Isolation and characterization of a cDNA encoding a CBF transcription factor from E. globulus

AP2/ERF, an important cold stress-related transcription factor family in plants: A review

Increasing the vulnerability of plants especially crops to a wide range of cold stress reduces plant growth, development, yield production, and plant distribution. Cold stress induces physiological, morphological, biochemical, phenotypic, and molecular changes in plants. Transcription factor (TF) is one of the most important regulators that mediate gene expression. TF is activated by the signal transduction pathway, together with cis-acting element modulate the transcription of cold-responsive genes which contribute to increasing cold tolerance in plants. Here, AP2/ERF TF family is one of the most important cold stress-related TF families that along with other TF families, such as WRKY, bHLH, bZIP, MYB, NAC, and C2H2 interrelate to enhance cold stress tolerance. Over the past decade, significant progress has been found to solve the role of transcription factors (TFs) in improving cold tolerance in plants, such as omics analysis. Furthermore, numerous studies have identified and characterized the complexity of cold stress mechanisms among TFs or between TFs and other factors (endogenous and exogenous) including phytohormones, eugenol, and light. The role, function, and relationship among these TFs or between TFs and other factors to enhance cold tolerance still need to be clarified. Here, the current study analysed the role of AP2/ERF TF and the linkages among AP2/ERF with MYB, WRKY, bZIP, bHLH, C2H2, or NAC against cold stress tolerance.

Characterization of the key region and putative phosphorylation sites of EcaICE1 in its molecular interaction with the EcaHOS1 protein in Eucalyptus camaldulensis

Inducer of CBF expression 1 (ICE1), a MYC-like bHLH transcriptional activator, plays an important role in plants under cold stress. The ubiquitination-proteasome pathway mediated by high expression of osmotically responsive gene1 (HOS1) can effectively induce the degradation of ICE1 and decrease the expression of CBFs and their downstream genes under cold stress response in Arabidopsis, but knowledge of ubiquitination regulation of ICE1 by HOS1 is still limited in woody plants. In this study, a E3 ubiquitin ligase gene EcaHOS1 were amplified from Eucalyptus camaldulensis and the protein interactions between EcaICE1 and EcaHOS1 were analysed. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assay results showed that EcaICE1 can interact with the EcaHOS1 protein in the nucleus and, further, the Y2H assay demonstrated that the 126-185 amino acid region at the N-terminus of the EcaICE1 protein was indispensable for its interaction with EcaHOS1 protein. Moreover, we found that the amino acids at positions 145, 158 and 184 within the key interaction region were the putative phosphorylation sites of EcaICE1, based on bioinformatics analysis, and only the substitution of serine (Ser) 158 by alanine (Ala) blocked the protein-protein interactions between EcaICE1 and EcaHOS1 based on Y2H and β-galactosidase activity assays using site-directed mutagenesis. We identified Ser 158 of EcaICE1 as the key putative phosphorylation site for its interaction with the EcaHOS1 protein.

Isolation and expression analysis of a CBF transcriptional factor gene from the mangrove Bruguiera gymnorrhiza

The present work isolated a CBF/DREB1 gene from mangrove Bruguiera gymnorrhiza (BgCBF1) and compared its expression levels in various tissues under normal condition and cold stress, and in leaves exposed to various environmental stimuli. Results showed that the BgCBF1 deduced protein showed almost 100% similarities to that of AcCBF1 from Aegiceras corniculatum and AmCBF1 from Avicennia marina. Real-time quantitative PCR analysis showed that BgCBF1 gene displayed constitute expression in leaf, stem and root samples of plantlets under normal condition, but with different expression levels and tissue preference. When exposed to cold, BgCBF1 could be rapidly, slightly and transiently induced in all tissues. Furthermore, the BgCBF1 gene in leaves displayed a transient and small induction after salt and drought (PEG) exposure, while exhibited relatively high up-regulated expression after the phytohormone abscisic acid (ABA) treatment. These results suggest that the BgCBF1 gene may participate in the ABA mediated development and protection of plant against cold and drought. Further studies on its promoters and downstream genes will be needed to better understand its functions.

