Citrus sinensis CBF1 Functions in Cold Tolerance by Modulating Putrescine Biosynthesis through Regulation of Arginine Decarboxylase

Sodium hydrosulfide application induces chilling tolerance in banana fruits by enhancing antioxidant gene expression through the upregulation of the ethylene response factors MaERF53L/121L

Sodium hydrosulfide (NaHS), a hydrogen sulfide (H₂S) donor, effectively mitigates chilling injury (CI) in bananas; however, the underlying molecular mechanisms remain unclear. This study demonstrated that NaHS alleviates CI symptoms by activating antioxidant defense systems that reduce oxidative stress induced by CI. Transcriptomic analysis revealed 1003 differentially expressed genes in three sample groups, with enrichment in pathways related to cellular processes, metabolic activity, and secondary metabolite biosynthesis. NaHS treatment significantly upregulated seven ethylene response factors, among which MaERF53L and MaERF121L functioned as transcriptional activators. Further investigation revealed that MaERF53L and MaERF121L directly bind to the promoters of MaPOD3 and MaGSTU18, enhancing their expression as well as the antioxidant enzyme activity. These findings indicate that the activation of antioxidant genes by MaERF53L and MaERF121L is central to NaHS-induced CI mitigation in bananas, providing novel insights into the role of H₂S in reducing CI across horticultural crops.

The transcription factor TGA2 orchestrates salicylic acid signal to regulate cold-induced proline accumulation in Citrus

Plants subjected to cold stress have been observed to accumulate proline, but the underlying regulatory mechanism remains to be elucidated. In this study, we identified a pyrroline-5-carboxylate synthetase (P5CS)-encoding gene (CtrP5CS1) from trifoliate orange (Citrus trifoliata L.), a cold-hardy citrus species, as a critical gene for cold-induced proline accumulation. CtrTGA2 bound directly to the TGACG motif of the CtrP5CS1 promoter and activated its expression. Moreover, CtrTGA2 functioned positively in cold tolerance via modulation of proline synthesis by regulating CtrP5CS1 expression. Up-regulation of CtrP5CS1 and CtrTGA2 under cold stress was dependent on salicylic acid (SA) biosynthesis. CtrTGA2 directly regulated the expression of CtrICS1, a gene encoding isochorismate synthase (ICS) involved in SA biosynthesis, forming a positive feedback loop to intensify the CtrTGA2-mediated transcriptional activation of CtrP5CS1. The cold-induced SA receptor NONEXPRESSOR OF PATHOGENESIS-RELATED GENES3 (CtrNPR3) interacted with CtrTGA2 to inhibit its transcriptional activation activity; however, the inhibition was released by SA. Our results uncover the CtrTGA2-CtrP5CS1/CtrICS1 regulatory module that orchestrates the SA signal to regulate proline synthesis, giving important insights into the transcriptional mechanism underlying proline accumulation in plants under cold stress.

A CsWRKY48 Gene from Tea Plants Intercropped with Chinese Chestnut Plays an Important Role in Resistance to Biotic and Abiotic Stresses

Tea plant (Camellia sinensis) is an important horticultural crop. The quality and productivity of tea plants is always threatened by various adverse environmental factors. Numerous studies have shown that intercropping tea plants with other plants can greatly improve the quality of their products. The intercropping system of Chinese chestnut (Castanea mollissima) and tea plants is an agricultural planting model in which the two species are grown on the same piece of land following a specific spacing and cultivation method. Based on a comparative transcriptome analysis between Chinese chestnut tea intercropped plantations and a pure tea plantation, it was found that the expression levels of the WRKY genes were significantly upregulated under the intercropping pattern. In this study, we cloned a candidate gene, CsWRKY48, and verified its functions in tobacco (Nicotiana tabacum) via heterologous transformation. The contents of protective enzyme activities and osmoregulatory substances were significantly increased, and the trichomes length and density were improved in the transgenic tobacco lines. This phenotype offered an enhanced resistance to both low temperatures and aphids for transgenic lines overexpressing CsWRKY48. Further analysis indicated that the CsWRKY48 transcription factor might interact with other regulators, such as CBF, ERF, MYC, and MYB, to enhance the resistance of tea plants to biotic and abiotic stresses. These findings not only confirm the elevated resistance of tea plants under intercropping, but also indicate a potential regulatory network mediated by the WRKY transcription factor.

