Enrichment of provitamin A content in wheat (Triticum aestivum L.) by introduction of the bacterial carotenoid biosynthetic genes CrtB and CrtI

Genetic biofortification: advancing crop nutrition to tackle hidden hunger

Malnutrition, often termed "hidden hunger," represents a pervasive global issue carrying significant implications for health, development, and socioeconomic conditions. Addressing the challenge of inadequate essential nutrients, despite sufficient caloric intake, is crucial. Biofortification emerges as a promising solution by enhance the presence of vital nutrients like iron, zinc, iodine, and vitamin A in edible parts of different crop plants. Crop biofortification can be attained through either agronomic methods or genetic breeding techniques. Agronomic strategies for biofortification encompass the application of mineral fertilizers through foliar or soil methods, as well as leveraging microbe-mediated mechanisms to enhance nutrient uptake. On the other hand, genetic biofortification involves the strategic crossing of plants to achieve a desired combination of genes, promoting balanced nutrient uptake and bioavailability. Additionally, genetic biofortification encompasses innovative methods such as speed breeding, transgenic approaches, genome editing techniques, and integrated omics approaches. These diverse strategies collectively contribute to enhancing the nutritional profile of crops. This review highlights the above-said genetic biofortification strategies and it also covers the aspect of reduction in antinutritional components in food through genetic biofortification.

Magnesium accelerates changes in the fruit ripening and carotenoid accumulation in Satsuma Mandarin pulp

This study aims to further examine the effect of Magnesium (Mg) application on fruit quality and carotenoid metabolism in Satsuma mandarin pulp. For this, a field experiment was using 20-year-old Satsuma mandarin (C. unshiu Marc.) for two treatment; (1) CK treatment (without Mg), (2) Mg fertilizer treatment (200 g MgO plant-1). Compared with CK, Mg treatment substantially raised the Mg content in pulp at 90 to 150 DAF (the fruit expansion period), increasing by 15.69%-21.74%. Mg treatment also increased fruit TSS content by 15.84% and 9.88%, decreased fruit TA content in by 34.25% and 33.26% at 195 DAF and 210 DAF (the fruit ripening period). Moreover, at 120 to 195 DAF, Mg treatment significantly increased the levels of lutein, β-cryptoxanthin, zeaxanthin and violaxanthin in the pulp. This can be explained by the increased expression of important biosynthetic genes, including CitPSY, CitPDS, CitLCYb1, CitLCYb2, CitLCYe, CitHYb, and CitZEP, that played a role in altering the carotenoid composition. The findings of this research offer a novel approach for augmenting both the economic and nutritional worth of citrus fruits.

Comprehensive Analyses of Breads Supplemented with Tannic Acids

Tannic acid (TA) has been recently considered as a new dough additive for improving the bread-making quality of wheat. However, the effects of TA supplementation on the sensory quality parameters (color, crumb grain structure, and sensory properties) of bread have not been studied. Further, the potential of TA supplementation in bread-making quality improvement has not been evaluated by using commercial flour. In the present study, three commercial wheat flours (namely, XL, QZG, and QZZ) with different gluten qualities were used to evaluate the effects of TA supplementation (in concentrations of 0.1% and 0.3%, respectively). TA supplementation did not change the proximate composition of the breads but increased the volumes and specific volumes of XL and QZG breads. TA supplementation enhanced antioxidant activities, with 0.3% TA significantly increasing the antioxidant capacities of bread made from all three flour samples by approximately four-fold (FRAP method)/three-fold (ABTS method). Positive effects of TA on the reduction in crumb hardness, gumminess, and chewiness were observed in the XL bread, as determined by the texture profile analysis. For the analyses on visual and sensory attributes, our results suggest that TA did not affect the crust color, but only slightly reduced the L* (lightness) and b* (yellowness) values of the crumb and increased the a* (redness) value. TA supplementation also increased the porosity, total cell area, and mean cell area. Satisfactorily, the sensory evaluation results demonstrate that TA-supplemented breads did not exhibit negative sensory attributes when compared to the non-TA-added breads; rather, the attributes were even increased. In summary, TA-supplemented breads generally had not only better baking quality attributes and enhanced antioxidant activities, but, more importantly, presented high consumer acceptance in multiple commercial flour samples. Our results support the commercial potential of TA to be used as a dough improver.

A straight-forward gene mining strategy to identify TaCIPK19 as a new regulator of drought tolerance in wheat

Drought stress is one of the most impactful abiotic stresses to global wheat production. Therefore, identifying key regulators such as the calcineurin B-like protein interacting protein kinase (CIPK) in the signaling cascades known to coordinate developmental cues and environmental stimuli represents a useful approach to improve drought tolerance. However, functional studies have been very limited partly due to the difficulties in prioritizing candidate genes from the large TaCIPK family. To address this issue, we demonstrate a straight-forward strategy by analyzing gene expression patterns in response to phytohormones or stresses and identified TaCIPK19 as a new regulator to improve drought tolerance. The effects of TaCIPK19 on drought tolerance were evaluated in both tobacco and wheat through transgenic approach. Ectopic expression of TaCIPK19 in tobacco greatly improves drought tolerance with enhanced ABA biosynthesis/signaling and ROS scavenging capacity. TaCIPK19 overexpression in wheat also confers the drought tolerance at both seedling and mature stages with enhanced ROS scavenging capacity. Additionally, potential CBL partners interacting with TaCIPK19 were investigated. Collectively, our finding exemplifies a straight-forward approach to facilitate reverse genetics related to abiotic stress improvement and demonstrates TaCIPK19 as a new candidate gene to improve ROS scavenging capacity and drought tolerance, which is useful for genetic improvement and breeding application in wheat.

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.

Integrative gene duplication and genome-wide analysis as an approach to facilitate wheat reverse genetics: An example in the TaCIPK family

INTRODUCTION

Reverse genetic studies conducted in the plant with a complex or polyploidy genome enriched with large gene families (like wheat) often meet challenges in identifying the key candidate genes related to important traits and prioritizing the genes for functional experiments.

OBJECTIVE

To overcome the above-mentioned challenges of reverse genetics, this work aims to establish an efficient multi-species strategy for genome-wide gene identification and prioritization of the key candidate genes.

METHODS

We established the integrative gene duplication and genome-wide analysis (iGG analysis) as a strategy for pinpointing key candidate genes deserving functional research. The iGG captures the evolution, and the expansion/contraction of large gene families across phylogeny-related species and integrates spatial-temporal expression information for gene function inference. Transgenic approaches were also employed to functional validation.

