The cbfs triple mutants reveal the essential functions of CBFs in cold acclimation and allow the definition of CBF regulons in Arabidopsis

Investigation of wheat cold response pathway regulated by TaICE41 and TaCBFⅣd-B9 through Brachypodium distachyon transformation

Wheat (Triticum aestivum L.), a major global crop, is vulnerable to freezing stress, particularly during late spring frosts. Enhancing freezing tolerance through cold acclimation, primarily via the ICE-CBF-COR pathway, is crucial for improving wheat productivity. This study focuses on identifying genes regulated by the ICE-CBF pathway and those that function independently in response to freezing stress. TaICE41 and TaCBFⅣd-B9, two key genes associated with cold tolerance, were cloned and analyzed for their phylogenetic characteristics and subcellular localization. Transgenic Brachypodium distachyon overexpressing these genes demonstrated enhanced freezing tolerance, with increased survival rates and proline content, compared to wild-type plants. RNA-seq analysis revealed distinct gene expression profiles under cold stress, highlighting both shared and unique pathways regulated by ICE41 and CBF. Notably, the TaICE41-overexpressing lines exhibited upregulation of genes involved in phenylpropanoid biosynthesis and starch-sucrose metabolism, contributing to stress response. This study provides new insights into the ICE-CBF pathway and its role in cold tolerance, emphasizing the importance of understanding both ICE-CBF-regulated and independent cold-responsive genes for improving freezing tolerance in crops.

Comprehensive transcriptome analysis reveals StMAPK7 regulate cold response in potato

Cultivated potato (Solanum tuberosum L.) is an important tuber crop in the world. Cold stress adversely affects productivity and quality of potato. However, the molecular mechanism underlying the cold stress responses remains unclear in potato. The chloroplast ultrastructure of S. cardiophyllum in non-acclimated and cold acclimation plants under -2 °C for 6 h contained fewer thylakoid membranes, more spherical than those in 0 h (control, non-acclimated). The chloroplast ultrastructure of S. commersonii in non-acclimated and cold acclimation plants under -2 °C 6 h were similar to the non-cold stress. RNA sequencing (RNA-seq) analysis showed that 3,623 DEGs (differentially expressed genes) were detected in the S. commersonii and S. cardiophyllum with or without cold acclimation. GO analysis revealed that the membrane protein complex, photosynthesis and molecular function regulator were enriched terms in three category of S. commersonii and S. cardiophyllum. KEGG analysis found that genes were enriched to photosynthesis and chlorophyll metabolism. A total of 27 distinct modules were identified by weighted gene co-expression network analysis, four regulatory networks contained cold related genes were constructed. The StMAPK7 were differently expressed in S. cardiophyllum. Subcellular location studies showed that the StMAPK7 protein is mainly localized to the nucleus in tobacco. Overexpression of StMAPK7 exhibited lower electrolyte leakage and less leaves injury area than that of wild type, indicating StMAPK7 positively regulates cold stress in potato. These findings would provide fundamental insight into the cold stress response regulatory networks and supply a theoretical basis for breeding cold-resistant potato cultivars.

GIGANTEA functions as a co-repressor of cold stress response with a histone-modifying complex

The circadian clock in plants is crucial for regulating stress responses, including cold tolerance. Cold stress induces the expression of C-REPEAT BINDING FACTOR (CBF) transcription factors, which activate COLD-REGULATED (COR) genes to mitigate cold-induced damage. Previously, we identified that HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENE15 (HOS15)-HISTONE DEACETYLASE 2C (HD2C) complex regulates cold tolerance by modulating histone deacetylation on the COR genes. Our research reports that the circadian oscillator GIGANTEA (GI) regulates the association of histone deacetylase complex on the COR promoter, controlling cold tolerance. We show that GI functions downstream of HOS15, as the hos15-2 gi-2 double mutant exhibits freezing tolerance and expression of the COR gene like gi-2. Consistent with the HOS15, GI doesn't affect CBF transcription, suggesting that GI involved cold stress responses through HOS15-mediated COR gene regulation. Moreover, GI reduces histone acetylation and CBF binding at the COR15A promoter under cold stress, repressing COR15A gene expression. We further demonstrate that GI forms a co-repressor with HOS15 and HD2C, inhibiting CBF binding and preventing COR gene activation under normal conditions. These findings provide insights into molecular mechanisms by which GI, HOS15, and HD2C coordinate cold stress responses, offering potential strategies for enhancing plant cold tolerance through chromatin-mediated regulation.

Multi-omics reveal the molecular mechanisms of Sodium Nitrophenolate in enhancing cold tolerance through hormonal and antioxidant pathways in cucumber

Sodium nitrophenate (CSN) enhanced cold tolerance of cucumber. However, at the omics-level, the molecular mechanism of CSN to cold stress remains unclear. Here, we found that CSN was comparable to abscisic acid and much stronger than 2, 4-epibrassinolide (EBR) in enhancing cold tolerance. RNA-seq indicated that CSN regulated the brassinolides (BR) and cytokinin (CK) synthesis in the late stage of cold stress (LS-CS). CSN reduced the source of BR synthesis, accelerated the conversion of intermediate substances to BR and the deactivation of BR. While, CSN accelerated CK synthesis and CK deactivation by cytokinin dehydrogenase. Hormone content determination showed that CSN increased BR and decreased CK contents during most time-points of cold stress. Kinds of hormone signaling genes at LS-CS were activated by CSN, which may be due to changes in BR and CK contents. CSN also enhanced the expression of 90 % phenylalanine ammonia-lyase genes, participated in phenylpropanoid biosynthesis, at LS-CS. Genes of phenylpropanoid biosynthesis pathway and hormones signal were co-expression during cold stress. The metabolome also showed that CSN participated phenylpropanoid biosynthesis at LS-CS too. However, as for lipid metabolome, CSN up-regulated anthocyanin, flavones and flavonols metabolism at the early stage of cold stress. The autumn and winter field yield test showed that CSN increase cucumber yield by approximately 17.67 % and economic income by 207.67 dollars/667 m2. Collectedly, CSN may regulate lipid metabolism and hormone signaling mediated antioxidant pathways to enhance cold tolerance in the early and late stages of cold stress, respectively.

Identification of the WRKY gene family in Bergenia purpurascens and functional analysis of BpWRKY13 under cold stress

Bergenia purpurascens, a medicinal alpine plant, exhibits remarkable stress resilience. WRKY transcription factors are central regulators of plant stress responses, yet their family in B. purpurascens remains uncharacterized. Here, we identified 57 BpWRKY genes from B. purpurascens transcriptome data. Expression analysis revealed 11 BpWRKY genes differentially expressed under cold stress, with BpWRKY13 showing the strongest induction. To investigate its function, we overexpressed BpWRKY13 in Arabidopsis thaliana. Transgenic plants displayed significantly enhanced cold tolerance, evidenced by reduced leaf damage, increased survival, and elevated accumulation of proline and soluble proteins. Furthermore, transgenic plants exhibited increased activity of antioxidant enzymes and upregulation of cold-responsive genes. These findings indicate that BpWRKY13 confers cold tolerance by promoting osmoprotection and activating antioxidant defense mechanisms. This study provides a crucial foundation for understanding the BpWRKY gene family and highlights BpWRKY13 as a key regulator of cold resistance in B. purpurascens.

Chromatin Accessibility and Translational Landscapes of Bermudagrass (Cynodon dactylon) Under Chilling Stress

Cold tolerance in plants is a complex trait regulated by a network of transcription factors (TFs) and their downstream genes. While C-repeat binding factors (CBFs) are well-known for their role in cold tolerance, other regulatory networks remain largely unexplored. This study utilizes a combined approach of Assay for Transposase-Accessible Chromatin with Sequencing (ATAC-seq) and RNA-seq to identify cold-responsive TFs in Cynodon dactylon (Bermudagrass), a species widely grown in southern China but limited by cold stress. Early-stage cold stress was found to induce dynamic changes in 331 differentially accessible regions (DARs), with over 45% located in gene promoter regions. Key TFs, including CAMTA1, CAMTA2, WRKY43, WRKY48, WRKY21, and DREB1G, were associated with gained DARs, highlighting their roles in cold response regulation. In contrast, several Heat Shock Factor (HSF) family members, such as HSFA6B, HSFB2A, HSFC1, and HSFB2B, were linked to lost DARs, underscoring their involvement in cold stress regulation. The correlation between chromatin accessibility and gene expression emphasizes the critical role of TFs in plant cold stress adaptation. This study highlights the potential of ATAC-seq and RNA-seq as powerful tools for uncovering novel TFs essential for cold tolerance in plants, offering insights for future research and breeding efforts.

