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1.
Transport properties and regulatory roles of nitrogen in arbuscular mycorrhizal symbiosis.
Chen, A, Gu, M, Wang, S, Chen, J, Xu, G
Seminars in cell & developmental biology. 2018;:80-88
Abstract
Many terrestrial plants can form root symbiosis with beneficial microorganisms for enhancing uptake of mineral nutrients or increasing fitness to adverse environmental challenges. Arbuscular mycorrhizal (AM) symbiosis that is formed by AM fungi and the roots of vascular flowering plants is the most widespread mutualistic associations in nature. As a typical endosymbiosis, AM interactions involves the differentiation of both symbionts to create novel symbiotic interfaces within the root cells, and requires a continuous nutrient exchange between the two partners. AM plants have two pathways for nutrient uptake, either direct uptake via the root hairs and root epidermis at the plant-soil interface, or indirectly through the AM fungal hyphae at the plant-fungus interface. Over the last few years, great progress has been made in deciphering the mechanisms underlying the AM-mediated modulation of nutrient uptake processes, and an increasing number of plant and fungal genes responsible for transporting nutrients from the soil or across the intraradical symbiotic interfaces have been identified and functionally characterized. Here, we summarize the recent advances in the nitrogen uptake, assimilation and translocation in the AM symbiosis, and also explore the current understanding of how the N status and interplay with C and P in modulating the development of AM associations.
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2.
Differences in resistance to nitrogen and phosphorus deficiencies explain male-biased populations of poplar in nutrient-deficient habitats.
Song, H, Lei, Y, Zhang, S
Journal of proteomics. 2018;:123-127
Abstract
UNLABELLED In most forest soils, the availability of nitrogen (N) and phosphorus (P) nutrients is low and unable to meet the requirement of tree growth. In the past decades, sex-based differences in poplar have been investigated in morphology and physiology. Proteomic techniques provide new insights into sex-specific differences at the molecular level. This review gives a comparative overview of the effects of N and P deficiencies on poplar physiological and proteomic characteristics. Male poplars are more efficient at photosynthesis and nutrient usage than females. Proteins related to carbohydrate metabolism, defence responses and transcription and translation processes are changed to adapt diversely in males and females. These results provide evidence that male poplar have better resistance to nutrient-limiting conditions than females, which may be reasonable for the male-biased sex ratio in nutrient-deficient habitats. Furthermore, this review also discusses the potential growth-defence trade-offs in male and female poplar coping with nutrient limitations. BIOLOGICAL SIGNIFICANCE In the past decades, the physiological and molecular responses of individual trees exposed to nutrient deficiency have been well studied. An important model woody plant, Populus, is dioecious and shows a male-biased sex ratio in nutrient-deficient habitats. Individually, different responses to nutrient limitation between the sexes determine the bias of population sex ratios. Proteomic techniques provide new insights into sex-based differences in the molecular mechanisms underlying nutrient deficiency. This review gives a comparative overview of the identification of nitrogen and phosphorus deficiency effects on physiological and proteomic characteristics. Male poplars are more resistant and have a smaller range of protein changes than females in response to N and P deficiency, which explains the observed male-biased sex ratios to a certain extent. Furthermore, this review also discusses the possible growth-defense trade-offs in male and female poplars coping with nutrient deficiency.
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3.
Roles of nitrogen and cytokinin signals in root and shoot communications in maximizing of plant productivity and their agronomic applications.