RESULTS

As a proof-of-concept for the iGG analysis, we took the wheat calcineurin B-like protein-interacting protein kinases (CIPKs) family as an example. We identified CIPKs from seven monocot species, established the orthologous relationship of CIPKs between rice and wheat, and characterized Triticeae-specific CIPK duplicates (e.g., CIPK4 and CIPK17). Integrated with our analysis of CBLs and CBL-CIPK interaction, we revealed that divergent expressions of TaCBLs and TaCIPKs could play an important role in keeping the stoichiometric balance of CBL-CIPK. Furthermore, we validated the function of TaCIPK17-A2 in the regulation of drought tolerance by using transgenic approaches. Overexpression of TaCIPK17 enhanced antioxidant capacity and improved drought tolerance in wheat.

CONCLUSION

The iGG analysis leverages evolutionary and comparative genomics of crops with large genomes to rapidly highlight the duplicated genes potentially associated with speciation, domestication and/or particular traits that deserve reverse-genetic functional studies. Through the identification of Triticeae-specific TaCIPK17 duplicates and functional validation, we demonstrated the effectiveness of the iGG analysis and provided a new target gene for improving drought tolerance in wheat.

A multi-omic resource of wheat seed tissues for nutrient deposition and improvement for human health

As a globally important staple crop, wheat seeds provide us with nutrients and proteins. The trend of healthy dietary has become popular recently, emphasizing the consumption of whole-grain wheat products and the dietary benefits. However, the dynamic changes in nutritional profiles of different wheat seed regions (i.e., the embryo, endosperm and outer layers) during developmental stages and the molecular regulation have not been well studied. Here, we provide this multi-omic resource of wheat seeds and describe the generation, technical assessment and preliminary analyses. This resource includes a time-series RNA-seq dataset of the embryo, endosperm and outer layers of wheat seeds and their corresponding metabolomic dataset, covering the middle and late stages of seed development. Our RNA-seq experiments profile the expression of 63,708 genes, while the metabolomic data includes the abundance of 984 metabolites. We believe that this was the first reported transcriptome and metabolome dataset of wheat seeds that helps understand the molecular regulation of the deposition of beneficial nutrients and hence improvements for nutritional and processing quality traits.

Genetic and molecular basis of carotenoid metabolism in cereals

Carotenoids are vital pigments for higher plants and play a crucial function in photosynthesis and photoprotection. Carotenoids are precursors of vitamin A synthesis and contribute to human nutrition and health. However, cereal grain endosperm contains a minor carotenoid measure and a scarce supply of provitamin A content. Therefore, improving the carotenoids in cereal grain is of major importance. Carotenoid content is governed by multiple candidate genes with their additive effects. Studies on genes related to carotenoid metabolism in cereals would increase the knowledge of potential metabolic steps of carotenoids and enhance the quality of crop plants. Recognizing the metabolism and carotenoid accumulation in various staple cereal crops over the last few decades has broadened our perspective on the interdisciplinary regulation of carotenogenesis. Meanwhile, the amelioration in metabolic engineering approaches has been exploited to step up the level of carotenoid and valuable industrial metabolites in many crops, but wheat is still considerable in this matter. In this study, we present a comprehensive overview of the consequences of biosynthetic and catabolic genes on carotenoid biosynthesis, current improvements in regulatory disciplines of carotenogenesis, and metabolic engineering of carotenoids. A panoptic and deeper understanding of the regulatory mechanisms of carotenoid metabolism and genetic manipulation (genome selection and gene editing) will be useful in improving the carotenoid content of cereals.

Biofortification: A long-term solution to improve global health- a review

Biofortification is a revolutionary technique for improving plant nutrition and alleviating human micronutrient deficiency. Fertilizers can help increase crop yield and growth, but applying too much fertilizer can be a problem because it leads to the release of greenhouse gases and eutrophication. One of the major global hazards that affects more than two million people globally is the decreased availability of micronutrients in food crops, which results in micronutrient deficiencies or "hidden hunger" in people. Micronutrients, like macronutrients, perform a variety of roles in plant and human nutrition. This review has highlighted the importance of micronutrients as well as their advantages. The uneven distribution of micronutrients in geological areas is not the only factor responsible for micronutrient deficiencies, other parameters including soil moisture, temperature, texture of the soil, and soil pH significantly affects the micronutrient concentration and their availability in the soil. To overcome this, different biofortification approaches are assessed in the review in which microbes mediated, Agronomic approaches, Plant breeding, and transgenic approaches are discussed. Hidden hunger can result in risky health conditions and diseases such as cancer, cardiovascular disease, osteoporosis, neurological disorders, and many more. Microbes-mediated biofortification is a novel and promising solution for the bioavailability of nutrients to plants in order to address these problems. Biofortification is cost effective, feasible, and environmentally sustainable. Bio-fortified crops boost our immunity, which helps us to combat these deadly viruses. The studies we discussed in this review have demonstrated that they can aid in the alleviation of hidden hunger.

Improving nutrition through biofortification-A systematic review

Nutritious foods are essential for human health and development. However, malnutrition and hidden hunger continue to be a challenge globally. In most developing countries, access to adequate and nutritious food continues to be a challenge. Although hidden hunger is less prevalent in developed countries compared to developing countries where iron (Fe) and zinc (Zn) deficiencies are common. The United Nations (UN) 2nd Sustainable Development Goal was set to eradicate malnutrition and hidden hunger. Hidden hunger has led to numerous cases of infant and maternal mortalities, and has greatly impacted growth, development, cognitive ability, and physical working capacity. This has influenced several countries to develop interventions that could help combat malnutrition and hidden hunger. Interventions such as dietary diversification and food supplementation are being adopted. However, fortification but mainly biofortification has been projected to be the most sustainable solution to malnutrition and hidden hunger. Plant-based foods (PBFs) form a greater proportion of diets in certain populations; hence, fortification of PBFs is relevant in combating malnutrition and hidden hunger. Agronomic biofortification, plant breeding, and transgenic approaches are some currently used strategies in food crops. Crops such as cereals, legumes, oilseeds, vegetables, and fruits have been biofortified through all these three strategies. The transgenic approach is sustainable, efficient, and rapid, making it suitable for biofortification programs. Omics technology has also been introduced to improve the efficiency of the transgenic approach.

