Manipulating the Phytic Acid Content of Rice Grain Toward Improving Micronutrient Bioavailability

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.

Negative regulators of grain yield and mineral contents in rice: potential targets for CRISPR-Cas9-mediated genome editing

Rice is a major global staple food crop, and improving its grain yield and nutritional quality has been a major thrust research area since last decades. Yield and nutritional quality are complex traits which are controlled by multiple signaling pathways. Sincere efforts during past decades of research have identified several key genetic and molecular regulators that governed these complex traits. The advent of clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9)-mediated gene knockout approaches has accelerated the development of improved varieties; however, finding out target gene with negative regulatory function in particular trait without giving any pleiotropic effect remains a challenge. Here, we have reviewed past and recent literature and identified important negative regulators of grain yield and mineral contents which could be potential targets for CRISPR-Cas9-mediated gene knockout. Additionally, we have also compiled a list of microRNAs (miRNAs), which target positive regulators of grain yield, plant stress tolerance, and grain mineral contents. Knocking out these miRNAs could help to increase expression of such positive regulators and thus improve the plant trait. The knowledge presented in this review would help to further accelerate the CRISPR-Cas9-mediated trait improvement in rice.

Zinc Oxide Nanoparticles Foliar Application Effectively Enhanced Zinc and Aroma Content in Rice (Oryza sativa L.) Grains

The search for an effective zinc fertilizer and its application method to effectively increase zinc content and enhance aroma in rice grains is a crucial objective. In this study, a 2-year field plot experiment was conducted to investigate the influence of ZnO NPs foliar spraying on rice quality, grain zinc and aroma content, along with exploring the physiological mechanisms underlying these effects. Our results demonstrated that the rice breakdown value and taste value of foliar spraying zinc oxide nanoparticles were improved by 31.0-41.7% and 8.2-13.0% compared with CK (control treatment involved spraying water), improving the tasting and steaming quality of rice. While Fe and Cu content in grains decreased for the application of zinc oxide nanoparticles, zinc oxide nanoparticles foliar spraying significantly increased the zinc content and accumulation of grains by 33.6-65.1% and 37.8-74.7%, respectively. Further analysis showed that the sprayed zinc oxide nanoparticles achieved effective enrichment of zinc in edible parts and increased the final bioavailability of Zn. In addition, foliar spraying of zinc oxide nanoparticles significantly increased activities of nitrate reductase and glutamine synthetase in leaves, which elevated nitrogen content in leaves and grains, and ultimately enhanced 2-acetyl-1-pyrroline (2-AP) content in grains at maturity by 6.1-21.4% compared to CK. Our findings indicated that zinc oxide nanoparticles can be practically applied as a foliar fertilizer at the gestation for quality improvement, zinc enrichment and aroma enhancement of rice grains.

Enhancing micronutrient absorption through simultaneous fortification and phytic acid degradation

Phytic acid (PA), an endogenous antinutrient in cereals and legumes, hinders mineral absorption by forming less bioavailable, stable PA-mineral complexes. For individual micronutrients, the PA-to-mineral molar ratio below the critical level ensures better bioavailability and is achieved by adding minerals or removing PA from cereals and pulses. Although several PA reduction and fortification strategies are available, the inability to completely eradicate or degrade PA using available techniques always subdues fortification's impact by hindering fortified micronutrient absorption. The bioavailability of micronutrients could be increased through simultaneous PA degradation and fortification. Following primary PA reduction of the raw material, the fortification step should also incorporate additional essential control stages to further PA inactivation, improving micronutrient absorption. In this review, the chemistry of PA interaction with metal ions, associated controlling parameters, and its impact on PA reduction during fortification is also evaluated, and further suggestions were made for the fortification's success.

