Expression Of Cold-responsive Genes Research Articles

Chinese wild-growing Vitis amurensis ICE1 and ICE2 encode MYC-type bHLH transcription activators that regulate cold tolerance in Arabidopsis.

Winter hardiness is an important trait for grapevine breeders and producers, so identification of the regulatory mechanisms involved in cold acclimation is of great potential value. The work presented here involves the identification of two grapevine ICE gene homologs, VaICE1 and VaICE2, from an extremely cold-tolerant accession of Chinese wild-growing Vitis amurnensis, which are phylogenetically related to other plant ICE1 genes. These two structurally different ICE proteins contain previously reported ICE-specific amino acid motifs, the bHLH-ZIP domain and the S-rich motif. Expression analysis revealed that VaICE1 is constitutively expressed but affected by cold stress, unlike VaICE2 that shows not such changed expression as a consequence of cold treatment. Both genes serve as transcription factors, potentiating the transactivation activities in yeasts and the corresponding proteins localized to the nucleus following transient expression in onion epidermal cells. Overexpression of either VaICE1 or VaICE2 in Arabidopsis increase freezing tolerance in nonacclimated plants. Moreover, we show that they result in multiple biochemical changes that were associated with cold acclimation: VaICE1/2-overexpressing plants had evaluated levels of proline, reduced contents of malondialdehyde (MDA) and decreased levels of electrolyte leakage. The expression of downstream cold responsive genes of CBF1, COR15A, and COR47 were significantly induced in Arabidopsis transgenically overexpressing VaICE1 or VaICE2 upon cold stress. VaICE2, but not VaICE1 overexpression induced KIN1 expression under cold-acclimation conditions. Our results suggest that VaICE1 and VaICE2 act as key regulators at an early step in the transcriptional cascade controlling freezing tolerance, and modulate the expression levels of various low-temperature associated genes involved in the C-repeat binding factor (CBF) pathway.

New clues for a cold case: nitric oxide response to low temperature

Low temperature is among the most frequent stresses met by plants during their lifespan, and a plant's ability to cold-acclimate is a determinant for further growth and development. Although intensive research has provided a good picture of the molecular and metabolic changes triggered by cold, the underlying regulatory mechanisms remain elusive and are thus being actively sought. Recent studies have shed light on the importance of nitric oxide (NO), a ubiquitous signalling molecule in eukaryotes, for plant tolerance to chilling and freezing. Indeed, NO formation following cold exposure has been reported in a range of plant species, and a series of proteins targeted by NO-based post-translational modifications have been identified. Moreover, key cold-regulated genes have been characterized as NO-dependent, suggesting the crucial importance of NO signalling for cold-responsive gene expression. This review provides a picture of our current understanding of the function of NO in the context of plant response to cold. Particular attention is dedicated to the open questions left by the fragmented data currently available concerning NO formation, transduction and biological significance for plant adaptation to low temperature.

The Arabidopsis Mediator Complex Subunits MED16, MED14, and MED2 Regulate Mediator and RNA Polymerase II Recruitment to CBF-Responsive Cold-Regulated Genes

The Mediator16 (MED16; formerly termed SENSITIVE TO FREEZING6 [SFR6]) subunit of the plant Mediator transcriptional coactivator complex regulates cold-responsive gene expression in Arabidopsis thaliana, acting downstream of the C-repeat binding factor (CBF) transcription factors to recruit the core Mediator complex to cold-regulated genes. Here, we use loss-of-function mutants to show that RNA polymerase II recruitment to CBF-responsive cold-regulated genes requires MED16, MED2, and MED14 subunits. Transcription of genes known to be regulated via CBFs binding to the C-repeat motif/drought-responsive element promoter motif requires all three Mediator subunits, as does cold acclimation-induced freezing tolerance. In addition, these three subunits are required for low temperature-induced expression of some other, but not all, cold-responsive genes, including genes that are not known targets of CBFs. Genes inducible by darkness also required MED16 but required a different combination of Mediator subunits for their expression than the genes induced by cold. Together, our data illustrate that plants control transcription of specific genes through the action of subsets of Mediator subunits; the specific combination defined by the nature of the stimulus but also by the identity of the gene induced.