An established protocol for generating transgenic wheat for wheat functional genomics via particle bombardment

Wheat is one of the most important food crops in the world and is considered one of the top targets in crop biotechnology. With the high-quality reference genomes of wheat and its relative species and the recent burst of genomic resources in Triticeae, demands to perform gene functional studies in wheat and genetic improvement have been rapidly increasing, requiring that production of transgenic wheat should become a routine technique. While established for more than 20 years, the particle bombardment-mediated wheat transformation has not become routine yet, with only a handful of labs being proficient in this technique. This could be due to, at least partly, the low transformation efficiency and the technical difficulties. Here, we describe the current version of this method through adaptation and optimization. We report the detailed protocol of producing transgenic wheat by the particle gun, including several critical steps, from the selection of appropriate explants (i.e., immature scutella), the preparation of DNA-coated gold particles, and several established strategies of tissue culture. More importantly, with over 20 years of experience in wheat transformation in our lab, we share the many technical details and recommendations and emphasize that the particle bombardment-mediated approach has fewer limitations in genotype dependency and vector construction when compared with the Agrobacterium-mediated methods. The particle bombardment-mediated method has been successful for over 30 wheat genotypes, from the tetraploid durum wheat to the hexaploid common wheat, from modern elite varieties to landraces. In conclusion, the particle bombardment-mediated wheat transformation has demonstrated its potential and wide applications, and the full set of protocol, experience, and successful reports in many wheat genotypes described here will further its impacts, making it a routine and robust technique in crop research labs worldwide.

Bread wheat with enhanced grain carotenoid content: a novel option for wheat biofortification

Colored wheat has piqued the interest of breeders and consumers alike. The chromosomal segment from 7E of Thinopyrum ponticum, which carries a leaf rust resistant gene, Lr19, has been rarely employed in wheat breeding operations due to its association with the Y gene, which gives a yellow tint to the flour. By prioritizing nutritional content over color preferences, consumer acceptance has undergone a paradigm change. Through marker-assisted backcross breeding, we introduced an alien segment harboring the Y (PsyE1) gene into a high yielding commercial bread wheat (HD 2967) background to generate rust resistant carotenoid biofortified bread wheat. Agro-morphological characterization was also performed on a subset of developed 70 lines having enhanced grain carotene content. In the introgression lines, carotenoid profiling using HPLC analysis demonstrated a considerable increase in β-carotene levels (up to 12 ppm). Thus, the developed germplasm caters the threat to nutritional security and can be utilized to produce carotenoid fortified wheat.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-022-01338-0.

Variation of vitamin B contents in maize inbred lines: Potential genetic resources for biofortification

Vitamin B and its derivatives possess diverse physiological functions and are essential micronutrients for humans. Their variation in crops is important for the identification of genetic resources used to develop new varieties with enhanced vitamin B. In this research, remarkable variations were observed in kernels of 156 maize inbred lines, ranging from 107.61 to 2654.54 μg per 100 g for vitamin B1, 1.19–37.37 μg per 100 g for B2, 19.60–213.75 μg per 100 g for B3, 43.47–590.86 μg per 100 g for B5, and 138.59–1065.11 μg per 100 g for B6. Growing inbreeds in Hainan and Hebei provinces of China revealed environmental and genotype interactions among these vitamins and the correlations between them in maize grain. Several inbred lines were identified as good sources of vitamin B and promising germplasms for maize breeding, namely By855 and Si273 are overall rich in all the studied vitamins, and GY386B and CML118 are specially enriched with derivatives of vitamin B6. The present study can assist maize breeders with germplasm resources of vitamin B for biofortification to offer people nutritious foods.

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.

Biocircuits in plants and eukaryotic algae

As one of synthetic biology's foundations, biocircuits are a strategy of genetic parts assembling to recognize a signal and to produce a desirable output to interfere with a biological function. In this review, we revisited the progress in the biocircuits technology basis and its mandatory elements, such as the characterization and assembly of functional parts. Furthermore, for a successful implementation, the transcriptional control systems are a relevant point, and the computational tools help to predict the best combinations among the biological parts planned to be used to achieve the desirable phenotype. However, many challenges are involved in delivering and stabilizing the synthetic structures. Some research experiences, such as the golden crops, biosensors, and artificial photosynthetic structures, can indicate the positive and limiting aspects of the practice. Finally, we envision that the modulatory structural feature and the possibility of finer gene regulation through biocircuits can contribute to the complex design of synthetic chromosomes aiming to develop plants and algae with new or improved functions.

Carotenoid fates in plant foods: Chemical changes from farm to table and nutrition

Carotenoids in plant foods are sources of pro-vitamin A and nutrients with several health benefits, including antioxidant and anticancer activities. However, humans cannot synthesize carotenoids de novo and must obtain them from the diet, typically via plant foods. We review the chemical changes of carotenoids in plant foods from farm to table and nutrition, including nutrient release and degradation during processing and metabolism in vivo. We also describe the influencing factors and proposals corresponding to enhancing the release, retention and utilization of carotenoids, thus benefiting human health. Processing methods influence the release and degradation of carotenoids, and nonthermal processing may optimize processing effects. The carotenoid profile, food matrix, and body status influence the digestion, absorption, and biotransformation of carotenoids in vivo; food design (diet and carotenoid delivery systems) can increase the bioavailability levels of carotenoids in the human body. In this review, the dynamic fate of carotenoids in plant foods is summarized systematically and deeply, focusing on changes in their chemical structure; identifying critical control points and influencing factors to facilitate carotenoid regulation; and suggesting multi-dimensional strategies based on the current state of food processing industries to achieve health benefits for consumers.

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.

Cytokinin and Its Key Role to Enrich the Plant Nutrients and Growth Under Adverse Conditions-An Update

Among the field crops, wheat is regarded as one of the most paramount cereal crops because it is widely grown, consumed as food across the world, and also known as the staple food for nearly 35 per cent of the world population. However, it is threatened by spot blotch disease causing considerable yield loss, with existing genotypes lacking the resistance and the necessary nutrients. Cytokinins (CKs) are key phytohormones that not only regulate the plant growth/development but also play an important role during stress and in the nutrient metabolic pathway of crop plants. Deficiency of important nutrients like zinc, iron, and vitamin A causes irreparable damage to the body, pressing the need to increase the accumulation of such micronutrients in the edible parts of the plant. Crop bio-fortification is one of the emerging approaches through which the quantities of these nutrients could be increased to an advisable amount. Cytokinin is observed to have a pivotal role in managing environmental stress/climate change and defense systems of plants, and apart from this, it is also found that it has an impact over Zn accumulation in cereal crops. Manipulation of the cytokine dehydrogenase (CKX) enzyme that degrades cytokinin could affect the yield, root growth, and important nutrients. Several instances revealed that an increment in the contents of Zn, S, Fe, and Mn in the seeds of cereals is a reflection of increasing the activity of CKX enzyme resulting the enhancement of the root system which not only helps in the absorption of water in a drought prone area but is also beneficial for scavenging nutrients to the deeper ends of the soil. Exploring micronutrients from the lithosphere via the root system helps in the uptake of the micronutrients and transporting them via the vascular system to the sink of crop plants, therefore, identification and incorporation of CKs/CKX linked gene(s) into targeted crop plants, exploring a bio-fortification approach including CRISPR-Cas9 through conventional and molecular breeding approaches could be the most paramount job for improving the important traits and stress management in order to enhance the plant growth, productivity, and nutritional value of the wheat crops, which would be useful for mankind.

