A novel cold-regulated gene, COR25, of Brassica napus is involved in plant response and tolerance to cold stress

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

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

Enhancing cold and drought tolerance in cotton: a protective role of SikCOR413PM1

The present study explored the potential role of cold-regulated plasma membrane protein COR413PM1 isolated from Saussurea involucrata (Matsum. & Koidz)(SikCOR413PM1), in enhancing cotton (Gossypium hirsutum) tolerance to cold and drought stresses through transgenic methods. Under cold and drought stresses, the survival rate and the fresh and dry weights of the SikCOR413PM1-overexpressing lines were higher than those of the wild-type plants, and the degree of leaf withering was much lower. Besides, overexpressing SikCOR413PM1 overexpression increased the relative water content, reduced malondialdehyde content and relative conductivity, and elevated proline and soluble sugar levels in cotton seedlings. These findings suggest that SikCOR413PM1 minimizes cell membrane damage and boosts plant stability under challenging conditions. Additionally, overexpression of this gene upregulated antioxidant enzyme-related genes in cotton seedlings, resulting in enhanced antioxidant enzyme activity, lowered peroxide content, and reduced oxidative stress. SikCOR413PM1 overexpression also modulated the expression of stress-related genes (GhDREB1A, GhDREB1B, GhDREB1C, GhERF2, GhNAC3, and GhRD22). In field trials, the transgenic cotton plants overexpressing SikCOR413PM1 displayed high yields and increased environmental tolerance. Our study thus demonstrates the role of SikCOR413PM1 in regulating stress-related genes, osmotic adjustment factors, and peroxide content while preserving cell membrane stability and improving cold and drought tolerance in cotton.

Applications of Molecular Markers for Developing Abiotic-Stress-Resilient Oilseed Crops

Globally, abiotic stresses, such as temperature (heat or cold), water (drought and flooding), and salinity, cause significant losses in crop production and have adverse effects on plant growth and development. A variety of DNA-based molecular markers, such as SSRs, RFLPs, AFLPs, SNPs, etc., have been used to screen germplasms for stress tolerance and the QTL mapping of stress-related genes. Such molecular-marker-assisted selection strategies can quicken the development of tolerant/resistant cultivars to withstand abiotic stresses. Oilseeds such as rapeseed, mustard, peanuts, soybeans, sunflower, safflower, sesame, flaxseed, and castor are the most important source of edible oil worldwide. Although oilseed crops are known for their capacity to withstand abiotic challenges, there is a significant difference between actual and potential yields due to the adaptation and tolerance to severe abiotic pressures. This review summarizes the applications of molecular markers to date to achieve abiotic stress tolerance in major oilseed crops. The molecular markers that have been reported for genetic diversity studies and the mapping and tagging of genes/QTLs for drought, heavy metal stress, salinity, flooding, cold and heat stress, and their application in the MAS are presented.

Transcriptome analysis of the 2,4-dichlorophenoxyacetic acid (2,4-D)-tolerant cotton chromosome substitution line CS-B15sh and its susceptible parental lines G. hirsutum L. cv. Texas Marker-1 and G. barbadense L. cv. Pima 379

The cotton chromosome substitution line, CS-B15sh, exhibits 41% lower injury from 2,4-D when applied at the field recommended rate of 1.12 kg ae ha-1 (1×) than does Texas Marker-1 (TM-1). CS-B15sh was developed in the genetic background of Gossypium hirsutum L. cv TM-1 and has chromosome introgression on the short arm of chromosome 15 from Gossypium barbadense L. cv. Pima 379. In a previous experiment, we observed reduced translocation of [14C]2,4-D outside the treated leaf tissue in CS-B15sh, which contrasted with an increased translocation of the herbicide in the tissues above and below the treated leaf in TM-1. Our results indicate a potential 2,4-D tolerance mechanism in CS-B15sh involving altered movement of 2,4-D. Here, we used RNA sequencing (RNA-seq) to determine the differential expression of genes between 2,4-D-challenged and control plants of the tolerant (CS-B15sh) and susceptible lines (TM-1 and Pima 379). Several components of the 2,4-D/auxin-response pathway-including ubiquitin E3 ligase, PB1|AUX/IAA, ARF transcription factors, and F-box proteins of the SCFTIR1/AFB complex-were upregulated with at least threefold higher expression in TM-1 compared with CS-B15sh, while both Pima 379 and TM-1 showed the same fold change expression for PB1|AUX/IAA mRNA. Some genes associated with herbicide metabolism, including flavin monooxygenase (Gohir.A01G174100) and FAD-linked oxidase (Gohir.D06G002600), exhibited at least a twofold increase in CS-B15sh than in TM-1 (the gene was not expressed in Pima 379), suggesting a potential relationship between the gene's expression and 2,4-D tolerance. It is interesting to note that glutathione S-transferase was differentially expressed in both CS-B15sh and Pima 379 but not in TM-1, while cytochrome P450 and other genes involved in the oxidation-reduction process were significantly expressed only in CS-B15sh in response to 2,4-D. Gene set enrichment analysis on the union DEGs of the three cotton genotypes revealed the depletion of transcripts involved in photosynthesis and enrichment of transcripts involved in ABA response and signaling.