ScDREBA5 Enhances Cold Tolerance by Regulating Photosynthetic and Antioxidant Genes in the Desert Moss Syntrichia caninervis

Extreme cold events, becoming more frequent, affect plant growth and development. Much is known about C-repeat binding transcription factor (CBF)-dependent cold-signaling pathways in plants. However, the CBF-independent regulatory pathway in angiosperms is unclear, and the cold-signaling pathways in non-angiosperms lacking CBFs, such as the extremely cold-tolerant desert moss Syntrichia caninervis, are largely unknown. In this study, we determined that fully hydrated S. caninervis without cold acclimation could tolerate a low-temperature of -16°C. Transcriptome analysis of S. caninervis under 4°C and -4°C treatments revealed that sugar and energy metabolism, lipid metabolism and antioxidant activity were altered in response to cold stress, and surprisingly, most photosynthesis-related genes were upregulated under cold treatment. Transcription factors analysis revealed that A-5 DREB genes, which share a common origin with CBFs, are the hubs in the freezing-stress response of S. caninervis, in which ScDREBA5 was upregulated ~1000-fold. Overexpressing ScDREBA5 significantly enhanced freezing tolerance in both S. caninervis and Physcomitrium patens by upregulating genes involved in photosynthetic and antioxidant pathways. This is the first study to uncover the mechanism regulating the cold-stress response in S. caninervis. Our findings increase our understanding of different cold-stress response strategies in non-angiosperms and provide valuable genetic resources for breeding cold-tolerant crops.

Analysis of the two-component system gene family and the positive role of CsRR5 in cold stress response in tea plants

The two-component system (TCS), a ubiquitous signaling network consisting of histidine kinases (HKs), phosphotransfers (HPs), and response regulator proteins (RRs), participates in various functions, including responses to abiotic stresses. However, a comprehensive identification of TCS genes in tea plants is still lacking. Here, we identified 60 CsTCS members in tea plants, including 23 HKs, 10 HPs, and 27 RRs. The analysis of promoter cis-regulatory elements indicated that CsTCS genes are involved in phytohormone signaling, stress responses, and growth and development. The expression of CsETR1, CsETR2b, CsERS1b, and CsEIN4b from the HK subfamily was down-regulated by ethylene, whereas CsHK2b and CsHK3a were down-regulated by cytokinin. Conversely, CsHK4a and CsHK4b were up-regulated by cytokinin. CsTCS genes were widely expressed in various tissues, with the majority associated with multiple stresses. Furthermore, we demonstrated that suppressing the type-A response regulator CsRR5 in tea plants reduced cold tolerance and the expression of CBF-COR pathway genes, indicating that CsRR5 positively regulates the cold stress response through the CBF pathway. Therefore, our study establishes a connection between the two-component system and its downstream regulation in tea plant cold stress response.

An RNA helicase coordinates with iron signal regulators to alleviate chilling stress in Arabidopsis

Chilling stress is one of the major environmental stresses that restrains plant development and growth. Our previous study showed that a potential iron sensor BTS (BRUTUS) was involved in temperature response in Arabidopsis plants. However, whether plant iron homeostasis is involved in plant response to temperature fluctuation is not known. In this study, we discover that BTS mutant bts-2 is sensitive to chilling stress, and the sensitivity is attributed to the accumulation of iron. The suppressor screening of bts-2 led to the discovery of RH24, a DEAD-box RNA helicase, that fully suppresses bts-2 chilling sensitivity. RH24 is accumulated under low temperatures, where it unwinds the iron regulator ILR3 (IAA-leucine resistant 3) mRNA and increases the ILR3 protein levels. Intriguingly, RH24 sequesters ILR3 in phase-separated condensates to reduce ILR3-mediated iron overload, and BTS or cold treatments further facilitated the condensate formation. Therefore, RH24 and BTS coordinately control ILR3 to reduce iron uptake under chilling stress. Our findings reveal that the RNA helicase RH24 and BTS finetunes ILR3 to maintain plant iron homeostasis in response to temperature fluctuations.

A comprehensive all-in-one CRISPR toolbox for large-scale screens in plants

Clustered regularly interspaced short palindromic repeats (CRISPR)-associated nuclease (Cas) technologies facilitate routine genome engineering of one or a few genes at a time. However, large-scale CRISPR screens with guide RNA libraries remain challenging in plants. Here, we have developed a comprehensive all-in-one CRISPR toolbox for Cas9-based genome editing, cytosine base editing, adenine base editing (ABE), Cas12a-based genome editing and ABE, and CRISPR-Act3.0-based gene activation in both monocot and dicot plants. We evaluated all-in-one T-DNA expression vectors in rice (Oryza sativa, monocot) and tomato (Solanum lycopersicum, dicot) protoplasts, demonstrating their broad and reliable applicability. To showcase the applications of these vectors in CRISPR screens, we constructed guide RNA (gRNA) pools for testing in rice protoplasts, establishing a high-throughput approach to select high-activity gRNAs. Additionally, we demonstrated the efficacy of sgRNA library screening for targeted mutagenesis of ACETOLACTATE SYNTHASE in rice, recovering novel candidate alleles for herbicide resistance. Furthermore, we carried out a CRISPR activation screen in Arabidopsis thaliana, rapidly identifying potent gRNAs for FLOWERING LOCUS T activation that confer an early-flowering phenotype. This toolbox contains 61 versatile all-in-one vectors encompassing nearly all commonly used CRISPR technologies. It will facilitate large-scale genetic screens for loss-of-function or gain-of-function studies, presenting numerous promising applications in plants.

ZmDREB1A Regulates myo-Inositol-1-phosphate Synthase 2 Controlling Maize Germination at Low Temperatures

Transcription factor DREB1A positively regulates plant chilling stress tolerance. However, its role in regulating seed germination at low temperatures has remained a mystery. Our research has unveiled that maize zmdreb1a mutant seeds exhibit decreased ZmMIPS2 expression and a lower germination percentage than the control under low temperatures. The overexpression of ZmDREB1A upregulated ZmMIPS2 expression, while the mutation of DRE motifs in the ZmMIPS2 promoter nullified the influence of ZmDREB1A on the target gene expression. In addition, we demonstrated that ZmDREB1A directly binds to the three DRE motifs in the promoter of ZmMIPS2 both in vitro and in vivo. Further investigation has shown that maize zmmips2 mutant seeds are more sensitive, while ZmMIPS2 overexpressing seeds are more tolerant of low temperatures during seed germination. These findings could be applied to develop new crop varieties that are more resilient to low temperatures during the vulnerable germination phase.

An integrative overview of cold response and regulatory pathways in horticultural crops

Global climate change challenges agricultural production, as extreme temperature fluctuations negatively affect crop growth and yield. Low temperature (LT) stress impedes photosynthesis, disrupts metabolic processes, and compromises the integrity of cell membranes, ultimately resulting in diminished yield and quality. Notably, many tropical or subtropical horticultural plants are particularly susceptible to LT stress. To address these challenges, it is imperative to understand the mechanisms underlying cold tolerance in horticultural crops. This review summarizes recent advances in the physiological and molecular mechanisms that enable horticultural crops to withstand LT stress, emphasizing discrepancies between horticultural crops and model systems. These mechanisms include C-repeat binding factor-dependent transcriptional regulation, post-translational modifications, epigenetic control, and metabolic regulation. Reactive oxygen species, plant hormones, and light signaling pathways are integrated into the cold response network. Furthermore, technical advances for improving cold tolerance are highlighted, including genetic improvement, the application of light-emitting diodes, the utility of novel plant growth regulators, and grafting. Finally, prospective directions for fundamental research and practical applications to boost cold tolerance are discussed.

Hexokinase gene CsHXK4 positively regulates cold resistance in tea plants (Camellia sinensis)

Low temperatures are a major abiotic stress factor that adversely affects the growth, development, and productivity of tea plants. Soluble sugars play a critical role in enhancing tea plants' resistance to cold stress. However, the mechanisms by which tea plants perceive and transmit sugar signals remain poorly understood. In this study, the transcription of CsHXK4, a type B hexokinase (HXK) gene in tea plants, was significantly upregulated by low temperatures and glucose signaling. CsHXK4 exhibited multiple subcellular localizations, particularly in the nucleus and mitochondria, and was ubiquitously expressed across various tissues, with predominant expression in younger organs. Hexose phosphorylation analysis using the HXK-deficient yeast triple mutant YSH7.4-3C demonstrated that CsHXK4 functions as a hexokinase with catalytic activity. Overexpression (OE) of CsHXK4 in Arabidopsis resulted in hypersensitivity to glucose, suggesting its role in sugar signal transduction. Furthermore, CsHXK4-OE Arabidopsis plants exhibited enhanced cold tolerance compared to wild-type plants, as evidenced by increased photosynthetic capacity, elevated sugar content, and stable cell membrane permeability. Transient induction of CsHXK4 expression in tea leaves improved freezing tolerance and activated the expression of cold-responsive marker genes, including CsCBF1/2/3/4, CsKIN2.2, CsCOR413, CsLEA14, and CsGOLS1, compared to the empty vector control. Overall, our findings reveal that CsHXK4 positively regulates cold resistance in tea plants by mediating sugar signaling and CBF signaling pathways.