Phytoene Synthase: The Key Rate-Limiting Enzyme of Carotenoid Biosynthesis in Plants

Phytoene synthase (PSY) catalyzes the first committed step in the carotenoid biosynthesis pathway and is a major rate-limiting enzyme of carotenogenesis. PSY is highly regulated by various regulators and factors to modulate carotenoid biosynthesis in response to diverse developmental and environmental cues. Because of its critical role in controlling the total amount of synthesized carotenoids, PSY has been extensively investigated and engineered in plant species. However, much remains to be learned on its multifaceted regulatory control and its catalytic efficiency for carotenoid enrichment in crops. Here, we present current knowledge on the basic biology, the functional evolution, the dynamic regulation, and the metabolic engineering of PSY. We also discuss the open questions and gaps to stimulate additional research on this most studied gene/enzyme in the carotenogenic pathway.

Vitamin A fortification: Recent advances in encapsulation technologies

Vitamin A is an essential micronutrient whose deficiency is still a major health concern in many regions of the world. It plays an essential role in human growth and development, immunity, and vision, but may also help prevent several other chronic diseases. The total amount of vitamin A in the human diet often falls below the recommended dietary allowance of approximately 900-1000 μ $ \umu $ g/day for a healthy adult. Moreover, a significant proportion of vitamin A may be degraded during food processing, storage, and distribution, thereby reducing its bioactivity. Finally, the vitamin A in some foods has a relatively low bioavailability, which further reduces its efficacy. The World Health Organization has recommended fortification of foods and beverages as a safe and cost-effective means of addressing vitamin A deficiency. However, there are several factors that must be overcome before effective fortified foods can be developed, including the low solubility, chemical stability, and bioavailability of this oil-soluble vitamin. Consequently, strategies are required to evenly disperse the vitamin throughout food matrices, to inhibit its chemical degradation, to avoid any adverse interactions with any other food components, to ensure the food is palatable, and to increase its bioavailability. In this review article, we discuss the chemical, physical, and nutritional attributes of vitamin A, its main dietary sources, the factors contributing to its current deficiency, and various strategies to address these deficiencies, including diet diversification, biofortification, and food fortification.

Current Status and Potential of Biofortification to Enhance Crop Nutritional Quality: An Overview

Around 2 billion people are suffering from chronic malnutrition or “hidden hunger”, which is the result of many diseases and disorders, including cognitive degeneration, stunting growth, and mortality. Thus, biofortification of staple food crops enriched with micronutrients is a more sustainable option for providing nutritional supplements and managing malnutrition in a society. Since 2001, when the concept of biofortification came to light, different research activities have been carried out, like the development of target populations, breeding or genetic engineering, and the release of biofortified cultivars, in addition to conducting nutritional efficacy trials and delivery plan development. Although, being a cost-effective intervention, it still faces many challenges, like easy accessibility of biofortified cultivars, stakeholders’ acceptance, and the availability of biofortified germplasm in the public domain, which varies from region to region. Hence, this review is focused on the recent potential, efforts made to crop biofortification, impacts analysis on human health, cost-effectiveness, and future perspectives to further strengthen biofortification programs. Through regular interventions of sustainable techniques and methodologies, biofortification holds huge potential to solve the malnutrition problem through regular interventions of nutrient-enriched staple food options for billions of people globally.

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.

Carotenoid fortification of zucchini fruits using a viral RNA vector

BACKGROUND

Carotenoids are health-promoting metabolites in livestock and human diets. Some important crops have been genetically modified to increase their content. Although the usefulness of transgenic plants to alleviate nutritional deficiencies is obvious, their social acceptance has been controversial.

RESULTS

Here, we demonstrate an alternative biotechnological strategy for carotenoid fortification of edible fruits in which no transgenic DNA is involved. A viral RNA vector derived from Zucchini yellow mosaic virus (ZYMV) was modified to express a bacterial phytoene synthase (crtB), and inoculated to zucchini (Cucurbita pepo L.) leaves nurturing pollinated flowers. After the viral vector moved to the developing fruit and expressed crtB, the rind and flesh of the fruits developed yellow-orange rather than green color. Metabolite analyses showed a substantial enrichment in health-promoting carotenoids, such as α- and β-carotene (provitamin A), lutein and phytoene, in both rind and flesh.

CONCLUSION

Although this strategy is perhaps not free from controversy due to the use of genetically modified viral RNA, our work does demonstrate the possibility of metabolically fortifying edible fruits using an approach in which no transgenes are involved. This article is protected by copyright. All rights reserved.

Nucleotide variation in the phytoene synthase (ClPsy1) gene contributes to golden flesh in watermelon (Citrullus lanatus L.)

A gene controlling golden flesh trait in watermelon was discovered and fine mapped to a 39.08 Kb region on chromosome 1 through a forward genetic strategy, and Cla97C01G008760 (annotated as phytoene synthase protein, ClPsy1 ) was recognized as the most likely candidate gene. Vitamin A deficiency is a worldwide public nutrition problem, and β-carotene is the precursor for vitamin A synthesis. Watermelon with golden flesh (gf, which occurs due to an accumulated abundance of β-carotene) is an important germplasm resource. In this study, a genetic analysis of segregated gf gene populations indicated that gf was controlled by a single recessive gene. BSA-seq (Bulked segregation analysis) and an initial linkage analysis placed the gf locus in a 290-Kb region on watermelon chromosome 1. Further fine mapping in a large population including over 1000 F₂ plants narrowed this region to 39.08 Kb harboring two genes, Cla97C01G008760 and Cla97C01G008770, which encode phytoene synthase (ClPsy1) and GATA zinc finger domain-containing protein, respectively. Gene sequence alignment and expression analysis between parental lines revealed Cla97C01G008760 as the best possible candidate gene for the gf trait. Nonsynonymous SNP mutations in the first exon of ClPsy1 between parental lines co-segregated with the gf trait only among individuals in the genetic population and were not related to flesh color in natural watermelon panels. Promoter sequence analysis of 26 watermelon accessions revealed two SNPs in the cis-acting element sequences corresponding to MYB and MYC2 transcription factors. RNA-seq data and qRT-PCR verification showed that two MYBs exhibited expression trends similar to that of ClPsy1 in the parental lines and may regulate the ClPsy1 expression. Further research findings indicate that the gf trait is determined not only by ClPsy1 but also by ClLCYB, ClCRTISO and ClNCED7, which play important roles in watermelon β-carotene accumulation.