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

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

Editor's introduction to this issue (G&I 19:1, 2021)

Brassica napus is the third most important oilseed crop in the world; however, in Korea, it is greatly affected by cold stress, limiting seed growth and production. Plants have developed specific stress responses that are generally divided into three categories: cold-stress signaling, transcriptional/post-transcriptional regulation, and stress-response mechanisms. Large numbers of functional and regulatory proteins are involved in these processes when triggered by cold stress. Here, our objective was to investigate the different genetic factors involved in the cold-stress responses of B. napus. Consequently, we treated the Korean B. napus cultivar Naehan at the 4-week stage in cold chambers under different conditions, and RNA and cDNA were obtained. An in silico analysis included 80 cold-responsive genes downloaded from the National Center for Biotechnology Information (NCBI) database. Expression levels were assessed by reverse transcription polymerase chain reaction, and 14 cold-triggered genes were identified under cold-stress conditions. The most significant genes encoded zinc-finger proteins (33.7%), followed by MYB transcription factors (7.5%). In the future, we will select genes appropriate for improving the cold tolerance of B. napus.

The JA-responsive MYC2-BADH-like transcriptional regulatory module in Poncirus trifoliata contributes to cold tolerance by modulation of glycine betaine biosynthesis

Glycine betaine (GB) is known to accumulate in plants exposed to cold, but the underlying molecular mechanisms and associated regulatory network remain unclear. Here, we demonstrated that PtrMYC2 of Poncirus trifoliata integrates the jasmonic acid (JA) signal to modulate cold-induced GB accumulation by directly regulating PtrBADH-l, a betaine aldehyde dehydrogenase (BADH)-like gene. PtrBADH-l was identified based on transcriptome and expression analysis in P. trifoliata. Overexpression and VIGS (virus-induced gene silencing)-mediated knockdown showed that PtrBADH-l plays a positive role in cold tolerance and GB synthesis. Yeast one-hybrid library screening using PtrBADH-l promoter as baits unraveled PtrMYC2 as an interacting candidate. PtrMYC2 was confirmed to directly bind to two G-box cis-acting elements within PtrBADH-l promoter and acts as a transcriptional activator. In addition, PtrMYC2 functions positively in cold tolerance through modulation of GB synthesis by regulating PtrBADH-l expression. Interestingly, we found that GB accumulation under cold stress was JA-dependent and that PtrMYC2 orchestrates JA-mediated PtrBADH-l upregulation and GB accumulation. This study sheds new light on the roles of MYC2 homolog in modulating GB synthesis. In particular, we propose a transcriptional regulatory module PtrMYC2-PtrBADH-l to advance the understanding of molecular mechanisms underlying the GB accumulation under cold stress.

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

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

A Chloroplast COR413 Protein From Physcomitrella patens Is Required for Growth Regulation Under High Light and ABA Responses

COR413 genes belong to a poorly characterized group of plant-specific cold-regulated genes initially identified as part of the transcriptional activation machinery of plants during cold acclimation. They encode multispanning transmembrane proteins predicted to target the plasma membrane or the chloroplast inner membrane. Despite being ubiquitous throughout the plant kingdom, little is known about their biological function. In this study, we used reverse genetics to investigate the relevance of a predicted chloroplast localized COR413 protein (PpCOR413im) from the moss Physcomitrella patens in developmental and abiotic stress responses. Expression of PpCOR413im was strongly induced by abscisic acid (ABA) and by various environmental stimuli, including low temperature, hyperosmosis, salinity and high light. In vivo subcellular localization of PpCOR413im-GFP fusion protein revealed that this protein is localized in chloroplasts, confirming the in silico predictions. Loss-of-function mutants of PpCOR413im exhibited growth and developmental alterations such as growth retardation, reduced caulonema formation and hypersensitivity to ABA. Mutants also displayed altered photochemistry under various abiotic stresses, including dehydration and low temperature, and exhibited a dramatic growth inhibition upon exposure to high light. Disruption of PpCOR413im also caused altered chloroplast ultrastructure, increased ROS accumulation, and enhanced starch and sucrose levels under high light or after ABA treatment. In addition, loss of PpCOR413im affected both nuclear and chloroplast gene expression in response to ABA and high light, suggesting a role for this gene downstream of ABA in the regulation of growth and environmental stress responses. Developmental alterations exhibited by PpCOR413im knockout mutants had remarkable similarities to those exhibited by hxk1, a mutant lacking a major chloroplastic hexokinase, an enzyme involved in energy homeostasis. Based on these findings, we propose that PpCOR413im is involved in coordinating energy metabolism with ABA-mediated growth and developmental responses.

