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In Arabidopsis, the C-repeat binding factors (CBFs) have been extensively studied as key transcription factors in the cold stress response. However, their exact functions in the cold response remains unclear due to the lack of a null cbf triple mutant. In this study, we used CRISPR/Cas9 technology to mutate CBF1 or CBF1/CBF2 in a cbf3 T-DNA insertion mutant to generate cbf1,3 double and cbf1 cbf2 cbf3 (cbfs) triple mutants. The response of the cbfs triple mutants to chilling stress is impaired. Furthermore, no significant difference in freezing tolerance was observed between the wild-type and the cbf1,3 and cbfs mutants without cold acclimation. However, the cbfs mutants were extremely sensitive to freezing stress after cold acclimation, and freezing sensitivity ranking was cbfs > cbf1,3 > cbf3. RNA-Seq analysis showed that 134 genes were CBF regulated, of which 112 were regulated positively and 22 negatively by CBFs. Our study reveals the essential functions of CBFs in chilling stress response and cold acclimation, as well as defines a set of genes as CBF regulon. It also provides materials for the genetic dissection of components in CBF-dependent cold signaling.

As one of the common abiotic stresses, chilling stress has negative effects on rice growth and development. Minimization of these adverse effects through various ways is vital for the productivity of rice. Nanoparticles (NPs) serve as one of the effective alleviation methods against abiotic stresses. In our research, zinc oxide (ZnO) NPs were utilized as foliar sprays on rice leaves to explore the mechanism underlying the effect of NPs against the negative impact of chilling stress on rice seedlings. We revealed that foliar application of ZnO NPs significantly alleviated chilling stress in hydroponically grown rice seedlings, including improved plant height, root length, and dry biomass. Besides, ZnO NPs also restored chlorophyll accumulation and significantly ameliorated chilling-induced oxidative stress with reduced levels of H2O2, MDA, proline, and increased activities of major antioxidative enzymes, superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). We further found that foliar application of ZnO NPs induced the chilling-induced gene expression of the antioxidative system (OsCu/ZnSOD1, OsCu/ZnSOD2, OsCu/ZnSOD3, OsPRX11, OsPRX65, OsPRX89, OsCATA, and OsCATB) and chilling response transcription factors (OsbZIP52, OsMYB4, OsMYB30, OsNAC5, OsWRKY76, and OsWRKY94) in leaves of chilling-treated seedlings. Taken together, our results suggest that foliar application of ZnO NPs could alleviate chilling stress in rice via the mediation of the antioxidative system and chilling response transcription factors.

For crops of tropical and subtropical origin, exposure to low temperatures often causes chilling injury symptoms, which can range from altered appearance (such as surface pitting and discoloration) to severe physiological disorders and impaired metabolism. To cope with suboptimal temperatures in the surrounding environment, crops have evolved complex mechanisms, which entail stress signal perception and transduction, activation of stress-responsive genes, and the synthesis of stressrelated molecules. Plant breeding programs have been instrumental in obtaining chilling-tolerant cultivars in a number of horticultural crops. More recently, the incorporation of molecular and omics-based techniques into conventional breeding procedures has vastly improved breeding strategies by enhancing the efficacy of screening for chilling tolerance-associated traits. Moreover, these new tools will boost knowledge of chilling responses and tolerance mechanisms, and the discovery of related pathways and genes. As a part of the 'Physiological, Molecular and Genetic Perspectives of Chilling Tolerance in Horticultural Crops' series (Lara et al., 2020), this Research Topic was launched with the aim of offering an overview of recent developments in this area. The papers in this collection explored the mechanisms involved in chilling tolerance in a number of plant species, including commercially important fruit crops such as pepper, tomato, banana and peach/nectarine, a medicinal plant (Tetrastigma hemsleyanum) and Arabidopsis. In addition to helping to reveal the mechanisms underlying cold stress tolerance, these findings provide the basis for future breeding programs, and offer clues for the alleviation of stress symptoms.

