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Ammonium acquisition by plant roots is mediated by AMMONIUM TRANSPORTERs (AMTs), ubiquitous membrane proteins with essential roles in nitrogen nutrition in all organisms. In microbial and plant cells, ammonium transport activity is controlled by ammonium-triggered feedback inhibition to prevent cellular ammonium toxicity. Data from heterologous expression in yeast indicate that oligomerization of plant AMTs is critical for allosteric regulation of transport activity, in which the conserved cytosolic C terminus functions as a trans -activator. Employing the coexpressed transporters AMT1;1 and AMT1;3 from Arabidopsis thaliana as a model, we show here that these two isoforms form functional homo- and heterotrimers in yeast and plant roots and that AMT1;3 carrying a phosphomimic residue in its C terminus regulates both homo- and heterotrimers in a dominant-negative fashion in vivo. 15NH4  + influx studies further indicate that allosteric inhibition represses ammonium transport activity in roots of transgenic Arabidopsis expressing a phosphomimic mutant together with functional AMT1;3 or AMT1;1. Our study demonstrates in planta a regulatory role in transport activity of heterooligomerization of transporter isoforms, which may enhance their versatility for signal exchange in response to environmental triggers. [ABSTRACT FROM AUTHOR]

Summary: Seed vigour, including rapid, uniform germination and robust seedling establishment under various field conditions, is becoming an increasingly essential agronomic trait for achieving high yield in crops. However, little is known about this important seed quality trait. In this study, we performed a genome‐wide association study to identify a key transcription factor ZmRap2.7, which regulates seed vigour through transcriptionally repressing expressions of three ABA signalling genes ZmPYL3, ZmPP2C and ZmABI5 and two phosphatidylethanolamine‐binding genes ZCN9 and ZCN10. In addition, ZCN9 and ZCN10 proteins could interact with ZmPYL3, ZmPP2C and ZmABI5 proteins, and loss‐of‐function of ZmRap2.7 and overexpression of ZCN9 and ZCN10 reduced ABA sensitivity and seed vigour, suggesting a complex regulatory network for regulation of ABA signalling mediated seed vigour. Finally, we showed that four SNPs in ZmRap2.7 coding region influenced its transcriptionally binding activity to the downstream gene promoters. Together with previously identified functional variants within and surrounding ZmRap2.7, we concluded that the distinct allelic variations of ZmRap2.7 were obtained independently during maize domestication and improvement, and responded separately for the diversities of seed vigour, flowering time and brace root development. These results provide novel genes, a new regulatory network and an evolutional mechanism for understanding the molecular mechanism of seed vigour. [ABSTRACT FROM AUTHOR]

Key message: A total of 389 and 344 QTLs were identified by GWAS and QTL mapping explaining accumulatively 32.2–65.0% and 23.7–63.4% of phenotypic variation for 14 shoot-borne root traits using more than 1300 individuals across multiple field trails. Efficient nutrient and water acquisition from soils depends on the root system architecture (RSA). However, the genetic determinants underlying RSA in maize remain largely unexplored. In this study, we conducted a comprehensive genetic analysis for 14 shoot-borne root traits using 513 inbred lines and 800 individuals from four recombinant inbred line (RIL) populations at the mature stage across multiple field trails. Our analysis revealed substantial phenotypic variation for these 14 root traits, with a total of 389 and 344 QTLs identified through genome-wide association analysis (GWAS) and linkage analysis, respectively. These QTLs collectively explained 32.2–65.0% and 23.7–63.4% of the trait variation within each population. Several a priori candidate genes involved in auxin and cytokinin signaling pathways, such as IAA26, ARF2, LBD37 and CKX3, were found to co-localize with these loci. In addition, a total of 69 transcription factors (TFs) from 27 TF families (MYB, NAC, bZIP, bHLH and WRKY) were found for shoot-borne root traits. A total of 19 genes including PIN3, LBD15, IAA32, IAA38 and ARR12 and 19 GWAS signals were overlapped with selective sweeps. Further, significant additive effects were found for root traits, and pyramiding the favorable alleles could enhance maize root development. These findings could contribute to understand the genetic basis of root development and evolution, and provided an important genetic resource for the genetic improvement of root traits in maize. [ABSTRACT FROM AUTHOR]

Summary: Nitrate (NO3−) is crucial for optimal plant growth and development and often limits crop productivity under low availability. In comparison with model plant Arabidopsis, the molecular mechanisms underlying NO3− acquisition and utilization remain largely unclear in maize. In particular, only a few genes have been exploited to improve nitrogen use efficiency (NUE). Here, we demonstrated that NO3−‐inducible ZmNRT1.1B (ZmNPF6.6) positively regulated NO3−‐dependent growth and NUE in maize. We showed that the tandem duplicated proteoform ZmNRT1.1C is irrelevant to maize seedling growth under NO3− supply; however, the loss of function of ZmNRT1.1B significantly weakened plant growth under adequate NO3− supply under both hydroponic and field conditions. The 15N‐labelled NO3− absorption assay indicated that ZmNRT1.1B mediated the high‐affinity NO3−‐transport and root‐to‐shoot NO3− translocation. Transcriptome analysis further showed, upon NO3− supply, ZmNRT1.1B promotes cytoplasmic‐to‐nuclear shuttling of ZmNLP3.1 (ZmNLP8), which co‐regulates the expression of genes involved in NO3− response, cytokinin biosynthesis and carbon metabolism. Remarkably, overexpression of ZmNRT1.1B in modern maize hybrids improved grain yield under N‐limiting fields. Taken together, our study revealed a crucial role of ZmNRT1.1B in high‐affinity NO3− transport and signalling and offers valuable genetic resource for breeding N use efficient high‐yield cultivars. [ABSTRACT FROM AUTHOR]

Protein kinase-mediated phosphorylation modulates the absorption of many nutrients in plants. CALCIUM-DEPENDENT PROTEIN KINASES (CPKs) are key players in plant signaling to translate calcium signals into diverse physiological responses. However, the regulatory role of CPKs in ammonium uptake remains largely unknown. Here, using methylammonium (MeA) toxicity screening, CPK32 was identified as a positive regulator of ammonium uptake in roots. CPK32 specifically interacted with AMMONIUM TRANSPORTER 1;1 (AMT1;1) and phosphorylated AMT1;1 at the non-conserved serine residue Ser450 in the C-terminal domain. Functional analysis in Xenopus oocytes showed that co-expression of CPK32 and AMT1;1 significantly enhanced the AMT1;1-mediated inward ammonium currents. In transgenic plants, the phosphomimic variant AMT1;1S450E, but not the non-phosphorylatable variant AMT1;1S450A, fully complemented the MeA insensitivity and restored high-affinity 15NH4+ uptake in both amt1;1 and cpk32 mutants. Moreover, in the CPK32 knockout background, AMT1;1 lost its ammonium transport activity entirely. These results indicate that CPK32 is a crucial positive regulator of ammonium uptake in roots and the ammonium transport activity of AMT1;1 is dependent on CPK32-mediated phosphorylation. [ABSTRACT FROM AUTHOR]

SUMMARY: High‐affinity ammonium uptake in roots mediate by AMT1‐type ammonium transporters, which are tightly controlled at multiple regulatory levels for adapting various nitrogen availability. For Arabidopsis AtAMT1;1 gene, in addition to the transcriptional and post‐translational controls, an organ‐dependent and N‐dependent post‐transcriptional regulation was suggested as an additional regulatory step for fine tuning ammonium uptake, but the underlying mechanisms remain to be elucidated. Here, we showed that degradation of AtAMT1;1 transcript in roots of Pro35s:AtAMT1;1‐transformed atamt1;1‐1 Arabidopsis plants resulted from RDR6‐dependent sense transgene‐induced post‐transcriptional gene silencing (S‐PTGS). The siRNAs for S‐PTGS may derive from the aberrant RNA, of which the production was co‐determined by sequence feature and excessive expression of AtAMT1;1. Switching to the expression of AtAMT1;1 driven by ProAtUBQ10 or of AtAMT1;1 mutated at two siRNA‐targeted hotspots reduced AtAMT1;1‐specific siRNAs and overcame S‐PTGS in roots. In roots of these lines, however, the steady‐state transcript levels of AtAMT1;1 still significantly decreased under conditions of N‐sufficiency compared with N‐deficiency, confirming a N‐dependent post‐transcriptional regulatory manner. A crucial role of the 207‐bp 3′‐end sequence of AtAMT1;1 was further demonstrated by N‐dependent accumulation of chimeric‐AtAMT1;1 transcript in T‐DNA insertion lines and of GFP‐tagged chimeric‐AtAMT1;1 transcript in transgenic lines. A novel non‐coding RNA (ncRNA), which was highly abundant in N‐sufficient roots, may target the above‐identified 3′‐end region for the degrading AtAMT1;1 transcript. This degradation could be prevented by a mutation on the AtAMT1;1 transcript at a potential cleavage site (+1458). These results suggested two distinct mechanisms of regulating AtAMT1;1 mRNA turnover by ncRNA for strictly control of ammonium uptake in roots. Significance Statement: Post‐transcriptional regulation of ammonium transporter AtAMT1;1 is a critical step for controlling ammonium uptake in Arabidopsis roots, but the underlying mechanism remains unclear. Here, we show that two distinct types of non‐coding RNAs in roots, the RDR6‐dependent transgene‐induced siRNAs and nitrogen‐induced ncRNA, were involved in the degradation of AtAMT1;1 transcripts by targeting the 3′‐end region, preventing from the over‐accumulation of AtAMT1;1 transcripts. [ABSTRACT FROM AUTHOR]