Polyamines: The valuable bio-stimulants and endogenous signaling molecules for plant development and stress response

Polyamines (PAs) are nitrogenous and polycationic compounds containing more than two amine residues. Numerous investigations have demonstrated that cellular PA homeostasis plays a key role in various developmental and physiological processes. The PA balance, which may be affected by many environmental factors, is finely maintained by the pathways of PA biosynthesis and degradation (catabolism). In this review, the advances in PA transport and distribution and their roles in plants were summarized and discussed. In addition, the interplay between PAs and phytohormones, NO, and H2O2 were detailed during plant growth, senescence, fruit repining, as well as response to biotic and abiotic stresses. Moreover, it was elucidated how environmental signals such as light, temperature, and humidity modulate PA accumulation during plant development. Notably, PA has been shown to exert a potential role in shaping the domestication of rice. The present review comprehensively summarizes these latest advances, highlighting the importance of PAs as endogenous signaling molecules in plants, and as well proposes future perspectives on PA research.

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.

A Transcriptome Analysis of Poncirus trifoliata, an Aurantioideae Species Tolerant to Asian Citrus Psyllid, Has Identified Potential Genes and Events Associated with Psyllid Resistance

Citrus huanglongbing (HLB) is a devastating disease for citrus production, largely caused by the Asian citrus psyllid (ACP). Poncirus trifoliata exhibits high resistance to ACP; however, this resistance is weakened when C. sinensis is co-cultivated. This study aimed to identify the differentially expressed genes (DEGs) during ACP feeding and to uncover potential ACP resistance genes in P. trifoliata. In comparison to independent cultivation, 1247 and 205 DEGs were identified in P. trifoliata when co-cultivated with C. sinensis after 7 and 14 days, respectively. Analysis of enriched Gene Ontology categories revealed that DEGs were significantly associated with the cell wall, glucometabolic activities, and secondary metabolites. Additionally, these genes were found to be involved in phytohormone signaling, cell wall metabolism, redox state homeostasis, and secondary metabolites, as well as a number of transcription factor genes (TFs). Furthermore, we examined the impact of the ACP feeding factor on the gene expression patterns in P. trifoliata. Results showed an increase in the JA signaling pathway and various TFs. The RNA-seq results were verified using reverse transcription quantitative PCR. Our findings shed light on the molecular basis of ACP resistance in P. trifoliata and identified potential genes associated with this resistance.

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.

Endophytic Bacillus pumilus G5 Interacting with Silicon to Improve Drought Stress Resilience in Glycyrrhiza uralensis Fisch. by Modulating Nitrogen Absorption, Assimilation, and Metabolism Pathways

Drought stress has become the primary severe threat to global agriculture production, including medicinal plants. Plant growth-promoting bacteria (PGPB) and environmentally friendly element silicon (Si) have emerged as effective methods in alleviating drought stress in various plants. Here, the effects of the plant endophytic G5 interaction with Si on regulating nitrogen absorption, assimilation, and metabolism pathways were investigated in the morphophysiological and gene attributes of Glycyrrhiza uralensis exposed to drought. Results showed that G5+Si application improved nitrogen absorption and assimilation by increasing the available nitrogen content in the soil, further improving the nitrogen utilization efficiency. Then, G5+Si triggered the accumulation of the major adjustment substances proline, γ-aminobutyric acid, putrescine, and chlorophyll, which played an important role in contributing to maintaining balance and energy supply in G. uralensis exposed to drought. These findings will provide new ideas for the combined application of PGPR and Si on both soil and plant systems in a drought habitat.

