Metabolomics combined with physiology and transcriptomics reveal how Nicotiana tabacum leaves respond to cold stress

Gaseous exchange-dependent in vitro culture extensively alters plant growth and metabolic landscape revealed by comprehensive metabolomics

A complex interplay of environmental factors profoundly influences plant cellular metabolism, with gaseous exchange serving as a fundamental physiological process critical to growth and survival. While well-characterized in natural environments, the role of gaseous exchange in plant in-vitro culture remains underexplored. Plant in-vitro culture offers a versatile platform for studying metabolism, where metabolic networks are highly flexible and sensitive to environmental factors. Despite advancements in understanding these dynamics, there has been relatively little investigation into how gaseous exchange within tissue culture systems affects cellular metabolism. In the present study, we investigated the effects of gaseous exchange on plant growth and metabolism by comparing traditional Parafilm- and micropore-tape-based cultures designed to facilitate different levels of gaseous exchange. A comprehensive metabolomics approach using liquid chromatography-high-resolution mass spectrometry and gas chromatography-mass spectrometry was employed to delineate the metabolic changes in Arabidopsis under Parafilm- and micropore-tape-sealed culture conditions at two and three weeks of growth. Metabolic profiling identified increased levels of oxidized glutathione, arginine, ornithine, and aspartic acid, and decreased levels of TCA cycle intermediates and phenylpropanoid metabolites, indicating that restricted gas exchange alters the redox status and reprograms primary and secondary metabolism. This reprogramming affected amino acid metabolism, arginine metabolism, energy metabolism, as well as phenylpropanoid and flavonoid biosynthetic pathways. Restricted gaseous exchange in Parafilm-wrapped cultures also led to altered accumulation of several essential macro- and microelements in Arabidopsis seedlings. The present study demonstrated that restricted gaseous exchange inhibits plant growth and disrupts metabolism.

Glutamate-related nitrogen metabolism regulates cold-adaptive synthesis of red pigment in polar fungus Geomyces sp. WNF-15A

The polar fungus Geomyces sp. WNF-15A produces high-quality red pigment (AGRP), but the cold-dependent characteristic of AGRP synthesis restricts its industrialization. This study employed transcriptome analysis to compare gene expression profiles of the wild-type strain with cold-independent mutants of scaffold1.t692 (Δ1-692) and scaffold2.t704 (Δ2-704). From the analysis, 23 candidate genes were identified and functionally characterized among 22,600 differentially expressed genes. Knockout and recovery of scaffold5.t61, scaffold7.t586, or scaffold7.t712 proved their regulatory functions in AGRP synthesis, among which scaffold5.t61 functioned as a transcription factor, while scaffold7.t586 and scaffold7.t712 were involved in the glutamate-related nitrogen metabolism. Exogenous addition of nitrate, glutamine, and glutamate, combined with transcriptional regulation studies, revealed the importance of glutamate metabolism for cold-adaptive synthesis of AGRP. Scaffold5.t61 responded to the cold environment and regulated the transcription of scaffold2.t704 and scaffold1.t692. It subsequently increased glutamate synthesis by regulating the key nitrogen metabolism genes of scaffold7.t586 and scaffold7.t712, ultimately resulting in cold-dependent synthesis of AGRP in Geomyces sp. WNF-15A. This study offers new insights into the mechanisms of cold adaptation in polar fungi and serves as a reference for the development of psychrophilic fungal resources.

Proteomic and physiological analyses reveal the mechanisms through which melatonin ameliorates heat stress-induced photoinhibition in Nicotiana tabacum

Raising temperature-induced heat stress under climate warming scenarios has become a predominant threat to crop growth and productivity. As a pleiotropic signaling molecule, melatonin offers an innovative solution for enhancing plant thermotolerance, although its mechanisms, particularly regarding leaf photosynthesis, remain insufficiently understood. This study employed proteomic and physiological analyses to reveal the potential benefits of endogenous melatonin in alleviating heat stress-induced damage to the photosynthetic performance of Nicotiana tabacum plants. Foliar application of melatonin at 50 μM effectively ameliorated heat stress induced-photoinhibition by preventing pigment degradation, enhancing Rubisco and FBPase activities, stimulating RuBP carboxylation and regeneration, and improving light energy transfer and utilization.The changes resulted in increased light-saturated photosynthesis rate and photochemical efficiency. Melatonin application also elevated starch and soluble sugar contents by stimulating photosynthetic carbon assimilation and suppressing dark respiration, thereby counteracting the harmful impact of heat stress. Proteomic analysis revealed that melatonin significantly upregulated the expression of two key enzymes (glutamyl-tRNA reductase and monomethyl ester aerobic oxidative cyclase) involved in the chlorophyll biosynthetic pathway, enhanced the expression of three proteins (PSII cytochrome b559, protein H, and 10 kDa polypeptide) related to the PSII photochemical reaction, stimulated the expression of fructose-1,6-bisphosphatase linked to the Calvin cycle, and increased the expression of granule-bound starch synthase related to carbohydrate metabolism, thereby positively mediating the photodamage induced by heat stress to plant photosynthetic performance. These results highlight the potential of endogenous melatonin application as an effective approach for boosting crop photosynthetic performance and thermotolerance to global warming.

