Folate Biofortification of Potato by Tuber-Specific Expression of Four Folate Biosynthesis Genes

CRISPR-mediated iron and folate biofortification in crops: advances and perspectives

Micronutrient deficiency conditions, such as anemia, are the most prevalent global health problem due to inadequate iron and folate in dietary sources. Biofortification advancements can propel the rapid amelioration of nutritionally beneficial components in crops that are required to combat the adverse effects of micronutrient deficiencies on human health. To date, several strategies have been proposed to increase micronutrients in plants to improve food quality, but very few approaches have intrigued `clustered regularly interspaced short palindromic repeats' (CRISPR) modules for the enhancement of iron and folate concentration in the edible parts of plants. In this review, we discuss two important approaches to simultaneously enhance the bioavailability of iron and folate concentrations in rice endosperms by utilizing advanced CRISPR-Cas9-based technology. This includes the 'tuning of cis-elements' and 'enhancer re-shuffling' in the regulatory components of genes that play a vital role in iron and folate biosynthesis/transportation pathways. In particular, base-editing and enhancer re-installation in native promoters of selected genes can lead to enhanced accumulation of iron and folate levels in the rice endosperm. The re-distribution of micronutrients in specific plant organs can be made possible using the above-mentioned contemporary approaches. Overall, the present review discusses the possible approaches for synchronized iron and folate biofortification through modification in regulatory gene circuits employing CRISPR-Cas9 technology.

Biofortification of potato nutrition

BACKGROUND

Potato (Solanum tuberosum L.) is the fourth most important food crop after rice, wheat and maize in the world with the potential to feed the world's population, and potato is a major staple food in many countries. Currently, potato is grown in more than 100 countries and is consumed by more than 1 billion people worldwide, and the global annual output exceeds 300 million tons. With the rapid increase in the global population, potato will play a key role in food supply. These aspects have driven scientists to genetically engineer potato for yield and nutrition improvement.

AIM OF REVIEW

Potato is an excellent source of carbohydrates, rich in vitamins, phenols and minerals. At present, the nutritional fortification of potato has made remarkable progress, and the biomass and nutrient compositions of potato have been significantly improved through agronomic operation and genetic improvement. This review aims to summarize recent advances in the nutritional fortification of potato protein, lipid and vitamin, and provides new insights for future potato research.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review comprehensively summarizes the biofortification of potato five nutrients from protein, lipid, starch, vitamin to mineral. Meanwhile, we also discuss the multilayered insights in the prospects of edible potato fruit, vaccines and high-value products synthesis, and diploid potato seeds reproduction.

Nullification of GFTs fortifies bioactive folates in foxtail millet

In foxtail millet (Setaria italica), knockout of the glutamate formiminotransferases SiGFT1 and 2 increased the accumulation of bioactive folates to approximately four times the level of wild-type plants and decreased levels of the bioinactive oxidation product MeFox by 95%, thus providing a promising route for folate biofortification in cereal crops.

B Vitamins: An Update on Their Importance for Plant Homeostasis

B vitamins are a source of coenzymes for a vast array of enzyme reactions, particularly those of metabolism. As metabolism is the basis of decisions that drive maintenance, growth, and development, B vitamin-derived coenzymes are key components that facilitate these processes. For over a century, we have known about these essential compounds and have elucidated their pathways of biosynthesis, repair, salvage, and degradation in numerous organisms. Only now are we beginning to understand their importance for regulatory processes, which are becoming an important topic in plants. Here, I highlight and discuss emerging evidence on how B vitamins are integrated into vital processes, from energy generation and nutrition to gene expression, and thereby contribute to the coordination of growth and developmental programs, particularly those that concern maintenance of a stable state, which is the foundational tenet of plant homeostasis.