Characterization of cold stress responses in different rapeseed ecotypes based on metabolomics and transcriptomics analyses

The winter oilseed ecotype is more tolerant to low temperature than the spring ecotype. Transcriptome and metabolome analyses of leaf samples of five spring Brassica napus L. (B. napus) ecotype lines and five winter B. napus ecotype lines treated at 4 °C and 28 °C were performed. A total of 25,460 differentially expressed genes (DEGs) of the spring oilseed ecotype and 28,512 DEGs of the winter oilseed ecotype were identified after cold stress; there were 41 differentially expressed metabolites (DEMs) in the spring and 47 in the winter oilseed ecotypes. Moreover, more than 46.2% DEGs were commonly detected in both ecotypes, and the extent of the changes were much more pronounced in the winter than spring ecotype. By contrast, only six DEMs were detected in both the spring and winter oilseed ecotypes. Eighty-one DEMs mainly belonged to primary metabolites, including amino acids, organic acids and sugars. The large number of specific genes and metabolites emphasizes the complex regulatory mechanisms involved in the cold stress response in oilseed rape. Furthermore, these data suggest that lipid, ABA, secondary metabolism, signal transduction and transcription factors may play distinct roles in the spring and winter ecotypes in response to cold stress. Differences in gene expression and metabolite levels after cold stress treatment may have contributed to the cold tolerance of the different oilseed ecotypes.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

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.

Salt-Induced Damage is Alleviated by Short-Term Pre-Cold Treatment in Bermudagrass (Cynodon dactylon)

Excess salinity is a major environmental stress that limits growth and development of plants. Improving salt stress tolerance of plants is important in order to enhance land utilization and crop yield. Cold priming has been reported to trigger the protective processes in plants that increase their stress tolerance. Bermudagrass (Cynodon dactylon) is one of the most widely used turfgrass species around the world. However, the effect of cold priming on salt tolerance of bermudagrass is largely unknown. In the present study, wild bermudagrass was pre-treated with 4 °C for 6 h before 150 mM NaCl treatment for one week. The results showed that the cell membrane stability, ion homeostasis and photosynthesis process which are usually negatively affected by salt stress in bermudagrass were alleviated by short-term pre-cold treatment. Additionally, the gene expression profile also corresponded to the change of physiological indexes in bermudagrass. The results suggest that cold priming plays a positive role in improving salt stress tolerance of bermudagrass.

Transcriptome Profile Analysis of Winter Rapeseed (Brassica napus L.) in Response to Freezing Stress, Reveal Potentially Connected Events to Freezing Stress

Winter rapeseed is not only an important oilseed crop, but also a winter cover crop in Northern China, where its production was severely limited by freezing stress. As an overwinter crop, the production is severely limited by freezing stress. Therefore, understanding the physiological and molecular mechanism of winter rapeseed (Brassica napus L.) in freezing stress responses becomes essential for the improvement and development of freezing-tolerant varieties of Brassica napus. In this study, morphological, physiological, ultrastructure and transcriptome changes in the Brassica napus line "2016TS(G)10" (freezing-tolerance line) that was exposed to -2 °C for 0 h, 1 h, 3 h and 24 h were characterized. The results showed that freezing stress caused seedling dehydration, and chloroplast dilation and degradation. The content of malondialdehyde (MDA), proline, soluble protein and soluble sugars were increased, as well as the relative electrolyte leakage (REL) which was significantly increased at frozen 24 h. Subsequently, RNA-seq analysis revealed a total of 98,672 UniGenes that were annotated in Brassica napus and 3905 UniGenes were identified as differentially expressed genes after being exposed to freezing stress. Among these genes, 2312 (59.21%) were up-regulated and 1593 (40.79%) were down-regulated. Most of these DEGs were significantly annotated in the carbohydrates and energy metabolism, signal transduction, amino acid metabolism and translation. Most of the up-regulated DEGs were especially enriched in plant hormone signal transduction, starch and sucrose metabolism pathways. Transcription factor enrichment analysis showed that the AP2/ERF, WRKY and MYB families were also significantly changed. Furthermore, 20 DEGs were selected to validate the transcriptome profiles via quantitative real-time PCR (qRT-PCR). In conclusion, the results provide an overall view of the dynamic changes in physiology and insights into the molecular regulation mechanisms of winter Brassica napus in response to freezing treatment, expanding our understanding on the complex molecular mechanism in plant response to freezing stress.