Ploidy levels influence cold tolerance of Cyclocarya paliurus: insight into the roles of WRKY genes

Cold stress in winter is one of the most severe abiotic stresses on plant growth and flourishing, and the selection of cold tolerant genotypes is an important strategy to ensure the safety of plant growth and development. Cyclocarya paliurus, a diclinous and versatile tree species originally in subtropical regions, has been introduced and cultivated in the warm temperate zone of China to meet the increasing market demand for its leaf yield. However, information regarding its cold tolerance remains limited. Based on the ploidy identification of tested materials, an imitation experiment was conducted to investigate the variation in freezing injury index and expression of the CpaWRKY family members in diploid and tetraploid C. paliurus seedlings. The results indicated a significant difference in freezing injury index between diploids and tetraploids under the imitating temperature of southern warm temperate zone, with diploids showing better cold tolerance than the tetraploids. A total of 88 CpaWRKY genes were identified from the C. paliurus genome, and RNA-Seq results showed significant differences in WRKY gene expression in C. paliurus under cold stress. Correlation analysis between differentially expressed genes and freezing injury index suggested that CpaWRKY14, CpaWRKY26 and CpaWRKY86 play essential roles in the diploids to respond to cold stress. In contrast, the major genes involved in the cold stress response in tetraploids were CpaWRKY14, CpaWRKY60, CpaWRKY63 and CpaWRKY81. Moreover, CpaWRKY14 expression was considerably higher in diploids compared to tetraploids. The results from this study not only enhance our comprehension of the role of the CpaWRKY genes in cold stress, but also provide a foundation for the genetic improvement of C. paliurus.

Effect of seed priming with zinc, iron and selenium on the low temperature tolerance of Nicotiana tabacum L. during seed germination

Tobacco is one of the important cash crops in China. It is sensitive to low temperature, especially in the early stage of tobacco seed germination and seedling growth. Low temperature stress directly affects the germination of tobacco seeds, leading to irregular emergence and slow growth of seedlings. Therefore, it is important to improve the vigor and cold tolerance of tobacco. In this study, two cold-sensitive tobacco varieties were primed individually with ZnSO4, FeSO4 and Na2SeO3 to test the effects of different microelements priming on seed germination. The results showed that under low temperature (11 °C), all three elements could improve tobacco seed vigor and promote seed germination, with selenium priming exhibiting the best effect. Selenium priming significantly increased the seed vigor index of YY97 by 29.60 % and of YY85 by 47.57 %. Moreover, selenium priming could effectively enhance POD activity in seeds, promote the oxidation of phenolic substances and enhance the activities of G-6-PDH and 6-P-GDH in the process of scavenging ROS and converting H2O2 to ·O2-. The results suggested that selenium played an important role in promoting tobacco seed germination under low temperature.

Construction of Freezing Injury Grade Index for Nanfeng Tangerine Plants Based on Physiological and Biochemical Parameters

Low-temperature freezing stress constitutes the most significant meteorological disaster during the overwintering period in the Nanfeng Tangerine (NT) production area, severely impacting the normal growth and development of the plants. Currently, the accuracy of meteorological disaster warnings and forecasts for NT orchards remains suboptimal, primarily due to the absence of quantitative meteorological indicators for low-temperature freezing stress. Therefore, this study employed NT plants as experimental subjects and conducted controlled treatment experiments under varying intensities of low-temperature freezing stress (0 °C, -2 °C, -5 °C, -7 °C, and -9 °C) and durations (1 h, 4 h, and 7 h). Subsequently, physiological and biochemical parameters were measured, including photosynthetic parameters, chlorophyll fluorescence parameters, reactive oxygen species, osmoregulatory substances, and antioxidant enzyme activities in NT plants. The results demonstrated that low-temperature freezing stress adversely affected the photosynthetic system of NT plants, disrupted the dynamic equilibrium of the antioxidant system, and compromised cellular stability. The severity of freezing damage increased with decreasing temperature and prolonged exposure. Chlorophyll (a/b) ratio (Chl (a/b)), maximum quantum yield of photosystem II (Fv/Fm), soluble sugar, and malondialdehyde (MDA) were identified as key indicators for assessing physiological and biochemical changes in NT plants. Utilizing these four parameters, a comprehensive score (CS) model of freezing damage was developed to quantitatively evaluate the growth status of NT plants across varying low-temperature freezing damage gradients and durations. Subsequently, the freezing damage grade index for NT plants during the overwintering period was established. Specifically, Level 1 for CS ≤ -0.50, Level 2 for -0.5 < CS ≤ 0, Level 3 for 0 < CS ≤ 0.5, and Level 4 for 0.5 < CS. The research results provide valuable data for agricultural meteorological departments to carry out disaster monitoring, early warning, and prevention and control.