Physiological and Transcriptomic Analyses Reveal the Mechanisms Underlying Methyl Jasmonate-Induced Mannitol Stress Resistance in Banana

Exogenous methyl jasmonate (MeJA) application has shown promising effects on plant defense under diverse abiotic stresses. However, the mechanisms underlying MeJA-induced stress resistance in bananas are unclear. Therefore, in this study, we treated banana plants with 100 μM MeJA before inducing osmotic stress using mannitol. Plant phenotype and antioxidant enzyme activity results demonstrated that MeJA improved osmotic stress resistance in banana plants. Thereafter, to explore the molecular mechanisms underlying MeJA-induced osmotic stress resistance in banana seedlings, we conducted high-throughput RNA sequencing (RNA-seq) using leaf and root samples of "Brazilian" banana seedlings treated with MeJA for 0 h and 8 h. RNA-seq analysis showed that MeJA treatment upregulated 1506 (leaf) and 3341 (root) genes and downregulated 1768 (leaf) and 4625 (root) genes. Then, we performed gene ontology and Kyoto Encyclopedia of Genes and Genomes analyses on the differentially expressed genes. We noted that linoleic acid metabolism was enriched in both root and leaf samples, and the genes of this pathway exhibited different expression patterns; 9S-LOX genes were highly induced by MeJA in the leaves, whereas 13S-LOX genes were highly induced in the roots. We also identified the promoters of these genes, as the differences in response elements may contribute to tissue-specific gene expression in response to MeJA application in banana seedlings. Overall, the findings of this study provide insights into the mechanisms underlying abiotic stress resistance in banana that may aid in the improvement of banana varieties relying on molecular breeding.

The role of orphan crops in the transition to nutritional quality-oriented crop improvement

Micronutrient malnutrition is a persisting problem threatening global human health. Biofortification via metabolic engineering has been proposed as a cost-effective and short-term means to alleviate this burden. There has been a recent rise in the recognition of potential that underutilized, orphan crops can hold in decreasing malnutrition concerns. Here, we illustrate how orphan crops can serve as a medium to provide micronutrients to populations in need, whilst promoting and maintaining dietary diversity. We provide a roadmap, illustrating which aspects to be taken into consideration when evaluating orphan crops. Recent developments have shown successful biofortification via metabolic engineering in staple crops. This review provides guidance in the implementation of these successes to relevant orphan crop species, with a specific focus on the relevant micronutrients iron, zinc, provitamin A and folates.

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.

The nutritional composition of the vegetable soybean (maodou) and its potential in combatting malnutrition

Introduction

Global malnutrition continues to be a canker owing to poor eating habits and over-reliance on the major staple crops. Vegetable soybean (maodou) is gaining popularity globally as an affordable snack and vegetable.

Methods

In this study, we profiled the nutritional composition of 12 soybean cultivars at the vegetable (R6-R7) and mature (R8) stages. We also conducted an RNA-seq analysis during seed development, focusing on key biosynthesis enzymes for quality traits.

Results

The results showed that 100 g of maodou contained 66.54% moisture, 13.49% protein, 7.81% fatty acids, 2.47% soluble sugar, abundant content of minerals, and micronutrients, including folate (462.27 μg FW) and carotenoids (3,935.41 μg FW). Also, the isoflavone content of maodou ranged between 129.26 and 2,359.35 μg/g FW. With regard to the recommended daily allowance, 100 g fresh weight of maodou can contribute 26.98, 115.57, and 11.60% of protein, folate, and zinc, respectively, and significant proportions of other nutrients including linoleic acid (21.16%), linolenic acid (42.96%), zinc (11.60%), and iron (18.01%). On a dry weight basis, maodou has two to six folds higher contents of folate, tocopherol, and carotenoid than the mature soybean. Furthermore, RNA-seq analysis revealed that key biosynthesis enzymes of quality traits are differentially expressed during seed development and may contribute to variations in the content of quality traits at the vegetable and mature stages. Correlation analysis of quality traits at both stages revealed that protein only correlated positively with zinc at the vegetable stage but negatively correlated with total tocopherol and total fatty acid at the mature stage. Complex associations among folates, soluble sugar, and isoflavones were also identified.

Discussion

This study provides insight into the nutritional contents of vegetable soybean and demonstrates that maodou is essential for meeting the nutritional requirements of most countries.