A major quantitative trait locus for cold-responsive gene expression is linked to frost-resistance gene <i>Fr-A2</i> in common wheat

Low temperature induces expression of Cor (cold-responsive)/Lea (late embryogenesis-abundant) gene family members through C-repeat binding factor (CBF) transcription factors in common wheat. However, the relationship between the genetic loci controlling cold-responsive gene expression and freezing tolerance is unclear. In expression quantitative trait locus (eQTL) analysis, accumulated transcripts of Cor/Lea and CBF genes were quantified in recombinant inbred lines derived from a cross between two common wheat cultivars with different levels of freezing tolerance. Four eQTLs controlling five cold-responsive genes were found, and the major eQTL with the greatest effect was located on the long arm of chromosome 5A. At least the 1D and 5A eQTLs played important roles in development of freezing tolerance in common wheat. The chromosomal location of the 5A eQTL, controlling four cold-responsive genes, coincided with a region homoeologous to a frost-tolerance locus (Fr-Am2) reported as a CBF cluster region in einkorn wheat. The 5A eQTL plays a significant role through Cor/Lea gene expression in cold acclimation of wheat. In addition, our results suggest that one or more CBF copies at the Fr-2 region positively regulate other copies, which might amplify the positive effects of the CBF cluster on downstream Cor/Lea gene activation.

Low‐temperature perception leading to gene expression and cold tolerance in higher plants

Plant species exhibit a range of tolerances to low temperatures, and these constitute a major determinant of their geographical distribution and use as crops. When tolerance is insufficient, either chilling or freezing injuries result. A variety of mechanisms are employed to evade the ravages of extreme or sub-optimal temperatures. Many of these involve cold-responsive gene expression and require that the drop in temperature is first sensed by the plant. Despite intensive research over the last 100 yr or longer, we still cannot easily answer the question of how plants sense low temperature. Over recent years, genomic and post-genomic approaches have produced a wealth of information relating to the sequence of events leading from cold perception to appropriate and useful responses. However, there are also crucial and significant gaps in the pathways constructed from these data. We describe the literature pertaining to the current understanding of cold perception, signalling and regulation of low-temperature-responsive gene expression in higher plants, raising some of the key questions that still intrigue plant biologists today and that could be targets for future work. Our review focuses on the control of gene expression in the pathways leading from cold perception to chilling and freezing tolerance.

Induction of jasmonate signalling regulators MaMYC2s and their physical interactions with MaICE1 in methyl jasmonate‐induced chilling tolerance in banana fruit

MYC2, a basic helix-loop-helix (bHLH) transcription factor, is a key regulator in the activation of jasmonate (JA) response. However, the molecular details of MYC2 involving in methyl jasmonate (MeJA)-induced chilling tolerance of fruit remain largely unclear. In the present work, two MYC2 genes, MaMYC2a and MaMYC2b, and one homolog of the inducer of the C-repeat-binding factor (CBF) gene, MaICE1 were isolated and characterized from banana fruit. MaMYC2s and MaICE1 were found to be all localized in the nucleus. In addition, the proline-rich domain (PRD) and the acidic domain (AD) in the N-terminus were important for the transcriptional activation of MaMYC2 in yeast cells. Unlike MaICE1's constitutive expression, MaMYC2a and MaMYC2b were induced rapidly following MeJA treatment during cold storage. Moreover, protein-protein interaction analysis confirmed that MaMYC2s interacted with MaICE1. The expression of ICE-CBF cold-responsive pathway genes including MaCBF1, MaCBF2, MaCOR1, MaKIN2, MaRD2 and MaRD5 was also significantly induced by MeJA. Taken together, our work provides strong evidence that MaMYC2 is involved in MeJA-induced chilling tolerance in banana fruit through physically interacting and likely functionally coordinating with MaICE1, revealing a novel mechanism for ICE1 in response to cold stress as well as during development of induced chilling tolerance.

FVE, an Arabidopsis homologue of the retinoblastoma-associated protein that regulates flowering time and cold response, binds to chromatin as a large multiprotein complex.

