Cold response in Phalaenopsis aphrodite and characterization of PaCBF1 and PaICE1

Isolation and functional characterization of cold-induced gene (AmCIP) promoter from Ammopiptanthus mongolicus

AmCIP is a dehydrin-like protein which involved in abiotic stress tolerance in xerophytes evergreen woody plant A. mongolicus. AmCIP could be induced in the cotyledon and radicle during cold acclimation. To further elucidate the regulation of the upstream region of the gene, we isolated and characterized the promoter of AmCIP. Herein, a 1115 bp 5'-flanking region of AmCIP genomic DNA was isolated and cloned by genome walking from A. mongolicus and the segment sequence was identified as "PrAmCIP" promoter. Analysis of the promoter sequence revealed the presences of some basic cis-acting elements, which were related to various environmental stresses and plant hormones. GUS histochemical staining of transgene tobacco showed that PrAmCIP was induced by 4℃, 55℃, NaCl, mannitol and ABA, whereas it could hardly drive GUS gene expression under normal conditions. Furthermore, we constructed three deletion fragments and genetically transformed them into Arabidopsis thaliana. GUS histochemical staining showed that the MYCATERD1 element of the CP7 fragment (-189 ∼ -1) may be a key element in response to drought. In conclusion, we provide an inducible promoter, PrAmCIP, which can be applied to the development of transgenic plants for abiotic stresse tolerance.

Genome-wide identification and expression analysis of the CBF transcription factor family in Lolium perenne under abiotic stress

C-repeat binding factor (CBF) subfamily genes encoding transcriptional activators are members of the AP2/ERF superfamily. CBFs play important roles in plant tolerance to abiotic stress. In this study, we identified and analyzed the structure, phylogeny, conserved motifs, and expression profiles of 12 CBFs of the grass species Lolium perenne cultured under abiotic stress. The identified LpCBFs were grouped into three phylogenetic clades according to their protein structures and motif organizations. LpCBF expression was differentially induced by cold, heat, water deficit, salinity, and abscisic acid, among which cold treatment induced LpCBF gene expression significantly. Furthermore, association network analysis indicated that different proteins, including certain stress-related proteins, potentially interact with LpCBFs. Altogether, these findings will enhance our understanding of LpCBFs protein structure and function in the regulation of L. perenne stress responses. Our results will provide valuable information for further functional research of LpCBF proteins in L. perenne stress resistance.

Genome-wide identification and functional analysis of ICE genes reveal that Gossypium thurberi "GthICE2" is responsible for cold and drought stress tolerance

Cold stress has been found to have a negative impact on cotton growth and annual production. To address this issue, the utilization of cold-tolerant gene resources from wild species of Gossypium is crucial for genetic improvements in cultivated cotton. ICE (inducer of CBF expression) are the key regulators of cold tolerance in plants, however, there is relatively little information on ICE genes in cotton. Herein, we performed comprehensive bioinformatics analyses of the ICE gene family in eight cotton species. Phylogenetic analysis showed that 52 ICE genes were clustered into four subgroups. Cis-regulatory elements analysis suggests that the expression of ICE genes might be regulated by light, plant hormones, and various environment stresses. Higher expression of GthICE2 was observed in leaves as compared to roots and stems, in response to cold, drought, and exogenous hormone ABA. Furthermore, overexpression of GthICE2 in A. thaliana led to higher germination and survival rates, longer root length, lower ion leakage, and induction under cold and drought stress. Histochemical staining showed that oxidative damage in transgenic lines was much lower compared to wild-type plants. Lower MDA contents and higher SOD and POD activities were observed in overexpressed plants. Y1H and LUC assays revealed that GthICE2 might activate the expression of GthCBF4, a cold-responsive gene, by connecting with the MYC cis-element present in the promoter of GthCBF4. GthICE2 confers cold and drought stress tolerance in cotton. Our findings add significantly to the existing knowledge regarding cold stress tolerance and helps to elucidate cold response mechanisms in cotton.

