COR Genes Research Articles

The transcription factor ICE1 functions in cold stress response by binding to the promoters of CBF and COR genes.

A recent paper byKidokoro et al. (2020) in The Plant Cell reported a transgene-dependent transcriptional silencing phenomenon in the dominant ice1-1 Arabidopsis mutant containing the CBF3-LUC reporter, and questioned whether ICE1 may regulate CBF genes and may be involved in plant cold response. Here, we evaluate available evidence supporting the involvement of ICE1 in plant cold response, and provide ChIP-seq data showing ICE1 binding to the promoters of CBF genes and other regulatory genes known to be critical for cold response as well as to the promoters of some COR genes.

Molecular cloning and functional analysis of a cold-regulated gene Wcor18 in wheat

To explore the function of COR gene in wheat, Wcor18 was cloned from wheat cultivar Jing 841. Expression level of Wcor18 increased with vernalization time prolongation. The full length of Wcor18 gene is 498 bp and encodes 165 amino acids. The predicted Wcor18 protein is a type of unstable hydrophilic protein and is prone to be hydrolyzed and to be oxidized. Gene structure analysis and phylogenetic tree analysis showed Wcor18 gene contains two exons and coding proteins are quite conservative among the donor ancestors of common wheat. Wcor18 can quickly respond to low temperature, high salt, drought, and ABA stresses at wheat seedling stage. The highly expression of Wcor18 gene under the − 15 °C and the rapid response of Wcor18 gene under several stress conditions indicated that the gene may play many roles in stress response of wheat.

Endogenous accumulation of glycine betaine confers improved low temperature resistance on transplastomic potato plants.

Glycine betaine (GB) plays a crucial role in plant response to abiotic stress, and its accumulation in chloroplasts is more effective than in the cytosol in improving the resistance of transgenic plants. Here, we report that the codA gene from Arthrobacter globiformis, which encodes a choline oxidase catalysing the conversion of choline to GB, was successfully introduced into the plastid genome of potato (Solanum tuberosum L.). Transgenic plants with plastid expression of codA showed increased tolerance to low temperature stress compared with the wild type (WT). Further studies revealed that under low temperature stress condition, transgenic plants presented a significantly higher photosynthetic performance by regulating the electron transport and energy distribution in PSII, and higher antioxidant enzyme activities and lower O2- and H2O2 accumulation than did the WT plants. A higher expression of the COR genes was also observed in transgenic plants. Our results suggest that chloroplast biosynthesis of GB could be an effective strategy for the engineering of plants with increased resistance to low temperature stress.

A novel cold-regulated protein isolated from Saussurea involucrata confers cold and drought tolerance in transgenic tobacco (Nicotiana tabacum)

Adverse environmental conditions, such as cold and drought, can inhibit plant growth, development, and productivity. The isolation and characterization of stress response genes from stress-tolerant plants can provide a better understanding of the underlying adaptive mechanisms. In this study, a novel cold-regulated gene, SikCOR413PM1, was isolated from Saussurea involucrata Kar. et Kir., which is a plant that survives at the high altitudes and in the low temperatures of alpine slopes in northwestern China. SikCOR413PM1 was induced in response to cold and drought in S. involucrata, and phylogenetic analysis revealed that the gene groups with a COR gene encoding a COR413PM protein family member. Subcellular localization of a SikCOR413PM1-green fluorescent fusion protein showed that SikCOR413PM1 was localized to the plasma membrane. A transgenic tobacco (Nicotiana tabacum) system was employed to investigate the possible role of SikCOR413PM1 in cold and drought tolerance. Analyses of growth, germination and survival rates, relative water content, malondialdehyde content, relative electrolyte leakage, and maximal photochemical efficiency of photosystem II showed that transgenic tobacco plants expressing SikCOR413PM1 were more tolerant to cold and drought stresses than WT plants. SikCOR413PM1 overexpression was also accompanied by constitutive activation of NtDREB1 and NtDREB3, two cold-responsive transcription factor genes, and NtERD10A and NtERD10B, two cold-induced genes. The expression levels of downstream transcription factor genes NtDREB3, NtERD10C, NtERD10D, and NtLEA5 were also induced in SikCOR413PM1-expressing transgenic plants under drought conditions. Our results suggest that the overexpression of SikCOR413PM1 induces changes in tobacco plants, and facilitates enhanced tolerance to cold and drought stresses.

