What we know about plant arginases?

Exploration of Freshness Identification Method for Refrigerated Vegetables Based on Metabolomics

Background: The rapid development of refrigerated transportation technology for fresh vegetables has extended their shelf life. Some vegetables may appear undamaged on the surface, but their freshness may have decreased, often resulting in the phenomenon of passing off inferior vegetables as good. It is very important to establish a detection method for identifying and assessing the freshness of vegetables. Methods: Therefore, based on metabolomics methods, this study innovatively employed UHPLC-Q-Exactive Orbitrap MS and GC-MS techniques to investigate the metabolites in the refrigerated storage of four vegetables, namely chard (Beta vulgaris var. cicla L), lettuce (Lactuca sativa var. ramose Hort.), crown daisy (Glebionis coronaria (L.) Cass. ex Spach), and tomato (Solanum lycopersicum L.), exploring key biomarkers for assessing their freshness. UPLC-TQ MS was used for the quantitative analysis of key metabolites. Results: The results showed that arginine biosynthesis and the metabolism of alanine, aspartate, and glutamate are key pathways in vegetable metabolism. Four key metabolites were selected from chard, five from lettuce, three from crown daisy, and five from tomato. Conclusions: Comparing the content of substances such as alanine and arginine can help infer the freshness and nutritional value of the vegetables, providing important references for detecting spoilage, determining storage time, and improving transportation conditions. This research holds significant relevance for the vegetable transportation industry.

Spatial organization of putrescine synthesis in plants

Three plant pathways for the synthesis of putrescine have been described to date. These are the synthesis of putrescine from ornithine, by ornithine decarboxylase (ODC); the synthesis of putrescine from arginine by arginine decarboxylase, agmatine iminohydrolase (AIH) and N-carbamoylputrescine amidohydrolase (NLP1); and arginine decarboxylase and agmatinase. To address how these pathways are organized in plants, we have used transient expression analysis of these genes in the leaves of Nicotiana benthamiana. Brassicas do not have ODC, but the single ODC gene from rice and one of the soybean genes, were localized to the ER. Transient expression of the rice agmatinase gene showed that it was localized to the mitochondria. In A. thaliana there are five isoforms of AIH and three isoforms of NLP1. Stable GFP-tagged transformants of the longest isoforms of AIH and NLP1 showed that both proteins were localized to the ER, but in tissues with chloroplasts, the localization was concentrated to lamellae adjacent to chloroplasts. Transient expression analyses showed that four of the isoforms of AIH and all of the isoforms of NLP1 were localized to the ER. However, AIH.4 was localized to the chloroplast. Combining these results with other published data, reveal that putrescine synthesis is excluded from the cytoplasm and is spatially localized to the chloroplast, ER, and likely the mitochondria. Synthesis of putrescine in the ER may facilitate cell to cell transport via plasmodesmata, or secretion via vesicles. Differential expression of these pathways may enable putrescine-mediated activation of hormone-responsive genes.

Transcriptome and metabolome reveal the primary and secondary metabolism changes in Larix gmelinii seedlings under abiotic stress

BACKGROUND

Larix gmelinii is an excellent stress resistant coniferous tree species with a wide distribution and important economic and ecological value. However, at seedling stage, L. gmelinii is extremely susceptible to abiotic stresses, and systematic research on the adaptation mechanisms of L. gmelinii seedlings to abiotic stress is still lacking.

RESULTS

Phenotypic observation and physiological index detection showed that L. gmelinii seedlings wilted with needles withered and yellowish at later stages of drought and salt stress; Under low temperature, the seedlings grew slowly and turned red at later stage. Under all 3 abiotic stresses, the chlorophyll content in seedlings significantly decreased, while the MDA content significantly increased; The activity of SOD and CAT showed a trend of increasing first and then decreasing. Transcriptome analysis revealed that DEGs were mainly involved in carbohydrate and amino acid metabolism, phenylpropanoid biosynthesis, and flavonoid synthesis metabolism. Metabolomic analysis found unique DAMs under 3 stress treatments. The combined analysis of transcriptome and metabolome showed that the changing patterns of DEGs and DAMs in primary and secondary metabolism were consistent: carbohydrate were significantly accumulated under low temperature stress; amino acids showed the most significant changes under salt stress. The variation pattern of secondary metabolism was similar under both drought and salt stress, while anthocyanin accumulation was the most obvious only under low temperature stress.

