Expression of a synthetic antifreeze protein in potato reduces electrolyte release at freezing temperatures

Cold-inducible promoter-driven knockdown of Brachypodium antifreeze proteins confers freezing and phytopathogen susceptibility

The model forage crop, Brachypodium distachyon, has a cluster of ice recrystallization inhibition (BdIRI) genes, which encode antifreeze proteins that function by adsorbing to ice crystals and inhibiting their growth. The genes were targeted for knockdown using a cold-induced promoter from rice (prOsMYB1R35) to drive miRNA. The transgenic lines showed no apparent pleiotropic developmental defects but had reduced antifreeze activity as assessed by assays for ice-recrystallization inhibition, thermal hysteresis, electrolyte leakage, and leaf infrared thermography. Strikingly, the number of cold-acclimated transgenic plants that survived freezing at -8°C was reduced by half or killed entirely, depending on the line, compared with cold-acclimated wild type plants. In addition, more leaf damage was apparent at subzero temperatures in knockdowns after infection with an ice nucleating pathogen, Pseudomonas syringae. Although antifreeze proteins have been studied for almost 60 years, this is the first unequivocal demonstration of their function by knockdown in any organism, and their dual contribution to freeze protection as well as pathogen susceptibility, independent of obvious developmental defects. These proteins are thus of potential interest in a wide range of biotechnological applications from cryopreservation, to frozen product additives, to the engineering of transgenic crops with enhanced pathogen and freezing tolerance.

Physiological Responses and Proteomic Analysis on the Cold Stress Responses of Annual Pitaya (Hylocereus spp.) Branches

In this study, the physiological response of the annual branches of three varieties of pitaya (Xianmi, Fulong, and Zihonglong) in cold stress was investigated using a multivariate statistical method. Physiological change results showed that cold stress could decrease the moisture and chlorophyll contents, on the contrary, increase the relative electric conductivity, the contents of malonadehyde, soluble protein, soluble sugar, and free proline, and enhance the enzyme activities of peroxidase, superoxide dismutase, and catalase. Meanwhile, a comparative proteomic approach was also conducted to clarify the cold resistance-related proteins and pathways in annual pitaya branches. Proteomics results concluded that the cold tolerance of annual pitaya branches could be improved by modulating autophagy. Therefore, we hypothesized that an increased autophagy ability may be an important characteristic of the annual pitaya branches in response to cold stress conditions. Our results provide a good understanding of the physiological responses and molecular mechanisms of the annual pitaya branches in response to cold stress.

Non-animal proteins as cutting-edge ingredients to reformulate animal-free foodstuffs: Present status and future perspectives

Consumer interest in protein rich diets is increasing, with more attention being paid to the protein source. Despite the occurrence of animal proteins in the human diet, non-animal proteins are gaining popularity around the world due to their health benefits, environmental sustainability, and ethical merit. These sources of protein qualify for vegan, vegetarian, and flexitarian diets. Non-animal proteins are versatile, derived mainly from cereals, vegetables, pulses, algae (seaweed and microalgae), fungi, and bacteria. This review's intent is to analyze the current and future direction of research and innovation in non-animal proteins, and to elucidate the extent (limitations and opportunities) of their applications in food and beverage industries. Prior knowledge provided relevant information on protein features (processing, structure, and techno-functionality) with particular focus on those derived from soy and wheat. In the current food landscape, beyond conventionally used plant sources, other plant proteins are gaining traction as alternative ingredients to formulate animal-free foodstuffs (e.g., meat alternatives, beverages, baked products, snack foods, and others). Microbial proteins derived from fungi and algae are also food ingredients of interest due to their high protein quantity and quality, however there is no commercial food application for bacterial protein yet. In the future, key points to consider are the importance of strain/variety selection, advances in extraction technologies, toxicity assessment, and how this source can be used to create food products for personalized nutrition.

Strategies of Plant Biotechnology to Meet the Increasing Demand of Food and Nutrition in India

A groundbreaking application of biotechnology research during the recent past has been improvement of crop health and production.  India being one of the most rapidly developing countries with an enormous population and remarkable biodiversity, plant biotechnology promises significant potential to contribute to characterization and conservation of the biodiversity, increasing its usefulness. However, India’s green revolution was noted to be insufficient to feed the country's teeming millions. Therefore, novel approaches in crop biotechnology had to be aimed at ensuring better productivity and quality of cultivars.  This paper provides a comprehensive review of research undertaken mainly in the last couple of decades along with potential strategies in plant biotechnology focusing on specific grain and seed crops of key agricultural as well as dietary importance to meet the growing demand of food and nutrition in India, while also proposing potential application of relevant global research findings in the Indian context.  The analysis would help address the ever-increasing worldwide socio-economic necessity for greater food security, particularly during times of crisis such as the recent Coronavirus Infectious Disease 2019 (COVID-19) pandemic.

