Low Nitrogen Conditions Research Articles

Up-regulated 2-alkenal reductase expression improves low-nitrogen tolerance in maize by alleviating oxidative stress.

In plants, cellular lipid peroxidation is enhanced under low nitrogen (LN) stress; this increases the lipid-derived reactive carbonyl species (RCS) levels. The cellular toxicity of RCS can be reduced by various RCS-scavenging enzymes. However, the roles of these enzymes in alleviating oxidative stress and improving nutrient use efficiency (NUE) under nutrient stress remain unknown. Here, we overexpressed maize endogenous NADPH-dependent 2-alkenal reductase (ZmAER) in maize; it significantly increased the tolerance of transgenic plants (OX-AER) to LN stress. Under LN condition, the biomass, nitrogen accumulation, NUE, and leaf photosynthesis of the OX-AER plants were significantly higher than those of the wild-type (WT) plants. The leaf and root malondialdehyde and H2 O2 levels in the transgenic plants were significantly lower than those in WT. The expression of antioxidant enzyme-related genes ZmCAT3, ZmPOD5 and ZmPOD13 was significantly higher in the transgenic lines than in WT. Under LN stress, the nitrate reductase activity in the OX-AER leaves was significantly increased compared with that in the WT leaves. Furthermore, under LN stress, ZmNRT1.1 and ZmNRT2.5 expression was upregulated in the OX-AER plants compared with that in WT. Overall, up-regulated ZmAER expression could enhance maize's tolerance to LN stress by alleviating oxidative stress and improve NUE.

Manipulating Amino Acid Metabolism to Improve Crop Nitrogen Use Efficiency for a Sustainable Agriculture.

In a context of a growing worldwide food demand coupled to the need to develop a sustainable agriculture, it is crucial to improve crop nitrogen use efficiency (NUE) while reducing field N inputs. Classical genetic approaches based on natural allelic variations existing within crops have led to the discovery of quantitative trait loci controlling NUE under low nitrogen conditions; however, the identification of candidate genes from mapping studies is still challenging. Amino acid metabolism is the cornerstone of plant N management, which involves N uptake, assimilation, and remobilization efficiencies, and it is finely regulated during acclimation to low N conditions and other abiotic stresses. Over the last two decades, biotechnological engineering of amino acid metabolism has led to promising results for the improvement of crop NUE, and more recently under low N conditions. This review summarizes current work carried out in crops and provides perspectives on the identification of new candidate genes and future strategies for crop improvement.

Durum Wheat Grain Yield and Quality under Low and High Nitrogen Conditions: Insights into Natural Variation in Low- and High-Yielding Genotypes.

The availability and management of N are major determinants of crop productivity, but N excessive use has an associated agro-ecosystems environmental impact. The aim of this work was to investigate the influence of N fertilization on yield and grain quality of 6 durum wheat genotypes, selected from 20 genotypes as high- and low-yielding genotypes. Two N levels were applied from anthesis to maturity: high (½ Hoagland nutrient solution) and low (modified ½ Hoagland with one-third of N). Together with the agronomic characterization, grain quality analyses were assessed to characterize carbohydrates concentration, mineral composition, glutenin and gliadin concentrations, polyphenol profile, and anti-radical activity. Nitrogen supply improved wheat grain yield with no effect on thousand-grain weight. Grain soluble sugars and gluten fractions were increased, but starch concentration was reduced, under high N. Mineral composition and polyphenol concentrations were also improved by N application. High-yielding genotypes had higher grain carbohydrates concentrations, while higher concentrations in grain minerals, gluten fractions, and polyphenols were recorded in the low-yielding ones. Decreasing the amount of N to one-third ensured a better N use efficiency but reduced durum wheat agronomic and quality traits.