Nutritional improvement of cereal crops to combat hidden hunger during COVID-19 pandemic: Progress and prospects

COVID-19 has posed a severe challenge on food security by limiting access to food for the marginally placed population. While access to food is a challenge, access to nutritional food is a greater challenge to the population. The present-day foods are not sufficient to meet the nutritional requirements of the human body. In a pandemic condition, providing nutritious food to the population is imperative to ensure the health and well-being of humankind. Exploiting the existing biodiversity of crop species and deploying classical and modern tools to improve the nutritional potential of these species holds the key to addressing the above challenge. Breeding has been a classical tool of crop improvement that relied predominantly on genetic diversity. Collecting and conserving diverse germplasms and characterizing their diversity using molecular markers is essential to preserve diversity and use them in genetic improvement programs. These markers are also valuable for association mapping analyses to identify the genetic determinants of traits-of-interest in crop species. Association mapping identifies the quantitative trait loci (QTL) underlying the trait-of-interest by exploring marker-trait associations, and these QTLs can further be exploited for the genetic improvement of cultivated species through genomics-assisted breeding. Conventional breeding and genomics approaches are also being applied to develop biofortified cereal crops to reduce nutritional deficiencies in consumers. In this context, chapter explains the prerequisites for association mapping, population structure, genetic diversity, different approaches of performing association mapping to dissect nutritional traits, use the information for genomics-assisted breeding for nutrient-rich cereal crops, and application of genomics strategies in crop biofortification. These approaches will ensure food and nutrition security for all amidst the current COVID-19 crisis.

Assessment of Biofortification Approaches Used to Improve Micronutrient-Dense Plants That Are a Sustainable Solution to Combat Hidden Hunger

Malnutrition causes diseases, immune system disorders, deterioration in physical growth, mental development, and learning capacity worldwide. Micronutrient deficiency, known as hidden hunger, is a serious global problem. Biofortification is a cost-effective and sustainable agricultural strategy for increasing the concentrations or bioavailability of essential elements in the edible parts of plants, minimizing the risks of toxic metals, and thus reducing malnutrition. It has the advantage of delivering micronutrient-dense food crops to a large part of the global population, especially poor populations. Agronomic biofortification and biofertilization, traditional plant breeding, and optimized fertilizer applications are more globally accepted methods today; however, genetic biofortification based on genetic engineering such as increasing or manipulating (such as CRISPR-Cas9) the expression of genes that affect the regulation of metal homeostasis and carrier proteins that serve to increase the micronutrient content for higher nutrient concentration and greater productivity or that affect bioavailability is also seen as a promising high-potential strategy in solving this micronutrient deficiency problem. Data that micronutrients can help strengthen the immune system against the COVID-19 pandemic and other diseases has highlighted the importance of tackling micronutrient deficiencies. In this study, biofortification approaches such as plant breeding, agronomic techniques, microbial fertilization, and some genetic and nanotechnological methods used in the fight against micronutrient deficiency worldwide were compiled.

Enrichment of provitamin A content in durum wheat grain by suppressing β-carotene hydroxylase 1 genes with a TILLING approach

The suppression of the HYD-1 gene by a TILLING approach increases the amount of β-carotene in durum wheat kernel. Vitamin A deficiency is a major public health problem that affects numerous countries in the world. As humans are not able to synthesize vitamin A, it must be daily assimilated along with other micro- and macronutrients through the diet. Durum wheat is an important crop for Mediterranean countries and provides a discrete amount of nutrients, such as carbohydrates and proteins, but it is deficient in some essential micronutrients, including provitamin A. In the present work, a targeting induced local lesions in genomes strategy has been undertaken to obtain durum wheat genotypes biofortified in provitamin A. In detail, we focused on the suppression of the β-carotene hydroxylase 1 (HYD1) genes, encoding enzymes involved in the redirection of β-carotene toward the synthesis of the downstream xanthophylls (neoxanthin, violaxanthin and zeaxanthin). Expression analysis of genes involved in carotenoid biosynthesis revealed a reduction of the abundance of HYD1 transcripts greater than 50% in mutant grain compared to the control. The biochemical profiling of carotenoid in the wheat mutant genotypes highlighted a significant increase of more than 70% of β-carotene compared to the wild-type sibling lines, with no change in lutein, α-carotene and zeaxanthin content. This study sheds new light on the molecular mechanism governing carotenoid biosynthesis in durum wheat and provides new genotypes that represent a good genetic resource for future breeding programs focused on the provitamin A biofortification through non-transgenic approaches.

Omics Technologies to Enhance Plant Based Functional Foods: An Overview

Functional foods are natural products of plants that have health benefits beyond necessary nutrition. Functional foods are abundant in fruits, vegetables, spices, beverages and some are found in cereals, millets, pulses and oilseeds. Efforts to identify functional foods in our diet and their beneficial aspects are limited to few crops. Advances in sequencing and availability of different omics technologies have given opportunity to utilize these tools to enhance the functional components of the foods, thus ensuring the nutritional security. Integrated omics approaches including genomics, transcriptomics, proteomics, metabolomics coupled with artificial intelligence and machine learning approaches can be used to improve the crops. This review provides insights into omics studies that are carried out to find the active components and crop improvement by enhancing the functional compounds in different plants including cereals, millets, pulses, oilseeds, fruits, vegetables, spices, beverages and medicinal plants. There is a need to characterize functional foods that are being used in traditional medicines, as well as utilization of this knowledge to improve the staple foods in order to tackle malnutrition and hunger more effectively.

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.