The properties, biotechnologies, and applications of antifreeze proteins

By natural selection, organisms evolve different solutions to cope with extremely cold weather. The emergence of an antifreeze protein gene is one of the most momentous solutions. Antifreeze proteins possess an importantly functional ability for organisms to survive in cold environments and are widely found in various cold-tolerant species. In this review, we summarize the origin of antifreeze proteins, describe the diversity of their species-specific properties and functions, and highlight the related biotechnology on the basis of both laboratory tests and bioinformatics analysis. The most recent advances in the applications of antifreeze proteins are also discussed. We expect that this systematic review will contribute to the comprehensive knowledge of antifreeze proteins to readers.

Ice Binding Proteins: Diverse Biological Roles and Applications in Different Types of Industry

More than 80% of Earth’s surface is exposed periodically or continuously to temperatures below 5 °C. Organisms that can live in these areas are called psychrophilic or psychrotolerant. They have evolved many adaptations that allow them to survive low temperatures. One of the most interesting modifications is production of specific substances that prevent living organisms from freezing. Psychrophiles can synthesize special peptides and proteins that modulate the growth of ice crystals and are generally called ice binding proteins (IBPs). Among them, antifreeze proteins (AFPs) inhibit the formation of large ice grains inside the cells that may damage cellular organelles or cause cell death. AFPs, with their unique properties of thermal hysteresis (TH) and ice recrystallization inhibition (IRI), have become one of the promising tools in industrial applications like cryobiology, food storage, and others. Attention of the industry was also caught by another group of IBPs exhibiting a different activity—ice-nucleating proteins (INPs). This review summarizes the current state of art and possible utilizations of the large group of IBPs.

A brief review of applications of antifreeze proteins in cryopreservation and metabolic genetic engineering

Antifreeze proteins (AFPs) confer the ability to survive at subzero temperatures and are found in many different organisms, including fish, plants, and insects. They prevent the formation of ice crystals by non-colligative adsorption to the ice surface and are essential for the survival of organisms in cold environments. These proteins are also widely used for cryopreservation, food technology, and metabolic genetic engineering over a range of sources and recipient cell types. This review summarizes successful applications of AFPs in the cryopreservation of animals, insects, and plants, and discusses challenges encountered in cryopreservation. Applications in metabolic genetic engineering are also described, specifically with the overexpression of AFP genes derived from different organisms to provide freeze protection to sensitive crops seasonally exposed to subzero temperatures. This review will provide information about potential applications of AFPs in the cryopreservation of animals and plants as well as in plant metabolic genetic engineering in hopes of furthering the development of cold-tolerant organisms.

Anti-freezing-protein type III strongly influences the expression of relevant genes in cryopreserved potato shoot tips

AFP improved cryopreservation efficiency of potato (Solanum tuberosum cv. Superior) by regulating transcript levels of CBF1 and DHN1. However, the optimal AFP concentration required for strong induction of the genes was dependent on the type of vitrification solution to which the AFP was added: This finding suggests that AFP increased cryopreservation efficiency by transcriptional regulation of these genes, which might protect plant cell membranes from cold stress during cryopreservation. Despite the availability of many studies reporting the benefits of anti-freeze protein III (AFP III) as a cryoprotectant, the role of AFP III in this process has not been well demonstrated using molecular analysis. In addition, AFP III has not been exploited in the cryopreservation of potato thus far. Therefore, we studied the effects of AFP III on the cryopreservation of potato (Solanum tuberosum cv. Superior). We found that CBF1 and DHN1 genes are low temperature-inducible in potato leaves (S. tuberosum cv. Superior). Transcript levels of these genes expressed in shoot tips cryopreserved with AFP III were higher than those of the controls. However, the optimal AFP III concentration required for strong induction of the genes was dependent on the type of cryoprotection solution to which the AFP III was added: 500 ng/mL worked best for PVS2, while 1500 ng/mL was optimal for LS. Interestingly, the involvement of AFP III in the cryoprotection solutions improved cryopreservation efficiency as compared to the control, and expression levels of the detected genes were associated with cryopreservation efficiency. This finding suggests that AFP III increased cryopreservation efficiency by transcriptional regulation of these genes, which might protect plant cell membranes from cold stress during cryopreservation. Therefore, we expect that our findings will lead to the successful application of AFP III as a potent cryoprotectant in the cryopreservation of rare and commercially important plant germplasms.