Molecular mechanism of response to low-temperature during the natural overwintering period of Rosa persica

KEY MESSAGE

The JA and ICE-CBF-COR signaling pathways play important roles in the low-temperature response of Rosa persica, with RpMYC2 interacting with multiple transcription factors and positively regulating tolerance to low-temperature stress. Rosa persica is highly resilient to cold and drought, making it a valuable resource for breeding in the Rosa. However, the response mechanism of R. persica during the overwintering period remains unclear. This study examined root and stem tissues of R. persica over an eight-month natural open field overwintering period, measuring physiological indices of cold tolerance and investigating changes in cold tolerance across different overwintering stages. The values of physiological indicators of cold hardiness of R. persica roots and stems increased and then decreased. Osmoregulatory substances were the primary contributors to cold hardiness of R. persica roots, while antioxidant enzyme systems played a dominant role in cold hardiness of stems. Differential gene enrichment analyses revealed that oxidative reactions, the synthesis of various secondary metabolites, and hormone signaling pathways are crucial in establishing cold tolerance of R. persica at different overwintering stages. Weighted gene co-expression network and time-ordered gene co-expression network analyses identified the gene RpMYC2 as potentially key to cold tolerance in R. persica. Yeast two-hybrid discovery revealed that RpMYC2 interacts with multiple transcription factors to regulate cold stress resistance in R. persica. Based on the transcriptome, key genes involved in response to low temperature were identified in this study, providing the physiological and molecular insights for cold tolerance breeding of Rosa.

Brassica rapa receptor-like cytoplasmic kinase BrRLCK1 negatively regulates freezing tolerance in transgenic Arabidopsis via the CBF pathway

Some winter rapeseed (Brassica rapa) varieties can endure extremely low temperatures (-20°C to -32°C). However, because of a lack of mutant resources, the molecular mechanisms underlying cold tolerance in B. rapa remain unclear. In this study, we identified a low-temperature-sensitive mutant receptor-like cytoplasmic kinase (RLCK), BrRLCK1, using the B. rapa--Arabidopsis (Arabidopsis thaliana) full-length cDNA-overexpressing gene hunting system mutant library. BrRLCK1, localized to the plasma membrane and retained its localization under low temperatures. Phylogenetic analysis showed that BrRLCK1 is highly conserved across six widely cultivated Brassica species, but exhibits complexity due to genome hybridization and polyploidization. Notably, β-glucuronidase activity and qRT-PCR analysis showed that B. rapa BrRLCK1 and its homologous gene BrRLCK2 were mainly expressed in the main root, shoot, and leaves, with their expression being activated by low temperatures. Transgenic Arabodipsis expressing BrRLCK1 and BrRLCK2 reduced freezing tolerance and promoted root elongation. These combined results indicated that low temperatures can activate the expression of BrRLCK1 and BrRLCK2, negatively regulating freezing tolerance via the C-repeat-binding factor (CBF) pathway.

Integration of GWAS and transcriptome analysis to identify temperature-dependent genes involved in germination of rapeseed (Brassica napus L.)

Low temperature germination (LTG) is one of crucial agronomic traits for field-grown rapeseed in the Yangtze River Basin, where delayed sowing frequently exposes germination to cold stress. Because of its importance, the genetic basis underlying rapeseed germination under different temperatures has been continuously focused. By long-term field observation, we screened out two cultivars with significantly different LTG performance (JY1621 and JY1605) in field and lab conditions, which therefore were further used for the transcriptome sequencings at three key timepoints under normal and low temperatures. Comparative analysis among multiple groups of differentially expressed genes (DEGs) revealed a set of either early or late temperature response germination (ETRG or LTRG) genes, as well as cold-tolerant (CDT) and temperature-insensitive (TPI) candidate regulators at different germination stages. Furthermore, we performed a genome-wide association study (GWAS) using germination index of 273 rapeseed accessions and identified 24 significant loci associated with germination potential under normal temperatures. Through integrated analysis of transcriptome sequencing and GWAS, we identified a series of candidate genes involved in temperature-dependent germination. Based on the comprehensive analysis, we hypothesized that BnaA3.CYP77A4 and BnaA3.NAC078 could be important candidate genes for LTG due to their expression patterns and haplotype distributions. This study performed the multi-omics analysis on temperature-dependent germination and provided potential genetic loci and candidate genes required for robust germination, which could be further considered for low-temperature germination breeding of rapeseed.

Regulation of alternative splicing by CBF-mediated protein condensation in plant response to cold stress

Cold acclimation is critical for the survival of plants in temperate regions under low temperatures, and C-REPEAT BINDING FACTORs (CBFs) are well established as key transcriptional factors that regulate this adaptive process by controlling the expression of cold-responsive genes. Here we demonstrate that CBFs are involved in modulating alternative splicing during cold acclimation through their interaction with subunits of the spliceosome complex. Under cold stress, CBF proteins accumulate and directly interact with SKI-INTERACTING PROTEIN (SKIP), a key component of the spliceosome, which positively regulates acquired freezing tolerance. This interaction facilitates the formation of SKIP nuclear condensates, which enhances the association between SKIP and specific cold-responsive transcripts, thereby increasing their splicing efficiency. Our findings uncover a regulatory role of CBFs in alternative splicing and highlight their pivotal involvement in the full development of cold acclimation, bridging transcriptional and post-transcriptional regulatory mechanisms.

The transcription factor WRKY41-FLAVONOID 3'-HYDROXYLASE module fine-tunes flavonoid metabolism and cold tolerance in potato

Cold stress adversely affects crop growth and productivity. Resolving the genetic basis of freezing tolerance is important for crop improvement. Wild potato (Solanum commersonii) exhibits excellent freezing tolerance. However, the genetic factors underlying its freezing tolerance remain poorly understood. Here, we identified flavonoid 3'-hydroxylase (F3'H), a key gene in the flavonoid biosynthesis pathway, as highly expressed in S. commersonii compared with cultivated potato (S. tuberosum L.). Loss of ScF3'H function impaired freezing tolerance in S. commersonii, while ScF3'H overexpression in cultivated potato enhanced its freezing tolerance. Metabolic analysis revealed that F3'H generates more downstream products by adding hydroxyl (-OH) groups to the flavonoid ring structures. These flavonoids enhance reactive oxygen species scavenging, thereby contributing to freezing tolerance. Furthermore, the W-box element in the F3'H promoter plays a critical role in cold responses. Cold-induced transcription factor ScWRKY41 directly binds to the ScF3'H promoter region and recruits histone acetyltransferase 1 (ScHAC1), which enhances histone acetylation at the F3'H locus and activates its transcription. Overall, we identified the cold-responsive WRKY41-F3'H module that enhances freezing tolerance by augmenting the antioxidant capacity of flavonoids. This study reveals a valuable natural gene module for breeding enhanced freezing tolerance in potato and other crops.

Convergent evolution in angiosperms adapted to cold climates

Convergent and parallel evolution occur more frequently than previously thought. Here, we focus on the evolutionary adaptations of angiosperms at sub-zero temperatures. We begin by introducing the history of research on convergent and parallel evolution, defining all independent similarities as convergent evolution. Our analysis reveals that frost zones (periodic or constant), which cover 49.1% of Earth's land surface, host 137 angiosperm families, with over 90% of their species thriving in these regions. In this context, we revisit the global biogeography and evolutionary trajectories of plant traits, such as herbaceous form and deciduous leaves, that are thought to be evasion strategies for frost adaptation. At the physiological and molecular levels, many angiosperms have independently evolved cold acclimation mechanisms through multiple pathways in addition to the well-characterized C-repeat binding factor/dehydration-responsive element binding protein 1 (CBF/DREB1) regulatory pathway. These convergent adaptations have occurred across various molecular levels, including amino acid substitutions and changes in gene duplication and expression within the same or similar functional pathways; however, identical amino acid changes are rare. Our results also highlight the prevalence of polyploidy in frost zones and the occurrence of paleopolyploidization events during global cooling. These patterns suggest repeated evolution in cold climates. Finally, we discuss plant domestication and predict climate zone shifts due to global warming and their effects on plant migration and in situ adaptation. Overall, the integration of ecological and molecular perspectives is essential for understanding and forecasting plant responses to climate change.

