Metal nutrition and transport in the process of symbiotic nitrogen fixation.

Symbiotic nitrogen fixation (SNF) facilitated by the interaction between legumes and rhizobia is a well-documented and eco-friendly alternative to chemical nitrogen fertilizers. Host plants obtain fixed nitrogen from rhizobia by providing carbon and mineral nutrients. These mineral nutrients, which are mostly in the form of metal ions, are implicated in various stages of the SNF process. This review describes the functional roles played by metal ions in nodule formation and nitrogen fixation and specifically addresses their transport mechanisms and associated transporters within root nodules. Future research directions and potential strategies for enhancing SNF efficiency are also discussed.

Two central circadian oscillators OsPRR59 and OsPRR95 modulate magnesium homeostasis and carbon fixation in rice.

Photosynthesis, which provides oxygen and energy for all living organisms, is circadian regulated. Photosynthesis-associated metabolism must tightly coordinate with the circadian clock to maximize the efficiency of the light-energy capture and carbon fixation. However, the molecular basis for the interplay of photosynthesis and the circadian clock is not fully understood, particularly in crop plants. Here, we report two central oscillator genes of circadian clock, OsPRR95 and OsPRR59 in rice, which function as transcriptional repressors to negatively regulate the rhythmic expression of OsMGT3 encoding a chloroplast-localized Mg2+ transporter. OsMGT3-dependent rhythmic Mg fluctuations modulate carbon fixation and consequent sugar output in rice chloroplasts. Furthermore, sugar triggers the increase of superoxide, which may act as a feedback signal to positively regulate the expression of OsPRR95 and OsPRR59. Taken together, our results reveal a negative-feedback loop that strengthens the crosstalk between photosynthetic carbon fixation and the circadian clock, which may improve plan adaptation and performance in fluctuating environments.

Carbon-nitrogen trading in symbiotic nodules depends on magnesium import.

Symbiotic nitrogen fixation provides large amounts of nitrogen for global agricultural systems with little environmental or economic costs. The basis of symbiosis is the nutrient exchange occurring between legumes and rhizobia, but key regulators controlling nutrient exchange are largely unknown. Here, we reveal that magnesium (Mg), an important nutrient factor that preferentially accumulates in inner cortical cells of soybean nodules, shows the most positive correlation with nodule carbon (C) import and nitrogen (N) export. We further identified a pair of Mg transporter genes, GmMGT4 and GmMGT5, that are specifically expressed in the nodule cortex, modulating both nodule Mg import and C-N transport processes. The GmMGT4&5-dependent Mg import activates the activity of a plasmodesmata-located ß-1,3-glucanase GmBG2 and consequently keeps plasmodesmata permeable for C-N transport in nodule inner cortical cells. Our studies discovered an important regulating pathway for host plants fine-tuning nodule C-N trading to achieve optimal growth, which may be helpful for optimizing nutrient management for soybean production.

A natural uORF variant confers phosphorus acquisition diversity in soybean.

Phosphorus (P) is an essential element for all organisms. Because P fertilizers are a non-renewable resource and high fixation in soils, sustainable agriculture requires researchers to improve crop P acquisition efficiency. Here, we report a strong association signal at a locus of CPU1 (component of phosphorus uptake 1), from a genome-wide association study of P acquisition efficiency in a soybean core collection grown in the field. A SEC12-like gene, GmPHF1, is identified as the causal gene for CPU1. GmPHF1 facilitates the ER (endoplasmic reticulum) exit of the phosphate transporter, GmPT4, to the plasma membrane of root epidermal cells. A common SNP in an upstream open reading frame (uORF) of GmPHF1, which alters the abundance of GmPHF1 in a tissue-specific manner, contributes to P acquisition diversity in soybean. A natural genetic variation conditions diversity in soybean P acquisition, which can be used to develop P-efficient soybean genotypes.

[Circuit Designed for Driving Blower in Non-invasive Positive Airway Pressure Respirator].

One of critical technologies in a non-invasive positive airway pressure respirator is to output the airflow for meeting the requirement of respiratory patient in breath. In order to develop a safe and reliable blower driving system, a circuit based on the special chips MC33035 and MC33039 was designed. The linear relationship between the input control voltage and the output air flow was achieved. This designed circuit will be embedded in the non-invasive ventilator system as a module. And based on this circuit, the secure and controllable ventilation flow can be performed.

Comparative genomics revealed the gene evolution and functional divergence of magnesium transporter families in Saccharum.