CONCLUSION

Our study provides insightful information about the different mechanisms that L. gmelinii seedlings employ in response to drought, low temperature or salt stress.

The loss-of-function of AtNATA2 enhances AtADC2-dependent putrescine biosynthesis and priming, improving growth and salinity tolerance in Arabidopsis

Putrescine (Put) is a promising small molecule-based biostimulant to enhance plant growth and resilience, though its mode of action remains unclear. This study investigated the Put priming effect on Arabidopsis mutant lines (Atadc1, Atadc2, Atnata1, and Atnata2) under control conditions and salinity to understand its role in regulating plant growth. The Atadc2 mutant, characterized by reduced endogenous Put levels, showed insensitivity to Put priming without growth enhancement, which was linked to significant imbalances in nitrogen metabolism, including a high Gln/Glu ratio. Contrarily, the Atnata2 mutant exhibited significant growth improvement and upregulated AtADC2 expression, particularly under Put priming, highlighting these genes' involvement in regulating plant development. Put priming enhanced plant growth by inducing the accumulation of specific polyamines (free, acetylated, conjugated, or bound form) and improving light-harvesting efficiency, particularly in the Atnata2 line. Our findings suggest that AtNATA2 may negatively regulate Put synthesis and accumulation via AtADC2 in the chloroplast, impacting light harvesting in photosystem II (PSII). Furthermore, the Atadc2 mutant line exhibited upregulated AtADC1 but reduced AcPut levels, pointing to a cross-regulation among these genes. The regulation by AtNATA2 on AtADC2 and AtADC2 on AtADC1 could be crucial for plant growth and overall stress tolerance by interacting with polyamine catabolism, which shapes the plant metabolic profile under different growth conditions. Understanding the regulatory mechanisms involving crosstalk between AtADC and AtNATA genes in polyamine metabolism and the connection with certain SMBBs like Put can lead to more effective agricultural practices, improving plant growth, nitrogen uptake, and resilience under challenging conditions.

Polyamines: pleiotropic molecules regulating plant development and enhancing crop yield and quality

Polyamines (PAs) are pleiotropic bioorganic molecules. Cellular PA contents are determined by a balance between PA synthesis and degradation. PAs have been extensively demonstrated to play vital roles in the modulation of plant developmental processes and adaptation to various environmental stresses. In this review, the latest advances on the diverse roles of PAs in a range of developmental processes, such as morphogenesis, organogenesis, growth and development, and fruit ripening, are summarized and discussed. Besides, the crosstalk between PAs and phytohormones or other signalling molecules, including H2O2 and NO, involved in these processes is dwelled on. In addition, the attempts made to improve the yield and quality of grain and vegetable crops through altering the PA catabolism are enumerated. Finally, several other vital questions that remain unanswered are proposed and discussed. These include the mechanisms underlying the cooperative regulation of developmental processes by PAs and their interplaying partners like phytohormones, H2O2 and NO; PA transport for maintaining homeostasis; and utilization of PA anabolism/catabolism for generating high-yield and good-quality crops. This review aims to gain new insights into the pleiotropic role of PAs in the modulation of plant growth and development, which provides an alternative approach for manipulating and engineering valuable crop varieties that can be used in the future.

Integrated Transcriptomic and Proteomic Analysis of Nutritional Quality-Related Molecular Mechanisms in "Longjia", "Yangpao", and "Niangqing" Walnuts (Juglans sigillata)

In this study, "Longjia (LJ)" and "Yangpao (YP)"exhibited higher contents of major nutrients compared to "Niangqing (NQ)" walnuts. The combination of transcriptome and proteome by RNA sequencing and isotope labeling for relative and absolute quantification techniques provides new insights into the molecular mechanisms underlying the nutritional quality of the three walnut species. A total of 4146 genes and 139 proteins showed differential expression levels in the three comparison groups. Combined transcriptome and proteome analyses revealed that these genes and proteins were mainly enriched in signaling pathways such as fatty acid biosynthesis, protein processing in endoplasmic reticulum, and amino acid metabolism, revealing their relationship with the nutritional quality of walnut kernels. This study identified key genes and proteins associated with nutrient metabolism and accumulation in walnut kernels, provided transcriptomic and proteomic information on the molecular mechanisms of nutrient differences in walnut kernels, and contributed to the elucidation of the mechanisms of nutrient differences and the selection and breeding of high-quality walnut seedlings.

