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As a result of global warming, vegetation suffers from repeated freeze-thaw cycles caused by more frequent short-term low temperatures induced by hail, snow, or night frost. Therefore, short-term freezing stress of plants should be investigated particularly in light of the current climatic conditions. Alcohol dehydrogenase (ADH) plays a central role in the metabolism of alcohols and aldehydes and it is a key enzyme in anaerobic fermentation. ADH1 responds to plant growth and environmental stress; however, the function of ADH1 in the response to short-term freezing stress remains unknown. Using real-time quantitative fluorescence PCR, the expression level of was analyzed at low temperature (4°C). The lethal temperature was calculated based on the electrolyte leakage tests for both deletion mutants ( ) and wild type (WT) plants. To further investigate the relationship between and cold tolerance in plants, low-Mr polar metabolite analyses of and WT were performed at cold temperatures using gas chromatography-mass spectrometry. This investigation focused on freezing treatments (cold acclimation group: -6°C for 2 h with prior 4°C for 7 d, cold shock group: -6°C for 2 h without cold acclimation) and recovery (23°C for 24 h) with respect to seedling growth at optimum temperature. The experimental results revealed a significant increase in expression during low temperature treatment (4°C) and at a higher lethal temperature in compared to that in the WT. Retention time indices and specific mass fragments were used to monitor 263 variables and annotate 78 identified metabolites. From these analyses, differences in the degree of metabolite accumulation between and WT were detected, including soluble sugars (e.g., sucrose) and amino acids (e.g., asparagine). In addition, the correlation-based network analysis highlighted some metabolites, e.g., melibiose, fumaric acid, succinic acid, glycolic acid, and xylose, which enhanced connectedness in network under cold chock. When considered collectively, the results showed that possessed a metabolic response to freezing stress and played an important role in the cold stress response of a plant. These results expands our understanding of the short-term freeze response of in plants.

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.

Plants are exposed to various environmental stresses and have therefore developed antioxidant enzymes and molecules to protect their cellular components against toxicity derived from reactive oxygen species (ROS). Ascorbate is a very important antioxidant molecule in plants, and monodehydroascorbate reductase (MDHAR; EC 1.6.5.4) and dehydroascorbate reductase (DHAR; EC 1.8.5.1) are essential to regeneration of ascorbate for maintenance of ROS scavenging ability. The MDHAR and DHAR genes from Brassica rapa were cloned, transgenic plants overexpressing either BrMDHAR and BrDHAR were established, and then, each transgenic plant was hybridized to examine the effects of co-expression of both genes conferring tolerance to freezing. Transgenic plants co-overexpressing BrMDHAR and BrDHAR showed activated expression of relative antioxidant enzymes, and enhanced levels of glutathione and phenolics under freezing condition. Then, these alteration caused by co-expression led to alleviated redox status and lipid peroxidation and consequently conferred improved tolerance against severe freezing stress compared to transgenic plants overexpressing single gene. The results of this study suggested that although each expression of BrMDHAR or BrDHAR was available to according tolerance to freezing, the simultaneous expression of two genes generated synergistic effects conferring improved tolerance more effectively even severe freezing.

IntroductionAlfalfa (Medicago sativa L.) is the most important perennial forage crop cultivated globally. However, extreme environmental conditions, such as freezing stress, can significantly impact alfalfa’s growth and development. The potential mechanisms through which alfalfa responds to freezing stress remain largely unexplored.MethodsIn this study, we analyzed the physiological indices, transcriptomes and proteomes of the cold-tolerant alfalfa cultivar “Dongnong NO.1” and the cold-sensitive cultivar “Bara 218TR” at -5°C.ResultsThe results indicated that the levels of antioxidant enzyme and osmoregulatory substances in “Dongnong NO.1” were significantly higher than in “Bara 218TR”. Additionally, the levels of malondialdehyde (MDA) and relative electrolyte leakage (REL) were found be lower in “Dongnong NO.1” than in “Bara 218TR”. Further transcriptomic analysis revealed that the differentially expressed genes (DEGs) found in both alfalfa cultivars were predominantly enriched in the AP2/ERF-ERF transcription factor family and in multiple signaling pathways. Weighted gene co-expression network analysis (WGCNA) revealed that the physiological processes associated with freezing stress tolerance in the two alfalfa cultivars are closely linked to DEGs that regulate protein synthesis, calcium signaling, the inhibition of iron toxicity, and the reduction of cell wall stiffness. Proteomics analysis indicates that differentially abundant proteins (DAPs) respond to frost damage by maintaining protein stability, antioxidant defense, and metabolic regulation. Integrated transcriptomic and proteomic analyses indicate that pathways related to carbohydrate metabolism, biotic stress defense, cell wall modification, and phenylpropanoid biosynthesis are key to alfalfa’s response to frost damage.DiscussionThis study improves our understanding of the molecular mechanisms underlying alfalfa’s freezing resistance and provides insights for the further screening and in-depth investigation of candidate genes with potential functions against freezing stress.

