From in planta Function to Vitamin-Rich Food Crops: The ACE of Biofortification

OsTH1 is a key player in thiamin biosynthesis in rice

Thiamin is a vital nutrient that acts as a cofactor for several enzymes primarily localized in the mitochondria. These thiamin-dependent enzymes are involved in energy metabolism, nucleic acid biosynthesis, and antioxidant machinery. The enzyme HMP-P kinase/thiamin monophosphate synthase (TH1) holds a key position in thiamin biosynthesis, being responsible for the phosphorylation of HMP-P into HMP-PP and for the condensation of HMP-PP and HET-P to form TMP. Through mathematical kinetic model, we have identified TH1 as a critical player for thiamin biofortification in rice. We further focused on the functional characterization of OsTH1. Sequence and gene expression analysis, along with phylogenetic studies, provided insights into OsTH1 bifunctional features and evolution. The indispensable role of OsTH1 in thiamin biosynthesis was validated by heterologous expression of OsTH1 and successful complementation of yeast knock-out mutants impaired in thiamin production. We also proved that the sole OsTH1 overexpression in rice callus significantly improves B1 concentration, resulting in 50% increase in thiamin accumulation. Our study underscores the critical role of OsTH1 in thiamin biosynthesis, shedding light on its bifunctional nature and evolutionary significance. The significant enhancement of thiamin accumulation in rice callus upon OsTH1 overexpression constitutes evidence of its potential application in biofortification strategies.

Biofortification as a solution for addressing nutrient deficiencies and malnutrition

Malnutrition, defined as both undernutrition and overnutrition, is a major global health concern affecting millions of people. One possible way to address nutrient deficiency and combat malnutrition is through biofortification. A comprehensive review of the literature was conducted to explore the current state of biofortification research, including techniques, applications, effectiveness and challenges. Biofortification is a promising strategy for enhancing the nutritional condition of at-risk populations. Biofortified varieties of basic crops, including rice, wheat, maize and beans, with elevated amounts of vital micronutrients, such as iron, zinc, vitamin A and vitamin C, have been successfully developed using conventional and advanced technologies. Additionally, the ability to specifically modify crop genomes to improve their nutritional profiles has been made possible by recent developments in genetic engineering, such as CRISPR-Cas9 technology. The health conditions of people have been shown to improve and nutrient deficiencies were reduced when biofortified crops were grown. Particularly in environments with limited resources, biofortification showed considerable promise as a long-term and economical solution to nutrient shortages and malnutrition. To fully exploit the potential of biofortified crops to enhance public health and global nutrition, issues such as consumer acceptance, regulatory permitting and production and distribution scaling up need to be resolved. Collaboration among governments, researchers, non-governmental organizations and the private sector is essential to overcome these challenges and promote the widespread adoption of biofortification as a key part of global food security and nutrition strategies.

A protocol for a turbidimetric assay using a Saccharomyces cerevisiae thiamin biosynthesis mutant to estimate total vitamin B1 content in plant tissue samples

BACKGROUND

Understanding thiamin (thiamine; vitamin B1) metabolism in plants is crucial, as it impacts plant nutritional value as well as stress tolerance. Studies aimed at elucidating novel aspects of thiamin in plants rely on adequate assessment of thiamin content. Mass spectrometry-based methods provide reliable quantification of thiamin as well as closely related biomolecules. However, these techniques require expensive equipment and expertise. Microbiological turbidimetric assays can evaluate the presence of thiamin in a given sample, only requiring low-cost, standard lab equipment. Although these microbiological assays do not reach the accuracy provided by mass spectrometry-based methods, the ease with which they can be deployed in an inexpensive and high-throughput manner, makes them a favorable method in many circumstances. However, the thiamin research field could benefit from a detailed step-by-step protocol to perform such assays as well as a further assessment of its potential and limitations.

