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

Biofortification: an approach to eradicate micronutrient deficiency

Micronutrient deficiency also known as "hidden hunger" refers to a condition that occurs when the body lacks essential vitamins and minerals that are required in small amounts for proper growth, development and overall health. These deficiencies are particularly common in developing countries, where a lack of access to a varied and nutritious diet makes it difficult for people to get the micronutrients they need. Micronutrient supplementation has been a topic of interest, especially during the Covid-19 pandemic, due to its potential role in supporting immune function and overall health. Iron (Fe), zinc (Zn), iodine (I), and selenium (Se) deficiency in humans are significant food-related issues worldwide. Biofortification is a sustainable strategy that has been developed to address micronutrient deficiencies by increasing the levels of essential vitamins and minerals in staple crops that are widely consumed by people in affected communities. There are a number of agricultural techniques for biofortification, including selective breeding of crops to have higher levels of specific nutrients, agronomic approach using fertilizers and other inputs to increase nutrient uptake by crops and transgenic approach. The agronomic approach offers a temporary but speedy solution while the genetic approach (breeding and transgenic) is the long-term solution but requires time to develop a nutrient-rich variety.

Domestication of newly evolved hexaploid wheat—A journey of wild grass to cultivated wheat

Domestication of wheat started with the dawn of human civilization. Since then, improvement in various traits including resistance to diseases, insect pests, saline and drought stresses, grain yield, and quality were improved through selections by early farmers and then planned hybridization after the discovery of Mendel’s laws. In the 1950s, genetic variability was created using mutagens followed by the selection of superior mutants. Over the last 3 decades, research was focused on developing superior hybrids, initiating marker-assisted selection and targeted breeding, and developing genetically modified wheat to improve the grain yield, tolerance to drought, salinity, terminal heat and herbicide, and nutritive quality. Acceptability of genetically modified wheat by the end-user remained a major hurdle in releasing into the environment. Since the beginning of the 21st century, changing environmental conditions proved detrimental to achieving sustainability in wheat production particularly in developing countries. It is suggested that high-tech phenotyping assays and genomic procedures together with speed breeding procedures will be instrumental in achieving food security beyond 2050.

Wheat Biofortification: Utilizing Natural Genetic Diversity, Genome-Wide Association Mapping, Genomic Selection, and Genome Editing Technologies

Alleviating micronutrients associated problems in children below five years and women of childbearing age, remains a significant challenge, especially in resource-poor nations. One of the most important staple food crops, wheat attracts the highest global research priority for micronutrient (Fe, Zn, Se, and Ca) biofortification. Wild relatives and cultivated species of wheat possess significant natural genetic variability for these micronutrients, which has successfully been utilized for breeding micronutrient dense wheat varieties. This has enabled the release of 40 biofortified wheat cultivars for commercial cultivation in different countries, including India, Bangladesh, Pakistan, Bolivia, Mexico and Nepal. In this review, we have systematically analyzed the current understanding of availability and utilization of natural genetic variations for grain micronutrients among cultivated and wild relatives, QTLs/genes and different genomic regions regulating the accumulation of micronutrients, and the status of micronutrient biofortified wheat varieties released for commercial cultivation across the globe. In addition, we have also discussed the potential implications of emerging technologies such as genome editing to improve the micronutrient content and their bioavailability in wheat.

Plant Molecular Farming, a Tool for Functional Food Production

The demand of functional food is increasing for improving human health. Plant molecular farming (PMF) employs plants as bioreactors for the production of pharmaceuticals. Now PMF has been used to produce antibodies, vaccines, and medicinal proteins, but it has not been well-studied for production of nutraceuticals and functional food. In this perspective, we extend the concept of PMF, present an updated overview of PMF for functional food development, including the progress, problem, and strategy, and then speculate how to use the PMF strategy to produce functional foods, especially with four major staple food crops (rice, wheat, maize, and soybean). Finally, we discuss the opportunities and challenges of PMF on functional food production in the future.

Biofortification of Cereals and Pulses Using New Breeding Techniques: Current and Future Perspectives

Cereals and pulses are consumed as a staple food in low-income countries for the fulfillment of daily dietary requirements and as a source of micronutrients. However, they are failing to offer balanced nutrition due to deficiencies of some essential compounds, macronutrients, and micronutrients, i.e., cereals are deficient in iron, zinc, some essential amino acids, and quality proteins. Meanwhile, the pulses are rich in anti-nutrient compounds that restrict the bioavailability of micronutrients. As a result, the population is suffering from malnutrition and resultantly different diseases, i.e., anemia, beriberi, pellagra, night blindness, rickets, and scurvy are common in the society. These facts highlight the need for the biofortification of cereals and pulses for the provision of balanced diets to masses and reduction of malnutrition. Biofortification of crops may be achieved through conventional approaches or new breeding techniques (NBTs). Conventional approaches for biofortification cover mineral fertilization through foliar or soil application, microbe-mediated enhanced uptake of nutrients, and conventional crossing of plants to obtain the desired combination of genes for balanced nutrient uptake and bioavailability. Whereas, NBTs rely on gene silencing, gene editing, overexpression, and gene transfer from other species for the acquisition of balanced nutritional profiles in mutant plants. Thus, we have highlighted the significance of conventional and NBTs for the biofortification of cereals and pulses. Current and future perspectives and opportunities are also discussed. Further, the regulatory aspects of newly developed biofortified transgenic and/or non-transgenic crop varieties via NBTs are also presented.