MbICE1 Confers Drought and Cold Tolerance through Up-Regulating Antioxidant Capacity and Stress-Resistant Genes in Arabidopsis thaliana

Malus baccata (L.) Borkh is an apple rootstock with good drought and cold resistance. The ICE gene is a key factor in the molecular mechanisms of plant drought and cold resistance. In the present research, the function of drought- and cold-induced MbICE1 of Malus baccata was investigated in Arabidopsis. According to GFP fluorescence images, MbICE1 was determined to be a nuclear protein. The MbICE1 was transferred to Arabidopsis, showing enhanced tolerance to drought and cold stresses. Under drought and cold treatments, the transgenic Arabidopsis had higher chlorophyll content and free proline content than WT plants, but the Malondialdehyde (MDA) content and electrolyte leakage (EL) were lower than those of WT plants. In addition, drought and cold led to a large accumulation of ROS (H₂O₂ and O^2-) content in Arabidopsis, while overexpression of MbICE1 enhanced the antioxidant enzyme activity in Arabidopsis and improved the plant's resistance to stresses. Moreover, the accumulation of MbICE1 promoted the expression of AtCBF1, AtCBF2, AtCBF3, AtCOR15a, AtCOR47 and AtKIN1 genes in Arabidopsis. These data indicate that MbICE1 is a key regulator of drought and cold and can be used as a backup gene for breeding Malus rootstocks.

Quantitative Proteomics Reveals SOS2-Related Proteins in Arabidopsis Under Salt Stress

Background:

Soil salinity is a major issue that seriously affects plant growth and cultivated land utilization. Salt tolerance is one of the most fundamental biological processes that ensures plant’s survival. SOS2 is one of the most important components of the Salt Overly Sensitive (SOS) signaling pathway, which maintains plant ion homeostasis under salt stress. The SOS2-related signaling pathways remain incompletely exploited especially at the proteomics level.

Objective:

In this paper, proteins potentially interacting with and regulated by SOS2 in Arabidopsis were identified.

Methods:

The proteomes of Arabidopsis Wild Type (WT) and SOS2-deficient mutant (sos2-2) exposed to 100 mM NaCl for 6 h were compared, proteins were identified using data-independent acquisition- based quantitative proteomics strategy.

Results:

A total of 7470 proteins were identified and quantified, 372 Differentially Expressed Proteins (DEP) were detected between WT and sos2-2 mutant under normal condition and 179 DEPs were identified under salt treatment. Functional analysis showed that the DEPs were mainly involved in protein binding and catalytic activity. Among the DEPs under salt stress, the protein expressions of AVP1, Photosystem II reaction center protein A, B, C, and stress-responsive protein (KIN2) were significantly up-regulated. LHCA1, LHCA2, LHCA4, ATPD and ATPE were significantly down-regulated. These proteins were involved in biological processes including: stress response, photosynthesis, transport and heat shock.

Conclusion:

These results revealed complexity of the functions of SOS2 in maintaining intracellular homeostasis, in addition to its function in sodium homeostasis. Plant salt resistance is not independent but closely related to metabolic processes including photosystem, ATP synthase, transport and other stress resistances.

Plant Dehydrins: Expression, Regulatory Networks, and Protective Roles in Plants Challenged by Abiotic Stress

Dehydrins, also known as Group II late embryogenesis abundant (LEA) proteins, are classic intrinsically disordered proteins, which have high hydrophilicity. A wide range of hostile environmental conditions including low temperature, drought, and high salinity stimulate dehydrin expression. Numerous studies have furnished evidence for the protective role played by dehydrins in plants exposed to abiotic stress. Furthermore, dehydrins play important roles in seed maturation and plant stress tolerance. Hence, dehydrins might also protect plasma membranes and proteins and stabilize DNA conformations. In the present review, we discuss the regulatory networks of dehydrin gene expression including the abscisic acid (ABA), mitogen-activated protein (MAP) kinase cascade, and Ca²⁺ signaling pathways. Crosstalk among these molecules and pathways may form a complex, diverse regulatory network, which may be implicated in regulating the same dehydrin.