RESULTS

Here, we show that the Saccharomyces cerevisiae thiamin biosynthesis mutant thi6 is an ideal candidate to be implemented in a turbidimetric assay aimed at assessing the content of thiamin and its phosphorylated equivalents (total vitamer B1). An optimized protocol was generated, adapted from a previously established microbiological assay using the thi4 mutant. A step-by-step guidance for this protocol is presented. Furthermore, the applicability of the assay is illustrated by assessment of different samples, including plant as well as non-plant materials. In doing so, our work provides an extension of the applicability of the microbiological assay on top of providing important considerations upon implementing the protocol.

CONCLUSIONS

An inexpensive, user-friendly protocol, including step-by-step guidance, which allows adequate estimation of vitamer B1 content of samples, is provided. The method is well-suited to screen materials to identify altered vitamer B1 content, such as in metabolic engineering or screening of germplasm.

Strategies to fortify the nutritional values of polished rice by implanting selective traits from brown rice: A nutrigenomics-based approach

Whole-grain cereals are important components of a healthy diet. It reduces the risk of many deadly diseases like cardiovascular diseases, diabetes, cancer, etc. Brown rice is an example of whole grain food, which is highly nutritious due to the presence of various bioactive compounds (flavonoids, phenolics, vitamins, phytosterols, oils, etc.) associated with the rice bran layer of brown rice. White rice is devoid of the nutritious rice bran layer and thus lacks the bioactive compounds which are the major attractants of brown rice. Therefore, to confer health benefits to the public at large, the nutrigenomic potential of white rice may be improved by integrating the phytochemicals associated with the rice bran layer of brown rice into it via biofortification processes like conventional breeding, agronomic practices, metabolic engineering, CRISPR/Cas9 technology, and RNAi techniques. Thus, this review article focuses on improving the nutritional qualities of white/polished rice through biofortification processes, utilizing new breeding technologies (NBTs).

Breeding and adoption of biofortified crops and their nutritional impact on human health

Micronutrient malnutrition has affected over two billion people worldwide and continues to be a health risk. A growing human population, poverty, and the prevalence of low dietary diversity are jointly responsible for malnutrition, particularly in developing nations. Inadequate bioavailability of key micronutrients, such as iron (Fe), zinc (Zn), and vitamin A, can be improved through agronomic and/or genetic interventions. The Consultative Group on International Agricultural Research prioritizes developing biofortified food crops that are rich in minerals and vitamins through the HarvestPlus initiative on biofortification. The objective of this review is to provide an overview of biofortified food crops along with evidence supporting their acceptability and adoption. Between 2004 and 2019, 242 biofortified varieties belonging to 11 major crops were released in 30 countries across Asia, Africa, and Latin America. These conventionally bred biofortified crops include Fe-enriched beans, pearl millet, and cowpea; Zn-enriched rice, wheat, and maize; both Fe- and Zn-enriched lentil and sorghum; and varieties with improved vitamin A in orange-fleshed sweet potato, maize, cassava, and banana/plantain. In addition to ongoing efforts, breeding innovations, such as speed breeding and CRISPR-based gene editing technologies, will be necessary for the next decade to reach two billion people with biofortified crops.