Role of miRNAs in regulation of SA-mediated upregulation of genes involved in folate and methionine metabolism in foxtail millet

The effect of exogenous salicylic acid (SA) on folate metabolism and the related gene regulatory mechanisms is still unclear. In this study, the panicle of foxtail millet treated with different SA concentrations showed that 6 mM SA doubled the 5-methyltetrahydrofolate content compared to that of the control. An untargeted metabolomic analysis revealed that 275 metabolites were enriched in amino acid metabolic pathways. Significantly, the relative content of methionine (Met) after 6 mM SA treatment was 3.14 times higher than the control. Transcriptome analysis revealed that differentially expressed genes were mainly enriched in the folate and amino acid biosynthesis pathways (including Met, Cys, Pro, Ser et al.). The miRNA-mRNA interactions related to the folate and Met metabolic pathways were analyzed and several likely structural gene targets for miRNAs were identified, miRNA-seq analysis revealed that 33 and 51 miRNAs targeted 11 and 15 genes related to the folate and Met pathways, respectively. Eight key genes in the folate metabolism pathway were likely to be up-regulated by 14 new miRNAs and 20 new miRNAs up-regulated the 9 key genes in the Met metabolism pathway. The 6 miRNA-mRNA interactions related to the folate and Met metabolism pathways were verified by qRT-PCR, and consistent with the prediction. The results showed that DHFR1 gene expression level related to folate synthesis was directly up-regulated by Nov-m0139-3p with 3.8 times, but DHFR2 was down-regulated by Nov-m0731-5p with 0.62 times. The expression level of CYSC1 and APIP related to Met synthesis were up-regulated by Nov-m0461-5p and Nov-m0664-3p with 4.27 and 1.32 times, respectively. Our results suggested that exogenous SA could induce the folate and Met accumulated in the panicle of foxtail millet. The higher expression level of DHFR1, FTHFD, CYSC1 and APIP in the folate and Met metabolism pathway and their regulators, including Nov-m0139-3p, Nov-m0717-5p, Nov-m0461-5p and Nov-m0664-3p, could be responsible for these metabolites accumulation. This study lays the theoretical foundation for elucidating the post-transcription regulatory mechanisms of folate and Met metabolism.

Reduced γ-glutamyl hydrolase activity likely contributes to high folate levels in Periyakulam-1 tomato

Tomato cultivars show wide variation in nutraceutical folate in ripe fruits, yet the loci regulating folate levels in fruits remain unexplored. To decipher regulatory points, we compared two contrasting tomato cultivars: Periyakulam-1 (PKM-1) with high folate and Arka Vikas (AV) with low folate. The progression of ripening in PKM-1 was nearly similar to AV but had substantially lower ethylene emission. In parallel, the levels of phytohormones salicylic acid, ABA, and jasmonic acid were substantially lower than AV. The fruits of PKM-1 were metabolically distinct from AV, with upregulation of several amino acids. Consistent with higher °Brix, the red ripe fruits also showed upregulation of sugars and sugar-derived metabolites. In parallel with higher folate, PKM-1 fruits also had higher carotenoid levels, especially lycopene and β-carotene. The proteome analysis showed upregulation of carotenoid sequestration and folate metabolism-related proteins in PKM-1. The deglutamylation pathway mediated by γ-glutamyl hydrolase (GGH) was substantially reduced in PKM-1 at the red-ripe stage. The red-ripe fruits had reduced transcript levels of GGHs and lower GGH activity than AV. Conversely, the percent polyglutamylation of folate was much higher in PKM-1. Our analysis indicates the regulation of GGH activity as a potential target to elevate folate levels in tomato fruits.

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.

Seeing the unseen: a trifoliate (MYB117) mutant allele fortifies folate and carotenoids in tomato fruits

In tomato (Solanum lycopersicum), mutations in the gene encoding the R2R3-MYB117 transcription factor elicit trifoliate leaves and initiate the formation of axillary meristems; however, their effects on fruit ripening remain unexplored. The fruits of a new trifoliate (tf) mutant (tf-5) were firmer and had higher °Brix values and higher folate and carotenoid contents. The transcriptome, proteome, and metabolome profiling of tf-5 reflected a broad-spectrum change in cellular homeostasis. The tf-5 allele enhanced the fruit firmness by suppressing cell wall softening-related proteins. tf-5 fruit displayed a substantial increase in amino acids, particularly γ-aminobutyric acid, with a parallel reduction in aminoacyl-tRNA synthases. The increased lipoxygenase protein and transcript levels seemingly elevated jasmonic acid levels. In addition, increased abscisic acid hydrolase transcript levels coupled with reduced precursor supply lowered abscisic acid levels. The upregulation of carotenoids was mediated by modulation of methylerythreitol and plastoquinone pathways and increased the levels of carotenoid isomerization proteins. The upregulation of folate in tf-5 was connoted by the increase in the precursor p-aminobenzoic acid and transcript levels of several folate biosynthesis genes. The reduction in pterin-6-carboxylate levels and γ-glutamyl hydrolase activity indicated that reduced folate degradation in tf-5 increased folate levels. Our study delineates that in addition to leaf development, MYB117 also influences fruit metabolism. The tf-5 allele can be used to increase γ-aminobutyric acid, carotenoid, and folate levels in tomato.