A C2H2-type zinc finger protein ZAT12 of Poncirus trifoliata acts downstream of CBF1 to regulate cold tolerance

The Cys2/His2 (C2H2)-type zinc finger family has been reported to regulate multiple aspects of plant development and abiotic stress response. However, the role of C2H2-type zinc finger proteins in cold tolerance remains largely unclear. Through RNA-sequence analysis, a cold-responsive zinc finger protein, named as PtrZAT12, was identified and isolated from trifoliate orange (Poncirus trifoliata L. Raf.), a cold-hardy plant closely related to citrus. Furthermore, we found that PtrZAT12 was markedly induced by various abiotic stresses, especially cold stress. PtrZAT12 is a nuclear protein, and physiological analysis suggests that overexpression of PtrZAT12 conferred enhanced cold tolerance in transgenic tobacco (Nicotiana tabacum) plants, while knockdown of PtrZAT12 by virus-induced gene silencing (VIGS) increased the cold sensitivity of trifoliate orange and repressed expression of genes involved in stress tolerance. The promoter of PtrZAT12 harbors a DRE/CRT cis-acting element, which was verified to be specifically bound by PtrCBF1 (Poncirus trifoliata C-repeat BINDING FACTOR1). VIGS-mediated silencing of PtrCBF1 reduced the relative expression levels of PtrZAT12 and decreased the cold resistance of trifoliate orange. Based on these results, we propose that PtrZAT12 is a direct target of CBF1 and plays a positive role in modulation of cold stress tolerance. The knowledge gains new insight into a regulatory module composed of CBF1-ZAT12 in response to cold stress and advances our understanding of cold stress response in plants.

PbrWRKY62-PbrADC1 module involves in superficial scald development of Pyrus bretschneideri Rehd.fruit via regulating putrescine biosynthesis

Putrescine plays a role in superficial scald development during the cold storage of pear fruit. However, the molecular mechanism behind this phenomenon has not been un-fully clarified until recently. In this study, a conjoint analysis of metabolites and gene expression profiles in the putrescine-metabolic pathway of P. bretschneideri Rehd. fruit followed by experimental validation revealed that PbrADC1, forming a homodimer in the chloroplast, was involved in putrescine biosynthesis and thus fruit chilling resistance. Additionally, the substrate-binding residue Cys546 in PbrADC1, whose activity was modified by H2O2, played a crucial role in arginine decarboxylation into agmatine. Through a combined analysis of the distribution of cis-acting elements in the PbrADC1 promoter as well as the expression profiles of related transcription factors (TFs), several TFs were identified as upstream regulators of PbrADC1 gene. Further investigation revealed that the nuclear PbrWRKY62 could directly bind to the W-box elements in the PbrADC1 promoter, activate its expression, enhance putrescine accumulation, and thus increase fruit chilling tolerance. In conclusion, our results suggest that the PbrWRKY62-PbrADC1 module is involved in the development of superficial scald in P. bretschneideri Rehd. fruit via regulating putrescine biosynthesis. Consequently, these findings could serve as valuable genetic resources for breeding scald-resistant pear fruit.

NtERF283 positively regulates water deficit tolerance in tobacco (Nicotianatabacum L.) by enhancing antioxidant capacity

Ethylene responsive factor (ERF) is a plant-specific transcription factor that plays a pivotal regulatory role in various stress responses. Although the genome of tobacco harbors 375 ER F genes, the functional roles of the majority of these genes remain unknown. Expression pattern analysis revealed that NtERF283 was induced by water deficit and salt stresses and mainly expressed in the roots and leaves. Subcellular localization and transcriptional activity assays confirmed that NtERF283 was localized in the nucleus and exhibited transcriptional activity. In comparison to the wild-type (WT), the NtERF283-overexpressing transgenic plants (OE) exhibited enhanced water deficit tolerance, whereas the knockout mutant erf283 displayed contrasting phenotypes. Transcriptional analysis demonstrated that several oxidative stress response genes were significantly altered in OE plants under water deficit conditions. 3,3'-diaminobenzidine (DAB) and nitroblue tetrazolium (NBT) staining showed that erf283 accumulated a higher level of reactive oxygen species (ROS) compared to the WT under water deficit conditions. Conversely, OE plants displayed the least amount of ROS accumulation. Furthermore, the activities of POD and SOD were higher in OE plants and lower in erf283, suggesting that NtERF283 enhanced the capacity to effectively eliminate ROS, consequently enhancing water deficit tolerance in tobacco. These findings strongly indicate the significance of NtERF283 in promoting tobacco water deficit tolerance through the activation of the antioxidant system.