Genomic identification of AP2/ERF transcription factors and functional characterization of two cold resistance-related AP2/ERF genes in celery (Apium graveolens L.).

This study analyzed the AP2/ERF transcription factors in celery and showed that two dehydration-responsive-element-binding (DREB) transcription factors, AgDREB1 and AgDREB2, contribute to the enhanced resistance to abiotic stress in transgenic Arabidopsis. The AP2/ERF family is a large family of transcription factors (TFs) in higher plants that plays a central role in plant growth, development, and response to environmental stress. Here, 209 AP2/ERF family members were identified in celery based on genomic and transcriptomic data. The TFs were classified into four subfamilies (i.e., DREB, ERF, RAV, and AP2) and Soloist. Evolution analysis indicated that the AP2/ERF TFs are ancient molecules and have expanded in the long-term evolution process of plants and whole-genome duplication events. AgAP2/ERF proteins may be associated with multiple biological processes as predicted by the interaction network. The expression profiles and sequence alignment analysis of the TFs in the DREB-A1 group showed that eight genes could be divided into four branches. Two genes, AgDREB1 and AgDREB2, from the DREB-A1 group were selected for further analysis. Subcellular localization assay suggested that the two proteins are nuclear proteins. Yeast one hybrid assay demonstrated that the two proteins could bind to the dehydration-responsive element (DRE). The overexpression of AgDREB1 and AgDREB2 in Arabidopsis induced the increased tolerance to cold treatment and the up-regulation of the COR genes expression. AgDREB1 and AgDREB2 might function as transcriptional activators in regulating the downstream genes by binding to corresponding DRE to enhance stress tolerance in celery.

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.

De novo transcriptome sequencing and gene expression profiling of sweet potato leaves during low temperature stress and recovery

Sweetpotato [Ipomoea batatas (L.) Lam] is an important crop used for food, animal feed, and production of industrial materials. Although it is adapted to a wide range of unfavorable conditions, including drought and high salt, sweetpotato is vulnerable to low temperature, making it difficult to cultivate in low temperature regions. To understand the molecular responses occurring in sweetpotato leaves under low temperature stress, de novo transcriptome assembly was performed in leaves under low temperature stress (LT) and during recovery (RC). In comparison with non-treated controls (NT), 2461 and 1017 differentially expressed genes (DEGs) were identified in LT and RC leaves, respectively. When expression in RC and LT samples was directly compared, 2053 DEGs were detected. To increase understanding of the DEGs, the three datasets were analyzed using Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genome (KEGG) database. The CBF transcriptional cascade, a well-known cold response pathway, was investigated using transcriptomic analysis. In contrast with reports from the cold-tolerant Arabidopsis thaliana, none of the COR genes identified in sweetpotato showed increased expression in response to low temperature. Genes involved in antioxidant enzyme pathways mediating responses to reactive oxygen species (ROS) were investigated during low temperature response. This work provides insight into the molecular basis of the responses of sweetpotato to cold stress. This increased understanding of gene regulation in response to cold stress in sweetpotato will be beneficial for future research into molecular-assisted breeding.

Role of carbon ion beams irradiation in mitigating cold stress in Arabidopsis thaliana

Carbon ion beams irradiation as an important type of ionizing radiation is one of the major approaches used to create mutants in plants. This study investigated the role of carbon ion beams irradiation in mitigating cold stress in Arabidopsis thaliana seedlings. The results showed that 50-Gy carbon ion beam irradiation appeared stimulatory effects on root length and fresh weight in Arabidopsis seedlings under cold stress. In comparison with control, the content of hydrogen peroxide, the production rate of superoxide anion radical, hydroxyl radical generation activity, and malondialdehyde content were obviously decreased in 50-Gy carbon ion beam irradiated seedlings in response to cold stress. Moreover, irradiated 50-Gy carbon ion beam in Arabidopsis seedlings were significantly triggered the efficiency of antioxidant under cold stress. Furthermore, we investigated the expression of cold-related genes in irradiated and non-irradiated samples. Carbon ion beams irradiation up-regulated the expression levels of C-REPEAT BINDING FACTORS (CBFs), INDUCER OF CBF EXPRESSION 1 (ICE1), ICE2, CALMODULIN-BINDING TRANSCRIPTION ACTIVATOR 3 (CAMTA3) and cold-regulated COR genes, in response to cold stress. This study suggests that low-dose carbon ion beams irradiation can modulate the physiological responses and up-regulate cold signaling genes in mitigating cold stress in the growth of Arabidopsis seedlings.

