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

Characterization of the bark storage protein gene (JcBSP) family in the perennial woody plant Jatropha curcas and the function of JcBSP1 in Arabidopsis thaliana

BACKGROUND

Bark storage protein (BSP) plays an important role in seasonal nitrogen cycling in perennial deciduous trees. However, there is no report on the function of BSP in the perennial woody oil plant Jatropha curcas.

METHODS

In this study, we identified six members of JcBSP gene family in J. curcas genome. The patterns, seasonal changes, and responses to nitrogen treatment in gene expression of JcBSPs were detected by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Overexpression of JcBSP1 in transgenic Arabidopsis thaliana was driven by a constitutive cauliflower mosaic virus (CaMV) 35S RNA promoter.

RESULTS

JcBSP members were found to be expressed in various tissues, except seeds. The seasonal changes in the total protein concentration and JcBSP1 expression in the stems of J. curcas were positively correlated, as both increased in autumn and winter and decreased in spring and summer. In addition, the JcBSP1 expression in J. curcas seedlings treated with different concentrations of an NH₄NO₃ solution was positively correlated with the NH₄NO₃ concentration and application duration. Furthermore, JcBSP1 overexpression in Arabidopsis resulted in a phenotype of enlarged rosette leaves, flowers, and seeds, and significantly increased the seed weight and yield in transgenic plants.

Employing CRISPR/Cas Technology for the Improvement of Potato and Other Tuber Crops

New breeding technologies have not only revolutionized biological science, but have also been employed to generate transgene-free products. Genome editing is a powerful technology that has been used to modify genomes of several important crops. This review describes the basic mechanisms, advantages and disadvantages of genome editing systems, such as ZFNs, TALENs, and CRISPR/Cas. Secondly, we summarize in detail all studies of the CRISPR/Cas system applied to potato and other tuber crops, such as sweet potato, cassava, yam, and carrot. Genes associated with self-incompatibility, abiotic-biotic resistance, nutrient-antinutrient content, and post-harvest factors targeted utilizing the CRISPR/Cas system are analyzed in this review. We hope that this review provides fundamental information that will be useful for future breeding of tuber crops to develop novel cultivars.

Plant Platforms for Efficient Heterologous Protein Production

Production of recombinant proteins is primarily established in cultures of mammalian, insect and bacterial cells. Concurrently, concept of using plants to produce high-value pharmaceuticals such as vaccines, antibodies, and dietary proteins have received worldwide attention. Newer technologies for plant transformation such as plastid engineering, agroinfiltration, magnifection, and deconstructed viral vectors have been used to enhance the protein production in plants along with the inherent advantage of speed, scale, and cost of production in plant systems. Production of therapeutic proteins in plants has now a more pragmatic approach when several plant-produced vaccines and antibodies successfully completed Phase I clinical trials in humans and were further scheduled for regulatory approvals to manufacture clinical grade products on a large scale which are safe, efficacious, and meet the quality standards. The main thrust of this review is to summarize the data accumulated over the last two decades and recent development and achievements of the plant derived therapeutics. It also attempts to discuss different strategies employed to increase the production so as to make plants more competitive with the established production systems in this industry.

The 21st Century Agriculture: When Rice Research Draws Attention to Climate Variability and How Weedy Rice and Underutilized Grains Come in Handy

Rice, the first crop to be fully sequenced and annotated in the mid-2000s, is an excellent model species for crop research due mainly to its relatively small genome and rich genetic diversity. The 130-million-year-old cereal came into the limelight in the 1960s when the semi-dwarfing gene sd-1, better known as the "green revolution" gene, resulted in the establishment of a high-yielding semi-dwarf variety IR8. Deemed as the miracle rice, IR8 saved millions of lives and revolutionized irrigated rice farming particularly in the tropics. The technology, however, spurred some unintended negative consequences, especially in prompting ubiquitous monoculture systems that increase agricultural vulnerability to extreme weather events and climate variability. One feasible way to incorporate resilience in modern rice varieties with narrow genetic backgrounds is by introgressing alleles from the germplasm of its weedy and wild relatives, or perhaps from the suitable underutilized species that harbor novel genes responsive to various biotic and abiotic stresses. This review reminisces the fascinating half-century journey of rice research and highlights the potential utilization of weedy rice and underutilized grains in modern breeding programs. Other possible alternatives to improve the sustainability of crop production systems in a changing climate are also discussed.