In Rats, Whole and Refined Grains Decrease Bone Mineral Density and Content through Modulating Osteoprotegerin and Receptor Activator of Nuclear Factor Kappa B

Wheat is a staple grain in most parts of the world and is also frequently used in livestock feed. The current study looked at the impact of a wheat grain diet on bone turnover markers. Thirty male rats (n = 10) were separated into three groups of ten. The rats in Group 1 were fed a chow diet, while the rats in Group 2 were provided whole grains. The rats in Group 3 were fed refined grains. Each rat's bone mineral content (BMC) and bone mineral density (BMD) were measured after 12 weeks in the tibia of the right hind limb. We also looked at the amounts of bone turnover indicators in the blood. TRAP-5b (Tartrate-resistant acid Phosphatase 5b), NTx (N-telopeptide of type I collagen), DPD (deoxypyridinoline), alkaline phosphatase (ALP), and osteocalcin (OC), as well as the levels of Receptor Activator of Nuclear Factor Kappa B (RANK) and osteoprotegerin (OPG). Rats fed whole and refined grains showed lower BMC and BMD (p < 0.05) than the control group rats. The grain diet resulted in lower OPG, OC, and ALP levels than the chow-fed rats, as well as significantly higher (p < 0.05) levels of RANK, DPD, TRAB 5b, and NTx. In a rat model, an exclusive whole or refined grain diet lowered bone turnover and mass.

Application of Inositol Hexaphosphate and Inositol in Dental Medicine: An Overview

Phosphorylated inositol hexaphosphate (IP6) is a naturally occurring carbohydrate, and its parent compound, myoinositol (Ins), is abundantly present in plants, particularly in certain high-fiber diets, but also in mammalian cells, where they regulate essential cellular functions. IP6 has profound modulation effects on macrophages, which warrants further research on the therapeutic benefits of IP6 for inflammatory diseases. Here, we review IP6 as a promising compound that has the potential to be used in various areas of dentistry, including endodontics, restorative dentistry, implantology, and oral hygiene products, due to its unique structure and characteristic properties. Available as a dietary supplement, IP6 + Ins has been shown to enhance the anti-inflammatory effect associated with preventing and suppressing the progression of chronic dental inflammatory diseases. IP6 in dentistry is now substantial, and this narrative review presents and discusses the different applications proposed in the literature and gives insights into future use of IP6 in the fields of orthodontics, periodontics, implants, and pediatric dentistry.

Evaluation of quantitative synchrotron radiation micro-X-ray fluorescence in rice grain

Concentrations of nutrients and contaminants in rice grain affect human health, specifically through the localization and chemical form of elements. Methods to spatially quantify the concentration and speciation of elements are needed to protect human health and characterize elemental homeostasis in plants. Here, an evaluation was carried out using quantitative synchrotron radiation microprobe X-ray fluorescence (SR-µXRF) imaging by comparing average rice grain concentrations of As, Cu, K, Mn, P, S and Zn measured with rice grain concentrations from acid digestion and ICP-MS analysis for 50 grain samples. Better agreement was found between the two methods for high-Z elements. Regression fits between the two methods allowed quantitative concentration maps of the measured elements. These maps revealed that most elements were concentrated in the bran, although S and Zn permeated into the endosperm. Arsenic was highest in the ovular vascular trace (OVT), with concentrations approaching 100 mg kg^-1 in the OVT of a grain from a rice plant grown in As-contaminated soil. Quantitative SR-µXRF is a useful approach for comparison across multiple studies but requires careful consideration of sample preparation and beamline characteristics.

Genetic engineering of complex feed enzymes into barley seed for direct utilization in animal feedstuff

Currently, feed enzymes are primarily obtained through fermentation of fungi, bacteria, and other microorganisms. Although the manufacturing technology for feed enzymes has evolved rapidly, the activities of these enzymes decline during the granulating process and the cost of application has increased over time. An alternative approach is the use of genetically modified plants containing complex feed enzymes for direct utilization in animal feedstuff. We co-expressed three commonly used feed enzymes (phytase, β-glucanase, and xylanase) in barley seeds using the Agrobacterium-mediated transformation method and generated a new barley germplasm. The results showed that these enzymes were stable and had no effect on the development of the seeds. Supplementation of the basal diet of laying hens with only 8% of enzyme-containing seeds decreased the quantities of indigestible carbohydrates, improved the availability of phosphorus, and reduced the impact of animal production on the environment to an extent similar to directly adding exogenous enzymes to the feed. Feeding enzyme-containing seeds to layers significantly increased the strength of the eggshell and the weight of the eggs by 10.0%-11.3% and 5.6%-7.7% respectively. The intestinal microbiota obtained from layers fed with enzyme-containing seeds was altered compared to controls and was dominated by Alispes and Rikenella. Therefore, the transgenic barley seeds produced in this study can be used as an ideal feedstuff for use in animal feed.