Unraveling the Strategies Used by the Underexploited Amaranth Species to Confront Salt Stress: Similarities and Differences With Quinoa Species

Yield losses due to cultivation in saline soils is a common problem all over the world as most crop plants are glycophytes and, hence, susceptible to salt stress. The use of halophytic crops could be an interesting alternative to cope with this issue. The Amaranthaceae family comprises by far the highest proportion of salt-tolerant halophytic species. Amaranth and quinoa belong to this family, and their seeds used as pseudo-cereal grains have received much attention in recent years because of their exceptional nutritional value. While advances in the knowledge of salt tolerance mechanisms of quinoa have been remarkable in recent years, much less attention was received by amaranth, despite evidences pointing to amaranth as a promising species to be grown under salinity. In order to advance in the understanding of strategies used by amaranth to confront salt stress, we studied the comparative responses of amaranth and quinoa to salinity (100 mM NaCl) at the physiological, anatomical, and molecular levels. Amaranth was able to exhibit salt tolerance throughout its life cycle, since grain production was not affected by the saline conditions applied. The high salt tolerance of amaranth is associated with a low basal stomatal conductance due to a low number of stomata (stomatal density) and degree of stomata aperture (in adaxial surface) of leaves, which contributes to avoid leaf water loss under salt stress in a more efficient way than in quinoa. With respect to Na⁺ homeostasis, amaranth showed a pattern of Na⁺ distribution throughout the plant similar to glycophytes, with the highest accumulation found in the roots, followed by the stem and the lowest one detected in the leaves. Contrarily, quinoa exhibited a Na⁺ includer character with the highest accumulation detected in the shoots. Expression levels of main genes involved in Na⁺ homeostasis (SOS1, HKT1s, and NHX1) showed different patterns between amaranth and quinoa, with a marked higher basal expression in amaranth roots. These results highlight the important differences in the physiological and molecular responses of amaranth and quinoa when confronted with salinity.

Choice of the Promoter for Tissue and Developmental Stage-Specific Gene Expression

Transgenic technologies belong to important tools of reverse genetics and biotechnology in plants. Targeted genetic modifications can reveal functions of genes of interest, change metabolic and regulatory pathways, or result in accumulation of valuable proteins or metabolites. However, to be efficient in targeted genetic modification, the chimeric gene construct should be designed properly. In particular, the promoters used to control transgene expression need to be carefully chosen. Most promoters in widely used vectors belong to strong and constitutively expressed variants. However, in many cases transgene expression has to be restricted to certain tissue, stage of development, or response to some internal or external stimuli. In turn, a large variety of tissue-specific promoters have been studied and information on their characteristics may be recovered from the literature. An appropriate promoter may be selected and used in genetic construct to optimize the transgene transcription pattern. We have previously designed the TGP database (TransGene Promoters, http://wwwmgs.bionet.nsc.ru/mgs/dbases/tgp/home.html ) collecting information from the publications in this field. Here we review the wide range of noncanonical tissue-specific and developmentally regulated promoters that might be used for transgene expression control.

Can wheat survive in heat? Assembling tools towards successful development of heat stress tolerance in Triticum aestivum L

Wheat is an important cereal crop that fulfils the calorie demands of the global humanity. Rapidly expanding populations are exposed to a fast approaching acute shortage in the adequate supply of food and fibre from agricultural resources. One of the significant threats to food security lies in the constantly increasing global temperatures which inflict serious injuries to the plants in terms of various physiological, biochemical and molecular processes. Wheat being a cool season crop is majorly impacted by the heat stress which adversely affects crop productivity and yield. These challenges would be potentially defeated with the implementation of genetic engineering strategies coupled with the new genome editing approaches. Development of transgenic plants for various crops has proved very effective for the incorporation of improved varietal traits in context of heat stress. With a similar approach, we need to target for the generation of heat stress tolerant wheat varieties which are capable of survival in such adverse conditions and yet produce well. In this review, we enumerate the current status of research on the heat stress responsive genes/factors and their potential role in mitigating heat stress in plants particularly in wheat with an aim to help the researchers get a holistic view of this topic. Also, we discuss on the prospective signalling pathway that is triggered in plants in general under heat stress.

