Low Nitrogen Stress Research Articles

Combining ability analysis of maize lines under optimal and low nitrogen stress

Most of the land for maize development in Indonesia has low N limiting factor, thus it is necessary to develop a proper maize breeding programs tolerant to low N conditions. One of the breeding methods suitable for low N evaluation is the diallel method between inbred parents (homozygous lines) that are tolerant of low N stress. The aim of this study was to assess the genotype tolerance to low N with comparable yields. The research consisted of two stages. The first stage is the development of hybrid maize grains (F1) using the half diallel cross method. This activity was carried out in KP. Maros, Research Center for Cereal Crops. A half-diallel cross refers to the Griffing IV method, by involving 11 low N-tolerant genotypes (AVLN 100-1, AVLN 118-2, AVLN 122-2, AVLN 124-4, AVLN 32-3, AVLN 83-1, AVLN 83-4, AVLN 83-6, AVLN 86-2, MAL 04, and AVLN 124-9). The second stage was carried out in KP. Bajeng to evaluate 52 genotypes of hybrid maize from diallel crosses plus four hybrid varieties Advanta 777, Bisi 18, P 27 and JH 37 for control. The experiment was carried out under conditions of low N stress (100 kg N/ha) and normal N (200 kg N/ha). The experiment used a randomized block design with three replications. Hybrids that are tolerant (T) under conditions of low N stress was best indicated by AVLN 83-4/AVLN 124-4 genotype pair, with significant higher grain yield than Bisi-18 and JH 37 varieties. This hybrid produced average grain yield of 7.87 t/ha under both conditions. Inbred maize genotypes classified as medium tolerant (MT) were AVLN 83-4/AVLN 124-9, AVLN 124-4/AVLN 86-2, AVLN 122-2/AVLN 124-4, AVLN 83-1/AVLN 124-9, has similar yield potential as to the control varieties.

Dynamic transcriptome and co-expression analysis suggest the potential roles of small secreted peptides from Tartary buckwheat (Fagopyrum tataricum) in low nitrogen stress response

Small secreted peptides (SSPs) regulate nitrogen (N) response and signaling in plants. Although much progress has been made in understanding the functions of SSPs in N response, very little information is available regarding non-model plants. Tartary buckwheat (Fagopyrum tataricum), a dicotyledonous crop, has a good adaptability to low N (LN) stress; however, little is known regarding the associated mechanisms underlying this adaptation. In this study, 932 putative SSPs were genome-wide characterized in TB genome. Of these SSPs, 233 SSPs were annotated as established SSPs, such as CLE, RALF, PSK, and CEP peptides. The gene expression of 675 putative SSPs was detected in five tissues and 258 SSPs were tissue-specific expressed genes. To analyze the responses of TB SSPs to LN, the dynamic expression analysis of TB roots under LN stress was conducted by RNA-seq. The expression of 378 putative TB SSP genes was detected with diverse expression patterns under LN stress, and some important LN-responsive SSPs were identified. Co-expression analysis suggested SSPs may regulate the adaptability of TB under LN conditions by modulating the expression of the genes involved in N transport and assimilation and IAA signaling. Furthermore, 53 LN stress-responsive RLKs encoding genes were identified and they were predicted as potential SSP receptors. This study expands the repertoire of SSPs in plants and provides useful information for further investigation of the functions of Tartary buckwheat SSPs in LN stress responses.

Improving abiotic stress tolerance in sorghum: focus on the nutrient transporters and marker-assisted breeding.

Identification of molecular markers and characterization of nutrient transporters could help to improve the tolerance under abiotic and low nutrient stresses in sorghum ensuring higher yield to conserve food security Sorghum is an important cereal crop delivering food and energy security in the semi-arid tropics of the world. Adverse climatic conditions induced by global warming and low input agriculture system in developing countries demand for the improvement of sorghum to tolerate various abiotic stresses. In this review, we discuss the application of marker-assisted breeding and nutrient transporter characterization studies targeted towards improving the tolerance of sorghum under drought, salinity, cold, low phosphate and nitrogen stresses. Family members of some nutrient transporters such as nitrate transporter (NRT), phosphate transporter (PHT) and sulphate transporter (SULTR) were identified and characterized for improving the low nutrient stress tolerance in sorghum. Several quantitative trait loci (QTL) were identified for drought, salinity and cold stresses with an intention to enhance the tolerance of sorghum under these stresses. A very few QTL and nutrient transporters have been identified and validated under low nitrogen and phosphorus stresses compared to those under drought, salinity and cold stresses. Marker-assisted breeding and nutrient transporter characterization have not yet been attempted in sorghum under other macro- and micro-nutrient stresses. We hope this review will raise awareness among plant breeders, scientists and biotechnologists about the importance of sorghum and need to conduct the studies on marker-assisted breeding and nutrient transporter under low nutrient stresses to improve the sorghum production.