Phosphorylation-dependent VaMYB4a regulates cold stress in grapevine by inhibiting VaPIF3 and activating VaCBF4

Cold stress severely impacts the quality and yield of grapevine (Vitis L.). In this study, we extend our previous work to elucidate the role and regulatory mechanisms of Vitis amurensis MYB transcription factor 4a (VaMYB4a) in grapevine's response to cold stress. Our results identified VaMYB4a as a key positive regulator of cold stress. We demonstrated that VaMYB4a undergoes phosphorylation by V. amurensis calcineurin B-like (CBL) proteins-interacting protein kinase 18 (VaCIPK18) under cold stress, a process that activates VaMYB4a transcriptional activity. Using chromatin immunoprecipitation sequencing (ChIP-seq). We performed a comprehensive genomic search to identify downstream components that interact with VaMYB4a, leading to the discovery of a basic helix-loop-helix transcription factor, V. amurensis phytochrome-interacting factor 3 (VaPIF3). VaMYB4a attenuated the transcriptional activity of VaPIF3 through a phosphorylation-dependent interaction under cold conditions. Furthermore, VaPIF3, which interacts with and inhibits V. amurensis C-repeat binding factor 4 (VaCBF4, a known positive regulator of cold stress), has its activity attenuated by VaMYB4a, which mediates the modulation of this pathway. Notably, VaMYB4a also interacted with and promoted the expression of VaCBF4 in a phosphorylation-dependent manner. Our study shows that VaMYB4a positively modulates cold tolerance in plants by simultaneously downregulating VaPIF3 and upregulating VaCBF4. These findings provide a nuanced understanding of the transcriptional response in grapevine under cold stress and contribute to the broader field of plant stress physiology.

The ubiquitin ligase VviPUB19 negatively regulates grape cold tolerance by affecting the stability of ICEs and CBFs

Cold stress seriously affects plant growth and development. The ubiquitination system plays an important role by degrading and modifying substrates at the protein level. In this study, the U-box type ubiquitin ligase VviPUB19 gene was induced by low temperature (4°C) in grapevine. In Arabidopsis thaliana, the pub19 mutant, a homologous mutation of VviPUB19, exhibited enhanced cold tolerance, and the resistance phenotype of the mutant could be attenuated by VviPUB19. VviPUB19-overexpressing grape lines exhibited lower cold tolerance. Furthermore, it was revealed that VviPUB19 interacted with the cold-related transcription factors VviICE1, 2, and 3 and VviCBF1 and 2, and was involved in the degradation of them. This is the first time that an E3 ligase (VviPUB19) that interacts with CBFs and affects its protein stability has been identified. It was also shown that VviICE1, 2, and 3 positively regulated VviPUB19 promoter activity. Therefore, our results suggest that VviPUB19 reduces grape cold tolerance via participating in the CBF-dependent pathway.

Crosstalk Between Abiotic and Biotic Stresses Responses and the Role of Chloroplast Retrograde Signaling in the Cross-Tolerance Phenomena in Plants

In the natural environment, plants are simultaneously exposed to multivariable abiotic and biotic stresses. Typical abiotic stresses are changes in temperature, light intensity and quality, water stress (drought, flood), microelements availability, salinity, air pollutants, and others. Biotic stresses are caused by other organisms, such as pathogenic bacteria and viruses or parasites. This review presents the current state-of-the-art knowledge on programmed cell death in the cross-tolerance phenomena and its conditional molecular and physiological regulators, which simultaneously regulate plant acclimation, defense, and developmental responses. It highlights the role of the absorbed energy in excess and its dissipation as heat in the induction of the chloroplast retrograde phytohormonal, electrical, and reactive oxygen species signaling. It also discusses how systemic- and network-acquired acclimation and acquired systemic resistance are mutually regulated and demonstrates the role of non-photochemical quenching and the dissipation of absorbed energy in excess as heat in the cross-tolerance phenomenon. Finally, new evidence that plants evolved one molecular system to regulate cell death, acclimation, and cross-tolerance are presented and discussed.

Transcriptomic Analysis of the CAM Species Kalanchoë fedtschenkoi Under Low- and High-Temperature Regimes

Temperature stress is one of the major limiting environmental factors that negatively impact global crop yields. Kalanchoë fedtschenkoi is an obligate crassulacean acid metabolism (CAM) plant species, exhibiting much higher water-use efficiency and tolerance to drought and heat stresses than C3 or C4 plant species. Previous studies on gene expression responses to low- or high-temperature stress have been focused on C3 and C4 plants. There is a lack of information about the regulation of gene expression by low and high temperatures in CAM plants. To address this knowledge gap, we performed transcriptome sequencing (RNA-Seq) of leaf and root tissues of K. fedtschenkoi under cold (8 °C), normal (25 °C), and heat (37 °C) conditions at dawn (i.e., 2 h before the light period) and dusk (i.e., 2 h before the dark period). Our analysis revealed differentially expressed genes (DEGs) under cold or heat treatment in comparison to normal conditions in leaf or root tissue at each of the two time points. In particular, DEGs exhibiting either the same or opposite direction of expression change (either up-regulated or down-regulated) under cold and heat treatments were identified. In addition, we analyzed gene co-expression modules regulated by cold or heat treatment, and we performed in-depth analyses of expression regulation by temperature stresses for selected gene categories, including CAM-related genes, genes encoding heat shock factors and heat shock proteins, circadian rhythm genes, and stomatal movement genes. Our study highlights both the common and distinct molecular strategies employed by CAM and C3/C4 plants in adapting to extreme temperatures, providing new insights into the molecular mechanisms underlying temperature stress responses in CAM species.

CaNAC76 enhances lignin content and cold resistance in pepper by regulating CaCAD1

Low temperature restricts the growth, development, and yield of peppers, significantly limiting the development of the pepper industry. NAC (NAM, ATAF1/2, and CUC2) transcription factors (TFs) are implicated in plant responses to cold stress, but their specific mechanisms in peppers are unclear. In this study, we isolated a cold-induced NAC transcription factor, CaNAC76, from pepper (Capsicum annuum L.). CaNAC76 is localized in the nucleus and cytoplasm and exhibits transcriptional activation activity. Silencing CaNAC76 expression reduced the activities of superoxide dismutase, peroxidase, and catalase enzymes, resulting in decreased cold tolerance in peppers. Conversely, overexpressing CaNAC76 increased the activities of antioxidant enzymes and the expression of cold stress-responsive genes (ICE-CBF-COR) in Arabidopsis, enhancing the plant's freezing tolerance. Transcriptional regulation analysis showed that CaNAC76 directly binds to the promoter region of CaCAD1 and induces its expression. Similarly, low temperatures induced the expression of CaCAD1. Ectopic expression of CaCAD1 improved Arabidopsis freezing tolerance, whereas silencing CaCAD1 expression increased sensitivity to low temperatures. Furthermore, we observed that CaNAC76 overexpression enhanced CAD activity and lignin content in Arabidopsis, leading to lignin deposition in the xylem and interfascicular fibers. In summary, the results demonstrate that CaNAC76 can enhance cold tolerance in peppers by affecting both CBF-dependent (ICE-CBF-COR) and CBF-independent pathways (promoting CaCAD1 expression).

Engineering cold resilience: implementing gene editing tools for plant cold stress tolerance

MAIN CONCLUSION

This paper highlights the need for innovative approaches to enhance cold tolerance. It underscores how genome-editing tools can deepen our understanding of genes involved in cold stress. Cold stress is a significant abiotic factor in high-altitude regions, adversely affecting plant growth and limiting crop productivity. Plants have evolved various mechanisms in response to low temperatures that enable resistance at both physiological and molecular levels during chilling and freezing stress. Several cold-inducible genes have been isolated and characterized, with most playing key roles in providing tolerance against low-temperature stress. However, many plants fail to survive at low temperatures due to the absence of cold acclimatization mechanisms. Conventional breeding techniques, such as inter-specific or inter-genic hybridization, have had limited effectiveness in enhancing the cold resistance of essential crops. Thus, it is crucial to develop crops with improved adaptability, high yields and resistance to cold stress using advanced genomic approaches. The current availability of gene editing tools offers the opportunity to introduce targeted modifications in plant genomes efficiently, thereby developing cold-tolerant varieties. This review discusses advancements in gene editing tools, including zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9)/Cas12a(Cpf1), prime editing (PE) and retron library recombineering (RLR). We focus specifically on the CRISPR/Cas system, which has garnered significant attention in recent years as a groundbreaking tool for genome editing across various species. These techniques will enhance our understanding of molecular interactions under low-temperature stress response and highlight the progress of genome editing in designing future climate-resilient crops.

