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Camellia japonica var. decumbens is a naturally occurring highly cold resistant variety of Camellia japonica which is suitable for snowy and cold regions. However, the underlying cold-adaptive mechanisms associated with gene regulation have been poorly investigated. We analyzed the transcriptomic changes caused by cold stress in a cold-tolerant accession. Samples were collected at the end of each temperature treatment (T1, T3, T5, T7 and T9 represent the temperatures 25°C, 0°C, -4°C, -8°C and -12°C, respectively). Sample T1 at 25°C was used as control. Based on transcriptome analysis, 2828, 2384, 3099 and 3075 differentially expressed genes (DEGs) were up-regulated, and 3184, 2592, 2373 and 2615 DEGs were down-regulated by analyzing T3/T1, T5/T1, T7/T1 and T9/T1, respectively. A gene ontology (GO) analysis revealed an enrichment of GO terms such as response to stimulus, metabolic process, catalytic activity or binding. Out of the larger number of DEGs, 67 functional and regulatory DEGs stood out, since they were functionally characterized in other models. These genes are cold-responsive transcription factors (26) or involved in cold sensor or signal transduction (17) and in the stabilization of the plasma membrane and osmosensing response (24). These results suggest rapid and multiple molecular mechanisms of perception, transduction and responses to cold stress in cold acclimation of Camellia japonica var. decumbens. They could also serve as a valuable resource for relevant research on cold-tolerance and help to explore cold-related genes to foster the understanding of low-temperature tolerance and plant-environment interactions.

Accumulated evidence has revealed the mitigation effects of exogenous melatonin on cold stress in plants. In this study, to investigate the defensive roles of exogenous melatonin in banana under cold stress, we researched the influences of exogenous melatonin on the chlorophyll fluorescence parameters, antioxidant defense indexes and expression levels of cold-responsive genes in cold-stressed ‘Brazil’ banana seedlings. Results showed that 100 μM of exogenous melatonin achieved the best cold-resistance-promoting effect in banana. Exogenous melatonin treatment significantly increased the electron transfer rate, light harvesting efficiency, total antioxidant capacity, catalase and superoxidase activities and proline and soluble sugar contents and significantly reduced the accumulations of malondialdehyde, superoxide anion and hydrogen peroxide in the leaves of cold-stressed banana. In addition, under cold stress, melatonin significantly induced the expression of low-temperature-responsive genes, such as MaChiI1, MaCSD1C, MaWhy1, MaKIN10, MaADA1 and MaHOS1. It was concluded that the application of exogenous melatonin enhanced antioxidant defense and induced the expression of cold-responsive genes, thereby improving the cold resistance of banana. Our study will provide a basis for the application of exogenous melatonin in improving plant cold resistance.

Cold acclimation is a process used by most temperate plants to cope with freezing stress. In this process, the expression of cold-responsive (COR) genes is activated and the genes undergo physiological changes in response to the exposure to low, non-freezing temperatures and other environmental signals. The C-repeat-binding factors (CBFs) have been demonstrated to regulate the expression of many COR genes. Recent studies have elucidated the molecular mechanisms of how plants transmit cold signals from the plasma membrane to the CBFs and the results have indicated that COR genes are also regulated through CBF-independent pathways. Climate change is expected to have a major impact on cold acclimation and freezing tolerance of plants. However, how climate change affects plant cold acclimation at the molecular level remains unclear. This mini-review focuses on recent advances in cold acclimation in Arabidopsis thaliana and discusses how signaling can be potentially impacted by climate change. Understanding how plants acquire cold acclimation is valuable for the improvement of the freezing tolerance in plants and for predicting the effects of climate change on plant distribution and agricultural yield.