Epigenetic switch from repressive to permissive chromatin in response to cold stress

Switching from repressed to active status in chromatin regulation is part of the critical responses that plants deploy to survive in an ever-changing environment. We previously reported that HOS15, a WD40-repeat protein, is involved in histone deacetylation and cold tolerance in Arabidopsis However, it remained unknown how HOS15 regulates cold responsive genes to affect cold tolerance. Here, we show that HOS15 interacts with histone deacetylase 2C (HD2C) and both proteins together associate with the promoters of cold-responsive COR genes, COR15A and COR47 Cold induced HD2C degradation is mediated by the CULLIN4 (CUL4)-based E3 ubiquitin ligase complex in which HOS15 acts as a substrate receptor. Interference with the association of HD2C and the COR gene promoters by HOS15 correlates with increased acetylation levels of histone H3. HOS15 also interacts with CBF transcription factors to modulate cold-induced binding to the COR gene promoters. Our results here demonstrate that cold induces HOS15-mediated chromatin modifications by degrading HD2C. This switches the chromatin structure status and facilitates recruitment of CBFs to the COR gene promoters. This is an apparent requirement to acquire cold tolerance.

Spatiotemporal oscillations of morphinan alkaloids in opium poppy

Here, a comprehensive endeavor is made to simultaneously scrutinize spatiotemporal oscillations of three imperative morphinan alkaloids (i.e. thebaine, codeine, and morphine) alongside dynamic transcriptional patterns of TYDC, SalAT, COR, T6ODM, and CODM genes in different tissues of Papaver somniferum (i.e. root, bottom part of stem, upper part of stem, leaf, capsule wall, and capsule content) over five distinguished ontogenic stages (i.e. rosette, bud initiation, pendulous bud, flowering, and lancing). Apart from bottom stem and leaf, the maximum thebaine content occurred in lancing stage, while its minimum content did not follow a systematic rhythm, either among six tissues or five various sampling times. Regarding codeine, excepting upper stem, the highest ratios of codeine were observed at flowering and lacing stages, while negligible amounts were overall detected at early stages of plant growth like rosette. Considering morphine, apart from upper stem, it appears that late ontogeneic times including lancing and flowering are the most appropriate phases to achieve high amounts of morphine, while at early stages the aforesaid alkaloid possessed lower accumulation. Furthermore, all the five genes under study, overall, exhibited a variety of transcript levels either among six tissues or five various sampling times. Interestingly, a connection occurred between transcript ratio of SalAT and thebaine content, suggesting that thebaine biosynthesis is coordinated tightly by the enzymatic function of SalAT enzyme. Meanwhile, despite low magnitudes of T6ODM and CODM transcripts in the root-harvested samples at pendulous bud and flowering stages, both codeine and morphine were surprisingly in acceptable quantities, plausibly owing to the translocation of both alkaloids from the producing (source) tissues to the roots (sink), known as a phenomenon of 'source-to-sink transportation'. The results, altogether, could provide us enough information in acquiring new insights towards potential impacts of spatiotemporal oscillations on the magnitudes of all the above-mentioned alkaloids alongside transcription ratios of the key genes in opium poppy.

Arabidopsis PCaP2 Plays an Important Role in Chilling Tolerance and ABA Response by Activating CBF- and SnRK2-Mediated Transcriptional Regulatory Network.

Chilling stress affects plant growth and productivity. However, the multi-underlying mechanisms of chilling tolerance are not well understood. Arabidopsis PCaP2 is involved in regulating the dynamic of microtubules (MTs) and F-actin and Ca2+-binding ability. Here, the results showed that the PCaP2 expression was highly induced in roots, cotyledons, true leaves, lateral roots and flowers under cold stress. Compared with the wild type, PCaP2-overexpressing plants displayed the enhanced tolerance, whereas its RNAi and mutant were more sensitive in seed germination, seedling and reproductive growth under chilling stress in Arabidopsis. In addition, PCaP2 was also a positive regulator of ABA signaling pathway by analyzing the expression of PCaP2 and the phenotypes of PCaP2-overexpressing, mutant and RNAi plants under ABA treatment. Interestingly, disruption of PCaP2 inhibited the expression of CBF1, -3 and CBF-target COR genes, while increased the CBF2 expression in response to cold or ABA. Moreover, we found that SnRK2s were involved in cold stress and PCaP2 mutants down-regulated the transcription level of SnRK2.2, -2.3 and SnRK2-mediated downstream genes including ABF2, RD29A, KIN1, KIN2, but up-regulated SnRK2.6, ABF1, -3, -4 in ABA and cold treatments. It is well-accepted that PCaP2 as a Ca2+-binding protein triggers the gene expression to enhance plant chilling tolerance. Our further studies showed that MT destabilizing activity of PCaP2, but not F-actin-severing function, may be involved in chilling stress. Taken together, our results highlight that PCaP2 plays an important role in chilling tolerance and ABA response by triggering the CBF- and SnRK2-meditated transcriptional regulatory pathways, providing novel evidences of underlying mechanisms of multi-pathways in chilling stress.