Research progress on the physiological response and molecular mechanism of cold response in plants

Low temperature is a critical environmental stress factor that restricts crop growth and geographical distribution, significantly impacting crop quality and yield. When plants are exposed to low temperatures, a series of changes occur in their external morphology and internal physiological and biochemical metabolism. This article comprehensively reviews the alterations and regulatory mechanisms of physiological and biochemical indices, such as membrane system stability, redox system, fatty acid content, photosynthesis, and osmoregulatory substances, in response to low-temperature stress in plants. Furthermore, we summarize recent research on signal transduction and regulatory pathways, phytohormones, epigenetic modifications, and other molecular mechanisms mediating the response to low temperatures in higher plants. In addition, we outline cultivation practices to improve plant cold resistance and highlight the cold-related genes used in molecular breeding. Last, we discuss future research directions, potential application prospects of plant cold resistance breeding, and recent significant breakthroughs in the research and application of cold resistance mechanisms.

Integrated Transcriptomics and Metabolomics Analyses Provide Insights into Qingke in Response to Cold Stress

The survival and productivity of qingke in high altitude (>4300 m, average yearly temperature <0 °C) of the Tibetan Plateau are significantly impacted by low-temperature stress. Uncovering the mechanisms underlying low-temperature stress response in cold-tolerant qingke varieties is crucial for qingke breeding. Herein, we conducted a comprehensive transcriptomic and metabolomic analysis on cold-sensitive (ZQ) and cold-tolerant (XL) qingke varieties under chilling and freezing treatments and identified lipid metabolism pathways as enriched in response to freezing treatment. Additionally, a significant positive correlation was observed between the expression of C-repeat (CRT) binding factor 10A (HvCBF10A) and Gly-Asp-Ser-Leu-motif lipase (HvGDSL) and the accumulation of multiple lipids. Functional analysis confirmed that HvCBF10A directly binds to HvGDSL, and silencing HvCBF10A resulted in a significant decrease in both HvGDSL and lipid levels, consequently impairing the cold tolerance. Overall, HvCBF10A and HvGDSL are functional units in actively regulating lipid metabolism to enhance freezing stress tolerance in qingke.

Transcriptomic analysis revealed the candidate metabolic pathways and genes associated with cold tolerance in a mutant without anthocyanin accumulation in common vetch (Vicia sativa L.)

Common vetch (Vicia sativa L.) is a leguminous crop used to feed livestock with vegetative organs or fertilize soils by returning to the field. Survival of fall-seeded plants is often affected by freezing damage during overwintering. This study aims to investigate the transcriptomic profiling in response to cold in a mutant with reduced accumulation of anthocyanins under normal growth and low-temperature conditions for understanding the underlying mechanisms. The mutant had increased cold a tolerance with higher survival rate and biomass during overwintering compared to the wild type, which led to increased forage production. Transcriptomic analysis in combination with qRT-PCR and physiological measurements revealed that reduced anthocyanins accumulation in the mutant resulted from reduced expression of serial genes involving in anthocyanin biosynthesis, which led to the altered metabolism, with an increased accumulation of free amino acids and polyamines. The higher levels of free amino acids and proline in the mutant under low temperature were associated with improved cold tolerance. The altered expression of some genes involved in ABA and GA signaling was also associated with increased cold tolerance in the mutant.