Chilling is a devastating stress that has led to a crisis of production for cucumber (Cucumis sativus L.). To determine the molecular mechanisms underlying chilling responses in cucumber, we investigated physiological changes and transcriptomic responses to chilling stress in the chilling-tolerant inbred line CC and chilling-susceptible inbred line R1461. Physiological analysis showed that CC had a higher survival rate, lower H2O2 accumulation, and ion leakage than R1461 after chilling treatment. RNA-seq analysis identified 938 differentially expressed genes (DEGs) in response to chilling and revealed that chilling stress regulated the transcript levels of genes related to hormones, including auxin, salicylic acid (SA), jasmonic acid (JA), and ethylene. RT-qPCR and pharmacological analysis suggested that cucumber chilling tolerance was associated with variation in the gene expression involved in ethylene biosynthesis and signaling. Exogenously applying 1-aminocyclopropane-1-carboxylic acid (ACC), the precursor of ethylene, improved the chilling tolerance of cucumber, while the exogenous application of the ethylene inhibitor AgNO3 impaired the chilling tolerance of cucumber. After ACC treatment, the difference in chilling tolerance between CC and R1461 disappeared, suggesting that the different chilling tolerance level between CC and R1461 is dependent on the ethylene biosynthesis and signaling pathway. In addition, a comparison of cucumber lines with different chilling tolerances revealed that chilling tolerance is highly associated with the up-regulation of C-repeat binding factor (CBF) genes, while natural variation in the promoter of CsCBF1 is associated with chilling response. This study thus provides information on transcriptomic responses in different varieties of chilling-tolerant cucumber and reveals potential chilling tolerance mechanisms that could be used to improve chilling tolerance in cucumber.

Reversible phosphorylation of photosystem II light harvesting complexes (LHCII) is a well-established protective mechanism enabling efficient response to changing light conditions. However, changes in LHCII phosphorylation were also observed in response to abiotic stress regardless of photoperiod. This study aimed to investigate the impact of dark-chilling on LHCII phosphorylation pattern in chilling-tolerant Arabidopsis thaliana and to check whether the disturbed LHCII phosphorylation process will impact the response of Arabidopsis to the dark-chilling conditions. We analyzed the pattern of LHCII phosphorylation, the organization of chlorophyll–protein complexes, and the level of chilling tolerance by combining biochemical and spectroscopy techniques under dark-chilling and dark conditions in Arabidopsis mutants with disrupted LHCII phosphorylation. Our results show that during dark-chilling, LHCII phosphorylation decreased in all examined plant lines and that no significant differences in dark-chilling response were registered in tested lines. Interestingly, after 24 h of darkness, a high increase in LHCII phosphorylation was observed, co-occurring with a significant FV/FM parameter decrease. The highest drop of FV/FM was detected in the stn7-1 line–mutant, where the LHCII is not phosphorylated, due to the lack of STN7 kinase. Our results imply that STN7 kinase activity is important for mitigating the adverse effects of prolonged darkness.

Banana is sensitive to cold stress and often suffers from chilling injury with browning peel and failure to normal ripening. We have previously reported that banana chilling injury is accompanied by a reduction of miR528 accumulation, alleviating the degradation of its target gene MaPPO and raising ROS levels that cause peel browning. Here, we further revealed that the miR528-MaPPO cold-responsive module was regulated by miR156-targeted SPL transcription factors, and the miR156c-MaSPL4 module was also responsive to cold stress in banana. Transient overexpression of miR156c resulted in a more severe chilling phenotype by decreasing the expression of MaSPL4 and miR528. Conversely, the browning was alleviated in STTM-miR156c silencing and OE- MaSPL4 samples. Furthermore, DNA affinity purification sequencing and MaSPL4 -overexpressing transcriptome jointly revealed that MaSPL4 may mediate the transcription of genes related to lipid metabolism and antioxidation, in addition to the miR528-MaPPO module, demonstrating MaSPL4 as a master regulator in the fruit cold response network. In summary, our results suggest that the miR156c-MaSPL4 module can mediate the chilling response in banana by regulating the miR528-MaPPO module and multiple other pathways, which provides evidence for the crosstalk between TFs and miRNAs that can be used for the molecular breeding of fruit cold tolerance.