Banana (Musa spp.), one of the most important fruits worldwide, is generally cold sensitive. In this study, by using the cold-sensitive banana variety Tianbaojiao (Musa acuminate) as the study material, we investigated the effects of Piriformospora indica on banana cold resistance. Seedlings with and without fungus colonization were subjected to 4 °C cold treatment. The changes in plant phenotypes, some physiological and biochemical parameters, chlorophyll fluorescence parameters, and the expression of eight cold-responsive genes in banana leaves before and after cold treatment were measured. Results demonstrated that P. indica colonization reduced the contents of malondialdehyde (MDA) and hydrogen peroxide (H2O2) but increased the activities of superoxide dismutase (SOD) and catalase (CAT) and the contents of soluble sugar (SS) and proline. Noteworthily, the CAT activity and SS content in the leaves of P. indica-colonized banana were significant (p < 0.05). After 24 h cold treatment, the decline in maximum photochemistry efficiency of photosystem II (Fv/Fm), photochemical quenching coefficient (qP), efficient quantum yield [Y(II)], and photosynthetic electron transport rate (ETR) in the leaves of P. indica-colonized banana was found to be lower than in the non-inoculated controls (p < 0.05). Moreover, although the difference was not significant, P. indica colonization increased the photochemical conversion efficiency and electron transport rate and alleviated the damage to the photosynthetic reaction center of banana leaves under cold treatment to some extent. Additionally, the expression of the most cold-responsive genes in banana leaves was significantly induced by P. indica during cold stress (p < 0.05). It was concluded that P. indica confers banana with enhanced cold resistance by stimulating antioxidant capacity, SS accumulation, and the expression of cold-responsive genes in leaves. The results obtained from this study are helpful for understanding the P. indica-induced cold resistance in banana.

Salicylic acid (SA) has been proven to be a multifunctional signaling molecule that participates in the response of plants to abiotic stresses. In this study, we used cold-sensitive cucumber and cold-tolerant pumpkin as experimental materials to examine the roles of SA in root–shoot communication responses to aerial or/and root-zone chilling stress in own-root and hetero-root grafted cucumber and pumpkin plants. The results showed that pumpkin ( Cm ) rootstock enhanced the chilling tolerance of grafted cucumber, as evidenced by the observed lower levels of electrolyte leakage (EL), malondialdehyde (MDA), and higher photosynthetic rate (Pn) and gene expression of Rubisco activase (RCA). However, cucumber ( Cs ) rootstock decreased the chilling tolerance of grafted pumpkins. Cs/Cm plants showed an increase in the mRNA expression of C-repeat-binding factor ( CBF1 ), an inducer of CBF expression ( ICE1 ), and cold-responsive ( COR47 ) genes and CBF1 protein levels in leaves under 5/25 and 5/5°C stresses, or in roots under 25/5 and 5/5°C stresses, respectively, compared with the Cs/Cs . Chilling stress increased the endogenous SA content and the activity of phenylalanine ammonia-lyase (PAL), and the increase in SA content and activity of PAL in Cs/Cm plants was much higher than in Cs/Cs plants. Transcription profiling analysis revealed the key genes of SA biosynthesis, PAL , ICS , and SABP2 were upregulated, while SAMT , the key gene of SA degradation, was downregulated in Cs/Cm leaves, compared with Cs/Cs leaves under chilling stress. The accumulation of SA in the Cs/Cm leaves was mainly attributed to an increase in SA biosynthesis in leaves and that in transport from roots under aerial and root-zone chilling stress, respectively. In addition, exogenous SA significantly upregulated the expression level of cold-responsive ( COR ) genes, enhanced actual photochemical efficiency ( Φ PSII ), maximum photochemical efficiency ( F v / F m ), and Pn, while decreased EL, MDA, and CI in grafted cucumber. These results suggest that SA is involved in rootstock–scion communication and grafting-induced chilling tolerance by upregulating the expression of COR genes in cucumber plants under chilling stress.

The human population is increasing at an alarming rate, whereas at the same time agricultural productivity is decreasing due to the effect of various environmental problems. In particular, cold stress is a serious threat to the sustainability of crop yields. Indeed, cold stress can lead to major crop losses. Various phenotypic symptoms in response to cold stress include poor germination, stunted seedlings, yellowing of leaves (chlorosis), reduced leaf expansion and wilting, and may lead to death of tissue (necrosis). Cold stress also severely hampers the reproductive development of plants. The major negative effect of cold stress is that it induces severe membrane damage. This damage is largely due to the acute dehydration associated with freezing during cold stress. Cold stress is perceived by the receptor at the cell membrane. Then a signal is transduced to switch on the cold-responsive genes and transcription factors for mediating stress tolerance. Understanding the mechanism of cold stress tolerance and genes involved in the cold stress signaling network is important for crop improvement. Here, I review cold stress tolerance mechanisms in plants. The major points discussed are the following: (1) physiological effects of cold stress, (2) sensing of cold temperatures and signal transduction, and (3) the role of various cold-responsive genes and transcription factors in the mechanism of cold stress tolerance.