Evaluation on morpho-physiological characters of synthetic maize genotypes on low soil nitrogen level condition

A study aimed to evaluate the growth and production of several synthetic maize lines at low nitrogen level was conducted at the Indonesian Cereals Research Institute Experimental Farm in Bajeng District, Gowa Regency, South Sulawesi. The research was carried out from September to December 2018. The study also aimed to determine the nitrogen dose that could be used for selection of synthetic maize genotypes against low nitrogen doses. The study was conducted in the form of an experiment using a Split Plot Design. Five levels of Nitrogen fertilizer were used namely 0, 50, 100, 150, and 200 kg N per hectare. Various genotypes treatment were consisted of 4 synthetic maize genotypes namely Syn 5, Syn 6, Syn 7, Syn 8 and 2 comparative varieties namely Bisma and Lamuru. The results show a significant interaction between the treatment of nitrogen doses and the synthetic maize genotype on the morphological and physiological characters of the maize genotypes. Genotypes gave the best results at nitrogen doses of 100 kg N ha−1 was Syn8 (8.67 tons ha−1) and 50 kg N ha−1 (6.47 tons ha−1). Nitrogen doses of 50 kg N ha−1 and 100 kg N ha−1 can be used for the selection of maize tolerant to low nitrogen condition with productivity of 4.57 tons ha−1 and 8.67 tons ha−1, respectively. There is potential for the Syn8 genotype to be developed for low-nitrogen-tolerant maize varieties due to higher production compared to the comparative variety.

Roles of Dhh1 RNA helicase in yeast filamentous growth: Analysis of N-terminal phosphorylation residues and ATPase domains.

In yeast Saccharomyces cerevisiae, the Dhh1 protein, a member of the DEAD-box RNA helicase, stimulates Dcp2/Dcp1-mediated mRNA decapping and functions as a general translation repressor. Dhh1 also positively regulates translation of a selected set of mRNAs, including Ste12, a transcription factor for yeast mating and pseudohyphal growth. Given the diverse functions of Dhh1, we investigated whether the putative phosphorylation sites or the conserved motifs for the DEAD-box RNA helicases were crucial in the regulatory roles of Dhh1 during pseudohyphal growth. Mutations in the ATPase A or B motif (DHH1-K96R or DHH1-D195A) showed significant defects in pseudohyphal colony morphology and agar invasive phenotypes. The N-terminal phospho-mimetic mutation, DHH1-T16E, showed defects in pseudohyphal phenotypes. Decreased levels of Ste12 protein were also observed in these pseudohyphal-defective mutant cells under filamentous-inducing low nitrogen conditions. We suggest that the ATPase motifs and the Thr16 phosphorylation site of Dhh1 are crucial to its regulatory roles in pseudohyphal growth under low nitrogen conditions.

Exogenous GABA promotes adaptation and growth by altering the carbon and nitrogen metabolic flux in poplar seedlings under low nitrogen conditions.

Nitrogen (N) deficiency adversely affects tree growth. Additionally, γ-aminobutyric acid (GABA) is closely associated with growth and stress responses because of its effects on carbon (C) and N metabolism. However, little is known about its roles related to plant adaptations to N-deficient conditions. In this study, we analyzed the effects of GABA (0, 2 and 10mM) applications on the growth traits and physiological responses of poplar (Populus alba×P. glandulosa '84K') seedlings under high N (HN) and low N (LN) conditions. We found that the added GABA interacted with N to affect more than half of the studied parameters, with greater effects in LN plants than in HN plants. Under LN conditions, the GABA application tended to increase poplar growth, accompanied by increased xylem fiber cell length and xylem width. In stems, exogenous GABA increased the abundance of non-structural carbohydrates (starch and sugars) and tricarboxylic acid cycle intermediates (succinate, malate and citrate), but had the opposite effect on the structural C contents (hemicellulose and lignin). Meanwhile, exogenous GABA increased the total soluble protein contents in leaves and stems, accompanied by significant increases in nitrate reductase, nitrite reductase and glutamine synthetase activities in leaves, but significant decreases in those (except for the increased glutamate synthetase activity) in stems. A multiple factorial analysis indicated that the nitrate assimilation pathway substantially influences poplar survival and growth in the presence of GABA under LN conditions. Interestingly, GABA applications also considerably attenuated the LN-induced increase in the activities of leaf antioxidant enzymes, including peroxidase and catalase, implying that GABA may regulate the relative allocation of C and N for growth activities by decreasing the energy cost associated with stress defense. Our results suggest that GABA enhances poplar growth and adaptation by regulating the C and N metabolic flux under N-deficient conditions.

