Improve Crop Nitrogen Use Research Articles

Is auxin the key to improve crop nitrogen use efficiency for greener agriculture?

Strengthening future food security through the application of unsustainable levels of inorganic nitrogen (N) fertilizers to crop fields may exacerbate environmental damage. Coordination of N-use efficiency (NUE) and plant growth is, therefore, crucial for sustainable agriculture. Auxin plays pivotal roles in developmental and signaling responses that affect NUE. Hence, a better understanding of these processes provides great potential to improve crop NUE. This review summarizes the effects of auxin on N-related and root developmental processes that either directly or indirectly affect NUE in the model plant Arabidopsis and major crop species to highlight the potential of fostering sustainable agricultural development in the future through modulating auxin-related processes.

The NIN-LIKE PROTINE1 (CsNLP1) transcription factor is involved in modulating the nitrate response in cucumber seedlings

Cucumber is one of the important vegetables cultivated in facilities in China. Due to the deterioration of soil quality in facilities and the low nitrogen use efficiency of existing varieties, it is common to pursue high yield through excessive application of nitrogen fertilizer. Improving crop nitrogen use efficiency is one of the important means to reduce nitrogen fertilizer input. Previous studies have shown that NLP (NIN-like protein) transcription factor family play an important role as transcription factors in regulating plant physiological responses to external nitrogen changes. However, there are few reports on NLPs in cucumber. Here we report that CsNLP1 is a potential candidate to improve cucumber nitrogen use ability. CsNLP1 silencing lines by virus-induced gene silencing (VIGS) showed a significant decrease in the plant biomass, chlorophyll content, nitrogen uptake, total nitrogen content, activities of NR, NIR, GDH, GOGAT and GS, and expression levels of genes involved in nitrogen assimilation and signalling under different nitrogen concentrations. In addition, transfer of CsNLP1 into Arabidopsis nlp7-1 mutant found that the phenotype, nitrate (NO3-) content, NR activity, NIR activity, GDH activity, GOGAT activity and GS activity in transgenic lines could be restored to the wild type level after NO3- treatment. Further study found that CsNLP1 could regulate the expression of NO3- responsive genes such as AtNIR1, AtNIA2, AtNRT1.1 and AtGS2 in plants. Overall, our data indicated that CsNLP1 can affect plant growth, and regulate nitrate assimilation by regulating nitrogen-related genes.

Gene Expression, Enzyme Activity, Nitrogen Use Efficiency, and Yield of Rice Affected by Controlled-Release Nitrogen.

Controlled- or slow-release urea can improve crop nitrogen use efficiencies and yields in many agricultural production systems. The effect of controlled-release urea on the relationships between levels of gene expression and yields has not been adequately researched. We conducted a 2 year field study with direct-seeded rice, which included treatments of controlled-release urea at four rates (120, 180, 240, and 360 kg N ha-1), a standard urea treatment (360 kg N ha-1), and a control treatment without applied nitrogen. Controlled-release urea improved the inorganic nitrogen concentrations of root-zone soil and water, functional enzyme activities, protein contents, grain yields, and nitrogen use efficiencies. Controlled-release urea also improved the gene expressions of nitrate reductase [NAD(P)H] (EC 1.7.1.2), glutamine synthetase (EC 6.3.1.2), and glutamate synthase (EC 1.4.1.14). With the exception of glutamate synthase activity, there were significant correlations among these indices. The results showed that controlled-release urea improved the content of inorganic nitrogen within the rice root zone. Compared with urea, the average enzyme activity of controlled-release urea increased by 50-200%, and the relative gene expression was increased by 3-4 times on average. The added soil nitrogen increased the level of gene expression, allowing enhanced synthesis of enzymes and proteins for nitrogen absorption and use. Hence, controlled-release urea improved the nitrogen use efficiency and the grain yield of rice. Controlled-release urea is an ideal nitrogen fertilizer showing great potential for improving rice production.

Overexpression of MYB-like transcription factor SiMYB30 from foxtail millet (Setaria italica L.) confers tolerance to low nitrogen stress in transgenic rice

