that play important regulatory roles in embryo formation, stem cell stability, and organogenesis. To date, there are few studies on the molecular mechanisms involved in this family of genes in response to stress. Thus, in this study, eight WOX genes were obtained from an endemic Chinese resilient tree species, Populus × xiaohei T. S. Hwang et Liang. Bioinformatic analysis showed that the WOX genes all contained a conserved structural domain consisting of 60 amino acids, with some differences in physicochemical properties. Phylogenetic analysis revealed that WOX members were divided into three evolutionary clades, with four, one, and three members in the ancient, intermediate, and modern evolutionary clades, respectively. The conserved structural domain species as well as the organization and gene structure of WOX genes within the same subfamily were highly uniform. Chromosomal distribution and genome synteny analyses revealed seven segmental−duplicated gene pairs among the PsnWOX gene family that were mainly under purifying selection conditions. Semi−quantitative interpretation (SQ−PCR) analysis showed that the WOX gene was differentially expressed in different tissues, and it was hypothesized that the functions performed by different members were diverse. The family members were strongly and differentially expressed under CdCl2, NaCl, NaHCO3, and PEG treatments, suggesting that WOX genes function in various aspects of abiotic stress defense responses. These results provide a theoretical basis for investigating the morphogenetic effects and abiotic stress responses of this gene family in woody plants.