Contents Summary 35 I. Introduction 35 II. Nitrogen acquisition and assimilation 36 III. Root-to-shoot transport of nitrogen 38 IV. Nitrogen storage pools in vegetative tissues 39 V. Nitrogen transport from source leaf to sink 40 VI. Nitrogen import into sinks 42 VII. Relationship between source and sink nitrogen transport processes and metabolism 43 VIII. Regulation of nitrogen transport 43 IX. Strategies for crop improvement 44 X. Conclusions 46 Acknowledgements 47 References 47 SUMMARY: Nitrogen is an essential nutrient for plant growth. World-wide, large quantities of nitrogenous fertilizer are applied to ensure maximum crop productivity. However, nitrogen fertilizer application is expensive and negatively affects the environment, and subsequently human health. A strategy to address this problem is the development of crops that are efficient in acquiring and using nitrogen and that can achieve high seed yields with reduced nitrogen input. This review integrates the current knowledge regarding inorganic and organic nitrogen management at the whole-plant level, spanning from nitrogen uptake to remobilization and utilization in source and sink organs. Plant partitioning and transient storage of inorganic and organic nitrogen forms are evaluated, as is how they affect nitrogen availability, metabolism and mobilization. Essential functions of nitrogen transporters in source and sink organs and their importance in regulating nitrogen movement in support of metabolism, and vegetative and reproductive growth are assessed. Finally, we discuss recent advances in plant engineering, demonstrating that nitrogen transporters are effective targets to improve crop productivity and nitrogen use efficiency. While inorganic and organic nitrogen transporters were examined separately in these studies, they provide valuable clues about how to successfully combine approaches for future crop engineering.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/nph.14876

Source and sink mechanisms of nitrogen transport and use

Heavy metal accumulation and signal transduction in herbaceous and woody plants: Paving the way for enhancing phytoremediation efficiency.

Application of chemical fertilizers, especially nitrogen (N), to crops has increased dramatically in the last half century and therefore developing crop varieties with improved N use efficiency (NUE) is urgent for sustainable agriculture. N utilization procedures generally can be divided into uptake, transport, and assimilation. Transporters for nitrate or ammonium acquisition and enzymes for assimilation are among the essential components determining NUE, and many transcription factors also play a pivotal role in regulating N use-associated genes, thereby contributing to NUE. Although some efforts in improving NUE have been made in various plants, the regulatory mechanisms underlying NUE are still elusive, and NUE improvement in crop breeding is very limited. In this review, the crucial components involved in N utilization and the candidates with the potential for NUE improvement in dicot Arabidopsis and monocot rice are summarized. In addition, strategies based on new techniques which can be used for dissecting regulatory mechanisms of NUE and also the possible ways in which NUE can be improved in crops are discussed.

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Nitrogen use efficiency in crops: lessons from Arabidopsis and rice.

We summarize nitrate transporters and discuss their potential in breeding for improved nitrogen use efficiency and yield.

Plant nitrate transporters: from gene function to application

Nitrogen (N) is a major driving force for crop yield improvement, but application of high levels of N delays flowering, prolonging maturation and thus increasing the risk of yield losses. Therefore, traits that enable utilization of high levels of N without delaying maturation will be highly desirable for crop breeding. Here, we show that OsNRT1.1A (OsNPF6.3), a member of the rice (Oryza sativa) nitrate transporter 1/peptide transporter family, is involved in regulating N utilization and flowering, providing a target to produce high yield and early maturation simultaneously. OsNRT.1A has functionally diverged from previously reported NRT1.1 genes in plants and functions in upregulating the expression of N utilization-related genes not only for nitrate but also for ammonium, as well as flowering-related genes. Relative to the wild type, osnrt1.1a mutants exhibited reduced N utilization and late flowering. By contrast, overexpression of OsNRT1.1A in rice greatly improved N utilization and grain yield, and maturation time was also significantly shortened. These effects were further confirmed in different rice backgrounds and also in Arabidopsis thaliana Our study paves a path for the use of a single gene to dramatically increase yield and shorten maturation time for crops, outcomes that promise to substantially increase world food security.

/pdf/expression-of-the-nitrate-transporter-gene-osnrt1-1a-osnpf6-1q1p1felc4.pdf

Expression of the Nitrate Transporter Gene OsNRT1.1A/OsNPF6.3 Confers High Yield and Early Maturation in Rice

The importance of the nitrate (NO3-) transporter for yield and nitrogen-use efficiency (NUE) in rice was previously demonstrated using map-based cloning. In this study, we enhanced the expression of the OsNRT2.1 gene, which encodes a high-affinity NO3- transporter, using a ubiquitin (Ubi) promoter and the NO3--inducible promoter of the OsNAR2.1 gene to drive OsNRT2.1 expression in transgenic rice plants. Transgenic lines expressing pUbi:OsNRT2.1 or pOsNAR2.1:OsNRT2.1 constructs exhibited the increased total biomass including yields of approximately 21% and 38% compared with wild-type (WT) plants. The agricultural NUE (ANUE) of the pUbi:OsNRT2.1 lines decreased to 83% of that of the WT plants, while the ANUE of the pOsNAR2.1:OsNRT2.1 lines increased to 128% of that of the WT plants. The dry matter transfer into grain decreased by 68% in the pUbi:OsNRT2.1 lines and increased by 46% in the pOsNAR2.1:OsNRT2.1 lines relative to the WT. The expression of OsNRT2.1 in shoot and grain showed that Ubi enhanced OsNRT2.1 expression by 7.5-fold averagely and OsNAR2.1 promoters increased by about 80% higher than the WT. Interestingly, we found that the OsNAR2.1 was expressed higher in all the organs of pUbi:OsNRT2.1 lines; however, for pOsNAR2.1:OsNRT2.1 lines, OsNAR2.1 expression was only increased in root, leaf sheaths and internodes. We show that increased expression of OsNRT2.1, especially driven by OsNAR2.1 promoter, can improve the yield and NUE in rice.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/pbi.12531

Agronomic nitrogen-use efficiency of rice can be increased by driving OsNRT2.1 expression with the OsNAR2.1 promoter.