Summary In the present study, PeSTZ1, a cysteine‐2/histidine‐2‐type zinc finger transcription factor, was isolated from the desert poplar, Populus euphratica, which serves as a model stress adaptation system for trees. PeSTZ1 was preferentially expressed in the young stems and was significantly up‐regulated during chilling and freezing treatments. PeSTZ1 was localized to the nucleus and bound specifically to the PeAPX2 promoter. To examine the potential functions of PeSTZ1, we overexpressed it in poplar 84K hybrids (Populus alba × Populus glandulosa), which are known to be stress‐sensitive. Upon exposure to freezing stress, transgenic poplars maintained higher photosynthetic activity and dissipated more excess light energy (in the form of heat) than wild‐type poplars. Thus, PeSTZ1 functions as a transcription activator to enhance freezing tolerance without sacrificing growth. Under freezing stress, PeSTZ1 acts upstream of ASCORBATE PEROXIDASE2 (PeAPX2) and directly regulates its expression by binding to its promoter. Activated PeAPX2 promotes cytosolic APX that scavenges reactive oxygen species (ROS) under cold stress. PeSTZ1 may operate in parallel with C‐REPEAT‐BINDING FACTORS to regulate COLD‐REGULATED gene expression. Moreover, PeSTZ1 up‐regulation reduces malondialdehyde and ROS accumulation by activating the antioxidant system. Taken together, these results suggested that overexpressing PeSTZ1 in 84K poplar enhances freezing tolerance through the modulation of ROS scavenging via the direct regulation of PeAPX2 expression.

ABC (ATP-binding cassette) transporter proteins are one of the most extensive protein families known to date and are ubiquitously found in animals, plants, and microorganisms. ABCs have a variety of functions, such as plant tissue development regulation, hormone transport, and biotic and abiotic stress resistance. However, the gene characterization and function of the ABC gene family in almond ( Prunus dulcis ) have not been thoroughly studied. In this study, we identified 117 PdABC genes using the whole genome of ‘Wanfeng’ almond obtained by sequencing and explored their protein characterization. The PdABC family members were classified into eight subfamilies. The members of the same subfamily had conserved motifs but poorly conserved numbers of exons and introns and were unevenly distributed among the eight subfamilies and on the eight chromosomes. Expression patterns showed that PdABC family members were significantly differentially expressed during almond development, dormant freezing stress, and salt stress. We found that PdABC59 and PdABC77 had extremely high expression levels in pollen. PdABC63 and PdABC64 had high expression levels during almond petal development and multiple stages of flower development. PdABC98 was highly expressed in annual dormant branches after six temperature-freezing stress treatments. PdABC29 , PdABC69 , and PdABC98 were highly expressed under different concentrations of salt stress. This study preliminarily investigated the expression characteristics of ABC genes in different tissues of almond during flower development, freezing stress and salt stress, and the results will provide a reference for further in-depth research and breeding of almond in the future.

Background Cytosine methylation, the main type of DNA methylation, regulates gene expression in plant response to environmental stress. The winter rapeseed has high economic and ecological value in China's Northwest, but the DNA methylation pattern of winter rapeseed during freezing stress remains unclear. Result This study integrated the methylome and transcriptome to explore the genome-scale DNA methylation pattern and its regulated pathway of winter rapeseed, using freezing-sensitive (NF) and freezing-resistant (NS) cultivars.The average methylation level decreased under freezing stress, and the decline in NF was stronger than NS after freezing stress. The CG methylation level was the highest among the three contexts of CG, CHG, and CHH. At the same time, the CHH proportion was high, and the methylation levels were highest 2 kb up/downstream, followed by the intron region. The C sub-genomes methylation level was higher than the A sub-genomes. The methylation levels of chloroplast and mitochondrial DNA were much lower than the B. napus nuclear DNA, the SINE methylation level was highest among four types of transposable elements (TEs), and the preferred sequence of DNA methylation did not change after freezing stress. A total of 1732 differentially expressed genes associated with differentially methylated genes (DMEGs) were identified in two cultivars under 12 h and 24 h in three contexts by combining whole-genome bisulfite sequencing( and RNA-Seq data. Function enrichment analysis showed that most DMEGs participated in linoleic acid metabolism, alpha-linolenic acid metabolism, carbon fixation in photosynthetic organisms, flavonoid biosynthesis, and plant hormone signal transduction pathways. Meanwhile, some DMEGs encode core transcription factors in plant response to stress. Conclusion Based on the findings of DNA methylation, the freezing tolerance of winter rapeseed is achieved by enhanced signal transduction, lower lipid peroxidation, stronger cell stability, increased osmolytes, and greater reactive oxygen species (ROS) scavenging. These results provide novel insights into better knowledge of the methylation regulation of tolerance mechanism in winter rapeseed under freezing stress.