Efficiency of indirect selection for grain yield in maize (Zea mays L.) under low nitrogen conditions through secondary traits under low nitrogen and grain yield under optimum conditions

Small-scale maize farmers in sub-Saharan Africa use meager amounts of nitrogen (N) in their maize crops. N use efficient varieties can provide a solution to the problem of low N conditions through efficient N uptake and utilization. The objectives of this study were to i) compare the quantitative genetic parameters of grain yield and secondary traits under different nitrogen levels and ii) assess the efficiency of indirect selection for grain yield under low N stress through yield under optimum N and secondary traits under low N stress in maize. Doubled haploid lines derived from five bi-parental populations were evaluated. Genotype effect for grain yield and secondary traits was significant at all sites. Genetic variance for grain yield was reduced by 17% under moderate N stress and 63% under severe N stress conditions, while genetic variance for days to anthesis and plant height increased under both moderate and severe low N stress. The heritability of most secondary traits was consistently higher than that of grain yield. Correlations of grain yield with plant and ear heights were positive under low N conditions. Despite the reduction in genetic variances under low N conditions, there was genetic variability for grain yield and secondary traits. Direct selection for grain yield under low N rather than under optimum conditions was more efficient for yield improvement under the low N condition. The use of an index of secondary traits could increase the efficiency of improving grain yield rather than selection for only grain yield under low N conditions.

Role of sucrose in modulating the low-nitrogen-induced accumulation of phenolic compounds in lettuce (Lactuca sativa L.).

Phenolic compounds are phytochemicals present in vegetables which contribute to human health. Although nitrogen deficiency and sucrose (Suc) are linked to phenolic production in vegetables, the relationship between them in the regulation of phenolic biosynthesis remains unknown. This study investigated the potential role of Suc in regulating phenolic biosynthesis of lettuce under low-nitrogen (LN) conditions. Our results showed that LN treatment significantly increased Suc content in lettuce by inducing rapid increases in activities of sucrose synthesis-related enzymes. Exogenous Suc further stimulated LN-induced phenolic accumulation in lettuce by upregulating the expression of genes (PAL, CHS, F3H, DFR, F35H and UFGT) involved in phenolic biosynthesis. The opposite effects were true for exogenous 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) application. No changes were observed in chlorophyll content in LN-treated lettuce, in either the presence or absence of Suc application. Notably, exogenous DCMU resulted in decreases of maximum quantum efficiency of photosystem II (PSII) photochemistry, actual efficiency of PSII and electron transport rate in PSII and increase of quantum yield of non-regulated energy dissipation in PSII in lettuce under LN conditions, whereas these effects were reversed on Suc application. Exogenous Suc also increased glutamine synthetase and glutamate synthase activities in LN-treated lettuce. These results suggest that Suc is involved in LN-induced phenolic production in lettuce by enhancing photosynthetic and nitrogen assimilation efficiency to increase the supply of carbon resources and precursors for phenolic biosynthesis. © 2020 Society of Chemical Industry.

Unravelling the different causes of nitrate and ammonium effects on coral bleaching

Mass coral bleaching represents one of the greatest threats to coral reefs and has mainly been attributed to seawater warming. However, reduced water quality can also interact with warming to increase coral bleaching, but this interaction depends on nutrient ratios and forms. In particular, nitrate (NO3−) enrichment reduces thermal tolerance while ammonium (NH4+) enrichment tends to benefit coral health. The biochemical mechanisms underpinning the different bleaching responses of corals exposed to DIN enrichment still need to be investigated. Here, we demonstrated that the coral Stylophora pistillata underwent a severe oxidative stress condition and reduced aerobic scope when exposed to NO3− enrichment combined with thermal stress. Such condition resulted in increased bleaching intensity compared to a low-nitrogen condition. On the contrary, NH4+ enrichment was able to amend the deleterious effects of thermal stress by favoring the oxidative status and energy metabolism of the coral holobiont. Overall, our results demonstrate that the opposite effects of nitrate and ammonium enrichment on coral bleaching are related to the effects on corals’ energy/redox status. As nitrate loading in coastal waters is predicted to significantly increase in the future due to agriculture and land-based pollution, there is the need for urgent management actions to prevent increases in nitrate levels in seawater. In addition, the maintenance of important fish stocks, which provide corals with recycled nitrogen such as ammonium, should be favoured.