Genome-Wide Identification of Freezing-Responsive Genes in a Rapeseed Line NTS57 Tolerant to Low-Temperature

Winter rapeseed is a high-oil crop that exhibits significant sensitivity to low temperatures, leading to a substantial reduction in production. Hence, it is of great significance to elucidate the genomic genetic mechanism of strong freezing-resistant winter rapeseed to improve their freezing-resistant traits. In this study, global transcriptome expression profiles of the freezing-resistant cultivar NTS57 (NS) under freezing stress were obtained for the years 2015, 2016, and 2017 by RNA sequencing (RNA-seq). Most differentially expressed genes (DEGs) were involved in the plant hormone signal transduction, alpha-linolenic acid metabolism, protein processing, glutathione metabolism, and plant-pathogen interaction pathways. Antioxidant enzyme activities and lipid peroxidation levels were significantly positively and negatively correlated with overwintering rate (OWR), respectively. After freezing treatment, the formation of freezing resistance of NS was attributed to the increase in antioxidant enzyme activities and content of osmotic regulation substances, as well as the decrease in lipid peroxidation level. Furthermore, quantitative reverse transcription polymerase chain reaction (qRT-PCR) and phenotypic verification indicated that heat stress transcription factor A2 (HSFA2) and 17.6 kDa class II heat shock protein (HSP17.6) participated in the response to freezing stress. This study will further refine the regulatory network of plants against freezing stress and help to screen candidate genes for improving plant freezing resistance.

γ-Aminobutyric acid mediated by MdCBF3- MdGAD1 mitigates low temperature damage in apple

Low temperatures can seriously affect apple yield and can also cause chilling injury to apple fruit. γ-aminobutyric acid (GABA) plays an important role in improving plant stress resistance. Some studies have reported that GABA can improve cold resistance in plants, only through exogenous treatment; however, the molecular mechanism of its resistance to low temperature is still unknown. This result suggested that exogenous GABA treatment of both apple seedlings and fruit could improve the resistance of apple to low temperatures. MdGAD1, a key gene involved in GABA synthesis, was overexpressed in tomato plants and apple callus to improve their cold tolerance. Both yeast one-hybrid and luciferase assay showed that MdCBF3 could bind to the MdGAD1 promoter to activate its expression and promote GABA synthesis. These results revealed a molecular mechanism utilizing the MdCBF3-MdGAD1 regulatory module that can enhance cold resistance by increasing endogenous GABA synthesis in apple.

AtPRMT3-RPS2B promotes ribosome biogenesis and coordinates growth and cold adaptation trade-off

Translation, a fundamental process regulating cellular growth and proliferation, relies on functional ribosomes. As sessile organisms, plants have evolved adaptive strategies to maintain a delicate balance between growth and stress response. But the underlying mechanisms, particularly on the translational level, remain less understood. In this study, we revealed the mechanisms of AtPRMT3-RPS2B in orchestrating ribosome assembly and managing translational regulation. Through a forward genetic screen, we identified PDCD2-D1 as a suppressor gene restoring abnormal development and ribosome biogenesis in atprmt3-2 mutants. Our findings confirmed that PDCD2 interacts with AtPRMT3-RPS2B, and facilitates pre-ribosome transport through nuclear pore complex, finally ensuring normal ribosome translation in the cytoplasm. Additionally, the dysfunction of AtPRMT3-RPS2B was found to enhance freezing tolerance. Moreover, we revealed that AtPRMT3-RPS2B promotes the translation of housekeeping mRNAs while concurrently repressing stress-related mRNAs. In summary, our study sheds light on the regulatory roles of AtPRMT3-RPS2B in ribosome assembly and translational balance, enabling the trade-off between growth and stress.

Differential phosphorylation of Ca2+-permeable channel CYCLIC NUCLEOTIDE-GATED CHANNEL20 modulates calcium-mediated freezing tolerance in Arabidopsis

Plants respond to cold stress at multiple levels, including increasing cytosolic calcium (Ca2+) influx and triggering the expression of cold-responsive genes. In this study, we show that the Ca2+-permeable channel CYCLIC NUCLEOTIDE-GATED CHANNEL20 (CNGC20) positively regulates freezing tolerance in Arabidopsis (Arabidopsis thaliana) by mediating cold-induced Ca2+ influx. Moreover, we demonstrate that the leucine-rich repeat receptor-like kinase PLANT PEPTIDE CONTAINING SULFATED TYROSINE1 RECEPTOR (PSY1R) is activated by cold, phosphorylating and enhancing the activity of CNGC20. The psy1r mutant exhibits decreased cold-evoked Ca2+ influx and freezing tolerance. Conversely, COLD-RESPONSIVE PROTEIN KINASE1 (CRPK1), a protein kinase that negatively regulates cold signaling, phosphorylates and facilitates the degradation of CNGC20 under prolonged periods of cold treatment, thereby attenuating freezing tolerance. This study thus identifies PSY1R and CRPK1 kinases that regulate CNGC20 activity and stability, respectively, thereby antagonistically modulating freezing tolerance in plants.

ATBS1-INTERACTING FACTOR 2 Positively Regulates Freezing Tolerance via INDUCER OF CBF EXPRESSION 1/C-REPEAT BINDING FACTOR-Induced Cold Acclimation Pathway

The INDUCER OF CBF EXPRESSION 1/C-REPEAT BINDING FACTOR (ICE1/CBF) pathway plays a crucial role in plant responses to cold stress, impacting growth and development. Here, we demonstrated that ATBS1-INTERACTING FACTOR 2 (AIF2), a non-DNA-binding basic helix-loop-helix transcription factor, positively regulates freezing tolerance through the ICE1/CBF-induced cold tolerance pathway in Arabidopsis. Cold stress transcriptionally upregulated AIF2 expression and induced AIF2 phosphorylation, thereby stabilizing the AIF2 protein during early stages of cold acclimation. The AIF2 loss-of-function mutant, aif2-1, exhibited heightened sensitivity to freezing before and after cold acclimation. In contrast, ectopic expression of AIF2, but not the C-terminal-deleted AIF2 variant, restored freezing tolerance. AIF2 enhanced ICE1 stability during cold acclimation and promoted the transcriptional expression of CBFs and downstream cold-responsive genes, ultimately enhancing plant tolerance to freezing stress. MITOGEN-ACTIVATED PROTEIN KINASES 3 and 6 (MPK3/6), known negative regulators of freezing tolerance, interacted with and phosphorylated AIF2, subjecting it to protein degradation. Furthermore, transient co-expression of MPK3/6 with AIF2 and ICE1 downregulated AIF2/ICE1-induced transactivation of CBF2 expression. AIF2 interacted preferentially with BRASSINOSTEROID-INSENSITIVE 2 (BIN2) and MPK3/6 during the early and later stages of cold acclimation, respectively, thereby differentially regulating AIF2 activity in a cold acclimation time-dependent manner. Moreover, AIF2 acted additively in a gain-of-function mutant of BRASSINAZOLE-RESISTANT 1 (BZR1; bzr1-1D) and a triple knockout mutant of BIN2 and its homologs (bin2bil1bil2) to induce CBFs-mediated freezing tolerance. This suggests that cold-induced AIF2 coordinates freezing tolerance along with BZR1 and BIN2, key positive and negative components, respectively, of brassinosteroid signaling pathways.

Salicylic acid improves chilling tolerance via CsNPR1-CsICE1 interaction in grafted cucumbers

Salicylic acid (SA) plays a role in the regulation of grafting-induced cold tolerance. However, the molecular mechanism behind it is still unknown. Here, we established that the phenylalanine ammonia-lyase (PAL) pathway-dependent elevate in SA content in grafted cucumber leaves was not only synthesized in the leaves but also transported from the roots under chilling stress. RNAi-CsPAL with low SA content as rootstock reduced SA accumulation in grafted seedling leaves while decreasing rootstock-induced cold tolerance, as evidenced by higher electrolyte leakage (EL), hydrogen peroxide (H2O2), and superoxide anion (O2 ·-) contents and lower expression of cold-responsive genes (CsICE1, CsDREB1A, CsDREB1B, and CsCOR47), whereas OE-CsPAL with high SA content as rootstock improved the cold tolerance of grafted plants in comparison with the wild type (WT). In addition, CsNPR1 was significantly upregulated in grafted cucumber under chilling stress, with exogenous and endogenous overexpressed SA inducing its transcriptional expression and protein stability, which exhibited higher expression in grafted plants than in self-root plants. While CsNPR1-overexpression (OE-CsNPR1) seedlings as scions were more tolerant to chilling stress than WT seedlings, CsNPR1-suppression (Anti-CsNPR1) seedlings as scions were more vulnerable to chilling stress. Notably, CsNPR1-CsICE1 interactions alleviated ROS accumulation and activated the expression of CsDREB1A, CsDREB1B, CsCOR47, CsCOR15, CsCOR413, and CsKIN1 to enhance SA-mediated chilling tolerance in grafted cucumber. Overall, our findings reveal that SA enhances chilling tolerance in grafted cucumbers via the model of the CsNPR1-CsICE1 transcriptional regulatory cascade.