Carotenoid metabolism: New insights and synthetic approaches

Carotenoids are well-known isoprenoid pigments naturally produced by plants, algae, photosynthetic bacteria as well as by several heterotrophic microorganisms. In plants, they are synthesized in plastids where they play essential roles in light-harvesting and in protecting the photosynthetic apparatus from reactive oxygen species (ROS). Carotenoids are also precursors of bioactive metabolites called apocarotenoids, including vitamin A and the phytohormones abscisic acid (ABA) and strigolactones (SLs). Genetic engineering of carotenogenesis made possible the enhancement of the nutritional value of many crops. New metabolic engineering approaches have recently been developed to modulate carotenoid content, including the employment of CRISPR technologies for single-base editing and the integration of exogenous genes into specific "safe harbors" in the genome. In addition, recent studies revealed the option of synthetic conversion of leaf chloroplasts into chromoplasts, thus increasing carotenoid storage capacity and boosting the nutritional value of green plant tissues. Moreover, transient gene expression through viral vectors allowed the accumulation of carotenoids outside the plastid. Furthermore, the utilization of engineered microorganisms allowed efficient mass production of carotenoids, making it convenient for industrial practices. Interestingly, manipulation of carotenoid biosynthesis can also influence plant architecture, and positively impact growth and yield, making it an important target for crop improvements beyond biofortification. Here, we briefly describe carotenoid biosynthesis and highlight the latest advances and discoveries related to synthetic carotenoid metabolism in plants and microorganisms.

The perils of planning strategies to increase vitamin C content in plants: Beyond the hype

Ever since the identification of vitamin C (ascorbic acid, AsA) as an essential molecule that humans cannot synthesize on their own, finding adequate dietary sources of AsA became a priority in nutrition research. Plants are the main producers of AsA for humans and other non-synthesizing animals. It was immediately clear that some plant species have more AsA than others. Further studies evidenced that AsA content varies in different plant organs, in different developmental stages/environmental conditions and even within different cell compartments. With the progressive discovery of the genes of the main (Smirnoff-Wheeler) and alternative pathways coding for the enzymes involved in AsA biosynthesis in plants, the simple overexpression of those genes appeared a suitable strategy for boosting AsA content in any plant species or organ. Unfortunately, overexpression experiments mostly resulted in limited, if any, AsA increase, apparently due to a tight regulation of the biosynthetic machinery. Attempts to identify regulatory steps in the pathways that could be manipulated to obtain unlimited AsA production were also less successful than expected, confirming the difficulties in "unleashing" AsA synthesis. A different approach to increase AsA content has been the overexpression of genes coding for enzymes catalyzing the recycling of the oxidized forms of vitamin C, namely monodehydroascorbate and dehydroascorbate reductases. Such approach proved mostly effective in making the overexpressors apparently more resistant to some forms of environmental stress, but once more did not solve the issue of producing massive AsA amounts for human diet. However, it should also be considered that a hypothetical unlimited increase in AsA content is likely to interfere with plant development, which is in many ways regulated by AsA availability itself. The present review article aims at summarizing the many attempts made so far to improve AsA production/content in plants, evidencing the most promising ones, and at providing information about the possible unexpected consequences of a pure biotechnological approach not keeping into account the peculiar features of the AsA system in plants.

Wheat and Rice beyond Phenolic Acids: Genetics, Identification Database, Antioxidant Properties, and Potential Health Effects

Wheat and rice play a vital role in human nutrition and food security. A better understanding of the potential health benefits associated with consuming these cereals, combined with studies by plant scientists and food chemists to view the entire food value chain from the field, pre and post-harvest processing, and subsequent "fork" consumption, may provide the necessary tools to optimize wheat and rice production towards the goal of better human health improvement and food security, providing tools to better adapt to the challenges associated with climate change. Since the available literature usually focuses on only one food chain segment, this narrative review was designed to address the identities and concentration of phenolics of these cereal crops from a farm-to-fork perspective. Wheat and rice genetics, phenolic databases, antioxidant properties, and potential health effects are summarized. These cereals contain much more than phenolic acids, having significant concentrations of flavonoids (including anthocyanins) and proanthocyanidins in a cultivar-dependent manner. Their potential health benefits in vitro have been extensively studied. According to a number of in vivo studies, consumption of whole wheat, wheat bran, whole rice, and rice bran may be strategies to improve health. Likewise, anthocyanin-rich cultivars have shown to be very promising as functional foods.