Chloroplastic ascorbate modifies plant metabolism and may act as a metabolite signal regardless of oxidative stress

Ascorbate (Asc) is a major plant metabolite that plays crucial roles in various processes, from reactive oxygen scavenging to epigenetic regulation. However, to what extent and how Asc modulates metabolism is largely unknown. We investigated the consequences of chloroplastic and total cellular Asc deficiencies by studying chloroplastic Asc transporter mutant lines lacking PHOSPHATE TRANSPORTER 4; 4 and the Asc-deficient vtc2-4 mutant of Arabidopsis (Arabidopsis thaliana). Under regular growth conditions, both Asc deficiencies caused minor alterations in photosynthesis, with no apparent signs of oxidative damage. In contrast, metabolomics analysis revealed global and largely overlapping alterations in the metabolome profiles of both Asc-deficient mutants, suggesting that chloroplastic Asc modulates plant metabolism. We observed significant alterations in amino acid metabolism, particularly in arginine metabolism, activation of nucleotide salvage pathways, and changes in secondary metabolism. In addition, proteome-wide analysis of thermostability revealed that Asc may interact with enzymes involved in arginine metabolism, the Calvin-Benson cycle, and several photosynthetic electron transport components. Overall, our results suggest that, independent of oxidative stress, chloroplastic Asc modulates the activity of diverse metabolic pathways in vascular plants and may act as an internal metabolite signal.

Coping with salt stress

Salt stress delays seed germination in plants by increasing the hydrolysis of arginine-derived urea.

Unraveling the role of urea hydrolysis in salt stress response during seed germination and seedling growth in Arabidopsis thaliana

Urea is intensively utilized as a nitrogen fertilizer in agriculture, originating either from root uptake or from catabolism of arginine by arginase. Despite its extensive use, the underlying physiological mechanisms of urea, particularly its adverse effects on seed germination and seedling growth under salt stress, remain unclear. In this study, we demonstrate that salt stress induces excessive hydrolysis of arginine-derived urea, leading to an increase in cytoplasmic pH within seed radical cells, which, in turn, triggers salt-induced inhibition of seed germination (SISG) and hampers seedling growth. Our findings challenge the long-held belief that ammonium accumulation and toxicity are the primary causes of SISG, offering a novel perspective on the mechanism underlying these processes. This study provides significant insights into the physiological impact of urea hydrolysis under salt stress, contributing to a better understanding of SISG.

Polyamines: Their Role in Plant Development and Stress

This review focuses on the intricate relationship between plant polyamines and the genetic circuits and signaling pathways that regulate various developmental programs and the defense responses of plants when faced with biotic and abiotic aggressions. Particular emphasis is placed on genetic evidence supporting the involvement of polyamines in specific processes, such as the pivotal role of thermospermine in regulating xylem cell differentiation and the significant contribution of polyamine metabolism in enhancing plant resilience to drought. Based on the numerous studies describing effects of the manipulation of plant polyamine levels, two conceptually different mechanisms for polyamine activity are discussed: direct participation of polyamines in translational regulation and the indirect production of hydrogen peroxide as a defensive mechanism against pathogens. By describing the multifaceted functions of polyamines, this review underscores the profound significance of these compounds in enabling plants to adapt and thrive in challenging environments.

Linking the key physiological functions of essential micronutrients to their deficiency symptoms in plants

In this review, we untangle the physiological key functions of the essential micronutrients and link them to the deficiency responses in plants. Knowledge of these responses at the mechanistic level, and the resulting deficiency symptoms, have improved over the last decade and it appears timely to review recent insights for each of them. A proper understanding of the links between function and symptom is indispensable for an accurate and timely identification of nutritional disorders, thereby informing the design and development of sustainable fertilization strategies. Similarly, improved knowledge of the molecular and physiological functions of micronutrients will be important for breeding programmes aiming to develop new crop genotypes with improved nutrient-use efficiency and resilience in the face of changing soil and climate conditions.