SUMMARY: Seed number and harvesting ability in maize (Zea mays L.) are primarily determined by the architecture of female inflorescence, namely the ear. Therefore, ear morphogenesis contributes to grain yield and as such is one of the key target traits during maize breeding. However, the molecular networks of this highly dynamic and complex grain‐bearing inflorescence remain largely unclear. As a first step toward characterizing these networks, we performed a high‐spatio‐temporal‐resolution investigation of transcriptomes using 130 ear samples collected from developing ears with length from 0.1 mm to 19.0 cm. Comparisons of these mRNA populations indicated that these spatio‐temporal transcriptomes were clearly separated into four distinct stages stages I, II, III, and IV. A total of 23 793 genes including 1513 transcription factors (TFs) were identified in the investigated developing ears. During the stage I of ear morphogenesis, 425 genes were predicted to be involved in a co‐expression network established by eight hub TFs. Moreover, 9714 ear‐specific genes were identified in the seven kinds of meristems. Additionally, 527 genes including 59 TFs were identified as especially expressed in ear and displayed high temporal specificity. These results provide a high‐resolution atlas of gene activity during ear development and help to unravel the regulatory modules associated with the differentiation of the ear in maize. Significance Statement: This article will provide a full transcriptional landscape of maize ear during its whole development period. [ABSTRACT FROM AUTHOR]

Background: Although the traditional contingent screening strategy is effective, there are still undetected low-risk trisomy 21. This study aims to define appropriate cut-off values of serum biochemical markers at low-risk and develop a strategy for sequential prenatal testing associated with first-trimester screening to increase the detection rate of trisomy 21. Methods: This was a 9-year retrospective analysis of singleton pregnant women who underwent serum biochemical screening or combined first-trimester screening (CFTS) in the first trimester. For the low-risk group, the cut-off values of the serum biochemical markers were adjusted to determine the appropriate detection efficiency. Gravidas with abnormal serum biochemical markers at low-risk were advised to undergo further non-invasive prenatal screening (NIPS), whereas others continued with routine prenatal care. Results: When cut-off values of free beta subunit of human chorionic gonadotropin (free β-hCG) multiples of the median (MoM) or pregnancy-associated plasma protein A (PAPP-A) MoM were defined with ≥ 2.75 or ≤ 0.5, 7.72% (2,194/28,405) in the serum biochemical screening group and 12.36% (4,005/32,403) in CFTS group could be detected as abnormal results for further NIPS. Finally, 55.56% (5/9) and 85.71% (6/7) of trisomy 21 cases with false-negative results were detected, and the overall detection rate for trisomy 21 was improved by 10.64% (5/47) and 12.77% (6/47), respectively. Conclusions: The new contingent screening strategy can increase the detection rate of trisomy 21 compared with the traditional contingent screening strategy. [ABSTRACT FROM AUTHOR]

Key Message: The genetic architecture of RSA traits was dissected by GWAS and coexpression networks analysis in a maize association population. Root system architecture (RSA) is a crucial determinant of water and nutrient uptake efficiency in crops. However, the maize genetic architecture of RSA is still poorly understood due to the challenges in quantifying root traits and the lack of dense molecular markers. Here, an association mapping panel including 356 inbred lines were crossed with a common tester, Zheng58, and the test crosses were phenotyped for 12 RSA traits in three locations. We observed a 1.3 ~ sixfold phenotypic variation for measured RSA in the association panel. The association panel consisted of four subpopulations, non-stiff stalk (NSS) lines, stiff stalk (SS), tropical/subtropical (TST), and mixed. Zheng58 × TST has a 2.1% higher crown root number (CRN) and 8.6% less brace root number (BRN) than Zheng58 × NSS and Zheng58 × SS, respectively. Using a genome-wide association study (GWAS) with 1.25 million SNPs and correction for population structure, 191 significant SNPs were identified for root traits. Ninety (47%) of the significant SNPs showed positive allelic effects, and 101 (53%) showed negative effects. Each locus could explain 0.39% to 11.8% of phenotypic variation. By integrating GWAS results and comparing coexpression networks, 26 high-priority candidate genes were identified. Gene GRMZM2G377215, which belongs to the COBRA-like gene family, affected root growth and development. Gene GRMZM2G468657 encodes the aspartic proteinase nepenthesin-1, related to root development and N-deficient response. Collectively, our research provides progress in the genetic dissection of root system architecture. These findings present the further possibility for the genetic improvement of root traits in maize. [ABSTRACT FROM AUTHOR]

Key message: A new strategy that integrated multiple public data resources was established to construct root gene co-expression network and mine genes regulating root system architecture in maize. A root gene co-expression network, containing 13,874 genes, was constructed. A total of 53 root hub genes and 16 priority root candidate genes were identified. One priority root candidate was further functionally verified using overexpression transgenic maize lines. Root system architecture (RSA) is crucial for crops productivity and stress tolerance. In maize, few RSA genes are functionally cloned, and effective discovery of RSA genes remains a great of challenge. In this work, we established a strategy to mine maize RSA genes by integrating functionally characterized root genes, root transcriptome, weighted gene co-expression network analysis (WGCNA) and genome-wide association analysis (GWAS) of RSA traits based on public data resources. A total of 589 maize root genes were collected by searching well-characterized root genes in maize or homologous genes of other species. We performed WGCNA to construct a maize root gene co-expression network containing 13874 genes based on public available root transcriptome data, and further discovered the 53 hub genes related to root traits. In addition, by the prediction function of obtained root gene co-expression network, a total of 1082 new root candidate genes were explored. By further overlapping the obtained new root candidate gene with the root-related GWAS of RSA candidate genes, 16 priority root candidate genes were identified. Finally, a priority root candidate gene, Zm00001d023379 (encodes pyruvate kinase 2), was validated to modulate root open angle and shoot-borne roots number using its overexpression transgenic lines. Our results develop an integration analysis method for effectively exploring regulatory genes of RSA in maize and open a new avenue to mine the candidate genes underlying complex traits. [ABSTRACT FROM AUTHOR]

Genotype-by-environment interaction (G-by-E) is a common but potentially problematic phenomenon in plant breeding. In this study, we investigated the genotypic performance and two measures of plasticity on a phenotypic and genetic level by assessing 234 maize doubled haploid lines from six populations for 15 traits in seven macro-environments with a focus on varying soil phosphorus levels. It was found intergenic regions contributed the most to the variation of phenotypic linear plasticity. For 15 traits, 124 and 31 quantitative trait loci (QTL) were identified for genotypic performance and phenotypic plasticity, respectively. Further, some genes associated with phosphorus use efficiency, such as Zm00001eb117170, Zm00001eb258520, and Zm00001eb265410, encode small ubiquitin-like modifier E3 ligase were identified. By significantly testing the main effect and G-by-E effect, 38 main QTL and 17 interaction QTL were identified, respectively, in which MQTL38 contained the gene Zm00001eb374120, and its effect was related to phosphorus concentration in the soil, the lower the concentration, the greater the effect. Differences in the size and sign of the QTL effect in multiple environments could account for G-by-E. At last, the superiority of G-by-E in genomic selection was observed. In summary, our findings will provide theoretical guidance for breeding P-efficient and broadly adaptable varieties. [ABSTRACT FROM AUTHOR]

Optimal plant growth and development rely on morphological and physiological adaptions of the root system to forage heterogeneously distributed nitrogen (N) in soils. Rice grows mainly in the paddy soil where ammonium (NH4+) is present as the major N source. Although root NH4+ foraging behaviors are expected to be agronomically relevant, the underlying mechanism remains largely unknown. Here, we showed that NH4+ supply transiently enhanced the high-affinity NH4+ uptake and stimulated lateral root (LR) branching and elongation. These synergistic physiological and morphological responses were closely related to NH4+-induced expression of NH4+ transporters OsAMT1;1 and OsAMT1;2 in roots. The two independent double mutants (dko) defective in OsAMT1;1 and OsAMT1;2 failed to induce NH4+ uptake and stimulate LR formation, suggesting that OsAMT1s conferred the substrate-dependent root NH4+ foraging. In dko plants, NH4+ was unable to activate the expression of OsPIN2 , and the OsPIN2 mutant (lra1) exhibited a strong reduction in NH4+-triggered LR branching, suggesting that the auxin pathway was likely involved in OsAMT1s-dependent LR branching. Importantly, OsAMT1s-dependent root NH4+ foraging behaviors facilitated rice growth and N acquisition under fluctuating NH4+ supply. These results revealed an essential role of OsAMT1s in synergizing root morphological and physiological processes, allowing for efficient root NH4+ foraging to optimize N capture under fluctuating N availabilities. [ABSTRACT FROM AUTHOR]

