The effect of overexpression of two Brassica CBF/DREB1-like transcription factors on photosynthetic capacity and freezing tolerance in Brassica napus

MicroRNA Profiling Revealed the Mechanism of Enhanced Cold Resistance by Grafting in Melon (Cucumis melo L.)

Grafting is widely used to improve the resistance to abiotic stresses in cucurbit plants, but the effect and molecular mechanism of grafting on cold stress are still unknown in melon. In this study, phenotypic characteristics, physiological indexes, small-RNA sequencing and expression analyses were performed on grafted plants with pumpkin rootstock (PG) and self-grafted plants (SG) to explore the mechanism of changed cold tolerance by grafting in melon. Compared with SG plants, the cold tolerance was obviously enhanced, the malondialdehyde (MDA) content was significantly decreased and the activities of antioxidant enzymes (superoxide dismutase, SOD; catalase, CAT; peroxidase, POD) were significantly increased in PG plants. Depend on differentially expressed miRNA (DEM) identification and expression pattern analyses, cme-miR156b, cme-miR156f and chr07_30026 were thought to play a key role in enhancing low-temperature resistance resulting from grafting. Subsequently, 24, 37 and 17 target genes of cme-miR156b, cme-miR156f and chr07_30026 were respectively predicted, and 21 target genes were co-regulated by cme-miR156b and cme-miR156f. Among these 57 unique target genes, the putative promoter of 13 target genes contained the low-temperature responsive (LTR) cis-acting element. The results of qRT-PCR indicated that six target genes (MELO3C002370, MELO3C009217, MELO3C018972, MELO3C016713, MELO3C012858 and MELO3C000732) displayed the opposite expression pattern to their corresponding miRNAs. Furthermore, MELO3C002370, MELO3C016713 and MELO3C012858 were significantly downregulated in cold-resistant cultivars and upregulated in cold-sensitive varieties after cold stimulus, and they acted as the key negative regulators of low-temperature response in melon. This study revealed three key miRNAs and three putative target genes involved in the cold tolerance of melon and provided a molecular basis underlying how grafting improved the low-temperature resistance of melon plants.

A large-effect fitness trade-off across environments is explained by a single mutation affecting cold acclimation

Identifying the genetic basis of local adaptation and fitness trade-offs across environments is a central goal of evolutionary biology. Cold acclimation is an adaptive plastic response for surviving seasonal freezing, and costs of acclimation may be a general mechanism for fitness trade-offs across environments in temperate zone species. Starting with locally adapted ecotypes of Arabidopsis thaliana from Italy and Sweden, we examined the fitness consequences of a naturally occurring functional polymorphism in CBF2. This gene encodes a transcription factor that is a major regulator of cold-acclimated freezing tolerance and resides within a locus responsible for a genetic trade-off for long-term mean fitness. We estimated the consequences of alternate genotypes of CBF2 on 5-y mean fitness and fitness components at the native field sites by comparing near-isogenic lines with alternate genotypes of CBF2 to their genetic background ecotypes. The effects of CBF2 were validated at the nucleotide level using gene-edited lines in the native genetic backgrounds grown in simulated parental environments. The foreign CBF2 genotype in the local genetic background reduced long-term mean fitness in Sweden by more than 10%, primarily via effects on survival. In Italy, fitness was reduced by more than 20%, primarily via effects on fecundity. At both sites, the effects were temporally variable and much stronger in some years. The gene-edited lines confirmed that CBF2 encodes the causal variant underlying this genetic trade-off. Additionally, we demonstrated a substantial fitness cost of cold acclimation, which has broad implications for potential maladaptive responses to climate change.

A comprehensive analysis of transcriptomic data for comparison of cold tolerance in two Brassica napus genotypes

Brassica napus is an important oil crop and cold stress severely limits its productivity. To date, several studies have reported the regulatory genes and pathways involved in cold-stress responses in B. napus. However, transcriptome-scale identification of the regulatory genes is still lacking. In this study, we performed comparative transcriptome analysis of cold-tolerant C18 (CT - C18) and cold-sensitive C6 (CS - C6) Brassica napus genotypes under cold stress for 7 days, with the primary purpose of identifying cold-responsive transcription in B. napus. A total of 6061 TFs belonging to 58 families were annotated in the B. napus genome, of which 3870 were expressed under cold stress in both genotypes. Among these, 451 TFs were differentially expressed (DE), with 21 TF genes expressed in both genotypes. Most TF members of the MYB (26), bHLH (23), and NAC (17) families were significantly expressed in the CT - C18 genotype compared with the CS - C6 B. napus genotype. GO classification showed a significant role in transcription regulation, DNA-binding transcription factor activity, response to chitin, and the ethylene-activated signaling pathway. KEGG pathway annotation revealed these TFs are involved in regulating more pathways, resulting in more tolerance. In conclusion, the results provide insights into the molecular regulation mechanisms of B. napus in response to freezing treatment, expanding our understanding of the complex molecular mechanisms in plants' response to freezing stress.

Ubiquitylome analysis reveals the involvement of ubiquitination in the cold responses of banana seedling leaves

Low temperature is a crucial environmental factor limiting the productivity and distribution of banana. Ubiquitination (Kub) is one of the main posttranslational modifications (PTMs) involved in plant responses to abiotic stresses. However, little information is available on the effects of Kub on banana under cold stress. In this study, we used label-free quantification (LFQ) to identify changes in the protein expression and Kub levels in banana seedling leaves after chilling treatment. In total, 4156 proteins, 1089 ubiquitinated proteins and 2636 Kub sites were quantified. Western blot assays showed that Kub was abundant in leaves after low-temperature treatment. Our results show that the proteome and ubiquitylome were negatively correlated, indicating that Kub could be involved in the degradation of proteins in banana after chilling treatment. Based on bioinformatics analysis, low-temperature stress-related signals and metabolic pathways such as cold acclimation, glutathione metabolism, calcium signaling, and photosynthesis signaling were identified. In addition, we found that transcription factors and chromatin remodeling factors related to low-temperature stress were ubiquitinated. Overall, our work presents the first systematic analysis of the Kub proteome in banana under cold stress and provides support for future studies on the regulatory mechanisms of Kub during the cold stress response in plants. SIGNIFICANCE: Banana is a typical tropical fruit tree with poor low-temperature tolerance,however, the role of PTMs such as Kub in the cold response of banana remains unclear. This study highlights the fact that the effects of low-temperature on proteome and ubiquitylome in the banana seedling leaves, we discussed the correlation between transcriptome and proteome, ubiquitylome and proteome, and we analyzed the expression and the changes of ubiquitination levels of low-temperature related proteins and pathway after chilling treatment, and we found that transcription factors and chromatin remodeling factors related to low-temperature stress were ubiquitinated. This study provides new insights into the ubiquitination pathway of banana under cold stress.

RsGLK2.1-RsNF-YA9a module positively regulates the chlorophyll biosynthesis by activating RsHEMA2 in green taproot of radish

Radish (Raphanus sativus L.) is an economically important and widely cultivated root vegetable crop. The coloration of the green skin and green flesh is an important trait influencing the nutrition and flavor quality in fruit radish. GOLDEN2-LIKEs (GLKs) play critically important roles in plastid development and chlorophyll biosynthesis in plants. However, the molecular mechanism underlying chlorophyll biosynthesis still remain elusive in green fruit radish taproot. Herein, the RsGLK2.1 gene exhibited higher expression level in taproot with a green skin (GS) and green flesh (GF) than that in taproot of the white or red radish genotypes. RsGLK2.1 is a nuclear transcription factor that has intrinsic transcriptional activation activity. Overexpression of RsGLK2.1 increased the total chlorophyll content of 20.68%-45.84% in radish leaves. Knockout of the RsGLK2.1 gene via CRISPR/Cas9 technology resulted in a significant decrease in the chlorophyll content. Overexpression of the RsGLK2.1 gene could restore the phenotype of the glk1glk2 mutant Arabidopsis. RsGLK2.1 was participated in regulating the chlorophyll biosynthesis by directly binding to the promoter of RsHEMA2 and activating its transcription. The interaction of RsNF-YA9a with RsGLK2.1 increased the transcriptional activity of the downstream gene RsHEMA2 under the light condition rather than the dark condition, indicating that both of them regulate the chlorophyll biosynthesis in a light-dependent manner of radish. Overall, these results provided insights into the molecular framework of the RsGLK2.1-RsNF-YA9a module, and could facilitate dissecting the regulatory mechanism underlying chlorophyll biosynthesis in green taproot of radish, and genetic improvement of quality traits in fruit radish breeding programs.