Biofortified Crops Generated by Breeding, Agronomy, and Transgenic Approaches Are Improving Lives of Millions of People around the World

Biofortification is an upcoming, promising, cost-effective, and sustainable technique of delivering micronutrients to a population that has limited access to diverse diets and other micronutrient interventions. Unfortunately, major food crops are poor sources of micronutrients required for normal human growth. The manuscript deals in all aspects of crop biofortification which includes-breeding, agronomy, and genetic modification. It tries to summarize all the biofortification research that has been conducted on different crops. Success stories of biofortification include lysine and tryptophan rich quality protein maize (World food prize 2000), Vitamin A rich orange sweet potato (World food prize 2016); generated by crop breeding, oleic acid, and stearidonic acid soybean enrichment; through genetic transformation and selenium, iodine, and zinc supplementation. The biofortified food crops, especially cereals, legumes, vegetables, and fruits, are providing sufficient levels of micronutrients to targeted populations. Although a greater emphasis is being laid on transgenic research, the success rate and acceptability of breeding is much higher. Besides the challenges biofortified crops hold a bright future to address the malnutrition challenge.

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.

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.

Salt stress-induced alterations in the root proteome of Amaranthus cruentus L

Salt stress is one of the major factors limiting crop productivity worldwide. Amaranth is a highly nutritious pseudocereal with remarkable nutraceutical properties; it is also a stress-tolerant plant, making it an alternative crop for sustainable food production in semiarid conditions. A two-dimensional electrophoresis gel coupled with a liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) approach was applied in order to analyze the changes in amaranth root protein accumulation in plants subjected to salt stress under hydroponic conditions during the osmotic phase (1 h), after recovery (24 h), and during the ionic phase of salt stress (168 h). A total of 101 protein spots were differentially accumulated in response to stress, in which 77 were successfully identified by LC-MS/MS and a database search against public and amaranth transcriptome databases. The resulting proteins were grouped into different categories of biological processes according to Gene Ontology. The identification of several protein isoforms with a change in pI and/or molecular weight reveals the importance of the salt-stress-induced posttranslational modifications in stress tolerance. Interestingly stress-responsive proteins unique to amaranth, for example, Ah24, were identified. Amaranth is a stress-tolerant alternative crop for sustainable food production, and the understanding of amaranth's stress tolerance mechanisms will provide valuable input to improve stress tolerance of other crop plants.

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.

Biolistic- and Agrobacterium-mediated transformation protocols for wheat

After rice, wheat is considered to be the most important world food crop, and the demand for high-quality wheat flour is increasing. Although there are no GM varieties currently grown, wheat is an important target for biotechnology, and we anticipate that GM wheat will be commercially available in 10-15 years. In this chapter, we summarize the main features and challenges of wheat transformation and then describe detailed protocols for the production of transgenic wheat plants both by biolistic and Agrobacterium-mediated DNA-delivery. Although these methods are used mainly for bread wheat (Triticum aestivum L.), they can also be successfully applied, with slight modifications, to tetraploid durum wheat (T. turgidum L. var. durum). The appropriate size and developmental stage of explants (immature embryo-derived scutella), the conditions to produce embryogenic callus tissues, and the methods to regenerate transgenic plants under increasing selection pressure are provided in the protocol. To illustrate the application of herbicide selection system, we have chosen to describe the use of the plasmid pAHC25 for biolistic transformation, while for Agrobacterium-mediated transformation the binary vector pAL156 (incorporating both the bar gene and the uidA gene) has been chosen. Beside the step-by-step methodology for obtaining stably transformed and normal fertile plants, procedures for screening and testing transgenic wheat plants are also discussed.

Accelerated hydrolysis method to estimate the amino acid content of wheat (Triticum durum Desf.) flour using microwave irradiation

The technique of microwave-assisted acid hydrolysis was applied to wholegrain wheat (Triticum durum Desf. cv. Balcali 2000) flour in order to speed the preparation of samples for analysis. The resultant hydrolysates were chromatographed and quantified in an automated amino acid analyzer. The effect of different hydrolysis temperatures, times and sample weights was examined using flour dispersed in 6 N HCl. Within the range of values tested, the highest amino acid recoveries were generally obtained by setting the hydrolysis parameters to 150 °C, 3 h and 200 mg sample weight. These conditions struck an optimal balance between liberating amino acid residues from the wheat matrix and limiting their subsequent degradation or transformation. Compared to the traditional 24 h reflux method, the hydrolysates were prepared in dramatically less time, yet afforded comparable ninhydrin color yields. Under optimal hydrolysis conditions, the total amino acid recovery corresponded to at least 85.1% of the total protein content, indicating the efficient extraction of amino acids from the flour matrix. The findings suggest that this microwave-assisted method can be used to rapidly profile the amino acids of numerous wheat grain samples, and can be extended to the grain analysis of other cereal crops.

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.