The plasticity of root architecture is crucial for plants to acclimate to unfavourable environments including low nitrogen ( LN) stress. How maize roots coordinate the growth of axile roots and lateral roots ( LRs), as well as longitudinal and radial cell behaviours in response to LN stress, remains unclear. Maize plants were cultivated hydroponically under control (4 m m nitrate) and LN (40 μ m) conditions. Temporal and spatial samples were taken to analyse changes in the morphology, anatomical structure and carbon/nitrogen ( C/N) ratio in the axile root and LRs. LN stress increased axile root elongation, reduced the number of crown roots and decreased LR density and length. LN stress extended cell elongation zones and increased the mature cell length in the roots. LN stress reduced the cell diameter and total area of vessels and increased the amount of aerenchyma, but the number of cell layers in the crown root cortex was unchanged. The C/N ratio was higher in the axile roots than in the LRs. Maize roots acclimate to LN stress by optimizing the anatomical structure and N allocation. As a result, axile root elongation is favoured to efficiently find available N in the soil. [ABSTRACT FROM AUTHOR]

Maize (Zea mays L.) has undergone profound changes in root anatomy for environmental adaptation during domestication. However, the genetic mechanism of plasticity of maize root anatomy during the domestication process remains unclear. In this study, high-resolution mapping was performed for nine root anatomical traits using a maize-teosinte population (mexicana × Mo17) across three environments. Large genetic variations were detected for different root anatomical traits. The cortex, stele, aerenchyma areas, xylem vessel number, and cortical cell number had large variations across three environments, indicating high plasticity. Sixteen quantitative trait loci (QTL) were identified, including seven QTL with QTL × environment interaction (EIQTL) for high plasticity traits and nine QTL without QTL × environment interaction (SQTL). Most of the root loci were consistent with shoot QTL depicting domestication signals. Combining transcriptome and genome-wide association studies revealed that AUXIN EFFLUX CARRIER PIN–FORMED LIKE 4 (ZmPILS4) serves as a candidate gene underlying a major QTL of xylem traits. The near-isogenic lines (NILs) with lower expression of ZmPILS4 had 18–24% more auxin concentration in the root tips and 8–15% more xylem vessels. Nucleotide diversity values analysis in the promoter region suggested that ZmPILS4 was involved in maize domestication and adaptation. These results revealed the potential genetic basis of root anatomical plasticity during domestication. [ABSTRACT FROM AUTHOR]

To investigate responses to nitrogen and phosphorus stress, 218 recombinant inbred maize ( Zea mays L.) lines were grown under low nitrogen, low phosphorus, and control (i.e., nitrogen and phosphorus sufficient) conditions and evaluated at the silking stage for various traits, including leaf area, leaf chlorophyll content, flowering time, the interval between anthesis and silking, and grain yield. Among the 83 quantitative trait loci (QTL) detected, 29 were for controls, another 29 were for low nitrogen, and 25 were low phosphorus. These loci indicate that there were both common and specific genetic mechanisms underlying the investigated traits. Overlapping QTL for leaf size (area, length, and width) leaf chlorophyll level, flowering time, anthesis-silking interval, and grain yield were located at chromosome bin 2.03/2.04, bin 2.06/2.07/2.08, bin 4.01/4.02, bin 5.03/5.04, bin 6.07, bin 9.03, and bin 10.03/10.04. Many of these loci overlapped with previously reported loci controlling root growth as well as tolerance or response to nutrient deficiency. These QTL identify chromosome regions as targets for genetic improvement of low nitrogen and low phosphorus tolerance. [ABSTRACT FROM AUTHOR]

In recent years, agricultural growth in China has accelerated remarkably, but most of this growth has been driven by increased yield per unit area rather than by expansion of the cultivated area. Looking towards 2030, to meet the demand for grain and to feed a growing population on the available arable land, it is suggested that annual crop production should be increased to around 580 Mt and that yield should increase by at least 2% annually. Crop production will become more difficult with climate change, resource scarcity (e.g. land, water, energy, and nutrients) and environmental degradation (e.g. declining soil quality, increased greenhouse gas emissions, and surface water eutrophication). To pursue the fastest and most practical route to improved yield, the near-term strategy is application and extension of existing agricultural technologies. This would lead to substantial improvement in crop and soil management practices, which are currently suboptimal. Two pivotal components are required if we are to follow new trajectories. First, the disciplines of soil management and agronomy need to be given increased emphasis in research and teaching, as part of a grand food security challenge. Second, continued genetic improvement in crop varieties will be vital. However, our view is that the biggest gains from improved technology will come most immediately from combinations of improved crops and improved agronomical practices. The objectives of this paper are to summarize the historical trend of crop production in China and to examine the main constraints to the further increase of crop productivity. The paper provides a perspective on the challenge faced by science and technology in agriculture which must be met both in terms of increased crop productivity but also in increased resource use efficiency and the protection of environmental quality. [ABSTRACT FROM PUBLISHER]

AMMONIUM TRANSPORTER (AMT) proteins are conserved in all domains of life and mediate the transport of ammonium or ammonia across cell membranes. AMTs form trimers and use intermolecular interaction between subunits to regulate activity. So far, binding forces that stabilize AMT protein complexes are not well characterized. High temperature or reducing agents released mono- and dimeric forms from trimeric complexes formed by AMT1;1 from Arabidopsis and tomato. However, in the paralogue LeAMT1;3, trimeric complexes were not detected. LeAMT1;3 differs from the other AMTs by an unusually short N-terminus, suggesting a role for the N-terminus in oligomer stability. Truncation of the N-terminus in LeAMT1;1 destabilized the trimer and led to loss of functionality when expressed in yeast. Swapping of the N-terminus between LeAMT1;1 and LeAMT1;3 showed that sequences in the N-terminus of LeAMT1;1 are necessary and sufficient for stabilization of the interaction among the subunits. Two N-terminal cysteine residues are highly conserved among AMT1 transporters in plants but are lacking in LeAMT1;3. C3S or C27S variants of LeAMT1;1 showed reduced complex stability, which coincided with lower transport capacity for the substrate analogue methylammonium. Both cysteine-substituted LeAMT1;1 variants showed weaker interactions with the wildtype as determined by a quantitative analysis of the complex stability using the mating-based split-ubiquitin assay. These data indicate that the binding affinity of AMT1 subunits is stabilized by cysteines in the N-terminus and suggest a role for disulphide bridge formation via apoplastic N-terminal cysteine residues. [ABSTRACT FROM PUBLISHER]

Boron (B) is essential for plants but toxic when present in excess. Arabidopsis thaliana BOR1 is a B exporter for xylem loading and is essential for efficient B translocation from roots to shoots under B limitation. B translocation to shoots was enhanced under B limitation in WT but not in bor1-1 mutant plants. The enhanced translocation was suppressed upon resupply of high levels of B within several hours. Unlike a number of transporters for essential mineral nutrients, BOR1 mRNA accumulation was not strongly affected by B conditions. However, accumulation of a constitutively expressed BOR1-GFP fusion protein was elevated under conditions of limited B supply. Upon resupply of high levels of B, BOR1-GFP was degraded within several hours. These findings demonstrate that posttranscriptional mechanisms play a major role in regulation of BOR1 accumulation. Confocal laser scanning microscopy of root tip cells showed that BOR1-GFP is localized to the plasma membrane under B limitation. Shortly after B application, the protein was observed in dot-like structures in the cytoplasm before degradation. Colocalization studies of the fusion protein with an endocytic tracer FM4-64 and an endosomal Rab-GTPase Ara7 fused to monomeric red fluorescent protein suggested that BOR1 is transferred from the plasma membrane via the endosomes to the vacuole for degradation. These results establish that endocytosis and degradation of BOR1 are regulated by B availability, to avoid accumulation of toxic levels of B in shoots under high-B supply, while protecting the shoot from B deficiency under B limitation. [ABSTRACT FROM AUTHOR]

Maize (Zea mays L.) is an important crop worldwide, but in many regions is increasingly faced with the issue of phosphorus (P)-deficient soils. The aim of this study was to screen for low P-tolerance in maize and to dissect the underlying phenotypic response. To this end, we evaluated a panel of 380 diverse inbred lines in the field under low and normal P conditions for 17 morphological, biomass- and yield-related traits. All traits showed a significant genotypic variation and a moderate to high repeatability for each P condition. Under P deficiency, all traits were significantly lower compared to the control with normal P availability. The variance due to the interaction between genotype and P condition was significant for most traits, but generally small compared to the genotypic variance. Regarding the low P tolerance index, i.e. the phenotype under low P relative to the control, we observed a generally similar response within the morphological, biomass- or yield-related traits. Interestingly, genotypes showing little yield reduction under low P appear to achieve this tolerance through different strategies. Based on our results, low-P tolerant and low-P sensitive lines were identified, which can be used for further genetic research as well as to improve this globally important trait in maize breeding. [ABSTRACT FROM AUTHOR]