Nitrogen fertilizers significantly increase crop yield; however, the negative impact of excessive nitrogen use on the environment and soil requires urgent attention. Improving crop nitrogen use efficiency (NUE) is crucial to increase yields and protect the environment. Foxtail millet (Setaria italica L.), a gramineous crop with significant tolerance to barren croplands, is an ideal model crop for studying abiotic stress resistance in gramineous crops. However, knowledge of the regulatory network for NUE in foxtail millet is fragmentary. Herein, we identified an R2R3-like MYB transcription factor in foxtail millet, SiMYB30, which belongs to MYB subfamily 17. The expression of SiMYB30 is responsive to low nitrogen (LN) concentration. Compared with wildtype Kitaake, seedlings of rice lines overexpressing SiMYB30 showed significantly increased shoot fresh and dry weights, plant height, and root area under LN treatment indoors. Consistently, overexpression of SiMYB30 in field experiments significantly increased grain and stem nitrogen contents, grain yield per plant, and stem weight in rice. Furthermore, qRT-PCR revealed that SiMYB30 effectively activated the expression of nitrogen uptake-related genes—OsNRT1, OsNRT1.1B, and OsNPF2.4—and nitrogen assimilation-related genes—OsGOGAT1, OsGOGAT2, and OsNIA2. Notably, SiMYB30 directly bound to the promoter of OsGOGAT2 and regulated its expression. These results highlight the novel and pivotal role of SiMYB30 in improving crop NUE.

A revised view on the evolution of glutamine synthetase isoenzymes in plants.

SUMMARYGlutamine synthetase (GS) is a key enzyme responsible for the incorporation of inorganic nitrogen in the form of ammonium into the amino acid glutamine. In plants, two groups of functional GS enzymes are found: eubacterial GSIIb (GLN2) and eukaryotic GSIIe (GLN1/GS). Only GLN1/GS genes are found in vascular plants, which suggests that they are involved in the final adaptation of plants to terrestrial life. The present phylogenetic study reclassifies the different GS genes of seed plants into three clusters: GS1a, GS1b and GS2. The presence of genes encoding GS2 has been expanded to Cycadopsida gymnosperms, which suggests the origin of this gene in a common ancestor of Cycadopsida, Ginkgoopsida and angiosperms. GS1a genes have been identified in all gymnosperms, basal angiosperms and some Magnoliidae species. Previous studies in conifers and the gene expression profiles obtained in ginkgo and magnolia in the present work could explain the absence of GS1a in more recent angiosperm species (e.g. monocots and eudicots) as a result of the redundant roles of GS1a and GS2 in photosynthetic cells. Altogether, the results provide a better understanding of the evolution of plant GS isoenzymes and their physiological roles, which is valuable for improving crop nitrogen use efficiency and productivity. This new view of GS evolution in plants, including a new cytosolic GS group (GS1a), has important functional implications in the context of plant metabolism adaptation to global changes.

Contrasting effects of straw and straw-derived biochar applications on soil carbon accumulation and nitrogen use efficiency in double-rice cropping systems

Increasing cropland soil carbon (C) sequestration and improving crop nitrogen use efficiency (NUE) are vital for sustainable agriculture and environmental protection. The incorporation of straw and application of straw-derived biochar to croplands may help to achieve these goals; however, the long-term effects on soil C sequestration and NUE in double-rice cropping systems are poorly understood. Here, a 6-y field experiment was conducted in a double-rice cropping system to investigate the variations in soil C sequestration and NUE with straw and straw-derived biochar amendments. The treatments were as follows: control with zero nitrogen (N0); conventional chemical fertilizer application (NPK); NPK plus 3 t rice straw dry matter (DM) incorporated per ha−1 season−1 (NPK + LS); NPK plus 6 t rice straw DM incorporated per ha−1 season−1 (NPK + HS); NPK plus 24 t straw-derived biochar DM incorporated per ha−1 (NPK + LC) applied once; and NPK plus 48 t straw-derived biochar DM incorporated per ha−1 (NPK + HC) applied once. Both the straw and biochar additions increased the soil C content in the topsoil, and the NPK + LC treatment sequestered 2.6-fold more soil C than the NPK + HS treatment over the 6-y period, when the input amounts of straw as well as the straw derived C were similar for both treatments. Besides input C directly into the fields, biochar application also increased soil original organic C accumulation in the NPK + LC treatment. Compared with NPK, 50 % and 100 % straw incorporation to the field increased the mean NUE by 22.3 % and 39.8 %, respectively, in the late rice season of 4–6 y, mainly due to increasing soil organic C. Rice grain yields decreased in the early rice season for the first 3 y of the straw treatments but increased in the first season when the biochar was applied, when compared with NPK. However, in the second 3 y after straw application, the grain yield of NPK + HS was significantly higher than that of NPK in late rice season. This investigation has indicated that biochar application had a higher potential in soil carbon sequestration than straw incorporation, and long-term (> 3 y) straw incorporation favored for the enhancement of NUE in paddy fields.

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.

Rice NIN-LIKE PROTEIN 1 rapidly responds to nitrogen deficiency and improves yield and nitrogen use efficiency.