Overexpressing Jatropha curcas CBF2 in Nicotiana benthamiana improved plant tolerance to drought stress

Jatropha curcas is an important bioenergy oil plant, and often planted on barren land to save the area of arable land. It is significant to improve the adaptability of J. curcas to various abiotic stresses. In the present study, we transferred a J. curcas gene, encoding a CBF2 transcription factor, into Nicotiana benthamiana. Under drought treatment, the JcCBF2 transgenic lines showed improved survival rate, leaf water retention and active oxygen scavenging capacity, but reduced photosynthesis and transpiration rate, suggesting that JcCBF2 played an important role in improving plant drought tolerance. Overexpressing JcCBF2 decreased leaf area and increased leaf thickness. To explore the possible mechanisms for the change of leaf anatomical structure, the leaves of wild-type and overexpression lines under drought stress were RNA sequenced. Genes involved in the plant hormones signal transduction were found to be enriched. Cytokinin and indole-3-acetic acid were the major plant hormones whose abundance increased. Quantitative RT-PCR analysis showed expression of NbMYB21, NbMYB86 and NbMYB44 and both abscisic acid (ABA) and jasmonic acid (JA) related genes in the overexpression lines were increased under drought stress. These results indicated that JcCBF2 was able to positively regulate plant drought response by changing the leaf anatomical structure and possibly through JA and ABA signalling pathways. Our work may help us to understand the drought tolerant mechanism.

Identification, Structural and Functional Characterization of Dormancy Regulator Genes in Apricot (Prunus armeniaca L.)

In the present study, we identified and characterized the apricot (Prunus armeniaca L.) homologs of three dormancy-related genes, namely the ParCBF1 (C-repeat binding factor), ParDAM5 (dormancy-associated MADS-BOX) and ParDAM6 genes. All highly conserved structural motifs and the 3D model of the DNA-binding domain indicate an unimpaired DNA-binding ability of ParCBF1. A phylogenetic analysis showed that ParCBF1 was most likely homologous to Prunus mume and Prunus dulcis CBF1. ParDAM5 also contained all characteristic domains of the type II (MIKC^C) subfamily of MADS-box transcription factors. The homology modeling of protein domains and a phylogenetic analysis of ParDAM5 suggest its functional integrity. The amino acid positions or small motifs that are diagnostic characteristics of DAM5 and DAM6 were determined. For ParDAM6, only a small part of the cDNA was sequenced, which was sufficient for the quantification of gene expression. The expression of ParCBF1 showed close association with decreasing ambient temperatures in autumn and winter. The expression levels of ParDAM5 and ParDAM6 changed according to CBF1 expression rates and the fulfillment of cultivar chilling requirements (CR). The concomitant decrease of gene expression with endodormancy release is consistent with a role of ParDAM5 and ParDAM6 genes in dormancy induction and maintenance. Cultivars with higher CR and delayed flowering time showed higher expression levels of ParDAM5 and ParDAM6 toward the end of endodormancy. Differences in the timing of anther developmental stages between early- and late-flowering cultivars and two dormant seasons confirmed the genetically and environmentally controlled mechanisms of dormancy release in apricot generative buds. These results support that the newly identified apricot gene homologs have a crucial role in dormancy-associated physiological mechanisms.

Metabolic responses of Eucalyptus species to different temperature regimes

Species and hybrids of Eucalyptus are the world's most widely planted hardwood trees. They are cultivated across a wide range of latitudes and therefore environmental conditions. In this context, comprehensive metabolomics approaches have been used to assess how different temperature regimes may affect the metabolism of three species of Eucalyptus, E. dunnii, E. grandis and E. pellita. Young plants were grown for 53 d in the greenhouse and then transferred to growth chambers at 10°C, 20°C or 30°C for another 7 d. In all three species the leaf chlorophyll content was positively correlated to temperature, and in E. pellita the highest temperature also resulted in a significant increase in stem biomass. Comprehensive metabolomics was performed using untargeted gas chromatography mass spectrometry (GC-MS) and liquid chromatography (LC)-MS. This approach enabled the comparison of the relative abundance of 88 polar primary metabolites from GC-MS and 625 semi-polar secondary metabolites from LC-MS. Using principal components analysis, a major effect of temperature was observed in each species which was larger than that resulting from the genetic background. Compounds mostly affected by temperature treatment were subsequently selected using partial least squares discriminant analysis and were further identified. These putative annotations indicated that soluble sugars and several polyphenols, including tannins, triterpenes and alkaloids were mostly influenced.