Manganese (Mn) plays an important role in the oxygen-evolving complex, where energy from light absorption is used for water splitting. Although changes in light intensity and Mn status can interfere with the functionality of the photosynthetic apparatus, the interaction between these two factors and the underlying mechanisms remain largely unknown. Here, maize seedlings were grown hydroponically and exposed to two different light intensities under Mn-sufficient or -deficient conditions. No visual Mn deficiency symptoms appeared even though the foliar Mn concentration in the Mn-deficient treatments was reduced to 2 µg g–1. However, the maximum quantum yield efficiency of PSII and the net photosynthetic rate declined significantly, indicating latent Mn deficiency. The reduction in photosynthetic performance by Mn depletion was further aggravated when plants were exposed to high light intensity. Integrated transcriptomic and proteomic analyses showed that a considerable number of genes encoding proteins in the photosynthetic apparatus were only suppressed by a combination of Mn deficiency and high light, thus indicating interactions between changes in Mn nutritional status and light intensity. We conclude that high light intensity aggravates latent Mn deficiency in maize by interfering with the abundance of PSII proteins. [ABSTRACT FROM AUTHOR]

The transmission of mobile wound signals along the phloem pathway is essential to the activation of wound-induced systemic response/resistance, which requires an upsurge of jasmonic acid (JA) in the distal undamaged leaves. Among these mobile signals, the electrical signal mediated by the glutamate-dependent activation of several clade three GLUTAMATE RECEPTOR-LIKE (GLR3) proteins is involved in the stimulation of JA production in distal leaves. However, whether JA acts as a mobile wound signal and, if so, how it is transmitted and interacts with the electrical signal remain unclear. Here, we show that JA was translocated from the local to distal leaves in Arabidopsis , and this process was predominantly regulated by two phloem-expressed and plasma membrane-localized jasmonate transporters, AtJAT3 and AtJAT4. In addition to the cooperation between AtJAT3/4 and GLR3.3 in the regulation of long-distance JA translocation, our findings indicate that importer-mediated cell–cell JA transport is important for driving the loading and translocation of JA in the phloem pathway in a self-propagating manner. Whether jasmonate (JA) can function as a mobile wound signal remains unclear. This study shows that two membrs of the jasmonate transporter family, AtJAT3 and AtJAT4, can import JA across the plasma membrane and regulate the translocation of wound-induced JA and systemic response/immunity. The findings suggest that transporter-mediated cell–cell transport drives the long-distance transmission of JA in a self-propagating manner. [ABSTRACT FROM AUTHOR]

In plants, nitrogen remobilization from source to sink organs is an important process regulated by complex transcriptional regulatory networks. However, the relationship between nitrogen remobilization and leaf senescence and the molecular regulatory network that controls them are unknown in maize. Here, using 15N labeling and a transcriptome approach, a dynamic analysis of the nitrogen remobilization process was conducted in two elite maize inbred lines (PH4CV and PH6WC) with contrasting leaf senescence. PH4CV showed higher nitrogen remobilization efficiency (NRE) than PH6WC, mainly in the middle and lower leaves from 15 d to 35 d after silking. The co-expression network analysis revealed that ethylene and cytokinin metabolism-related genes triggered the onset of nitrogen remobilization, while abscisic acid and jasmonic acid biosynthesis-related genes controlled the progression of nitrogen remobilization. By integrating genetic analysis, functional annotation, and gene expression, two candidate genes underlying a major quantitative trait locus of NRE were identified, namely an early senescence acting gene (ZmASR6) and an ATP-dependent Clp protease gene (GRMZM2G172230). Hormone-coupled transcription factors and downstream target genes reveal a gene regulatory network for the nitrogen remobilization process after silking in maize. These results uncovered a sophisticated regulatory mechanism for nitrogen remobilization, and further provided characterization of valuable genes for genetic improvement of nitrogen use efficiency in maize. [ABSTRACT FROM AUTHOR]

Plants can develop root systems with distinct anatomical features and morphological plasticity to forage nutrients distributed heterogeneously in soils. Lateral root proliferation is a typical nutrient-foraging response to a local supply of nitrate, which has been investigated across many plant species. However, the underlying mechanism in maize roots remains largely unknown. Here, we report on identification of a maize truncated MIKC-type MADS-box transcription factor (ZmTMM1) lacking K- and C-domains, expressed preferentially in the lateral root branching zone and induced by the localized supply of nitrate. ZmTMM1 belongs to the AGL17-like MADS-box transcription factor family that contains orthologs of ANR1, a key regulator for root nitrate foraging in Arabidopsis. Ectopic overexpression of ZmTMM1 recovers the defective growth of lateral roots in the Arabidopsis anr1 agl21 double mutant. The local activation of glucocorticoid receptor fusion proteins for ZmTMM1 and an artificially truncated form of AtANR1 without the K- and C-domains stimulates the lateral root growth of the Arabidopsis anr1 agl21 mutant, providing evidence that ZmTMM1 encodes a functional MADS-box that modulates lateral root development. However, no phenotype was observed in ZmTMM1-RNAi transgenic maize lines, suggesting a possible genetic redundancy of ZmTMM1 with other AGL17-like genes in maize. A comparative genome analysis further suggests that a nitrate-inducible transcriptional regulation is probably conserved in both truncated and non-truncated forms of ZmTMM1-like MADS-box transcription factors found in grass species. [ABSTRACT FROM AUTHOR]

To discuss combinations of traditional screening and noninvasive prenatal screening (NIPS) and to compare which traditional screening is the most suitable first-line screening approach to NIPS, pregnant women were recruited in this retrospective observational study. Pregnant women underwent one of four traditional screening tests. The 9 contingent models were combined by high risk cut-offs of 1:50, 1:100, 1:270 and intermediate risk cut-offs of 1:1000, 1:1500, 1:2000. We analyzed cost and performance of various screening models with contingent screening of different risk cut-offs. Compared with other screening tests, combined first-trimester screening (CFTS) had the lowest proportion of high risk (≥1:270) with the highest detection rate (DR) (78.79%) and the lowest proportion of intermediate risk (1:271~1:1000). When intermediate risk was 1:51 ~1:1500, CFTS as first-line screening had the lowest cost with DR of 93.94%. Other screening tests as the first-line screening with intermediate risk of 1:51~1:1000 had the lowest cost, there DR were 90.91%, 84.62%, 91.67%, respectively. Our study demonstrated if only one traditional screening was allowed to screen pregnant women, CFTS was recommended as the first choice. According to local health and economic conditions, adopting appropriate traditional screening with suitable cut-offs as first-line screening will contributed to a cost-effective screening model. [ABSTRACT FROM AUTHOR]

Aims: Arbuscular mycorrhizal fungi play important roles in plant phosphorus (P) accumulation. The aim of this study was to uncover how and to what extent soil plant-available P levels and maize genotypes influence the contribution of mycorrhizal P uptake pathway to plant P nutrition. Methods: We selected an old genotype HMY and a modern genotype XY335, combined with 32P labeling and qPCR to quantify P uptake efficiency of the direct pathway (DP) and the mycorrhizal pathway (MP) at three Olsen-P levels: 4.5 (low), 8 (medium) and 50 (high) mg kg−1. Results: The P uptake efficiency ratio PAE-MP/PAE-DP was highest in the treatment with medium Olsen-P, and was correlated positively with MP contribution. The traits of arbuscular mycorrhizal fungi, such as percent colonization, hyphal length density, P uptake per unit hyphae length, and the expression of the mycorrhiza-specific P transporter ZmPT1;6 were higher in XY335 than HMY in high-P soil, which was in accordance with the importance of the MP contribution. Conclusions: Greater mycorrhizal responsiveness in the modern maize genotype than the old genotype under high P soil condition is related to higher P uptake efficiency of MP than DP; the inherent potential of MP can be maximized by managing soil plant P availability to achieve optimal P supply in intensive farming. [ABSTRACT FROM AUTHOR]

In plants, nutrient transporters require tight regulation to ensure optimal uptake in complex environments. The activities of many nutrient transporters are post-translationally regulated by reversible phosphorylation, allowing rapid adaptation to variable environmental conditions. Here, we show that the Arabidopsis root epidermis-expressed ammonium transporter AtAMT1;3 was dynamically (de-)phosphorylated at multiple sites in the cytosolic C-terminal region (CTR) responding to ammonium and nitrate signals. Under ammonium resupply rapid phosphorylation of a Thr residue (T464) in the conserved part of the CTR (CTRC) effectively inhibited AtAMT1;3-dependent NH4+ uptake. Moreover, phosphorylation of Thr (T494), one of three phosphorylation sites in the non-conserved part of the CTR (CRTNC), moderately decreased the NH4+ transport activity of AtAMT1;3, as deduced from functional analysis of phospho-mimic mutants in yeast, oocytes, and transgenic Arabidopsis. Double phospho-mutants indicated a role of T494 in fine-tuning the NH4+ transport activity when T464 was non-phosphorylated. Transient dephosphorylation of T494 with nitrate resupply closely paralleled a transient increase in ammonium uptake. These results suggest that T464 phosphorylation at the CTRC acts as a prime switch to prevent excess ammonium influx, while T494 phosphorylation at the CTRNC fine tunes ammonium uptake in response to nitrate. This provides a sophisticated regulatory mechanism for plant ammonium transporters to achieve optimal ammonium uptake in response to various nitrogen forms. [ABSTRACT FROM AUTHOR]