Overexpression of Arabidopsis ICE1 enhances yield and multiple abiotic stress tolerance in indica rice

ICE1 (Inducer of CBF Expression 1), a MYC-type bHLH transcription factor, is a regulator of cold tolerance in Arabidopsis. Indica rice, which occupies the major rice cultivated area, is highly sensitive to cold stress. Hence in this study, Arabidopsis ICE1 (AtICE1) was overexpressed in indica rice to analyze its role in reproductive stage cold and other abiotic stress tolerance to indica rice. AtICE1 was overexpressed by using stress inducible AtRD29A promoter in mega rice cv. MTU1010. Under cold stress conditions, AtICE1 overexpression lines showed lower accumulation of MDA and H2O2, higher membrane stability, and thus higher seedling survival rate than the WT plants. Expression levels of OsDREB1A, OsMYB3R2, and OsTPP1 were significantly higher in transgenics as compared with WT under cold stress conditions. AtICE1 transgenic rice plants produced 44-60% higher grain yield as compared with WT plants under control conditions in three independent experiments. Of the three AtICE1 overexpression lines, two lines produced significantly higher grain yield as compared with WT plants after recovery from cold, salt and drought stresses. AtICE1 overexpression lines showed significantly higher stomatal density and conductance under non-stress conditions. qRT-PCR analysis showed that expression levels of stomatal pathway genes viz., OsSPCH1, OsSPCH2, OsSCR1, OsSCRM1, OsSCRM2 and OsMUTE were significantly higher in AtICE1 transgenics as compared with WT plants. The components of water use viz., stomatal conductance, photosynthesis, and instantaneous WUE were higher in transgenics as compared with WT plants. The results showed that AtICE1 confers multiple stress tolerance to indica rice, and the role of ICE1 in stress tolerance and stomatal development is conserved across species.

A novel basic helix-loop-helix transcription factor, ZjICE2 from Zoysia japonica confers abiotic stress tolerance to transgenic plants via activating the DREB/CBF regulon and enhancing ROS scavenging

ZjICE2 works as a positive regulator in abiotic stress responses and ZjICE2 is a valuable genetic resource to improve abiotic stress tolerance in the molecular breeding program of Zoysia japonica. The basic helix-loop-helix (bHLH) family transcription factors (TFs) play an important role in response to biotic or abiotic stresses in plants. However, the functions of bHLH TFs in Zoysia japonica, one of the warm-season turfgrasses, remain poorly understood. Here, we identified ZjICE2 from Z. japonica, a novel MYC-type bHLH transcription factor that was closely related to ICE homologs in the phylogenetic tree, and its expression was regulated by various abiotic stresses. Transient expression of ZjICE2-GFP in onion epidermal cells revealed that ZjICE2 was a nuclear-localized protein. Also, ZjICE2 bound the MYC cis-element in the promoter of dehydration responsive element binding 1 of Z. japonica (ZjDREB1) using yeast one-hybrid assay. A phenotypic analysis showed that overexpression of the ZjICE2 in Arabidopsis enhanced tolerance to cold, drought, and salt stresses. The transgenic Arabidopsis and Z. japonica accumulated more transcripts of cold-responsive DREB/CBFs and their downstream genes than the wild type (WT) after cold treatment. Furthermore, the transgenic plants exhibited an enhanced Reactive oxygen species (ROS) scavenging ability, which resulted in an efficient maintenance of oxidant-antioxidant homeostasis. In addition, overexpression of the ZjICE2 in Z. japonica displayed intensive cold tolerance with increases in chlorophyll contents and photosynthetic efficiency. Our study suggests that ZjICE2 works as a positive regulator in abiotic stress responses and the ICE-DREB/CBFs response pathway involved in cold stress tolerance is also conserved in Z. japonica. These results provide a valuable genetic resource for the molecular breeding program especially for warm-season grasses as well as other leaf crop plants.