Gu, J, Li, Z, Mao, Y, Struik, PC, Zhang, H, Liu, L, Wang, Z, Yang, J
Plant science : an international journal of experimental plant biology. 2018;:320-331
Abstract
Nitrogen is an essential, often limiting, factor in plant growth and development. To regulate growth under limited nitrogen supply, plants sense the internal and external nitrogen status, and coordinate various metabolic processes and developmental programs accordingly. This coordination requires the transmission of various signaling molecules that move across the entire plant. Cytokinins, phytohormones derived from adenine and synthesized in various parts of the plant, are considered major local and long-distance messengers. Cytokinin metabolism and signaling are closely associated with nitrogen availability. They are systemically transported via the vasculature from plant roots to shoots, and vice versa, thereby coordinating shoot and root development. Tight linkage exists between the nitrogen signaling network and cytokinins during diverse developmental and physiological processes. However, the cytokinin-nitrogen interactions and the communication systems involved in sensing rhizospheric nitrogen status and in regulating canopy development remain obscure. We review current knowledge on cytokinin biosynthesis, transport and signaling, nitrogen acquisition, metabolism and signaling, and their interactive roles in regulating root-shoot morphological and physiological characteristics. We also discuss the role of spatio-temporal regulation of cytokinins in enhancing beneficial crop traits of yield and nitrogen use efficiency.
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4.
Different adaptive strategies in E. coli populations evolving under macronutrient limitation and metal ion limitation.
Warsi, OM, Andersson, DI, Dykhuizen, DE
BMC evolutionary biology. 2018;(1):72
Abstract
BACKGROUND Adaptive responses to nutrient limitation involve mutations that increase the efficiency of usage or uptake of the limiting nutrient. However, starvation of different nutrients has contrasting effects on physiology, resulting in different evolutionary responses. Most studies performed to understand these evolutionary responses have focused only on macronutrient limitation. Hence our understanding of adaptation under limitation of other forms of nutrients is limited. In this study, we compared the evolutionary response in populations evolving under growth-limiting conditions for a macronutrient and a major cation. RESULTS We evolved eight populations of E. coli in nutrient-limited chemostats for 400 generations to identify the genetic basis of the mechanisms involved in efficient usage of two nutrients: nitrogen and magnesium. Our population genomic sequencing work, based on this study and previous work, allowed us to identify targets of selection under these nutrient limiting conditions. Global transcriptional regulators glnGL were targets of selection under nitrogen starvation, while proteins involved in outer-membrane biogenesis (genes from the lpt operon) were targets of selection under magnesium starvation. The protein involved in cell-cycle arrest (yhaV) was a target of selection in both environments. We re-constructed specific mutants to analyze the effect of individual mutations on fitness in nutrient limiting conditions in chemostats and in batch cultures. We further demonstrated that adaptation to nitrogen starvation proceeds via a nutrient specific mechanism, while that to magnesium starvation involves a more general mechanism. CONCLUSIONS Our results show two different forms of adaptive strategies under limitation of nutrients that effect cellular physiology in different ways. Adaptation to nitrogen starvation proceeds by upregulation of transcriptional regulator glnG and subsequently of transporter protein amtB, both of which results in increased nitrogen scavenging ability of the cell. On the other hand, adaptation to magnesium starvation proceeds via the restructuring of the cell outer-membrane, allowing magnesium to be redistributed to other biological processes. Also, adaptation to the chemostat environment involves selection for loss of function mutations in genes that under nutrient-limiting conditions interfere with continuous growth.
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5.
Crops, Nitrogen, Water: Are Legumes Friend, Foe, or Misunderstood Ally?
Adams, MA, Buchmann, N, Sprent, J, Buckley, TN, Turnbull, TL
Trends in plant science. 2018;(6):539-550
Abstract
Biological nitrogen fixation (BNF) by crop legumes reduces demand for industrial nitrogen fixation (INF). Nonetheless, rates of BNF in agriculture remain low, with strong negative feedback to BNF from reactive soil nitrogen (N) and drought. We show that breeding for yield has resulted in strong relationships between photosynthesis and leaf N in non-leguminous crops, whereas grain legumes show strong relations between leaf N and water use efficiency (WUE). We contrast these understandings with other studies that draw attention to the water costs of grain legume crops, and their potential for polluting the biosphere with N. We propose that breeding grain legumes for reduced stomatal conductance can increase WUE without compromising production or BNF. Legume crops remain a better bet than relying on INF.