PDF1.5 Enhances Adaptation to Low Nitrogen Levels and Cadmium Stress.

Environmental acclimation ability plays a key role in plant growth, although the mechanism remains unclear. Here, we determined the involvement of Arabidopsis thaliana PLANT DEFENSIN 1 gene AtPDF1.5 in the adaptation to low nitrogen (LN) levels and cadmium (Cd) stress. Histochemical analysis revealed that AtPDF1.5 was mainly expressed in the nodes and carpopodium and was significantly induced in plants exposed to LN conditions and Cd stress. Subcellular localization analysis revealed that AtPDF1.5 was cell wall- and cytoplasm-localized. AtPDF1.5 overexpression significantly enhanced adaptation to LN and Cd stress and enhanced the distribution of metallic elements. The functional disruption of AtPDF1.5 reduced adaptations to LN and Cd stress and impaired metal distribution. Under LN conditions, the nitrate transporter AtNRT1.5 expression was upregulated. Nitrate transporter AtNRT1.8 expression was downregulated when AtPDF1.5 was overexpressed, resulting in enhanced transport of NO3− to shoots. In response to Cd treatment, AtPDF1.5 regulated the expression of metal transporter genes AtHMP07, AtNRAMP4, AtNRAMP1, and AtHIPP3, resulting in higher Cd accumulation in the shoots. We conclude that AtPDF1.5 is involved in the processing or transmission of signal substances and plays an important role in the remediation of Cd pollution and LN adaptation.

Morphological, physiological, and transcriptional responses to low nitrogen stress in Populus deltoides Marsh. clones with contrasting nitrogen use efficiency

BackgroundNitrogen (N) is one of the main factors limiting the wood yield in poplar cultivation. Understanding the molecular mechanism of N utilization could play a guiding role in improving the nitrogen use efficiency (NUE) of poplar.ResultsIn this study, three N-efficient genotypes (A1-A3) and three N-inefficient genotypes (C1-C3) of Populus deltoides were cultured under low N stress (5 μM NH4NO3) and normal N supply (750 μM NH4NO3). The dry matter mass, leaf morphology, and chlorophyll content of both genotypes decreased under N starvation. The low nitrogen adaptation coefficients of the leaves and stems biomass of group A were significantly higher than those of group C (p < 0.05). Interestingly, N starvation induced fine root growth in group A, but not in group C. Next, a detailed time-course analysis of enzyme activities and gene expression in leaves identified 2062 specifically differentially expressed genes (DEGs) in group A and 1118 in group C. Moreover, the sensitivity to N starvation of group A was weak, and DEGs related to hormone signal transduction and stimulus response played an important role in the low N response this group. Weighted gene co-expression network analysis identified genes related to membranes, catalytic activity, enzymatic activity, and response to stresses that might be critical for poplar’s adaption to N starvation and these genes participated in the negative regulation of various biological processes. Finally, ten influential hub genes and twelve transcription factors were identified in the response to N starvation. Among them, four hub genes were related to programmed cell death and the defense response, and PodelWRKY18, with high connectivity, was involved in plant signal transduction. The expression of hub genes increased gradually with the extension of low N stress time, and the expression changes in group A were more obvious than those in group C.ConclusionsUnder N starvation, group A showed stronger adaptability and better NUE than group C in terms of morphology and physiology. The discovery of hub genes and transcription factors might provide new information for the analysis of the molecular mechanism of NUE and its improvement in poplar.