MYB Transcription Factor CDC5 Activates CBF3 Expression to Positively Regulates Freezing Tolerance via Cooperating With ICE1 and Histone Modification in Arabidopsis

The freezing temperature greatly limits the growth, development and productivity of plants. The C-repeat/DRE binding factor (CBF) plays a major role in cold acclimation, enabling plants to increase their freezing tolerance. Notably, the INDUCER OF CBF EXPRESSION1 (ICE1) protein has garnered attention for its pivotal role in bolstering plants' resilience against freezing through transcriptional upregulation of DREB1A/CBF3. However, the research on the interaction between ICE1 and other transcription factors and its function in regulating cold stress tolerance is largely inadequate. In this study, we found that a R2R3 MYB transcription factor CDC5 interacts with ICE1 and regulates the expression of CBF3 by recruiting RNA polymerase II, overexpression of ICE1 can complements the freezing deficient phenotype of cdc5 mutant. CDC5 increases the expression of CBF3 in response to freezing. Furthermore, CDC5 influences the expression of CBF3 by altering the chromatin status through H3K4me3 and H3K27me3 modifications. Our work identified a novel component that regulates CBF3 transcription in both ICE1-dependent and ICE1-independent manner, improving the understanding of the freezing signal transduction in plants.

Genome-wide investigation of the PIF gene family in alfalfa (Medicago sativa L.) expression profiles during development and stress

BACKGROUND

Phytochrome-interacting factors (PIFs) plays an important role in plants as hubs for intracellular signaling regulation. The PIF gene family has been identified and characterized in many plants, but alfalfa (Medicago sativa L.), an important perennial high-quality legume forage, has not been reported on the PIF gene family.

RESULTS

In this study, we presented the identification and characterization of five MsPIF genes in alfalfa (Medicago sativa L.). Phylogenetic analysis indicated that PIFs from alfalfa and other four plant species could be divided into three groups supported by similar motif analysis. The collinearity analysis of the MsPIF gene family showed the presence of two gene pairs, and the collinearity analysis with AtPIFs showed three gene pairs, indicating that the evolutionary process of this family is relatively conservative. Analysis of cis-acting elements in promoter regions of MsPIF genes indicated that various elements were related to light, abiotic stress, and plant hormone responsiveness. Gene expression analyses demonstrated that MsPIFs were primarily expressed in the leaves and were induced by various abiotic stresses.

CONCLUSION

This study conducted genome-wide identification, evolution, synteny analysis, and expression analysis of the PIFs in alfalfa. Our study lays a foundation for the study of the biological functions of the PIF gene family and provides a useful reference for improving abiotic stress resistance in alfalfa.

CaAOS as a hub gene based on physiological and transcriptomic analyses of cold-resistant and cold-sensitive pepper cultivars

The yield and quality of pepper are considerably influenced by the cold conditions. Herein, we performed morphological, physiological and transcriptomic analyses by using two pepper seedlings, '2379' (cold-resistant) and '2380' (cold-sensitive). Briefly, 60 samples from each cultivar were analyzed at four distinct time points (0, 6, 24 and 48 h) at 5 °C in darkness. The physiological indices and activities of enzymes exhibited marked differences between the two cultivars. Transcriptomic analysis indicated that, compared to the control group, 11,415 DEGs were identified in '2379' and '2380' at 24 h. In the early stage, the number of DEGs in '2379' was 5.68 times higher than that in '2380', potentially explaining the observed differences in tolerance to colds. Processes such as protein targeting to membranes, jasmonic acid (JA)-mediated signalling, cold response and abscisic acid-activated signalling were involved. Subsequently, we identified a hub gene, CaAOS, that is involved in JA biosynthesis, positively influences cold tolerance and is a target of CaMYC2. Variations in the GC-motif of the CaAOS's promoter may influence the expression levels of CaAOS under cold treatment. The result of this study may lead to the development of more effective strategies for enhancing cold tolerance, potentially benefitting pepper breeding in cold regions.

Physiological and transcriptomic profiles reveal key regulatory pathways involved in cold resistance in sunflower seedlings

During sunflower growth, cold waves often occur and impede plant growth. Therefore, it is crucial to study the underlying mechanism of cold resistance in sunflowers. In this study, physiological analysis revealed that as cold stress increased, the levels of ROS, malondialdehyde, ascorbic acid, and dehydroascorbic acid and the activities of antioxidant enzymes increased. Transcriptomics further identified 10,903 DEGs between any two treatments. Clustering analysis demonstrated that the expression of MYB44a, MYB44b, MYB12, bZIP2 and bZIP4 continuously upregulated under cold stress. Cold stress can induce ROS accumulation, which interacts with hormone signals to activate cold-responsive transcription factors regulating target genes involved in antioxidant defense, secondary metabolite biosynthesis, starch and sucrose metabolism enhancement for improved cold resistance in sunflowers. Additionally, the response of sunflowers to cold stress may be independent of the CBF pathway. These findings enhance our understanding of cold stress resistance in sunflowers and provide a foundation for genetic breeding.

The Role of Brassinosteroids in Plant Cold Stress Response

Temperature affects plant growth and geographical distribution. Cold stress occurs when temperatures fall below the physiologically optimal range for plants, causing permanent and irreversible damage to plant growth, development, and production. Brassinosteroids (BRs) are steroid hormones that play an important role in plant growth and various stress responses. Recent studies have shown that low temperatures affect BR biosynthesis in many plant species and that BR signaling is involved in the regulation of plant tolerance to low temperatures, both in the CBF-dependent and CBF-independent pathways. These two regulatory pathways correspond to transient and acclimation responses of low temperature, respectively. The crosstalk between BRs and other hormones is a significant factor in low-temperature tolerance. We provide an overview of recent developments in our knowledge of BRs' function in plant responses to cold stress and how they interact with other plant hormones in this review.

Discovery of candidate genes involved in ethylene biosynthesis and signal transduction pathways related to peach bud cold resistance

Background: Low temperature pose significant challenges to peach cultivation, causing severe damage to peach buds and restricting production and distribution. Ethylene, an important phytohormone, plays a critical role in enhancing plant cold resistance. Structural genes and transcription factors involved in ethylene biosynthesis and signal transduction pathways are associated with cold resistance. However, no research has specifically addressed their roles in peach cold resistance. Methods: In this study, we aimed for cold-resistance gene discovery in cold-sensitive peach cultivar "21Shiji" (21SJ) and cold-resistance cultivar "Shijizhixing" (SJZX) using RNA-seq and gas chromatography. Results: The findings revealed that under cold stress conditions, ethylene biosynthesis in "SJZX" was significantly induced. Subsequently, a structural gene, PpACO1-1, involved in ethylene biosynthesis in peach buds was significantly upregulated and showed a higher correlation with ethylene release rate. To identify potential transcription factors associated with PpACO1-1 expression and ethylene signal transduction, weighted gene co-expression network analysis was conducted using RNA-seq data. Four transcription factors: PpERF2, PpNAC078, PpWRKY65 and PpbHLH112, were identified. Conclusion: These findings provide valuable theoretical insights for investigating the regulatory mechanisms of peach cold resistance and guiding breeding strategies.

Integrated Metabolomics and Transcriptomics Reveal the Key Role of Flavonoids in the Cold Tolerance of Chrysanthemum

Chrysanthemum (Chrysanthemum morifolium, ground-cover Chrysanthemums), one of the important garden flowers, has a high ornamental and economic value. However, its ornamental value is significantly diminished by the low temperature experienced in northeastern China. Here, metabolomics and transcriptomics were performed on three Chrysanthemum cultivars before and after a low temperature to investigate the dynamic metabolite changes and the molecular regulatory mechanisms. The results showed that 1324 annotated metabolites were detected, among which 327 were identified as flavonoids derived from Chrysanthemum. The accumulation of metabolites and gene expression related to the flavonoid biosynthesis pathway significantly increased in the three cultivars under the low temperature, indicating flavonoid metabolism actively participates in the Chrysanthemum cold response. Specifically, the content of cyanidin and pelargonidin derivatives and the expression of anthocyanin biosynthesis genes significantly increases in XHBF, providing a reasonable explanation for the change in petal color from white to purple under the low temperature. Six candidate UDP-glycosyltransferase genes involved in the glycosylation of flavonoids were identified through correlation networks and phylogenetic analysis. CmNAC1, CmbZIP3, and other transcription factors potentially regulating flavonoid metabolism and responding to low temperatures were discovered by correlation analysis and weighted gene co-expression network analysis (WGCNA). In conclusion, this study elucidated the specific response of flavonoids to low temperatures in Chrysanthemums, providing valuable insights and metabolic data for investigating cold tolerance.