BACKGROUND: Sugarcane served as the model plant for discovery of the C4 photosynthetic pathway. Magnesium is the central atom of chlorophyll, and thus is considered as a critical nutrient for plant development and photosynthesis. In plants, the magnesium transporter (MGT) family is composed of a number of membrane proteins, which play crucial roles in maintaining Mg homeostasis. However, to date there is no information available on the genomics of MGTs in sugarcane due to the complexity of the Saccharum genome. RESULTS: Here, we identified 10 MGTs from the Saccharum spontaneum genome. Phylogenetic analysis of MGTs suggested that the MGTs contained at least 5 last common ancestors before the origin of angiosperms. Gene structure analysis suggested that MGTs family of dicotyledon may be accompanied by intron loss and pseudoexon phenomena during evolution. The pairwise synonymous substitution rates corresponding to a divergence time ranged from 142.3 to 236.6 Mya, demonstrating that the MGTs are an ancient gene family in plants. Both the phylogeny and Ks analyses indicated that SsMGT1/SsMGT2 originated from the recent ρWGD, and SsMGT7/SsMGT8 originated from the recent σ WGD. These 4 recently duplicated genes were shown low expression levels and assumed to be functionally redundant. MGT6, MGT9 and MGT10 weredominant genes in the MGT family and werepredicted to be located inthe chloroplast. Of the 3 dominant MGTs, SsMGT6 expression levels were found to be induced in the light period, while SsMGT9 and SsMTG10 displayed high expression levels in the dark period. These results suggested that SsMGT6 may have a function complementary to SsMGT9 and SsMTG10 that follows thecircadian clock for MGT in the leaf tissues of S. spontaneum. MGT3, MGT7 and MGT10 had higher expression levels Insaccharum officinarum than in S. spontaneum, suggesting their functional divergence after the split of S. spontaneum and S. officinarum. CONCLUSIONS: This study of gene evolution and expression of MGTs in S. spontaneum provided basis for the comprehensive genomic study of the entire MGT genes family in Saccharum. The results are valuable for further functional analyses of MGT genes and utilization of the MGTs for Saccharum genetic improvement.

OsMGT1 Confers Resistance to Magnesium Deficiency By Enhancing the Import of Mg in Rice.

Magnesium (Mg) is an essential nutrient element for plant growth and plays an important role in numerous physiological and biochemical processes. Mg deficiency inhibits plant growth and has become a growing problem for crop productions in agriculture. However, the molecular mechanisms for the resistance to Mg deficiency in plants were not well understood. In this study, we identified a Mg transporter gene OsMGT1 that confers resistance to Mg deficiency in rice (Oryza sativa). The expression of OsMGT1 was highly induced by Mg deficiency in shoots. Investigation of tissue expression patterns revealed that OsMGT1 was mainly expressed in the phloem region; however, Mg deficiency remarkably enhanced its expression in xylem parenchyma and mesophyll cells in shoots. Knockout of OsMGT1 resulted in a significant reduction in Mg content and biomass when grown at Mg-limited conditions. Furthermore, the sensitivity to low-Mg in mutants was intensified by excessive calcium supply. In addition, overexpression of OsMGT1 increased Mg content and biomass under low-Mg supply. In conclusion, our results indicate that OsMGT1 plays an important role in rice Mg import and is required for the resistance to Mg deficiency, which can be utilized for molecular breeding of low-Mg tolerant plants.

A nodule-localized phosphate transporter GmPT7 plays an important role in enhancing symbiotic N2 fixation and yield in soybean.

Symbiotic nitrogen (N2 ) fixation plays a vital role in sustainable agriculture. Efficient N2 fixation requires various materials, including phosphate (Pi); however, the molecular mechanism underlying the transport of Pi into nodules and bacteroids remains largely unknown. A nodule-localized Pi transporter, GmPT7, was functionally characterized in soybean (Glycine max) and its role in N2 fixation and yield was investigated via composite and whole transgenic plants. GmPT7 protein was localized to the plasma membrane and showed transport activity for Pi in yeast. Altered expression of GmPT7 changed 33 Pi uptake from rhizosphere and translocation to bacteroids. GmPT7 was mainly localized to the outer cortex and fixation zones of the nodules. Overexpression of GmPT7 promoted nodulation, and increased plant biomass, shoot nitrogen and phosphorus content, resulting in improved soybean yield by up to 36%. Double suppression of GmPT5 and GmPT7 led to nearly complete elimination of nodulation and over 50% reduction in plant biomass, shoot nitrogen and phosphorus content, indicating that both GmPT7 and GmPT5 contribute to Pi transport for N2 fixation. Taken together, our results indicate that GmPT7 is a transporter responsible for direct Pi entry to nodules and further to fixation zones, which is required for enhancing symbiotic N2 fixation and grain yield of soybean.

Association between FSP, CVHI, inflammatory cytokines and the incidence of primary stroke.