In vitro Anthocyanin Induction and Metabolite Analysis in Malus spectabilis Leaves Under Low Nitrogen Conditions

Absract Anthocyanins are the most widely produced secondary metabolites in plants, and they play an important role in plant growth and reproduction. The nitrogen source is an important factor affecting anthocyanin production, but the nitrogen concentrations on metabolism and the underlying genetic basis remain unclear. In this study, in vitro anthocyanin induction was conducted on Malus spectabilis. The leaf explants were cultivated in media containing different nitrogen concentrations. The results suggested that when the nitrogen contents decreased in limit, the color of leaf explants turned from green to red, and increased anthocyanin accumulation led to a change in phenotype. Furthermore, the content of other flavonoids, such as dihydroquercetin, epicatechin, and catechin, increased under low nitrogen conditions. The transcription levels of the general flavonoid pathway genes, from phenylalanine ammonia lyase (PAL) to anthocyanidin synthase (ANS), were associated with the concentration of corresponding flavonoid compounds and phenotype changes. In particular, the expression level of ANS increased substantially under a low nitrogen treatment, which was significantly and positively correlated with the anthocyanin levels (R2 = 0.72, P

Effects of Nitrogen Supplementation Status on CO2 Biofixation and Biofuel Production of the Promising Microalga Chlorella sp. ABC-001.

The use of microalgal biomass as feedstock for biofuels has been discussed for decades as it provides a sustainable approach to producing fuels for the future. Nonetheless, its feasibility has not been established yet and various aspects of biomass applications such as CO2 biofixation should also be explored. Therefore, in this study, the CO2 biofixation and lipid/carbohydrate production potential of Chlorella sp. ABC-001 were examined under various nitrogen concentrations. The highest biomass productivity and CO2 biofixation rate of 0.422 g/l/d and 0.683 g/l/d, respectively, were achieved under a nitrogen-rich condition (15 mM nitrate). Carbohydrate content was generally proportional to initial nitrate concentration and showed the highest value of 41.5% with 15 mM. However, lipid content showed an inverse relationship with nitrogen supplementation and showed the highest value of 47.4% with 2.5 mM. In consideration as feedstock for biofuels (bioethanol, biodiesel, and biogas), the sum of carbohydrate and lipid contents were examined and the highest value of 79.6% was achieved under low nitrogen condition (2.5 mM). For lipid-based biofuel production, low nitrogen supplementation should be pursued. However, considering the lower feasibility of biodiesel, pursuing CO2 biofixation and the production of carbohydrate-based fuels under nitrogenrich condition might be more rational. Thus, nitrogen status as a cultivation strategy must be optimized according to the objective, and this was confirmed with the promising alga Chlorella sp. ABC-001.

A Decrease in Mesophyll Conductance by Cell-Wall Thickening Contributes to Photosynthetic Downregulation.

It has been argued that accumulation of nonstructural carbohydrates triggers a decrease in Rubisco content, which downregulates photosynthesis. However, a decrease in the sink-source ratio in several plant species leads to a decrease in photosynthesis and increases in both structural and nonstructural carbohydrate content. Here, we tested whether increases in cell-wall materials, rather than starch content, impact directly on photosynthesis by decreasing mesophyll conductance. We measured various morphological, anatomical, and physiological traits in primary leaves of soybean (Glycine max) and French bean (Phaseolus vulgaris) grown under high- or low-nitrogen conditions. We removed other leaves 2 weeks after sowing to decrease the sink-source ratio and conducted measurements 0, 1, and 2 weeks after defoliation.