Nitrogen-use efficiency of indica varieties of rice is superior to that of japonica varieties. We apply 16S ribosomal RNA gene profiling to characterize root microbiota of 68 indica and 27 japonica varieties grown in the field. We find that indica and japonica recruit distinct root microbiota. Notably, indica-enriched bacterial taxa are more diverse, and contain more genera with nitrogen metabolism functions, than japonica-enriched taxa. Using genetic approaches, we provide evidence that NRT1.1B, a rice nitrate transporter and sensor, is associated with the recruitment of a large proportion of indica-enriched bacteria. Metagenomic sequencing reveals that the ammonification process is less abundant in the root microbiome of the nrt1.1b mutant. We isolated 1,079 pure bacterial isolates from indica and japonica roots and derived synthetic communities (SynComs). Inoculation of IR24, an indica variety, with an indica-enriched SynCom improved rice growth in organic nitrogen conditions compared with a japonica-enriched SynCom. The links between plant genotype and root microbiota membership established in this study will inform breeding strategies to improve nitrogen use in crops. Rice coordinates recruitment of the root microbiota to optimize nitrogen acquisition from soil. [ABSTRACT FROM AUTHOR]

The use of mixed nitrate and ammonium as a nitrogen source can improve plant growth. Here, we used metabolomics and transcriptomics to study the underlying mechanisms. Maize plants were grown hydroponically in the presence of three forms of nitrogen (nitrate alone, 75%/25% nitrate/ammonium, and ammonium alone). Plants grown with mixed nitrogen had a higher photosynthetic rate than those supplied only with nitrate, and had the highest leaf area and shoot and root biomass among the three nitrogen treatments. In shoot and root, the concentration of nitrogenous compounds (ammonium, glutamine, and asparagine) and carbohydrates (sucrose, glucose, and fructose) in plants with a mixed nitrogen supply was higher than that with nitrate supply, but lower than that with ammonium supply. The activity of the related enzymes (glutamate synthase, asparagine synthase, phosphoenolpyruvate carboxylase, invertase, and ADP-glucose pyrophosphorylase) changed accordingly. Specifically, the mixed nitrogen source enhanced auxin synthesis via the shikimic acid pathway, as indicated by the higher levels of phosphoenolpyruvate and tryptophan compared with the other two treatments. The expression of corresponding genes involving auxin synthesis and response was up-regulated. Supply of only ammonium resulted in high levels of glutamine and asparagine, starch, and trehalose hexaphosphate. We conclude that, in addition to increased photosynthesis, mixed nitrogen supply enhances leaf growth via increasing auxin synthesis to build a large sink for carbon and nitrogen utilization, which, in turn, facilitates further carbon assimilation and nitrogen uptake. [ABSTRACT FROM AUTHOR]

The use of mixed nitrate and ammonium as a nitrogen source can improve plant growth. Here, we used metabolomics and transcriptomics to study the underlying mechanisms. Maize plants were grown hydroponically in the presence of three forms of nitrogen (nitrate alone, 75%/25% nitrate/ammonium, and ammonium alone). Plants grown with mixed nitrogen had a higher photosynthetic rate than those supplied only with nitrate, and had the highest leaf area and shoot and root biomass among the three nitrogen treatments. In shoot and root, the concentration of nitrogenous compounds (ammonium, glutamine, and asparagine) and carbohydrates (sucrose, glucose, and fructose) in plants with a mixed nitrogen supply was higher than that with nitrate supply, but lower than that with ammonium supply. The activity of the related enzymes (glutamate synthase, asparagine synthase, phosphoenolpyruvate carboxylase, invertase, and ADP-glucose pyrophosphorylase) changed accordingly. Specifically, the mixed nitrogen source enhanced auxin synthesis via the shikimic acid pathway, as indicated by the higher levels of phosphoenolpyruvate and tryptophan compared with the other two treatments. The expression of corresponding genes involving auxin synthesis and response was up-regulated. Supply of only ammonium resulted in high levels of glutamine and asparagine, starch, and trehalose hexaphosphate. We conclude that, in addition to increased photosynthesis, mixed nitrogen supply enhances leaf growth via increasing auxin synthesis to build a large sink for carbon and nitrogen utilization, which, in turn, facilitates further carbon assimilation and nitrogen uptake. [ABSTRACT FROM AUTHOR]

Highlights • Four GWAS-identified loci in Alzheimer's disease don't contribute to PD, ALS, and MSA risk in a Chinese population. • Rs28834970 in the PTK2B gene may modulate the phenotype of cognitive function in PD. • No significant differences were found in MAFs between these variants and the different subgroups in different diseases. Abstract Background A number of genetic variants have previously been identified and associated with the risk of Alzheimer's disease (AD), including rs10838725 in CELF1 , rs28834970 in PTK2B , rs17125944 in FERMT2, and rs10410544 in SIRT2 based on genome-wide association studies. Considering the overlap between the clinical manifestation and pathological characteristics of AD and Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS) and multiple system atrophy (MSA), we conducted a large sample study to investigate the associations between these variants and these three common neurodegenerative diseases in a Chinese population. Methods A total of 2449 patients, including 1219 PD, 870 sporadic ALS, and 360 MSA, and 821 healthy controls were examined for this study. All cases were genotyped for single-nucleotide polymorphisms using Sequenom iPLEX assay technology. Results No significant differences were found in genotype distribution and minor allele frequencies between the four candidate variants and the three neurodegenerative diseases. However, a significant difference was found in the minor allele frequency of rs28834970 in PTK2B between PD patients with normal and abnormal cognitive function (p = 0.001). Moreover, the minor allele "C" was associated with an increased risk for cognitive impairment in PD (OR = 1.84). Although this observation was not significant (p = 0.064), the mean Addenbrooke's Cognitive Examination-Revised (ACER) score of PD patients with the risk allele of rs28834970 was 2.913 ± 1.569 points lower than that of PD patients without the risk allele. Conclusion This study provides new insight into some of the phenotypes that may share the common pathogenesis of different neurodegenerative diseases. [ABSTRACT FROM AUTHOR]

Remobilization of leaf nitrogen (N) contributes greatly to grain N in maize, but leads to low photosynthetic rate (P n ). P n is determined by various N components involving in light harvest and CO 2 reduction. However, it is less clear which N component is the major contributor for the reduction of photosynthesis in modern stay-green maize hybrids. In this study, we analyzed the relationship between remobilization of different N components and P n during grain filling stage under low N (no N application) and high N (180 kg N ha −1 ) in a field experiment. The remobilization efficiency of photosynthetic enzymes (PEPc, PPDK and Rubisco) in the leaf was much higher than that of thylakoid N and other N components. Low N supply increased the remobilization efficiency of all the leaf N components. During grain filling stage, the amount of all the N components decreased together with P n . The ratio of P n to the N in the PEPc, PPDK and Rubisco kept increase in the whole grain filling stage, while the ratio of P n to chlorophyll and thylakoid-N decreased. Correlation analysis indicated that P n was more related to the content of photosynthetic enzymes than to chlorophyll and thylakoid N. It is concluded that photosynthetic enzymes serve as an N storage reservoir at early grain filling stage and their degradation is critical in the reduction of P n during later grain filling stage. Future breeding targets may be focused on enhancing the efficiency of photosynthetic enzymes during late grain filling stage. [ABSTRACT FROM AUTHOR]

One strategy for plants to adapt to low nitrogen is to reduce shoot growth and allocate more nitrogen and carbon for root growth. The mechanism underlying the response of leaf growth to low-nitrogen remains unknown. In this study, we investigated cell division and elongation in maize leaf growth in response to low-nitrogen by using an integrated approach. Kinematic analysis revealed that low-nitrogen inhibited leaf elongation mainly by shortening length of division zone, reducing cell flux and elemental growth rate. Hormone analysis revealed that changes of gibberellins caused by low-nitrogen correlate with the observed changes in division zone size and elemental growth rate in response to low-nitrogen, suggesting role of gibberellin in low-nitrogen induced inhibition of leaf elongation. RNA-Seq identified that GA20ox4 (GRMZM2G060940), a key enzyme for synthesis of gibberellins, was down-regulated in both division and elongation zone of leaf under low-nitrogen supply. Furthermore, exogenous GA 3 application on low-nitrogen plants restored leaf growth. However, application of gibberellin biosynthesis inhibitor reduced leaf growth. It is concluded that low-nitrogen reduces cell flux and elemental growth rate in maize leaf via reducing gibberellin synthesis. As a result, leaf elongation rate was slower and leaf area was smaller, freeing nitrogen for export to roots. [ABSTRACT FROM AUTHOR]