Transcriptomic and Physiological Analyses Reveal Potential Genes Involved in Photoperiod-Regulated β-Carotene Accumulation Mechanisms in the Endocarp of Cucumber (Cucumis sativus L.) Fruit

The accumulation of carotenoids in plants is a key nutritional quality in many horticultural crops. Although the structural genes encoding the biosynthetic enzymes are well-characterized, little is known regarding photoperiod-mediated carotenoid accumulation in the fruits of some horticultural crops. Herein, we performed physiological and transcriptomic analyses using two cucumber genotypes, SWCC8 (XIS-orange-fleshed and photoperiod-sensitive) and CC3 (white-fleshed and photoperiod-non-sensitive), established under two photoperiod conditions (8L/16D vs. 12L/12D) at four fruit developmental stages. Day-neutral treatments significantly increased fruit β-carotene content by 42.1% compared to short day (SD) treatments in SWCC8 at 40 DAP with no significant changes in CC3. Day-neutral condition elevated sugar levels of fruits compared to short-day treatments. According to GO and KEGG analyses, the predominantly expressed genes were related to photosynthesis, carotenoid biosynthesis, plant hormone signaling, circadian rhythms, and carbohydrates. Consistent with β-carotene accumulation in SWCC8, the day-neutral condition elevated the expression of key carotenoid biosynthesis genes such as PSY1, PDS, ZDS1, LYCB, and CHYB1 during later stages between 30 to 40 days of fruit development. Compared to SWCC8, CC3 showed an expression of DEGs related to carotenoid cleavage and oxidative stresses, signifying reduced β-carotene levels in CC3 cucumber. Further, a WGCNA analysis revealed co-expression between carbohydrate-related genes (pentose-phosphatase synthase, β-glucosidase, and trehalose-6-phosphatase), photoperiod-signaling genes (LHY, APRR7/5, FKF1, PIF3, COP1, GIGANTEA, and CK2) and carotenoid-biosynthetic genes, thus suggesting that a cross-talk mechanism between carbohydrates and light-related genes induces β-carotene accumulation. The results highlighted herein provide a framework for future gene functional analyses and molecular breeding towards enhanced carotenoid accumulation in edible plant organs.

Wheat grain proteomic and protein-metabolite interactions analyses provide insights into plant growth promoting bacteria-arbuscular mycorrhizal fungi-wheat interactions

Proteomic, protein-protein and protein-metabolite interaction analyses in wheat inoculated with PGPB and AMF identified key proteins and metabolites that may have a role in enhancing yield and biofortification. Plant growth-promoting bacteria (PGPB) and arbuscular mycorrhizal fungi (AMF) have an impact on grain yield and nutrition. This dynamic yet complex interaction implies a broad reprogramming of the plant's metabolic and proteomic activities. However, little information is available regarding the role of native PGPB and AMF and how they affect the plant proteome, especially under field conditions. Here, proteomic, protein-protein and protein-metabolite interaction studies in wheat triggered by PGPB, Bacillus subtilis CP4 either alone or together with AMF under field conditions was carried out. The dual inoculation with native PGPB (CP4) and AMF promoted the differential abundance of many proteins, such as histones, glutenin, avenin and ATP synthase compared to the control and single inoculation. Interaction study of these differentially expressed proteins using STRING revealed that they interact with other proteins involved in seed development and abiotic stress tolerance. Furthermore, these interacting proteins are involved in carbon fixation, sugar metabolism and biosynthesis of amino acids. Molecular docking predicted that wheat seed storage proteins, avenin and glutenin interact with secondary metabolites, such as trehalose, and sugars, such as xylitol. Mapping of differentially expressed proteins to KEGG pathways showed their involvement in sugar metabolism, biosynthesis of secondary metabolites and modulation of histones. These proteins and metabolites can serve as markers for improving wheat-PGPB-AMF interactions leading to higher yield and biofortification.