Coping with the cold: unveiling cryoprotectants, molecular signaling pathways, and strategies for cold stress resilience

Low temperature stress significantly threatens crop productivity and economic sustainability. Plants counter this by deploying advanced molecular mechanisms to perceive and respond to cold stress. Transmembrane proteins initiate these responses, triggering a series of events involving secondary messengers such as calcium ions (Ca2+), reactive oxygen species (ROS), and inositol phosphates. Of these, calcium signaling is paramount, activating downstream phosphorylation cascades and the transcription of cold-responsive genes, including cold-regulated (COR) genes. This review focuses on how plants manage freeze-induced damage through dual strategies: cold tolerance and cold avoidance. Tolerance mechanisms involve acclimatization to decreasing temperatures, fostering gradual accumulation of cold resistance. In contrast, avoidance mechanisms rely on cryoprotectant molecules like potassium ions (K+), proline, glycerol, and antifreeze proteins (AFPs). Cryoprotectants modulate intracellular solute concentration, lower the freezing point, inhibit ice formation, and preserve plasma membrane fluidity. Additionally, these molecules demonstrate antioxidant activity, scavenging ROS, preventing protein denaturation, and subsequently mitigating cellular damage. By forming extensive hydrogen bonds with water molecules, cryoprotectants also limit intercellular water movement, minimizing extracellular ice crystal formation, and cell dehydration. The deployment of cryoprotectants is a key adaptive strategy that bolsters plant resilience to cold stress and promotes survival in freezing environments. However, the specific physiological and molecular mechanisms underlying these protective effects remain insufficiently understood. Therefore, this review underscores the need for further research to elucidate these mechanisms and assess their potential impact on crop productivity and sustainability, contributing to the progressive discourse in plant biology and environmental science.

The salt-activated CBF1/CBF2/CBF3-GALS1 module fine-tunes galactan-induced salt hypersensitivity in Arabidopsis

Plant growth and development are significantly hampered in saline environments, limiting agricultural productivity. Thus, it is crucial to unravel the mechanism underlying plant responses to salt stress. β-1,4-Galactan (galactan), which forms the side chains of pectic rhamnogalacturonan I, enhances plant sensitivity to high-salt stress. Galactan is synthesized by GALACTAN SYNTHASE1 (GALS1). We previously showed that NaCl relieves the direct suppression of GALS1 transcription by the transcription factors BPC1 and BPC2 to induce the excess accumulation of galactan in Arabidopsis (Arabidopsis thaliana). However, how plants adapt to this unfavorable environment remains unclear. Here, we determined that the transcription factors CBF1, CBF2, and CBF3 directly interact with the GALS1 promoter and repress its expression, leading to reduced galactan accumulation and enhanced salt tolerance. Salt stress enhances the binding of CBF1/CBF2/CBF3 to the GALS1 promoter by inducing CBF1/CBF2/CBF3 transcription and accumulation. Genetic analysis suggested that CBF1/CBF2/CBF3 function upstream of GALS1 to modulate salt-induced galactan biosynthesis and the salt response. CBF1/CBF2/CBF3 and BPC1/BPC2 function in parallel to regulate GALS1 expression, thereby modulating the salt response. Our results reveal a mechanism in which salt-activated CBF1/CBF2/CBF3 inhibit BPC1/BPC2-regulated GALS1 expression to alleviate galactan-induced salt hypersensitivity, providing an activation/deactivation fine-tune mechanism for dynamic regulation of GALS1 expression under salt stress in Arabidopsis.

The role of ethylene in plant temperature stress response

Temperature influences the seasonal growth and geographical distribution of plants. Heat or cold stress occur when temperatures exceed or fall below the physiological optimum ranges, resulting in detrimental and irreversible damage to plant growth, development, and yield. Ethylene is a gaseous phytohormone with an important role in plant development and multiple stress responses. Recent studies have shown that, in many plant species, both heat and cold stress affect ethylene biosynthesis and signaling pathways. In this review, we summarize recent advances in understanding the role of ethylene in plant temperature stress responses and its crosstalk with other phytohormones. We also discuss potential strategies and knowledge gaps that need to be adopted and filled to develop temperature stress-tolerant crops by optimizing ethylene response.

Molecular Evolution and Genetic Variation of G2-Like Transcription Factor Genes in Wheat (Triticum aestivum L.)

The GOLDEN2-LIKE (G2-like) gene family members provide significant contributions to the growth and development of plants. In this study, a total of 76 wheat G2-like gene family members (TaG1-TaG76) were detected in the wheat genome and were categorized into three groups (including six subgroups) based on the gene structure and protein motif analyses. These genes were unevenly distributed in 19 of 21 wheat chromosomes. A total of 63 segmental duplication pairs of TaG2-like genes were identified in the wheat genome. The expression levels of all the TaG2-like genes indicated that TaG2-like genes showed different expression patterns in various organs and tissues. Moreover, the transcriptions of TaG2-like genes were significantly affected under abiotic stress (cold, ABA, NaCl, and PEG). This study offered valuable insights into the functional characterization of TaG2-like genes in wheat.

MaDREB1F confers cold and drought stress resistance through common regulation of hormone synthesis and protectant metabolite contents in banana

Adverse environmental factors severely affect crop productivity. Improving crop resistance to multiple stressors is an important breeding goal. Although CBFs/DREB1s extensively participate in plant resistance to abiotic stress, the common mechanism underlying CBFs/DREB1s that mediate resistance to multiple stressors remains unclear. Here, we show the common mechanism for MaDREB1F conferring cold and drought stress resistance in banana. MaDREB1F encodes a dehydration-responsive element binding protein (DREB) transcription factor with nuclear localization and transcriptional activity. MaDREB1F expression is significantly induced after cold, osmotic, and salt treatments. MaDREB1F overexpression increases banana resistance to cold and drought stress by common modulation of the protectant metabolite levels of soluble sugar and proline, activating the antioxidant system, and promoting jasmonate and ethylene syntheses. Transcriptomic analysis shows that MaDREB1F activates or alleviates the repression of jasmonate and ethylene biosynthetic genes under cold and drought conditions. Moreover, MaDREB1F directly activates the promoter activities of MaAOC4 and MaACO20 for jasmonate and ethylene syntheses, respectively, under cold and drought conditions. MaDREB1F also targets the MaERF11 promoter to activate MaACO20 expression for ethylene synthesis under drought stress. Together, our findings offer new insight into the common mechanism underlying CBF/DREB1-mediated cold and drought stress resistance, which has substantial implications for engineering cold- and drought-tolerant crops.

Biochemical and Transcriptional Responses in Cold-Acclimated and Non-Acclimated Contrasting Camelina Biotypes under Freezing Stress

Cold-acclimated and non-acclimated contrasting Camelina (Camelina sativa L.) biotypes were investigated for changes in stress-associated biomarkers, including antioxidant enzyme activity, lipid peroxidation, protein, and proline content. In addition, a well-known freezing tolerance pathway participant known as C-repeat/DRE-binding factors (CBFs), an inducer of CBF expression (ICE1), and a cold-regulated (COR6.6) genes of the ICE-CBF-COR pathway were studied at the transcriptional level on the doubled-haploid (DH) lines. Freezing stress had significant effects on all studied parameters. The cold-acclimated DH34 (a freezing-tolerant line) showed an overall better performance under freezing stress than non-acclimated plants. The non-cold-acclimated DH08 (a frost-sensitive line) showed the highest electrolyte leakage after freezing stress. The highest activity of antioxidant enzymes (glutathione peroxidase, superoxide dismutase, and catalase) was also detected in non-acclimated plants, whereas the cold-acclimated plants showed lower enzyme activities upon stress treatment. Cold acclimation had a significantly positive effect on the total protein and proline content of stressed plants. The qRT-PCR analysis revealed significant differences in the expression and cold-inducibility of CsCBF1-3, CsICE1, and CsCOR6.6 genes among the samples of different treatments. The highest expression of all CBF genes was recorded in the non-acclimated frost-tolerant biotype after freezing stress. Interestingly a significantly higher expression of COR6.6 was detected in cold-acclimated samples of both frost-sensitive and -tolerant biotypes after freezing stress. The presented results provide more insights into freezing tolerance mechanisms in the Camelina plant from both a biochemical point of view and the expression of the associated genes.