The NAC056 transcription factor confers freezing tolerance by positively regulating expression of CBFs and NIA1 in Arabidopsis

Freezing stress can seriously affect plant growth and development, but the mechanisms of these effects and plant responses to freezing stress require further exploration. Here, we identified a NAM, ATAF1/2, and CUC2 (NAC)-family transcription factor (TF), NAC056, that can promote freezing tolerance in Arabidopsis. NAC056 mRNA levels are strongly induced by freezing stress in roots, and the nac056 mutant exhibits compromised freezing tolerance. NAC056 acts positively in response to freezing by directly promoting key C-repeat-binding factor (CBF) pathway genes. Interestingly, we found that CBF1 regulates nitrate assimilation by regulating the nitrate reductase gene NIA1 in plants; therefore, NAC056-CBF1-NIA1 form a regulatory module for the assimilation of nitrate and the growth of roots under freezing stress. In addition, 35S::NAC056 transgenic plants show enhanced freezing tolerance, which is partially reversed in the cbfs triple mutant. Thus, NAC056 confers freezing tolerance through the CBF pathway, mediating plant responses to balance growth and freezing stress tolerance.

Integrated analysis of DNA methylome and transcriptome revealing epigenetic regulation of CRIR1-promoted cold tolerance

BACKGROUND

DNA methylation contributes to the epigenetic regulation of nuclear gene expression, and is associated with plant growth, development, and stress responses. Compelling evidence has emerged that long non-coding RNA (lncRNA) regulates DNA methylation. Previous genetic and physiological evidence indicates that lncRNA-CRIR1 plays a positive role in the responses of cassava plants to cold stress. However, it is unclear whether global DNA methylation changes with CRIR1-promoted cold tolerance.

RESULTS

In this study, a comprehensive comparative analysis of DNA methylation and transcriptome profiles was performed to reveal the gene expression and epigenetic dynamics after CRIR1 overexpression. Compared with the wild-type plants, CRIR1-overexpressing plants present gained DNA methylation in over 37,000 genomic regions and lost DNA methylation in about 16,000 genomic regions, indicating a global decrease in DNA methylation after CRIR1 overexpression. Declining DNA methylation is not correlated with decreased/increased expression of the DNA methylase/demethylase genes, but is associated with increased transcripts of a few transcription factors, chlorophyll metabolism and photosynthesis-related genes, which could contribute to the CRIR1-promoted cold tolerance.

CONCLUSIONS

In summary, a first set of transcriptome and epigenome data was integrated in this study to reveal the gene expression and epigenetic dynamics after CRIR1 overexpression, with the identification of several TFs, chlorophyll metabolism and photosynthesis-related genes that may be involved in CRIR1-promoted cold tolerance. Therefore, our study has provided valuable data for the systematic study of molecular insights for plant cold stress response.

INDUCER OF CBF EXPRESSION 1 promotes cold-enhanced immunity by directly activating salicylic acid signaling

Cold stress affects plant immune responses, and this process may involve the salicylic acid (SA) signaling pathway. However, the underlying mechanism by which low-temperature signals coordinate with SA signaling to regulate plant immunity remains unclear. Here, we found that low temperatures enhanced the disease resistance of Arabidopsis thaliana against Pseudomonas syringae pv. tomato DC3000. This process required INDUCER OF CBF EXPRESSION 1 (ICE1), the core transcription factor in cold-signal cascades. ICE1 physically interacted with NONEXPRESSER OF PATHOGENESIS-RELATED GENES 1 (NPR1), the master regulator of the SA signaling pathway. Enrichment of ICE1 on the PATHOGENESIS-RELATED GENE 1 (PR1) promoter and its ability to transcriptionally activate PR1 were enhanced by NPR1. Further analyses revealed that cold stress signals cooperate with SA signals to facilitate plant immunity against pathogen attack in an ICE1-dependent manner. Cold treatment promoted interactions of NPR1 and TGACG-BINDING FACTOR 3 (TGA3) with ICE1 and increased the ability of the ICE1-TGA3 complex to transcriptionally activate PR1. Together, our results characterize a critical role of ICE1 as an indispensable regulatory node linking low-temperature-activated and SA-regulated immunity. Understanding this crucial role of ICE1 in coordinating multiple signals associated with immunity broadens our understanding of plant-pathogen interactions.

Overexpression of PavHIPP16 from Prunus avium enhances cold stress tolerance in transgenic tobacco

BACKGROUND

The heavy metal-associated isoprenylated plant protein (HIPP) is an important regulatory element in response to abiotic stresses, especially playing a key role in low-temperature response.

RESULTS

This study investigated the potential function of PavHIPP16 up-regulated in sweet cherry under cold stress by heterologous overexpression in tobacco. The results showed that the overexpression (OE) lines' growth state was better than wild type (WT), and the germination rate, root length, and fresh weight of OE lines were significantly higher than those of WT. In addition, the relative conductivity and malondialdehyde (MDA) content of the OE of tobacco under low-temperature treatment were substantially lower than those of WT. In contrast, peroxidase (POD), superoxide dismutase (SOD), catalase (CAT) activities, hydrogen peroxide (H2O2), proline, soluble protein, and soluble sugar contents were significantly higher than those of WT. Yeast two-hybrid assay (Y2H) and luciferase complementation assay verified the interactions between PavbHLH106 and PavHIPP16, suggesting that these two proteins co-regulated the cold tolerance mechanism in plants. The research results indicated that the transgenic lines could perform better under low-temperature stress by increasing the antioxidant enzyme activity and osmoregulatory substance content of the transgenic plants.

CONCLUSIONS

This study provides genetic resources for analyzing the biological functions of PavHIPPs, which is important for elucidating the mechanisms of cold resistance in sweet cherry.

A major gene for chilling tolerance variation in Indica rice codes for a kinase OsCTK1 that phosphorylates multiple substrates under cold

Rice is susceptible to chilling stress. Identifying chilling tolerance genes and their mechanisms are key to improve rice performance. Here, we performed a genome-wide association study to identify regulatory genes for chilling tolerance in rice. One major gene for chilling tolerance variation in Indica rice was identified as a casein kinase gene OsCTK1. Its function and natural variation are investigated at the physiological and molecular level by its mutants and transgenic plants. Potential substrates of OsCTK1 were identified by phosphoproteomic analysis, protein-protein interaction assay, in vitro kinase assay, and mutant characterization. OsCTK1 positively regulates rice chilling tolerance. Three of its putative substrates, acidic ribosomal protein OsP3B, cyclic nucleotide-gated ion channel OsCNGC9, and dual-specific mitogen-activated protein kinase phosphatase OsMKP1, are each involved in chilling tolerance. In addition, a natural OsCTK1 chilling-tolerant (CT) variant exhibited a higher kinase activity and conferred greater chilling tolerance compared with a chilling-sensitive (CS) variant. The CT variant is more prevalent in CT accessions and is distributed more frequently in higher latitude compared with the CS variant. This study thus enables a better understanding of chilling tolerance mechanisms and provides gene variants for genetic improvement of chilling tolerance in rice.

Chilling stress response in tobacco seedlings: insights from transcriptome, proteome, and phosphoproteome analyses

Tobacco (Nicotiana tabacum L.) is an important industrial crop, which is sensitive to chilling stress. Tobacco seedlings that have been subjected to chilling stress readily flower early, which seriously affects the yield and quality of their leaves. Currently, there has been progress in elucidating the molecular mechanisms by which tobacco responds to chilling stress. However, little is known about the phosphorylation that is mediated by chilling. In this study, the transcriptome, proteome and phosphoproteome were analyzed to elucidate the mechanisms of the responses of tobacco shoot and root to chilling stress (4 °C for 24 h). A total of 6,113 differentially expressed genes (DEGs), 153 differentially expressed proteins (DEPs) and 345 differential phosphopeptides were identified in the shoot, and the corresponding numbers in the root were 6,394, 212 and 404, respectively. This study showed that the tobacco seedlings to 24 h of chilling stress primarily responded to this phenomenon by altering their levels of phosphopeptide abundance. Kyoto Encyclopedia of Genes and Genomes analyses revealed that starch and sucrose metabolism and endocytosis were the common pathways in the shoot and root at these levels. In addition, the differential phosphopeptide corresponding proteins were also significantly enriched in the pathways of photosynthesis-antenna proteins and carbon fixation in photosynthetic organisms in the shoot and arginine and proline metabolism, peroxisome and RNA transport in the root. These results suggest that phosphoproteins in these pathways play important roles in the response to chilling stress. Moreover, kinases and transcription factors (TFs) that respond to chilling at the levels of phosphorylation are also crucial for resistance to chilling in tobacco seedlings. The phosphorylation or dephosphorylation of kinases, such as CDPKs and RLKs; and TFs, including VIP1-like, ABI5-like protein 2, TCP7-like, WRKY 6-like, MYC2-like and CAMTA7 among others, may play essential roles in the transduction of tobacco chilling signal and the transcriptional regulation of the genes that respond to chilling stress. Taken together, these findings provide new insights into the molecular mechanisms and regulatory networks of the responses of tobacco to chilling stress.