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6.
Isotopic evidence of biotrophy and unusual nitrogen nutrition in soil-dwelling Hygrophoraceae.
Halbwachs, H, Easton, GL, Bol, R, Hobbie, EA, Garnett, MH, Peršoh, D, Dixon, L, Ostle, N, Karasch, P, Griffith, GW
Environmental microbiology. 2018;(10):3573-3588
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Abstract
Several lines of evidence suggest that the agaricoid, non-ectomycorrhizal members of the family Hygrophoraceae (waxcaps) are biotrophic with unusual nitrogen nutrition. However, methods for the axenic culture and lab-based study of these organisms remain to be developed, so our current knowledge is limited to field-based investigations. Addition of nitrogen, lime or organophosphate pesticide at an experimental field site (Sourhope) suppressed fruiting of waxcap basidiocarps. Furthermore, stable isotope natural abundance in basidiocarps were unusually high in 15 N and low in 13 C, the latter consistent with mycorrhizal nutritional status. Similar patterns were found in waxcap basidiocarps from diverse habitats across four continents. Additional data from 14 C analysis of basidiocarps and 13 C pulse label experiments suggest that these fungi are not saprotrophs but rather biotrophic endophytes and possibly mycorrhizal. The consistently high but variable δ15 N values (10-20‰) of basidiocarps further indicate that N acquisition or processing differ from other fungi; we suggest that N may be derived from acquisition of N via soil fauna high in the food chain.
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7.
Potential of vegetation indices combined with laser-induced fluorescence parameters for monitoring leaf nitrogen content in paddy rice.
Yang, J, Du, L, Gong, W, Shi, S, Sun, J, Chen, B
PloS one. 2018;(1):e0191068
Abstract
Nitrogen (N) is important for the growth of crops. Leaf nitrogen content (LNC) serves as a crucial indicator of the growth status of crops and can help determine the dose of N fertilizer. Laser-induced fluorescence (LIF) technology and the reflectance spectra of crops are widely used to detect the biochemical content of leaves. Many vegetation indices (VIs) and fluorescence parameters have been developed to estimate LNC. However, the comparison among VIs and between fluorescence parameters and VIs has been rarely studied in the estimation of LNC. In this study, the performances of several published empirical VIs and fluorescence parameters for the estimation of paddy rice LNC were analyzed using the support vector machine (SVM) algorithm. Then, the optimal VIs (TVI, MTVI1, MTVI2, and MSAVI) and fluorescence parameters (F735/F460 and F685/F460), which were suitable for LNC monitoring in this study, were chosen. In addition, the combination of the VIs and fluorescence parameters was proposed as the input variables in the SVM model and used to estimate the LNC. Experimental results exhibited the promising potential of the LIF technology combined with reflectance for the accurate estimation of LNC, which provided guidance for monitoring the LNC.
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Rerouting of Metabolism into Desired Cellular Products by Nutrient Stress: Fluxes Reveal the Selected Pathways in Cyanobacterial Photosynthesis.
Qian, X, Zhang, Y, Lun, DS, Dismukes, GC
ACS synthetic biology. 2018;(5):1465-1476
Abstract
Boosting cellular growth rates while redirecting metabolism to make desired products are the preeminent goals of gene engineering of photoautotrophs, yet so far these goals have been hardly achieved owing to lack of understanding of the functional pathways and their choke points. Here we apply a 13C mass isotopic method (INST-MFA) to quantify instantaneous fluxes of metabolites during photoautotrophic growth. INST-MFA determines the globally most accurate set of absolute fluxes for each metabolite from a finite set of measured 13C-isotopomer fluxes by minimizing the sum of squared residuals between experimental and predicted mass isotopomers. We show that the widely observed shift in biomass composition in cyanobacteria, demonstrated here with Synechococcus sp. PCC 7002, favoring glycogen synthesis during nitrogen starvation is caused by (1) increased flux through a bottleneck step in gluconeogenesis (3PG → GAP/DHAP), and (2) flux overflow through a previously unrecognized hybrid gluconeogenesis-pentose phosphate (hGPP) pathway. Our data suggest the slower growth rate and biomass accumulation under N starvation is due to a reduced carbon fixation rate and a reduced flux of carbon into amino acid precursors. Additionally, 13C flux from α-ketoglutarate to succinate is demonstrated to occur via succinic semialdehyde, an alternative to the conventional TCA cycle, in Synechococcus 7002 under photoautotrophic conditions. We found that pyruvate and oxaloacetate are synthesized mainly by malate dehydrogenase with minimal flux into acetyl coenzyme-A via pyruvate dehydrogenase. Nutrient stress induces major shifts in fluxes into new pathways that deviate from historical metabolic pathways derived from model bacteria.