Comprehensive evaluation of freezing tolerance in prickly ash and its correlation with ecological and geographical origin factors

Low temperatures are a key factor affecting the growth, development, and geographical distribution of prickly ash. This study investigated the impact of ecological and geographical factors on the freezing tolerance of prickly ash germplasm. Thirty-seven germplasm samples from 18 different origins were collected, and their freezing tolerance was comprehensively evaluated. The correlation between freezing tolerance and the ecological and geographical factors of their origins was also analyzed. Significant differences in freezing tolerance were observed among germplasm from different origins. The semi-lethal temperature of the germplasm ranged from - 12.37 to 1.08 °C. As temperatures decreased, the relative conductivity (REC) and catalase (CAT) activity of the germplasm gradually increased, while soluble sugar (SS), soluble protein (SP), free proline (Pro), and Peroxidase (POD) activities decreased and then increased. Superoxide dismutase (SOD) activity initially increased and then decreased. A comprehensive evaluation of freezing tolerance was conducted using a logistic equation, membership function, and cluster analysis. Germplasm from Tongchuan and Hancheng (Shaanxi Province, China), Asakura (Japan), and Yuncheng (Shanxi Province, China) exhibited the highest freezing tolerance, whereas those from Rongchang (Chongqing Municipality, China), Qujing (Yunnan Province, China), and Honghe (Yunnan Province, China) had the lowest. The correlation analysis revealed a significant positive correlation between freezing tolerance and latitude, and a significant negative correlation with the temperature of origin. Germplasm from higher latitudes showed higher SS content, SOD and CAT activities, stronger antioxidant enzyme activity, and better freezing tolerance compared to those from lower latitudes. REC was lower in germplasm originating from low-temperature areas than in those from high-temperature areas. Additionally, SP, Pro content, SOD, and POD activities were higher, indicating effective scavenging of active oxygen free radicals. No significant correlation was found between altitude and longitude of origin and freezing tolerance. However, at similar latitudes, prickly ash from higher altitudes displayed higher antioxidant enzyme activity and stronger freezing tolerance compared to those from lower altitudes. These findings provide a scientific basis for breeding prickly ash cultivars suited to different ecological regions.

Identification of common and specific cold resistance pathways from cold tolerant and non-cold tolerant mango varieties

Mango has frequently encountered severe climate and environmental challenges such as low temperatures, seriously affecting the sustainable development of the industry. In the study, physiological measurements showed that the activities of superoxide dismutase (SOD) and peroxidase (POD) were found to be higher in Jinhuang (JH) mango plants than those of Tainong (TN) mango plants under cold stress, indicating cold tolerant (JH) and non-cold tolerant (TN) mango varieties were firstly determined. Subsequently, transcriptomics showed 8,337 and 7,996 differentially expressed genes (DEGs) were respectively identified in JH and TN mango varieties treated at 4 °C for 36 h, while more DEGs (10,683 and 10,723) were screened when treated at 4 °C for 72 h. Quantitative real-time PCR (qRT-PCR) of the selected DEGs confirmed their transcriptional levels displayed agreement to the transcriptome data. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed two primary cold resistant regulation pathways, photosynthesis-antenna proteins pathway and photosynthesis pathway, were both significant annotated in the two mango varieties, indicating share the common regulation mechanism response to cold stress. However, five specific cold resistant pathways, such as amino acid and carbohydrate metabolisms, were identified in JH mango variety with cold stress for longer duration, indicating the specific regulation pathways in the cold tolerant mango varieties. Furthermore, 43 ethylene-responsive transcription factors (ERFs) were significantly annotated in JH mango after cold-treated for 72 h comparing with the control group, and three of them ERF109-1, ERF017-1 and ERF017-2 were highly expressed, which may play important regulatory roles in plant cold resistance. These results provided insights into the primary and specific molecular mechanisms of different mango varieties resistance to chill.