SnRK2.4-mediated phosphorylation of ABF2 regulates ARGININE DECARBOXYLASE expression and putrescine accumulation under drought stress

Arginine decarboxylase (ADC)-mediated putrescine (Put) biosynthesis plays an important role in plant abiotic stress response. SNF1-related protein kinases 2s (SnRK2s) and abscisic acid (ABA)-response element (ABRE)-binding factors (ABFs), are core components of the ABA signaling pathway involved in drought stress response. We previously reported that ADC of Poncirus trifoliata (PtrADC) functions in drought tolerance. However, whether and how SnRK2 and ABF regulate PtrADC to modulate putrescine accumulation under drought stress remains largely unclear. Herein, we employed a set of physiological, biochemical, and molecular approaches to reveal that a protein complex composed of PtrSnRK2.4 and PtrABF2 modulates putrescine biosynthesis and drought tolerance by directly regulating PtrADC. PtrABF2 was upregulated by dehydration in an ABA-dependent manner. PtrABF2 activated PtrADC expression by directly and specifically binding to the ABRE core sequence within its promoter and positively regulated drought tolerance via modulating putrescine accumulation. PtrSnRK2.4 interacts with and phosphorylates PtrABF2 at Ser93. PtrSnRK2.4-mediated PtrABF2 phosphorylation is essential for the transcriptional regulation of PtrADC. Besides, PtrSnRK2.4 was shown to play a positive role in drought tolerance by facilitating putrescine synthesis. Taken together, this study sheds new light on the regulatory module SnRK2.4-ABF2-ADC responsible for fine-tuning putrescine accumulation under drought stress, which advances our understanding on transcriptional regulation of putrescine synthesis.

OliveAtlas: A Gene Expression Atlas Tool for Olea europaea

The olive (Olea europaea L.) is an ancient crop of great importance in the Mediterranean basin due to the production of olive oil and table olives, which are important sources of fat and have benefits for human health. This crop is expanding and increasing its production worldwide and five olive genomes have recently been sequenced, representing a wild olive and important cultivars in terms of olive oil production, intensive agriculture, and adaptation to the East Asian climate. However, few bioinformatic and genomic resources are available to assist olive research and breeding, and there are no platforms to query olive gene expression data. Here, we present OliveAtlas, an interactive gene expression atlas for olive with multiple bioinformatics tools and visualization methods, enabling multiple gene comparison, replicate inspection, gene set enrichment, and data downloading. It contains 70 RNA-seq experiments, organized in 10 data sets representing the main olive plant organs, the pollen germination and pollen tube elongation process, and the response to a collection of biotic and abiotic stresses, among other experimental conditions. OliveAtlas is a web tool based on easyGDB with expression data based on the 'Picual' genome reference and gene annotation.

Advances in understanding cold tolerance in grapevine

Grapevine (Vitis ssp.) is a deciduous perennial fruit crop, and the canes and buds of grapevine should withstand low temperatures annually during winter. However, the widely cultivated Vitis vinifera is cold-sensitive and cannot survive the severe winter in regions with extremely low temperatures, such as viticulture regions in northern China. By contrast, a few wild Vitis species like V. amurensis and V. riparia exhibit excellent freezing tolerance. However, the mechanisms underlying grapevine cold tolerance remain largely unknown. In recent years, much progress has been made in elucidating the mechanisms, owing to the advances in sequencing and molecular biotechnology. Assembly of grapevine genomes together with resequencing and transcriptome data enable researchers to conduct genomic and transcriptomic analyses in various grapevine genotypes and populations to explore genetic variations involved in cold tolerance. In addition, a number of pivotal genes have been identified and functionally characterized. In this review, we summarize recent major advances in physiological and molecular analyses of cold tolerance in grapevine and put forward questions in this field. We also discuss the strategies for improving the tolerance of grapevine to cold stress. Understanding grapevine cold tolerance will facilitate the development of grapevines for adaption to global climate change.

Two polyamines -responsive WRKY transcription factors from Anoectochilus roxburghii play opposite functions on flower development