ScCBF1 plays a stronger role in cold, salt and drought tolerance than StCBF1 in potato (Solanum tuberosum)

Solanum tuberosum (St) and Solanum commersonii (Sc) are two potato varieties with different freezing tolerance. Among them, St is a freezing-sensitive variety and. Sc is a cold-resistant wild potato. CBF/DREB family members mainly function in response to freezing stress. In order to explore the different roles of St C-Repeat Binding Factor1 (StCBF1) and Sc C-Repeat Binding Factor1 (ScCBF1) in potato plants (Solanum tuberosum) under stress conditions, two kinds of potato lines were obtained with ScCBF1 and StCBF1 overexpressing respectively. Phenotypes analysis showed that both overexpressing ScCBF1 and StCBF1 caused smaller leaves, and reduced tuber yield. While the limited phenotypes of StCBF1 lines were more severe than that of ScCBF lines. After freezing treatment, StCBF1 over expression plants grown better than WT plants and worse than ScCBF1 over expression plants. Specifically, compared with wild-type lines, overexpressing ScCBF1 could up-regulate fatty acid desaturase genes, key enzyme of Calvin cycle genes, and antioxidant enzyme genes. Both ScCBF1 and StCBF1 lines showed higher PSII activity, thus maintaining a higher photosynthetic rate under cold stress. In addition, we also found that overexpression ScCBF1 and StCBF1 could also enhance the drought and salt tolerance in potato. In summary, ScCBF1 plays a stronger role in cold, salt, and drought tolerance than StCBF1 in potato (Solanum tuberosum).

Integrated Transcriptome and Metabolome Analysis of Color Change and Low-Temperature Response during Flowering of Prunus mume

In China, Prunus mume is a famous flowering tree that has been cultivated for 3000 years. P. mume grows in tropical and subtropical regions, and most varieties lack cold resistance; thus, it is necessary to study the low-temperature response mechanism of P. mume to expand the scope of its cultivation. We used the integrated transcriptomic and metabolomic analysis of a cold-resistant variety of P. mume 'Meiren', to identify key genes and metabolites associated with low temperatures during flowering. The 'Meiren' cultivar responded in a timely manner to temperature by way of a low-temperature signal transduction pathway. After experiencing low temperatures, the petals fade and wilt, resulting in low ornamental value. At the same time, in the cold response pathway, the activities of related transcription factors up- or downregulate genes and metabolites related to low temperature-induced proteins, osmotic regulators, protective enzyme systems, and biosynthesis and metabolism of sugars and acids. Our findings promote research on the adaptation of P. mume to low temperatures during wintering and early flowering for domestication and breeding.

Isolation and Functional Analysis of MbCBF2, a Malus baccata (L.) Borkh CBF Transcription Factor Gene, with Functions in Tolerance to Cold and Salt Stress in Transgenic Arabidopsis thaliana

CBF transcription factors (TFs) are key regulators of plant stress tolerance and play an integral role in plant tolerance to adverse growth environments. However, in the current research situation, there are few reports on the response of the CBF gene to Begonia stress. Therefore, this experiment investigated a novel CBF TF gene, named MbCBF2, which was isolated from M. baccata seedlings. According to the subcellular localization results, the MbCBF2 protein was located in the nucleus. In addition, the expression level of MbCBF2 was higher in new leaves and roots under low-temperature and high-salt induction. After the introduction of MbCBF2 into Arabidopsis thaliana, the adaptability of transgenic A. thaliana to cold and high-salt environments was significantly enhanced. In addition, the high expression of MbCBF2 can also change many physiological indicators in transgenic A. thaliana, such as increased chlorophyll and proline content, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activity, and reduced malondialdehyde (MDA) content. Therefore, it can be seen from the above results that MbCBF2 can positively regulate the response of A. thaliana to low-temperature and osmotic stress. In addition, MbCBF2 can also regulate the expression of its downstream genes in transgenic lines. It can not only positively regulate the expression of the downstream key genes AtCOR15a, AtERD10, AtRD29a/b and AtCOR6.6/47, related to cold stress at low temperatures, but can also positively regulate the expression of the downstream key genes AtNCED3, AtCAT1, AtP5CS, AtPIF1/4 and AtSnRK2.4, related to salt stress. That is, the overexpression of the MbCBF2 gene further improved the adaptability and tolerance of transgenic plants to low-temperature and high-salt environments.

Comprehensive analysis of cucumber C-repeat/dehydration-responsive element binding factor family genes and their potential roles in cold tolerance of cucumber

BACKGROUND

Cold stress is one of the main abiotic stresses limiting cucumber (Cucumis sativus L.) growth and production. C-repeat binding factor/Dehydration responsive element-binding 1 protein (CBF/DREB1), containing conserved APETALA2 (AP2) DNA binding domains and two characteristic sequences, are key signaling genes that can be rapidly induced and play vital roles in plant response to low temperature. However, the CBF family has not been systematically elucidated in cucumber, and the expression pattern of this family genes under cold stress remains unclear.

RESULTS

In this study, three CsCBF family genes were identified in cucumber genome and their protein conserved domain, protein physicochemical properties, gene structure and phylogenetic analysis were further comprehensively analyzed. Subcellular localization showed that all three CsCBFs were localized in the nucleus. Cis-element analysis of the promoters indicated that CsCBFs might be involved in plant hormone response and abiotic stress response. Expression analysis showed that the three CsCBFs could be significantly induced by cold stress, salt and ABA. The overexpression of CsCBFs in cucumber seedlings enhanced the tolerance to cold stress, and importantly, the transcript levels of CsCOR genes were significantly upregulated in 35S:CsCBFs transgenic plants after cold stress treatment. Biochemical analyses ascertained that CsCBFs directly activated CsCOR genes expression by binding to its promoter, thereby enhancing plant resistance to cold stress.

CONCLUSION

This study provided a foundation for further research on the function of CsCBF genes in cold stress resistance and elucidating its mechanism.

Inositol Improves Cold Tolerance Through Inhibiting CBL1 and Increasing Ca2+ Influx in Rapeseed (Brassica napus L.)

Rapeseed (Brassica napus L.) is an important oilseed crop worldwide. However, its productivity is significantly affected by various abiotic stresses, including cold stress. Among various stresses, cold stress is an important abiotic factor affecting plant growth, yield, and quality. The calcium channels are regarded as key pathways affecting cold tolerance in plants. Thus, improvement in cold tolerance is of great significance for crop improvement. The current study was designed to examine the beneficial role of exogenous inositol in improving cold stress tolerance in rapeseed. From the RNA-seq results, we identified 35 differently expressed genes encoding different inositol enzymes. The results show that inositol (a cyclic polyol) positively regulated cold tolerance by increasing calcium ion (Ca²⁺) influx in rapeseed. Furthermore, we found that the expression of calcineurin B-like (CBL1) gene was inhibited by inositol. On the other hand, overexpressed plant mediated the Ca²⁺ flux under cold stress suggesting the key role of inositol-Ca²⁺ pathway in cold tolerance. Moreover, the overexpression of BnCBL1-2 in Arabidopsis represented that transgenic plants mediated the Ca²⁺ flux highlighting the vital role of the inositol-Ca²⁺ pathway in conferring cold stress. Our study provides new insights into rapeseed cold tolerance mechanism and introduces a feasible method to improve the cold tolerance of rapeseed quickly.

Distinct Cold Acclimation of Productivity Traits in Arabidopsis thaliana Ecotypes

Improvement of crop climate resilience will require an understanding of whole-plant adaptation to specific local environments. This review places features of plant form and function related to photosynthetic productivity, as well as associated gene-expression patterns, into the context of the adaptation of Arabidopsis thaliana ecotypes to local environments with different climates in Sweden and Italy. The growth of plants under common cool conditions resulted in a proportionally greater emphasis on the maintenance of photosynthetic activity in the Swedish ecotype. This is compared to a greater emphasis on downregulation of light-harvesting antenna size and upregulation of a host of antioxidant enzymes in the Italian ecotype under these conditions. This differential response is discussed in the context of the climatic patterns of the ecotypes’ native habitats with substantial opportunity for photosynthetic productivity under mild temperatures in Italy but not in Sweden. The Swedish ecotype’s response is likened to pushing forward at full speed with productivity under low temperature versus the Italian ecotype’s response of staying safe from harm (maintaining redox homeostasis) while letting productivity decline when temperatures are transiently cold. It is concluded that either strategy can offer directions for the development of climate-resilient crops for specific locations of cultivation.