Multi-strategy engineering greatly enhances provitamin A carotenoid accumulation and stability in Arabidopsis seeds

Staple grains with low levels of provitamin A carotenoids contribute to the global prevalence of vitamin A deficiency and therefore are the main targets for provitamin A biofortification. However, carotenoid stability during both seed maturation and postharvest storage is a serious concern for the full benefits of carotenoid biofortified grains. In this study, we utilized Arabidopsis as a model to establish carotenoid biofortification strategies in seeds. We discovered that manipulation of carotenoid biosynthetic activity by seed-specific expression of Phytoene synthase (PSY) increases both provitamin A and total carotenoid levels but the increased carotenoids are prone to degradation during seed maturation and storage, consistent with previous studies of provitamin A biofortified grains. In contrast, stacking with Orange (OR ^His ), a gene that initiates chromoplast biogenesis, dramatically enhances provitamin A and total carotenoid content and stability. Up to 65- and 10-fold increases of β-carotene and total carotenoids, respectively, with provitamin A carotenoids composing over 63% were observed in the seeds containing OR ^His and PSY. Co-expression of Homogentisate geranylgeranyl transferase (HGGT) with OR ^His and PSY further increases carotenoid accumulation and stability during seed maturation and storage. Moreover, knocking-out of β-carotene hydroxylase 2 (BCH2) by CRISPR/Cas9 not only potentially facilitates β-carotene accumulation but also minimizes the negative effect of carotenoid over production on seed germination. Our findings provide new insights into various processes on carotenoid accumulation and stability in seeds and establish a multiplexed strategy to simultaneously target carotenoid biosynthesis, turnover, and stable storage for carotenoid biofortification in crop seeds.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42994-021-00046-1.

Metabolomics Intervention Towards Better Understanding of Plant Traits

The majority of the most economically important plant and crop species are enriched with the availability of high-quality reference genome sequences forming the basis of gene discovery which control the important biochemical pathways. The transcriptomics and proteomics resources have also been made available for many of these plant species that intensify the understanding at expression levels. However, still we lack integrated studies spanning genomics–transcriptomics–proteomics, connected to metabolomics, the most complicated phase in phenotype expression. Nevertheless, for the past few decades, emphasis has been more on metabolome which plays a crucial role in defining the phenotype (trait) during crop improvement. The emergence of modern high throughput metabolome analyzing platforms have accelerated the discovery of a wide variety of biochemical types of metabolites and new pathways, also helped in improving the understanding of known existing pathways. Pinpointing the causal gene(s) and elucidation of metabolic pathways are very important for development of improved lines with high precision in crop breeding. Along with other-omics sciences, metabolomics studies have helped in characterization and annotation of a new gene(s) function. Hereby, we summarize several areas in the field of crop development where metabolomics studies have made its remarkable impact. We also assess the recent research on metabolomics, together with other omics, contributing toward genetic engineering to target traits and key pathway(s).

Genome wide association study and genomic prediction for stover quality traits in tropical maize (Zea mays L.)

Maize is rapidly replacing traditionally cultivated dual purpose crops of South Asia, primarily due to the better economic remuneration. This has created an impetus for improving maize for both grain productivity and stover traits. Molecular techniques can largely assist breeders in determining approaches for effectively integrating stover trait improvement in their existing breeding pipeline. In the current study we identified a suite of potential genomic regions associated to the two major stover quality traits-in-vitro organic matter digestibility (IVOMD) and metabolizable energy (ME) through genome wide association study. However, considering the fact that the loci identified for these complex traits all had smaller effects and accounted only a small portion of phenotypic variation, the effectiveness of following a genomic selection approach for these traits was evaluated. The testing set consists of breeding lines recently developed within the program and the training set consists of a panel of lines from the working germplasm comprising the founder lines of the newly developed breeding lines and also an unrelated diversity set. The prediction accuracy as determined by the Pearson's correlation coefficient between observed and predicted values of these breeding lines were high even at lower marker density (200 random SNPs), when the training and testing set were related. However, the accuracies were dismal, when there was no relationship between the training and the testing set.

Functional Validation of Phytoene Synthase and Lycopene ε-Cyclase Genes for High Lycopene Content in Autumn Olive Fruit (Elaeagnus umbellata)

Lycopene is the most potent antioxidant among all carotenoids and is beneficial to human health. A ripe fruit of autumn olive (Elaeagnus umbellata Thunb.) accumulates a high level of lycopene, which is 5-20 times higher than that in an ordinary tomato fruit. During fruit ripening of autumn olive, only phytoene synthase (EutPSY) expression pattern shows a tight positive correlation with the increased lycopene content observed at four ripening stages, while the lycopene ε-cyclase (EutLCYe) transcript could not be detected throughout fruit ripening. Here, we investigated whether the two genes are important targets for engineering lycopene biosynthesis. The full-length cDNAs of EutPSY and EutLCYe were first isolated. Fruit-specific overexpression of EutPSY in tomato fruits resulted in elevated contents of lycopene and β-carotene through feedforward regulation of carotenogenic genes, i.e., downregulation of SlLCYe and upregulation of SlLCYb and SlCYCB. These fruits were decreased in ethylene production throughout ripening. Transcript levels of genes for system-2 ethylene synthesis (SlACS2, SlACS4, SlACO1, and SlACO3), perception (SlNR/ETR3 and SlETR4), and response (SlE4 and SlE8) were also inhibited in EutPSY-overexpressing fruits. Repressing ethylene synthesis and signaling transduction delayed fruit climacteric ripening of transgenic tomato plants. Additionally, RNAi suppression of SlLCYe enhanced β-carotene but not lycopene accumulation through altered expression of carotenogenic genes in transgenic tomato fruits by both feedforward and feedback regulatory mechanisms. Ethylene production in SlLCYe-RNAi fruits decreased, thereby delaying fruit ripening. Collectively, these results confirmed that transcriptional regulation of EutPSY and EutLCYe plays a crucial role and a part in massive lycopene accumulation in autumn olive fruits, respectively. EutPSY overexpression enhanced lycopene accumulation in tomato fruits independently of the ethylene pathway but did not influence the size and weight of tomato fruits. EutPSY can be used as an effective strategy capable of elevating the lycopene content in fruits for improving quality.

Genomics-Integrated Breeding for Carotenoids and Folates in Staple Cereal Grains to Reduce Malnutrition

Globally, two billion people suffer from micronutrient deficiencies. Cereal grains provide more than 50% of the daily requirement of calories in human diets, but they often fail to provide adequate essential minerals and vitamins. Cereal crop production in developing countries achieved remarkable yield gains through the efforts of the Green Revolution (117% in rice, 30% in wheat, 530% in maize, and 188% in pearl millet). However, modern varieties are often deficient in essential micronutrients compared to traditional varieties and land races. Breeding for nutritional quality in staple cereals is a challenging task; however, biofortification initiatives combined with genomic tools increase the feasibility. Current biofortification breeding activities include improving rice (for zinc), wheat (for zinc), maize (for provitamin A), and pearl millet (for iron and zinc). Biofortification is a sustainable approach to enrich staple cereals with provitamin A, carotenoids, and folates. Significant genetic variation has been found for provitamin A (96-850 μg and 12-1780 μg in 100 g in wheat and maize, respectively), carotenoids (558-6730 μg in maize), and folates in rice (11-51 μg) and wheat (32.3-89.1 μg) in 100 g. This indicates the prospects for biofortification breeding. Several QTLs associated with carotenoids and folates have been identified in major cereals, and the most promising of these are presented here. Breeding for essential nutrition should be a core objective of next-generation crop breeding. This review synthesizes the available literature on folates, provitamin A, and carotenoids in rice, wheat, maize, and pearl millet, including genetic variation, trait discovery, QTL identification, gene introgressions, and the strategy of genomics-assisted biofortification for these traits. Recent evidence shows that genomics-assisted breeding for grain nutrition in rice, wheat, maize, and pearl millet crops have good potential to aid in the alleviation of micronutrient malnutrition in many developing countries.