A novel insight into nitrogen and auxin signaling in lateral root formation in tea plant [Camellia sinensis (L.) O. Kuntze

BackgroundTea plant (Camellia sinensis) is one of the most popular non-alcoholic beverages worldwide. In tea, lateral roots (LRs) are the main organ responsible for the absorption of moisture and mineral nutrients from the soil. Lateral roots formation and development are regulated by the nitrogen and auxin signaling pathways. In order to understand the role of auxin and nitrogen signaling in LRs formation and development, transcriptome analysis was employed to investigate the differentially expressed genes involved in lateral roots of tea plants treated with indole-3-butyric acid (IBA), N-1-naphthylphthalamic acid (NPA), low and high concentrations of nitrogen.ResultsA total of 296 common differentially expressed genes were identified and annotated to four signaling pathways, including nitrogen metabolism, plant hormone signal transduction, glutathione metabolism and transcription factors. RNA-sequencing results revealed that majority of differentially expressed genes play important roles in nitrogen metabolism and hormonal signal transduction. Low nitrogen condition induced the biosynthesis of auxin and accumulation of transcripts, thereby, regulating lateral roots formation. Furthermore, metabolism of cytokinin and ethylene biosynthesis were also involved in lateral roots development. Transcription factors like MYB genes also contributed to lateral roots formation of tea plants through secondary cell wall biosynthesis. Reversed phase ultra performance liquid chromatography (RP-UPLC) results showed that the auxin concentration increased with the decreased nitrogen level in lateral roots. Thus, tea plant lateral roots formation could be induced by low nitrogen concentration via auxin biosynthesis and accumulation.ConclusionThis study provided insights into the mechanisms associated with nitrogen and auxin signaling pathways in LRs formation and provides information on the efficient utilization of nitrogen in tea plant at the genetic level.

Short Communication: Polymorphism of Fumarate Hydratase 1 (FUM1) gene associated with nitrogen uptake in oil palm (Elaeis guineensis)

Abstract. Maryanto SD, Tanjung ZA, Sudania WM, Kusnandar AS, Roberdi, Pujianto, Utomo C, Liwang T. 2020. Short Communication: Polymorphism of Fumarate Hydratase 1 (FUM1) gene associated with nitrogen uptake in oil palm (Elaeis guineensis). Biodiversitas 21: 2462-2466. Nitrogen (N) is an essential element for oil palm vegetative growth and fruit development. Fumarase is known to participate in the tricarboxylic acid (TCA) cycle in the mitochondrial matrix. The FUM gene is required for fumarate accumulation in leaves and necessary to enhance growth under low nitrogen condition. SNPs were obtained in oil palm FUM1 gene based on in silico analysis using local database. The SNP is further verified with Sanger sequencing and qPCR analysis. The genomic DNA of oil palm with high and low efficient to N based on phenotype characters was sequenced using Sanger method. The EgFUM1 gene was located in chromosome 14 and had two SNP positions located in 9.0711 cM and 9.0714 cM. Furthermore, four months oil palm seedlings from three progenies were treated with 30% (N-low) and 100% (control) dosages. Transcription level of EgFUM1 gene was measured using Real-Time Quantitative Polymerase Chain Reaction (RT-qPCR) method. The value of fold changes was significantly up-regulated (6.14-fold) on Progeny 1 (high efficient characters); 1.05-fold on Progeny 2 (medium efficient characters); and 1.08-fold on Progeny 3 (low moderate efficient characters) in the leaf. According the result, there was correlation between SNP and transcription level of EgFUM1 gene. Therefore SNP markers of EgFUM1 gene could be used in oil palm selection with potential N uptake efficiency.

A framework for the computational prediction and analysis of non-coding RNAs in microbial environmental populations and their experimental validation

Small regulatory RNAs and antisense RNAs play important roles in the regulation of gene expression in bacteria but are underexplored, especially in natural populations. While environmentally relevant microbes often are not amenable to genetic manipulation or cannot be cultivated in the laboratory, extensive metagenomic and metatranscriptomic datasets for these organisms might be available. Hence, dedicated workflows for specific analyses are needed to fully benefit from this information. Here, we identified abundant sRNAs from oceanic environmental populations of the ecologically important primary producer Prochlorococcus starting from a metatranscriptomic differential RNA-Seq (mdRNA-Seq) dataset. We tracked their homologs in laboratory isolates, and we provide a framework for their further detailed characterization. Several of the experimentally validated sRNAs responded to ecologically relevant changes in cultivation conditions. The expression of the here newly discovered sRNA Yfr28 was highly stimulated in low-nitrogen conditions. Its predicted top targets include mRNAs encoding cell division proteins, a sigma factor, and several enzymes and transporters, suggesting a pivotal role of Yfr28 in the coordination of primary metabolism and cell division. A cis-encoded antisense RNA was identified as a possible positive regulator of atpF encoding subunit b’ of the ATP synthase complex. The presented workflow will also be useful for other environmentally relevant microorganisms for which experimental validation abilities are frequently limiting although there is wealth of sequence information available.