Genome-wide identification and characterization of seed storage proteins (SSPs) of foxtail millet (Setaria italica (L.) P. Beauv.)

We report the identification of 47 foxtail millet (Setaria italica (L.) P. Beauv.) seed storage proteins (SSPs) consisting of 14 albumins, 12 prolamins, 18 globulins and 3 glutelins using computational approaches and compared their essential amino acid composition with 225 SSPs of rice, barley, sorghum and maize. Comparative analysis revealed several unique foxtail millet SSPs containing high amounts of essential amino acids. These include three 2s-albumin proteins containing 11.9%, 10.9%, 9.82% lysine, one 10-kDa prolamin containing 20% methionine residues and one each 7S-globulin, 10-kDa prolamin, alpha-zein proteins containing 9.2% threonine, 9.35% phenylalanine and 2.5% tryptophan, respectively. High lysine containing albumins and high methionine containing prolamins were also detected in other cereals indicating that these SSPs are widespread in cereals. Phylogenetic studies revealed that the foxtail millet SSPs are closer to sorghum and maize. The lysine-rich albumins and the methionine-rich prolamins formed a separate cluster. Motif analysis of lysine-rich albumins displayed several lysine containing conserved motifs across cereals including foxtail millet. The 10-kDa prolamin protein containing 20% methionine was unique as it lacked the characteristic repeat motifs of methionine found in the high methionine containing zeins and kafirins. The motif "NPAAFWQQQQLL" was uniquely repeated in the foxtail millet high tryptophan prolamin protein. The findings of the present study provide new insights in foxtail millet seed storage protein characterization and their nutritional importance in terms of essential amino acid composition.

Embryo-specific expression of a visual reporter gene as a selection system for citrus transformation

The embryo-specific Dc3 gene promoter driving the VvMybA1 anthocyanin regulatory gene was used to develop a visual selection system for the genetic transformation of citrus. Agrobacterium-mediated transformation of cell suspension cultures resulted in the production of purple transgenic somatic embryos that could be easily separated from the green non-transgenic embryos. The somatic embryos produced phenotypically normal plants devoid of any visual purple coloration. These results were also confirmed using protoplast transformation. There was minimal gene expression in unstressed one-year-old transgenic lines. Cold and drought stress did not have any effect on gene expression, while exogenous ABA and NaCl application resulted in a minor change in gene expression in several transgenic lines. When gas exchange was measured in intact leaves, the transgenic lines were similar to controls under the same environment. Our results provide conclusive evidence for the utilization of a plant-derived, embryo-specific visual reporter system for the genetic transformation of citrus. Such a system could aid in the development of an all-plant, consumer-friendly GM citrus tree.

Genetic Engineering: A Possible Strategy for Protein-Energy Malnutrition Regulation

Protein-energy malnutrition (PEM) has adversely affected the generations of developing countries. It is a syndrome that in severity causes death. PEM generally affects infants of 1-5 age group. This manifestation is maintained till adulthood in the form of poor brain and body development. The developing nations are continuously making an effort to curb PEM. However, it is still a prime concern as it was in its early years of occurrence. Transgenic crops with high protein and enhanced nutrient content have been successfully developed. Present article reviews the studies documenting genetic engineering-mediated improvement in the pulses, cereals, legumes, fruits and other crop plants in terms of nutritional value, stress tolerance, longevity and productivity. Such genetically engineered crops can be used as a possible remedial tool to eradicate PEM.

Production of Marker-free Transgenic Rice (Oryza sativa L.) with Improved Nutritive Quality Expressing AmA1

Background: Rice seed proteins are lacking essential amino acids (EAAs). Genetic engineering offers a fast and sustainable method to solve this problem as it allows the specific expression of heterologous EAA-rich proteins. The use of selectable marker gene is essential for generation of transgenic crops, but might also lead to potential environmental and food safety problems. Therefore, the production of marker-free transgenic crops is becoming an extremely attractive alternative and could contribute to the public acceptance of transgenic crops. Objectives: The present study was conducted to examine whether AmA1 can be expressed specifically in rice seeds, and generate marker-free transgenic rice with improved nutritive value. Materials and Methods:AmA1 was transferred into rice using Agrobacterium-mediated co-transformation system with a twin T-DNA binary vector and its integration in rice genome was confirmed by southern blot. Transcription of AmA1 was analyzed by Real-Time PCR and its expression was verified by western analysis. Protein and amino acid content were measured by the Kjeldahl method and the high-speed amino acid analyzer, respectively. Results: Five selectable marker-free homozygous transgenic lines were obtained from the progeny. The expression of recombinant AmA1 was confirmed by the observation of a 35 kDa band in SDS-PAGE and western blot. Compared to the wild-type control, the total protein contents in the seeds of five homozygous lines were increased by 1.06~12.87%. In addition, the content of several EAAs, including lysine, threonine, and valine was increased significantly in the best expressing line. Conclusions: The results indicated that the amino acid composition of rice grain could be improved by seed-specific expression of AmA1.