The ICE-like transcription factor HbICE2 is involved in jasmonate-regulated cold tolerance in the rubber tree (Hevea brasiliensis)

An ICE-like transcription factor mediates jasmonate-regulated cold tolerance in the rubber tree (Hevea brasiliensis), and confers cold tolerance in transgenic Arabidopsis. The rubber tree (Hevea brasiliensis) is susceptible to low temperatures, and understanding the mechanisms regulating cold stress is of great potential value for enhancing tolerance to this environmental variable. In this study, we find that treatment with exogenous methyl jasmonate (MeJA) could significantly enhance Hevea brasiliensis cold tolerance. In addition, yeast two-hybrid and bimolecular fluorescence complementation (BiFC) experiments show that JASMONATE ZIM-DOMAIN(JAZ) proteins, HbJAZ1 and HbJAZ12, key repressors of JA signaling pathway, interact with HbICE2, a novel ICE (Inducer of CBF Expression)-like protein. HbICE2 was nuclear-localised and bound to the MYC recognition (MYCR) sequence. The transcriptional activation activity of HbICE2 in yeast cells was dependent on the N-terminus, and overexpression of HbICE2 in Arabidopsis resulted in elevated tolerance to chilling stress. Furthermore, dual-luciferase transient assay reveals that HbJAZ1 and HbJAZ12 proteins inhibit the transcriptional function of HbICE2. The expression of C-repeat-binding factor (CBF) signalling pathway genes including HbCBF1, HbCBF2 and HbCOR47 were up-regulated by MeJA. Taken together, our data suggest that the new ICE-like transcription factor HbICE2 is involved in jasmonate-regulated cold tolerance in Hevea brasiliensis.

The Overexpression of a Transcription Factor Gene VbWRKY32 Enhances the Cold Tolerance in Verbena bonariensis

Cold stress poses a serious threat to the survival and bloom of Verbena bonariensis. The enhancement of the cold tolerance of V. bonariensis is the central concern of our research. The WRKY transcription factor (TF) family was paid great attention to in the field of abiotic stress. The VbWRKY32 gene was obtained from V. bonariensis. The VbWRKY32 predicted protein contained two typical WRKY domains and two C2H2 zinc-finger motifs. Under cold stress, VbWRKY32 in leaves was more greatly induced than that in stems and roots. The overexpression (OE) in V. bonariensis increased cold tolerance compared with wild-type (WT). Under cold stress, the OE lines possessed showed greater recovery after cold-treatment restoration ratios, proline content, soluble sugar content, and activities of antioxidant enzymes than WT; the relative electrolyte conductivity (EL), the accumulation of malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and superoxide anion (O₂ ^-) are lower in OE lines than that in WT. In addition, a series of cold-response genes of OE lines were compared with WT. The results revealed that VbWRKY32 worked as a positive regulator by up-regulating transcription levels of cold-responsive genes. The genes above can contribute to the elevation of antioxidant activities, maintain the membrane stability, and raise osmotic regulation ability, leading to the enhancement of the survival capacity under cold stress. According to this work, VbWRKY32 could serve as an essential gene to confer enhanced cold tolerance in plants.

PsCor413pm2, a Plasma Membrane-Localized, Cold-Regulated Protein from Phlox subulata, Confers Low Temperature Tolerance in Arabidopsis

Low temperature stress adversely affects plant growth and development. Isolation and characterization of cold response genes from cold-tolerant plants help to understand the mechanism underlying low temperature tolerance. In this study, PsCor413pm2, a cold-regulated (COR) gene isolated from Phlox subulata, was transferred to Arabidopsis plants to investigate its function. Real-time quantitative PCR analysis revealed that PsCor413pm2 expression was induced by cold. Subcellular localization revealed that the PsCor413pm2-green fluorescent protein (GFP) fusion protein localized to the plasma membrane in tobacco and Arabidopsis plants. Furthermore, overexpression of PsCor413pm2 in Arabidopsis plants enhanced tolerance to low temperature stress. Transgenic Arabidopsis roots had more influx of Ca²⁺ after a cold shock than wild-type plants, as shown using non-invasive micro-test technology (NMT). Moreover, the transcription abundance of five COR and two C-repeat (CRT) binding factor (CBF) genes in transgenic Arabidopsis plants was higher than that in the wild-type plants under cold stress. Taken together, our results suggest that overexpression of PsCor413pm2 enhances low temperature tolerance in Arabidopsis plants by affecting Ca²⁺ flux and the expression of stress-related COR and CBF genes.