English

In this research, we isolated three CBF (C-repeat-Binding Factors) genes from two genotypes of Boechera stricta with contrasting freezing tolerance and characterized their structure and expression patterns in response to cold treatment. An amino acid sequence comparison revealed that the CBF genes in B. stricta showed high conservation in the AP2 domain and PKKP/RAGR motif like other cold adaptable Brassicaceae. The pairwise sequence alignment of the CBF genes isolated from two genotypes of B. stricta showed non-synonymous mutations in CBF 2 and 3. Gene expression analysis demonstrated that CBF genes in B. stricta have expression patterns similar to CBFs in A. thaliana in response to cold treatment, while differential expression at the molecular level in CBF and COR genes was presented between two genotypes of B. stricta. Our results suggest that signal transduction of three CBF genes can be one of the central pathways in the development of freezing tolerance in B. stricta.

Overexpression of a wheat (Triticum aestivum L.) bZIP transcription factor gene, TabZIP6, decreased the freezing tolerance of transgenic Arabidopsis seedlings by down-regulating the expression of CBFs

The basic leucine zipper (bZIP) proteins play important roles against abiotic stress in plants, including cold stress. However, most bZIPs involved in plant freezing tolerance are positive regulators. Only a few bZIPs function negatively in cold stress response. In this study, TabZIP6, a Group C bZIP transcription factor gene from common wheat (Triticum aestivum L.), was cloned and characterized. The transcript of TabZIP6 was strongly induced by cold treatment (4 °C). TabZIP6 is a nuclear-localized protein with transcriptional activation activity. Arabidopsis plants overexpressing TabZIP6 showed decreased tolerance to freezing stress. Microarray as well as quantitative real-time PCR (qRT-PCR) analysis showed that CBFs and some key COR genes, including COR47 and COR15B, were down-regulated by cold treatment in TabZIP6-overexpressing Arabidopsis lines. TabZIP6 was capable of binding to the G-box motif and the CBF1 and CBF3 promoters in yeast cells. A yeast two-hybrid assay revealed that TabZIP6, as well as the other two Group S bZIP proteins involved in cold stress tolerance in wheat, Wlip19 and TaOBF1, can form homodimers by themselves and heterodimers with each other. These results suggest that TabZIP6 may function negatively in the cold stress response by binding to the promoters of CBFs, and thereby decreasing the expression of downstream COR genes in TabZIP6-overexpressing Arabidopsis seedlings.

BZR1 Positively Regulates Freezing Tolerance via CBF-Dependent and CBF-Independent Pathways in Arabidopsis

Cold stress is a major environmental factor that adversely affects plant growth and development. The C-repeat binding factor/DRE binding factor 1 (CBF/DREB1) transcriptional regulatory cascade has been shown to play important roles in plant response to cold. Here we demonstrate that two key components of brassinosteroid (BR) signaling modulate freezing tolerance of Arabidopsis plants. The loss-of-function mutant of the GSK3-like kinases involved in BR signaling, bin2-3 bil1 bil2, showed increased freezing tolerance, whereas overexpression of BIN2 resulted in hypersensitivity to freezing stress under both non-acclimated and acclimated conditions. By contrast, gain-of-function mutants of the transcription factors BZR1 and BES1 displayed enhanced freezing tolerance, and consistently cold treatment could induce the accumulation of dephosphorylated BZR1. Biochemical and genetic analyses showed that BZR1 acts upstream of CBF1 and CBF2 to directly regulate their expression. Moreover, we found that BZR1 also regulated other COR genes uncoupled with CBFs, such as WKRY6, PYL6, SOC1, JMT, and SAG21, to modulate plant response to cold stress. Consistently, wrky6 mutants showed decreased freezing tolerance. Taken together, our results indicate that BZR1 positively modulates plant freezing tolerance through CBF-dependent and CBF-independent pathways.