Genetically modified (GM) crops: milestones and new advances in crop improvement

New advances in crop genetic engineering can significantly pace up the development of genetically improved varieties with enhanced yield, nutrition and tolerance to biotic and abiotic stresses. Genetically modified (GM) crops can act as powerful complement to the crops produced by laborious and time consuming conventional breeding methods to meet the worldwide demand for quality foods. GM crops can help fight malnutrition due to enhanced yield, nutritional quality and increased resistance to various biotic and abiotic stresses. However, several biosafety issues and public concerns are associated with cultivation of GM crops developed by transgenesis, i.e., introduction of genes from distantly related organism. To meet these concerns, researchers have developed alternative concepts of cisgenesis and intragenesis which involve transformation of plants with genetic material derived from the species itself or from closely related species capable of sexual hybridization, respectively. Recombinase technology aimed at site-specific integration of transgene can help to overcome limitations of traditional genetic engineering methods based on random integration of multiple copy of transgene into plant genome leading to gene silencing and unpredictable expression pattern. Besides, recently developed technology of genome editing using engineered nucleases, permit the modification or mutation of genes of interest without involving foreign DNA, and as a result, plants developed with this technology might be considered as non-transgenic genetically altered plants. This would open the doors for the development and commercialization of transgenic plants with superior phenotypes even in countries where GM crops are poorly accepted. This review is an attempt to summarize various past achievements of GM technology in crop improvement, recent progress and new advances in the field to develop improved varieties aimed for better consumer acceptance.

Ectopic expression of amaranth seed storage albumin modulates photoassimilate transport and nutrient acquisition in sweetpotato

Storage proteins in plants, because of high nutrient value, have been a subject of intensive investigation. These proteins are synthesized de novo in the cytoplasm and transported to the storage organelles where they serve as reservoir of energy and supplement of nitrogen during rapid growth and development. Sweetpotato is the seventh most important food crop worldwide, and has a significant contribution to the source of nutrition, albeit with low protein content. To determine the behaviour of seed storage proteins in non-native system, a seed albumin, AmA1, was overexpressed in sweetpotato with an additional aim of improving nutritional quality of tuber proteins. Introduction of AmA1 imparted an increase in protein and amino acid contents as well as the phytophenols. The proteometabolomics analysis revealed a rebalancing of the proteome, with no significant effects on the global metabolome profile of the transgenic tubers. Additionally, the slower degradation of starch and cellulose in transgenic tubers, led to increased post-harvest durability. Present study provides a new insight into the role of a seed storage protein in the modulation of photoassimilate movement and nutrient acquisition.

Revealing the seed proteome of the health benefitting grain amaranth (Amaranthus cruentus L.)

Amaranth, a staple food source in ancient Aztec, Maya and Inca cultures, has been recognized as a 21st century crop. This superfood, known as Inca wheat, attracts the worldwide attention of researchers and farmers for its superior agronomical and technological properties but especially because of its exceptional nutritive value. A combination of two-dimensional electrophoresis (2-DE) with MS facilitating the effective differentiation of 13 classes of

Global hunger: a challenge to agricultural, food, and nutritional sciences

Hunger has been a concern for generations and has continued to plague hundreds of millions of people around the world. Although many efforts have been devoted to reduce hunger, challenges such as growing competitions for natural resources, emerging climate changes and natural disasters, poverty, illiteracy, and diseases are posing threats to food security and intensifying the hunger crisis. Concerted efforts of scientists to improve agricultural and food productivity, technology, nutrition, and education are imperative to facilitate appropriate strategies for defeating hunger and malnutrition. This paper provides some aspects of world hunger issues and summarizes the efforts and measures aimed to alleviate food problems from the food and nutritional sciences perspectives. The prospects and constraints of some implemented strategies for alleviating hunger and achieving sustainable food security are also discussed. This comprehensive information source could provide insights into the development of a complementary framework for dealing with the global hunger issue.