Anoectochilus roxburghii is a rare and precious plant with medicinal and healthcare functions. Embryo abortion caused the lack of resources. Polyamine promoted its flowering and stress resistance in our previous study. But the mechanism remains unclear. The WRKY transcription factor family has been linked to a variety of biological processes in plants. In this study, two WRKY TFs (ArWRKY5 and ArWRKY20) of A. roxburghii, which showed significant response to Spd treatment, were identified and functionally analyzed. Tissue specific expression analyzation showed both of them mostly present in the flower. And ArWRKY5 expressed highest in the flower bud stage (-1 Flowering), while ArWRKY20 showed the highest expression in earlier flower bud stage (-2 Flowering) and the expression gradually decreased with flowering. The transcriptional activation activity assay and subcellular localization revealed that ArWRKY5 and ArWRKY20 were located in the nucleus and ArWRKY20 showed transcriptional activity. The heterologous expression of ArWRKY5 in Arabidopsis thaliana showed earlier flowering, while overexpression of ArWRKY20 delayed flowering. But the OE-ArWRKY20 lines had a robust body shape and a very significant increase in the number of rosette leaves. Furthermore, stamens and seed development were positively regulated by these two ArWRKYs. These results indicated that ArWRKY5 and ArWRKY20 not only play opposite roles in the floral development, but also regulate the plant growth and seed development in A. thaliana. But their specific biological functions and mechanism in A. roxburghii need to be investigated further.

QTL Mapping and a Transcriptome Integrative Analysis Uncover the Candidate Genes That Control the Cold Tolerance of Maize Introgression Lines at the Seedling Stage

Chilling injury owing to low temperatures severely affects the growth and development of maize (Zea mays.L) seedlings during the early and late spring seasons. The existing maize germplasm is deficient in the resources required to improve maize's ability to tolerate cold injury. Therefore, it is crucial to introduce and identify excellent gene/QTLs that confer cold tolerance to maize for sustainable crop production. Wild relatives of maize, such as Z. perennis and Tripsacum dactyloides, are strongly tolerant to cold and can be used to improve the cold tolerance of maize. In a previous study, a genetic bridge among maize that utilized Z. perennis and T. dactyloides was created and used to obtain a highly cold-tolerant maize introgression line (MIL)-IB030 by backcross breeding. In this study, two candidate genes that control relative electrical conductivity were located on MIL-IB030 by forward genetics combined with a weighted gene co-expression network analysis. The results of the phenotypic, genotypic, gene expression, and functional verification suggest that two candidate genes positively regulate cold tolerance in MIL-IB030 and could be used to improve the cold tolerance of cultivated maize. This study provides a workable route to introduce and mine excellent genes/QTLs to improve the cold tolerance of maize and also lays a theoretical and practical foundation to improve cultivated maize against low-temperature stress.

Identification and Analysis of the CBF Gene Family in Three Species of Acer under Cold Stress

The C-Repeat Binding Factor (CBF) gene family has been identified and characterized in multiple plant species, and it plays a crucial role in responding to low temperatures. Presently, only a few studies on tree species demonstrate the mechanisms and potential functions of CBFs associated with cold resistance, while our study is a novel report on the multi-aspect differences of CBFs among three tree species, compared to previous studies. In this study, genome-wide identification and analysis of the CBF gene family in Acer truncatum, Acer pseudosieboldianum, and Acer yangbiense were performed. The results revealed that 16 CBF genes (five ApseCBFs, four AcyanCBFs, and seven AtruCBFs) were unevenly distributed across the chromosomes, and most CBF genes were mapped on chromosome 2 (Chr2) and chromosome 11 (Chr11). The analysis of phylogenetic relationships, gene structure, and conserved motif showed that 16 CBF genes could be clustered into three subgroups; they all contained Motif 1 and Motif 5, and most of them only spanned one exon. The cis-acting elements analysis showed that some CBF genes might be involved in hormone and abiotic stress responsiveness. In addition, CBF genes exhibited tissue expression specificity. High expressions of ApseCBF1, ApseCBF3, AtruCBF1, AtruCBF4, AtruCBF6, AtruCBF7, and ApseCBF3, ApseCBF4, ApseCBF5 were detected on exposure to low temperature for 3 h and 24 h. Low expressions of AtruCBF2, AtruCBF6, AtruCBF7 were detected under cold stress for 24 h, and AtruCBF3 and AtruCBF5 were always down-regulated under cold conditions. Taken together, comprehensive analysis will enhance our understanding of the potential functions of the CBF genes on cold resistance, thereby providing a reference for the introduction of Acer species in our country.