The basic leucine zipper (bZIP) regulates plant growth and responds to stress as a key transcription factor of the Abscisic acid (ABA) signaling pathway. In this study, TabZIP genes were identified in wheat and the gene structure, physicochemical properties, cis-acting elements, and gene collinearity were analyzed. RNA-Seq and qRT-PCR analysis showed that ABA and abiotic stress induced most TabZIP genes expression. The ectopic expression of TaABI5 up-regulated the expression of several cold-responsive genes in Arabidopsis. Physiological indexes of seedlings of different lines under freezing stress showed that TaABI5 enhanced the freezing tolerance of plants. Subcellular localization showed that TaABI5 is localized in the nucleus. Furthermore, TaABI5 physically interacted with cold-resistant transcription factor TaICE1 in yeast two-hybrid system. In conclusion, this study identified and analyzed members of the TabZIP gene family in wheat. It proved for the first time that the gene TaABI5 affected the cold tolerance of transgenic plants and was convenient for us to understand the cold resistance molecular mechanism of TaABI5. These results will provide a new inspiration for further study on improving plant abiotic stress resistance.

Background Global warming intensifies climate extremes, with rising temperatures and more frequent heatwaves. This situation may make it more difficult for species in high-temperature regions, such as the Cycas panzhihuaensis . Introduction and domestication are vital for conservation, but low temperatures limit the spread of tropical and subtropical plants to higher latitudes and altitudes. Phytohormones mediate cold adaptation through complex signaling networks that regulate physiological and molecular responses. However, the hormonal regulation and molecular mechanisms underlying freezing tolerance in C. panzhihuaensis remain poorly understood. Results This study used C. panzhihuaensis as the research subject. We exposed the plant to freezing stress and measures leaf hormone levels under CK (control group), F1(-5 °C for 1.5 h), and F2(-5 °C for 6 h). Additionally, we conducted transcriptomic analysis to explore gene expression differences in plant hormone signal transduction pathways. The findings indicated that with prolonged freezing treatment, the contents of cis-12-oxophytodienoic acid (cis-OPDA), gibberellin A4 (GA4), and salicylic acid (SA) initially increased significantly but subsequently decreased markedly. After F2 treatment, abscisic acid (ABA) levels significantly decreased, whereas castasterone (CS), 1-aminocyclopropanecarboxylic acid (ACC), and cytokinin (CTK) exhibited notable increases. Through transcriptomic analysis, a total of 4,036 differentially expressed genes (DEGs) associated with freezing stress were identified. In the plant hormone signal transduction pathway, 69 DEGs were enriched as determined by KEGG enrichment analysis. Further analysis indicated that the altered gene expression in this pathway was closely associated with hormonal level variations and the freezing resistance of C. panzhihuaensis . This research offers essential understanding of the molecular processes behind the freezing resistance of C. panzhihuaensis and provides theoretical advice for its introduction and cultivation. Conclusions This study revealed that C. panzhihuaensis adapted to freezing stress through dynamic hormonal regulation and transcriptional reprogramming. Key phytohormones (cis-OPDA, GA4, SA, ABA, ACC, CS, and CTK) exhibited stage-specific accumulation patterns, and the plant hormone signal transduction pathway may be involved in regulating the cold resistance mechanism in C. panzhihuaensis . These findings provide crucial insights into cold resistance mechanisms of C. panzhihuaensis and establish a preliminary theoretical foundation for introducing this species to higher latitudes.

BackgroundMost terrestrial vascular plants can assimilate soil obtained NO3- in their root and shoot.ScopeData from the literature are collated and analysed with respect to genotype and environmental effects on the partitioning of NO3- assimilation between root and shoot of terrestrial vascular plants.ConclusionsTemperate evergreen woody species in the Ericaceae and Pinaceae carry out most of their NO3- assimilation in the root when growing in low (0.5 mM) up to at least 5 mM soil NO3-. The root is the main site of NO3- assimilation for temperate deciduous woody species and perennial and annual herbaceous legume species at 0.5–1 mM NO3- but for many, shoot assimilation increases in importance with increased NO3- supply. Temperate perennial grasses and annual non-legume species and tropical/ sub-tropical species regardless of life-form, carry out a substantial, usually major proportion of their NO3- assimilation in shoots at NO3- concentrations above 0.5 mM. Furthermore, high NH4+ supply, mycorrhizal infection and infection by parasitic plants can increase the proportion of total plant NO3- assimilation carried out in the shoot while abiotic stress and elevated atmospheric [CO2] can cause this to decrease. Shoot NO3- assimilation is an advantage under non-stress conditions due to its positive effect on leaf expansion but can be a disadvantage under freezing and chilling stress conditions. Increased reliance on root NO3- assimilation at elevated CO2 was associated with increased and conversely decreased plant growth and NO3- assimilation depending on study. Resolution of these different findings across studies is an important area for further research.