Leaf, as a photosynthetic organ of crops, its senescence process has an important impact on yield formation, but the relationship between leaf senescence and phyllosphere microorganisms has been less studied. In order to explore the impact of the senescence process of maize leaves on the phyllosphere bacterial community, this study used three maize varieties of different maturity time (early-maturation variety Heike Yu 17 (H17), mid-maturation variety Zhongdan 111 (Z111), and late-maturation variety Shen Yu 21 (S21) in Northeast China as the experimental materials, and the leaves of the ear position of the three maize varieties were sampled five times starting from the blooming stage of early- maturation varieties, and the physiological indexes of senescence were determined. And at the same time, the community composition of endogenous and exogenous bacteria in/on the leaves was determined based on high-throughput sequencing technology. The results showed that at the late reproductive stage, leaf water content, POD and SOD activities were significantly higher in the mid- and late-maturation varieties than in the early-maturation varieties. At the phylum level, Cyanobacteria were endemic to mid- and late-maturation cultivars; at the genus level, the relative abundance of the endogenous shared bacteria Sphingomonas, Methylobacterium, and Deinococcus in maize leaves decreased significantly at later stages of maturation (IV and V). The relative abundance of endogenous bacteria Streptomyces and exogenous bacteria P3OB-42 were significantly enriched in the late senescence period, with similar trends and significant differences in relative abundance among the three species. The relative abundance of endogenous and exogenous bacteria differed significantly, with the top 5 exogenous bacteria accounting for more than 60%, while for endogenous bacteria, the top 5 accounted for only more than 30%. Soluble sugar content, photosynthetic pigment content and SOD activity were significantly correlated with bacterial community structure and abundance. In conclusion, mid- and late-maturation varieties were effective in prolonging leaf greening period, maintaining late leaf physiological activity with delaying senescence. The effects of senescence on the composition and diversity of endogenous bacterial communities were significantly greater than those of exogenous bacteria, and there were significantly different genera among three maize varieties studied. Moreover, soluble sugar content, photosynthetic pigment content and SOD activity were the key factors affecting the phyllosphere bacterial communities as well as the dominant species.

Multi-environment field testing is an important way to select optimize maize yield and yield stability varieties. However, because of its high cost, it has gradually become a challenge in plant breeding. The combination of field sparse testing and genome-wide prediction method can be used to predict untested phenotypes, reduced the effort and cost on field testing. In this experiment, 244 inbred lines of natural populations were planted in Shunyi, Beijing and Mishan, Heilongjiang in 2022 and 2023. Six agronomic traits were studied, including days to anthesis, plant height, ear height, ear length, kernel number per row and ear row number. The effects of four different models (Single, Across, M×E and R-norm), two different cross-validation schemes (CV1 and CV2) and three different training sets sampling ratios (0.5, 0.7 and 0.9) on the prediction accuracy were compared. The results showed that the average prediction accuracy of the six agronomic traits was 0.67, 0.58, 0.50, 0.33, 0.33 and 0.48. The average prediction accuracy of the Single model, Across model, M×E model and R-norm model was 0.36, 0.52, 0.53 and 0.53 for each trait. In CV1, the average prediction accuracy of each model in six traits ranged from 0.19 to 0.65, and in CV2, the average prediction accuracy ranged from 0.47 to 0.89. The comparison of different training set sampling ratios shows that the improvement of the proportion of the training sets has limited improvement in the prediction accuracy of different traits in different models, and the maximum is only 0.05. The results show that the CV2 training set can be used to form a scheme and include phenotypic data from multiple environments in the prediction model to provide good prediction accuracy for multi-environment prediction.

Flowering time is a critical point in the life cycle of angiosperm plants. Arabidopsis thaliana of the Brassicaceae is widely distributed around the world, and the natural populations of this species have been found at altitude 4 000 m in the Qinghai-Tibet Plateau. The cold/short summer plateau climate has shaped their flowering time to be moderately early compared with those living in low altitude areas. In this study, we constructed an F₂ mapping population and utilized whole-genome sequencing-based QTL-seq analysis to locate the major effect QTLs in Lhasa population of A. thaliana, and identified a haplotype-specific deletion of 2 307 bp within the first intron of FLC, which is unique to Tibetan A. thaliana. Lhasa population flc^-/- mutant was constructed by CRISPR-Cas9 gene editing technique. The mutant exhibited significantly earlier flowering time than Lhasa. The above findings suggested that the deletion in the first intron of FLC in Tibetan A. thaliana was most likely the major cause for the early flowering phenotype, although it did not cause complete function loss of the FLC. This variation may have facilitated the adaptation of Tibetan A. thaliana to the unique climatic environment of the Qinghai-Tibet Plateau.

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 tolerance. In this study, through the analysis of the full-length transcriptome data of A. 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. Overexpression 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 wild type 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 transgenic line increased by 20.3% compared to the wild type, showing higher stress tolerance. In this study, we identified AmCOMT1 from A. 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.

INTRODUCTION Nitrogen (N) is one of the most essential nutrients for the plant growth and development, and NH₄⁺-N is the main form of N source. Appropriate amount of NH₄⁺ promotes plant growth and increase crop yield. However, when used as the only N source, NH₄⁺ suppresses the growth and production of crops. Wheat (Triticum aestivum) is the third largest cereal crop in China, and its production has a profound impact on the food production. As the indispensable raw material for foods, wheat is crucial to daily life, so studying NH₄⁺ toxicity and mitigation mechanisms are of great significance for wheat production.

RATIONALE NH₄⁺toxicity is a ubiquitous issue in plants. The mechanisms of how NH₄⁺ causes phytotoxicity are not fully understood. To explore the mechanisms of NO₃^--dependent alleviation of NH₄⁺toxicity in the roots of wheat, both transcriptomic and proteomic approaches were used to investigate the differential expressions of genes and proteins under different nitrogen treatments.

RESULTS Compared with 7.5 mmol·L^-1NO₃^- (control), 7.5 mmol·L^-1NH₄⁺treatment inhibited the root growth of wheat seedlings. Transcriptome analysis showed that sole NH₄⁺ treatment upregulated the expressions of genes encoding glycolysis- and fermentation-related enzymes, including pyruvate decarboxylase, alcohol dehydrogenase and lactate dehydrogenase, while downregulated the 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 were downregulated. The addition of 1 mmol·L^-1NO₃^- to the solution containing 7.5 mmol·L^-1NH₄⁺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. Proteome 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 the expressions of glycolysis enzymes, fermentation enzymes, Rbohs and AOX and upregulated expressions of PIP-type aquaporins.

CONCLUSION 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 in 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.

Changes in transcription level of DEGs involved in fermentation pathway and TCA cycle under different N treatments in the roots of wheat seedlings. Sole NH₄⁺ treatment may induce the fermentation pathway, inhibit the capacity of TCA cycle, and ultimately inhibit the root growth in wheat. The addition of NO₃^- remarkably alleviates the sole NH₄⁺-induced inhibitory effects on the root growth.