A miR169c-NFYA10 module confers tolerance to low-nitrogen stress to Betula luminifera

Betula species constitute a large portion of species in forest ecosystems, are a key player in biomass resources and are recognized as pioneer species with strong stress tolerance. The miR169-NFYA module plays essential roles in the response to abiotic stress, including nutrient stress. However, the functional roles of the miR169-NFYA module in Betula luminifera, an important subtropical and pioneer forestry tree species, in response to nitrogen (N) starvation are not well documented. In the present study, ten BlNFYA genes were identified in B. luminifera. The expression of most BlNFYAs increased under low-nitrogen (LN) stress, while the expression of BlmiR169 was inhibited; among them, BlmiR169c and its corresponding target gene BlNFYA10 might play important regulatory roles in response to N availability. We then functionally investigated BlmiR169c-BlNFYA10 in response to LN stress and determined its regulatory roles in response to N starvation by analyzing the expression patterns, miRNA-mRNA interactions, phenotypes, and physiological and transcriptomic responses of transgenic Arabidopsis and birch roots under LN stress. Overexpression of BlmiR169c and BlNFYA10 resulted in contrasting tolerance to N starvation, and BlNFYA10 provided transgenic plants with LN tolerance with lower growth costs compared with those of the wild type under LN stress. This tolerance might involve a trade-off between growth and defense by upregulating defense- and downregulating photosynthesis- and translation-related activities under LN stress. On the other hand, BlNFYA10 provided transgenic plants with enhanced uptake and assimilation of N, effectively compensating for the defense-growth trade-offs in BlNFYA10-overexpressing plants. Our data demonstrate that a potential regulatory mechanism of BlmiR169c-BlNFYA10 is involved in the LN stress response, providing a basis for increasing the nitrogen-use efficiency (NUE) of B. luminifera and/or other forestry tree species.

Enhancement of root architecture and nitrate transporter gene expression improves plant growth and nitrogen uptake under long-term low-nitrogen stress in barley (Hordeum vulgare L.) seedlings

Over application of nitrogen (N) fertilizers to crops ultimately causes N pollution in the ecosphere. Studying the response of plant growth and N uptake to low-N stress may aid in elucidating the mechanism of low N tolerance in plants and developing crop cultivars with high nitrogen use efficiency (NUE). In this study, a high-NUE mutant line A9-29 and the wild-type barley cultivar Hua30 were subjected to hydroponic culture with high and low N supply, and the dry weight, N accumulation, root morphology, and expression levels of the potential genes involved in nitrate uptake and assimilation were measured at seedling stage. The results showed that under low-N conditions, A9-29 had a higher dry weight, N content, N influx rate and larger root uptake area than did Hua30. Under long-term low-N stress, compared with Hua30, A9-29 demonstrated higher expression of the HvNRT2/3 genes, especially HvNRT2.1, HvNRT2.5, and HvNRT3.3. Similarly, the expression levels of N assimilation genes including HvNIA1, HvNIR1, HvGS1_1, HvGS1_3, and HvGLU2 increased significantly in A9-29. Taken together, our results suggested that the larger root area and the upregulation of nitrate transporter and assimilation genes may contribute to stronger N uptake capacity for plant growth and N accumulation in responding to long-term low-N stress. These findings may aid in understanding the mechanism of low N tolerance and developing barley cultivars with high-NUE.

Rapid Generation and Analysis of a Barley Doubled Haploid Line with Higher Nitrogen Use Efficiency Than Parental Lines by F1 Microspore Embryogenesis.

Creating varieties with high nitrogen use efficiency (NUE) is crucial for sustainable agriculture development. In this study, a superior barley doubled haploid line (named DH45) with improved NUE was produced via F1 microspore embryogenesis with three rounds of screening in different nitrogen levels by hydroponic and field experiments. The molecular mechanisms responsible for the NUE of DH45 surpassing that of its parents were investigated by RNA-seq analysis. A total of 1027 differentially expressed genes (DEGs) were identified that were up- or down-regulated in DH45 under low nitrogen conditions but showed no significant differences in the parents. GO analysis indicated that genes involved in nitrogen compound metabolic processes were significantly enriched in DH45 compared with the parents. KEGG analysis showed the MAPK signaling pathway plant to be highly enriched in DH45 relative to its parents, as well as genes involved in alanine, aspartate and glutamate metabolism, and arginine biosynthesis. In conclusion, our study revealed the potential to fix trait superiority in a line by combining crossing with F1 microspore culture technologies in future crop breeding and also identified several candidate genes that are expressed in shoots and may enable barley to cope with low-nitrogen stress.

Genetic diversity and inter-trait relationship of tropical extra-early maturing quality protein maize inbred lines under low soil nitrogen stress.

