Genome-wide associated study identifies NAC42-activated nitrate transporter conferring high nitrogen use efficiency in rice

Phylogeny and gene expression of the complete NITRATE TRANSPORTER 1/PEPTIDE TRANSPORTER FAMILY in Triticum aestivum

NPF genes encode membrane transporters involved in the transport of a large variety of substrates including nitrate and peptides. The NPF gene family has been described for many plants, but the whole NPF gene family for wheat has not been completely identified. The release of the wheat reference genome has enabled the identification of the entire wheat NPF gene family. A systematic analysis of the whole wheat NPF gene family was performed, including responses of specific gene expression to development and nitrogen supply. A total of 331 NPF genes (113 homoeologous groups) have been identified in wheat. The chromosomal location of the NPF genes is unevenly distributed, with predominant occurrence in the long arms of the chromosomes. The phylogenetic analysis indicated that wheat NPF genes are closely clustered with Arabidopsis, Brachypodium, and rice orthologues, and subdivided into eight subfamilies. The expression profiles of wheat NPF genes were examined using RNA-seq data, and a subset of 44 NPF genes (homoeologous groups) with contrasting expression responses to nitrogen and/or development in different tissues were identified. The systematic identification of gene composition, chromosomal locations, evolutionary relationships, and expression profiles contributes to a better understanding of the roles of the wheat NPF genes and lays the foundation for further functional analysis in wheat.

Nitrate in 2020: Thirty Years from Transport to Signaling Networks

Nitrogen (N) is an essential macronutrient for plants and a major limiting factor for plant growth and crop production. Nitrate is the main source of N available to plants in agricultural soils and in many natural environments. Sustaining agricultural productivity is of paramount importance in the current scenario of increasing world population, diversification of crop uses, and climate change. Plant productivity for major crops around the world, however, is still supported by excess application of N-rich fertilizers with detrimental economic and environmental impacts. Thus, understanding how plants regulate nitrate uptake and metabolism is key for developing new crops with enhanced N use efficiency and to cope with future world food demands. The study of plant responses to nitrate has gained considerable interest over the last 30 years. This review provides an overview of key findings in nitrate research, spanning biochemistry, molecular genetics, genomics, and systems biology. We discuss how we have reached our current view of nitrate transport, local and systemic nitrate sensing/signaling, and the regulatory networks underlying nitrate-controlled outputs in plants. We hope this summary will serve not only as a timeline and information repository but also as a baseline to define outstanding questions for future research.

Genome-wide identification of the peptide transporter family in rice and analysis of the PTR expression modulation in two near-isogenic lines with different nitrogen use efficiency

BACKGROUND

Nitrogen (N) is a major nutrient element for crop growth. In plants, the members of the peptide transporter (PTR) gene family may involve in nitrate uptake and transport. Here, we identified PTR gene family in rice and analyzed their expression profile in near-isogenic lines.

RESULTS

We identified 96, 85 and 78 PTR genes in Nipponbare, R498 and Oryza glaberrima, and the phylogenetic trees were similar in Asian cultivated rice and African cultivated rice. The number of PTR genes was higher in peanut (125) and soybean (127). The 521 PTR genes in rice, maize, sorghum, peanut, soybean and Arabidopsis could be classified into 4 groups, and their distribution was different between monocots and dicots. In Nipponbare genome, the 25 PTR genes were distributed in 5 segmental duplication regions on chromosome 1, 2, 3, 4, 5, 7, 8, 9, and 10. The PTR genes in rice have 0-11 introns and 1-12 exons, and 16 of them have the NPF (NRT1/PTR family) domain. The results of RNA-seq showed that the number of differentially expressed genes (DEGs) between NIL15 and NIL19 at three stages were 928, 1467, and 1586, respectively. Under low N conditions, the number of differentially expressed PTR genes increased significantly. The RNA-seq data was analyzed using WGCNA to predict the potential interaction between genes. We classified the genes with similar expression pattern into one module, and obtained 25 target modules. Among these modules, three modules may be involved in rice N uptake and utilization, especially the brown module, in which hub genes were annotated as protein kinase that may regulate rice N metabolism.