Proteomic Analysis of the Function of a Novel Cold-Regulated Multispanning Transmembrane Protein COR413-PM1 in Arabidopsis

The plasma membrane is the first subcellular organ that senses low temperature, and it includes some spanning transmembrane proteins that play important roles in cold regulation. COR413-PM1 is a novel multispanning transmembrane cold-regulated protein; however, the related functions are not clear in Arabidopsis. We found the tolerance to freezing stress of cor413-pm1 was lower than wild-type (WT). A proteomics method was used to analyze the differentially abundant proteins (DAPs) between cor413-pm1 and WT. A total of 4143 protein groups were identified and 3139 were accurately quantitated. The DAPs associated with COR413-PM1 and freezing treatment were mainly involved in the metabolism of fatty acids, sugars, and purine. Quantitative real-time PCR (qRT-PCR) confirmed the proteomic analysis results of four proteins: fatty acid biosynthesis 1 (FAB1) is involved in fatty acid metabolism and might affect the plasma membrane structure; fructokinase 3 (FRK3) and sucrose phosphate synthase A1 (SPSA1) play roles in sugar metabolism and may influence the ability of osmotic adjustment under freezing stress; and GLN phosphoribosyl pyrophosphate amidotransferase 2 (ASE2) affects freezing tolerance through purine metabolism pathways. In short, our results demonstrate that the multispanning transmembrane protein COR413-PM1 regulates plant tolerance to freezing stress by affecting the metabolism of fatty acids, sugars, and purine in Arabidopsis.

Perspective Research Progress in Cold Responses of Capsella bursa-pastoris

Plants respond to cold stress by modulating biochemical pathways and array of molecular events. Plant morphology is also affected by the onset of cold conditions culminating at repression in growth as well as yield reduction. As a preventive measure, cascades of complex signal transduction pathways are employed that permit plants to endure freezing or chilling periods. The signaling pathways and related events are regulated by the plant hormonal activity. Recent investigations have provided a prospective understanding about plant response to cold stress by means of developmental pathways e.g., moderate growth involved in cold tolerance. Cold acclimation assays and bioinformatics analyses have revealed the role of potential transcription factors and expression of genes like CBF, COR in response to low temperature stress. Capsella bursa-pastoris is a considerable model plant system for evolutionary and developmental studies. On different occasions it has been proved that C. bursa-pastoris is more capable of tolerating cold than A. thaliana. But, the mechanism for enhanced low or freezing temperature tolerance is still not clear and demands intensive research. Additionally, identification and validation of cold responsive genes in this candidate plant species is imperative for plant stress physiology and molecular breeding studies to improve cold tolerance in crops. We have analyzed the role of different genes and hormones in regulating plant cold resistance with special reference to C. bursa-pastoris. Review of collected data displays potential ability of Capsella as model plant for improvement in cold stress regulation. Information is summarized on cold stress signaling by hormonal control which highlights the substantial achievements and designate gaps that still happen in our understanding.

Dynamic transcriptome analysis reveals AP2/ERF transcription factors responsible for cold stress in rapeseed (Brassica napus L.)

The APETALA2/ethylene response factor (AP2/ERF) transcription factor (TF) superfamily plays an important regulatory role in signal transduction of the plant responses to various stresses including low temperature. Significant progress has been made in understanding the mechanism of cold resistance in Brassica napus, an important oilseed crop. However, comprehensive studies on the induction and activity of these TFs under low temperature have been lacking. In this study, 132 AP2/ERF genes were identified by transcriptome sequencing of rapeseed leaves exposed to 0, 2, 6, 12, and 24 h of low (4 °C) temperature stress. The genes were classified into 4 subfamilies (AP2, DREB, ERF, and RAV) and 13 subgroups, among which the DREB subfamily and ERF subfamily contained 114 genes, no genes were assigned to soloist or DREB A3 subgroups. One hundred and eighteen genes were located on chromosomes A1 to C9. GO functional analysis and promoter sequence analysis revealed that these genes are involved in many molecular pathways that may enhance cold resistance in plants, such as the low-temperature responsiveness, methyl jasmonate, abscisic acid, and ethylene-responsiveness pathways. Their expression patterns revealed dynamic control at different times following initiation of cold stress; the RAV and DREB subfamilies were expressed at the early stage of cold stress, whereas the AP2 subfamily was expressed later. Quantitative PCR analyses of 13 cold-induced AP2/ERF TFs confirmed the accuracy of above results. This study is the first dynamic analysis of the AP2/ERF TFs responsible for cold stress in rapeseed. These findings will serve as a reference for future functional research on transcription in rapeseed.