NM, Jebakani K. S, Selvaraj S, Pramitha J. L, Selvaraj R, Petchiammal K. I, Kather Sheriff S, Thinakaran J, Rathinamoorthy S, Kumar P. R. Genetic manipulation of anti-nutritional factors in major crops for a sustainable diet in future

The consumption of healthy food, in order to strengthen the immune system, is now a major focus of people worldwide and is essential to tackle the emerging pandemic concerns. Moreover, research in this area paves the way for diversification of human diets by incorporating underutilized crops which are highly nutritious and climate-resilient in nature. However, although the consumption of healthy foods increases nutritional uptake, the bioavailability of nutrients and their absorption from foods also play an essential role in curbing malnutrition in developing countries. This has led to a focus on anti-nutrients that interfere with the digestion and absorption of nutrients and proteins from foods. Anti-nutritional factors in crops, such as phytic acid, gossypol, goitrogens, glucosinolates, lectins, oxalic acid, saponins, raffinose, tannins, enzyme inhibitors, alkaloids, β-N-oxalyl amino alanine (BOAA), and hydrogen cyanide (HCN), are synthesized in crop metabolic pathways and are interconnected with other essential growth regulation factors. Hence, breeding with the aim of completely eliminating anti-nutrition factors tends to compromise desirable features such as yield and seed size. However, advanced techniques, such as integrated multi-omics, RNAi, gene editing, and genomics-assisted breeding, aim to breed crops in which negative traits are minimized and to provide new strategies to handle these traits in crop improvement programs. There is also a need to emphasize individual crop-based approaches in upcoming research programs to achieve smart foods with minimum constraints in future. This review focuses on progress in molecular breeding and prospects for additional approaches to improve nutrient bioavailability in major crops.

Alleviating effects of zinc and 24-epibrassionlide on cadmium accumulation in rice plants under nitrogen application

Heavy metals such as cadmium (Cd) in farmland soil not only affect crop production, but also endanger human health through the food chain. Rice is the main food crop with the strongest ability to absorb Cd, remediation techniques to reduce soil uptake and grain accumulation of Cd are urgently required, for which the application of foliar spraying seems to be a convenient and auspicious method. This study clarified the effects of nitrogen (N), zinc (Zn), 24-epibrassionlide (EBL) and their combined application on the growth performance and physiological characteristics of Cd and Zn in rice plants under Cd stress. Experimental results showed that N and its combination with Zn, EBL treatments promoted rice growth and yield, especially raised the yield level by 81.12% under N + EBL treatment. Additionally, three EBL treatments (EBL, N + EBL, Zn + EBL) significantly reduced the TF values of Cd in TF _stems-grains, TF _{leaves-grains} and TF _{glumes-grains} by 42.70%, 43.67% and 50.33%, while the EF _soil-roots under Zn and N + Zn treatments was the lowest, which decreased by 55.39% and 57.71%, respectively. Further, the application of N, Zn, EBL and their combined treatments significantly increased glutathione (GSH) and phytochelatins (PCs) content as well as enhanced Cd distribute into cell walls of rice shoots and roots by 15.18% and 13.20%, respectively. In addition, N, Zn, EBL and their combined application increased Zn concentration, free amino acid and glutelin content, and decreased the Cd accumulation in albumin, glutelin and globulin, thus lowered Cd concentration in grains by 27.55%, 58.29% and 51.56%, respectively. These results comprehensive suggest that the possibility of N management combined with Zn or EBL application for maintaining high yield and alleviating Cd stress by regulating the absorption and remobilization process under mild stress.