Insights into temperature modulation of the Eucalyptus globulus and Eucalyptus grandis antioxidant and lignification subproteomes

Eucalyptus grandis and Eucalyptus globulus are among the most widely cultivated trees, differing in lignin composition and plantation areas, as E. grandis is mostly cultivated in tropical regions while E. globulus is preferred in temperate areas. As temperature is a key modulator in plant metabolism, a large-scale proteome analysis was carried out to investigate changes in the antioxidant system and the lignification metabolism in plantlets grown at different temperatures. Our strategy allowed the identification of 3111 stem proteins. A total of 103 antioxidant proteins were detected in the stems of both species. Hierarchical clustering revealed that alterations in the antioxidant proteins are more prominent when Eucalyptus seedlings were exposed to high temperature and that the superoxide isoforms coded by the gene Eucgr.B03930 are the most abundant antioxidant enzymes induced by thermal stimulus. Regarding the lignin biosynthesis, our proteomics approach resulted in the identification of 13 of the 17 core proteins involved in this metabolism, corroborating with gene predictions and the proposed lignin toolbox. Quantitative analyses revealed significant differences in 8 protein isoforms, including the ferulate 5-hydroxylase isoform F5H1, a key enzyme in catalyzing the synthesis of sinapyl alcohol, and the cinnamyl alcohol dehydrogenase isoform CAD2, the last enzyme in monolignol biosynthesis. Data are available via ProteomeXchange with identifier PXD005743.

Dehydration responsive element binding transcription factors and their applications for the engineering of stress tolerance

Dehydration responsive element binding (DREB) factors or CRT element binding factors (CBFs) are members of the AP2/ERF family, which comprises a large number of stress-responsive regulatory genes. This review traverses almost two decades of research, from the discovery of DREB/CBF factors to their optimization for application in plant biotechnology. In this review, we describe (i) the discovery, classification, structure, and evolution of DREB genes and proteins; (ii) induction of DREB genes by abiotic stresses and involvement of their products in stress responses; (iii) protein structure and DNA binding selectivity of different groups of DREB proteins; (iv) post-transcriptional and post-translational mechanisms of DREB transcription factor (TF) regulation; and (v) physical and/or functional interaction of DREB TFs with other proteins during plant stress responses. We also discuss existing issues in applications of DREB TFs for engineering of enhanced stress tolerance and improved performance under stress of transgenic crop plants.

Evaluation of organic and inorganic amendments on maize growth and uptake of cd and zn from contaminated paddy soils

Pot and field experiments were conducted to investigate the effects of soil amendments (cow manure, rice straw, zeolite, dicalcium phosphate) on the growth and metal uptake (Cd, Zn) of maize (Zea mays) grown in Cd/Zn contaminated soil. The addition of cow manure and rice straw significantly increased the dry biomass, shoot and root length, and grain yield of maize when compared with the control. In pot study, cow manure, rice straw, and dicalcium phosphate all proved effective in reducing Cd and Zn concentrations in shoots and roots. Cd and Zn concentrations in the grains of maize grown in field study plots with cow manure and dicalcium phosphate amendments to highly contaminated soil (Cd 36.5 mg kg(-1) and Zn 1520.8 mg kg(-1)) conformed to acceptable standards for animal feed. Additionally both cow manure and dicalcium phosphate amendments resulted in the significant decrease of Cd and Zn concentrations in shoots of maize.

Identification of quantitative trait loci and a candidate locus for freezing tolerance in controlled and outdoor environments in the overwintering crucifer Boechera stricta

Development of chilling and freezing tolerance is complex and can be affected by photoperiod, temperature and photosynthetic performance; however, there has been limited research on the interaction of these three factors. We evaluated 108 recombinant inbred lines of Boechera stricta, derived from a cross between lines originating from Montana and Colorado, under controlled long day (LD), short-day (SD) and in an outdoor environment (OE). We measured maximum quantum yield of photosystem II, lethal temperature for 50% survival and electrolyte leakage of leaves. Our results revealed significant variation for chilling and freezing tolerance and photosynthetic performance in different environments. Using both single- and multi-trait analyses, three main-effect quantitative trait loci (QTL) were identified. QTL on linkage group (LG)3 were SD specific, whereas QTL on LG4 were found under both LD and SD. Under all conditions, QTL on LG7 were identified, but were particularly predictive for the outdoor experiment. The co-localization of photosynthetic performance and freezing tolerance effects supports these traits being co-regulated. Finally, the major QTL on LG7 is syntenic to the Arabidopsis C-repeat binding factor locus, known regulators of chilling and freezing responses in Arabidopsis thaliana and other species.