Some genetic studies indicate that plant homologues of proteins involved in chromatin modification and remodeling in other organisms may regulate plant development. Previously, we described an Arabidopsis mutant with altered cold-responsive gene expression (acg1) displaying a late flowering phenotype, a null allele of fve. FVE is a homologue of the mammalian retinoblastoma-associated protein (RbAp), one component of a histone deacetylase (HDAC) complex involved in transcriptional repression, and has been shown to be involved in the deacetylation of the FLOWERING LOCUS C (FLC) chromatin encoding for a repressor of flowering. In an effort to gain insight into the biochemical functions of FVE, we overexpressed FVE tagged with the hemagglutinin (HA) and FLAG epitope at the N-terminus in acg1 mutants. The results of physiological and molecular analyses demonstrated that FVE overexpression in acg1 rescued the mutant phenotypes, including late flowering and alterations in floral pathway gene expression such as FLC, SUPPRESSOR OF OVEREXPRESSION OF CO1 (SOC1), and FLOWERING LOCUS T (FT), and also super-induced cold-responsive reporter gene expression. The chromatin immunoprecipitation experiments revealed the amplification of specific DNA regions of FLC and COLD-REGULATED 15A (COR15A), indicating that FVE may bind to the FLC and COR15A chromatin. Gel-filtration chromatography and the immunoprecipitation of putative FVE complexes showed that FVE forms a protein complex of approximately 1.0 MDa. These results demonstrate that FVE may exist as a multiprotein complex, similar to the mammalian HDAC complex harboring RbAp, to regulate flowering time and cold response by associating with the FLC and COR chromatin.

Genome-wide gene expression analysis supports a developmental model of low temperature tolerance gene regulation in wheat (Triticum aestivum L.)

BackgroundTo identify the genes involved in the development of low temperature (LT) tolerance in hexaploid wheat, we examined the global changes in expression in response to cold of the 55,052 potentially unique genes represented in the Affymetrix Wheat Genome microarray. We compared the expression of genes in winter-habit (winter Norstar and winter Manitou) and spring-habit (spring Manitou and spring Norstar)) cultivars, wherein the locus for the vernalization gene Vrn-A1 was swapped between the parental winter Norstar and spring Manitou in the derived near-isogenic lines winter Manitou and spring Norstar. Global expression of genes in the crowns of 3-leaf stage plants cold-acclimated at 6°C for 0, 2, 14, 21, 38, 42, 56 and 70 days was examined.ResultsAnalysis of variance of gene expression separated the samples by genetic background and by the developmental stage before or after vernalization saturation was reached. Using gene-specific ANOVA we identified 12,901 genes (at p < 0.001) that change in expression with respect to both genotype and the duration of cold-treatment. We examined in more detail a subset of these genes (2,771) where expression was highly influenced by the interaction between these two main factors. Functional assignments using GO annotations showed that genes involved in transport, oxidation-reduction, and stress response were highly represented. Clustering based on the pattern of transcript accumulation identified genes that were up or down-regulated by cold-treatment. Our data indicate that the cold-sensitive lines can up-regulate known cold-responsive genes comparable to that of cold-hardy lines. The levels of expression of these genes were highly influenced by the initial rate and the duration of the gene's response to cold. We show that the Vrn-A1 locus controls the duration of gene expression but not its initial rate of response to cold treatment. Furthermore, we provide evidence that Ta.Vrn-A1 and Ta.Vrt1 originally hypothesized to encode for the same gene showed different patterns of expression and therefore are distinct.ConclusionThis study provides novel insight into the underlying mechanisms that regulate the expression of cold-responsive genes in wheat. The results support the developmental model of LT tolerance gene regulation and demonstrate the complex genotype by environment interactions that determine LT adaptation in winter annual cereals.

The myb transcription factor MdMYB6 suppresses anthocyanin biosynthesis in transgenic Arabidopsis

The R2R3-Myb proteins comprise a large family of plant transcription factors that regulate the expression of multiple drought-responsive and cold-responsive genes by binding special cis-elements at the promoter. There have been previous studies in transgenic plant over-expression of the myb protein. In this article, we analyzed the function of MdMYB6, an R2R3-type Myb transcription factor from apples (Malus × domestica), in transgenic Arabidopsis plants. In contrast to wild type plants, these transgenic lines accumulated less anthocyanin. Equimolar concentrations of sorbitol did not alter the anthocyanin accumulation. Real-time polymerase chain reaction (PCR) indicated that MdMYB6 over-expression suppressed enzymes involved in anthocyanin biosynthesis and some Arabidopsis basic helix-loop-helix (bHLH) genes. The MdMYB6 transcription faction may be an important repressor of anthocyanin biosynthesis in plants.

Characterisation and natural variation of a dehydrin gene in Quercus petraea (Matt.) Liebl.