Identifying genes associated with abiotic stress tolerance suitable for CRISPR/Cas9 editing in upland rice cultivars adapted to acid soils

Five genes of large phenotypic effect known to confer abiotic stress tolerance in rice were selected to characterize allelic variation in commercial Colombian tropical japonica upland rice cultivars adapted to drought-prone acid soil environments (cv. Llanura11 and Porvenir12). Allelic variants of the genes ART1, DRO1, SUB1A, PSTOL1, and SPDT were characterized by PCR and/or Sanger sequencing in the two upland cultivars and compared with the Nipponbare and other reference genomes. Two genes were identified as possible targets for gene editing: SUB1A (Submergence 1A), to improve tolerance to flooding, and SPDT (SULTR3;4) (SULTR-like Phosphorus Distribution Transporter), to improve phosphorus utilization efficiency and grain quality. Based on technical and regulatory considerations, SPDT was targeted for editing. The two upland cultivars were shown to carry the SPDT wild-type (nondesirable) allele based on sequencing, RNA expression, and phenotypic evaluations under hydroponic and greenhouse conditions. A gene deletion was designed using the CRISPR/Cas9 system, and specialized reagents were developed for SPDT editing, including vectors targeting the gene and a protoplast transfection transient assay. The desired edits were confirmed in protoplasts and serve as the basis for ongoing plant transformation experiments aiming to improve the P-use efficiency of upland rice grown in acidic soils.

Kernel color and fertilization as factors of enhanced maize quality

Maize is an important staple crop and a significant source of various nutrients. We aimed to determine the macronutrients, antioxidants, and essential elements in maize genotypes (white, yellow, and red kernel) using three different fertilizers, which could be used as a basis to increase the nutrient density of maize. The fertilizer treatments used bio- and organic fertilizers as a sustainable approach, urea, as a commonly used mineral fertilizer, and the control (no fertilization). We evaluated the yield, concentration of macronutrient (protein, oil, and starch), nonenzymatic antioxidants (phenolics, yellow pigment, total glutathione (GSH), and phytic phosphorus), and reduction capacity of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, as well as essential elements that are commonly deficient in the diet (Mg, Ca, Fe, Mn, Zn, Cu, and S) and their relationships with phytic acid. The genotype expressed the strongest effect on the variability of grain yield and the analyzed grain constituents. The red-kernel hybrid showed the greatest accumulation of protein, oil, phenolics, and essential elements (Ca, Fe, Cu, and S) than a yellow and white hybrid, especially in the biofertilizer treatment. The yellow kernel had the highest concentrations of yellow pigment, GSH, phytic phosphorous, Mg, Mn, and Zn (19.61 µg g^-1, 1,134 nmol g^-1, 2.63 mg g^-1, 1,963 µg g^-1, 11.7 µg g^-1, and 33.9 µg g^-1, respectively). The white kernel had a greater starch concentration (2.5% higher than that in the red hybrid) and the potential bioavailability of essential metals, particularly under no fertilization. This supports the significance of white maize as a staple food in many traditional diets across the world. Urea was important for the enhancement of the antioxidant status (with 88.0% reduction capacity for the DPPH radical) and increased potential Zn bioavailability in the maize kernels (13.3% higher than that in the biofertilizer treatment). This study underlines the differences in the yield potential and chemical composition of red, yellow, and white-kernel maize and their importance as a necessary part of a sustainable human diet. This information can help determine the most appropriate genotype based on the antioxidants and/or essential elements targeted for kernel improvement.

A tale of two metals: Biofortification of rice grains with iron and zinc

Iron (Fe) and zinc (Zn) are essential micronutrients needed by virtually all living organisms, including plants and humans, for proper growth and development. Due to its capacity to easily exchange electrons, Fe is important for electron transport in mitochondria and chloroplasts. Fe is also necessary for chlorophyll synthesis. Zn is a cofactor for several proteins, including Zn-finger transcription factors and redox metabolism enzymes such as copper/Zn superoxide dismutases. In humans, Fe participates in oxygen transport, electron transport, and cell division whereas Zn is involved in nucleic acid metabolism, apoptosis, immunity, and reproduction. Rice (Oryza sativa L.) is one of the major staple food crops, feeding over half of the world's population. However, Fe and Zn concentrations are low in rice grains, especially in the endosperm, which is consumed as white rice. Populations relying heavily on rice and other cereals are prone to Fe and Zn deficiency. One of the most cost-effective solutions to this problem is biofortification, which increases the nutritional value of crops, mainly in their edible organs, without yield reductions. In recent years, several approaches were applied to enhance the accumulation of Fe and Zn in rice seeds, especially in the endosperm. Here, we summarize these attempts involving transgenics and mutant lines, which resulted in Fe and/or Zn biofortification in rice grains. We review rice plant manipulations using ferritin genes, metal transporters, changes in the nicotianamine/phytosiderophore pathway (including biosynthetic genes and transporters), regulators of Fe deficiency responses, and other mutants/overexpressing lines used in gene characterization that resulted in Fe/Zn concentration changes in seeds. This review also discusses research gaps and proposes possible future directions that could be important to increase the concentration and bioavailability of Fe and Zn in rice seeds without the accumulation of deleterious elements. We also emphasize the need for a better understanding of metal homeostasis in rice, the importance of evaluating yield components of plants containing transgenes/mutations under field conditions, and the potential of identifying genes that can be manipulated by gene editing and other nontransgenic approaches.