Rice SnRK protein kinase OsSAPK8 acts as a positive regulator in abiotic stress responses

SnRK2 (sucrose non-fermenting 1-related protein kinases 2) protein kinase family involves in several abiotic stress response in plants. Although the regulatory mechanism of SnRK2 have been well demonstrated in Arabidopsis thaliana, their functions in rice are still largely unknown. Here, we report a SnRK2 family gene, OsSAPK8, can be strongly induced by abiotic stresses, including low-temperature, drought and high salt stress. The ossapk8 mutants showed lower tolerance to low-temperature, high salinity and drought stresses at the vegetative stages. Moreover, the expressions of marker genes for those abiotic stresses, e.g. OsDREB1, OsDREB2, OsNCED and OsRAB21, were downregulated in the ossapk8 mutants. We further confirmed that the yield was reduced in ossapk8 mutant lines compared with the wild type. Our results provide evidence for OsSAPK8 acting as a positive regulator in cold, drought, and salt stress responses.

Zoysia japonica MYC type transcription factor ZjICE1 regulates cold tolerance in transgenic Arabidopsis

ICE1 (Inducer of CBF Expression 1) is a regulator of cold-induced transcriptome, which plays an important role in plant cold response pathway. To enhance the cold tolerance of Zoysia japonica, one of the warm-season turfgrasses, it is helpful to understand the cold response mechanism in Zoysia japonica. We identified stress-responsive ZjICE1 from Zoysia japonica and characterized its function in cold stress. Our results showed that ZjICE1 shared the typical feature of ICE homolog proteins belonging to a nucleic protein. Transactivation activity assay revealed that ZjICE1 bound to the MYC cis-element in the ZjDREB1's promotor. The ZjICE1 overexpressed transgenic Arabidopsis showed enhanced tolerance to cold stress with an increases in SOD, POD, and free proline content and reduction in MDA content. They also induced the transcripts abundance of cold-responsive genes (CBF1, CBF2, CBF3, COR47A, KIN1, and RD29A) after cold treatment. These results suggest that ZjICE1 is a positive regulator in Zoysia japonica plant during cold stress and can be a useful gene for the molecular breeding program to develop the cold tolerant zoysiagrass. Furthermore, the ZjICE1 also conferred resistance to salt and drought stresses, providing the better understanding of the basic helix-loop-helix (bHLH) gene family in abiotic stress responses.

Characterization and expression profiling of the ICE-CBF-COR genes in wheat

Cold stress is one of the major abiotic stresses that limit crop production. The ICE-CBF-COR pathway is associated with cold stress response in a wide variety of crop species. However, the ICE-CBF-COR genes has not been well characterized in wheat (Triticum aestivum). This study identified, characterized and examined the expression profiles of the ICE, CBF and COR genes for cold defense in wheat. Five ICE (inducer of CBF expression) genes, 37 CBF (C-repeat binding factor) genes and 11 COR (cold-responsive or cold-regulated) genes were discovered in the wheat genome database. Phylogenetic trees based on all 53 genes revealed that CBF genes were more diverse than ICE and COR genes. Twenty-two of the 53 genes appeared to include 11 duplicated pairs. Twenty rice (Oryza sativa) genes and 21 sorghum (Sorghum bicolor) and maize (Zea mays) genes showed collinearity with the wheat ICE, CBF and COR genes. Transcriptome data and qRT-PCR analyses revealed tissue-specific expression patterns of the ICE, CBF and COR genes, and identified similarities in the expression pattern of genes from the same family when subjected to drought, heat, drought plus heat, and cold stress. These results provide information for better understanding the biological roles of ICE, CBF, COR genes in wheat.