Transcriptomics Combined with Physiology and Metabolomics Reveals the Mechanism of Tolerance to Lead Toxicity in Maize Seedling

Lead (Pb) exposure can induce molecular changes in plants, disrupt metabolites, and impact plant growth. Therefore, it is essential to comprehend the molecular mechanisms involved in Pb tolerance in plants to evaluate the long-term environmental consequences of Pb exposure. This research focused on maize as the test subject to study variations in biomass, root traits, genes, and metabolites under hydroponic conditions under Pb conditions. The findings indicate that high Pb stress significantly disrupts plant growth and development, leading to a reduction in catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) activities by 17.12, 5.78, and 19.38%, respectively. Conversely, Pb stress led to increase malondialdehyde (MDA) contents, ultimately impacting the growth of maize. The non-targeted metabolomics analysis identified 393 metabolites categorized into 12 groups, primarily consisting of organic acids and derivatives, organ heterocyclic compounds, lipids and lipid-like molecules and benzenoids. Further analysis indicated that Pb stress induced an accumulation of 174 metabolites mainly enriched in seven metabolic pathways, for example phenylpropanoid biosynthesis and flavonoid biosynthesis. Transcriptome analysis revealed 1933 shared differentially expressed genes (DEGs), with 1356 upregulated and 577 downregulated genes across all Pb treatments. Additionally, an integrated analysis identified several DEGs and differentially accumulated metabolites (DAMs), including peroxidase, alpha-trehalose, and D-glucose 6-phosphate, which were linked to cell wall biosynthesis. These findings imply the significance of this pathway in Pb detoxification. This comprehensive investigation, employing multiple methodologies, provides a detailed molecular-level insight into maize's response to Pb stress.

Perfluorobutanoic acid triggers metabolic and transcriptional reprogramming in wheat seedlings

The environmental risks of fluorinated alternatives are of great concern with the phasing out of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate. Here, multi-omics (i.e., metabolomics and transcriptomics) coupled with physiological and biochemical analyses were employed to investigate the stress responses of wheat seedings (Triticum aestivum L.) to perfluorobutanoic acid (PFBA), one of the short-chain per- and polyfluoroalkyl substances (PFAS) and PFOA alternatives, at environmentally relevant concentrations (0.1-100 ng/g). After 28 days of soil exposure, PFBA boosted the generation of OH and O2- in wheat seedlings, resulting in lipid peroxidation, protein perturbation and impaired photosynthesis. Non-enzymatic antioxidant defense systems (e.g., glutathione, phenolics, and vitamin C) and enzymatic antioxidant copper/zinc superoxide dismutase were strikingly activated (p < 0.05). PFBA-triggered oxidative stress induced metabolic and transcriptional reprogramming, including carbon and nitrogen metabolisms, lipid metabolisms, immune responses, signal transduction processes, and antioxidant defense-related pathways. Down-regulation of genes related to plant-pathogen interaction suggested suppression of the immune-response, offering a novel understanding on the production of reactive oxygen species in plants under the exposure to PFAS. The identified MAPK signaling pathway illuminated a novel signal transduction mechanism in plant cells in response to PFAS. These findings provide comprehensive understandings on the phytotoxicity of PFBA to wheat seedlings and new insights into the impacts of PFAS on plants.

Integrated transcriptomic and metabolomic data reveal the cold stress responses molecular mechanisms of two coconut varieties

Among tropical fruit trees, coconut holds significant edible and economic importance. The natural growth of coconuts faces a challenge in the form of low temperatures, which is a crucial factor among adverse environmental stresses impacting their geographical distribution. Hence, it is essential to enhance our comprehension of the molecular mechanisms through which cold stress influences various coconut varieties. We employed analyses of leaf growth morphology and physiological traits to examine how coconuts respond to low temperatures over 2-hour, 8-hour, 2-day, and 7-day intervals. Additionally, we performed transcriptome and metabolome analyses to identify the molecular and physiological shifts in two coconut varieties displaying distinct sensitivities to the cold stress. As the length of cold stress extended, there was a prominent escalation within the soluble protein (SP), proline (Pro) concentrations, the activity of peroxidase (POD) and superoxide dismutase (SOD) in the leaves. Contrariwise, the activity of glutathione peroxidase (GSH) underwent a substantial reduction during this period. The widespread analysis of metabolome and transcriptome disclosed a nexus of genes and metabolites intricately cold stress were chiefly involved in pathways centered around amino acid, flavonoid, carbohydrate and lipid metabolism. We perceived several stress-responsive metabolites, such as flavonoids, carbohydrates, lipids, and amino acids, which unveiled considerably, lower in the genotype subtle to cold stress. Furthermore, we uncovered pivotal genes in the amino acid biosynthesis, antioxidant system and flavonoid biosynthesis pathway that presented down-regulation in coconut varieties sensitive to cold stress. This study broadly enriches our contemporary perception of the molecular machinery that contributes to altering levels of cold stress tolerance amid coconut genotypes. It also unlocks several unique prospects for exploration in the areas of breeding or engineering, aiming to identifying tolerant and/or sensitive coconut varieties encompassing multi-omics layers in response to cold stress conditions.