Recent developments and applications of genetic transformation and genome editing technologies in wheat

Wheat (Triticum aestivum) is a staple crop across the world and plays a remarkable role in food supplying security. Over the past few decades, basic and applied research on wheat has lagged behind other cereal crops due to the complex and polyploid genome and difficulties in genetic transformation. A breakthrough called as PureWheat was made in the genetic transformation of wheat in 2014 in Asia, leading to a noticeable progress of wheat genome editing. Due to this great achievement, it is predicated that wheat biotechnology revolution is arriving. Genome editing technologies using zinc finger nucleases, transcription activator-like effector nuclease, and clustered regularly interspaced short palindromic repeats-associated endonucleases (CRISR/Cas) are becoming powerful tools for crop modification which can help biologists and biotechnologists better understand the processes of mutagenesis and genomic alteration. Among the three genome editing systems, CRISR/Cas has high specificity and activity, and therefore it is widely used in genetic engineering. Generally, the genome editing technologies depend on an efficient genetic transformation system. In this paper, we summarize recent progresses and applications on genetic transformation and genome editing in wheat. We also examine the future aspects of genetic transformation and genome editing. We believe that the technologies for wheat efficient genetic engineering and functional studies will become routine with the emergence of high-quality genomic sequences.

Plant Synthetic Metabolic Engineering for Enhancing Crop Nutritional Quality

Nutrient deficiencies in crops are a serious threat to human health, especially for populations in poor areas. To overcome this problem, the development of crops with nutrient-enhanced traits is imperative. Biofortification of crops to improve nutritional quality helps combat nutrient deficiencies by increasing the levels of specific nutrient components. Compared with agronomic practices and conventional plant breeding, plant metabolic engineering and synthetic biology strategies are more effective and accurate in synthesizing specific micronutrients, phytonutrients, and/or bioactive components in crops. In this review, we discuss recent progress in the field of plant synthetic metabolic engineering, specifically in terms of research strategies of multigene stacking tools and engineering complex metabolic pathways, with a focus on improving traits related to micronutrients, phytonutrients, and bioactive components. Advances and innovations in plant synthetic metabolic engineering would facilitate the development of nutrient-enriched crops to meet the nutritional needs of humans.

Carotenoids in Cereal Food Crops: Composition and Retention throughout Grain Storage and Food Processing

Carotenoids are C40 isoprenoids synthesized by plants, as well as some bacteria, fungi and algae, that have been reported to be responsible for a number of benefits conferred on human health. The inability of animals and humans to synthesize de novo these compounds is the reason why they must be introduced from dietary sources. In cereal grains, carotenoids are important phytochemicals responsible for the characteristic yellow colour of the endosperm, which confers nutritional and aesthetic quality to cereal-based products. Cereals are staple foods for a large portion of the world population, and the biofortification of cereal grains with carotenoids may represent a simple way to prevent many human diseases and disorders. Unfortunately, evidence exists that the storage and processing of cereal grains into food products may negatively impact their carotenoid content; so, this loss should be taken into consideration when analysing the potential health benefits of the cereal-based products. Focusing on the recent updates, this review summarizes the chemical composition of the carotenoids in the grains of staple cereals, including wheat, maize, rice and sorghum, the main factors that affect their carotenoid content during storage and processing and the most fruitful strategies used improve the grain carotenoid content and limit the carotenoid post-harvest losses.

Provitamin A Biofortification of Durum Wheat through a TILLING Approach

Macro- and micronutrients, essential for the maintenance of human metabolism, are assimilated daily through the diet. Wheat and other major cereals are a good source of nutrients, such as carbohydrates and proteins, but cannot supply a sufficient amount of essential micronutrients, including provitamin A. As vitamin A deficiency (VAD) leads to several serious diseases throughout the world, the biofortification of a major staple crop, such as wheat, represents an effective way to preserve human health in developing countries. In the present work, a key enzyme involved in the branch of carotenoids pathway producing β-carotene, lycopene epsilon cyclase, has been targeted by a Targeting Induced Local Lesions in Genomes (TILLING) approach in a “block strategy” perspective. The null mutant genotype showed a strong reduction in the expression of the lcyE gene and also interesting pleiotropic effects on an enzyme (β-ring hydroxylase) acting downstream in the pathway. Biochemical profiling of carotenoids in the wheat mutant lines showed an increase of roughly 75% in β-carotene in the grains of the complete mutant line compared with the control. In conclusion, we describe here the production and characterization of a new wheat line biofortified with provitamin A obtained through a nontransgenic approach, which also sheds new light on the molecular mechanism governing carotenoid biosynthesis in durum wheat.

A Neighboring Aromatic-Aromatic Amino Acid Combination Governs Activity Divergence between Tomato Phytoene Synthases

Carotenoids exert multifaceted roles to plants and are critically important to humans. Phytoene synthase (PSY) is a major rate-limiting enzyme in the carotenoid biosynthetic pathway. PSY in plants is normally found as a small enzyme family with up to three members. However, knowledge of PSY isoforms in relation to their respective enzyme activities and amino acid residues that are important for PSY activity is limited. In this study, we focused on two tomato (Solanum lycopersicum) PSY isoforms, PSY1 and PSY2, and investigated their abilities to catalyze carotenogenesis via heterologous expression in transgenic Arabidopsis (Arabidopsis thaliana) and bacterial systems. We found that the fruit-specific PSY1 was less effective in promoting carotenoid biosynthesis than the green tissue-specific PSY2. Examination of the PSY proteins by site-directed mutagenesis analysis and three-dimensional structure modeling revealed two key amino acid residues responsible for this activity difference and identified a neighboring aromatic-aromatic combination in one of the PSY core structures as being crucial for high PSY activity. Remarkably, this neighboring aromatic-aromatic combination is evolutionarily conserved among land plant PSYs except PSY1 of tomato and potato (Solanum tuberosum). Strong transcription of tomato PSY1 likely evolved as compensation for its weak enzyme activity to allow for the massive carotenoid biosynthesis in ripe fruit. This study provides insights into the functional divergence of PSY isoforms and highlights the potential to rationally design PSY for the effective development of carotenoid-enriched crops.