Summary: Transporters involved in manganese (Mn) uptake and intracellular Mn homeostasis in Arabidopsis and rice are well characterized, while much less is known for barley, which is particularly prone to Mn deficiency. In this study we have investigated the role of the iron‐regulated transporter 1 (IRT1) for Mn uptake and translocation in barley plants. We employed an RNAi approach to reduce HvIRT1 expression to 5% of the wild‐type level. This enabled characterization of the functional role of HvIRT1 by use of advanced imaging and phenotyping techniques applied to plants growing in hydroponics or soils with different Mn availability. Our results highlight the importance of HvIRT1 for the transport of Mn across the root endodermis into the stele. In the hvirt1‐RNAi lines, a chlorotic phenotype with reduced shoot Mn concentration and impaired photosynthetic functionality was observed, especially under conditions with low Mn availability. We also document that HvIRT1 controlled the Mn distribution within the barley grain. Surprisingly, unlike other IRT1 orthologues, HvIRT1 played no significant role in iron uptake. We conclude that the barley IRT1 orthologue has a novel function with respect to ensuring sufficient shoot Mn concentrations. The preference of IRT1 for Mn instead of Fe is discussed in an evolutionary context. [ABSTRACT FROM AUTHOR]

High-affinity ammonium uptake in maize roots is mainly mediated by AMT1-type ammonium transporters ZmAMT1;1a and ZmAMT1;3, but whether the increased expression of ZmAMTs genes is able to enhance ammonium uptake capacity and subsequently improves overall nitrogen use efficiency remains to be elucidated. In this work, ZmAMT1;1a-overexpression transgenic maize plants were generated with the elevated levels of transcripts and proteins, and phenotypically analyzed together with wild-type plants grown in nutrient solution under two regimes of ammonium supply. Under low ammonium nutrition (0.04 mM), in relative to wild-type plants, the maize transgenic lines showed an approximately 17% increases in the high-affinity ammonium uptake capacity of roots as revealed by 15N-labeled ammonium influx assay and further contributed to about 7% increases in the total nitrogen uptake at the whole plant level. By contrast, when ammonium was supplied in high amounts (1 mM), wild-type plants expressed higher levels of ZmAMT1;1a, but exhibited a lower ammonium uptake capacity in roots. Furthermore, the transgenic maize line accumulated more amounts of ZmAMT1;1a protein, but did not translate into an enhanced ammonium acquisition, suggesting a possible post-translational down-regulation of ZmAMT1;1a by high ammonium. This study proved the possibility to enhance ammonium acquisition by elevating ZmAMTs expression in maize roots and provided an effective transgenic approach on developing high nitrogen use efficient maize cultivars. [ABSTRACT FROM AUTHOR]

Ammonium uptake in plant roots is mediated by AMT/MEP/Rh-type ammonium transporters. Out of five AMTs being expressed in Arabidopsis roots, four AMT1-type transporters contribute to ammonium uptake, whereas no physiological function has so far been assigned to the only homolog belonging to the MEP subfamily, AMT2;1. Based on the observation that under ammonium supply, the transcript levels of AMT2;1 increased and its promoter activity shifted preferentially to the pericycle, we assessed the contribution of AMT2;1 to xylem loading. When exposed to 15 N-labeled ammonium, amt2;1 mutant lines translocated less tracer to the shoots and contained less ammonium in the xylem sap. Moreover, in an amt1;1 amt1;2 amt1;3 amt2;1 quadruple mutant ( qko ), co-expression of AMT2;1 with either AMT1;2 or AMT1;3 significantly enhanced 15 N translocation to shoots, indicating a cooperative action between AMT2;1 and AMT1 transporters. Under N deficiency, proAMT2;1-GFP lines showed enhanced promoter activity predominantly in cortical root cells, which coincided with elevated ammonium influx conferred by AMT2;1 at millimolar substrate concentrations. Our results indicate that in addition to contributing moderately to root uptake in the low-affinity range, AMT2;1 functions mainly in root-to-shoot translocation of ammonium, depending on its cell-type-specific expression in response to the plant nutritional status and to local ammonium gradients. [ABSTRACT FROM AUTHOR]

Modern maize cultivars have high nitrogen responsiveness of grain yield. However, the underlying physiological mechanism is unclear. In the present study, from 17 cultivars released from 1950 s to 2010 s in China, three maize cultivars released in 1950 s (BMY), 1970 s (ZD2), and 1990 s (ZD958) were selected according to their growth responses to nitrogen supply. Nitrogen responsiveness of shoot biomass was highest in the new cultivar ZD958, and the lowest in the old cultivar BMY, with the medium cultivar ZD2 in between. Shoot biomass was closely related to leaf elongation rate. Leaf elongation was further analyzed using kinematic analysis method. Cell division rate and cell production rate were greater and more responsive to nitrogen supply in ZD958 than in the other cultivars. In agreement, there were more cells in the elongation zone of ZD958 and they were more responsive to increasing supply, resulting a longer leaf elongation zone. The interaction effect between cultivar and nitrogen supply on leaf elongation was in consistence with the change in gibberellin (GA 1 and GA 3) concentration in leaf growth zone. Accordingly, the genes encoding gibberellin biosynthesis or signal transduction was more up-regulated in ZD958, which was positively correlated to the up-regulation of genes related to cell cycle and DNA replication. On the contrary, the genes related to the inactivation of gibberellin was more down-regulated in ZD958. Exogenous application of bioactive gibberellin or its biosynthesis inhibitor eliminated the interaction effect between cultivar and nitrogen supply on leaf elongation rate. In conclusion, modern maize breeding may have increased nitrogen responsiveness in maize by enhancing the gibberellins-dependent leaf elongation response to high nitrogen supply. • Nitrogen responsiveness is partly explained by leaf elongation rate. • Nitrogen responsiveness of leaf elongation is driven by gain in cell division. • Nitrogen-dependent gibberellin biosynthesis and signal transduction promote cell division in leaf growth zone. [ABSTRACT FROM AUTHOR]

To control gene expression by directly responding to hormone concentrations, both animal and plant cells have exploited comparable mechanisms to sense small-molecule hormones in nucleus. Whether nuclear entry of these hormones is actively transported or passively diffused, as conventionally postulated, through the nuclear pore complex, remains enigmatic. Here, we identified and characterized a jasmonate transporter in Arabidopsis thaliana , AtJAT1/AtABCG16, which exhibits an unexpected dual localization at the nuclear envelope and plasma membrane. We show that AtJAT1/AtABCG16 controls the cytoplasmic and nuclear partition of jasmonate phytohormones by mediating both cellular efflux of jasmonic acid (JA) and nuclear influx of jasmonoyl-isoleucine (JA-Ile), and is essential for maintaining a critical nuclear JA-Ile concentration to activate JA signaling. These results illustrate that transporter-mediated nuclear entry of small hormone molecules is a new mechanism to regulate nuclear hormone signaling. Our findings provide an avenue to develop pharmaceutical agents targeting the nuclear entry of small molecules. [ABSTRACT FROM AUTHOR]

In order to understand the regulation of source-sink relationship on leaf senescence in maize, we investigated the effect of pollination prevention on leaf senescence, post-silking dry matter and nitrogen accumulation and remobilization in different vegetative organs in one landrace and ten representative maize hybrids released between 1973 and 2000 in China. When pollination was prevented by covering silk with paper bags at silking stage, leaf senescence of Nongda 60, Yedan 13, Shendan 7 and Zhengdan 958 was delayed as shown by the remaining green leaf area per plant at maturity. However, pollination-prevention did not have obvious effect on the leaf senescence of Baimaya, Danyu 6, Yedan 2 and Xianyu 335. By contrast, pollination-prevention accelerated the leaf senescence of maize hybrids Zhongdan 2, Danyu13 and Yedan 4. It was found that leaf senescence of the late-released (since 1985) Chinese hybrids tended to be delayed by pollination-prevention, except XY335. From silking to physiological maturity, nitrogen content increased in the stem (plus the sheath, cob, husk, and tassel) and root of the non-pollinated plants. However, there was still a net reduction in leaf nitrogen content. We also found that pollination-prevention reduced leaf nitrogen remobilization efficiency, with genotypic difference and variation between the two years of testing. The results suggested that the response of leaf senescence to pollination-prevention is at least partially due to the change of leaf nitrogen remobilization efficiency. Leaf senescence tended to be delayed if leaf nitrogen remobilization efficiency is highly reduced by pollination-prevention. [ABSTRACT FROM AUTHOR]