The transcription factor RhMYB17 regulates the homeotic transformation of floral organs in rose (Rosa hybrida) under cold stress

Low temperatures affect flower development in rose (Rosa hybrida), increasing petaloid stamen number and reducing normal stamen number. We identified the low-temperature-responsive R2R3-MYB transcription factor RhMYB17, which is homologous to Arabidopsis MYB17 by similarity of protein sequences. RhMYB17 was up-regulated at low temperatures, and RhMYB17 transcripts accumulated in floral buds. Transient silencing of RhMYB17 by virus-induced gene silencing decreased petaloid stamen number and increased normal stamen number. According to the ABCDE model of floral organ identity, class A genes APETALA 1 (AP1) and AP2 contribute to sepal and petal formation. Transcription factor binding analysis identified RhMYB17 binding sites in the promoters of rose APETALA 2 (RhAP2) and APETALA 2-LIKE (RhAP2L). Yeast one-hybrid assays, dual-luciferase reporter assays, and electrophoretic mobility shift assays confirmed that RhMYB17 directly binds to the promoters of RhAP2 and RhAP2L, thereby activating their expression. RNA sequencing further demonstrated that RhMYB17 plays a pivotal role in regulating the expression of class A genes, and indirectly influences the expression of the class C gene. This study reveals a novel mechanism for the homeotic transformation of floral organs in response to low temperatures.

Functional Divergence in Orthologous Transcription Factors: Insights from AtCBF2/3/1 and OsDREB1C

Despite traditional beliefs of orthologous genes maintaining similar functions across species, growing evidence points to their potential for functional divergence. C-repeat binding factors/dehydration-responsive element binding protein 1s (CBFs/DREB1s) are critical in cold acclimation, with their overexpression enhancing stress tolerance but often constraining plant growth. In contrast, a recent study unveiled a distinctive role of rice OsDREB1C in elevating nitrogen use efficiency (NUE), photosynthesis, and grain yield, implying functional divergence within the CBF/DREB1 orthologs across species. Here, we delve into divergent molecular mechanisms of OsDREB1C and AtCBF2/3/1 by exploring their evolutionary trajectories across rice and Arabidopsis genomes, regulatomes, and transcriptomes. Evolutionary scrutiny shows discrete clades for OsDREB1C and AtCBF2/3/1, with the Poaceae-specific DREB1C clade mediated by a transposon event. Genome-wide binding profiles highlight OsDREB1C's preference for GCCGAC compared to AtCBF2/3/1's preference for A/GCCGAC, a distinction determined by R12 in the OsDREB1C AP2/ERF domain. Cross-species multiomic analyses reveal shared gene orthogroups (OGs) and underscore numerous specific OGs uniquely bound and regulated by OsDREB1C, implicated in NUE, photosynthesis, and early flowering, or by AtCBF2/3/1, engaged in hormone and stress responses. This divergence arises from gene gains/losses (∼16.7% to 25.6%) and expression reprogramming (∼62.3% to 66.2%) of OsDREB1C- and AtCBF2/3/1-regulated OGs during the extensive evolution following the rice-Arabidopsis split. Our findings illustrate the regulatory evolution of OsDREB1C and AtCBF2/3/1 at a genomic scale, providing insights on the functional divergence of orthologous transcription factors following gene duplications across species.

Regulatory networks in plant responses to drought and cold stress

Drought and cold represent distinct types of abiotic stress, each initiating unique primary signaling pathways in response to dehydration and temperature changes, respectively. However, a convergence at the gene regulatory level is observed where a common set of stress-responsive genes is activated to mitigate the impacts of both stresses. In this review, we explore these intricate regulatory networks, illustrating how plants coordinate distinct stress signals into a collective transcriptional strategy. We delve into the molecular mechanisms of stress perception, stress signaling, and the activation of gene regulatory pathways, with a focus on insights gained from model species. By elucidating both the shared and distinct aspects of plant responses to drought and cold, we provide insight into the adaptive strategies of plants, paving the way for the engineering of stress-resilient crop varieties that can withstand a changing climate.

Overexpression of MsDREB1C Modulates Growth and Improves Forage Quality in Tetraploid Alfalfa (Medicago sativa L.)

DREB has been reported to be involved in plant growth and response to environmental factors. However, the function of DREB in growth and development has not been elucidated in alfalfa (Medicago sativa L.), a perennial tetraploid forage cultivated worldwide. In this study, an ortholog of MtDREB1C was characterized from alfalfa and named MsDREB1C accordingly. MsDREB1C was significantly induced by abiotic stress. The transcription factor MsDREB1C resided in the nucleus and had self-transactivation activity. The MsDREB1C overexpression (OE) alfalfa displayed growth retardation under both long-day and short-day conditions, which was supported by decreased MsGA20ox and upregulated MsGA2ox in the OE lines. Consistently, a decrease in active gibberellin (GA) was detected, suggesting a negative effect of MsDREB1C on GA accumulation in alfalfa. Interestingly, the forage quality of the OE lines was better than that of WT lines, with higher crude protein and lower lignin content, which was supported by an increase in the leaf-stem ratio (LSR) and repression of several lignin-synthesis genes (MsNST, MsPAL1, MsC4H, and Ms4CL). Therefore, this study revealed the effects of MsDREB1C overexpression on growth and forage quality via modifying GA accumulation and lignin synthesis, respectively. Our findings provide a valuable candidate for improving the critical agronomic traits of alfalfa, such as overwintering and feeding value of the forage.

ERF54 regulates cold tolerance in Rosa multiflora through DREB/COR signalling pathways

Ethylene-responsive factors (ERFs) participate in a wide range of physiological and biological processes. However, many of the functions of ERFs in cold stress responses remain unclear. We, therefore, characterised the cold responses of RmERF54 in Rosa multiflora, a rose-related cold-tolerant species. Overexpression of RmERF54, which is a nuclear transcription factor, increases the cold resistance of transgenic tobacco and rose somatic embryos. In contrast, virus-induced gene silencing (VIGS) of RmERF54 increased cold susceptibility of R. multiflora. The overexpression of RmERF54 resulted in extensive transcriptional reprogramming of stress response and antioxidant enzyme systems. Of these, the levels of transcripts encoding the PODP7 peroxidase and the cold-related COR47 protein showed the largest increases in the somatic embryos with ectopic expression of RmERF54. RmERF54 binds to the promoters of the RmPODP7 and RmCOR47 genes and activates expression. RmERF54-overexpressing lines had higher antioxidant enzyme activities and considerably lower levels of reactive oxygen species. Opposite effects on these parameters were observed in the VIGS plants. RmERF54 was identified as a target of Dehydration-Responsive-Element-Binding factor (RmDREB1E). Taken together, provide new information concerning the molecular mechanisms by which RmERF54 regulates cold tolerance.

Allelic variation of PmCBF03 contributes to the altitude and temperature adaptability in Japanese apricot (Prunus mume Sieb. et Zucc.)

Japanese apricot is an important subtropical deciduous fruit tree in China, widely distributed in different altitude areas. How does it adapt to the different temperature environments in these areas? In this study, we identified a low-temperature transcription factor PmCBF03 on chromosome 7 through adaptive analysis of populations at different altitudes, which has an early termination single nucleotide polymorphism mutation. There were two different types of variation, PmCBF03A type in high-altitude areas and PmCBF03T type in low-altitude areas. PmCBF03A gene increased the survival rate, Fv/Fm values, antioxidant enzyme activity, and expression levels of antioxidant enzyme genes, and reducing electrolyte leakage and accumulation of reactive oxygen species in transgenic Arabidopsis under low temperature and freezing stress. Simultaneously, PmCBF03A gene promoted the dormancy of transgenic Arabidopsis seeds than wild-type. Biochemical analysis demonstrated that PmCBF03A directly bound to the DRE/CRT element in the promoters of the PmCOR413, PmDAM6 and PmABI5 genes, promoting their transcription and enhanced the cold resistance and dormancy of the overexpressing PmCBF03A lines. While PmCBF03T gene is unable to bind to the promoters of PmDAM6 and PmABI5 genes, leading to early release of dormancy to adapt to the problem of insufficient chilling requirement in low-altitude areas.