Genotype-dependent contribution of CBF transcription factors to long-term acclimation to high light and cool temperature

When grown under cool temperature, winter annuals upregulate photosynthetic capacity as well as freezing tolerance. Here, the role of three cold-induced C-repeat-binding factor (CBF1-3) transcription factors in photosynthetic upregulation and freezing tolerance was examined in two Arabidopsis thaliana ecotypes originating from Italy (IT) or Sweden (SW), and their corresponding CBF1-3-deficient mutant lines it:cbf123 and sw:cbf123. Photosynthetic, morphological and freezing-tolerance phenotypes, as well as gene expression profiles, were characterized in plants grown from the seedling stage under different combinations of light level and temperature. Under high light and cool (HLC) growth temperature, a greater role of CBF1-3 in IT versus SW was evident from both phenotypic and transcriptomic data, especially with respect to photosynthetic upregulation and freezing tolerance of whole plants. Overall, features of SW were consistent with a different approach to HLC acclimation than seen in IT, and an ability of SW to reach the new homeostasis through the involvement of transcriptional controls other than CBF1-3. These results provide tools and direction for further mechanistic analysis of the transcriptional control of approaches to cold acclimation suitable for either persistence through brief cold spells or for maximisation of productivity in environments with continuous low temperatures.

Temperature-induced dynamics of plant carbohydrate metabolism

Carbohydrates are direct products of photosynthetic CO₂ assimilation. Within a changing temperature regime, both photosynthesis and carbohydrate metabolism need tight regulation to prevent irreversible damage of plant tissue and to sustain energy metabolism, growth and development. Due to climate change, plants are and will be exposed to both long-term and short-term temperature changes with increasing amplitude. Particularly sudden fluctuations, which might comprise a large temperature amplitude from low to high temperature, pose a challenge for plants from the cellular to the ecosystem level. A detailed understanding of fundamental regulatory processes, which link photosynthesis and carbohydrate metabolism under such fluctuating environmental conditions, is essential for an estimate of climate change consequences. Further, understanding these processes is important for biotechnological application, breeding and engineering. Environmental light and temperature regimes are sensed by a molecular network that comprises photoreceptors and molecular components of the circadian clock. Photosynthetic efficiency and plant productivity then critically depend on enzymatic regulation and regulatory circuits connecting plant cells with their environment and re-stabilising photosynthetic efficiency and carbohydrate metabolism after temperature-induced deflection. This review summarises and integrates current knowledge about re-stabilisation of photosynthesis and carbohydrate metabolism after perturbation by changing temperature (heat and cold).

The direct targets of CBFs: In cold stress response and beyond

Cold acclimation in Arabidopsis thaliana triggers a significant transcriptional reprogramming altering the expression patterns of thousands of cold-responsive (COR) genes. Essential to this process is the C-repeat binding factor (CBF)-dependent pathway, involving the activity of AP2/ERF (APETALA2/ethylene-responsive factor)-type CBF transcription factors required for plant cold acclimation. In this study, we performed chromatin immunoprecipitation assays followed by deep sequencing (ChIP-seq) to determine the genome-wide binding sites of the CBF transcription factors. Cold-induced CBF proteins specifically bind to the conserved C-repeat (CRT)/dehydration-responsive elements (CRT/DRE; G/ACCGAC) of their target genes. A Gene Ontology enrichment analysis showed that 1,012 genes are targeted by all three CBFs. Combined with a transcriptional analysis of the cbf1,2,3 triple mutant, we define 146 CBF regulons as direct CBF targets. In addition, the CBF-target genes are significantly enriched in functions associated with hormone, light, and circadian rhythm signaling, suggesting that the CBFs act as key integrators of endogenous and external environmental cues. Our findings not only define the genome-wide binding patterns of the CBFs during the early cold response, but also provide insights into the role of the CBFs in regulating multiple biological processes of plants.

Transcriptional memories mediate the plasticity of cold stress responses to enable morphological acclimation in Brachypodium distachyon

Plants that successfully acclimate to stress can resume growth under stressful conditions. The grass Brachypodium distachyon can grow a cold-adaptive morphology during cold acclimation. Studies on transcriptional memory (TM) have revealed that plants can be primed for stress by adjusting their transcriptional responses, but the function of TM in stress acclimation is not well understood. We investigated the function of TM during cold acclimation in B. distachyon. Quantitative polymerase chain reaction (qPCR), RNA-seq and chromatin immunoprecipitation qPCR analyses were performed on plants exposed to repeated episodes of cold to characterize the presence and stability of TM during the stress and growth responses of cold acclimation. Transcriptional memory mainly dampened stress responses as growth resumed and as B. distachyon became habituated to cold stress. Although permanent on vernalization gene VRN1, TMs were short-term and reversible on cold-stress genes. Growing under cold conditions also coincided with the acquisition of new and targeted cold-induced transcriptional responses. Overall, TM provided plasticity to cold stress responses during cold acclimation in B. distachyon, leading to stress habituation, acquired stress responses, and resumed growth. Our study shows that chromatin-associated TMs are involved in tuning plant responses to environmental change and, as such, regulate both stress and developmental components that characterize cold-climate adaptation in B. distachyon.

Omics: The way forward to enhance abiotic stress tolerance in Brassica napus L

Plant abiotic stresses negative affects growth and development, causing a massive reduction in global agricultural production. Rapeseed (Brassica napus L.) is a major oilseed crop because of its economic value and oilseed production. However, its productivity has been reduced by many environmental adversities. Therefore, it is a prime need to grow rapeseed cultivars, which can withstand numerous abiotic stresses. To understand the various molecular and cellular mechanisms underlying the abiotic stress tolerance and improvement in rapeseed, omics approaches have been extensively employed in recent years. This review summarized the recent advancement in genomics, transcriptomics, proteomics, metabolomics, and their imploration in abiotic stress regulation in rapeseed. Some persisting bottlenecks have been highlighted, demanding proper attention to fully explore the omics tools. Further, the potential prospects of the CRISPR/Cas9 system for genome editing to assist molecular breeding in developing abiotic stress-tolerant rapeseed genotypes have also been explained. In short, the combination of integrated omics, genome editing, and speed breeding can alter rapeseed production worldwide.

Genome-Wide Association Studies of Salt Tolerance at Seed Germination and Seedling Stages in Brassica napus

Most crops are sensitive to salt stress, but their degree of susceptibility varies among species and cultivars. In order to understand the salt stress adaptability of Brassica napus to salt stress, we collected the phenotypic data of 505 B. napus accessions at the germination stage under 150 or 215 mM sodium chloride (NaCl) and at the seedling stage under 215 mM NaCl. Genome-wide association studies (GWAS) of 16 salt tolerance coefficients (STCs) were applied to investigate the genetic basis of salt stress tolerance of B. napus. In this study, we mapped 31 salts stress-related QTLs and identified 177 and 228 candidate genes related to salt stress tolerance were detected at germination and seedling stages, respectively. Overexpression of two candidate genes, BnCKX5 and BnERF3 overexpression, were found to increase the sensitivity to salt and mannitol stresses at the germination stage. This study demonstrated that it is a feasible method to dissect the genetic basis of salt stress tolerance at germination and seedling stages in B. napus by GWAS, which provides valuable loci for improving the salt stress tolerance of B. napus. Moreover, these candidate genes are rich genetic resources for the following exploration of molecular mechanisms in adaptation to salt stress in B. napus.