Identification and expression analysis of cold and freezing stress responsive genes of Brassica oleracea

Cold and freezing stress is a major environmental constraint to the production of Brassica crops. Enhancement of tolerance by exploiting cold and freezing tolerance related genes offers the most efficient approach to address this problem. Cold-induced transcriptional profiling is a promising approach to the identification of potential genes related to cold and freezing stress tolerance. In this study, 99 highly expressed genes were identified from a whole genome microarray dataset of Brassica rapa. Blast search analysis of the Brassica oleracea database revealed the corresponding homologous genes. To validate their expression, pre-selected cold tolerant and susceptible cabbage lines were analyzed. Out of 99 BoCRGs, 43 were differentially expressed in response to varying degrees of cold and freezing stress in the contrasting cabbage lines. Among the differentially expressed genes, 18 were highly up-regulated in the tolerant lines, which is consistent with their microarray expression. Additionally, 12 BoCRGs were expressed differentially after cold stress treatment in two contrasting cabbage lines, and BoCRG54, 56, 59, 62, 70, 72 and 99 were predicted to be involved in cold regulatory pathways. Taken together, the cold-responsive genes identified in this study provide additional direction for elucidating the regulatory network of low temperature stress tolerance and developing cold and freezing stress resistant Brassica crops.

Characterization of two highly similar CBF/DREB1-like genes, PhCBF4a and PhCBF4b, in Populus hopeiensis

The C-repeat binding factors (CBFs)/dehydration-responsive element-binding protein (DREBs) are a group of conserved transcription factors that play an important role in the response and adaptation to environmental stress in many plants. Two highly similar CBF/DREB1-like genes, PhCBF4a and PhCBF4b, were previously identified in Populus hopeiensis. In this paper, we describe the function of these proteins in detail in terms of abiotic stress tolerance. Phylogenic analysis suggests that PhCBF4a and PhCBF4b are expressed as two distinct alleles. Expression of both genes is induced mainly by dehydration, low-temperature, and high-salinity. Agroinfiltration experiments in tobacco leaves revealed differential transcriptional activation of the genes, likely driven by differences in their C-terminal regions. When constitutively expressed in Arabidopsis, PhCBF4a and PhCBF4b induced elevated expression of the CBF/DREB1 regulons without prior stimulus, resulting in dwarfism, delayed flowering, and greater drought tolerance compared with vector controls. These results demonstrate that PhCBF4a and PhCBF4b are functional transcriptional regulators involved in the response of P. hopeiensis to abiotic stresses.

Molecular characterization of cotton C-repeat/dehydration-responsive element binding factor genes that are involved in response to cold stress

Low temperature, drought and salinity are major abiotic stresses that influence survival, productivity and geographical distribution of many important crops across the globe. The C-repeat/dehydration-responsive element binding transcription factors (CBF/DREB) are important proteins involved in response to abiotic stresses in plants. In this study, twenty-one CBF genes were identified in cotton (Gossypium hirsutum) by bioinformatic approach. The twenty-one CBF genes (named as GhCBF1--GhCBF21) were characterized to encode proteins that share high similarity with those plant cold stress-related CBF proteins, which contain the classic AP2 domain of 58 amino acid residues. Phylogenetic analysis revealed that the isolated cotton CBF genes can be classified into 4 groups: GhCBF I, GhCBF II, GhCBF III and GhCBF IV. RT-PCR analysis indicated that GhCBF genes were up-regulated in cotton plants under cold stress. Furthermore, four GhCBF genes were up-regulated in cotton under salinity and drought treatments. Our data provided valuable information for further exploring the roles of the CBF genes in cotton development and in response to cold stress.