Ice-binding proteins confer freezing tolerance in transgenic Arabidopsis thaliana

Lolium perenne is a freeze-tolerant perennial ryegrass capable of withstanding temperatures below -13 °C. Ice-binding proteins (IBPs) presumably help prevent damage associated with freezing by restricting the growth of ice crystals in the apoplast. We have investigated the expression, localization and in planta freezing protection capabilities of two L. perenne IBP isoforms, LpIRI2 and LpIRI3, as well as a processed IBP (LpAFP). One of these isoforms, LpIRI2, lacks a conventional signal peptide and was assumed to be a pseudogene. Nevertheless, both LpIRI2 and LpIRI3 transcripts were up-regulated following cold acclimation. LpIRI2 also demonstrated ice-binding activity when produced recombinantly in Escherichia coli. Both the LpIRI3 and LpIRI2 isoforms appeared to accumulate in the apoplast of transgenic Arabidopsis thaliana plants. In contrast, the fully processed isoform, LpAFP, remained intracellular. Transgenic plants expressing either LpIRI2 or LpIRI3 showed reduced ion leakage (12%-39%) after low-temperature treatments, and significantly improved freezing survival, while transgenic LpAFP-expressing lines did not confer substantial subzero protection. Freeze protection was further enhanced by with the introduction of more than one IBP isoform; ion leakage was reduced 26%-35% and 10% of plants survived temperatures as low as -8 °C. Our results demonstrate that apoplastic expression of multiple L. perenne IBP isoforms shows promise for providing protection to crops susceptible to freeze-induced damage.

Ice-Binding Proteins in Plants

Sub-zero temperatures put plants at risk of damage associated with the formation of ice crystals in the apoplast. Some freeze-tolerant plants mitigate this risk by expressing ice-binding proteins (IBPs), that adsorb to ice crystals and modify their growth. IBPs are found across several biological kingdoms, with their ice-binding activity and function uniquely suited to the lifestyle they have evolved to protect, be it in fishes, insects or plants. While IBPs from freeze-avoidant species significantly depress the freezing point, plant IBPs typically have a reduced ability to lower the freezing temperature. Nevertheless, they have a superior ability to inhibit the recrystallization of formed ice. This latter activity prevents ice crystals from growing larger at temperatures close to melting. Attempts to engineer frost-hardy plants by the controlled transfer of IBPs from freeze-avoiding fish and insects have been largely unsuccessful. In contrast, the expression of recombinant IBP sequences from freeze-tolerant plants significantly reduced electrolyte leakage and enhanced freezing survival in freeze-sensitive plants. These promising results have spurred additional investigations into plant IBP localization and post-translational modifications, as well as a re-evaluation of IBPs as part of the anti-stress and anti-pathogen axis of freeze-tolerant plants. Here we present an overview of plant freezing stress and adaptation mechanisms and discuss the potential utility of IBPs for the generation of freeze-tolerant crops.

De Novo Assembly and Transcriptome Analysis of Bulb Onion (Allium cepa L.) during Cold Acclimation Using Contrasting Genotypes

Bulb onion (Allium cepa) is the second most widely cultivated and consumed vegetable crop in the world. During winter, cold injury can limit the production of bulb onion. Genomic resources available for bulb onion are still very limited. To date, no studies on heritably durable cold and freezing tolerance have been carried out in bulb onion genotypes. We applied high-throughput sequencing technology to cold (2°C), freezing (-5 and -15°C), and control (25°C)-treated samples of cold tolerant (CT) and cold susceptible (CS) genotypes of A. cepa lines. A total of 452 million paired-end reads were de novo assembled into 54,047 genes with an average length of 1,331 bp. Based on similarity searches, these genes were aligned with entries in the public non-redundant (nr) database, as well as KEGG and COG database. Differentially expressed genes (DEGs) were identified using log₁₀ values with the FPKM method. Among 5,167DEGs, 491 genes were differentially expressed at freezing temperature compared to the control temperature in both CT and CS libraries. The DEG results were validated with qRT-PCR. We performed GO and KEGG pathway enrichment analyses of all DEGs and iPath interactive analysis found 31 pathways including those related to metabolism of carbohydrate, nucleotide, energy, cofactors and vitamins, other amino acids and xenobiotics biodegradation. Furthermore, a large number of molecular markers were identified from the assembled genes, including simple sequence repeats (SSRs) 4,437 and SNP substitutions of transition and transversion types of CT and CS. Our study is the first to provide a transcriptome sequence resource for Allium spp. with regard to cold and freezing stress. We identified a large set of genes and determined their DEG profiles under cold and freezing conditions using two different genotypes. These data represent a valuable resource for genetic and genomic studies of Allium spp.