Hydrogen sulfide is required for salicylic acid-induced chilling tolerance of cucumber seedlings

Salicylic acid (SA) and hydrogen sulfide (H₂S) have been proved to be multifunctional signal molecules to participate in the response of plants to abiotic stresses. However, it is still unclear whether there is interaction between SA and H₂S in response to chilling intensity of cucumber seedlings. Here, we found SA was sensitive to chilling intensity. Under normal condition, NaHS (H₂S donor) or removing endogenous H₂S with hypotaurine (HT, a specific scavenger of H₂S) and DL-propargylglycine (PAG, a specific inhibitor of H₂S) has no effect on endogenous SA level; however, SA induced endogenous H₂S content and activated the activities and mRNA level of L-/D-cysteine desulfhydrase (L-/D-CD), and inhibiting endogenous SA with paclobutrazol (PAC) or 2-aminoindan-2-phosphonic acid (AIP) blocked this effect, implying H₂S may play a role after SA signal. Further studies showed that both SA and NaHS notably alleviated chilling injury, which was evidenced by lower electrolyte leakage (EL), MDA content, and ROS accumulation, compared with H₂O treatment. Of note, SA and H₂S improved the activities and mRNA level of antioxidant enzymes (SOD, POD, CAT, APX, and GR) as well as the contents of AsA and GSH. Additionally, the chilling-response genes (ICE, CBF1, and COR) were obviously upregulated by exogenous SA and NaHS. However, the positive effect of SA on chilling tolerance was inhibited by HT, whereas PAC or AIP did not affect NaHS-induced chilling tolerance. Taken together, the data reveals that H₂S acts as a downstream signal of SA-induced chilling tolerance of cucumber via modulating antioxidant system and chilling-response genes.

A Brassica napus Reductase Gene Dissected by Associative Transcriptomics Enhances Plant Adaption to Freezing Stress

Cold treatment (vernalization) is required for winter crops such as rapeseed (Brassica napus L.). However, excessive exposure to low temperature (LT) in winter is also a stress for the semi-winter, early-flowering rapeseed varieties widely cultivated in China. Photosynthetic efficiency is one of the key determinants, and thus a good indicator for LT tolerance in plants. So far, the genetic basis underlying photosynthetic efficiency is poorly understood in rapeseed. Here the current study used Associative Transcriptomics to identify genetic loci controlling photosynthetic gas exchange parameters in a diversity panel comprising 123 accessions. A total of 201 significant Single Nucleotide Polymorphisms (SNPs) and 147 Gene Expression Markers (GEMs) were detected, leading to the identification of 22 candidate genes. Of these, Cab026133.1, an ortholog of the Arabidopsis gene AT2G29300.2 encoding a tropinone reductase (BnTR1), was further confirmed to be closely linked to transpiration rate. Ectopic expressing BnTR1 in Arabidopsis plants significantly increased the transpiration rate and enhanced LT tolerance under freezing conditions. Also, a much higher level of alkaloids content was observed in the transgenic Arabidopsis plants, which could help protect against LT stress. Together, the current study showed that AT is an effective approach for dissecting LT tolerance trait in rapeseed and that BnTR1 is a good target gene for the genetic improvement of LT tolerance in plant.

Drought Stress Tolerance and Photosynthetic Activity of Alloplasmic Lines T. dicoccum x T. aestivum

Tetraploid species T. dicoccum Shuebl is a potential source of drought tolerance for cultivated wheat, including common wheat. This paper describes the genotyping of nine stable allolines isolated in the offspring from crossing of T. dicoccum x T. aestivum L. using 21 microsatellite (simple sequence repeats-SSR) markers and two cytoplasmic mitochondrial markers to orf256, rps19-p genes; evaluation of drought tolerance of allolines at different stages of ontogenesis (growth parameters, relative water content, quantum efficiency of Photosystem II, electron transport rate, energy dissipated in Photosystem II); and the study of drought tolerance regulator gene Dreb-1 with allele-specific PCR (AS-MARKER) and partial sequence analysis. Most allolines differ in genomic composition and T. dicoccum introgressions. Four allolines-D-b-05, D-d-05, D-d-05b, and D-41-05-revealed signs of drought tolerance of varying degrees. The more drought tolerant D-41-05 line was also characterized by Dreb-B1 allele introgression from T. dicoccum. A number of non-specific patterns and significant differences in allolines in regulation of physiological parameters in drought conditions is identified. Changes in photosynthetic activity in stress-drought are shown to reflect the level of drought tolerance of the forms studied. The contribution of different combinations of nuclear/cytoplasmic genome and alleles of Dreb-1 gene in allolines to the formation of stress tolerance and photosynthetic activity is discussed.

Ectopic Expression of AhGLK1b (GOLDEN2-like Transcription Factor) in Arabidopsis Confers Dual Resistance to Fungal and Bacterial Pathogens

GOLDEN2-LIKE (GLK) is a member of the myeloblastosis (MYB) family transcription factor and it plays an important role in the regulation of plastid development and stress tolerance. In this study, a gene named AhGLK1b was identified from a cultivated peanut showing down-regulation in response to low calcium with a complete open reading frame (ORF) of 1212 bp. The AhGLK1b has 99.26% and 96.28% sequence similarities with its orthologs in Arachis ipaensis and A. duranensis, respectively. In the peanut, the AhGLK1b was localized in the nucleus and demonstrated the highest expression in the leaf, followed by the embryo. Furthermore, the expression of AhGLK1b was induced significantly in response to a bacterial pathogen, Ralstonia solanacearum infection. Ectopic expression of AhGLK1b in Arabidopsis showed stronger resistance against important phytopathogenic fungi S. sclerotiorum. It also exhibited high resistance to infection of the bacterial pathogen Pst DC3000. AhGLK1b-expressing Arabidopsis induced defense-related genes including PR10 and Phox/Bem 1 (PBI), which are involved in multiple disease resistance. Taken together, the results suggest that AhGLK1b might be useful in providing dual resistance to fungal and bacterial pathogens as well as tolerance to abiotic stresses.

Engineering Multiple Abiotic Stress Tolerance in Canola, Brassica napus

Impacts of climate change like global warming, drought, flooding, and other extreme events are posing severe challenges to global crop production. Contribution of Brassica napus towards the oilseed industry makes it an essential component of international trade and agroeconomics. Consequences from increasing occurrences of multiple abiotic stresses on this crop are leading to agroeconomic losses making it vital to endow B. napus crop with an ability to survive and maintain yield when faced with simultaneous exposure to multiple abiotic stresses. For an improved understanding of the stress sensing machinery, there is a need for analyzing regulatory pathways of multiple stress-responsive genes and other regulatory elements such as non-coding RNAs. However, our understanding of these pathways and their interactions in B. napus is far from complete. This review outlines the current knowledge of stress-responsive genes and their role in imparting multiple stress tolerance in B. napus. Analysis of network cross-talk through omics data mining is now making it possible to unravel the underlying complexity required for stress sensing and signaling in plants. Novel biotechnological approaches such as transgene-free genome editing and utilization of nanoparticles as gene delivery tools are also discussed. These can contribute to providing solutions for developing climate change resilient B. napus varieties with reduced regulatory limitations. The potential ability of synthetic biology to engineer and modify networks through fine-tuning of stress regulatory elements for plant responses to stress adaption is also highlighted.

Genome-wide identification of cold responsive transcription factors in Brassica napus L

BACKGROUND

Cold stress is one of the primary environmental factors that affect plant growth and productivity, especially for crops like Brassica napus that live through cold seasons. Till recently, although a number of genes and pathways involved in B. napus cold response have been revealed by independent studies, a genome-wide identification of the key regulators and the regulatory networks is still lack. In this study, we investigated the transcriptomes of cold stressed semi-winter and winter type rapeseeds in short day condition, mainly with the purpose to systematically identify the functional conserved transcription factors (TFs) in cold response of B. napus.

RESULTS

Global modulation of gene expression was observed in both the semi-winter type line (158A) and the winter type line (SGDH284) rapeseeds, in response to a seven-day chilling stress in short-day condition. Function analysis of differentially expressed genes (DEGs) revealed enhanced stresses response mechanisms and inhibited photosynthesis in both lines, as well as a more extensive inhibition of some primary biological processes in the semi-winter type line. Over 400 TFs were differentially expressed in response to cold stress, including 56 of them showed high similarity to the known cold response TFs and were consistently regulated in 158A and SGDH284, as well as 25 TFs which targets were over-represented in the total DEGs. A further investigation based on their interactions indicated the critical roles of several TFs in cold response of B. napus.

CONCLUSION

In summary, our results revealed the alteration of gene expression in cold stressed semi-winter and winter ecotype B. napus lines and provided a valuable collection of candidate key regulators involved in B. napus response to cold stress, which could expand our understanding of plant stress response and benefit the future improvement of the breed of rapeseeds.