B vitamin supply in plants and humans: the importance of vitamer homeostasis

B vitamins are a group of water-soluble micronutrients that are required in all life forms. With the lack of biosynthetic pathways, humans depend on dietary uptake of these compounds, either directly or indirectly, from plant sources. B vitamins are frequently given little consideration beyond their role as enzyme accessory factors and are assumed not to limit metabolism. However, it should be recognized that each individual B vitamin is a family of compounds (vitamers), the regulation of which has dedicated pathways. Moreover, it is becoming increasingly evident that individual family members have physiological relevance and should not be sidelined. Here, we elaborate on the known forms of vitamins B₁ , B₆ and B₉ , their distinct functions and importance to metabolism, in both human and plant health, and highlight the relevance of vitamer homeostasis. Research on B vitamin metabolism over the past several years indicates that not only the total level of vitamins but also the oft-neglected homeostasis of the various vitamers of each B vitamin is essential to human and plant health. We briefly discuss the potential of plant biology studies in supporting human health regarding these B vitamins as essential micronutrients. Based on the findings of the past few years we conclude that research should focus on the significance of vitamer homeostasis - at the organ, tissue and subcellular levels - which could improve the health of not only humans but also plants, benefiting from cross-disciplinary approaches and novel technologies.

Heterologous Expression of SiFBP, a Folate-Binding Protein from Foxtail Millet, Confers Increased Folate Content and Altered Amino Acid Profiles with Nutritional Potential to Arabidopsis

The mechanism underlying folate degradation in foxtail millet grains remains unclear. Here, we identified SiFBP (Setaria italica folate-binding protein) from foxtail millet. A phylogenetic tree revealed that FBPs have close genetic relationships among cereal crop species. Docking analysis and heterologous expression of SiFBP in yeast showed that it could bind folic acid (FA). The SiFBP localized to the plasma membrane in tobacco mesophyll cells by transient expression. In Arabidopsis, it was expressed specifically in the roots and germinating seeds. Overexpressing SiFBP in yeast and Arabidopsis significantly increased folate contents. Untargeted metabolome analysis revealed differentially accumulated metabolites between the transgenic lines (TLs) and wild type (WT); these metabolites were mainly enriched in the amino acid metabolism pathway. The relative contents of lysine and leucine, threonine, and l-methionine were significantly higher in the TLs than in WT. Genes related to the folate and lysine synthesis pathways were upregulated in the TLs. Thus, SiFBP can be used for biofortification of folate and important amino acids in crops via genetic engineering.

Applications of Genomic Tools in Plant Breeding: Crop Biofortification

Crop breeding has mainly been focused on increasing productivity, either directly or by decreasing the losses caused by biotic and abiotic stresses (that is, incorporating resistance to diseases and enhancing tolerance to adverse conditions, respectively). Quite the opposite, little attention has been paid to improve the nutritional value of crops. It has not been until recently that crop biofortification has become an objective within breeding programs, through either conventional methods or genetic engineering. There are many steps along this long path, from the initial evaluation of germplasm for the content of nutrients and health-promoting compounds to the development of biofortified varieties, with the available and future genomic tools assisting scientists and breeders in reaching their objectives as well as speeding up the process. This review offers a compendium of the genomic technologies used to explore and create biodiversity, to associate the traits of interest to the genome, and to transfer the genomic regions responsible for the desirable characteristics into potential new varieties. Finally, a glimpse of future perspectives and challenges in this emerging area is offered by taking the present scenario and the slow progress of the regulatory framework as the starting point.