Reduction of oxalate levels in tomato fruit and consequent metabolic remodeling following overexpression of a fungal oxalate decarboxylase

The plant metabolite oxalic acid is increasingly recognized as a food toxin with negative effects on human nutrition. Decarboxylative degradation of oxalic acid is catalyzed, in a substrate-specific reaction, by oxalate decarboxylase (OXDC), forming formic acid and carbon dioxide. Attempts to date to reduce oxalic acid levels and to understand the biological significance of OXDC in crop plants have met with little success. To investigate the role of OXDC and the metabolic consequences of oxalate down-regulation in a heterotrophic, oxalic acid-accumulating fruit, we generated transgenic tomato (Solanum lycopersicum) plants expressing an OXDC (FvOXDC) from the fungus Flammulina velutipes specifically in the fruit. These E8.2-OXDC fruit showed up to a 90% reduction in oxalate content, which correlated with concomitant increases in calcium, iron, and citrate. Expression of OXDC affected neither carbon dioxide assimilation rates nor resulted in any detectable morphological differences in the transgenic plants. Comparative proteomic analysis suggested that metabolic remodeling was associated with the decrease in oxalate content in transgenic fruit. Examination of the E8.2-OXDC fruit proteome revealed that OXDC-responsive proteins involved in metabolism and stress responses represented the most substantially up- and down-regulated categories, respectively, in the transgenic fruit, compared with those of wild-type plants. Collectively, our study provides insights into OXDC-regulated metabolic networks and may provide a widely applicable strategy for enhancing crop nutritional value.

The contribution of transgenic plants to better health through improved nutrition: opportunities and constraints

Malnutrition is a prevalent and entrenched global socioeconomic challenge that reflects the combined impact of poverty, poor access to food, inefficient food distribution infrastructure, and an over-reliance on subsistence mono-agriculture. The dependence on staple cereals lacking many essential nutrients means that malnutrition is endemic in developing countries. Most individuals lack diverse diets and are therefore exposed to nutrient deficiencies. Plant biotechnology could play a major role in combating malnutrition through the engineering of nutritionally enhanced crops. In this article, we discuss different approaches that can enhance the nutritional content of staple crops by genetic engineering (GE) as well as the functionality and safety assessments required before nutritionally enhanced GE crops can be deployed in the field. We also consider major constraints that hinder the adoption of GE technology at different levels and suggest policies that could be adopted to accelerate the deployment of nutritionally enhanced GE crops within a multicomponent strategy to combat malnutrition.

Generation and immunogenicity of transgenic potato expressing the GP5 protein of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important pathogen that has caused huge economic losses in the global swine industry. The advent of molecular farming has provided a cost-effective strategy for the development of transgenic plants as bioreactors to produce recombinant proteins. In this study, transgenic potato expressing GP5 protein of PRRSV was produced by Agrobacterium-mediated transformation, and confirmed using Southern blot and RT-PCR analyses. Recombinant GP5 protein was detected by ELISA and Western blot analyses. Mice immunized with transgenic potato extracts generated both serum and gut mucosal-specific antibodies, although low levels of neutralizing antibodies were elicited. This study provides a new approach for the production of vaccines against PRRSV.

Transgenic biofortification of the starchy staple cassava (Manihot esculenta) generates a novel sink for protein

Although calorie dense, the starchy, tuberous roots of cassava provide the lowest sources of dietary protein within the major staple food crops (Manihot esculenta Crantz). (Montagnac JA, Davis CR, Tanumihardjo SA. (2009) Compr Rev Food Sci Food Saf 8:181-194). Cassava was genetically modified to express zeolin, a nutritionally balanced storage protein under control of the patatin promoter. Transgenic plants accumulated zeolin within de novo protein bodies localized within the root storage tissues, resulting in total protein levels of 12.5% dry weight within this tissue, a fourfold increase compared to non-transgenic controls. No significant differences were seen for morphological or agronomic characteristics of transgenic and wild type plants in the greenhouse and field trials, but relative to controls, levels of cyanogenic compounds were reduced by up to 55% in both leaf and root tissues of transgenic plants. Data described here represent a proof of concept towards the potential transformation of cassava from a starchy staple, devoid of storage protein, to one capable of supplying inexpensive, plant-based proteins for food, feed and industrial applications.

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.