Over-expression of OsPTR6 in rice increased plant growth at different nitrogen supplies but decreased nitrogen use efficiency at high ammonium supply

Summary
The nitrate (NO3-) transporter has been selected as an important gene maker in the process of environmental adoption in rice cultivars. In this work, we transfered another native OsNAR2.1 promoter with driving OsNAR2.1 gene into rice plants. The transgenic lines with exogenous pOsNAR2.1:OsNAR2.1 constructs showed enhanced OsNAR2.1 expression level, compared with wild type (WT), and 15N influx in roots increased 21–32% in response to 0.2 mM and 2.5 mM 15NO3− and 1.25 mM 15NH415NO3. Under these three N conditions, the biomass of the pOsNAR2.1:OsNAR2.1 transgenic lines increased 143, 129, and 51%, and total N content increased 161, 242, and 69%, respectively, compared to WT. Furthermore in field experiments we fould the grain yield, agricultural nitrogen use efficiency (ANUE), and dry matter transfer of pOsNAR2.1:OsNAR2.1 plants increased by about 21, 22, and 21%, compared to WT. We also compared the phenotypes of pOsNAR2.1:OsNAR2.1 and pOsNAR2.1:OsNRT2.1 transgenic lines in the field, found that post-anthesis N uptake differed significantly between them, and in comparison with the WT. Post-anthesis N uptake (PANU) increased approximately 39% and 85%, in the pOsNAR2.1:OsNAR2.1 and pOsNAR2.1:OsNRT2.1 transgenic lines, respectively, possibly because OsNRT2.1 expression was less in the pOsNAR2.1:OsNAR2.1 lines than in the pOsNAR2.1:OsNRT2.1 lines during the late growth stage. These results show that rice NO3– uptake, yield, and NUE were improved by increased OsNAR2.1 expression via its native promoter.

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https://onlinelibrary.wiley.com/doi/pdf/10.1111/pbi.12714

pOsNAR2.1:OsNAR2.1 expression enhances nitrogen uptake efficiency and grain yield in transgenic rice plants.

The NO3 - transporter plays an important role in rice nitrogen acquisition and nitrogen-use efficiency. Our previous studies have shown that the high affinity systems for nitrate uptake in rice is mediated by a two-component NRT2/NAR2 transport system. In this study, transgenic plants were successful developed by overexpression of OsNAR2.1 alone, OsNRT2.3a alone and co-overexpression of OsNAR2.1 and OsNRT2.3a. Our field experiments indicated that transgenic lines expressing p35S:OsNAR2.1 or p35S:OsNAR2.1-p35S:OsNRT2.3a constructs exhibited increased grain yields of approximately 14.1% and 24.6% compared with wild-type (cv. Wuyunjing 7, WT) plants, and the agricultural nitrogen use efficiency increased by 15.8% and 28.6%, respectively. Compared with WT, the 15N influx in roots of p35S:OsNAR2.1 and p35S: OsNAR2.1-p35S:OsNRT2.3a lines increased 18.9%‑27.8% in response to 0.2 mM, 2.5 mM 15NO3 -, and 1.25 mM 15NH4 15NO3, while there was no significant difference between p35S:OsNAR2.1 and p35S:OsNAR2.1-p35S:OsNRT2.3a lines; only the 15N distribution ratio of shoot to root for p35S:OsNAR2.1-p35S:OsNRT2.3a lines increased significantly. However, there were no significant differences in nitrogen use efficiency, 15N influx in roots and the yield between the p35S:NRT2.3a transgenic lines and WT. This study indicated that co-overexpression of OsNAR2.1 and OsNRT2.3a could increase rice yield and nitrogen use efficiency.

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Co-Overexpression of OsNAR2.1 and OsNRT2.3a Increased Agronomic Nitrogen Use Efficiency in Transgenic Rice Plants.

Cadmium (Cd), as a heavy metal, presents substantial biological toxicity and has harmful effects on human health To lower the ingress levels of human Cd, it is necessary for Cd content in food crops to be reduced, which is of considerable significance for ensuring food safety This review will summarize the genetic traits of Cd accumulation in rice and examine the mechanism of Cd uptake and translocation in rice The status of genes related to Cd stress and Cd accumulation in rice in recent years will be summarized, and the genes related to Cd accumulation in rice will be classified according to their functions In addition, an overview of quantitative trait loci (QTLs) mapping populations in rice will be introduced, aiming to provide a theoretical reference for the breeding of rice varieties with low Cd accumulation Finally, existing problems and prospects will be put forward

Jingguang Chen

Papers

Agronomic nitrogen-use efficiency of rice can be increased by driving OsNRT2.1 expression with the OsNAR2.1 promoter.

Over-expression of OsPTR6 in rice increased plant growth at different nitrogen supplies but decreased nitrogen use efficiency at high ammonium supply

pOsNAR2.1:OsNAR2.1 expression enhances nitrogen uptake efficiency and grain yield in transgenic rice plants.

Co-Overexpression of OsNAR2.1 and OsNRT2.3a Increased Agronomic Nitrogen Use Efficiency in Transgenic Rice Plants.

Advances in the Uptake and Transport Mechanisms and QTLs Mapping of Cadmium in Rice