To explore the mechanisms of NO₃^–-dependent alleviation of NH₄⁺ toxicity in the roots of wheat (Triticum aestivum), both transcriptomic and proteomic approaches were used to investigate the differential expressions of genes and proteins under different nitrogen treatments. Compared with 7.5 mmol·L^-1 NO₃^‑ (control), 7.5 mmol·L^-1 NH₄⁺ inhibited the root growth of wheat seedlings. Transcriptome analysis showed that sole NH₄⁺ treatment upregulated expressions of genes encoding glycolysis- and fermentation-related enzymes, including pyruvate decarboxylase, alcohol dehydrogenase and lactate dehydrogenase, while downregulating expressions of genes encoding TCA cycle enzymes and the ATP synthases in the roots compared with control. Expressions of genes encoding the respiratory burst oxidase homologs (Rbohs), alternative oxidase (AOX) and dioxygenases were significantly upregulated, and expression of the PIP-type aquaporin genes was downregulated. The addition of 1 mmol·L^-1 NO₃^– to the solution containing 7.5 mmol·L^-1 NH₄⁺ downregulated the expression of genes encoding glycolysis enzymes, fermentation enzymes, Rbohs, AOX and dioxygenases, and increased the expression of genes encoding the TCA cycle enzymes, the ATP synthases and PIP-type aquaporins. Proteomic analysis showed that expressions of glycolysis enzymes, fermentation enzymes and AOX were upregulated, while PIP-type aquaporins were downregulated under sole NH₄⁺ conditions compared with the control. The addition of NO₃^– downregulated expressions of glycolysis enzymes, fermentation enzymes, Rbohs and AOX and upregulated expressions of PIP-type aquaporins. In conclusion, sole NH₄⁺ treatment promotes glycolytic and fermentation pathways, inhibits the TCA cycle and energy generation, and ultimately inhibits root growth of wheat seedlings. The inhibition of root growth may be due to the sole NH₄⁺-induced hypoxic stress on the roots. The addition of NO₃^– inhibits the glycolysis and fermentation pathways, promotes the TCA cycle and energy production, significantly alleviates the hypoxia stress and thereby attenuates the inhibitory effect of NH₄⁺ on root growth.

Agropyron mongolicum is one of northern China’s most representative perennial forage grasses, showing strong tolerance to cold and drought. In plants, caffeic acid O-methyltransferase (COMT) is a key gene involved in the biosynthesis of lignin and melatonin, and plays an important role in regulating plant growth, biomass quality, and stress resistance. In this study, through the analysis of the full-length transcriptome data of Agropyron mongolicum, the COMT candidate gene AmCOMT1 was cloned. AmCOMT1 is highly expressed in tissues with high lignin content, such as stem and root, and its expression is induced by a variety of abiotic stresses, including drought and salt. Expression of AmCOMT1 in Arabidopsis wild type (Col-0) and mutant (omt1-2) significantly promoted the synthesis of lignin in transgenic Arabidopsis, restoring the lignin content and composition of the mutant to wildtype level and the lignin content in Col-0/35S:AmCOMT1 was increased by 11%. In addition, overexpression of AmCOMT1 increased the melatonin content in Col-0/35S:AmCOMT1 transgenic Arabidopsis. Under salt stress conditions, the average root length of this strain increased by 20.3% compared to the wildtype, showing higher stress resistance. In this study, we identified AmCOMT1 from Agropyron mongolicum as a key gene regulating both lignin biosynthesis and melatonin biosynthesis, improving the stress tolerance of transgenic Arabidopsis. Our results highlighted the application potential of AmCOMT1 in genetic improvement of forage grasses through molecular breeding.

In this study, the chloroplast genomes from 19 species (11 genera) in Oleaceae were compared to reveal the general characteristics and structural variations. The chloroplast genome sizes in Oleaceae were 154-165 kb, and the differences were mainly caused by the length of large single-copy regions. The chloroplast genome sizes of 3 species from the genus Jasminum differed greatly from that for other species; in addition, the introns from the clpP and accD genes were lost in Jasminum. Synteny analyses showed several gene rearrangements in 3 Jasminum species that were probably caused by inversions. The boundary genes between IRb/small single copy (SSC) and SSC/IRa regions in 3 Jasminum species differed from others. Repeat sequences and simple sequence repeat detection demonstrated that Jasminum had significant differences in repeat number and repeat length as compared with other genera. On the basis of shared protein-coding genes among 19 species, Abeliophyllum distichum and Forsythia suspensa were the early-diverging clades in Oleaceae.

The evolution of gene composition of a species is a highly dynamic process, wherein lineage- and species-specific genes originated relatively recently are continuously integrated into the original gene network of older genes. These young genes play important roles in shaping the genome architecture, thereby leading to improved adaptation for organisms. Gene duplication and de novo origination of new genes are two ways to create new genes, causing different gene families with various copy numbers. To what extent and how the evolutionary pattern of genes depends on the timing of gene origination are still largely unexplored in soybean. In this study, we selected 19 representative angiosperms and analyzed the potential relations of the gene content dynamics with the origination of soybean (Glycine max) genes. Using the gene emergence approach, we found that 58.7% of soybean genes could be dated to ~150 million years ago and 21.7% orphan genes had recently originated. As expected, in comparison with young genes, older genes tend to be subjected to stronger purifying selection and were more conserved. In addition, older genes featured higher expression levels and were more likely to undergo alternative splicing. Furthermore, genes with different copy numbers showed a difference in these aspects. These findings may help understand the evolutionary models of genes with different ages.

Increasing nitrogen deposition influences carbon sequestration in grassland ecosystems, but we have no consistent results on how it impacts the exchange of CO₂ at the ecosystem level. As well, the impact of different types of N fertilizers and rates of N increase are not clear yet. This study aimed to evaluate the effect of N addition on ecosystem CO₂ exchange and was performed in a meadow steppe in Erguna, Inner Mongolia. A field experiment compared two types of N fertilizers (urea and slow-release urea) with five N addition rates (0, 5.0, 10.0, 20.0 and 50.0 g N·m^-2·a^-1). At the start and middle stage of the growing season, N addition had weak and inhibitive effects on ecosystem CO₂ exchange when precipitation was low, and significantly increased ecosystem CO₂ exchange in the late growing season when precipitation was high. Both net ecosystem CO₂ exchange and gross ecosystem photosynthesis increased significantly with N addition rate but showed a tendency of saturation when the N addition rate reached 10 g N·m^-2·a^-1. The two types of N fertilizers resulted in slightly different responses of ecosystem CO₂ exchange: slow-release urea had a stronger positive effect at 5 g N·m^-2·a^-1 with no significant difference at other addition rates. Our study suggests that increasing N deposition has significant effects on carbon assimilation in this semi-arid grassland, but the direction and magnitude of effects are strongly affected by seasonal pattern and amount of precipitation. The effects of different types of N fertilizers (i.e., urea and slow-release urea) on ecosystem CO₂ exchange may differ.