Review of recent transgenic studies on abiotic stress tolerance and future molecular breeding in potato

Global warming has become a major issue within the last decade. Traditional breeding programs for potato have focused on increasing productivity and quality and disease resistance, thus, modern cultivars have limited tolerance of abiotic stresses. The introgression of abiotic stress tolerance into modern cultivars is essential work for the future. Recently, many studies have investigated abiotic stress using transgenic techniques. This manuscript focuses on the study of abiotic stress, in particular drought, salinity and low temperature, during this century. Dividing studies into these three stress categories for this review was difficult. Thus, based on the study title and the transgene property, transgenic studies were classified into five categories in this review; oxidative scavengers, transcriptional factors, and above three abiotic categories. The review focuses on studies that investigate confer of stress tolerance and the identification of responsible factors, including wild relatives. From a practical application perspective, further evaluation of transgenic potato with abiotic stress tolerance is required. Although potato plants, including wild species, have a large potential for abiotic stress tolerance, exploration of the factors responsible for conferring this tolerance is still developing. Molecular breeding, including genetic engineering and conventional breeding using DNA markers, is expected to develop in the future.

Genome-wide transcriptome analysis of two contrasting Brassica rapa doubled haploid lines under cold-stresses using Br135K oligomeric chip

Genome wide transcription analysis in response to stresses is important to provide a basis of effective engineering strategies to improve stress tolerance in crop plants. We assembled a Brassica rapa oligomeric microarray (Br135K microarray) using sequence information from 41,173 unigenes and analyzed the transcription profiles of two contrasting doubled haploid (DH) lines, Chiifu and Kenshin, under cold-treatments. The two DH lines showed great differences in electrolyte leakage below −4°C, but similar patterns from 4°C to −2°C. Cold-treatments induced 885 and 858 genes in Chiifu and Kenshin, respectively. Overall, 134, and 56 genes showed an intrinsic difference in expression in Chiifu and Kenshin, respectively. Among 5,349 genes that showed no hit found (NHF) in public databases, 61 and 24 were specifically expressed in Chiifu and Kenshin, respectively. Many transcription factor genes (TFs) also showed various characteristics of expression. BrMYB12, BrMYBL2, BrbHLHs, BrbHLH038, a C2H2, a WRKY, BrDREB19 and a integrase-type TF were induced in a Chiifu-specific fashion, while a bHLH (Bra001826/AT3G21330), bHLH, cycling Dof factor and two Dof type TFs were Kenshin specific. Similar to previous studies, a large number of genes were differently induced or regulated among the two genotypes, but many genes, including NHFs, were specifically or intrinsically expressed with genotype specificity. Expression patterns of known-cold responsive genes in plants resulted in discrepancy to membrane leakage in the two DH lines, indicating that timing of gene expression is more important to conferring freezing tolerance rather than expression levels. Otherwise, the tolerance will be related to the levels of transcripts before cold-treatment or regulated by other mechanisms. Overall, these results indicate common signaling pathways and various transcriptional regulatory mechanisms are working together during cold-treatment of B. rapa. Our newly developed Br135K oligomeric microarray will be useful for transcriptome profiling, and will deliver valuable insight into cold stresses in B. rapa.

Heterologous expression of antifreeze protein gene AnAFP from Ammopiptanthus nanus enhances cold tolerance in Escherichia coli and tobacco

Antifreeze proteins are a class of polypeptides produced by certain animals, plants, fungi and bacteria that permit their survival under the subzero environments. Ammopiptanthus nanus is the unique evergreen broadleaf bush endemic to the Mid-Asia deserts. It survives at the west edge of the Tarim Basin from the disappearance of the ancient Mediterranean in the Tertiary Period. Its distribution region is characterized by the arid climate and extreme temperatures, where the extreme temperatures range from -30 °C to 40 °C. In the present study, the antifreeze protein gene AnAFP of A. nanus was used to transform Escherichia coli and tobacco, after bioinformatics analysis for its possible function. The transformed E. coli strain expressed the heterologous AnAFP gene under the induction of isopropyl β-D-thiogalactopyranoside, and demonstrated significant enhancement of cold tolerance. The transformed tobacco lines expressed the heterologous AnAFP gene in response to cold stress, and showed a less change of relative electrical conductivity under cold stress, and a less wilting phenotype after 16 h of -3 °C cold stress and thawing for 1h than the untransformed wild-type plants. All these results imply the potential value of the AnAFP gene to be used in genetic modification of commercially important crops for improvement of cold tolerance.