Next-generation protein-rich potato expressing the seed protein gene AmA1 is a result of proteome rebalancing in transgenic tuber

Protein deficiency is the most crucial factor that affects physical growth and development and that increases morbidity and mortality especially in developing countries. Efforts have been made to improve protein quality and quantity in crop plants but with limited success. Here, we report the development of transgenic potatoes with enhanced nutritive value by tuber-specific expression of a seed protein, AmA1 (Amaranth Albumin 1), in seven genotypic backgrounds suitable for cultivation in different agro-climatic regions. Analyses of the transgenic tubers revealed up to 60% increase in total protein content. In addition, the concentrations of several essential amino acids were increased significantly in transgenic tubers, which are otherwise limited in potato. Moreover, the transgenics also exhibited enhanced photosynthetic activity with a concomitant increase in total biomass. These results are striking because this genetic manipulation also resulted in a moderate increase in tuber yield. The comparative protein profiling suggests that the proteome rebalancing might cause increased protein content in transgenic tubers. Furthermore, the data on field performance and safety evaluation indicate that the transgenic potatoes are suitable for commercial cultivation. In vitro and in vivo studies on experimental animals demonstrate that the transgenic tubers are also safe for human consumption. Altogether, these results emphasize that the expression of AmA1 is a potential strategy for the nutritional improvement of food crops.

Genetic engineering to enhance crop-based phytonutrients (nutraceuticals) to alleviate diet-related diseases

Nutrition studies have provided unambiguous evidence that a number of human health maladies including chronic coronary artery, hypertension, diabetes, osteoporosis, cancer and age- and lifestyle-related diseases are associated with the diet. Several favorable and a few deleterious natural dietary ingredients have been identified that predispose human populations to various genetic and epigenetic based disorders. Media dissemination of this information has greatly raised public awareness of the beneficial effects due to increased consumption of fruit, vegetables and whole grain cereals-foods rich in phytonutrients, protein and fiber. However, the presence of intrinsically low levels of the beneficial phytonutrients in the available genotypes of crop plants is not always at par with the recommended daily allowance (RDA) for different phytonutrients (nutraceuticals). Molecular engineering of crop plants has offered a number of tools to markedly enhance intracellular concentrations of some of the beneficial nutrients, levels that, in some cases, are closer to the RDA threshold. This review brings together literature on various strategies utilized for bioengineering both major and minor crops to increase the levels of desirable phytonutrients while also decreasing the concentrations of deleterious metabolites. Some of these include increases in: protein level in potato; lysine in corn and rice; methionine in alfalfa; carotenoids (beta-carotene, phytoene, lycopene, zeaxanthin and lutein) in rice, potato, canola, tomato; choline in tomato; folates in rice, corn, tomato and lettuce; vitamin C in corn and lettuce; polyphenolics such as flavonol, isoflavone, resveratrol, chlorogenic acid and other flavonoids in tomato; anthocyanin levels in tomato and potato; alpha-tocopherol in soybean, oil seed, lettuce and potato; iron and zinc in transgenic rice. Also, molecular engineering has succeeded in considerably reducing the levels of the offending protein glutelin in rice, offering proof of concept and a new beginning for the development of super-low glutelin cereals for celiac disease patients.

Levels and Stability of Expression of Transgenes

It is well known that in a given cell, at a particular time, only a fraction of the entire genome is expressed. Expression of a gene, nuclear, or organellar starts with the onset of transcription and ends in the synthesis of the functional protein. The regulation of gene expression is a complex process that requires the coordinated activity of different proteins and nucleic acids that ultimately determine whether a gene is transcribed, and if transcribed, whether it results in the production of a protein that develops a phenotype. The same also holds true for transgenic crops, which lie at the very core of insert design.

There are multiple checkpoints at which the expression of a gene can be regulated and controlled. Much of the emphasis of studies related to gene expression has been on regulation of gene transcription, and a number of methods are used to effect the control of gene expression. Controlling transgene expression for a commercially valuable trait is necessary to capture its value. Many gene functions are either lethal or produce severe deformity (resulting in loss of value) if over-expressed. Thus, expression of a transgene at a particular site or in response to a particular elicitor is always desirable.