This case-control study was designed to establish a new risk-prediction model for primary stroke using Framingham stroke profile (FSP), cerebral vascular hemodynamic indexes (CVHI) and plasma inflammatory cytokines including hs-CRP, IL-6, TNF-α and Lp-PLA2. A total of 101 primary stroke patients admitted to Dongguan Houjie Hospital between August 2014 and June 2015 were assigned into the case group, and 156 age- and gender-matched healthy subjects from the Houjie Community were allocated into the control group. The prognostic values of FSP, CVHI and inflammatory cytokines including high sensitive C-reactive protein (hs-CRP), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and lipoprotein-associated phospholipase A2 (Lp-PLA2) were assessed by multivariate logistic regression analysis. Seven risk-prediction models (FSP, CVHI, inflammatory cytokine, FSP+CVHI, FSP+inflammatory cytokine, CVHI+inflammatory cytokine, CVHI+FSP+inflammatory cytokine) were successfully established and the prognostic values were statistically compared by ROC curve and Z test. For FSP, the stroke risk was significantly elevated by 2.85 times when the FSP score was increased by 1 level (P=0.043), increased by 3.25 times for CVHI (P=0.036), 6.53 times for IL-6 (P=0.003), and 7.75 times for Lp-PLA2 (P=0.000). The sensitivity of FSP+CVHI+inflammatory cytokine and CVHI+inflammatory cytokine models was higher than 90%. For model specificity, the specificity of FSP+CVHI+inflammatory cytokine model alone exceeded 90%. FSP, CVHI, IL-6 and Lp-PLA2 are independent risk factors of stroke. Integrating IL-6 and Lp-PLA2 into the models can significantly enhance the risk prediction accuracy of primary stroke. Combined application of FSP+CVHI+inflammatory cytokine is of potential for risk prediction of primary stroke.

Metabolomics Reveals Distinct Carbon and Nitrogen Metabolic Responses to Magnesium Deficiency in Leaves and Roots of Soybean [Glycine max (Linn.) Merr.].

Magnesium (Mg) deficiency, a widespread yet overlooked problem in agriculture, has been reported to retard plant growth and development, through affecting key metabolic pathways. However, the metabolic responses of plant to Mg deficiency is still not fully understood. Here we report a metabolomic study to evaluate the metabolic responses to Mg deficiency in soybean leaves and roots. Hydroponic grown soybean were exposed to Mg starvation for 4 and 8 days, respectively. Metabolic changes in the first mature trifoliolate leaves and roots were quantified by conducting GC-TOF-MS based metabolomic analysis. Principal component analysis (PCA) showed that Mg deficient plants became distinguishable from controls at 4 days after stress (DAS) at metabolic level, and were clearly discriminated at 8 DAS. Mg deficiency could cause large metabolite alterations on carbon and nitrogen metabolism. At 8 DAS, carbon allocation from shoot to root is decreased by Mg deficiency. Remarkably, most amino acids (such as phenylalanine, asparagine, leucine, isoleucine, glycine, glutamine, and serine) showed pronounced accumulation in the leaves, while most organic acids (including pyruvic acid, citric acid, 2-keto-glutaric acid, succinic acid, fumaric acid, and malic acid) were significantly decreased in the roots. Our study shows that the carbon and nitrogen metabolic responses are distinct in leaves and roots under Mg deficiency.

A tonoplast-localized half-size ABC transporter is required for internal detoxification of aluminum in rice.

Toxic aluminum enters the root cells rapidly, therefore internal detoxification is required. However, the molecular mechanisms underlying this process are poorly understood. Here we functionally characterized a rice gene, Os03g0755100 (OsALS1), that is regulated by ART1, a C2H2-type zinc finger transcription factor. OsALS1 encodes a half-size ABC transporter that is a member of the TAP (transporter associated with antigen processing) sub-group. Expression of OsALS1 was rapidly and specifically induced by Al in the roots, but not by other metals or low pH. OsALS1 was localized at all cells of the roots. Furthermore, OsALS1 is localized to the tonoplast. These expression patterns and cell specificity of localization are different from those of the homologous gene AtALS1 in Arabidopsis. Knockout of OsALS1 in three independent lines resulted in significant increased sensitivity to Al, but did not affect the sensitivity to other metals and low pH. Comparison of Al accumulation patterns between wild-type and osals1 mutants showed that there was no difference in Al levels in the cell sap of root tips between wild-type and the mutants, but the mutants accumulated more Al in the cytosol and nucleus than the wild-type. Expression of OsALS1 in yeast resulted in increased Al sensitivity due to mis-localization. These results indicate that OsALS1 localized at the tonoplast is responsible for sequestration of Al into the vacuoles, which is required for internal detoxification of Al in rice.