Cloning of galactinol synthase gene from Ammopiptanthus mongolicus and its expression in transgenic Photinia serrulata plants

A cold induced galactinol synthase gene (AmGS) and its promoter sequence were identified and cloned from the cold-tolerant tree Ammopiptanthus mongolicus by using cDNA-AFLP, RACE-PCR and TAIL-PCR strategies combined with its expression pattern analysis after cold inducing treatment. Accession number of the AmGS gene in GenBank is DQ519361. The open reading frame (ORF) region of the AmGS gene is 987 nucleotides encoding for 328 amino acid residues and a stop codon. The genomic DNA sequence of AmGS gene contains 3 exons and 2 introns. Moreover, a variety of temporal gene expression patterns of AmGS was detected, which revealed the up-regulation of AmGS gene in stresses of cold, ABA and others. Then the AmGS gene was transformed into Photinia serrulata tree by Agrobacterium-mediated transformation, and the transgenic plants exhibited higher cold-tolerance comparing with non-transformed plants.

Functional characterization of two almond C-repeat-binding factors involved in cold response

Low temperature plays a crucial role in seasonal development of woody plants and may directly impact crop production, more particularly in temperate fruit trees. Given its high genetic variability and adaptability to different climatic conditions, almond (Prunus dulcis Mill.) is an interesting model to understand the mechanisms regulating low temperature sensing in fruit trees. In this paper, we report the cloning and characterization of two genes (PdCBF1 and PdCBF2) belonging to the C-repeat-binding factor (CBF) family of transcription factors. Southern blotting analysis showed that this family is composed of at least five members. In almond shoots propagated in vitro, transcription of these genes was rapidly induced by low temperature, suggesting an involvement in cold acclimation. Transactivation assays showed that PdCBF1 and PdCBF2 could bind to dehydration responsive element/C-repeat containing sequences, as activators of gene expression. In addition, induction of both PdCBFs by cold was higher towards the end of the day, which agreed with the expression pattern of PdDehydrin1, a predicted CBF target gene. Furthermore, PdCBF1 and PdCBF2 were also transiently induced by abscisic acid and drought treatments. Considering the bin mapping analysis that correlated PdCBFs and PdDHN1 (respectively in linkage groups 5 and 7) with two different quantitative trait locicontrolling blooming time, it is relevant to perform further association studies that may validate their effect on this trait.

Improvement of paper mulberry tolerance to abiotic stresses by ectopic expression of tall fescue FaDREB1

Dehydration-responsive element binding/C-repeat-binding factors (DREB/CBF) control the activity of multiple stress response genes and therefore represent attractive targets for genetic improvement of abiotic stress tolerance. Paper mulberry (Broussonetia papyrifera L. Vent) is well known for its bark fibers and high levels of chalcone and flavonoid derivatives. Transgenic paper mulberry plants expressing a tall fescue (Festuca arundinacea Schreb.) FaDREB1 gene under the control of CaMV 35S were produced to examine the potential utility of FaDREB1 to increase the tolerance of paper mulberry plants to abiotic stress. The overexpressing FaDREB1 plants showed higher salt and drought tolerance than the wild-type plants (WT). After 13 days of withholding water, or 15 days in the presence of 250 mM NaCl, all the WT plants died, while the over-expressing FaDREB1 plants survived. The FaDREB1 plants had higher leaf water and leaf chlorophyll contents, accumulated more proline and soluble sugars, and had less ion leakage (which reflects membrane damage) than the WT plants had under high salt- and water-deficient conditions. The 35S promoter-driven expression of FaDREB1 did not cause growth retardation under normal growth conditions. Therefore, improved tolerance to multiple environmental stresses in paper mulberry might be achieved via genetic engineering through the ectopic expression of an FaDREB1 gene.

Identification and expression analysis of CBF/DREB1 and COR15 genes in mutants of Brassica oleracea var. botrytis with enhanced proline production and frost resistance

Frost resistant mutants of Brassica oleracea var. botrytis were investigated for the presence of CBF/DREB1 and COR15a gene products and induced frost resistance. Total RNA of clones was isolated after 3 h, 6 h, 24 h and 14 d acclimation at 4 °C and proteins and free proline were isolated after 14 d acclimation. cDNA was produced using RT-PCR and the first CBF gene in B. oleracea detected and did quantify. Through SDS-PAGE and Western blotting, the COR15a protein was detected for the first time in B. oleracea. The results confirmed the first report of the presence of BoCBF/DREB1 in B. oleracea and this only appeared under cold acclimation. The sequence analysis of predicted amino acids revealed a very high homology (90%) with CBF sequences of other Brassica species (BnCBF5/DREB1, BrDREB1 and BjDREB1B) and homology reduced to 67% when compared to plants other than Brassicas. BoCBF/DREB1 transcript levels increased up to 24 h acclimation and then declined. Some mutants showed BoCBF/DREB1 expression at 3 h while others only after 6 h and 24 h acclimation. The genotypes showed positive significant correlation between BoCBF/DREB1 expression and frost resistance (R(2) = 0.9343). The proline level under acclimation increased about 8 fold and demonstrated positive and significant correlation with BoCBF/DREB1 expression. Proline also showed positive and significant correlation with frost resistance under cold acclimation but very not under non-acclimation. All clones were positive for COR15a protein after 14 d cold acclimation and expression correlated with frost resistance. Under non-acclimation COR15a was constitutively expressed in 3 mutants.