Comparative Transcriptome Analysis Reveals Mechanisms of Folate Accumulation in Maize Grains

Previously, the complexity of folate accumulation in the early stages of maize kernel development has been reported, but the mechanisms of folate accumulation are unclear. Two maize inbred lines, DAN3130 and JI63, with different patterns of folate accumulation and different total folate contents in mature kernels were used to investigate the transcriptional regulation of folate metabolism during late stages of kernel formation by comparative transcriptome analysis. The folate accumulation during DAP 24 to mature kernels could be controlled by circumjacent pathways of folate biosynthesis, such as pyruvate metabolism, glutamate metabolism, and serine/glycine metabolism. In addition, the folate variation between these two inbred lines was related to those genes among folate metabolism, such as genes in the pteridine branch, para-aminobenzoate branch, serine/tetrahydrofolate (THF)/5-methyltetrahydrofolate cycle, and the conversion of THF monoglutamate to THF polyglutamate. The findings provided insight into folate accumulation mechanisms during maize kernel formation to promote folate biofortification.

Red light enhances folate accumulation in wheat seedlings

Red, white, blue, green, and yellow lights were applied to investigate their effects on folate accumulation in wheat seedlings. The different lights, especially red light, significantly increased the total folate content. Total folate showed maximum accumulation under 30 μmol/(m²·s) of red light, with an increase of 24% compared with the control (darkness). 5-Methyl-tetrahydrofolate (5-CH₃-THF) was the dominant folate component, and was significantly increased by red light irradiation. In addition, under red light, the folate content of leaves was higher and more sensitive to light than that of endosperm or roots. Red light up-regulated the expression of guanosine triphosphate (GTP) cyclohydrolase 1 (GCH1) and aminodeoxychorismate synthase(ADCS), enhanced the activity of GCH1 and ADCS, and increased the content of precursors of folate synthesis, including pterin and p-aminobenzoic acid (pABA). Hence, the increased folate accumulation promoted by light could be attributed to the increased content of folate synthesis precursors, the activity of key enzymes, and related gene expression.

Potato biofortification: an effective way to fight global hidden hunger

Hidden hunger is leading to extensive health problems in the developing world. Several strategies could be used to reduce the micronutrient deficiencies by increasing the dietary uptake of essential micronutrients. These include diet diversification, pharmaceutical supplementation, food fortification and crop biofortification. Among all, crop biofortification is the most sustainable and acceptable strategy to overcome the global issue of hidden hunger. Since most of the people suffering from micronutrient deficiencies, have monetary issues and are dependent on staple crops to fulfil their recommended daily requirements of various essential micronutrients. Therefore, increasing the micronutrient concentrations in cost effective staple crops seems to be an effective solution. Potato being the world's most consumed non-grain staple crop with enormous industrial demand appears to be an ideal candidate for biofortification. It can be grown in different climatic conditions, provide high yield, nutrition and dry matter in lesser time. In addition, huge potato germplasm have natural variations related to micronutrient concentrations, which can be utilized for its biofortification. This review discuss the current scenario of micronutrient malnutrition and various strategies that could be used to overcome it. The review also shed a light on the genetic variations present in potato germplasm and suggest effective ways to incorporate them into modern high yielding potato varieties.

Antioxidants in Potatoes: A Functional View on One of the Major Food Crops Worldwide

With a growing world population, accelerating climate changes, and limited arable land, it is critical to focus on plant-based resources for sustainable food production. In addition, plants are a cornucopia for secondary metabolites, of which many have robust antioxidative capacities and are beneficial for human health. Potato is one of the major food crops worldwide, and is recognized by the United Nations as an excellent food source for an increasing world population. Potato tubers are rich in a plethora of antioxidants with an array of health-promoting effects. This review article provides a detailed overview about the biosynthesis, chemical and health-promoting properties of the most abundant antioxidants in potato tubers, including several vitamins, carotenoids and phenylpropanoids. The dietary contribution of diverse commercial and primitive cultivars are detailed and document that potato contributes much more than just complex carbohydrates to the diet. Finally, the review provides insights into the current and future potential of potato-based systems as tools and resources for healthy and sustainable food production.

Multiplying the efficiency and impact of biofortification through metabolic engineering

Ending all forms of hunger by 2030, as set forward in the UN-Sustainable Development Goal 2 (UN-SDG2), is a daunting but essential task, given the limited timeline ahead and the negative global health and socio-economic impact of hunger. Malnutrition or hidden hunger due to micronutrient deficiencies affects about one third of the world population and severely jeopardizes economic development. Staple crop biofortification through gene stacking, using a rational combination of conventional breeding and metabolic engineering strategies, should enable a leap forward within the coming decade. A number of specific actions and policy interventions are proposed to reach this goal.