Crop biofortification for iron (Fe), zinc (Zn) and vitamin A with transgenic approaches

Micronutrient malnutrition is an important issue in the developing countries especially in Asia and Africa where millions of school-going children and pregnant women are affected. Poor people are more exposed to risks of malnutrition and hidden hunger due to intake of carbohydrate rich but micronutrient deficient plant based food. The expansion of high yielding but micronutrient poor cultivars further intensified the malnutrition. The existing approaches viz., supplementation and food fortification of staple food with minerals and vitamins can address the issue of adequate nutrition security. But supplementation and fortification is neither feasible for each nutrient specially iron nor viable due to recurrent cost. Recently, genetic bio-fortification of crops is emerged as self-targeted and non-recurrent approach to address the micronutrient malnutrition. Most of the traditional breeding approaches were limited due to non-availability of enough genetic variation in the crossable genepools. Additionally, it also lacks the modulation of target gene expression underlying the micronutrient accumulation. At this juncture, genetic engineering based food biofortification is promising way to address the hidden hunger especially, where breeding is not rewarding due to lack of genetic variability. Genetic modification through gene technology is swift and accurate method to develop nutrient denser crops without any recurrent investment as compared to different strategies.

A global perspective on carotenoids: Metabolism, biotechnology, and benefits for nutrition and health

Carotenoids are lipophilic isoprenoid compounds synthesized by all photosynthetic organisms and some non-photosynthetic prokaryotes and fungi. With some notable exceptions, animals (including humans) do not produce carotenoids de novo but take them in their diets. In photosynthetic systems carotenoids are essential for photoprotection against excess light and contribute to light harvesting, but perhaps they are best known for their properties as natural pigments in the yellow to red range. Carotenoids can be associated to fatty acids, sugars, proteins, or other compounds that can change their physical and chemical properties and influence their biological roles. Furthermore, oxidative cleavage of carotenoids produces smaller molecules such as apocarotenoids, some of which are important pigments and volatile (aroma) compounds. Enzymatic breakage of carotenoids can also produce biologically active molecules in both plants (hormones, retrograde signals) and animals (retinoids). Both carotenoids and their enzymatic cleavage products are associated with other processes positively impacting human health. Carotenoids are widely used in the industry as food ingredients, feed additives, and supplements. This review, contributed by scientists of complementary disciplines related to carotenoid research, covers recent advances and provides a perspective on future directions on the subjects of carotenoid metabolism, biotechnology, and nutritional and health benefits.

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.

Carotenoid Metabolism in Plants: The Role of Plastids

Carotenoids are indispensable to plants and critical in human diets. Plastids are the organelles for carotenoid biosynthesis and storage in plant cells. They exist in various types, which include proplastids, etioplasts, chloroplasts, amyloplasts, and chromoplasts. These plastids have dramatic differences in their capacity to synthesize and sequester carotenoids. Clearly, plastids play a central role in governing carotenogenic activity, carotenoid stability, and pigment diversity. Understanding of carotenoid metabolism and accumulation in various plastids expands our view on the multifaceted regulation of carotenogenesis and facilitates our efforts toward developing nutrient-enriched food crops. In this review, we provide a comprehensive overview of the impact of various types of plastids on carotenoid biosynthesis and accumulation, and discuss recent advances in our understanding of the regulatory control of carotenogenesis and metabolic engineering of carotenoids in light of plastid types in plants.

Effect of extra cysteine residue of new mutant 1Ax1 subunit on the functional properties of common wheat

Subunit pair 1Dx5 + 1Dy10 was recognized as superior subunit combination in wheat and contained an extra repetitive-domain cysteine residue in 1Dx5 that was important for understanding the formation of dough viscoelasticity. In this research, one specific serine codon of the 1Ax1 gene corresponding to the extra cysteine residue of 1Dx5 was substituted by a cysteine codon through site-directed mutagenesis. Four homozygous transgenic lines (T₄) expressing the mutant 1Ax1 gene (mut1Ax1) were produced. Their greater dough strength and stability were confirmed by mixograph and were associated with highly increased gluten index, larger amounts of gluten macropolymers, larger size distribution for glutenin macropolymer particles and varied sodium-dodecyl-sulfate sedimentation volumes, compared with those of the one line expressing wild 1Ax1 that had similar expression level of transgene. The contents of β-sheets in dough and disulfide groups in gluten of the mut1Ax1 transgenic lines were significantly increased. The microstructure of dough mixed to peak showed a more continuous gluten matrix in the mutant transgenic lines than the one line mentioned-above. It was concluded that the extra cysteine residue of mutant 1Ax1 subunit plays a positive role in contributing to dough strength and stability of wheat by cross-linking into gluten aggregates through inter-chain disulfide bonds.

Synthetic genetic circuits in crop plants

The love affair between crop breeding and genetics began over a century ago and has continued unabated, from mass selection programs to targeted genome modifications. Synthetic genetic circuits, a recent development, are combinations of regulatory and coding DNA introduced into a crop plant to achieve a desired function. Genetic circuits could accelerate crop improvement, allowing complex traits to be rationally designed and requisite DNA parts delivered directly into a genome of interest. However, there is not yet a standardized pipeline from exploratory laboratory testing to crop trials, and bringing transgenic products to market remains a considerable barrier. We highlight successes so far and future developments necessary to make genetic circuits a viable crop improvement technology over this century.

Metabolomics-assisted biotechnological interventions for developing plant-based functional foods and nutraceuticals

Today, the dramatic changes in types of food consumed have led to an increased burden of chronic diseases. Therefore, the emphasis of food research is not only to ensure quality food that can supply adequate nutrients to prevent nutrition related diseases, but also to ensure overall physical and mental-health. This has led to the concept of functional foods and nutraceuticals (FFNs), which can be ideally produced and delivered through plants. Metabolomics can help in getting the most relevant functional information, and thus has been considered the greatest -OMICS technology to date. However, metabolomics has not been exploited to the best potential in plant sciences. The technology can be leveraged to identify the health promoting compounds and metabolites that can be used for the development of FFNs. This article reviews (i) plant-based FFNs-related metabolites and their health benefits; (ii) use of different analytic platforms for targeted and non-targeted metabolite profiling along with experimental considerations; (iii) exploitation of metabolomics to develop FFNs in plants using various biotechnological tools; and (iv) potential use of metabolomics in plant breeding. We have also provided some insights into integration of metabolomics with latest genome editing tools for metabolic pathway regulation in plants.