Physiological and Molecular Mechanism of Nitric Oxide (NO) Involved in Bermudagrass Response to Cold Stress

Bermudagrass is widely utilized in parks, lawns, and golf courses. However, cold is a key factor limiting resource use in bermudagrass. Therefore, it is meaningful to study the mechanism of bermudagrass response to cold. Nitric oxide (NO) is a crucial signal molecule with multiple biological functions. Thus, the objective of this study was to investigate whether NO play roles in bermudagrass response to cold. Sodium nitroprusside (SNP) was used as NO donor, while 2-phenyl-4,4,5,5-tetramentylimidazoline-l-oxyl-3-xide (PTIO) plus NG-nitro-L-arginine methyl ester (L-NAME) were applied as NO inhibitor. Wild bermudagrass was subjected to 4 °C in a growth chamber under different treatments (Control, SNP, PTIO + L-NAME). The results indicated lower levels of malondialdehyde (MDA) content and electrolyte leakage (EL), higher value for chlorophyll content, superoxide dismutase (SOD) and peroxidase (POD) activities after SNP treatment than that of PTIO plus L-NAME treatments under cold stress. Analysis of Chlorophyll (Chl) a fluorescence transient displayed that the OJIP transient curve was higher after treatment with SNP than that of treated with PTIO plus L-NAME under cold stress. The values of photosynthetic fluorescence parameters were higher after treatment with SNP than that of treated with PTIO plus L-NAME under cold stress. Expression of cold-responsive genes was altered under cold stress after treated with SNP or PTIO plus L-NAME. In summary, our findings indicated that, as an important strategy to protect bermudagrass against cold stress, NO could maintain the stability of cell membrane, up-regulate the antioxidant enzymes activities, recover process of photosystem II (PSII) and induce the expression of cold-responsive genes.

Cell Wall Metabolism in Response to Abiotic Stress

This review focuses on the responses of the plant cell wall to several abiotic stresses including drought, flooding, heat, cold, salt, heavy metals, light, and air pollutants. The effects of stress on cell wall metabolism are discussed at the physiological (morphogenic), transcriptomic, proteomic and biochemical levels. The analysis of a large set of data shows that the plant response is highly complex. The overall effects of most abiotic stress are often dependent on the plant species, the genotype, the age of the plant, the timing of the stress application, and the intensity of this stress. This shows the difficulty of identifying a common pattern of stress response in cell wall architecture that could enable adaptation and/or resistance to abiotic stress. However, in most cases, two main mechanisms can be highlighted: (i) an increased level in xyloglucan endotransglucosylase/hydrolase (XTH) and expansin proteins, associated with an increase in the degree of rhamnogalacturonan I branching that maintains cell wall plasticity and (ii) an increased cell wall thickening by reinforcement of the secondary wall with hemicellulose and lignin deposition. Taken together, these results show the need to undertake large-scale analyses, using multidisciplinary approaches, to unravel the consequences of stress on the cell wall. This will help identify the key components that could be targeted to improve biomass production under stress conditions.

Structural alteration of cell wall pectins accompanies pea development in response to cold

Pea (Pisum sativum) cell wall metabolism in response to chilling was investigated in a frost-sensitive genotype 'Terese' and a frost-tolerant genotype 'Champagne'. Cell walls isolated from stipules of cold acclimated and non-acclimated plants showed that cold temperatures induce changes in polymers containing xylose, arabinose, galactose and galacturonic acid residues. In the tolerant cultivar Champagne, acclimation is accompanied by increases in homogalacturonan, xylogalacturonan and highly branched Rhamnogalacturonan I with branched and unbranched (1→5)-α-arabinans and (1→4)-β-galactans. In contrast, the sensitive cultivar Terese accumulates substantial amounts of (1→4)-β-xylans and glucuronoxylan, but not the pectins. Greater JIM7 labeling was observed in Champagne compared to Terese, indicating that cold acclimation also induces an increase in the degree of methylesterification of pectins. Significant decrease in polygalacturonase activities in both genotypes were observed at the end of cold acclimation. These data indicate a role for esterified pectins in cold tolerance. The possible functions for pectins and their associated arabinans and galactans in cold acclimation are discussed.