Genotypic difference in nitrogen responsiveness of maize grain yield has gained considerable attention, however, the underlying physiological mechanism is less understood. Leaf area and plant type are important factors determining biomass production, and both of them are regulated by nitrogen supply. The current research aims to assess whether high nitrogen responsiveness is related to leaf growth and plant type. A 2-year field experiment was conducted with three maize cultivars (BMY, ZD2 and ZD958) differing in nitrogen responsiveness under a wide range of nitrogen supply (0, 60, 120, 180 and 240 kg N ha-1). The links between grain yield, leaf area dynamics, leaf angle and orientation value, and radiation use efficiency were investigated. Nitrogen responsiveness, defined as yield increment per unit of increased nitrogen supply, was 8.3–29.1% higher in ZD958 compared with the other cultivars. The maximum grain yield of ZD958 was 21.4–74.6% higher than that of the other cultivars. With increasing nitrogen supply, the increments in maximum leaf area and linear growth rate of leaf area were greater in ZD958, which was positively correlated with grain yield. The interaction effect between cultivar and nitrogen supply was significant on leaf length, but not on leaf width. Across the combinations between cultivar and nitrogen supply, the variation in grain yield was explained by leaf length rather than leaf width. High nitrogen supply increased leaf angle and reduced leaf orientation value, so as to make the leaf more horizontally distributed. However, this change was less significant in ZD958, indicating that the plant type was more compact under high nitrogen supply in maize cultivars with high nitrogen responsiveness. Radiation use efficiency, defined as the slope of the linear relationship between above-ground biomass produced and cumulated intercepted photosynthetic active radiation (PAR) was 5.2–13.2% higher in ZD958 than that of BMY. In conclusion, with increasing nitrogen supply, the cultivars with fast leaf growth and compact plant type have higher conversion efficiency of intercepted PAR into the above-ground biomass and get higher grain yield. • Nitrogen increased leaf area to a larger extent in the maize cultivar with high N responsiveness. • A compact plant type contributed to high N responsiveness under high N supply. • Grain yield increased via gains in radiation use efficiency under high N supply. [ABSTRACT FROM AUTHOR]

The introduction of new hybrids and integrated crop-soil management has been causing maize grain yield to increase. However, less attention has been paid on the nutrient concentration of the grain; this aspect is of great importance to supplying calories and nutrients in the diets of both humans and animals worldwide. Increasing the retranslocation of nutrients from vegetative organs to grain can effectively increase the nutrient concentration of grain and general nutrient use efficiency. The present study involved monitoring the dynamic change of macro- and micronutrients in different organs of maize during the grain filling stage. In addition, the mobility of different elements and their contribution to grain nutrient content were evaluated in a 2-year experiment under low (LN, no N supplied) and high N (HN, 180 kg N ha −1 ) supply. Under HN supply, the net remobilization efficiency ( RE ) of the vegetative organs as a whole (calculated as nutrient remobilization amount divided by nutrient content at silking) of N, P, K, Mn, and Zn were 44%, 60%, 13%, 15%, and 25%, respectively. The other nutrients (Mg, Ca, Fe, Cu, and B) showed a net accumulation in the vegetative organs as a whole during the grain filling stage. Among the different organs, N, P, and Zn were remobilized more from the leaves ( RE of 44%, 51% and 43%, respectively) and the stalks (including leaf sheaths and tassels) ( RE of 48%, 71% and 43%, respectively). K was mainly remobilized from the leaves with RE of 51%. Mg, Ca, Fe, Mn, and Cu were mostly remobilized from the stalks with the RE of 23%, 9%, 10%, 42%, and 28%, respectively. However, most of the remobilized Mg, Ca, Fe, Mn, Cu, and Zn were translocated to the husk and cob, which seemingly served as the buffer sink for these nutrients. The RE s of all the nutrients except for P, K, and Zn were vulnerable to variations in conditions annually and were reduced when the grain yield and harvest index were lower in 2014 compared with 2013. Under LN stress, the RE was reduced in P and Zn in 2013, increased in Cu and unchanged in other nutrients. The concentration of these nutrients in the grain was either unchanged (P, K, Ca, Zn, and B) or decreased (N, Mg, Fe, Mn, and Cu). It is concluded that grain N, P, K, Mn, and Zn, but not Mg, Ca, Fe, Cu, and B concentration, can be improved by increasing their remobilization from vegetative organs. However, enhancing the senescence of maize plant via LN stress seems unable to increase grain mineral nutrient concentration. Genetic improvement aiming to increase nutrient remobilization should take into account the organ-specific remobilization pattern of the target nutrient. [ABSTRACT FROM AUTHOR]

Increasing the response of maize yield to nitrogen (N) application is essential for food security and economic benefits of the farmers. However, the physiological mechanism underlining N responsiveness is unclear. Three maize cultivars with different N-responsiveness, BMY (the low), ZD2 (the medium) and ZD958 (the high) were grown in the field under a wide range of N supply (from 0 to 240 kg N per ha) in two years. Plant growth rate, plant N uptake rate, ear growth rate and ear N allocation rate, and their relationship to grain yield formation were investigated during the early critical period (14 days before silking). The direct path coefficient of grain number to grain yield was 0.82, which explained 96% of the variation in grain yield (R2 = 0.91). There was not a trade-off between grain number and other yield components. ZD958 got more grains per ear than the other cultivars in response to N supplies. The variation in grain number was mostly explained by the number of floret primordia (57% for BMY, 93% for ZD2 and ZD958). When N supply increased from 0 to 240 kg N ha-1, ZD2 and ZD958 did not differ in nitrogen nutrition index, and were 7.2–32.8% higher than BMY. The number of grains and floret primordia was independent of plant growth rate and plant N uptake rate, although these rates increased with N supply. Ear growth rate and ear N allocation rate of ZD958 were higher compared with the other cultivars, especially under high N supply. Except BMY, the number of floret primordium and grain per ear depended on ear growth rate and ear N allocation rate. There was a positive correlation between ear growth rate and ear N allocation rate in ZD2 and ZD958. However, ear N allocation rate of BMY did not increase when its ear growth rate was greater than 19.2 mg oC-1. It is concluded that, with increasing N supply, N-responsive maize cultivars had high ear growth rate and allocated more N into the ear during the early critical period, which enhanced the differentiation of floret primordia, hence increasing grain number and final grain yield. • High N-responsiveness of grain yield depends on grain number per ear. • Genotypic variation in grains number is explained by floret primordium development. • Floret primordium number in response to N depends on ear growth and ear N allocation. [ABSTRACT FROM AUTHOR]

Although the remobilization of vegetative nitrogen (N) and post-silking N both contribute to grain N in maize (Zea mays L.), their regulation by grain sink strength is poorly understood. Here we use 15N labeling to analyze the dynamic behaviors of both pre- and post-silking N in relation to source and sink manipulation in maize plants. The results showed that the remobilization of pre-silking N started immediately after silking and the remobilized pre-silking N had a greater contribution to grain N during early grain filling, with post-silking N importance increasing during the later filling stage. The amount of post-silking N uptake was largely driven by post-silking dry matter accumulation in both grain as well as vegetative organs. Prevention of pollination during silking had less effect on post-silking N uptake, as a consequence of compensatory growth of stems, husk + cob and roots. Also, leaves continuously export N even though grain sink was removed. The remobilization efficiency of N in the leaf and stem increased with increasing grain yield (hence N requirement). It is suggested that the remobilization of N in the leaf is controlled by sink strength but not the leaf per se. Enhancing post-silking N uptake rather than N remobilization is more likely to increase grain N accumulation. [ABSTRACT FROM AUTHOR]

A plant's ability to maintain or improve its yield under limiting conditions, such as nutrient deficiency or drought, can be strongly influenced by root system architecture (RSA), the three-dimensional distribution of the different root types in the soil. The ability to image, track and quantify these root system attributes in a dynamic fashion is a useful tool in assessing desirable genetic and physiological root traits. Recent advances in imaging technology and phenotyping software have resulted in substantive progress in describing and quantifying RSA. We have designed a hydroponic growth system which retains the three-dimensional RSA of the plant root system, while allowing for aeration, solution replenishment and the imposition of nutrient treatments, as well as high-quality imaging of the root system. The simplicity and flexibility of the system allows for modifications tailored to the RSA of different crop species and improved throughput. This paper details the recent improvements and innovations in our root growth and imaging system which allows for greater image sensitivity (detection of fine roots and other root details), higher efficiency, and a broad array of growing conditions for plants that more closely mimic those found under field conditions. [ABSTRACT FROM AUTHOR]

Maize ( Zea mays L.) root morphology exhibits a high degree of phenotypic plasticity to nitrogen (N) deficiency, but the underlying genetic architecture remains to be investigated. Using an advanced BC4F3 population, we investigated the root growth plasticity under two contrasted N levels and identified the quantitative trait loci (QTLs) with QTL-environment (Q × E) interaction effects. Principal components analysis (PCA) on changes of root traits to N deficiency (ΔLN-HN) showed that root length and biomass contributed for 45.8% in the same magnitude and direction on the first PC, while root traits scattered highly on PC2 and PC3. Hierarchical cluster analysis on traits for ΔLN-HN further assigned the BC4F3 lines into six groups, in which the special phenotypic responses to N deficiency was presented. These results revealed the complicated root plasticity of maize in response to N deficiency that can be caused by genotype-environment (G × E) interactions. Furthermore, QTL mapping using a multi-environment analysis identified 35 QTLs for root traits. Nine of these QTLs exhibited significant Q × E interaction effects. Taken together, our findings contribute to understanding the phenotypic and genotypic pattern of root plasticity to N deficiency, which will be useful for developing maize tolerance cultivars to N deficiency. [ABSTRACT FROM AUTHOR]