An increasing number of studies provide evidence that priming (pre-exposure of plants to moderate stress or chemical stimulus) can confer plant tolerance to a later occurring severe stress. The main objective of this study was to explore and compare the physiological mechanisms of salicylic acid (SA) and cold priming to enhance freezing tolerance. Wheat plants were firstly primed with SA (100 μM) or cold temperature (day/night temperature of 6 °C/2 °C), and then grown without any treatment for 8 days, and subsequently subjected to a freezing stress (day/night temperature of 2 °C/0 °C on the first day and − 2 °C/− 4 °C on the second day) at the jointing stage. The results showed that primed plants up-regulated the expression level of WRKY gene (WRKY19), heat shock transcription factor (HSF3), mitochondrial alternative oxidase (AOX1a), and heat shock protein (HSP70) under freezing stress, which contribute to increase of antioxidant capacity and protection of photosystem in parallel with lower malonaldehyde content, superoxide radical production and higher photochemistry efficiency of photosystem II under freezing stress as compared with non-primed plants. Furthermore, primed plants had a better photosynthesis performance and higher biomass production during the recovery period, and higher grain yield at maturity as compared with non-primed plants. Collectively, these results indicated that SA and cold priming effectively upregulated the expression of cold-responsive genes under freezing stress, resulting in increased antioxidant activity and cyanide-resistant respiration capacity and molecular chaperones level, maintaining cellular redox homeostasis and protecting photosynthetic apparatus, thereby conferring tolerance to freezing stress in wheat plants.

Cold stress is a major abiotic stress that seriously hinders plant growth and development, ultimately affecting crop yields. During the process of evolution, plants have evolved sophisticated adaptive strategies encompassing acclimation processes and tolerance mechanisms. Over the past two decades, substantial research breakthroughs have been made in elucidating the core components and complex regulatory networks underlying cold tolerance. This review systematically synthesizes the recent progress in three fundamental aspects: cold stress perception and signal transduction pathways, downstream physiological and molecular responses, and the pivotal regulatory roles of transcription factors (particularly CBF/DREB1 family) and cold-responsive miRNAs. In addition, we also investigated the intricate crosstalk between cold response and other biological processes including photoperiod sensing, flowering regulation, circadian rhythm, phytohormone signaling, and the dedicated discussion addresses how plants achieve metabolic and developmental trade-offs when allocating resources between cold defense and other vital traits. Looking forward, we propose four promising research directions: identifying novel cryo-sensors beyond currently known receptors, post-translational modification dynamics of CBF proteins, homeostatic control mechanisms among competing regulatory factors, and translational applications of cold stress pathways in precision breeding programs. Addressing these knowledge gaps will not only deepen our understanding of plant cold adaptation at molecular level, but also facilitate the development of climate-resilient crops through molecular design breeding.

The current study describes a novel species with the strain name ERMR1:05T isolated from the forefield soil of East Rathong Glacier in West Sikkim Himalaya (India). The isolate was facultatively anaerobic, gram-stain negative, non-spore-forming, rod-shaped, and oxidase negative. Whole-genome-based bacterial core gene phylogenetic analysis placed the strain in the genus Rahnella, well separated from Rouxiella spp. The digital DNA–DNA hybridisation and average nucleotide identity values between strain ERMR1:05T and other members of genus Rahnella were below the proposed thresholds for the species delineation. Based on these results, a new species, Rahnella sikkimica sp. nov., is proposed with strain ERMR1:05T (CIP 111636T, MTCC 12598T) as the type strain. The bacterium showed upregulation of cold-stress genes in cold conditions. Additionally, the genome analysis of the bacterium showed the presence of plant growth-promotion factors suggesting its role in crop improvement in cold hilly regions.