For the first time in sessile oak [Quercus petraea (Matt.) Liebl.], the isolation and characterisation of a full-length dehydrin gene and its promoter region, as well as its allelic variation in natural populations, is reported. Dehydrins (Dhn) are stress-related genes important for the survival of perennial plants in a seasonal climate. A full-length dehydrin gene (Dhn3) was characterised at the nucleotide level and the protein structure was modelled. Additionally, the allelic variation was analysed in five natural populations of Quercus petraea (Matt.) Liebl. sampled along an altitudinal gradient in the French Pyrenees. The analysed sequences contain typical domains of the K(n) class of dehydrins in the coding region. Also, the 5'untranslated region (promoter) of the gene was amplified, which shows typical motifs essential for drought- and cold-responsive gene expression. Single nucleotide substitutions and indels (insertions/deletions) within the coding region determine large biochemical differences at the protein level. However, only low levels of genetic differentiation between populations from different altitudes were detectable.

A matter of fat

We recently evidenced that plant response to cold stress includes a rapid formation of nitric oxide (NO) that participates in the control of cold-responsive gene expression. Unexpectedly we also shed light on a novel downstream element of NO signalling that is phosphosphingolipid (PS) metabolism. Indeed, two phosphosphingolipid species, phytosphingosine phosphate (PHS-P) and a ceramide phosphate (Cer-P) are specifically synthesized upon cold exposure. Manipulating NO levels by pharmacological or genetic means dramatically modified the cold-triggered synthesis of PHS-P and Cer-P, but did not affect the cold-responsive formation of phosphatidic acid (PtdOH), a ubiquitous lipid signal derived from phospholipid degradation. So far no crosstalk between NO and PS signalling had been reported in plants. How NO might modulate PS formation and whether this regulation might be extended to other physiological processes are further discussed.

NO way to treat a cold

Gupta, K. J., Hinch, D. K., Mur, L. A. (2011). NO way to treat a cold. New Phytologist, 189, (2), 360-363. IMPF: 06.64

Impact of grafting on cold responsive gene expression in Satsuma mandarin (Citrus unshiu)

The major limitation preventing the expansion of Satsuma mandarin (Citrus unshiu) production in the Gulf Coast regions of the US is the risk of freeze damage. Poncirus trifoliata (L.) Raf has been widely used as a cold hardy rootstock for citrus production in freeze-prone environments. In this study, relative quantitative real-time RT–PCR was used to study cold responsive genes in Satsuma mandarin (C. unshiu), C. unshiu grafted on P. trifoliata rootstock and P. trifoliata following exposure to cold shock or cold acclimation treatments. Major changes in gene expression occurred in the different species during cold stress especially with respect to nitrate transporter, auxin responsive GH3, UDP-glycosyltransferase (UGT) and chalcone-flavanone isomerase. Very high levels of nitrate transporter were reached early in Poncirus following 60 h of cold shock treatment at 4°C, and in C. unshiu after 3 weeks of gradual cold acclimation. Also, high levels of auxin responsive GH3 were reached in Poncirus following both cold shock and cold acclimation, while levels in C. unshiu were low or reduced. Poncirus rootstock significantly affected gene expression in C. unshiu scion, resulting in a reduction of nitrate transporter, UGT and trehalose 6-phosphate synthase expression levels, and an increase in auxin responsive GH3 gene during cold acclimation. The impact of rootstock on citrus scion during cold stress might be associated with partitioning of nutrients and hormones.

A nuclear-localized protein, KOLD SENSITIV-1, affects the expression of cold-responsive genes during prolonged chilling in Arabidopsis

Plants respond to cold by transcriptional and metabolic responses which underlie tolerance and acclimation mechanisms, but details at the molecular level are incomplete. Here we describe KOLD SENSITIV-1 ( KOS1), a new gene required for responses to cold. KOS1 protein is predicted to have coiled-coil, Structural Maintenance of Chromosomes and nuclear-targeting domains. GFP-labeled KOS1 localizes to the nucleus. Null mutants could not be isolated but two independent knockdown T-DNA mutants were obtained. Growth and development of kos1 knockdown mutant plants was comparable to wild type when grown at 21 °C. However, when grown at 4 °C these mutants exhibited accelerated leaf yellowing and smaller rosette size than wild type. Quantitative RT-PCR revealed that in the cold kos1 mutants had reduced expression of cold-responsive transcripts COR15A, COR15B, BAM3 and AMY3. Metabolite profiling revealed that ascorbate levels were lower in the mutants in the cold relative to wild type. KOS1 therefore represents a new gene that influences the regulation of transcript and metabolite levels in response to prolonged chilling temperatures.