CRISPR/Cas9-mediated mutation in auxin efflux carrier OsPIN9 confers chilling tolerance by modulating reactive oxygen species homeostasis in rice

Phytohormone auxin plays a vital role in plant development and responses to environmental stresses. The spatial and temporal distribution of auxin mainly relies on the polar distribution of the PIN-FORMED (PIN) auxin efflux carriers. In this study, we dissected the functions of OsPIN9, a monocot-specific auxin efflux carrier gene, in modulating chilling tolerance in rice. The results showed that OsPIN9 expression was dramatically and rapidly suppressed by chilling stress (4°C) in rice seedlings. The homozygous ospin9 mutants were generated by CRISPR/Cas9 technology and employed for further research. ospin9 mutant roots and shoots were less sensitive to 1-naphthaleneacetic acid (NAA) and N-1-naphthylphthalamic acid (NPA), indicating the disturbance of auxin homeostasis in the ospin9 mutants. The chilling tolerance assay showed that ospin9 mutants were more tolerant to chilling stress than wild-type (WT) plants, as evidenced by increased survival rate, decreased membrane permeability, and reduced lipid peroxidation. However, the expression of well-known C-REPEAT BINDING FACTOR (CBF)/DEHYDRATION-RESPONSIVE ELEMENT-BINDING PROTEIN 1 (DREB)-dependent transcriptional regulatory pathway and Ca²⁺ signaling genes was significantly induced only under normal conditions, implying that defense responses in ospin9 mutants have probably been triggered in advance under normal conditions. Histochemical staining of reactive oxygen species (ROS) by 3'3-diaminobenzidine (DAB) and nitroblue tetrazolium (NBT) showed that ospin9 mutants accumulated more ROS than WT at the early stage of chilling stress, while less ROS was observed at the later stage of chilling treatment in ospin9 mutants. Consistently, antioxidant enzyme activity, including catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD), improved significantly during the early chilling treatments, while was kept similar to WT at the later stage of chilling treatment, implying that the enhanced chilling tolerance of ospin9 mutants is mainly attributed to the earlier induction of ROS and the improved ROS scavenging ability at the subsequent stages of chilling treatment. In summary, our results strongly suggest that the OsPIN9 gene regulates chilling tolerance by modulating ROS homeostasis in rice.

Grafting Watermelon Onto Pumpkin Increases Chilling Tolerance by Up Regulating Arginine Decarboxylase to Increase Putrescine Biosynthesis

Low temperature is a major environmental factor that severely impairs plant growth and productivity. Watermelon (Citrullus lanatus) is a chilling-sensitive crop. Grafting of watermelon onto pumpkin rootstock is an effective technique to increase the chilling tolerance of watermelon when exposure to short-time chilling stress. However, the mechanism by which pumpkin rootstock increases chilling tolerance remains poorly understood. Under 10°C/5°C (day/night) chilling stress treatment, pumpkin-grafted watermelon seedlings showed higher chilling tolerance than self-grafted watermelon plants with significantly reduced lipid peroxidation and chilling injury (CI) index. Physiological analysis revealed that pumpkin rootstock grafting led to the notable accumulation of putrescine in watermelon seedlings under chilling conditions. Pre-treat foliar with 1 mM D-arginine (inhibitor of arginine decarboxylase, ADC) increased the electrolyte leakage (EL) of pumpkin-grafted watermelon leaves under chilling stress. This result can be ascribed to the decrease in transcript levels of ADC, ornithine decarboxylase, spermidine synthase, and polyamine oxidase genes involved in the synthesis and metabolism of polyamines. Transcriptome analysis showed that pumpkin rootstock improved chilling tolerance in watermelon seedlings by regulating differential gene expression under chilling stress. Pumpkin-grafted seedling reduced the number and expression level of differential genes in watermelon scion under chilling stress. It specifically increased the up-regulated expression of ADC (Cla97C11G210580), a key gene in the polyamine metabolism pathway, and ultimately promoted the accumulation of putrescine. In conclusion, pumpkin rootstock grafting increased the chilling tolerance of watermelon through transcription adjustments, up regulating the expression level of ADC, and promoting the synthesis of putrescine, which ultimately improved the chilling tolerance of pumpkin-grafted watermelon plants.