Transgenic approach to improve wheat (Triticum aestivum L.) nutritional quality

An amaranth (Amaranthus hypochondriacus) albumin gene, encoding the 35-kDa AmA1 protein of the seed, with a high content of essential amino acids, was used in the biolistic transformation of bread wheat (Triticum aestivum L.) variety Cadenza. The transformation cassette carried the ama1 gene under the control of a powerful wheat endosperm-specific promoter (1Bx17 HMW-GS). Southern-blot analysis of T(1) lines confirmed the integration of the foreign gene, while RT-PCR and Western-blot analyses of the samples confirmed the transcription and translation of the transgene. The effects of the extra albumin protein on the properties of flour, produced from bulked T(2) seeds, were calculated using total protein and essential amino acid content analysis, polymeric/monomeric protein and HMW/LMW glutenin subunit ratio measurements. The results indicated that not only can essential amino acid content be increased, but some parameters associated with functional quality may also be improved because of the expression of the AmA1 protein.

Plants as bioreactors: Recent developments and emerging opportunities

In recent years, the use of plants as bioreactors has emerged as an exciting area of research and significant advances have created new opportunities. The driving forces behind the rapid growth of plant bioreactors include low production cost, product safety and easy scale up. As the yield and concentration of a product is crucial for commercial viability, several strategies have been developed to boost up protein expression in transgenic plants. Augmenting tissue-specific transcription, elevating transcript stability, tissue-specific targeting, translation optimization and sub-cellular accumulation are some of the strategies employed. Various kinds of products that are currently being produced in plants include vaccine antigens, medical diagnostics proteins, industrial and pharmaceutical proteins, nutritional supplements like minerals, vitamins, carbohydrates and biopolymers. A large number of plant-derived recombinant proteins have reached advanced clinical trials. A few of these products have already been introduced in the market.

Performing IgE serum testing due to bioinformatics matches in the allergenicity assessment of GM crops

Proteins introduced into genetically modified (GM) organisms through genetic engineering must be evaluated for their potential to cause allergic disease under various national laws and regulations. The Codex Alimentarius Commission guidance document (2003) calls for testing of serum IgE binding to the introduced protein if the gene was from an allergenic source, or the sequence of the transferred protein has >35% identity in any segment of 80 or more amino acids to a known allergen or shares significant short amino acid identities. The Codex guidance recognized that the assessment will evolve based on new scientific knowledge. Arguably, the current criteria are too conservative as discussed in this paper and they do not provide practical guidance on serum testing. The goals of this paper are: (1) to summarize evidence supporting the level of identity that indicates potential risk of cross-reactivity for those with existing allergies; (2) to provide example bioinformatics results and discuss their interpretation using published examples of proteins expressed in transgenic crops; and (3) to discuss key factors of experimental design and methodology for serum IgE tests to minimize the rate of false negative and false positive identification of potential allergens and cross-reactive proteins.

A rice promoter containing both novel positive and negative cis-elements for regulation of green tissue-specific gene expression in transgenic plants

The tissue-specific expression of transgenes is essential in plant breeding programmes to avoid the fitness costs caused by constitutive expression of a target gene. However, knowledge on the molecular mechanisms of tissue-specific gene expression and practicable tissue-specific promoters is limited. In this study, we identified the cis-acting elements of a tissue-specific promoter from rice, P(D54O), and tested the application of original and modified P(D54O) and its cis-elements in the regulation of gene expression. P(D54O) is a green tissue-specific promoter. Five novel tissue-specific cis-elements (LPSE1, LPSE2, LPSRE1, LPSRE2, PSE1) were characterized from P(D54O). LPSE1 activated gene expression in leaf and young panicle. LPSRE2 suppressed gene expression in leaf, root, young panicle and stem, and PSE1 suppressed gene expression in young panicle and stem. LPSRE1 and LPSE2 had dual roles in the regulation of tissue-specific gene expression; both functioned as activators in leaf, but LPSRE1 acted as a repressor in stem and LPSE2 as a repressor in young panicle and root. Transgenic rice plants carrying cry1Ac encoding Bacillus thuringiensis endotoxin, regulated by P(D54O), were resistant to leaf-folders, with no Cry1Ac protein found in endosperm or embryo. A reporter gene regulated by a series of truncated P(D54O) showed various tissue-specific expression patterns. Different fragments of P(D54O) fused with the constitutive cauliflower mosaic virus 35S promoter suppressed 35S-regulated gene expression in various tissues. P(D54O), truncated P(D54O) and the tissue-specific cis-elements provide useful tools for the regulation of tissue-specific gene expression in rice breeding programmes.