Urea Cycle of Bacillus thuringiensis Affects Its Survival under UV Stress

Bacillus thuringiensis (Bt) is widely used to produce biological pesticides. However, its persistence is limited because of ultraviolet (UV) rays. In our previous study, we found that exogenous intermediates of the urea cycle were beneficial to Bt for survival under UV stress. To further explore the effect of the urea cycle on the resistance mechanism of Bt, the rocF/argG gene, encoding arginase and argininosuccinate synthase, respectively, were knocked out and recovered in this study. After the target genes were removed, respectively, the urea cycle in the tested Bt was inhibited to varying degrees. The UV stress test showed that the urea cycle disorder could reduce the resistance of Bt under UV stress. Meanwhile, the antioxidant enzyme activities of Bt were also decreased to varying degrees due to the knockout of the target genes. All of these results revealed that the urea cycle can metabolically regulate the stress resistance of Bt.

The Roles of Functional Amino Acids in Plant Growth and Development

Plants incorporate acquired carbon and nitrogen into amino acid metabolism, whereby the building blocks of proteins and the precursors of various metabolites are produced. This fundamental demand requires tight amino acid metabolism to sustain physiological homeostasis. There is increasing evidence that amino acid metabolism undergoes plastic alteration to orchestrate specific growth and developmental events. Consequently, there has been a gradual exploration of the interface at which amino acid metabolism and plant morphogenesis are mutually affected. This research progress offers an opportunity to explore amino acid metabolism, with the goal to understand how it can be modulated to serve special cellular needs and regulate specific growth and developmental pathways. Continuous improvements in the sensitivity and coverage of metabolomics technology, along with the development of chemoinformatics, have allowed the investigation of these research questions. In this review, we summarize the roles of threonine, serine, arginine and γ-aminobutyric acid as representative examples of amino acids relevant to specific developmental processes in plants ('functional amino acids'). Our objective is to expand perspectives regarding amino acid metabolism beyond the conventional view that it is merely life-supporting machinery.

Nutrient Solution Flowing Environment Affects Metabolite Synthesis Inducing Root Thigmomorphogenesis of Lettuce (Lactuca sativa L.) in Hydroponics

The principal difference between hydroponics and other substrate cultivation methods is the flowing liquid hydroponic cultivation substrate. Our previous studies have revealed that a suitable flowing environment of nutrient solution promoted root development and plant growth, while an excess flow environment was unfavorable for plants. To explain the thigmomorphogenetic response of excess flow-induced metabolic changes, six groups of lettuce (Lactuca sativa L.), including two flow conditions and three time periods, were grown. Compared with the plants without flow, the plants with flow showed decreased root fresh weight, total root length, root surface area, and root volume but increased average root diameter and root density. The roots with flow had more upregulated metabolites than those without flow, suggesting that the flow may trigger metabolic synthesis and activity. Seventy-nine common differential metabolites among six groups were screened, and enrichment analysis showed the most significant enrichment in the arginine biosynthesis pathway. Arginine was present in all the groups and exhibited greater concentrations in roots with flow than without flow. It can be speculated from the results that a high-flowing environment of nutrient solution promotes arginine synthesis, resulting in changes in root morphology. The findings provide insights on root thigmomorphogenesis affected by its growing conditions and help understand how plants respond to environmental mechanical forces.