Advances and challenges in uncovering cold tolerance regulatory mechanisms in plants

Contents Summary I. Introduction II. Cold stress and physiological responses in plants III. Sensing of cold signals in plants IV. Messenger molecules involved in cold signal transduction V. Cold signal transduction in plants VI. Conclusions and perspectives Acknowledgements References SUMMARY: Cold stress is a major environmental factor that seriously affects plant growth and development, and influences crop productivity. Plants have evolved a series of mechanisms that allow them to adapt to cold stress at both the physiological and molecular levels. Over the past two decades, much progress has been made in identifying crucial components involved in cold-stress tolerance and dissecting their regulatory mechanisms. In this review, we summarize recent major advances in our understanding of cold signalling and put forward open questions in the field of plant cold-stress responses. Answering these questions should help elucidate the molecular mechanisms underlying plant tolerance to cold stress.

Genes associated with chloroplasts and hormone-signaling, and transcription factors other than CBFs are associated with differential survival after low temperature treatments of Camelina sativa biotypes

Winter annual biotypes of Camelina sativa regularly survive after winter conditions experienced in northern regions of the U.S., whereas summer annual biotypes do not. To determine potential molecular mechanisms associated with these biotype differences in survival after low temperature treatments, we examined genetic and transcript variations in both a winter- (Joelle) and a summer- (CO46) biotype. It was determined that as few as one or two dominant genes may control differential survival after low temperature treatments. Of the 1797 genes that were differentially expressed in response to cold in both the winter and summer biotypes many COR genes were identified, indicating that the CBF regulon is functional in both. However, only 153 and 76 genes from Joelle and CO46, respectively, were either differentially expressed or not expressed at all in one biotype versus the other following cold acclimation. We hypothesize that these 229 genes play a significant role in, or are primarily responsive to, differences in survival after freezing between these two biotypes. Promoter analysis provided few clues as to the regulation or these genes; however, genes that were down-regulated specifically in the winter biotype Joelle were enriched with the sequence TGGCCCTCGCTCAC, which is over-represented among genes associated with chloroplasts in Arabidopsis. Additionally, several genes involved in auxin signaling were down-regulated specifically in Joelle. A transcription factor with strong similarity to MYB47, known to be up-regulated by salt, drought, and jasmonic acid, but not cold in Arabidopsis, was essentially off in the freezing sensitive biotype CO46, but was cold-induced in the winter biotype Joelle. Several other transcription factors genes including three with similarity to WRKY70, that may be involved in SA/JA-dependent responses, a HOMEOBOX 6 gene involved in ABA signaling, and two others (NUCLEAR FACTOR Y and CONSTANS-like 2) known to be implicated in photoperiodic flowering were also differentially expressed between the two biotypes.

Copy number variants in kiwifruit ETHYLENE RESPONSE FACTOR/APETALA2 (ERF/AP2)-like genes show divergence in fruit ripening associated cold and ethylene responses in C-REPEAT/DRE BINDING FACTOR-like genes

The ETYHLENE RESPONSE FACTOR/APETALA2 (ERF/AP2) transcription factors have been shown to control a wide range of developmental and environmental responses in plants. These include hormonal responses to ethylene and Abscisic Acid (ABA) as well as to cold and drought. In Actinidia chinensis (kiwifruit), ripening is unusual: although it is sometimes classed as a climacteric fruit (ethylene-associated ripening), much of fruit ripening occurs independently from autocatalytic ethylene production. Initiation of ripening appears to be strongly developmentally controlled and modulated by low temperature. In this study, fruit treated with different temperatures showed an increase in soluble sugar accumulation, and a corresponding increase in ß-AMYLASE (BAM) genes (predominantly BAM3.2 and BAM9) with lower temperatures. To investigate the potential role of the AP2/ERF gene family in the control of fruit ripening in kiwifruit this family was investigated further. Using the new genome annotation and further genome sequence analysis we identified 226 ERF-like genes, 10 AP2L/RAV-like genes and 32 AP2-like genes. An RNA-seq screen from kiwifruit of different maturities, and following treatment with ethylene and temperatures between 0 and 16°C, revealed 4%, 26% and 18% of the ERF-like genes were upregulated by maturation, ethylene and cold temperatures, respectively. Focusing on the C-REPEAT/DRE BINDING FACTOR (CBF) cold master regulators, nine potential genes were identified based on sequence similarity. Five of these CBF-like genes were found in a copy number variant (CNV) cluster of six genes on chromosome 14. Expression analysis showed that two homeologous genes (ERF41 and ERF180) increased in abundance with cold and ethylene, while the cluster of CNV CBF-like genes had lost the ability to respond to cold and increased only with ethylene, suggesting an evolutionary progression of function of these genes.

Crop Improvement Through Temperature Resilience

Abnormal environmental temperature affects plant growth and threatens crop production. Understanding temperature signal sensing and the balance between defense and development in plants lays the foundation for improvement of temperature resilience. Here, we summarize the current understanding of cold signal perception/transduction as well as heat stress response. Dissection of plant responses to different levels of cold stresses (chilling and freezing) illustrates their common and distinct signaling pathways. Axillary bud differentiation in response to chilling is presented as an example of the trade-off between defense and development. Vernalization is a cold-dependent development adjustment mediated by O-GlcNAcylation and phosphorylation to sense long-term cold. Recent progress on major quantitative trait loci genes for heat tolerance has been summarized. Molecular mechanisms in utilizing temperature-sensitive sterility in super hybrid breeding in China are revealed. The way to improve crop temperature resilience using integrative knowledge of omics as well as systemic and synthetic biology, especially the molecular module program, is summarized.

Microtubule dynamics modulate sensing during cold acclimation in grapevine suspension cells

Cold acclimation is of practical relevance, since it can avoid cold-induced damage in various crops. To efficiently activate cold acclimation requires that the chilling stress is perceived and processed efficiently. In the current work, we use a transgenic cell line of V. rupestris expressing a GFP-labelled tubulin to follow the effect of cold acclimation and the relation between microtubules and the expression of the transcription factor Cold Box Factor 4 (CBF4) as molecular readout for adaptive responses to cold stress. We find that chilling induced cold tolerance correlated with increased CBF4 expression. We show that cold acclimation can be achieved through stabilisation of microtubules by taxol, as well as through transient elimination of microtubules by pronamide in the absence of cold stress. Furthermore, results from inhibitor studies indicate that transcriptional activation of CBF4 appears to be under control of calcium influx. We screened a population of the ancestor of V. sylvestris and could identify different clades with strong induction of CBF4, indicative of genetic variation in cold adaptability that can be used for breeding. We summarize our findings into a working model where microtubule dynamics controls the sensitivity of cold induced calcium influx mediating the induction of CBF4 culminating in cold hardening.

A DREB1 gene from zoysiagrass enhances Arabidopsis tolerance to temperature stresses without growth inhibition

The DREB (dehydration-responsive element binding) protein family comprises transcription factors that can increase the survivability of a plant under abiotic stresses by regulating expression of multiple genes and altering downstream metabolism at the cost of growth retardation and developmental delay. In this study, a gene for the DREB1-type transcription factor, designated ZjDREB1.4, was isolated from zoysiagrass (Zoysia japonica Steud.), a popular warm-season turfgrass. This gene contains a conserved AP2/ERF DNA-binding domain flanking the signature sequence of DREB1 and belongs to a DREB1 branch in the grass family that expands in the warm-season species. The expression of ZjDREB1.4 was significantly induced by chilling stress (4-15 °C), moderately induced by salt stress, and only slightly induced by drought stress. The product of ZjDREB1.4 was targeted to the nucleus and showed strong transactivation activity but weak binding to the DRE with ACCGAC as the core sequence. The ZjDREB1.4 protein bound to GCCGAC more preferentially than to ACCGAC. Overexpression of ZjDREB1.4 in Arabidopsis induced the expression of multiple genes including a part of the CBF-regulon, and moderately increased the levels of proline and soluble sugars under normal growth conditions. The transgenic Arabidopsis plants showed an increase in tolerance to high and freezing temperature stresses without obvious growth inhibition and with only a few days delay in bolting. ZjDREB1.4 is potentially useful for producing transgenic plants that are tolerant to high temperature and/or cold stresses with few negative effects.