Overexpression of a homopeptide repeat-containing bHLH protein gene (OrbHLH001) from Dongxiang Wild Rice confers freezing and salt tolerance in transgenic Arabidopsis

Dongxiang Wild Rice (Oryza rufipogon) is the northernmost wild rice in the world known to date and has extremely high cold tolerance and many other adversity-resistant properties. To identify the genes responsible for the high stress tolerance, we isolated and characterized a basic helix-loop-helix (bHLH) protein gene OrbHLH001 from Dongxiang Wild Rice. The gene encodes an ICE1-like protein containing multiple homopeptide repeats. Expression of OrbHLH001 is induced by salt stress and is predominant in the shoots of wild rice seedlings. Overexpression of OrbHLH001 enhanced the tolerance to freezing and salt stresses in transgenic Arabidopsis. Examination of the expression of cold-responsive genes in transgenic Arabidopsis showed that the function of OrbHLH001 differs from that of ICE1 and is independent of a CBF/DREB1 cold-response pathway.

Overexpression of SlCZFP1, a Novel TFIIIA-type Zinc Finger Protein from Tomato, Confers Enhanced Cold Tolerance in Transgenic Arabidopsis and Rice

The C2H2-type (also called TFIIIA-type) zinc finger protein family is a major family of eukaryotic transcription factors. C2H2-type zinc finger proteins in plants play important roles in regulating various developmental processes or responses to abiotic stresses. We isolated a complementary deoxyribonucleic acid (cDNA) clone, designated Solanumlycopersicumcold zinc finger protein 1 (SlCZFP1), from tomato by analyzing the previous microarray data of the low-temperature transcriptome of tomato. SlCZFP1 encodes a novel TFIIIA-type zinc finger protein, which contains two typical zinc finger motifs, CX2–4 CX3FX3QALGGHX3–5H, and a potential nuclear localization signal (NLS). The SlCZFP1–GFP fusion protein was localized to the nucleus in a transient expression assay. Expression of SlCZFP1 was strongly induced by cold stress, dehydration, and salt treatment, but not by abscisic acid (ABA). Overexpression of SlCZFP1 in transgenic Arabidopsis and rice induced constitutive expression of cold-regulated (COR) or cold-responsive genes and conferred enhanced tolerance to freezing or cold treatments for non-acclimate transgenic plants, compared with wild-type plants. However, there was no obvious enhancement observed in drought and salt tolerance. Our data suggest that SlCZFP1 plays an important role in plant responses to cold stress by regulating cold-responsive gene expression and that SlCZEP1 might be a useful gene for improving cold tolerance in crop plants.

Proteolytic processing of anArabidopsismembrane-bound NAC transcription factor is triggered by cold-induced changes in membrane fluidity

Changes in membrane fluidity are the earliest cellular events that occur in plant cells upon exposure to cold. This subsequently triggers physiological processes, such as calcium influx and reorganization of actin cytoskeletons, and induces expression of cold-responsive genes. The plasma-membrane-anchored NAC (NAM/ATAF/CUC) transcription factor NTL6 is of particular interest. Cold triggers proteolytic activation of the dormant NTL6 protein, which in turn elicits pathogen-resistance responses by inducing a small group of cold-inducible PR (pathogenesis-related) genes in Arabidopsis. In the present study, we show that proteolytic processing of NTL6 is regulated by cold-induced remodelling of membrane fluidity. NTL6 processing was stimulated rapidly by cold. The protein stability of NTL6 was also enhanced by cold. The effects of cold on NTL6 processing and protein stability were significantly reduced in cold-acclimatized plants, supporting the regulation of NTL6 processing by membrane fluidity. Consistent with this, although NTL6 processing was stimulated by pharmacological agents that reduce membrane fluidity and thus mimic cold, it was inhibited when plants were treated with a 18:3 unsaturated fatty acid, linolenic acid. In addition, the pattern of NTL6 processing was changed in Arabidopsis mutants with altered membrane lipid compositions. Assays employing chemicals that inhibit activities of the proteasome and proteases showed that NTL6 processing occurs via the regulated intramembrane proteolysis mechanism. Interestingly, a metalloprotease inhibitor blocked the NTL6 processing. These observations indicate that a metalloprotease activity is responsible for NTL6 processing in response to cold-induced changes in membrane fluidity.