Information on the genetic diversity, population structure, and trait associations of germplasm resources is crucial for predicting hybrid performance. The objective of this study was to dissect the genetic diversity and population structure of extra-early yellow and orange quality protein maize (QPM) inbred lines and identify secondary traits for indirect selection for enhanced grain yield under low-soil nitrogen (LN). One hundred and ten inbred lines were assessed under LN (30 kg ha -1) and assayed for tryptophan content. The lines were genotyped using 2500 single nucleotide polymorphism (SNP) markers. Majority (85.4%) of the inbred lines exhibited wide pairwise genetic distances between 0.4801 and 0.600. Genetic distances were wider between yellow and orange endosperm lines and predicted high heterosis in crosses between parents of different endosperm colors. The unweighted pair group method with arithmetic mean (UPGMA) and the admixture model-based population structure method both grouped the lines into five clusters. The clustering was based on endosperm color, pedigree, and selection history but not on LN tolerance or tryptophan content. Genotype by trait biplot analysis revealed association of grain yield with plant height and ear height. TZEEQI 394 and TZEEIORQ 73A had high expressivity for these traits. Indirect selection for high grain yield among the inbred lines could be achieved using plant and ear heights as selection criteria. The wide genetic variability observed in this study suggested that the inbred lines could be important sources of beneficial alleles for LN breeding programs in SSA.

Morphological and physiological plasticity response to low nitrogen stress in black cottonwood (Populus deltoides Marsh.)

It is important to evaluate nitrogen use efficiency and nitrogen tolerance of trees in order to improve their productivity. In this study, both were evaluated for 338 Populus deltoides genotypes from six provenances. The plants were cultured under normal nitrogen (750 μM NH4NO3) and low nitrogen (5 μM NH4NO3) conditions for 3 months. Growth, chlorophyll content and glutamine synthetase activity of each genotype were measured. Under low nitrogen, heights, ground diameter, leaf area, leaf and root biomass, and chlorophyll contents were significantly lower than those under normal nitrogen level. Correlation analysis showed that nutrient distribution changed under different nitrogen treatments. There was a negative correlation between leaf traits and root biomass under normal nitrogen level, however, the correlation became positive in low nitrogen treatment. Moreover, with the decrease of nitrogen level, the negative correlation between leaf morphology and chlorophyll levels became weakened. The growth of the genotypes under the two treatments was evaluated by combining principal component analysis with a fuzzy mathematical membership function; the results showed that leaf traits accounted for a large proportion of the variation in the evaluation model. According to the results of comprehensive evaluation of plants under the two treatments, the 338 P. deltoides genotypes could be divided into nine categories, with wide genotypic diversity in nitrogen use efficiency and low nitrogen tolerance. As a result, 26 N-efficient genotypes and 24 N-inefficient genotypes were selected. By comparative analysis of their morphological and physiological traits under the two treatments, leaf traits could be significant indicators for nitrogen use efficiency and nitrogen tolerance, which is of considerable significance for breeding poplar varieties with high nitrogen use efficiencies.

Screening the rate-limiting genes in the ω6 polyunsaturated fatty acid biosynthesis pathway in Nannochloropsis oceanica

The enrichment of polyunsaturated fatty acids has made Nannochloropsis sp. a promising candidate for the production of polyunsaturated fatty acids. Although most of the genes involved in polyunsaturated fatty acid biosynthesis have been cloned, the regulatory mechanism at the molecular level has not been elucidated. To target the rate-limiting genes in the ω6 polyunsaturated fatty acid biosynthesis pathway in Nannochloropsis oceanica, we performed the following experiments. The function of the Δ9 fatty acid desaturase gene of N. oceanica was verified in Saccharomyces cerevisiae with a substrate preference for stearic acid. With gas chromatography–mass spectrometry (GC–MS) analysis, the fatty acid profiles in N. oceanica under different stress conditions (high nitrogen, low nitrogen, high temperature, and low temperature) were measured. The results showed that high nitrogen and low temperature stresses played significant roles in promoting polyunsaturated fatty acid biosynthesis. In contrast, low nitrogen and high temperature stresses were beneficial for the accumulation of monounsaturated fatty acids. We further measured the transcriptional abundances of all six genes in the ω6 polyunsaturated fatty acid biosynthesis pathway in N. oceanica and found that the Δ6 fatty acid elongase and the Δ12, Δ5, and Δ17 fatty acid desaturase genes were more sensitive to the stresses set in this study. Pearson correlation analysis showed that the Δ9 fatty acid desaturase was significantly associated with monounsaturated fatty acid biosynthesis, while Δ12, Δ5, and Δ17 fatty acid desaturases were proposed to be the rate-limiting enzymes in polyunsaturated fatty acid biosynthesis. This study helps to thoroughly elucidate the responses of N. oceanica to nitrogen and temperature stresses and optimize cultivation for high yield and quality of polyunsaturated fatty acids. More importantly, the selected rate-limiting genes may benefit further genetic engineering in N. oceanica.