Antifreeze peptides and glycopeptides, and their derivatives: potential uses in biotechnology

Antifreeze proteins (AFPs) and glycoproteins (AFGPs), collectively called AF(G)Ps, constitute a diverse class of proteins found in various Arctic and Antarctic fish, as well as in amphibians, plants, and insects. These compounds possess the ability to inhibit the formation of ice and are therefore essential to the survival of many marine teleost fishes that routinely encounter sub-zero temperatures. Owing to this property, AF(G)Ps have potential applications in many areas such as storage of cells or tissues at low temperature, ice slurries for refrigeration systems, and food storage. In contrast to AFGPs, which are composed of repeated tripeptide units (Ala-Ala-Thr)_n with minor sequence variations, AFPs possess very different primary, secondary, and tertiary structures. The isolation and purification of AFGPs is laborious, costly, and often results in mixtures, making characterization difficult. Recent structural investigations into the mechanism by which linear and cyclic AFGPs inhibit ice crystallization have led to significant progress toward the synthesis and assessment of several synthetic mimics of AFGPs. This review article will summarize synthetic AFGP mimics as well as current challenges in designing compounds capable of mimicking AFGPs. It will also cover our recent efforts in exploring whether peptoid mimics can serve as structural and functional mimics of native AFGPs.

Expression of freeze-responsive proteins, Fr10 and Li16, from freeze-tolerant frogs enhances freezing survival of BmN insect cells

To date, two novel freeze-responsive proteins, Fr10 and Li16, have been discovered in the wood frog, Rana sylvatica, and likely support freezing survival. Although previous studies have established tissue distribution of each protein, there have been no studies that explore their functional consequences in intolerant cells. To assess the ability of Fr10 and Li16 to confer freeze tolerance, we transfected each protein into a freeze-intolerant silkworm cell line (BmN). Selected controls were the transfection of an unrelated protein (CAT) and a no-transfection sample. Li16 and Fr10 showed 1.8 ± 0.1- and 1.7 ± 0.2-fold, respectively, greater survival after freezing at -6°C for 1 h than did transfection controls. To investigate how these novel proteins protect cells from freezing damage, protein structures were predicted from primary amino acid sequences. Analysis of the structures indicated that Fr10 is a secreted protein and may be a new type IV antifreeze protein, whereas Li16 may have intracellular membrane associated functions. This study shows that freezing protection can be provided to intolerant cells by the overexpression of transfected Li16 and Fr10 frog proteins. Results from this study will provide new insights into adapting intolerant cells for medical organ cryoprotection using a natural vertebrate model of tolerance.

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

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

Application of genetic engineering in potato breeding

Potato breeding programmes worldwide are undergoing a period of rapid change. In order to be successful, breeders must adapt and incorporate the newest up-to-date techniques as they become available. Recent advances in biotechnology make it possible to develop and cultivate more and more sophisticated transgenic crops with multiple modified traits. Gene transfer methods can be used for a wide range of fundamental studies, contributing to a better understanding of the mechanisms of plant/pathogen interactions and the metabolic pathways in plants. Transgenic potato plants are being generated worldwide to investigate the impact of transgene expression on parameters as complex as yield. Historically, potato was one of the first successfully transformed crop plants. Nowadays, transgenic potatoes have been introduced into the food chain of people and animals in several countries. Some of the genetic modifications give potato plants increased resistance to biotic and abiotic environmental factors, while others lead to improved nutritional value, or cause the plants to produce proteins of the immune system of humans or animals or substances that may be used as vaccines in humans or veterinary medicine. The trend today is towards the generation of crops with output traits, e.g. modified starch or carotenoids, or the production of pharmaceuticals in tubers, whereas the early targets were input traits, e.g. herbicide resistance, pest or virus resistance. This review provides a summary of examples illustrating the versatility and applicability of transgenic biology in potato improvement.

Composition of transgenic Volvariella volvacea tolerant to cold stress is equivalent to that of conventional control

Transgenic Volvariella volvacea strains, which are tolerant to cold stress, were generated by the stable insertion of antifreeze protein gene isolated from budworm into the genome of a conventional variety V23 of V. volvacea. As a part of the safety assessment program, transgenic V. volvacea strains were compared to a nontransgenic near-isogenic V. volvacea strain V23 grown contemporaneously by applying the principle of substantial equivalence. Compositional analyses were conducted by measuring proximates, amino acids, fatty acids, minerals, vitamins, 5'-nucleotides, nucleic acid, and antinutrients such as tannin and cyanide in V. volvacea strains harvested at egg-shaped stage. Results of the comparisons indicate that these transgenic strains are compositionally equivalent to the conventional control.