CONCLUSIONS

In this study, we comprehensively analyzed the PTR gene family in rice. 96 PTR genes were identified in Nippobare genome and 25 of them were located on five large segmental duplication regions. The Ka/Ks ratio indicated that many PTR genes had undergone positive selection. The RNA-seq results showed that many PTR genes were involved in rice nitrogen use efficiency (NUE), and protein kinases might play an important role in this process. These results provide a fundamental basis to improve the rice NUE via molecular breeding.

Improvement of nutrient use efficiency in rice: current toolbox and future perspectives

Modern agriculture relies heavily on chemical fertilizers, especially in terms of cereal production. The excess application of fertilizers not only increases production cost, but also causes severe environmental problems. As one of the major cereal crops, rice (Oryza sativa L.) provides the staple food for nearly half of population worldwide, especially in developing countries. Therefore, improving rice yield is always the priority for rice breeding. Macronutrients, especially nitrogen (N) and phosphorus (P), are two most important players for the grain yield of rice. However, with economic development and improved living standard, improving nutritional quality such as micronutrient contents in grains has become a new goal in order to solve the "hidden hunger." Micronutrients, such as iron (Fe), zinc (Zn), and selenium (Se), are critical nutritional elements for human health. Therefore, breeding the rice varieties with improved nutrient use efficiency (NUE) is thought to be one of the most feasible ways to increase both grain yield and nutritional quality with limited fertilizer input. In this review, we summarized the progresses in molecular dissection of genes for NUE by reverse genetics on macronutrients (N and P) and micronutrients (Fe, Zn, and Se), exploring natural variations for improving NUE in rice; and also, the current genetic toolbox and future perspectives for improving rice NUE are discussed.

Nitrogen Use Efficiency Phenotype and Associated Genes: Roles of Germination, Flowering, Root/Shoot Length and Biomass

Crop improvement for Nitrogen Use Efficiency (NUE) requires a well-defined phenotype and genotype, especially for different N-forms. As N-supply enhances growth, we comprehensively evaluated 25 commonly measured phenotypic parameters for N response using 4 N treatments in six indica rice genotypes. For this, 32 replicate potted plants were grown in the green-house on nutrient-depleted sand. They were fertilized to saturation with media containing either nitrate or urea as the sole N source at normal (15 mM N) or low level (1.5 mM N). The variation in N-response among genotypes differed by N form/dose and increased developmentally from vegetative to reproductive parameters. This indicates survival adaptation by reinforcing variation in every generation. Principal component analysis segregated vegetative parameters from reproduction and germination. Analysis of variance revealed that relative to low level, normal N facilitated germination, flowering and vegetative growth but limited yield and NUE. Network analysis for the most connected parameters, their correlation with yield and NUE, ranking by Feature selection and validation by Partial least square discriminant analysis enabled shortlisting of eight parameters for NUE phenotype. It constitutes germination and flowering, shoot/root length and biomass parameters, six of which were common to nitrate and urea. Field-validation confirmed the NUE differences between two genotypes chosen phenotypically. The correspondence between multiple approaches in shortlisting parameters for NUE makes it a novel and robust phenotyping methodology of relevance to other plants, nutrients or other complex traits. Thirty-Four N-responsive genes associated with the phenotype have also been identified for genotypic characterization of NUE.

Novel Aspects of Nitrate Regulation in Arabidopsis

Nitrogen (N) is one of the most essential macronutrients for plant growth and development. Nitrate (NO₃ ^-), the major form of N that plants uptake from the soil, acts as an important signaling molecule in addition to its nutritional function. Over the past decade, significant progress has been made in identifying new components involved in NO₃ ^- regulation and starting to unravel the NO₃ ^- regulatory network. Great reviews have been made recently by scientists on the key regulators in NO₃ ^- signaling, NO₃ ^- effects on plant development, and its crosstalk with phosphorus (P), potassium (K), hormones, and calcium signaling. However, several novel aspects of NO₃ ^- regulation have not been previously reviewed in detail. Here, we mainly focused on the recent advances of post-transcriptional regulation and non-coding RNA (ncRNAs) in NO₃ ^- signaling, and NO₃ ^- regulation on leaf senescence and the circadian clock. It will help us to extend the general picture of NO₃ ^- regulation and provide a basis for further exploration of NO₃ ^- regulatory network.