The AabHLH35 Transcription Factor Identified from Anthurium andraeanum is Involved in Cold and Drought Tolerance

Anthurium andraeanum Lind. is a popular potted and cut-flower plant with an attractive spathe and foliage. It is native to tropical rainforest areas and is able to blossom throughout the year under suitable conditions. However, various abiotic stresses seriously restrict the ornamental value of A. andraeanum and increase the costs of cultivation. A dark green (dg) leaf color mutant of A. andraeanum ‘Sonate’, which accumulates high levels of anthocyanin, has shown increased vigor and tolerance to stresses during cultivation and is, thus, an ideal germplasm for studying stress tolerance in this species. Here, we show that the anthocyanin content in dg mutant plants at different stages of leaf development was higher than in wild-type (WT) plants, and the ability to tolerate under low-temperature (LT, 14 °C) stress was stronger in dg than in WT plants. RNA-Seq of cDNA libraries from young leaves of dg and WT identified AabHLH35 as a differentially expressed gene (DEG) that was significantly up-regulated in dg. Furthermore, heterologous expression of AabHLH35 improved tolerance to cold and drought stresses in Arabidopsis. These results have built an important molecular foundation for further study of stress tolerance in A. andraeanum.

Two ICE isoforms showing differential transcriptional regulation by cold and hormones participate in Brassica juncea cold stress signaling

C-repeat binding factor (CBF) dependent cold stress signaling cascade is well studied in the model plant arabidopsis but is relatively lesser studied in the crop plants. In the present study, two novel isoforms of an upstream regulator of CBF, Inducer of CBF expression (ICE), BjICE46 (1314 bp, accession number HQ446510) and BjICE53 (1494 bp, accession number HQ857208) were isolated from Brassica juncea seedlings. Genomic clones of both the isoforms (accession numbers HQ433510 and JX571043) showed three introns, out of which one intron was spanning the bHLH (basic helix-loop-helix) domain. Interestingly, the constitutive expression of BjICE53 was 21 fold higher than BjICE46. Real time quantitative expression (RT-qPCR) showed BjICE53 to be cold induced but non-responsive to phytohormones. Interestingly, BjICE46 was salinity stress induced and showed upregulation with methyl jasmonate (MeJa) and abscisic acid (ABA). This was supported by the presence of ABA, MeJa and defense related cis- acting regulatory elements in the promoter region of BjICE46. The downstream transcription factor BjCBF (645 bp) was also isolated. The promoter region of BjCBF showed three E-boxes, the binding site for ICE. BjCBF was expressed and purified from E. coli and binding of purified BjCBF with the DRE/CRT elements (present in the promoter of cold responsive genes) was EMSA confirmed. Overall, this study shows that ICE-CBF pathway is conserved in Brassica juncea along with the differential regulation of the ICE isoforms indicating cross-talk between cold and defense signaling.

PpCBFs selectively regulate PpDAMs and contribute to the pear bud endodormancy process

PpCBF2 directly binds to the promoters of PpCBF3 and PpCBF4 to activate their expressions and selectively regulates PpDAMs during the leaf bud endodormancy process of 'Wonhwang' pear (Pyrus pyrifolia). Endodormancy is critical for temperate plant survival under freezing winter conditions, and low temperature is a vital environmental factor in endodormancy regulation. A C-repeat binding factor (CBF) has been found to regulate important DAM transcription factors during endodormancy in pear (Pyrus pyrifolia). In this study, we analyzed the regulation of pear DAM genes by CBFs in further detail. Four CBF and three DAM genes were identified in the pear cultivar 'Wonhwang'. Under natural conditions, PpDAM1 expression decreased from the start of chilling accumulation, while the other two DAM and three CBF genes peaked during endodormancy release. Under chilling treatment, the expressions of PpDAM1, PpDAM2 and PpCBF1 genes were similar to those under natural conditions. Different biochemical methods revealed that PpCBF2/4 can bind to the promoter of PpDAM1 and activate its expression and that PpCBF1/4 can activate PpDAM3. Interestingly, we found that PpCBF2 can activate PpCBF3/4 transcription by directly binding to their promoters. The ICE-CBF regulon is conserved in some plants; three ICE genes were identified in pear, but their expressions did not obviously change under natural and artificial chilling conditions. On the contrary, the selective transcriptional induction of PpCBFs by PpICE1s was observed in a dual-luciferase assay. Considering all these results, we propose that the PpCBF1-PpDAM2 regulon mainly responds to low temperature during endodormancy regulation, with further post-translational regulation by PpICE3. Our results provide basic information on CBF genes functional redundancy and differentiation and demonstrate that the CBF-DAM signaling pathway is involved in the pear bud endodormancy process.