Allene oxide cyclase from Camptotheca acuminata improves tolerance against low temperature and salt stress in tobacco and bacteria

Allene oxide cyclase (AOC, E 5.3.99.6) is an essential enzyme in jasmonate (JA) biosynthetic pathway. An AOC gene (defined as CaAOC, Database Accession No. AY863428) had been isolated from Camptotheca acuminata in previous work. Real-time quantitative PCR analysis indicated that mRNA expression of CaAOC was induced by salt stress (120 mM NaCl) and low temperature (4 degrees C). In order to further investigate the role of AOC gene in the processes, CaAOC was introduced into tobacco via Agrobacterium tumefaciens, and the transgenic lines were subjected to the examination of tolerance against salt stress and low temperature. Under salt stress, the chlorophyll content in transgenic tobacco was higher than that of in the wild plants. The electrolyte leakage test revealed that transgenic tobacco plants were more resistant to low temperature over control. Furthermore, 5'-truncated CaAOC was inserted into pET30 and then expressed in Escherichia coli strain BL21DE3 (pLysS). Interestingly, the transformants could grow on 2YT agar containing 400 mM NaCl. Although these mechanisms are not clear yet, this study suggested that CaAOC could not only be a potential target gene in the engineering of plants and bacteria for improved endurance against salt stress, but also be quite useful in enhancing plant tolerance to cold.

Expression of insect (Microdera puntipennis dzungarica) antifreeze protein MpAFP149 confers the cold tolerance to transgenic tobacco

To elucidate the function of antifreeze protein from Microdera puntipennis dzhungarica for freezing stress tolerance in plant, the construct of MpAFP149 gene with the signal peptide sequence responsible for secreting the native MpAFP149 into the apoplast space under control of a cauliflower mosaic virus 35S promoter was introduced into tobacco by Agrobacterium tumefaciens-mediated transformation. The observation of immunogold localization by TEM (transmission electron microscope) showed that the heterologous MpAFP149 protein was mainly distributed on the cell wall in apoplast of the transgenic tobacco plant. T1 generation transgenic tobacco plants displayed a more frost resistant phenotype and kept the lower ion leakage ratio and MDA (malondialdehyde) content in the leaves compared with wild-type ones at -1 degrees C for 3 days. The results showed that MpAFP149 provided protection and conferred cold tolerance to transgenic tobacco plant during freezing stress.

Targeted expression of redesigned and codon optimised synthetic gene leads to recrystallisation inhibition and reduced electrolyte leakage in spring wheat at sub-zero temperatures

Antifreeze proteins (AFPs) adsorb to ice crystals and inhibit their growth, leading to non-colligative freezing point depression. Crops like spring wheat, that are highly susceptible to frost damage, can potentially be made frost tolerant by expressing AFPs in the cytoplasm and apoplast where ice recrystallisation leads to cellular damage. The protein sequence for HPLC-6 alpha-helical antifreeze protein from winter flounder was rationally redesigned after removing the prosequences in the native protein. Wheat nuclear gene preferred amino acid codons were used to synthesize a recombinant antifreeze gene, rAFPI. Antifreeze protein was targeted to the apoplast using a Murine leader peptide sequence from the mAb24 light chain or retained in the endoplasmic reticulum using C-terminus KDEL sequence. The coding sequences were placed downstream of the rice Actin promoter and Actin-1 intron and upstream of the nopaline synthase terminator in the plant expression vectors. Transgenic wheat lines were generated through micro projectile bombardment of immature embryos of spring wheat cultivar Seri 82. Levels of antifreeze protein in the transgenic lines without any targeting peptide were low (0.06-0.07%). The apoplast-targeted protein reached a level of 1.61% of total soluble protein, 90% of which was present in the apoplast. ER-retained protein accumulated in the cells at levels up to 0.65% of total soluble proteins. Transgenic wheat line T-8 with apoplast-targeted antifreeze protein exhibited the highest levels of antifreeze activity and provided significant freezing protection even at temperatures as low as -7 degrees C.

Stable transmission and transcription of newfoundland ocean pout type III fish antifreeze protein (AFP) gene in transgenic mice and hypothermic storage of transgenic ovary and testis

Here we describe the generation of transgenic mice carrying type III fish antifreeze protein (AFP) gene and evaluate whether AFP type III protects transgenic mouse ovaries and testes from hypothermic storage. AFPs exist in many different organisms. In fish, AFPs protect the host from freezing at temperatures below the colligative freezing point by adsorbing to the surface of nucleating ice crystals and inhibiting their growth. The transgenic expression of AFP holds great promise for conferring freeze-resistant plant and animal species. AFP also exhibits a potential for the cryopreservation of tissues and cells. In this study, we have generated 42 founder mice harboring the Newfoundland ocean pout (OP5A) type III AFP transgene and established one transgenic line (the line #6). This study demonstrated that AFP gene construct has been stably transmitted to the mouse progeny in the F3 generations in the line #6. Furthermore, the presence of AFP transcripts was confirmed by RT-PCR analysis on cDNAs from liver, kidney, ovarian, and testis tissues of the mouse from F3 generation in this line. These results indicate that ocean pout type III AFP gene could be integrated and transmitted to the next generation and stably transcribed in transgenic mice. In histological analysis of testis and ovarian tissues of nontransgenic control and AFP transgenic mice it has been shown that both tissues of AFP transgenic mice were protected from hypothermic storage (+4 degrees C). The AFP III transgenic mice obtained for the first time in this study would be useful for investigating the biological functions of AFP in mammalian systems and also its potential role in cryopreservation.