Cucumber ( Cucumis sativus L.) over-expressing cold-induced transcriptome regulator ICE1 exhibits changed morphological characters and enhances chilling tolerance

Cold is an environmental factor that limits the growing season of cucumber and adversely affects fruit quality and productivity. ICE1 is a positive regulator of CBF3 and has a critical role in cold stress ( Chinnusamy et al., 2003). To test the function and potential use of cold-induced transcriptome regulator ICE1 (inducer of CBF expression) in improving the chill tolerance of cucumbers, the Arabidopsis ICE1 gene driven by super promoter was introduced into cucumbers by Agrobacterium-mediated transformation. Transgenic plants were obtained, and were confirmed by PCR and southern blot, then the expression of ICE1 was tested by RT-PCR. Transgenic plants exhibited dwarf phenotypes, and shorter internodes, with higher nodes in the first female flowers and a lower female flower rate of every node than wild type plants. Under cold stress, the chilling index of four transgenic lines (IF3, IF6, IF7, and IF10) was decreased significantly, indicating their improved chilling tolerance. Over-expression of ICE1 in cucumbers could induce the expression of cold-responsive genes, further activating the accumulation of soluble sugars and free proline, and inhibiting malondialdehyde (MDA) accumulation. This leads to electrolyte leakage and regulation of osmotic potential to osmotic stress under cold stress.

Cold resistance in plants: A mystery unresolved

Herbaceous temperate plants are capable of developing freezing tolerance when they are exposed to low nonfreezing temperatures. Acquired freezing tolerance involves extensive reprogramming of gene expression and metabolism. Recent full-genome transcript profiling studies, in combination with mutational and transgenic plant analyses, have provided a snapshot of the complex transcriptional network that operates under cold stress. The changes in expression of hundreds of genes in response to cold temperatures are followed by increases in the levels of hundreds of metabolites, some of which are known to have protective effects against the damaging effects of cold stress. Genetic analysis has revealed important roles for cellular metabolic signals, and for RNA splicing, export and secondary structure unwinding, in regulating cold-responsive gene expression and chilling and freezing tolerance. These results along with many of the others summarized here further our understanding of the basic mechanisms that plants have evolved to survive freezing temperatures. In addition, the findings have potential practical applications, as freezing temperatures are a major factor limiting the geographical locations suitable for growing crop and horticultural plants and periodically account for significant losses in plant productivity. Although, great progress has been made in the field but lacunae still remain since it appears that the cold resistance is more complex than perceived and involves more than one pathway.

Effects of molybdenum on expression of cold-responsive genes in abscisic acid (ABA)-dependent and ABA-independent pathways in winter wheat under low-temperature stress

Molybdenum (Mo) is an essential trace element for higher plants. It has been shown that application of Mo enhances the cold resistance of winter wheat. In order to improve our understanding of the molecular mechanisms of cold resistance arising from application of Mo in winter wheat, investigations were made regarding the transcription of cold-responsive (COR) genes in abscisic acid (ABA)-dependent and ABA-independent pathways in winter wheat regulated by Mo application under low-temperature stress. Two cultivars of winter wheat (Triticum aestivum), Mo-efficient cultivar '97003' and Mo-inefficient cultivar '97014', were grown in control (-Mo) and Mo fertilizer (+Mo) treatments for 40 d at 15/12 degrees C (day/night), and the temperature was then reduced to 5/2 degrees C (day/night) to create low-temperature stress. Aldehyde oxidase (AO) activities, ABA contents, the transcripts of basic leucine zipper (bZIP)-type transcription factor (TF) genes, ABA-dependent COR genes, CBF/DREB transcription factor genes and ABA-independent COR genes were investigated at 0, 3, 6 and 48 h post cold stress. Mo application significantly increased AO activity, ABA levels, and expression of bZIP-type TF genes (Wlip19 and Wabi5) and ABA-dependent COR genes (Wrab15, Wrab17, Wrab18 and Wrab19). Mo application increased expression levels of CBF/DREB transcription factor genes (TaCBF and Wcbf2-1) and ABA-independent COR genes (Wcs120, Wcs19, Wcor14 and Wcor15) after 3 and 6 h exposure to low temperature. Mo might regulate the expression of ABA-dependent COR genes through the pathway: Mo --> AO --> ABA --> bZIP --> ABA-dependent COR genes in winter wheat. The response of the ABA-dependent pathway to Mo was prior to that of the ABA-independent pathway. Similarities and differences between the Mo-efficient and Mo-inefficient wheat cultivars in response to Mo under cold stress are discussed.