Two EguCBF1 genes overexpressed in Eucalyptus display a different impact on stress tolerance and plant development

Two C-repeat binding factor genes (EguCBF1a/b), isolated from E. gunnii and differentially cold-regulated, were constitutively overexpressed in a cold-sensitive Eucalyptus hybrid. In addition to the expected improvement on freezing tolerance, some resulting transgenic lines (EguCBF1a-OE and EguCBF1b-OE) exhibited a decrease in stomata density and an over-accumulation of anthocyanins also observed to a lesser extent in a cold-acclimated control plant. Given that the induction of five putative CBF target genes was observed in CBF-overexpressing lines as well as in the cold-acclimated control line, these phenotypes might be related to cold acclimation. In comparison with the control plant, the most altered transgenic line (EguCBF1a-OE A1 line), exhibited reduced growth and better water retention capacity. This modified phenotype includes reduced leaf area and thickness associated with a decrease in cell size, as well as a higher oil gland density and a wax deposition on the cuticle. Surprisingly, the EguCBF1b-OE B9 line, with a level of transgene expression equivalent to the A1 line, showed a less marked phenotype, suggesting a difference in transactivation efficiency between EguCBF1A and B factors. The features of these transgenic lines provide the first signs of adaptive mechanisms controlled by CBF transcription factors in an evergreen broad-leaved tree. These data also open new prospects towards genetic improvement on Eucalyptus for freezing tolerance.

Expression of a rice DREB1 gene, OsDREB1D, enhances cold and high-salt tolerance in transgenic Arabidopsis

OsDREB1D, a special DREB (dehydration responsive element binding protein) homologous gene, whose transcripts cannot be detected in rice (Oryza sativa L), either with or without stress treatments, was amplified from the rice genome DNA. The yeast one-hybrid assay revealed that OsDREB1D was able to form a complex with the dehydration responsive element/C-repeat motif. It can also bind with a sequence of LTRE (low temperature responsive element). To analyze the function of OsDREB1D, the gene was transformed and over-expressed in Arabidopsis thaliana cv. Columbia. Results indicated that the over-expression of OsDREB1D conferred cold and high-salt tolerance in transgenic plants, and that transgenic plants were also insensitive to ABA (abscisic acid). From these data, we deduced that this OsDREB1D gene functions similarly as other DREB transcription factors. The expression of OsDREB1D in rice may be controlled by a special mechanism for the redundancy of function.

Complementary regulation of four Eucalyptus CBF genes under various cold conditions

CBF transcription factors play central roles in the control of freezing tolerance in plants. The isolation of two additional CBF genes, EguCBF1c and EguCBF1d, from E. gunnii, one of the cold-hardiest Eucalyptus species, is described. While the EguCBF1D protein sequence is very similar to the previously characterized EguCBF1A and EguCBF1B sequences, EguCBF1C is more distinctive, in particular in the AP2-DBD (AP2-DNA binding domain). The expression analysis of the four genes by RT-qPCR reveals that none of them is specific to one stress but they are all preferentially induced by cold, except for the EguCBF1c gene which is more responsive to salt. The calculation of the transcript copy number enables the quantification of constitutive CBF gene expression. This basal level, significant for the four genes, greatly influences the final EguCBF1 transcript level in the cold. A cold shock at 4 degrees C, as well as a progressive freezing which mimics a natural frost episode, trigger a fast and strong response of the EguCBF1 genes, while growth at acclimating temperatures results in a lower but more durable induction. The differential expression of the four EguCBF1 genes under these cold regimes suggests that there is a complementary regulation. The high accumulation of the CBF transcript, observed in response to the different types of cold conditions, might be a key for the winter survival of this evergreen broad-leaved tree.