Transcriptome and Metabolome Analyses Reveal Mechanisms Underlying the Response of Quinoa Seedlings to Nitrogen Fertilizers

Quinoa (Chenopodium quinoa Willd.) is a dicotyledonous annual amaranth herb that belongs to the family Chenopodiaceae. Quinoa can be cultivated across a wide range of climatic conditions. With regard to its cultivation, nitrogen-based fertilizers have a demonstrable effect on the growth and development of quinoa. How crops respond to the application of nitrogen affects grain quality and yield. Therefore, to explore the regulatory mechanisms that underlie the responses of quinoa seedlings to the application of nitrogen, we selected two varieties (i.e., Dianli-1299 and Dianli-71) of quinoa seedlings and analyzed them using metabolomic and transcriptomic techniques. Specifically, we studied the mechanisms underlying the responses of quinoa seedlings to varying concentrations of nitrogen by analyzing the dynamics of metabolites and genes involved in arginine biosynthesis; carbon fixation; and alanine, aspartate, and glutamate biosynthetic pathways. Overall, we found that differentially expressed genes (DEGs) and differentially expressed metabolites (DEMs) of quinoa are affected by the concentration of nitrogen. We detected 1057 metabolites, and 29,012 genes were annotated for the KEGG. We also found that 15 DEMs and 8 DEGs were key determinants of the differences observed in quinoa seedlings under different nitrogen concentrations. These contribute toward a deeper understanding of the metabolic processes of plants under different nitrogen treatments and provide a theoretical basis for improving the nitrogen use efficiency (NUE) of quinoa.

Physiological response mechanism of alfalfa seedlings roots to typical explosive cyclotrimethylene trinitramine (RDX)

This study explored the physiological response mechanism of alfalfa seedlings roots to a typical explosive, cyclotrimethylenetrinitramine (RDX), so as to improve the efficiency of phytoremediation. The response of plants to different levels of RDX were analyzed from the perspectives of mineral nutrition and metabolic networks. Exposure to RDX at 10-40 mg L^-1 had no significant effect on root morphology, but the plant roots significantly accumulated RDX in solution (17.6-40.9%). A 40 mg L^-1 RDX exposure induced cell gap expansion and disrupted root mineral metabolism, The key response elements, P, Cu, and Mg, were significantly increased by 1.60-1.66, 1.74-1.90, and 1.85-2.50 times, respectively. The 40 mg L^-1 RDX exposure also significantly disturbed root basal metabolism, resulting in a total of 197 differentially expressed metabolites (DEMs). The main response metabolites were lipids and lipid-like molecules, and the key physiological response pathways were arginine biosynthesis and aminoacyl-tRNA biosynthesis. A total of 19 DEMs in root metabolic pathways, including L-arginine, L-asparagine, and ornithine, were significantly responsive to RDX exposure. The physiological response mechanism of roots to RDX therefore involve mineral nutrition and metabolic networks and are of great significance for improving phytoremediation efficiency.

Impacts of a bacterial algicide on metabolic pathways in Chlorella vulgaris

Chlorella is a dominant species during harmful algal blooms (HABs) worldwide, which bring about great environmental problems and are also a serious threat to drinking water safety. Application of bacterial algicides is a promising way to control HABs. However, the identified bacterial algicides against Chlorella and the understanding of their effects on algal metabolism are very limited. Here, we isolated a novel bacterium Microbacterium paraoxydans strain M1 that has significant algicidal activities against Chlorella vulgaris (algicidal rate 64.38 %, at 120 h). Atrazine-desethyl (AD) was then identified from strain M1 as an effective bacterial algicide, with inhibition or algae-lysing concentration values (EC50) of 1.64 μg/mL and 1.38 μg/mL, at 72 h and 120 h, respectively. LAD (2 μg/mL AD) or HAD (20 μg/mL AD) causes morphology alteration and ultrastructure damage, chlorophyll a reduction, gene expression regulation (for example, psbA, 0.05 fold at 24 h, 2.97 fold at 72 h, and 0.23 fold of the control in HAD), oxidative stress, lipid oxidation (MDA, 2.09 and 3.08 fold of the control in LAD and HAD, respectively, at 120 h) and DNA damage (average percentage of tail DNA 6.23 % at 120 h in HAD, slight damage: 5∼20 %) in the algal cells. The impacts of AD on algal metabolites and metabolic pathways, as well as the algal response to the adverse effects were investigated. The results revealed that amino acids, amines, glycosides and urea decreased significantly compared to the control after 24 h exposure to AD (p < 0.05). The main up-regulated metabolic pathways implied metabonomic resistance and defense against osmotic pressure, oxidative stress, photosynthesis inhibition or partial cellular structure damage, such as phenylalanine metabolism, arginine biosynthesis. The down-regulated glycine, serine and threonine metabolism is a major lead in the algicidal mechanism according to the value of pathway impact. The down-regulated glycine, and serine are responsible for the downregulation of glyoxylate and dicarboxylate metabolism, aminoacyl-tRNA biosynthesis, glutathione metabolism, and sulfur metabolism, which strengthen the algae-lysing effect. It is the first time to highlight the pivotal role of glycine, serine and threonine metabolism in algicidal activities, which provided a new perspective for understanding the mechanism of bacterial algicides exerting on algal cells at the metabolic level.