Cold-loving microbes, plants, and animals--fundamental and applied aspects

Microorganisms, plants, and animals have successfully colonized cold environments, which represent the majority of the biosphere on Earth. They have evolved special mechanisms to overcome the life-endangering influence of low temperature and to survive freezing. Cold adaptation includes a complex range of structural and functional adaptations at the level of all cellular constituents, such as membranes, proteins, metabolic activity, and mechanisms to avoid the destructive effect of intracellular ice formation. These strategies offer multiple biotechnological applications of cold-adapted organisms and/or their products in various fields. In this review, we describe the mechanisms of microorganisms, plants, and animals to cope with the cold and the resulting biotechnological perspectives.

Housekeeping gene selection for real-time RT-PCR normalization in potato during biotic and abiotic stress

Plant stress studies are more and more based on gene expression. The analysis of gene expression requires sensitive, precise, and reproducible measurements for specific mRNA sequences. Real-time RT-PCR is at present the most sensitive method for the detection of low abundance mRNA. To avoid bias, real-time RT-PCR is referred to one or several internal control genes, which should not fluctuate during treatments. Here, the non-regulation of seven housekeeping genes (beta-tubulin, cyclophilin, actin, elongation factor 1-alpha (ef1alpha), 18S rRNA, adenine phosphoribosyl transferase (aprt), and cytoplasmic ribosomal protein L2) during biotic (late blight) and abiotic stresses (cold and salt stress) was tested on potato plants using geNorm software. Results from the three experimental conditions indicated that ef1alpha was the most stable among the seven tested. The expression of the other housekeeping genes tested varied upon stress. In parallel, a study of the variability of expression of hsp20.2, shown to be implicated in late blight stress, was realized. The relative quantification of the hsp20.2 gene varied according to the internal control and the number of internal controls used, thus highlighting the importance of the choice of internal controls in such experiments.

Antifreeze proteins in overwintering plants: a tale of two activities

Antifreeze proteins are found in a wide range of overwintering plants where they inhibit the growth and recrystallization of ice that forms in intercellular spaces. Unlike antifreeze proteins found in fish and insects, plant antifreeze proteins have multiple, hydrophilic ice-binding domains. Surprisingly, antifreeze proteins from plants are homologous to pathogenesis-related proteins and also provide protection against psychrophilic pathogens. In winter rye (Secale cereale), antifreeze proteins accumulate in response to cold, short daylength, dehydration and ethylene, but not pathogens. Transferring single genes encoding antifreeze proteins to freezing-sensitive plants lowered their freezing temperatures by approximately 1 degrees C. Genes encoding dual-function plant antifreeze proteins are excellent models for use in evolutionary studies to determine how genes acquire new expression patterns and how proteins acquire new activities.

Acquired tolerance to temperature extremes

Acquired tolerance to temperature stresses is a major protective mechanism. Recent advances have revealed key components of stress signal transduction pathways that trigger enhanced tolerance, and several determinants of acquired tolerance have been identified. Although high and low temperature stresses impose different metabolic and physical challenges, acquired tolerance appears to involve general as well as stress-specific components. Transcriptome studies and other genomic-scale approaches have accelerated the pace of gene discovery, and will be invaluable in efforts to integrate all the different protective and repair mechanisms that function in concert to confer acquired tolerance.

Plants in a cold climate

Plants are able to survive prolonged exposure to sub-zero temperatures; this ability is enhanced by pre-exposure to low, but above-zero temperatures. This process, known as cold acclimation, is briefly reviewed from the perception of cold, through transduction of the low-temperature signal to functional analysis of cold-induced gene products. The stresses that freezing of apoplastic water imposes on plant cells is considered and what is understood about the mechanisms that plants use to combat those stresses discussed, with particular emphasis on the role of the extracellular matrix.