This paper examines the ability of recent versions of the Geophysical Fluid Dynamics Laboratory Operational Hurricane Forecast Model (GHM) to reproduce the observed relationship between hurricane intensity and hurricane‐induced Sea Surface Temperature (SST) cooling. The analysis was performed by taking a Lagrangian composite of all hurricanes in the North Atlantic from 1998–2009 in observations and 2005–2009 for the GHM. A marked improvement in the intensity‐SST relationship for the GHM compared to observations was found between the years 2005 and 2006–2009 due to the introduction of warm‐core eddies, a representation of the loop current, and changes to the drag coefficient parameterization for bulk turbulent flux computation. A Conceptual Hurricane Intensity Model illustrates the essential steady‐state characteristics of the intensity‐SST relationship and is explained by two coupled equations for the atmosphere and ocean. The conceptual model qualitatively matches observations and the 2006–2009 period in the GHM, and presents supporting evidence for the conclusion that weaker upper oceanic thermal stratification in the Gulf of Mexico, caused by the introduction of the loop current and warm core eddies, is crucial to explaining the observed SST‐intensity pattern. The diagnostics proposed by the conceptual model offer an independent set of metrics for comparing operational hurricane forecast models to observations. Key Points SST observations allow evaluation of coupled behavior of GFDL hurricane model Parameterization and initialization changes improved SST response for 2006‐2009 Conceptual hurricane intensity model matches SST observations and GFDL response

Chilling stress can have severe impacts on the growth, development and productivity of maize worldwide. In the present study, cDNA amplified fragment length polymorphism (cDNA-AFLP) analysis was used to evaluate gene expression in maize during chilling treatments (6°C) over four time periods (0, 2, 6 and 12 h). A total of 441 transcript-derived fragments (TDFs) induced by low-temperature treatment were detected. Based on the sequence analysis, the 58 TDFs of known functions were involved in metabolism, photosynthesis, signal transduction and defence responses etc., suggesting that maize undergoes a complex adaptive process in response to low temperatures. Three full-length cDNA, encoding MAPKKK (mitogen-activated protein kinase kinase kinase), CLC-D (chloride channel D) and RLK (receptor-like protein kinases) homologues, were isolated from maize through in silico cloning and named as ZmMAPKKK, ZmCLC-D and ZmRLK, respectively. Finally, the expression patterns of the three genes showed a significant increase of differential expression after chilling stress as analysed by semi-quantitative RT-PCR and real-time qRT-PCR. This study provides important clues to understanding low-temperature regulation mechanisms in maize and the three candidate genes involved in chilling responses need further research to determine their usefulness in breeding new resistance cultivars.

This study investigates the combined influence of advanced lubrication and cooling techniques on enhancing the machinability of Monel 400, a nickel-based superalloy widely employed in marine, chemical, and aerospace applications due to its exceptional corrosion resistance and mechanical strength. Four machining conditions—dry cutting, Minimum Quantity Lubrication (MQL), nano-enhanced MQL (NMQL), and a hybrid approach integrating cryogenic liquid nitrogen with NMQL (Cryo + NMQL)—were systematically compared. The experiments were performed using fixed machining parameters: a cutting speed of 80 m/min, feed rate of 0.15 mm/tooth, radial depth of cut of 6 mm, and axial depth of cut of 0.8 mm. Among these, Cryo + NMQL, featuring carbon nanotube (CNT)-enriched sunflower oil nanofluid combined with liquid nitrogen (LN₂) as the cryogenic medium, achieved superior outcomes, reducing cutting force, cutting temperature, surface roughness, and tool wear by 23.99%, 24.66%, 44.58%, and 54.85%, respectively, compared to dry cutting. SEM analysis confirmed adhesion and abrasion as dominant wear mechanisms, which were significantly mitigated under Cryo + NMQL. Multi-Objective Response Surface Methodology (MORSM) optimized the machining parameters to achieve an ideal balance of performance metrics, with a composite desirability index of 0.956. This study shows that combining LN₂ cryogenic cooling with CNT-based NMQL provides superior machinability of Monel 400—offering lower forces, temperatures, surface roughness, and tool wear—while contributing new insights for an alloy rarely examined under hybrid cooling environments. The findings validate Cryo + NMQL as an eco-benign, high-performance machining strategy, offering enhanced tool life, improved surface finish, and sustainable outcomes.