Circadian and Plastid Signaling Pathways Are Integrated to Ensure Correct Expression of the CBF and COR Genes during Photoperiodic Growth.

The circadian clock synchronizes a wide range of biological processes with the day/night cycle, and correct circadian regulation is essential for photosynthetic activity and plant growth. We describe here a mechanism where a plastid signal converges with the circadian clock to fine-tune the regulation of nuclear gene expression in Arabidopsis (Arabidopsis thaliana). Diurnal oscillations of tetrapyrrole levels in the chloroplasts contribute to the regulation of the nucleus-encoded transcription factors C-REPEAT BINDING FACTORS (CBFs). The plastid signal triggered by tetrapyrrole accumulation inhibits the activity of cytosolic HEAT SHOCK PROTEIN90 and, as a consequence, the maturation and stability of the clock component ZEITLUPE (ZTL). ZTL negatively regulates the transcription factor LONG HYPOCOTYL5 (HY5) and PSEUDO-RESPONSE REGULATOR5 (PRR5). Thus, low levels of ZTL result in a HY5- and PRR5-mediated repression of CBF3 and PRR5-mediated repression of CBF1 and CBF2 expression. The plastid signal thereby contributes to the rhythm of CBF expression and the downstream COLD RESPONSIVE expression during day/night cycles. These findings provide insight into how plastid signals converge with, and impact upon, the activity of well-defined clock components involved in circadian regulation.

SFR6 Protein of freezing tolerance in Arabidopsis does not affect localization of CBF1 protein

SFR6 (SENSITIVE TO FREEZING6) is one of plant mediator proteins which has been identified first with its involvement to tolerance against freezing in Arabidopsis. The freezing sensitive sfr6 mutant is lack of expression of downstream genes in CBF cold response pathway. SFR6 also mediates tolerance to osmotic stress induced by drought and salinity. However, sfr6-1 mutant shows normal levels of CBF gene expression suggesting that SFR6 acts downstream of CBF transcription. The over-expression of CBF1 and CBF2 in the sfr6-1 mutant did not in- crease downstream cold gene expression. Further, SFR6 does not affect the level of accumulation of CBF protein suggesting that SFR6 may effect on localization of CBF proteins in Arabidopsis. Therefore, the localization of CBF1 protein in the sfr6-1 mutant was examined in this study. sfr6-1 and Col-0 plants were crossed with wild type plants over-expressing 35S::CBF1::GFP and F3 generation was used to visualize CBF1 localization. However, the localization of CBF1 protein was not altered in sfr6-1 mutant compared to the wild type Arabidopsis indicating that the involvement of SFR6 for COR gene expression needs to be further studied. Tropical Agricultural Research and Extension 16(2): 2013: page 49-53

Time-dependent deacclimation after cold acclimation in Arabidopsis thaliana accessions.

During low temperature exposure, Arabidopsis thaliana and many other plants from temperate climates increase in freezing tolerance in a process termed cold acclimation. However, the correct timing and rate of deacclimation, resulting in loss of freezing tolerance and initiation of growth is equally important for plant fitness and survival. While the molecular basis of cold acclimation has been investigated in detail, much less information is available about deacclimation. We have characterized the responses of 10 natural accessions of Arabidopsis thaliana that vary widely in their freezing tolerance, to deacclimation conditions. Sugar, proline and transcript levels declined sharply over three days in all accessions after transfer of cold acclimated plants to ambient temperatures, while freezing tolerance only declined in tolerant accessions. Correlations between freezing tolerance and the expression levels of COR genes and the content of glucose, fructose and sucrose, as well as many correlations among transcript and solute levels, that were highly significant in cold acclimated plants, were lost during deacclimation. Other correlations persisted, indicating that after three days of deacclimation, plant metabolism had not completely reverted back to the non-acclimated state. These data provide the basis for further molecular and genetic studies to unravel the regulation of deacclimation.