Nitrogen (N) is indispensable for crop growth and yield, but excessive agricultural application of nitrogenous fertilizers has generated severe environmental problems. A desirable and economical solution to cope with these issues is to improve crop nitrogen use efficiency (NUE). Plant NUE has been a focal point of intensive research worldwide, yet much still has to be learned about its genetic determinants and regulation. Here, we show that rice (Oryza sativa L.) NIN-LIKE PROTEIN 1 (OsNLP1) plays a fundamental role in N utilization. OsNLP1 protein localizes in the nucleus and its transcript level is rapidly induced by N starvation. Overexpression of OsNLP1 improves plant growth, grain yield, and NUE under different N conditions, while knockout of OsNLP1 impairs grain yield and NUE under N-limiting conditions. OsNLP1 regulates nitrate and ammonium utilization by cooperatively orchestrating multiple N uptake and assimilation genes. Chromatin immunoprecipitation and yeast one-hybrid assays showed that OsNLP1 can directly bind to the promoter of these genes to activate their expression. Therefore, our results demonstrate that OsNLP1 is a key regulator of N utilization and represents a potential target for improving NUE and yield in rice.

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.

Exploring optimal nitrogen management practices within site-specific ecological and socioeconomic conditions

Abstract The “4R” fertilizer management principles of using the right rate, right source, right timing and right place is emergently required for enhancing crop production and improving crop Nitrogen Use Efficiency (NUE) in intensive small farming system. However, the methodology is still vague to design and implement technologies and management practices (TMPs) following the “4R” principles in these regions. This study designs various TMPs and evaluates their agronomic, environmental, and economic impacts in two typical intensive cereals cropping systems in China to explore how TMPs interact with biophysical conditions, and finally establish methodologies to recommend local optimal TMPs. Among 5 designed TMPs, the optimal TMPs for each site and cropping system were selected, which achieved the sustainable targets for productivity (80% of the achievable yield potential), NUE (0.60), and economic profitability. But several TMPs failed to satisfy the integrated targets, which implied the TMPs must be carefully designed to fit site-specific biophysical contexts. This work provided some basic guidelines for determining each “R”: The “Right rate” can be determined by balancing with crop aboveground N uptake where soil testing is not always available. The “Right timing” must consider the fertilizer products and local climatic features. Split application is not always better than one-time application, e.g., applying urea at 11th-leaf stage decreased spring maize yield by 9% at Lishu due to a 20-day sustained high temperature and drought condition. For the “Right source”, the adoption of enhanced efficiency fertilizers should take soil properties (especially soil pH) into consideration, e.g., urease inhibitors are effective in increasing NUE (by 44%) on alkaline soils, but the efficacy on acid soils is greatly reduced (by 19%). The “Right place” needs to be designed according to characteristics of crop root distribution and fertilizer sources, e.g., surface application of urease inhibitors in winter wheat gained greater NUE (0.62) and grain yield (8.3 Mg ha−1) than deep placement of urea and calcium ammonium nitrate. Considering the biophysical condition variations and its great influence on TMPs, a long-term trial research network to design, test and reshape the site-specific optimal TMPs following “4R” principles will be necessary.

Nitrogen Deficiency Induced Alterations in the Root Proteome of a Pair of Potato (Solanum tuberosum L.) Varieties Contrasting for their Response to Low N.

Improving crop nitrogen use efficiency is important both from the economic and the environmental viewpoint. Here, the aim is to highlight differences between the proteomic response of the roots of two potato cultivars contrasting in their response to nitrogen (N) deficiency, in an effort to understand which proteins and metabolic pathways contribute to the tolerance of N deprivation. The two cultivars ''Topas'' (tolerant) and ''Lambada'' (sensitive) are grown under both an N sufficient and an N deficient regime, using an in vitro-based cultivation system. Responsive proteins are identified and quantified using label-free quantitative shotgun proteomics. The contrasting cultivars differed with respect to components of the glutamine synthetase/glutamine oxoglutarate aminotransferase pathway, tricarboxylic acid cycle, the glycolysis/gluconeogenesis pathway as well as protein and amino acid synthesis machinery. Additional differences are associated with protein catabolism and defense mechanisms.

Cytosolic glutamine synthetase: a target for improvement of crop nitrogen use efficiency?

Overexpression of the cytosolic enzyme glutamine synthetase 1 (GS1) has been investigated in numerous cases with the goal of improving crop nitrogen use efficiency. However, the outcome has generally been inconsistent. Here, we review possible reasons underlying the lack of success and conclude that GS1 activity may be downregulated via a chain of processes elicited by metabolic imbalances and environmental constraints. We suggest that a pivotal role of GS1 may be related to the maintenance of essential nitrogen (N) flows and internal N sensing during critical stages of plant development. A number of more refined overexpression strategies exploiting gene stacking combined with tissue and cell specific targeting to overcome metabolic bottlenecks are considered along with their potential in relation to new N management strategies.