Involvement of multiple types of dehydrins in the freezing response in loquat (Eriobotrya japonica)

Dehydrins (DHNs) are a family of plant proteins typically induced in response to stress conditions that cause cellular dehydration, such as low temperatures, high salinity, and drought. Loquat (Eriobotrya japonica) is a perennial fruit crop that blossoms during winter. Loquat fruitlets are frequently injured by freezing. To evaluate the role of the EjDHNs in freezing resistance in loquat fruitlets, two cultivars of loquat, the freezing-sensitive 'Ninghaibai' (FS-NHB) and the freezing-tolerant 'Jiajiao' (FT-JJ), were analyzed under induced freezing stress. Freezing stress led to obvious accumulation of reactive oxygen species and considerable lipid peroxidation in membranes during the treatment period. Both these phenomena were more pronounced in 'FS-NHB' than in 'FS-JJ.' Immunogold labeling of dehydrin protein was performed. DHN proteins were found to be concentrated mainly in the vicinity of the plasma membrane, and the density of the immunogold labeling was significantly higher after freezing treatment, especially in the more freezing-tolerant cultivar 'FT-JJ.' Seven DHNs, showing four different structure types, were obtained from loquat fruitlets and used to study the characteristics of different EjDHN proteins. These DHN proteins are all highly hydrophilic, but they differ significantly in size, ranging from 188 to 475 amino acids, and in biochemical properties, such as theoretical pI, aliphatic index, and instability index. Freezing treatment resulted in up-regulation of the expression levels of all seven EjDHNs, regardless of structure type. The accumulation of the transcripts of these EjDHN genes was much more pronounced in 'FT-JJ' than in 'FS-NHB.' Altogether, this study provides evidence that EjDHNs are involved in the cryoprotection of the plasma membrane during freeze-induced dehydration in loquat fruitlets.

Comparative analysis of the variable 3' UTR and gene expression of the KIN and KIN-homologous LEA genes in Capsella bursa-pastoris

As the crucial members of the cold-regulated (COR) gene family, KIN genes are involved in diverse abiotic stress responses in plants. In the present study, KIN genes from the widespread plant Capsella bursa-pastoris were identified and analyzed to better understand the powerful adaptation of this species. Two KIN genes were cloned and sequenced by 3' RACE. As some COR genes are homologous to LEA genes, three KIN-homologous LEA genes were also identified. We deduced the amino acid sequences of the five proteins to estimate their phylogenetic relationships, and grouped them into three subfamilies (CI, CII, and CIII). Variable 3' UTRs were found in CI, CII, and CIII genes. Using qPCR, we evaluated the transcriptional levels of the five genes in different organs and embryonic stages. Two CI genes were exclusively expressed in early embryos and flowers. The CII and CIII genes showed obvious up-regulation in young leaves after heat stress, cold stress, and ABA treatment. Two of the CI genes, however, rarely responded to those stresses in young leaves. In contrast, all five genes showed differential responses in flowers when C. bursa-pastoris plants were sprayed with ABA. Furthermore, the expression of these genes in C. bursa-pastoris was compared to that of the corresponding Arabidopsis genes, and similar gene expression profiles were found in both species. Our findings suggest that these five genes play different roles in development and the responses to abiotic stresses in C. bursa-pastoris. Key message We characterized two KIN and three KIN-homologous LEA genes, and analyzed their variable 3'UTR and organ-specific, embryo-developmental, stress-induced gene expression in Capsella bursa-pastoris.

Transgenic tobacco plants over expressing cold regulated protein CbCOR15b from Capsella bursa-pastoris exhibit enhanced cold tolerance

Low temperature is among the most significant abiotic stresses, restricting the habitats of sessile plants and reducing crop productivity. Cold regulated (COR) genes are low temperature-responsive genes expressing under regulation of a specific signal transduction pathway, which is designated C-repeat-binding-factor (CBF) signaling pathway. In the present article, cold bioassay showed that the transcript level of cold regulated gene CbCOR15b from shepherd's purse (Capsella bursa-pastoris) was obviously elevated under cold treatments. Reverse transcription-PCR (RT-PCR) and GUS report system revealed that unlike AtCOR15b, CbCOR15b expressed not only in leaves but also in stems and maturation zone of roots. When transgenic tobacco plants ectopically expressing CbCOR15b were exposed to chilling and freezing temperatures, they displayed more cold tolerance compared to control plants. According to the electrolyte leakage, the relative water content, the glucose content and the phenotype observation, CbCOR15b transformants suffered less damage under cold stress. Further investigation of the subcellular localization of CbCOR15b by transient expression of fusion protein CbCOR15b-GFP revealed that it was localized exclusively in the chloroplasts of tobacco mesophyll cells and in the cytoplasm of onion epidermal cells. It can be concluded that CbCOR15b which located in the chloroplasts and in the cytoplasm of cells without chloroplasts was involved in cold response of C. bursa-pastoris and conferred enhanced cold tolerance in transgenic tobacco plants.