Over-expression of miR397 improves plant tolerance to cold stress in Arabidopsis thaliana

Cold stress is an environmental factor that limits the geographical distribution and growing season of plants. The plant response to cold involves different metabolic pathways and gene regulation. Although the expression of some miRNAs is significantly altered in cold stress, little is known about the regulatory function of miRNAs in plant resistance to cold. In this study, we generated transgenic Arabidopsis plants which harbor an over-expression construct of 35S::miR397a. Analysis by RNA blotting revealed high levels of miR397a transcripts in the transformed plants. Plant cold tolerance assays demonstrated that over-expression of miR397a improved plant tolerance to chilling and freezing stresses. In addition, this study showed that the freezing tolerance of miR397a-ov plants was improved by cold acclimation at 4°C. Northern blot analysis revealed that overexpression of miR397a affected the expression of coldregulated CBF genes and downstream COR genes. These findings provide evidence demonstrating a regulatory role of miR397 in the cold signaling pathway and plant tolerance to chilling and freezing stresses.

The grapevine basic helix-loop-helix (bHLH) transcription factor positively modulates CBF-pathway and confers tolerance to cold-stress in Arabidopsis.

Basic helix-loop-helix (bHLH)-type transcription factors play diverse roles in plant physiological response and stress-adaptive regulation network. Here, we identified one grapevine bHLH transcription factor from a cold-tolerant accession 'Heilongjiang seedling' of Chinese wild Vitis amurensis (VabHLH1) as a transcriptional activator involved in cold stress. We also compared with its counterpart from a cold-sensitive Vitis vinifera cv. Cabernet Sauvignon (VvbHLH1). These two putative proteins are characterized by the presence of the identically conserved regions of 54 amino acid residues of bHLH signature domain, and shared 99.1% amino acid identity, whereas several stress-related cis-regulatory elements located in both promoter regions differed in types and positions. Expressions of two bHLHs in grapevine leaves were induced by cold stress, but evidently differ between two grapevine genotypes upon cold exposure. Two grapevine bHLH proteins were exclusively localized to the nucleus and exhibited strong transcriptional activation activities in yeast cells. Overexpression of either VabHLH1 or VvbHLH1 transcription factor did not affect the growth and development of transgenic Arabidopsis plants, but enhanced tolerance to cold stress. The improved tolerance in VabHLH1- or VvbHLH1-overexpressing Arabidopsis plants is associated with multiple physiological and biochemical changes that occurred during the time-course cold stress. These most common changes include the evaluated levels of proline, decreased amounts of malondialdehyde and reduced membrane injury as reflected by electrolyte leakage. VabHLH1 and VvbHLH1 displayed overlapping, but not identical, roles in activating the corresponding CBF cold signaling pathway, especially in regulating the expression of CBF3 and RD29A. Our findings demonstrated that two grapevine bHLHs act as positive regulators of the cold stress response, modulating the level of COR gene expression, which in turn confer tolerance to cold stress.

Comparative analysis of the cold acclimation and freezing tolerance capacities of seven diploid Brachypodium distachyon accessions

Background and AimsCold is a major constraint for cereal cultivation under temperate climates. Winter-hardy plants interpret seasonal changes and can acquire the ability to resist sub-zero temperatures. This cold acclimation process is associated with physiological, biochemical and molecular alterations in cereals. Brachypodium distachyon is considered a powerful model system to study the response of temperate cereals to adverse environmental conditions. To date, little is known about the cold acclimation and freezing tolerance capacities of Brachypodium. The main objective of this study was to evaluate the cold hardiness of seven diploid Brachypodium accessions.MethodsAn integrated approach, involving monitoring of phenological indicators along with expression profiling of the major vernalization regulator VRN1 orthologue, was followed. In parallel, soluble sugars and proline contents were determined along with expression profiles of two COR genes in plants exposed to low temperatures. Finally, whole-plant freezing tests were performed to evaluate the freezing tolerance capacity of Brachypodium.Key ResultsCold treatment accelerated the transition from the vegetative to the reproductive phase in all diploid Brachypodium accessions tested. In addition, low temperature exposure triggered the gradual accumulation of BradiVRN1 transcripts in all accessions tested. These accessions exhibited a clear cold acclimation response by progressively accumulating proline, sugars and COR gene transcripts. However, whole-plant freezing tests revealed that these seven diploid accessions only have a limited capacity to develop freezing tolerance when compared with winter varieties of temperate cereals such as wheat and barley. Furthermore, little difference in terms of survival was observed among the accessions tested despite their previous classification as either spring or winter genotypes.ConclusionsThis study is the first to characterize the freezing tolerance capacities of B. distachyon and provides strong evidence that some diploid accessions such as Bd21 have a facultative growth habit.