Identification of genes from the ICE-CBF-COR pathway under cold stress in Aegilops-Triticum composite group and the evolution analysis with those from Triticeae

Adverse environmental conditions limit various aspects of plant growth, productivity, and ecological distribution. To get more insights into the signaling pathways under low temperature, we identified 10 C-repeat binding factors (CBFs), 9 inducer of CBF expression (ICEs) and 10 cold-responsive (CORs) genes from Aegilops-Triticum composite group under cold stress. Conserved amino acids analysis revealed that all CBF, ICE, COR contained specific and typical functional domains. Phylogenetic analysis of CBF proteins from Triticeae showed that these CBF homologs were divided into 11 groups. CBFs from Triticum were found in every group, which shows that these CBFs generated prior to the divergence of the subfamilies of Triticeae. The evolutionary relationship among the ICE and COR proteins in Poaceae were divided into four groups with high multispecies specificity, respectively. Moreover, expression analysis revealed that mRNA accumulation was altered by cold treatment and the genes of three types involved in the ICE-CBF-COR signaling pathway were induced by cold stress. Together, the results make CBF, ICE, COR genes family in Triticeae more abundant, and provide a starting point for future studies on transcriptional regulatory network for improvement of chilling tolerance in crop.

Overexpression of Hevea brasiliensis HbICE1 Enhances Cold Tolerance in Arabidopsis

Rubber trees (Hevea brasiliensis) were successfully introduced to south China in the 1950s on a large-scale; however, due to the climate, are prone to cold injury during the winter season. Increased cold tolerance is therefore an important goal, yet the mechanism underlying rubber tree responses to cold stress remains unclear. This study carried out functional characterization of HbICE1 (Inducer of CBF Expression 1) from H. brasiliensis. A nucleic protein with typical features of ICEs, HbICE1 was able to bind to MYC recognition sites and had strong transactivation activity. HbICE1 was constitutively expressed in all tested tissues, with highest levels in the bark, and was up-regulated when subjected to various stresses including cold, dehydration, salinity and wounding. When overexpressed in Arabidopsis, 35S::HbICE1 plants showed enhanced cold resistance with increased proline content, reduced malondialdehyde (MDA) metabolism and electrolyte leakage, and decreased reactive oxygen species (ROS) accumulation. Expression of the cold responsive genes (COR15A, COR47, RD29A, and KIN1) was also significantly promoted in 35S::HbICE1 compared to wild-type plants under cold stress. Differentially expressed genes (DEGs) analysis showed that cold treatment changed genes expression profiles involved in many biological processes and phytohormones perception and transduction. Ethylene, JA, ABA, as well as ICE-CBF signaling pathways might work synergistically to cope with cold tolerance in rubber tree. Taken together, these findings suggest that HbICE1 is a member of the ICE gene family and a positive regulator of cold tolerance in H. brasiliensis.