Overexpression of OsMYB305 in Rice Enhances the Nitrogen Uptake Under Low-Nitrogen Condition.

Excessive nitrogen fertilizer application causes severe environmental degradation and drives up agricultural production costs. Thus, improving crop nitrogen use efficiency (NUE) is essential for the development of sustainable agriculture. Here, we characterized the roles of the MYB transcription factor OsMYB305 in nitrogen uptake and assimilation in rice. OsMYB305 encoded a transcriptional activator and its expression was induced by N deficiency in rice root. Under low-N condition, OsMYB305 overexpression significantly increased the tiller number, shoot dry weight and total N concentration. In the roots of OsMYB305-OE rice lines, the expression of OsNRT2.1, OsNRT2.2, OsNAR2.1, and OsNiR2 was up-regulated and 15NO3– influx was significantly increased. In contrast, the expression of lignocellulose biosynthesis-related genes was repressed so that cellulose content decreased, and soluble sugar concentration increased. Certain intermediates in the glycolytic pathway and the tricarboxylic acid cycle were significantly altered and NADH-GOGAT, Pyr-K, and G6PDH were markedly elevated in the roots of OsMYB305-OE rice lines grown under low-N condition. Our results revealed that OsMYB305 overexpression suppressed cellulose biosynthesis under low-nitrogen condition, thereby freeing up carbohydrate for nitrate uptake and assimilation and enhancing rice growth. OsMYB305 is a potential molecular target for increasing NUE in rice.

A single gene transfer of gibberellin biosynthesis gene cluster increases gibberellin production in a Fusarium fujikuroi strain with gibberellin low producibility

AbstractFusarium fujikuroi, the causative agent of bakanae disease in rice, produces many kinds of secondary metabolites. Recently, two phylogenetic subgroups (F and G groups) of Japanese F. fujikuroi have been identified and found to have differences in their gibberellin (GA) and fumonisin production. G‐group F. fujikuroi produces large amounts of GA, but is a fumonisin nonproducer. F‐group produces large amounts of fumonisin, but is a GA low or nonproducer. We investigated the cause of low GA production in the F‐group. Genetic mapping suggests that low GA production in the F‐group strain Gfc0825009 is due to a GA gene cluster for GA biosynthesis. Analysis of the nucleotide and amino acid sequences of the genes in the GA gene cluster showed >98.4% homology between the F‐group strain Gfc0825009 and the G‐group strain Gfc0801001. Following a 7‐day culture under low nitrogen conditions, we found that expression of P450‐1, P450‐4, and P450‐2 in the cluster increased in the G‐group strain and not in the F‐group strain. We hypothesized that complementation by GA genes in the G‐group strain would be required to increase GA production in the F‐group strain. However, we found that this occurred with a single gene complementation of DES, P450‐1, P450‐4, or P450‐2. Simultaneous increase in the expression of P450‐1, P450‐4, and P450‐2 were detected in the complementary transformants. Moreover, the same phenomenon was observed by reintegration of its own P450‐1. Our results suggest the presence of unknown regulatory mechanisms of the GA gene cluster in F. fujikuroi.