Agro-morphological and metabolomics analysis of low nitrogen stress response in Axonopus compressus.

Axonopus compressus also known as carpet grass is a robust, stoloniferous grass that can grow in minimal fertilization and resists well to abiotic and biotic stresses including low nitrogen (LN) stress. This study aimed at characterizing the agro-morphological and metabolome responses to LN in carpet grass leaves. Under LN stress, carpet grass increased yellowness of leaves and root dry matter while reduced turf quality and shoot dry weight. The metabolome comparison between samples from optimum and LN conditions indicated 304 differentially accumulated metabolites (DAMs), which could be classified into 12 major and 31 subclasses. The results revealed that the leaf tissues accumulated more anthocyanins and other flavonoid metabolites under LN stress. Conversely, amino acids, nucleic acids and their derivatives were reduced in response to LN stress. The overall evaluation of individual metabolites and pathways, and previous studies on metabolomes indicated that carpet grass reduced its energy consumption in leaves and increased the level of organic acid metabolism and secondary metabolism in order to resist LN stress conditions.

QTL Mapping and Favorable Allele Mining of Nitrogen Deficiency Tolerance Using an Interconnected Breeding Population in Rice.

Nitrogen is one of the most important nutrients for rice growth and development. Breeding of nitrogen deficiency tolerance (NDT) variety is considered to be the most economic measure to solve the constrain of low nitrogen stress on grain yield in rice. An interconnected breeding (IB) population of 497 lines developed using Huanghuazhan (HHZ) as the recurrent parent and eight elite lines as the donor parents were tested for five traits including grain yield, biomass, harvest index, thousand grain weight, and spikelet fertility under two nitrogen treatments in three growing seasons. Association analysis using 7,388 bins generated by sequencing identified a total of 14, 14, and 12 QTLs for the five traits under low nitrogen (LN), normal nitrogen (NN), and LN/NN conditions, respectively, across three seasons. Favorable alleles were dissected for the 40 QTLs at the 10 NDT regions, and OM1723 was considered as the most important parent with the highest frequency of favorable alleles contributing to NDT-related traits. Six superior lines all showed significantly higher GY in LN environments and similar GY under NN environments except for H10. Substitution mapping using near-isogenic introgression lines delimited the qTGW2-1, which was identified on chromosome 2 under LN, NN, and LN/NN conditions into two QTLs, which were located in the two regions of about 200 and 350 kb with different favorable alleles. The bins 16, 1301, 1465, 1486, 3464, and 6249 harbored the QTLs for NDT detected in this study, and the QTLs/genes previously identified for NDT or nitrogen use efficiency (NUE) could be used for enhancing NDT and NUE by marker-assisted selection (MAS).

Metabolomics insights into the mechanism by which Epichloë gansuensis endophyte increased Achnatherum inebrians tolerance to low nitrogen stress

Epichloe gansuensis increases the tolerance of host plants to abiotic stress. However, little is known about the mechanism by which E. gansuensis improves grass growth under low nitrogen availability stress. Achnatherum inebrians with E. gansuensis (E+) and without E. gansuensis (E-) were treated with modified 1/2 Hoagland containing 0.01 mM (low N) or 7.5 mM N (normal level) for 18 weeks. After 18 weeks of treatment with N, the dry weight of E+ and E- plants were measured, and the metabolomics analysis of leaves and roots grown under two different N concentrations was conducted with GS-MS to determine differential metabolites and metabolic pathways. E+ A. inebrians had higher dry weight of leaves and roots compared to the E- A. inebrians under low N stress. E. gansuensis increased the tolerance of A. inebrians to low N stress by its capability to increase the content of organic acids (salicylic acid and 3-hydroxypropionic acid) and glucose-6-phosphate in leaves, and E. gansuensis increased the content of fatty acids (linolenic acid and oleic acid) and amino acids (glycine and 4-aminobutyric acid) in roots under low N stress. Finally, E. gansuensis reprogramed the metabolic pathway of amino acids of host grasses to adapt to the different N concentration. Our results reveal the chemical mechanism by which E. gansuensis enhances the tolerance of host grasses to low N, and provide the theoretical basis for utilizing E. gansuensis, improving of grasses and crops, and for developing new germplasm for low-N tolerant grasses.