Biotechnological applications of plant freezing associated proteins

Plants use a wide array of proteins to protect themselves against low temperature and freezing conditions. The identification of these freezing tolerance associated proteins and the elucidation of their cryoprotective functions will have important applications in several fields. Genes encoding structural proteins, osmolyte producing enzymes, oxidative stress scavenging enzymes, lipid desaturases and gene regulators have been used to produce transgenic plants. These studies have revealed the potential capacity of different genes to protect against temperature related stresses. In some cases, transgenic plants with significant cold tolerance have been produced. Furthermore, the biochemical characterization of the cold induced antifreeze proteins and dehydrins reveals many applications in the food and the medical industries. These proteins are being considered as food additives to improve the quality and shelf-life of frozen foods, as cryoprotective agents for organ and cell cryopreservation, and as chemical adjuvant in cancer cryosurgery.

Thermal hysteresis proteins

Extreme environments present a wealth of biochemical adaptations. Thermal hysteresis proteins (THPs) have been found in vertebrates, invertebrates, plants, bacteria and fungi and are able to depress the freezing point of water (in the presence of ice crystals) in a non-colligative manner by binding to the surface of nascent ice crystals. The THPs comprise a disparate group of proteins with a variety of tertiary structures and often no common sequence similarities or structural motifs. Different THPs bind to different faces of the ice crystal, and no single mechanism has been proposed to account for THP ice binding affinity and specificity. Experimentally THPs have been used in the cryopreservation of tissues and cells and to induce cold tolerance in freeze susceptible organisms. THPs represent a remarkable example of parallel and convergent evolution with different proteins being adapted for an anti-freeze role.

Increased nutritive value of transgenic potato by expressing a nonallergenic seed albumin gene from Amaranthus hypochondriacus

Improvement of nutritive value of crop plants, in particular the amino acid composition, has been a major long-term goal of plant breeding programs. Toward this end, we reported earlier the cloning of the seed albumin gene AmA1 from Amaranthus hypochondriacus. The AmA1 protein is nonallergenic in nature and is rich in all essential amino acids, and the composition corresponds well with the World Health Organization standards for optimal human nutrition. In an attempt to improve the nutritional value of potato, the AmA1 coding sequence was successfully introduced and expressed in tuber-specific and constitutive manner. There was a striking increase in the growth and production of tubers in transgenic populations and also of the total protein content with an increase in most essential amino acids. The expressed protein was localized in the cytoplasm as well as in the vacuole of transgenic tubers. Thus we have been able to use a seed albumin gene with a well-balanced amino acid composition as a donor protein to develop a transgenic crop plant. The results document, in addition to successful nutritional improvement of potato tubers, the feasibility of genetically modifying other crop plants with novel seed protein composition.

Increased nutritive value of transgenic potato by expressing a nonallergenic seed albumin gene from Amaranthus hypochondriacus

Improvement of nutritive value of crop plants, in particular the amino acid composition, has been a major long-term goal of plant breeding programs. Toward this end, we reported earlier the cloning of the seed albumin gene AmA1 from Amaranthus hypochondriacus. The AmA1 protein is nonallergenic in nature and is rich in all essential amino acids, and the composition corresponds well with the World Health Organization standards for optimal human nutrition. In an attempt to improve the nutritional value of potato, the AmA1 coding sequence was successfully introduced and expressed in tuber-specific and constitutive manner. There was a striking increase in the growth and production of tubers in transgenic populations and also of the total protein content with an increase in most essential amino acids. The expressed protein was localized in the cytoplasm as well as in the vacuole of transgenic tubers. Thus we have been able to use a seed albumin gene with a well-balanced amino acid composition as a donor protein to develop a transgenic crop plant. The results document, in addition to successful nutritional improvement of potato tubers, the feasibility of genetically modifying other crop plants with novel seed protein composition.

Type II fish antifreeze protein accumulation in transgenic tobacco does not confer frost resistance

Type II fish antifreeze protein (AFP) is active in both freezing point depression and the inhibition of ice recrystallization. This extensively disulfide-bonded 14 kDa protein was targeted for accumulation in its pro- and mature forms in the cytosol and apoplast of transgenic tobacco plants. Type II AFP gene constructs under control of a duplicate cauliflower mosaic virus 35S promoter, both with and without a native plant transit peptide sequence, were introduced into tobacco by Agrobacterium tumefaciens-mediated transformation. AFP did not accumulate in the cytosol of transgenic plants, but active AFP was present as 2% the total protein present in the apoplast. Plant-produced AFP was the same size as mature Type II AFP isolated from fish, and was comparable to wild-type AFP in thermal hysteresis activity and its effect on ice crystal morphology. Field trials conducted in late summer on R1 generation transgenic plants showed similar AFP accumulation in plants under field conditions at levels suitable for large-scale production: but no difference in frost resistance was observed between transgenic and wild-type plants during the onset of early fall frosts.