Mapping of quantitative trait loci related to cold resistance in Brassica napus L

Cold stress is one of the major abiotic stresses that seriously limit rapeseed production worldwide. However, few studies on the mechanism of cold resistance in Brassica napus have been reported. In this study, an F_2:3 population including 147 lines was developed to identify the quantitative trait loci (QTLs) related to cold resistance in B. napus. As a result, a genetic linkage map based on 333 simple sequence repeat (SSR) markers covering 1317.70 cM was constructed. Up to 11 QTLs for four indicators were identified in the two locations. These QTLs accounted for 1.09% to 42.50% of the phenotypic variations, and six major QTLs accounted for more than 10% of the phenotypic variations. Three QTLs, qSPADYL-6, qSPADYS-6, and qMDAYS-6, were mapped to the same region of linkage group 6 (LG6). Blast analysis indicated that the sequences of the markers related to these three QTLs showed great collinearity with those on the A08 chromosome of Brassica rapa, and that the target genes might exist in the region from 1.069 to 15.652 M on A08. Two genes, BnaA08g05330D and BnaA08g15470D, encoding the respective cold-regulated proteins in B. napus, were identified. They exhibited high similarity with Bra039858 and Bra010579 (stress-responsive proteins) in the candidate region. RT-qPCR analysis showed a significant difference in gene expression between the two parents. These two genes were hence identified as the genes responsible for cold resistance.

Insights into the regulation of C-repeat binding factors in plant cold signaling

Cold temperatures, a major abiotic stress, threaten the growth and development of plants, worldwide. To cope with this adverse environmental cue, plants from temperate climates have evolved an array of sophisticated mechanisms to acclimate to cold periods, increasing their ability to tolerate freezing stress. Over the last decade, significant progress has been made in determining the molecular mechanisms underpinning cold acclimation, including following the identification of several pivotal components, including candidates for cold sensors, protein kinases, and transcription factors. With these developments, we have a better understanding of the CBF-dependent cold-signaling pathway. In this review, we summarize recent progress made in elucidating the cold-signaling pathways, especially the C-repeat binding factor-dependent pathway, and describe the regulatory function of the crucial components of plant cold signaling. We also discuss the unsolved questions that should be the focus of future work.

Molecular Regulation of CBF Signaling in Cold Acclimation

Cold stress restricts plant growth, development, and distribution. Understanding how plants transduce and respond to cold signals has long been a topic of interest. Traditional genetic and molecular analyses have identified C-repeat/DREB binding factors (CBFs) as key transcription factors that function in cold acclimation. Recent studies revealed the involvement of pivotal protein kinases and transcription factors in CBF-dependent signaling, expanding our knowledge of cold signal transduction from perception to downstream gene expression events. In this review, we summarize recent advances in our understanding of the molecular regulation of these core components of the CBF cold signaling pathway. Knowledge of the mechanism underlying the ability of plants to survive freezing temperatures will facilitate the development of crop plants with increased freezing tolerance.

Optimization of Photosynthetic Productivity in Contrasting Environments by Regulons Controlling Plant Form and Function

We review the role of a family of transcription factors and their regulons in maintaining high photosynthetic performance across a range of challenging environments with a focus on extreme temperatures and water availability. Specifically, these transcription factors include CBFs (C-repeat binding factors) and DREBs (dehydration-responsive element-binding), with CBF/DREB1 primarily orchestrating cold adaptation and other DREBs serving in heat, drought, and salinity adaptation. The central role of these modulators in plant performance under challenging environments is based on (i) interweaving of these regulators with other key signaling networks (plant hormones and redox signals) as well as (ii) their function in integrating responses across the whole plant, from light-harvesting and sugar-production in the leaf to foliar sugar export and water import and on to the plant's sugar-consuming sinks (growth, storage, and reproduction). The example of Arabidopsisthaliana ecotypes from geographic origins with contrasting climates is used to describe the links between natural genetic variation in CBF transcription factors and the differential acclimation of plant anatomical and functional features needed to support superior photosynthetic performance in contrasting environments. Emphasis is placed on considering different temperature environments (hot versus cold) and light environments (limiting versus high light), on trade-offs between adaptations to contrasting environments, and on plant lines minimizing such trade-offs.

Genetic dissection of early-season cold tolerance in sorghum: genome-wide association studies for seedling emergence and survival under field and controlled environment conditions

A QTL on sorghum chromosome SBI-06 putatively improves field emergence under low-temperature conditions. Low temperatures decisively limit seedling emergence and vigor during early growth of sorghum and, thus, strongly impair geographical expansion. To broaden sorghum cultivation to temperate regions, the establishment of cold-tolerant genotypes is a prioritized breeding goal. The present study aims at the quantification of seedling emergence and survival under chilling temperatures and the detection of marker-trait associations controlling temperature-related seedling establishment. A diversity set consisting of 194 biomass sorghum lines was subjected to extensive phenotyping comprising field trials and controlled environment experiments. The final emergence percentage (FEP) under field conditions was significantly reduced under cold stress. Broad-sense heritability was h ² = 0.87 for FEP in the field and h ² = 0.93 for seedling survival rate (SR) under controlled conditions. Correlations between FEP in the field and under controlled conditions were low; higher correlations were observed between field FEP and SR in controlled environments. Genome-wide association studies (GWAS) were conducted using 44,515 single nucleotide polymorphisms (SNPs) and revealed eight regions with suggestive marker-trait associations for FEP and SR on chromosomes SBI-01, -02, -03, -06, -09, and -10 (p < 5.7 × 10^-5) and a significant association on SBI-06 for field FEP (p < 2.9 × 10^-6). Although not significant under controlled conditions, SR of genotypes carrying the minor allele on the field FEP quantitative trait loci (QTL) on SBI-06 was on average 13.1% higher, while FEP under controlled conditions was on average 9.7% higher with a linearly decreasing effect with increasing temperatures (R ² = 0.82). Promising candidate genes putatively conferring seedling cold tolerance were identified.

Acclimation of Swedish and Italian ecotypes of Arabidopsis thaliana to light intensity

This study addressed whether ecotypes of Arabidopsis thaliana from Sweden and Italy exhibited differences in foliar acclimation to high versus low growth light intensity, and compared CO₂ uptake under growth conditions with light- and CO₂-saturated intrinsic photosynthetic capacity and leaf morphological and vascular features. Differential responses between ecotypes occurred mainly at the scale of leaf architecture, with thicker leaves with higher intrinsic photosynthetic capacities and chlorophyll contents per leaf area, but no difference in photosynthetic capacity on a chlorophyll basis, in high light-grown leaves of the Swedish versus the Italian ecotype. Greater intrinsic photosynthetic capacity per leaf area in the Swedish ecotype was accompanied by a greater capacity of vascular infrastructure for sugar and water transport, but this was not associated with greater CO₂ uptake rates under growth conditions. The Swedish ecotype with its thick leaves is thus constructed for high intrinsic photosynthetic and vascular flux capacity even under growth chamber conditions that may not permit full utilization of this potential. Conversely, the Swedish ecotype was less tolerant of low growth light intensity than the Italian ecotype, with smaller rosette areas and lesser aboveground biomass accumulation in low light-grown plants. Foliar vein density and stomatal density were both enhanced by high growth light intensity with no significant difference between ecotypes, and the ratio of water to sugar conduits was also similar between the two ecotypes during light acclimation. These findings add to the understanding of the foliar vasculature's role in plant photosynthetic acclimation and adaptation.

Identification and functional prediction of stress responsive AP2/ERF transcription factors in Brassica napus by genome-wide analysis

Using homology and domain authentication, 321 putative AP2/ERF transcription factors were identified in Brassica napus, called BnAP2/ERF TFs. BnAP2/ERF TFs were classified into five major subfamilies, including DREB, ERF, AP2, RAV, and BnSoloist. This classification is based on phylogenetic analysis, motif identification, gene structure analysis, and physiochemical characterization. These TFs were annotated based on phylogenetic relationship with Brassica rapa. BnAP2/ERF TFs were located on 19 chromosomes of B. napus. Orthologs and paralogs were identified using synteny-based methods Ks calculation within B. napus genome and between B. napus with other species such as B. rapa, Brassica oleracea, and Arabidopsis thaliana indicated that BnAP2/ERF TFs were formed through duplication events occurred before B. napus formation. Kn/Ks values were between 0 and 1, suggesting the purifying selection among BnAP2/ERF TFs. Gene ontology annotation, cis-regulatory elements and functional interaction networks suggested that BnAP2/ERF TFs participate in response to stressors, including drought, high salinity, heat and cold as well as developmental processes particularly organ specification and embryogenesis. The identified cis-regulatory elements in the upstream of BnAP2/ERF TFs were responsive to abscisic acid. Analysis of the expression data derived from Illumina Hiseq 2000 RNA sequencing revealed that BnAP2/ERF genes were highly expressed in the roots comparing to flower buds, leaves, and stems. Also, the ERF subfamily was over-expressed under salt and fungal treatments. BnERF039 and BnERF245 are candidates for salt-tolerant B. napus. BnERF253-256 and BnERF260-277 are potential cytokinin response factors. BnERF227, BnERF228, BnERF234, BnERF134, BnERF132, BnERF176, and BnERF235 were suggested for resistance against Leptosphaeria maculan and Leptosphaeria biglobosa.