Transgenic maize endosperm containing a milk protein has improved amino acid balance

In order to meet the protein nutrition needs of the world population, greater reliance on plant protein sources will become necessary. The amino acid balance of most plant protein sources does not match the nutritional requirements of monogastric animals, limiting their nutritional value. In cereals, the essential amino acid lysine is deficient. Maize is a major component of human and animal diets worldwide and especially where sources of plant protein are in critical need such as sub-Saharan Africa. To improve the amino acid balance of maize, we developed transgenic maize lines that produce the milk protein alpha-lactalbumin in the endosperm. Lines in which the transgene was inherited as a single dominant genetic locus were identified. Sibling kernels with or without the transgene were compared to determine the effect of the transgene on kernel traits in lines selected for their high content of alpha-lactalbumin. Total protein content in endosperm from transgene positive kernels was not significantly different from total protein content in endosperm from transgene negative kernels in three out of four comparisons, whereas the lysine content of the lines examined was 29-47% greater in endosperm from transgene positive kernels. The content of some other amino acids was changed to a lesser extent. Taken together, these changes resulted in the transgenic endosperms having an improved amino acid balance relative to non-transgenic endosperms produced on the same ear. Kernel appearance, weight, density and zein content did not exhibit substantial differences in kernels expressing the transgene when compared to non-expressing siblings. Assessment of the antigenicity and impacts on animal health will be required in order to determine the overall value of this technology.

Enhancement of essential amino acid contents in crops by genetic engineering and protein design

The importance and urgency of providing humans and animals with quality proteins are reflected in the growing scientific and industrial interest in augmenting the nutritive value of the world's protein sources. Such nutritive value is determined by the protein content in 'essential amino acids', those that cannot be synthesized de novo and that must be supplied from the diet. It is the object of this review to discuss recent advances in the genetic modification of crops that aim to provide enhanced quantities of essential amino acids.

Allermatch, a webtool for the prediction of potential allergenicity according to current FAO/WHO Codex alimentarius guidelines

Background

Novel proteins entering the food chain, for example by genetic modification of plants, have to be tested for allergenicity. Allermatch™ is a webtool for the efficient and standardized prediction of potential allergenicity of proteins and peptides according to the current recommendations of the FAO/WHO Expert Consultation, as outlined in the Codex alimentarius.

Description

A query amino acid sequence is compared with all known allergenic proteins retrieved from the protein databases using a sliding window approach. This identifies stretches of 80 amino acids with more than 35% similarity or small identical stretches of at least six amino acids. The outcome of the analysis is presented in a concise format. The predictive performance of the FAO/WHO criteria is evaluated by screening sets of allergens and non-allergens against the Allermatch databases. Besides correct predictions, both methods are shown to generate false positive and false negative hits and the outcomes should therefore be combined with other methods of allergenicity assessment, as advised by the FAO/WHO.

Conclusions

Allermatch™ provides an accessible, efficient, and useful webtool for analysis of potential allergenicity of proteins introduced in genetically modified food prior to market release that complies with current FAO/WHO guidelines.

Accumulation, assembly, and digestibility of amarantin expressed in transgenic tropical maize

An amaranth ( Amaranthus hypochondriacus) 11S globulin cDNA, encoding one of the most important storage proteins (amarantin) of the seed, with a high content of essential amino acids, was used in the transformation of CIMMYT tropical maize genotype. Constructs contained the amarantin cDNA under the control of a tissue-specific promoter from rice glutelin-1 ( osGT1) or a constitutive ( CaMV 35S) promoter with and without the first maize alcohol dehydrogenase intron ( AdH). Southern-blot analysis confirmed the integration of the amarantin cDNA, and copy number ranged from one to more than ten copies per maize genome. Western-blot and ultracentrifugation analyses of transgenic maize indicate that the expressed recombinant amarantin precursors were processed into the mature form, and accumulated stably in maize endosperm. Total protein and some essential amino acids of the best expressing maize augmented 32% and 8-44%, respectively, compared to non-transformed samples. The soluble expressed proteins were susceptible to digestion by simulated gastric and intestinal fluids, and it is suggested that they show no allergenic activity. These findings demonstrate the feasibility of using genetic engineering to improve the amino acid composition of grain crops.