Selenium and Nano-Selenium Biofortification for Human Health: Opportunities and Challenges

Selenium is an essential micronutrient required for the health of humans and lower plants, but its importance for higher plants is still being investigated. The biological functions of Se related to human health revolve around its presence in 25 known selenoproteins (e.g., selenocysteine or the 21st amino acid). Humans may receive their required Se through plant uptake of soil Se, foods enriched in Se, or Se dietary supplements. Selenium nanoparticles (Se-NPs) have been applied to biofortified foods and feeds. Due to low toxicity and high efficiency, Se-NPs are used in applications such as cancer therapy and nano-medicines. Selenium and nano-selenium may be able to support and enhance the productivity of cultivated plants and animals under stressful conditions because they are antimicrobial and anti-carcinogenic agents, with antioxidant capacity and immune-modulatory efficacy. Thus, nano-selenium could be inserted in the feeds of fish and livestock to improvise stress resilience and productivity. This review offers new insights in Se and Se-NPs biofortification for edible plants and farm animals under stressful environments. Further, extensive research on Se-NPs is required to identify possible adverse effects on humans and their cytotoxicity.

Milk fermented with Lactococcus lactis KLDS4.0325 alleviates folate status in deficient mice

Folate is an essential B vitamin and its deficiency is common in many parts of the world. Natural folate produced by microorganisms may be an alternative to chemically synthesized folic acid (FA) as a dietary supplement. Previously, two lactic acid bacteria (LAB) strains, a high folate-producing Lactococcus lactis subsp. lactis KLDS4.0325 and a weak folate-producing Lactococcus lactis subsp. lactis KLDS4.0613, were identified. The aim of this study was to evaluate the effect of milk fermented with L. lactis KLDS4.0325 (folate-enriched fermented milk, FEFM) in alleviating folate deficiency status using murine folate deficiency models. In addition, the link between gut microbiota diversity and folate levels in mice was investigated. Results showed that FEFM increased FA and 5-methyltetrahydrofolate (5-MTHF) concentrations in the whole blood and liver, and decreased plasma homocysteine (Hcy) levels. 16S rDNA sequence analysis also revealed that the supplementation of FEFM (containing 0.6 μg mL^-1 folate) and 0.6 μg d^-1 FA (FEFM + LFA) significantly improved the poor status of the gut microbiota composition caused by folate deficiency, and the effect was better than that with 1.2 μg d^-1 FA (HFA) supplementation. Our findings show that FEFM can be used as a folate-fortified food to alleviate folate deficiency effectively. In addition, it may be considered as a partial or total replacement for synthetic FA.

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.

Expression Levels of the γ-Glutamyl Hydrolase I Gene Predict Vitamin B9 Content in Potato Tubers

Biofortification of folates in staple crops is an important strategy to help eradicate human folate deficiencies. Folate biofortification using genetic engineering has shown great success in rice grain, tomato fruit, lettuce, and potato tuber. However, consumers’ skepticism, juridical hurdles, and lack of economic model have prevented the widespread adoption of nutritionally-enhanced genetically-engineered (GE) food crops. Meanwhile, little effort has been made to biofortify food crops with folate by breeding. Previously we reported >10-fold variation in folate content in potato genotypes. To facilitate breeding for enhanced folate content, we attempted to identify genes that control folate content in potato tuber. For this, we analyzed the expression of folate biosynthesis and salvage genes in low- and high-folate potato genotypes. First, RNA-Seq analysis showed that, amongst all folate biosynthesis and salvage genes analyzed, only one gene, which encodes γ-glutamyl hydrolase 1 (GGH1), was consistently expressed at higher levels in high- compared to low-folate segregants of a Solanum boliviense Dunal accession. Second, quantitative PCR showed that GGH1 transcript levels were higher in high- compared to low-folate segregants for seven out of eight pairs of folate segregants analyzed. These results suggest that GGH1 gene expression is an indicator of folate content in potato tubers.