Mining of Potential Gene Resources for Breeding Nutritionally Improved Maize

Maize is one of the leading food crops and its kernel is rich in starch, lipids, protein and other energy substances. In addition, maize kernels also contain many trace elements that are potentially beneficial to human health, such as vitamins, minerals and other secondary metabolites. However, gene resources that could be applied for nutrient improvement are limited in maize. In this review, we summarized 107 genes that are associated with nutrient content from different plant species and identified 246 orthologs from the maize genome. In addition, we constructed physical maps and performed a detailed expression pattern analysis for the 246 maize potential gene resources. Combining expression profiles and their potential roles in maize nutrient improvement, genetic engineering by editing or ectopic expression of these genes in maize are expected to improve resistant starch, oil, essential amino acids, vitamins, iron, zinc and anthocyanin levels of maize grains. Thus, this review provides valuable gene resources for maize nutrient improvement.

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.

Ascorbic Acid Content and Transcriptional Profiling of Genes Involved in Its Metabolism during Development of Petals, Leaves, and Fruits of Orange (Citrus sinensis cv. Valencia Late)

Citrus fruit is one of the most important contributors to the ascorbic acid (AsA) intake in humans. Here, we report a comparative analysis of AsA content and transcriptional changes of genes related to its metabolism during development of petals, leaves and fruits of Valencia Late oranges (Citrus sinensis). Petals of close flowers and at anthesis contained the highest concentration of AsA. In fruits, AsA content in the flavedo reached a maximum at color break, whereas the pulp accumulated lower levels and experienced minor fluctuations during development. AsA levels in leaves were similar to those in the flavedo at breaker stage. The transcriptional profiling of AsA biosynthetic, degradation, and recycling genes revealed a complex and specific interplay of the different pathways for each tissue. The D-galacturonic acid pathway appeared to be relevant in petals, whereas in leaves the L-galactose pathway (GGP and GME) also contributed to AsA accumulation. In the flavedo, AsA content was positively correlated with the expression of GGP of the L-galactose pathway and negatively with DHAR1 gene of the recycling pathway. In the pulp, AsA appeared to be mainly controlled by the coordination among the D-galacturonic acid pathway and the MIOX and GalDH genes. Analysis of the promoters of AsA metabolism genes revealed a number of cis-acting elements related to developmental signals, but their functionalities remain to be investigated.

Metabolic engineering provides insight into the regulation of thiamin biosynthesis in plants

Thiamin (or thiamine) is a water-soluble B-vitamin (B1), which is required, in the form of thiamin pyrophosphate, as an essential cofactor in crucial carbon metabolism reactions in all forms of life. To ensure adequate metabolic functioning, humans rely on a sufficient dietary supply of thiamin. Increasing thiamin levels in plants via metabolic engineering is a powerful strategy to alleviate vitamin B1 malnutrition and thus improve global human health. These engineering strategies rely on comprehensive knowledge of plant thiamin metabolism and its regulation. Here, multiple metabolic engineering strategies were examined in the model plant Arabidopsis thaliana. This was achieved by constitutive overexpression of the three biosynthesis genes responsible for B1 synthesis, HMP-P synthase (THIC), HET-P synthase (THI1), and HMP-P kinase/TMP pyrophosphorylase (TH1), either separate or in combination. By monitoring the levels of thiamin, its phosphorylated entities, and its biosynthetic intermediates, we gained insight into the effect of either strategy on thiamin biosynthesis. Moreover, expression analysis of thiamin biosynthesis genes showed the plant's intriguing ability to respond to alterations in the pathway. Overall, we revealed the necessity to balance the pyrimidine and thiazole branches of thiamin biosynthesis and assessed its biosynthetic intermediates. Furthermore, the accumulation of nonphosphorylated intermediates demonstrated the inefficiency of endogenous thiamin salvage mechanisms. These results serve as guidelines in the development of novel thiamin metabolic engineering strategies.