Functional and rheological properties of amaranth albumins extracted from two Mexican varieties

The functional and rheological properties of amaranth albumins isolates extracted from two new Mexican varieties were determined. Functional properties tested were protein solubility, foaming, water and oil absorption capacities, emulsifying activity, and emulsion stability. The maximum solubility values for both amaranth albumins were found above pH 6 and values were compared to the solubility of egg albumins. Albumins from amaranth showed excellent foaming capacity and foaming stability at pH 5, suggesting that this protein could be used as whipping agents as egg albumins, also the water and oil absorption capacities reached their maximum values at acidic pH, suggesting that amaranth albumins could be appropriate in preparation of acidic foods. The rheological test based on farinograms and alveograms showed that wheat flour supplemented with 1% amaranth albumins improves the dough properties due to higher mixing stability and the bread had better crumb characteristics. In addition of the known high nutritional values of amaranth albumins, our results indicate the high potential for use of these proteins as an ingredient in food preparations.

Plant molecular biology and biotechnology research in the post-recombinant DNA era

After the beginning of the recombinant DNA era in the mid-1970s, researchers in India started to make use of the new technology to understand the structure of plant genes and regulation of their expression. The outcome started to appear in print in early the 1980s and genes for histones, tubulin, photosynthetic membrane proteins, phototransduction components, organelles and those regulated differentially by developmental and extrinsic signals were sequenced and characterized. Some genes of biotechnological importance like those encoding an interesting seed protein and the enzyme glyoxalase were also isolated. While work on the characterization of genome structure and organization was started quite early, it remained largely focused on the identification of DNA markers and genetic variability. In this context, the work on mustard, rice and wheat is worth mentioning. In the year 2000, India became a member of the international consortium to sequence entire rice genome. Several laboratories have also given attention to regulated expression of plastid and nuclear genes as well as to isolate target-specific promoters or design promoters with improved potential. Simultaneously, transgenic systems for crops like mustard, rice, wheat, cotton, legumes and several vegetables have been established. More recently, genes of agronomic importance like those for insect resistance, abiotic stress tolerance, nutritional improvement and male sterility, isolated in India or abroad, have been utilized for raising transgenics for crop improvement. Some of these transgenics have already shown their potential in containment facility or limited field trials conducted under the stipulated guidelines. Plant molecular biology and biotechnology are thus clearly poised to make an impact on research in basic biology and agriculture in the near future.

Increasing maize seed methionine by mRNA stability

The amino acid methionine is a common protein building block that is also important in other cellular processes. Plants, unlike animals, synthesize methionine de novo and are thus a dietary source of this nutrient. A new approach for using maize as a source of nutrient methionine is described. Maize seeds, a major component of animal feeds, have variable levels of protein-bound methionine. This variability is a result of post-transcriptional regulation of the Dzs10 gene, which encodes a seed-specific high-methionine storage protein. Here we eliminate methionine variability by identifying and replacing the cis-acting site for Dzs10 regulation using transgenic seeds. Interestingly, two different mechanisms affect mRNA accumulation, one dependent on and the other independent of the untranslated regions (UTRs) of Dzs10 RNA. Accumulation of chimeric Dzs10 mRNA was not reduced in hybrid crosses and was uncoupled from genomic imprinting by Dzr1, a regulator of Dzs10. Uniform high levels of Dzs10 protein were maintained over five backcross generations of the transgene. The increased level of methionine in these transgenic seeds allowed the formulation of a useful animal feed ration without the addition of synthetic methionine.

Antisense inhibition of threonine synthase leads to high methionine content in transgenic potato plants

Methionine (Met) and threonine (Thr) are members of the aspartate family of amino acids. In plants, their biosynthetic pathways diverge at the level of O-phosphohomo-serine (Ser). The enzymes cystathionine gamma-synthase and Thr synthase (TS) compete for the common substrate O-phosphohomo-Ser with the notable feature that plant TS is activated through S-adenosyl-Met, a metabolite derived from Met. To investigate the regulation of this branch point, we engineered TS antisense potato (Solanum tuberosum cv Désirée) plants using the constitutive cauliflower mosaic virus 35S promoter. In leaf tissues, these transgenics exhibit a reduction of TS activity down to 6% of wild-type levels. Thr levels are reduced to 45% wild-type controls, whereas Met levels increase up to 239-fold depending on the transgenic line and environmental conditions. Increased levels of homo-Ser and homo-cysteine indicate increased carbon allocation into the aspartate pathway. In contrast to findings in Arabidopsis, increased Met content has no detectable effect on mRNA or protein levels or on the enzymatic activity of cystathionine gamma-synthase in potato. Tubers of TS antisense potato plants contain a Met level increased by a factor of 30 and no reduction in Thr. These plants offer a major biotechnological advance toward the development of crop plants with improved nutritional quality.