ICE1 of Pyrus ussuriensis functions in cold tolerance by enhancing PuDREBa transcriptional levels through interacting with PuHHP1

ICE1 transcription factor plays an important role in plant cold stress via regulating the expression of stress-responsive genes. In this study, a PuICE1 gene isolated from Pyrus ussuriensis was characterized for its function in cold tolerance. The expression levels of the PuICE1 were induced by cold, dehydration and salt, with the greatest induction under cold conditions. PuICE1 was localized in the nucleus and could bind specifically to the MYC element in the PuDREBa promoter. The PuICE1 fused to the GAL4 DNA-binding domain to have transcriptional activation activity. Ectopic expression of the PuICE1 in tomato conferred enhanced tolerance to cold stress at cold temperatures, less electrolyte leakage, less MDA content, higher chlorophyll content, higher survival rate, higher proline content, higher activities of enzymes. In additon, steady-state mRNA levels of six stress-responsive genes coding for either functional or regulatory genes were induced to higher levels in the transgenic lines by cold stress. Yeast two-hybrid, transient assay, split luciferase complementation and BiFC assays all revealed that PuHHP1 protein can physically interact with PuICE1. Taken together, these results demonstrated that PuICE1 plays a positive role in cold tolerance, which may be due to enhancement of PuDREBa transcriptional levels through interacting with the PuHHP1.

An Efficient Approach for the Development of Locus Specific Primers in Bread Wheat (Triticum aestivum L.) and Its Application to Re-Sequencing of Genes Involved in Frost Tolerance

Recent declines in costs accelerated sequencing of many species with large genomes, including hexaploid wheat (Triticum aestivum L.). Although the draft sequence of bread wheat is known, it is still one of the major challenges to developlocus specific primers suitable to be used in marker assisted selection procedures, due to the high homology of the three genomes. In this study we describe an efficient approach for the development of locus specific primers comprising four steps, i.e. (i) identification of genomic and coding sequences (CDS) of candidate genes, (ii) intron- and exon-structure reconstruction, (iii) identification of wheat A, B and D sub-genome sequences and primer development based on sequence differences between the three sub-genomes, and (iv); testing of primers for functionality, correct size and localisation. This approach was applied to single, low and high copy genes involved in frost tolerance in wheat. In summary for 27 of these genes for which sequences were derived from Triticum aestivum, Triticum monococcum and Hordeum vulgare, a set of 119 primer pairs was developed and after testing on Nulli-tetrasomic (NT) lines, a set of 65 primer pairs (54.6%), corresponding to 19 candidate genes, turned out to be specific. Out of these a set of 35 fragments was selected for validation via Sanger's amplicon re-sequencing. All fragments, with the exception of one, could be assigned to the original reference sequence. The approach presented here showed a much higher specificity in primer development in comparison to techniques used so far in bread wheat and can be applied to other polyploid species with a known draft sequence.

ICE1 of Poncirus trifoliata functions in cold tolerance by modulating polyamine levels through interacting with arginine decarboxylase

ICE1 (Inducer of CBF Expression 1) encodes a MYC-like basic helix-loop-helix transcription factor that acts as a central regulator of cold response. In this study, we elucidated the function and underlying mechanisms of PtrICE1 from trifoliate orange [Poncirus trifoliata (L.) Raf.]. PtrICE1 was upregulated by cold, dehydration, and salt, with the greatest induction under cold conditions. PtrICE1 was localized in the nucleus and could bind to a MYC-recognizing sequence. Ectopic expression of PtrICE1 in tobacco and lemon conferred enhanced tolerance to cold stresses at either chilling or freezing temperatures. Yeast two-hybrid screening revealed that 21 proteins belonged to the PtrICE1 interactome, in which PtADC (arginine decarboxylase) was confirmed as a bona fide protein interacting with PtrICE1. Transcript levels of ADC genes in the transgenic lines were slightly elevated under normal growth condition but substantially increased under cold conditions, consistent with changes in free polyamine levels. By contrast, accumulation of the reactive oxygen species, H2O2 and O2 (-), was appreciably alleviated in the transgenic lines under cold stress. Higher activities of antioxidant enzymes, such as superoxide dismutase and catalase, were detected in the transgenic lines under cold conditions. Taken together, these results demonstrated that PtrICE1 plays a positive role in cold tolerance, which may be due to modulation of polyamine levels through interacting with the ADC gene.