Unravelling the Effect of Provitamin A Enrichment on Agronomic Performance of Tropical Maize Hybrids

Maize is consumed in different traditional diets as a source of macro- and micro-nutrients across Africa. Significant investment has thus been made to develop maize with high provitamin A content to complement other interventions for alleviating vitamin A deficiencies. The current breeding focus on increasing β-carotene levels to develop biofortified maize may affect the synthesis of other beneficial carotenoids. The changes in carotenoid profiles, which are commonly affected by environmental factors, may also lead to a trade-off with agronomic performance. The present study was therefore conducted to evaluate provitamin A biofortified maize hybrids across diverse field environments. The results showed that the difference in accumulating provitamin A and other beneficial carotenoids across variable growing environments was mainly regulated by the genetic backgrounds of the hybrids. Many hybrids, accumulating more than 10 µg/g of provitamin A, produced higher grain yields (>3600 kg/ha) than the orange commercial maize hybrid (3051 kg/ha). These hybrids were also competitive, compared to the orange commercial maize hybrid, in accumulating lutein and zeaxanthins. Our study showed that breeding for enhanced provitamin A content had no adverse effect on grain yield in the biofortified hybrids evaluated in the regional trials. Furthermore, the results highlighted the possibility of developing broadly adapted hybrids containing high levels of beneficial carotenoids for commercialization in areas with variable maize growing conditions in Africa.

Vitamins in Cereals: A Critical Review of Content, Health Effects, Processing Losses, Bioaccessibility, Fortification, and Biofortification Strategies for Their Improvement

Around the world, cereals are stapled foods and good sources of vitamins A, B, and E. As cereals are inexpensive and consumed in large quantities, attempts are being made to enrich cereals using fortification and biofortification in order to address vitamin deficiency disorders in a vulnerable population. The processing and cooking of cereals significantly affect vitamin content. Depending on grain structure, milling can substantially reduce vitamin content, while cooking methods can significantly impact vitamin retention and bioaccessibility. Pressure cooking has been reported to result in large vitamin losses, whereas minimal vitamin loss was observed following boiling. The fortification of cereal flour with vitamins B1, B2, B3, and B9, which are commonly deficient, has been recommended; and in addition, region-specific fortification using either synthetic or biological vitamins has been suggested. Biofortification is a relatively new concept and has been explored as a method to generate vitamin-rich crops. Once developed, biofortified crops can be utilized for several years. A recent cereal biofortification success story is the enrichment of maize with provitamin A carotenoids.

Metabolic engineering of rice endosperm towards higher vitamin B1 accumulation

Rice is a major food crop to approximately half of the human population. Unfortunately, the starchy endosperm, which is the remaining portion of the seed after polishing, contains limited amounts of micronutrients. Here, it is shown that this is particularly the case for thiamin (vitamin B1). Therefore, a tissue-specific metabolic engineering approach was conducted, aimed at enhancing the level of thiamin specifically in the endosperm. To achieve this, three major thiamin biosynthesis genes, THIC, THI1 and TH1, controlled by strong endosperm-specific promoters, were employed to obtain engineered rice lines. The metabolic engineering approaches included ectopic expression of THIC alone, in combination with THI1 (bigenic) or combined with both THI1 and TH1 (trigenic). Determination of thiamin and thiamin biosynthesis intermediates reveals the impact of the engineering approaches on endosperm thiamin biosynthesis. The results show an increase of thiamin in polished rice up to threefold compared to WT, and stable upon cooking. These findings confirm the potential of metabolic engineering to enhance de novo thiamin biosynthesis in rice endosperm tissue and aid in steering future biofortification endeavours.