Advanced pathway engineering for phototrophic putrescine production

The polyamine putrescine (1,4-diaminobutane) contributes to cellular fitness in most organisms, where it is derived from the amino acids ornithine or arginine. In the chemical industry, putrescine serves as a versatile building block for polyamide synthesis. The green microalga Chlamydomonas reinhardtii accumulates relatively high putrescine amounts, which, together with recent advances in genetic engineering, enables the generation of a powerful green cell factory to promote sustainable biotechnology for base chemical production. Here, we report a systematic investigation of the native putrescine metabolism in C. reinhardtii, leading to the first CO₂ -based bio-production of putrescine, by employing modern synthetic biology and metabolic engineering strategies. A CRISPR/Cas9-based knockout of key enzymes of the polyamine biosynthesis pathway identified ornithine decarboxylase 1 (ODC1) as a gatekeeper for putrescine accumulation and demonstrated that the arginine decarboxylase (ADC) route is likely inactive and that amine oxidase 2 (AMX2) is mainly responsible for putrescine degradation in C. reinhardtii. A 4.5-fold increase in cellular putrescine levels was achieved by engineered overexpression of potent candidate ornithine decarboxylases (ODCs). We identified unexpected substrate promiscuity in two bacterial ODCs, which exhibited co-production of cadaverine and 4-aminobutanol. Final pathway engineering included overexpression of recombinant arginases for improved substrate availability as well as functional knockout of putrescine degradation, which resulted in a 10-fold increase in cellular putrescine titres and yielded 200 mg/L in phototrophic high cell density cultivations after 10 days.

Genetic control of rhizosheath formation in pearl millet

The rhizosheath, the layer of soil that adheres strongly to roots, influences water and nutrients acquisition. Pearl millet is a cereal crop that plays a major role for food security in arid regions of sub-Saharan Africa and India. We previously showed that root-adhering soil mass is a heritable trait in pearl millet and that it correlates with changes in rhizosphere microbiota structure and functions. Here, we studied the correlation between root-adhering soil mass and root hair development, root architecture, and symbiosis with arbuscular mycorrhizal fungi and we analysed the genetic control of this trait using genome wide association (GWAS) combined with bulk segregant analysis and gene expression studies. Root-adhering soil mass was weakly correlated only to root hairs traits in pearl millet. Twelve QTLs for rhizosheath formation were identified by GWAS. Bulk segregant analysis on a biparental population validated five of these QTLs. Combining genetics with a comparison of global gene expression in the root tip of contrasted inbred lines revealed candidate genes that might control rhizosheath formation in pearl millet. Our study indicates that rhizosheath formation is under complex genetic control in pearl millet and suggests that it is mainly regulated by root exudation.

Innovating the Synergistic Assets of β-Amino Butyric Acid (BABA) and Selenium Nanoparticles (SeNPs) in Improving the Growth, Nitrogen Metabolism, Biological Activities, and Nutritive Value of Medicago interexta Sprouts