Overexpressing IbCBF3 increases low temperature and drought stress tolerance in transgenic sweetpotato

Dehydration-responsive element-binding/C-repeat-binding factor (DREB/CBF) proteins regulate the transcription of genes involved in cold acclimation in several species. However, little is known about the physiological functions of CBF proteins in the low temperature-sensitive crop sweetpotato. We previously reported that the DREB1/CBF-like sweetpotato gene SwDREB1/IbCBF3 is involved in responses to diverse abiotic stresses. In this study, we confirmed that IbCBF3 is localized to the nucleus and binds to the C-repeat/dehydration-responsive elements (CRT/DRE) in the promoters of cold-regulated (COR) genes. We generated transgenic sweetpotato plants overexpressing IbCBF3 under the control of the CaMV 35S promoter (referred to as SC plants) and evaluated their responses to various abiotic stresses. IbCBF3 expression was dramatically induced by cold and drought but much less strongly induced by high salinity and ABA. We further characterized two SC lines (SC3 and SC6) with high levels of IbCBF3 transcript. The SC plants displayed enhanced tolerance to cold, drought, and oxidative stress on the whole-plant level. Under cold stress treatment (4 °C for 48 h), severe wilting and chilling injury were observed in the leaves of wild-type (WT) plants, whereas SC plants were not affected by cold stress. In addition, the COR genes were significantly upregulated in SC plants compared with the WT. The SC plants also showed significantly higher tolerance to drought stress than the WT, which was associated with higher photosynthesis efficiency and lower hydrogen peroxide levels. These results indicate that IbCBF3 is a functional transcription factor involved in the responses to various abiotic stresses in sweetpotato.

Transcriptome Profiling Reveals the Negative Regulation of Multiple Plant Hormone Signaling Pathways Elicited by Overexpression of C-Repeat Binding Factors

C-repeat binding factors (CBF) are a subfamily of AP2 transcription factors that play critical roles in the regulation of plant cold tolerance and growth in low temperature. In the present work, we sought to perform a detailed investigation into global transcriptional regulation of plant hormone signaling associated genes in transgenic plants engineered with CBF genes. RNA samples from Arabidopsis thaliana plants overexpressing two CBF genes, CBF2 and CBF3, were subjected to Illumina HiSeq 2000 RNA sequencing (RNA-Seq). Our results showed that more than half of the hormone associated genes that were differentially expressed in CBF2 or CBF3 transgenic plants were related to auxin signal transduction and metabolism. Most of these alterations in gene expression could lead to repression of auxin signaling. Accordingly, the IAA content was significantly decreased in young tissues of plants overexpressing CBF2 and CBF3 compared with wild type. In addition, genes associated with the biosynthesis of Jasmonate (JA) and Salicylic acid (SA), as well as the signal sensing of Brassinolide (BR) and SA, were down-regulated, while genes associated with Gibberellin (GA) deactivation were up-regulated. In general, overexpression of CBF2 and CBF3 negatively affects multiple plant hormone signaling pathways in Arabidopsis. The transcriptome analysis using CBF2 and CBF3 transgenic plants provides novel and integrated insights into the interaction between CBFs and plant hormones, particularly the modulation of auxin signaling, which may contribute to the improvement of crop yields under abiotic stress via molecular engineering using CBF genes.

The genetic architecture of freezing tolerance varies across the range of Arabidopsis thaliana

The capacity to tolerate freezing temperatures limits the geographical distribution of many plants, including several species of agricultural importance. However, the genes involved in freezing tolerance remain largely unknown. Here, we describe the variation in constitutive freezing tolerance that occurs among worldwide accessions of Arabidopsis thaliana. We found that although plants from high latitudes tend to be more freezing tolerant than plants from low latitudes, the environmental factors that shape cold adaptation differ across the species range. Consistent with this, we found that the genetic architecture of freezing tolerance also differs across its range. Conventional genome-wide association studies helped identify a priori and other promising candidate genes. However, simultaneously modelling climate variables and freezing tolerance together pinpointed other excellent a priori candidate genes. This suggests that if the selective factor underlying phenotypic variation is known, multi-trait mixed models may aid in identifying the genes that underlie adaptation.

Photosynthetic acclimation, vernalization, crop productivity and 'the grand design of photosynthesis'

Daniel Arnon first proposed the notion of a 'grand design of photosynthesis' in 1982 to illustrate the central role of photosynthesis as the primary energy transformer for all life on Earth. However, we suggest that this concept can be extended to the broad impact of photosynthesis not only in global energy transformation but also in the regulation of plant growth, development, survival and crop productivity through chloroplast redox signalling. We compare and contrast the role of chloroplast redox imbalance, measured as excitation pressure, in governing acclimation to abiotic stress and phenotypic plasticity. Although all photoautrophs sense excessive excitation energy through changes in excitation pressure, the response to this chloroplast redox signal is species dependent. Due to a limited capacity to adjust metabolic sinks, cyanobacteria and green algae induce photoprotective mechanisms which dissipate excess excitation energy at a cost of decreased photosynthetic performance. In contrast, terrestrial, cold tolerant plants such as wheat enhance metabolic sink capacity which leads to enhanced photosynthetic performance and biomass accumulation with minimal dependence on photoprotection. We suggest that the family of nuclear C-repeat binding transcription factors (CBFs) associated with the frost resistance locus, FR2, contiguous with the vernalization locus,VRN1, and mapped to chromosome 5A of wheat, may be critical components that link leaf chloroplast redox regulation to enhanced photosynthetic performance, the accumulation of growth-active gibberellins and the dwarf phenotype during cold acclimation prior to the vegetative to reproductive transition controlled by vernalization in winter cereals. Further genetic, molecular and biochemical research to confirm these links and to elucidate the molecular mechanism by which chloroplast redox modulation of CBF expression leads to enhanced photosynthetic performance is required. Because of the superior abiotic stress tolerance of cold tolerant winter wheat and seed yields that historically exceed those of spring wheat by 30-40%, we discuss the potential to exploit winter cereals for the maintenance or perhaps even the enhancement of cereal productivity under future climate change scenarios that will be required to feed a growing human population.

Molecular Evolution and Genetic Variation of G2-Like Transcription Factor Genes in Maize

The productivity of maize (Zea mays L.) depends on the development of chloroplasts, and G2-like transcription factors play a central role in regulating chloroplast development. In this study, we identified 59 G2-like genes in the B73 maize genome and systematically analyzed these genes at the molecular and evolutionary levels. Based on gene structure character, motif compositions and phylogenetic analysis, maize G2-like genes (ZmG1- ZmG59) were divided into seven groups (I-VII). By synteny analysis, 18 collinear gene pairs and strongly conserved microsyntny among regions hosting G2-like genes across maize and sorghum were found. Here, we showed that the vast majority of ZmG gene duplications resulted from whole genome duplication events rather than tandem duplications. After gene duplication events, some ZmG genes were silenced. The functions of G2-like genes were multifarious and most genes that are expressed in green tissues may relate to maize photosynthesis. The qRT-PCR showed that the expression of these genes was sensitive to low temperature and drought. Furthermore, we analyzed differences of ZmGs specific to cultivars in temperate and tropical regions at the population level. Interestingly, the single nucleotide polymorphism (SNP) analysis revealed that nucleotide polymorphism associated with different temperature zones. Above all, G2-like genes were highly conserved during evolution, but polymorphism could be caused due to a different geographical location. Moreover, G2-like genes might be related to cold and drought stresses.