The coenzyme thiamine diphosphate displays a daily rhythm in the Arabidopsis nucleus

In plants, metabolic homeostasis—the driving force of growth and development—is achieved through the dynamic behavior of a network of enzymes, many of which depend on coenzymes for activity. The circadian clock is established to influence coordination of supply and demand of metabolites. Metabolic oscillations independent of the circadian clock, particularly at the subcellular level is unexplored. Here, we reveal a metabolic rhythm of the essential coenzyme thiamine diphosphate (TDP) in the Arabidopsis nucleus. We show there is temporal separation of the clock control of cellular biosynthesis and transport of TDP at the transcriptional level. Taking advantage of the sole reported riboswitch metabolite sensor in plants, we show that TDP oscillates in the nucleus. This oscillation is a function of a light-dark cycle and is independent of circadian clock control. The findings are important to understand plant fitness in terms of metabolite rhythms.

Noordally et al. show that the essential coenzyme thiamine diphosphate exhibits a daily rhythm in the Arabidopsis nucleus, which is driven by light-dark cycles and not by the circadian clock. This study provides insight into our understanding of the optimization of plant fitness.

Prospects for Carotenoid Biofortification Targeting Retention and Catabolism

Due to the ongoing prevalence of vitamin A deficiency (VAD) in developing countries there has been a large effort towards increasing the carotenoid content of staple foods via biofortification. Common strategies used for carotenoid biofortification include altering flux through the biosynthesis pathway to direct synthesis to a specific product, generally β-carotene, or via increasing the expression of genes early in the carotenoid biosynthesis pathway. Recently, carotenoid biofortification strategies are turning towards increasing the retention of carotenoids in plant tissues either via altering sequestration within the cell or via downregulating enzymes known to cause degradation of carotenoids. To date, little attention has focused on increasing the stability of carotenoids, which may be a promising method of increasing carotenoid content in staple foods.

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.

Genetic Engineering for Global Food Security: Photosynthesis and Biofortification

Increasing demands for food and resources are challenging existing markets, driving a need to continually investigate and establish crop varieties with improved yields and health benefits. By the later part of the century, current estimates indicate that a >50% increase in the yield of most of the important food crops including wheat, rice and barley will be needed to maintain food supplies and improve nutritional quality to tackle what has become known as 'hidden hunger'. Improving the nutritional quality of crops has become a target for providing the micronutrients required in remote communities where dietary variation is often limited. A number of methods to achieve this have been investigated over recent years, from improving photosynthesis through genetic engineering, to breeding new higher yielding varieties. Recent research has shown that growing plants under elevated [CO2] can lead to an increase in Vitamin C due to changes in gene expression, demonstrating one potential route for plant biofortification. In this review, we discuss the current research being undertaken to improve photosynthesis and biofortify key crops to secure future food supplies and the potential links between improved photosynthesis and nutritional quality.

Construction, characteristics and high throughput molecular screening methodologies in some special breeding populations: a horticultural perspective

Advanced marker technologies are widely used for evaluation of genetic diversity in cultivated crops, wild ancestors, landraces or any special plant genotypes. Developing agricultural cultivars requires the following steps: (i) determining desired characteristics to be improved, (ii) screening genetic resources to help find a superior cultivar, (iii) intercrossing selected individuals, (iv) generating genetically hybrid populations and screening them for agro-morphological or molecular traits, (v) evaluating the superior cultivar candidates, (vi) testing field performance at different locations, and (vii) certifying. In the cultivar development process valuable genes can be identified by creating special biparental or multiparental populations and analysing their association using suitable markers in given populations. These special populations and advanced marker technologies give us a deeper knowledge about the inherited agronomic characteristics. Unaffected by the changing environmental conditions, these provide a higher understanding of genome dynamics in plants. The last decade witnessed new applications for advanced molecular techniques in the area of breeding,with low costs per sample. These, especially, include next-generation sequencing technologies like reduced representation genome sequencing (genotyping by sequencing, restriction site-associated DNA). These enabled researchers to develop new markers, such as simple sequence repeat and single- nucleotide polymorphism, for expanding the qualitative and quantitative information onpopulation dynamics. Thus, the knowledge acquired from novel technologies is a valuable asset for the breeding process and to better understand the population dynamics, their properties, and analysis methods.