Genetic mapping of folate QTLs using a segregated population in maize

As essential B vitamin for humans, folates accumulation in edible parts of crops, such as maize kernels, is of great importance for human health. But its breeding is always limited by the prohibitive cost of folate profiling. The molecular breeding is a more executable and efficient way for folate fortification, but is limited by the molecular knowledge of folate regulation. Here we report the genetic mapping of folate quantitative trait loci (QTLs) using a segregated population crossed by two maize lines, one high in folate (GEMS31) and the other low in folate (DAN3130). Two folate QTLs on chromosome 5 were obtained by the combination of F₂ whole-exome sequencing and F₃ kernel-folate profiling. These two QTLs had been confirmed by bulk segregant analysis using F₆ pooled DNA and F₇ kernel-folate profiling, and were overlapped with QTLs identified by another segregated population. These two QTLs contributed 41.6% of phenotypic variation of 5-formyltetrahydrofolate, the most abundant storage form among folate derivatives in dry maize grains, in the GEMS31×DAN3130 population. Their fine mapping and functional analysis will reveal details of folate metabolism, and provide a basis for marker-assisted breeding aimed at the enrichment of folates in maize kernels.

Evolution of folate biosynthesis and metabolism across algae and land plant lineages

Tetrahydrofolate and its derivatives, commonly known as folates, are essential for almost all living organisms. Besides acting as one-carbon donors and acceptors in reactions producing various important biomolecules such as nucleic and amino acids, as well as pantothenate, they also supply one-carbon units for methylation reactions. Plants along with bacteria, yeast and fungi synthesize folates de novo and therefore constitute a very important dietary source of folates for animals. All the major steps of folate biosynthesis and metabolism have been identified but only few have been genetically characterized in a handful of model plant species. The possible differences in the folate pathway between various plant and algal species have never been explored. In this study we present a comprehensive comparative study of folate biosynthesis and metabolism of all major land plant lineages as well as green and red algae. The study identifies new features of plant folate metabolism that might open new directions to folate research in plants.

Improved folate accumulation in genetically modified maize and wheat

Folates are indispensable co-factors for one-carbon metabolism in all organisms. In humans, suboptimal folate intake results in serious disorders. One promising strategy for improving human folate status is to enhance folate levels in food crops by metabolic engineering. In this study, we cloned two GmGCHI (GTP cyclohydrolase I) genes (Gm8gGCHI and Gm3gGCHI) and one GmADCS (aminodeoxychorismate synthase) gene from soybean, which are responsible for synthesizing the folate precursors pterin and p-aminobenzoate, respectively. We initially confirmed their functions in transgenic Arabidopsis plants and found that Gm8gGCHI increased pterin and folate production more than Gm3gGCHI did. We then co-expressed Gm8gGCHI and GmADCS driven by endosperm-specific promoters in maize and wheat, two major staple crops, to boost their folate metabolic flux. A 4.2-fold and 2.3-fold increase in folate levels were observed in transgenic maize and wheat grains, respectively. To optimize wheat folate enhancement, codon-optimized Gm8gGCHI and tomato LeADCS genes under the control of a wheat endosperm-specific glutenin promoter (1Dx5) were co-transformed. This yielded a 5.6-fold increase in folate in transgenic wheat grains (Gm8gGCHI+/LeADCS+). This two-gene co-expression strategy therefore has the potential to greatly enhance folate levels in maize and wheat, thus improving their nutritional value.

Toward Eradication of B-Vitamin Deficiencies: Considerations for Crop Biofortification

'Hidden hunger' involves insufficient intake of micronutrients and is estimated to affect over two billion people on a global scale. Malnutrition of vitamins and minerals is known to cause an alarming number of casualties, even in the developed world. Many staple crops, although serving as the main dietary component for large population groups, deliver inadequate amounts of micronutrients. Biofortification, the augmentation of natural micronutrient levels in crop products through breeding or genetic engineering, is a pivotal tool in the fight against micronutrient malnutrition (MNM). Although these approaches have shown to be successful in several species, a more extensive knowledge of plant metabolism and function of these micronutrients is required to refine and improve biofortification strategies. This review focuses on the relevant B-vitamins (B1, B6, and B9). First, the role of these vitamins in plant physiology is elaborated, as well their biosynthesis. Second, the rationale behind vitamin biofortification is illustrated in view of pathophysiology and epidemiology of the deficiency. Furthermore, advances in biofortification, via metabolic engineering or breeding, are presented. Finally, considerations on B-vitamin multi-biofortified crops are raised, comprising the possible interplay of these vitamins in planta.