In view of the wide traditional uses of legume sprouts, several strategies have been approved to improve their growth, bioactivity, and nutritive values. In this regard, the present study aimed at investigating how priming with selenium nanoparticles (SeNPs, 25 mg L^-1) enhanced the effects of β-amino butyric acid (BABA, 30 mM) on the growth, physiology, nitrogen metabolism, and bioactive metabolites of Medicago interexta sprouts. The results have shown that the growth and photosynthesis of M. interexta sprouts were enhanced by the treatment with BABA or SeNPs, being higher under combined treatment. Increased photosynthesis provided the precursors for the biosynthesis of primary and secondary metabolites. In this regard, the combined treatment had a more pronounced effect on the bioactive primary metabolites (essential amino acids), secondary metabolites (phenolics, GSH, and ASC), and mineral profiles of the investigated sprouts than that of sole treatments. Increased amino acids were accompanied by increased nitrogen metabolism, i.e., nitrate reductase, glutamate dehydrogenase (GDH), glutamate synthase (GOGAT), glutamine synthase (GS), cysteine synthesis serine acetyltransferase, arginase, threonine synthase, and methionine synthase. Further, the antioxidant capacity (FRAP), the anti-diabetic activities (i.e., α-amylase and α-glucosidase inhibition activities), and the glycemic index of the tested sprouts were more significantly improved by the combined treatment with BABA and SeNPs than by individual treatment. Overall, the combined effect of BABA and SeNPs could be preferable to their individual effects on plant growth and bioactive metabolites.

Rapid Generation and Analysis of a Barley Doubled Haploid Line with Higher Nitrogen Use Efficiency Than Parental Lines by F1 Microspore Embryogenesis

Creating varieties with high nitrogen use efficiency (NUE) is crucial for sustainable agriculture development. In this study, a superior barley doubled haploid line (named DH45) with improved NUE was produced via F₁ microspore embryogenesis with three rounds of screening in different nitrogen levels by hydroponic and field experiments. The molecular mechanisms responsible for the NUE of DH45 surpassing that of its parents were investigated by RNA-seq analysis. A total of 1027 differentially expressed genes (DEGs) were identified that were up- or down-regulated in DH45 under low nitrogen conditions but showed no significant differences in the parents. GO analysis indicated that genes involved in nitrogen compound metabolic processes were significantly enriched in DH45 compared with the parents. KEGG analysis showed the MAPK signaling pathway plant to be highly enriched in DH45 relative to its parents, as well as genes involved in alanine, aspartate and glutamate metabolism, and arginine biosynthesis. In conclusion, our study revealed the potential to fix trait superiority in a line by combining crossing with F₁ microspore culture technologies in future crop breeding and also identified several candidate genes that are expressed in shoots and may enable barley to cope with low-nitrogen stress.

Unfinished story of polyamines: Role of conjugation, transport and light-related regulation in the polyamine metabolism in plants

Polyamines play a fundamental role in the functioning of all cells. Their regulatory role in plant development, their function under stress conditions, and their metabolism have been well documented as regards both synthesis and catabolism in an increasing number of plant species. However, the majority of these studies concentrate on the levels of the most abundant polyamines, sometimes providing data on the enzyme activity or gene expression levels during polyamine synthesis, but generally making no mention of the fact that changes in the polyamine pool are very dynamic, and that other processes are also involved in the regulation of actual polyamine levels. Differences in the distribution of individual polyamines and their conjugation with other compounds were described some time ago, but these have been given little attention. In addition, the role of polyamine transporters in plants is only now being recognised. The present review highlights the importance of conjugated polyamines and also points out that investigations should not only deal with the polyamine metabolism itself, but should also cover other important questions, such as the relationship between light perception and the polyamine metabolism, or the involvement of polyamines in the circadian rhythm.

Diversity, properties and functions of bacterial arginases

The metalloenzyme arginase hydrolyzes L-arginine to produce L-ornithine and urea. In bacteria, arginase has important functions in basic nitrogen metabolism and redistribution, production of the key metabolic precursor L-ornithine, stress resistance and pathogenesis. We describe the regulation and specific functions of the arginase pathway as well as summarize key characteristics of related arginine catabolic pathways. The use of arginase-derived ornithine as a precursor molecule is reviewed. We discuss the biochemical and transcriptional regulation of arginine metabolism, including arginase, with the latter topic focusing on the RocR and AhrC transcriptional regulators in the model organism Bacillus subtilis. Finally, we consider similarities and contrasts in the structure and catalytic mechanism of the arginases from Bacillus caldovelox and Helicobacter pylori. The overall aim of this review is to provide a panorama of the diversity of physiological functions, regulation, and biochemical features of arginases in a variety of bacterial species.