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9.
Nitrogen - essential macronutrient and signal controlling flowering time.
Weber, K, Burow, M
Physiologia plantarum. 2018;(2):251-260
Abstract
Nitrogen, as limiting nutrient for plant growth and crop yield, is a main component of fertilizers and heavily used in modern agriculture. Early reports from over-application of fertilizers in crop production have shown to repress the transition from vegetative to reproductive phase. For the model plant Arabidopsis thaliana, there is evidence that low nitrogen conditions promote early flowering, while high nitrogen as well as nitrogen starvation conditions display the opposite effect. To gain a better understanding of how nitrogen affects the onset of flowering, we reviewed the existing literature for A. thaliana and carried out a meta-analysis on available transcriptomics data, seeking for potential genes and pathways involved in both nitrogen responses and flowering time control. With this strategy, we aimed at identifying potential gateways for integration of nitrogen signaling and potential regulators that might link the regulatory networks controlling nitrogen and flowering in A. thaliana. We found that photoperiodic pathway genes have high potential to be involved in nitrogen-dependent flowering.
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10.
[Effects of Environmental Factors on the Synergy of Functional Bacteria in Completely Autotrophic Granular Sludge].
Chen, X, Qian, FY, Wang, JF, Gao, JJ, Shen, YL, Jia, X
Huan jing ke xue= Huanjing kexue. 2018;(4):1756-1762
Abstract
To obtain experimental evidences for optimizing a completely autotrophic nitrogen removal process based on granules, the effects of dissolved oxygen (DO) concentration, temperature (t), initial ammonium (NH4+-N) concentration, and solution pH conditions on the synergy between the aerobic and anaerobic ammonium-oxidizing bacteria (AOB and AMX) were investigated using a single factor batch experiment, while the analysis of the microbial community structure within them was conducted using MiSeq high-throughput pyrosequencing. Results revealed that AOB (genus Nitrosomonas) and AMX (genus Candidatus Kuenenia) dominated in the granules, representing relative abundances of 32.9% and 9.8%, respectively. For the granules, the highest specific nitrogen removal rate of q(TN)=(17.7±1.0) mg·(g·h)-1 was obtained at a DO concentration of 2 mg·L-1, while the initial NH4+-N concentration was set at 100 mg·L-1. And a lower DO level resulted in partial nitritation became the rate-limiting step of process, otherwise, it would be the ANAMMOX reaction instead. According to the free energy of the reactions, the activity of AMX was more sensitive to low temperature than that of AOB. When the reaction temperature was lower than 30℃, nitrite accumulation could be observed in bulk liquid, with the significant decrease of q(TN) for the granules. Under the same oxygen supply conditions, an initial NH4+-N concentration lower than 100 mg·L-1 could inhibit the activity of AMX partly. However, with an initial NH4+-N concentration over 150 mg·L-1, either oxygen-limiting or high free ammonia concentration could lead to the dramatic decrease of q(TN). In addition, the effective synergy of the two types of ammonium oxidizers in granules was always achieved at solution pH in the range of 7.0-8.5.