Transcriptome sequencing of wild soybean revealed gene expression dynamics under low nitrogen stress.

Nitrogen is one of the essential elements for plant growth. Wild soybeans (Glycine soja) have strong abilities to survive in harsh and barren environments, and hence become ideal plant model for studying plant adaptability to low nitrogen (LN) conditions. In this study, we analyzed and compared the transcriptomes of wild soybean subjected to LN treatments. We totally identified 1095 (681 up and 414 down) and 5490 (2998 up and 2492 down) differentially expressed genes (DEGs) in the aerial parts (leaf and stem, LS) and roots, respectively. Gene ontology classification analysis revealed that the categories related to LN stress (including oxidation reduction, transcriptional regulation, membrane, and protein phosphorylation) were highly enriched among DEGs. In addition, a total of 784 transcription factor (TF) and 84 transporter protein (TP) genes were determined in LS DEGs, of which some TF genes (NAC1, NAC35, ZFP1, CIM1, and WRKY25) and TP genes like NRT2.5 (nitrate transporter) and ABCC12 (ABC transporter) were widely upregulated under LN stress. Nevertheless, a total of 3859 TF and 370 TP genes were identified in root DEGs, of which some TF genes (NAC6, NAC14, MYB29, MYB92, bZIP62, bZIP72, WRKY60, WRKY58) and TP genes like NRT2.4 and HAK5 (potassium transporter) were upregulated under LN stress. These findings suggest that the identified DEGs may play vital roles in plant responses to LN stress, providing important genetic resources for further functional dissection of plant molecular mechanisms to LN stress.

Glucose-6-Phosphate Dehydrogenase Is Involved in the Tolerance of Soybean Seedlings to Low Nitrogen Stress

Nitrogen (N) deficiency affects plant growth and crop yield. In this study, we investigated the role of glucose-6-phosphate dehydrogenase (G6PDH) in response to N availability in three soybean cultivars, JINDOU 19 (JD19), LONGHUANG 3 (LH3), and LONGDOU 2 (LD2), that have different tolerances to low-N stress. The results showed that the leaf area and primary root length of JD19 and LH3 were greater than that of LD2 under low-N stress, suggesting that the growth of JD19 and LH3 were impaired less than LD2, and thus are more tolerant to low-N stress than LD2 is. Interestingly, the G6PDH expression showed different degrees of change in these soybean cultivars under low-N conditions, and the G6PDH activity in JD19 and LH3 was higher than that in LD2. When G6PDH was inhibited by glucosamine (GlcN), the contents of malondialdehyde (MDA) and H2O2 were dramatically increased under low-N stress. Meanwhile, the activities of N metabolism-related enzymes were inhibited. These results indicate that G6PDH is involved in the tolerance of soybean cultivars to low-N stress through affecting the N metabolism. Furthermore, under low-N conditions, the contents of NADP+ and reduced glutathione (GSH) in JD19 and LH3 were increased more than that in LD2. In contrast, the activity of the plasma membrane (PM), NADPH oxidase, and the NADPH content in JD19 and LH3 were lower than that in LD2. In conclusion, G6PDH reduces the accumulation of ROS in plant cells by modulating NADPH/NADP+ and GSH levels to maintain the growth of soybeans under low-N conditions.

Nitrate dose-responsive transcriptome analysis identifies transcription factors and small secreted peptides involved in nitrogen response in Tartary buckwheat

Tartary buckwheat (Fagopyrum tataricum Gaertn.) is an economically important pseudocereal crop, which can adapt well to extreme environments, including low nitrogen (LN) stress. However, little is known regarding the associated molecular mechanisms. In this study, the molecular mechanism of Tartary buckwheat roots in response to different doses of nitrate was investigated by combining physiological changes with transcriptional regulatory network. LN improved elongation and branching of lateral roots, indicating that the plasticity of lateral roots drives the adaption of Tartary buckwheat under LN condition. The roots of the seedlings that were cultivated under four N conditions were selected for RNA-Seq analysis. In total 1686 nitrate dose-responsive genes were identified. Of these genes, 16 genes encoding N transporters showed response to N availability, and they may play important roles in N transport and root system architecture in Tartary buckwheat roots. 108 transcription factors (TFs) showed dose-response to N availability, and they may regulate N response and root growth under varied N conditions by modulating the expression of N transporters. A NIN-like protein, FtNLP7, was identified and it may contribute to the transcriptional regulation of N transporters. Furthermore, 81 N-responsive genes were identified as the small secreted peptides (SSPs). 48 N-responsive SSPs were annotated as hypothetical proteins and they may be the species-specific proteins of Tartary buckwheat. This paper provides useful information for further investigation of the mechanisms underlying the adaptation of Tartary buckwheat under N-deficient condition.