Comparative analysis of nitrogen metabolism-related genes in two inbred maize lines with different low-nitrogen tolerance

Maize is an important crop and its nitrogen use efficiency (NUE) has been an issue for plant scientists and breeders for many years. To meet the demand of genetic diversity in cultivating local elite maize cultivars, researchers need to isolate germplasms with a high NUE. In this study, 30 maize inbred lines were screened under hydroponic conditions, and three inbred lines that tolerate low nitrogen concentration were identified. A comparative analysis of genes involved in N uptake, transport, and assimilation between two lines with different tolerances revealed that the low-nitrogen-tolerant inbred line MBST exhibited higher expressions of nitrate and ammonium transporters, especially ZmNRT3.1B, than less tolerant B73. This suggests that the MBST line had a more efficient high-affinity transporter system. We also showed that low-nitrogen conditions down-regulated the expressions of master genes, ZmNLPs, which were negatively correlated with the expressions of the nitrate transporters ZmNRTs. This indicates the existence of regulators that antagonize the function of ZmNLPs. Some genes related to N assimilation and carbon metabolism were also more expressed in MBST. This research shows that the low-nitrogen-tolerant line, MBST, transported nitrate and ammonium more effectively than the B73 line. The NUE was also higher in MBST than in B73.

Transcription Factor TaDof1 Improves Nitrogen and Carbon Assimilation Under Low-Nitrogen Conditions in Wheat

A single transcription factor is known to coordinate expression of a set of metabolites in a biochemical pathway; its use therefore can be a functional strategy in generating plants with desired traits. Triticum aestivum Dof1 (TaDof1) transcription factor is mainly associated with improved nitrogen assimilation in plants. In the current research, the transgenic wheat overexpressing TaDof1 transcription factor, under a constitutive promoter, was developed by Agrobacterium-mediated transformation. The two elite wheat cultivars (Galaxy and Faisalabad-2008) were selected for transformation study. The T0 plants were subjected to screening using selection medium containing herbicide BASTA. PCR results confirmed that only 8 out of 31 plants possessed the complete TaDof1 cassette. A transformation efficiency of 0.46% for Galaxy and 0.08% for Faisalaad-2008 was obtained. The quantitative RT-PCR was performed on T1 plants grown under nitrogen-limiting conditions. A substantial rise in the expression of citrate synthase (CS), isocitrate dehydrogenase (ICDH), phosphoenolpyruvate carboxylase (PEPC), and pyruvate kinase (PK) genes regulated by TaDof1 was observed after 4 weeks of nitrogen stress in T1 plants. The maximum fold increase of 464 was recorded for ICDH. Our findings indicate a cooperative modification of nitrogen and carbon metabolisms since they are intimately linked together. Overexpression of TaDof1 in wheat resulted in a significant increase in various agronomic traits. Furthermore, various physiological and biochemical markers (chlorophyll, protein, and soluble sugar contents) exhibited a profound change in TaDof1 transgenic plants in comparison with wild type plants. The results clearly depict the merits of employing transcription factors in engineering plant metabolisms.

Identification of Wheat Cultivars for Low Nitrogen Tolerance Using Multivariable Screening Approaches

A set of thirty-six wheat cultivars were grown for two consecutive years under low and high nitrogen conditions. The interactions of cultivars with different environmental factors were shown to be highly significant for most of the studied traits, suggesting the presence of wider genetic variability which may be utilized for the genetic improvement of desired trait(s). Three cultivars, i.e., RAJ 4037, DBW 39 and GW 322, were selected based on three selection indices, i.e., tolerance index (TOL), stress susceptibility index (SSI), and yield stability index (YSI), while two cultivars, HD 2967 and MACS 6478, were selected based on all four selection indices which were common in both of the study years. According to Kendall’s concordance coefficient, the consistency of geometric mean productivity (GMP) was found to be highest (0.778), followed by YSI (0.556), SSI (0.472), and TOL (0.200). Due to the high consistency of GMP followed by YSI and SSI, the three selection indices could be utilized as a selection tool in the identification of high-yielding genotypes under low nitrogen conditions. The GMP and YSI selection indices had a positive and significant correlation with grain yield, whereas TOL and SSI exhibited a significant but negative correlation with grain yield under both high and low nitrogen conditions in both years. The common tolerant genotypes identified through different selection indices could be utilized as potential donors in active breeding programs to incorporate the low nitrogen tolerant genes to develop high-yielding wheat varieties for low nitrogen conditions. The study also helps in understanding the physiological basis of tolerance in high-yielding wheat genotypes under low nitrogen conditions.