Efficient nitrogen (N) utilization is crucial for maintaining grain yield under low N input. Less is known about the role of within-plant N allocation and reallocation on ear development and the factors determining N allocation during the critical period around silking. In this study, two maize hybrids, ZD958 (N-efficient) and LY99 (N-inefficient), were evaluated in a 2-year field experiment under two N rates (60 and 180 kg N ha-1). N transport and allocation into the ear during critical period were investigated using 15N stable isotopic tracer. The number and area of vascular bundles in ear shank, above- and below-ear internode were measured. The two hybrids did not differ in grain yields under high N rate. However, the grain yield of ZD958 was 43.6% higher than that of LY99 under low N rate, deriving from 26.3% and 13.9% increment in grain number and grain weight, respectively. At early critical growth stage before silking, ZD958 increased allocation of soil-derived N to the ear by 225.2% compared with LY99 under low N rate. At late critical growth stage after silking, ZD958 increased allocation of soil-derived N and reallocation of vegetative-N to the ear by 45.5% and 116.6%, respectively, compared with LY99 under low N rate. As a result, ear growth rate and ear N content of ZD958 was 22.2% and 69.1% higher than that of LY99 at the end of critical period. During N allocation and N reallocation, the lower leaves were sacrificed and the N status of the ear leaf and upper leaves was mostly maintained to sustain photosynthesis. In the ear shank, flux rate and N concentration of the xylem sap in ZD958 were 53.1% and 32.5% greater at silking stage, and were 40.8% and 27.5% greater at 14-days after silking, respectively, compared with LY99 under low N rate. Correspondingly, the number and average area of big vascular bundles in ear shank of ZD958 were 56.2% and 31.0% greater compared with LY99. Parameters characterizing the number and area of big vascular bundles were positively correlated with N allocation and grain yield, while that of small vascular bundles were negative. It is concluded that efficient N allocation to the ear at critical period is essential for ear growth and the subsequent vegetative-N remobilization, so as to improve low-N tolerance in high-yielding maize hybrids. A superior vascular system around the ear, especially in the ear shank, can enhance N allocation into the ear and could be regarded as a physiological selection trait in maize breeding to improve nitrogen use efficiency. [Display omitted] • N-efficient cultivar developed more and heavier grains under low-N stress. • N-efficient cultivar allocated more soil-derived N to the ear before silking. • N-efficient cultivar reallocated more vegetative-N to the ear after silking. • Less N was allocated to and more N was reallocated from the lower leaves and stem. • A superior vascular system contributed to efficient N allocation and reallocation. [ABSTRACT FROM AUTHOR]

Key message: Understanding the correlations of seven minerals for concentration, content and yield in maize grain, and exploring their genetic basis will help breeders to develop high grain quality maize. Abstract: Biofortification by enhanced mineral accumulation in grain through genetic improvement is an efficient way to solve global nutrient malnutrition, in which one key step is to detect the underlying quantitative trait loci (QTL). Herein, a maize recombinant inbred population (RIL) was field grown to maturity across four environments (two locations × two years). Phenotypic data for grain mineral concentration, content and yield were determined for copper (Cu), iron (Fe), manganese (Mn), zinc (Zn), magnesium (Mg), potassium (K) and phosphorus (P). Significant effects of genotype, location and year were observed for all investigated traits. The strongest location effects were found for Zn accumulation traits probably due to distinct soil Zn availabilities across locations. Heritability ( H) of different traits varied with higher H (72-85 %) for mineral concentration and content, and lower (48-63 %) for mineral yield. Significant positive correlations for grain concentration were revealed between several minerals. QTL analysis revealed 28, 25, and 12 QTL for mineral concentration, content and yield, respectively; and identified 8 stable QTL across at least two environments. All these QTL were assigned into 12 distinct QTL clusters. A cluster at chromosome Bin 6.07/6.08 contained 6 QTL for kernel weight, mineral concentration (Mg) and content (Zn, K, Mg, P). Another cluster at Bin 4.05/4.06 contained a stable QTL for Mn concentration, which were previously identified in other maize and rice RIL populations. These results highlighted the phenotypic and genetic performance of grain mineral accumulation, and revealed two promising chromosomal regions for genetic improvement of grain biofortification in maize. [ABSTRACT FROM AUTHOR]

Root breeding has been proposed as a key factor in the “second green revolution” for increasing crop yield and the efficient use of nutrient and water resources. However, few studies have demonstrated that the genetic improvement of root characteristics directly contributes to enhancing nutrient-use-efficiency in crops. In this study, we evaluated the contribution of root growth improvement to efficient nitrogen (N) acquisition and grain yield under two different N-levels in a 3-year field experiment. We used two near-isogenic maize testcrosses, T-213 (large-root) and T-Wu312 (small-root), derived from a backcross of a BC 4 F 3 population from two parents (Ye478 and Wu312) with contrasting root size. We found that the root length density, root surface area, and dry weight at the silking stage were 9.6–19.5% higher in T-213 compared with the control T-Wu312. The root distribution pattern in the soil profile showed no significant differences between the two genotypes. The overall increase in root growth in T-213 enhanced post-silking N uptake, which increased grain yield by 17.3%. Correspondingly, soil nitrate concentrations in the >30 cm soil layer were reduced in T-213 under the high N treatment. These positive effects occurred under both adequate and inadequate N-supply and different weather conditions. Our study provides a successful case that increasing root size via genetic manipulation contributes directly to efficient N-uptake and higher yield. [ABSTRACT FROM AUTHOR]

Nitrogen (N), the most important mineral nutrient for plants, is critical to agricultural production systems. N deficiency severely affects rice growth and decreases rice yields. However, excessive use of N fertilizer has caused severe pollution to agricultural and ecological environments. The necessity of breeding of crops that require lower input of N fertilizer has been recognized. Here we identified a major quantitative trait locus on chromosome 12, Tolerance Of Nitrogen Deficiency 1 ( TOND1), that confers tolerance to N deficiency in the indica cultivar Teqing. Sequence verification of 75 indica and 75 japonica cultivars from 18 countries and regions demonstrated that only 27.3% of cultivars (41 indica cultivars) contain TOND1, whereas 72.7% of cultivars, including the remaining 34 indica cultivars and all 75 japonica cultivars, do not harbor the TOND1 allele. Over-expression of TOND1 increased the tolerance to N deficiency in the TOND1-deficient rice cultivars. The identification of TOND1 provides a molecular basis for breeding rice varieties with improved grain yield despite decreased input of N fertilizers. [ABSTRACT FROM AUTHOR]

A target in crop production is to simultaneously increase grain yield (GY) and grain nitrogen concentration (GNC). In maize, nitrogen (N) and genotype are two major factors affecting GY and GNC. Both N remobilization from vegetative tissues and post-silking N uptake contribute to grain N, but their relative contributions are genotype specific, and are affected by the N application rate. It is unclear whether the responses of GY and GNC to N application differ between genotypes with different post-silking N uptake and vegetative N remobilization characteristics. We investigated the effect of N application rate on post-silking N uptake, vegetative N remobilization, GY, and GNC of two high-yielding maize hybrids, ZD958 and XY335, which have contrasting N remobilization characteristics. We tested five N application rates (0, 60, 120, 180, 240 kg N ha −1 ) in a 4-year field study (from 2010 to 2013). There was a significant year × N × genotype interaction in the amount of vegetative N remobilization and N remobilization efficiency (NRE), and residual stalk N concentration at maturity. Compared with the low-NRE cultivar ZD958, XY335 showed the same GY but higher GNC because it had higher vegetative N remobilization, NRE but lower residual stalk N concentration under the favorable weather condition in 2010. The response of GNC to increasing N levels was the same between XY335 and ZD958 and was not affected by year conditions. The N level required to obtain the highest GY was the same in the two hybrids (156 ± 13 kg ha −1 and 159 ± 19 kg ha −1 ), but that required to obtain the highest GNC was greater in XY335 (216 ± 30 kg ha −1 ) than in ZD958 (195 ± 23 kg ha −1 ). From these results, we conclude that precise N fertilizer management as well as the selection of high-yielding hybrids with high NRE can increase GNC without negatively affecting GY or leading to surplus N storage in vegetative organs. [ABSTRACT FROM AUTHOR]

Producing more food with less input is imperative in feeding the increasing world population. Here, for the first time we characterize the multipartite responses of maize to nutrient-rich patches and demonstrate significant synergistic effects between root morphological and physiological responses on improving nutrient-use efficiency and yield. Our results showed that maize root length, lateral root formation, acid phosphatase (APase) secretion, and expression of ammonium transporter genes increased in the ammonium-containing patches; moreover, ammonium-induced rhizosphere acidification enhanced activity of APase. These root responses were associated with improved maize nutrition and growth even with reduced fertilizer input, suggesting an adaptive benefit of synergistic root foraging strategies. These new findings improve our understanding of root-foraging responses to nutrient-specific cues and are crucial for engineering root and rhizosphere properties to improve nutrient-use efficiency for sustainable crop production. • Producing more food with less input is imperative for sustainable intensification of agriculture. • Rhizosphere dynamics is key to controlling nutrient-use efficiency (NUE). • Localized nutrient-supply maximizes root/rhizosphere efficiency for improving NUE. • Harnessing root foraging provides a new approach for sustainable maize production. [ABSTRACT FROM AUTHOR]