Transcriptomic and genome-wide association study reveal long noncoding RNAs responding to nitrogen deficiency in maize

BackgroundLong noncoding RNAs (lncRNAs) play important roles in essential biological processes. However, our understanding of lncRNAs as competing endogenous RNAs (ceRNAs) and their responses to nitrogen stress is still limited.ResultsHere, we surveyed the lncRNAs and miRNAs in maize inbred line P178 leaves and roots at the seedling stage under high-nitrogen (HN) and low-nitrogen (LN) conditions using lncRNA-Seq and small RNA-Seq. A total of 894 differentially expressed lncRNAs and 38 different miRNAs were identified. Co-expression analysis found that two lncRNAs and four lncRNA-targets could competitively combine with ZmmiR159 and ZmmiR164, respectively. To dissect the genetic regulatory by which lncRNAs might enable adaptation to limited nitrogen availability, an association mapping panel containing a high-density single–nucleotide polymorphism (SNP) array (56,110 SNPs) combined with variable LN tolerant-related phenotypes obtained from hydroponics was used for a genome-wide association study (GWAS). By combining GWAS and RNA-Seq, 170 differently expressed lncRNAs within the range of significant markers were screened. Moreover, 40 consistently LN-responsive genes including those involved in glutamine biosynthesis and nitrogen acquisition in root were identified. Transient expression assays in Nicotiana benthamiana demonstrated that LNC_002923 could inhabit ZmmiR159-guided cleavage of Zm00001d015521.ConclusionsThese lncRNAs containing trait-associated significant SNPs could consider to be related to root development and nutrient utilization. Taken together, the results of our study can provide new insights into the potential regulatory roles of lncRNAs in response to LN stress, and give valuable information for further screening of candidates as well as the improvement of maize resistance to LN stress.

Sorghum rhizosphere effects reduced soil bacterial diversity by recruiting specific bacterial species under low nitrogen stress

Rhizosphere microbiota play a pivotal role in promoting plant growth and defending against pathogens, but their responses to abiotic environmental stress remain largely elusive. Here, we investigated the influences of low-N stress on rhizosphere bacteria of six sorghum cultivars in a glasshouse experiment. The alpha diversity of bacteria (as revealed by Shannon diversity and Chao1 richness indices) was remarkably lower in rhizosphere soils than in bulk soils, and was significantly higher under low-N stress than under N addition. Principal coordinates analysis revealed that the bacterial community compositions in rhizosphere soils were clearly separated from bulk soils, and the rhizosphere soils under low-N stress or with N fertilization were clearly separated, indicating that both rhizosphere effects and N fertilization impacted the rhizosphere bacterial community. Notably, the relative abundances of beneficial bacteria such as Bacillaceae and Streptomycetaceae significantly increased in rhizosphere soils under low-N stress, which had significantly positive correlations with the sorghum N uptake. The relative abundance of Nitrosomonadaceae in rhizosphere soils was significantly lower than that in bulk soils, while the relative abundance of Rhizobiaceae showed an opposite pattern. Taken together, our results suggested that sorghum rhizosphere effects can reduce soil bacterial diversity possibly through recruiting specific bacterial species under low N stress.

Identification, Structural and Expression Analyses of &lt;i&gt;SPX&lt;/i&gt; Genes in Giant Duckweed ( &lt;i&gt;Spirodela Polyrhiza&lt;/i&gt;) Reveals its Role in Response to Low Phosphorus and Nitrogen Stresses

Identification, Structural and Expression Analyses of &lt;i&gt;SPX&lt;/i&gt; Genes in Giant Duckweed ( &lt;i&gt;Spirodela Polyrhiza&lt;/i&gt;) Reveals its Role in Response to Low Phosphorus and Nitrogen Stresses