Characterization of the variable 3' UTR and expression of the two intron-containing KIN transcripts from Capsella bursa-pastoris

KIN genes are crucial members of the cold-regulated (COR) gene family, and are exclusively involved in normal developmental processes in many organs and respond to a variety of abiotic stresses in plants. Here, we cloned and sequenced not only two completely-spliced KIN transcripts (CbKIN1-S and CbKIN2-S), but also two intron-containing KIN transcripts (CbKIN1-U and CbKIN2-U), from Capsella bursa-pastoris, a widespread plant of the Brassicaceae family. The CbKIN1-U and CbKIN2-U transcripts each contained one additional intron in the coding region compared to the corresponding CbKIN1-S and CbKIN2-S transcripts. In addition, the two intron-containing KIN transcripts were found by rapid amplification of cDNA 3' ends (3' RACE) analysis with specific primers to have variable 3' untranslated regions (3' UTRs). We also analyzed CbKIN1-U and CbKIN2-U levels in different organs and embryonic stages by quantitative polymerase chain reaction (qPCR). They were found to be expressed in middle-stage embryos and flowers. After abscisic acid (ABA) treatment, CbKIN1-U and CbKIN2-U showed strong responses in young leaves and weak responses in flowers. Levels of the two intron-containing KIN transcripts were markedly increased in young leaves when plants were exposed to cold and heat stress. Both of them showed stronger responses to ABA treatment and cold stress than that to heat stress. CbKIN1-U and CbKIN2-U share similar gene expression profiles in development and in response to exposure to different stresses, suggesting that they probably play similar biological roles in C. bursa-pastoris.

GhAGP31, a cotton non-classical arabinogalactan protein, is involved in response to cold stress during early seedling development

Arabinogalactan proteins (AGPs), a superfamily of highly glycosylated hydroxyproline-rich glycoproteins, are widely implicated in plant growth and development. A gene (including its cDNA), designated GhAGP31, encoding a non-classical AGP protein was isolated from cotton (Gossypium hirsutum). The deduced GhAGP31 protein contains the conserved features of non-classical AGPs: a putative signal peptide, N-terminal histidine-rich stretch, middle repetitive proline-rich domain and a cysteine-containing 'PAC' domain. GFP fluorescence assay demonstrated that GhAGP31 protein was localised on cell walls. GhAGP31 transcripts were mainly detected in roots, hypocotyls and ovules, but little or almost none were detected in other tissues. In particular, expression of GhAGP31 was developmentally regulated in roots. Further study demonstrated that GhAGP31 expression in cotton roots was remarkably up-regulated by cold stress. Expression of the GUS gene driven by the GhAGP31 promoter was also dramatically enhanced in roots of transgenic Arabidopsis seedlings under cold treatment. Additionally, overexpression of GhAGP31 in yeast and Arabidopsis significantly improved the freezing tolerance of yeast cells and cold tolerance of Arabidopsis seedlings. These data imply that GhAGP31 protein may be involved in the response to cold stress during early root development of cotton.

GhHyPRP4, a cotton gene encoding putative hybrid proline-rich protein, is preferentially expressed in leaves and involved in plant response to cold stress

Plant hybrid proline-rich proteins (HyPRPs) usually consist of an N-terminal signal peptide, a central proline-rich domain, and a conserved eight-cysteine motif C-terminal domain. In this study, one gene (designated as GhHyPRP4) encoding putative HyPRP was isolated from cotton cDNA library. Northern blot and quantitative reverse transcriptase-polymerase chain reaction analyses revealed that GhHyPRP4 was preferentially expressed in leaves. Under cold stress, GhHyPRP4 expression was significantly up-regulated in leaves of cotton seedlings. Using the genome walking approach, a promoter fragment of GhHyPRP4 gene was isolated from cotton genome. GUS (β-glucuronidase) gene driven by GhHyPRP4 promoter was specifically expressed in leaves and cotyledons of the transgenic Arabidopsis thaliana. Furthermore, GUS expression in leaves was remarkably induced by cold stress. Overexpression of GhHyPRP4 in yeast (Schizosaccharomyces pombe) significantly enhanced the cell survival rate upon treatment under -20°C for 60 h. These data suggested that GhHyPRP4 may be involved in plant response to cold stress during seedling development of cotton.