Prospects of genetics and breeding for low-phosphate tolerance: an integrated approach from soil to cell

Improving phosphorus (P) crop nutrition has emerged as a key factor toward achieving a more resilient and sustainable agriculture. P is an essential nutrient for plant development and reproduction, and phosphate (Pi)-based fertilizers represent one of the pillars that sustain food production systems. To meet the global food demand, the challenge for modern agriculture is to increase food production and improve food quality in a sustainable way by significantly optimizing Pi fertilizer use efficiency. The development of genetically improved crops with higher Pi uptake and Pi-use efficiency and higher adaptability to environments with low-Pi availability will play a crucial role toward this end. In this review, we summarize the current understanding of Pi nutrition and the regulation of Pi-starvation responses in plants, and provide new perspectives on how to harness the ample repertoire of genetic mechanisms behind these adaptive responses for crop improvement. We discuss on the potential of implementing more integrative, versatile, and effective strategies by incorporating systems biology approaches and tools such as genome editing and synthetic biology. These strategies will be invaluable for producing high-yielding crops that require reduced Pi fertilizer inputs and to develop a more sustainable global agriculture.

Genetic Approaches for Iron and Zinc Biofortification and Arsenic Decrease in Oryza sativa L. Grains

Rice is the staple diet to half of the world's population, being a major source of carbohydrates, vitamins, and some essential elements. However, rice naturally contains low amounts of essential minerals such as iron (Fe) and zinc (Zn), which are drastically decreased after milling. Thus, populations that consume mostly rice may have micronutrient deficiency, which is associated with different diseases. On the other hand, rice irrigated by flooding has a high ability to accumulate arsenic (As) in the grain. Therefore, when rice is grown in areas with contaminated soil or irrigation water, it represents a risk factor for consumers, since As is associated with cancer and other diseases. Different strategies have been used to mitigate micronutrient deficiencies such as Fe and Zn and to prevent As from entering the food chain. Each strategy has its positive and its negative sides. The development of genetically biofortified rice plants with Fe and Zn and with low As accumulation is one of the most promising strategies, since it does not represent an additional cost for farmers, and gives benefits to consumers as well. Considering the importance of genetic improvement (traditional or molecular) to decrease the impact of micronutrient deficiencies such as Fe and Zn and contamination with As, this review aimed to summarize the major efforts, advances, and challenges for genetic biofortification of Fe and Zn and decrease in As content in rice grains.

Agro-Morphological Characterization and Nutritional Profiling of Traditional Himalayan Crop Landraces for Their Promotion Toward Mainstream Agriculture

The northwest Indian Himalayas are often regarded as a biological hotspot for the presence of rich agro-biodiversity harboring locally adapted traditional crop landraces facing utter neglect owing to modern agricultural systems promoting high-yielding varieties. Addressing this challenge requires extricating the potential of such cultivars in terms of agro-morphological and nutritional attributes. In this study, 29 traditional crop landraces of maize (11), paddy (07), finger millet (03), buckwheat (05), and naked barley (03) were characterized and evaluated for target traits of interest. In maize, Chitkanu emerged as an early maturing landrace (107 days) with high concentrations of zinc (Zn), iron (Fe), and potassium (K), and Safed makki showed the highest 100-seed weight (28.20 g). Similarly, Bamkua dhan exhibited high concentrations of K and phosphorus (P), and Lamgudi dhan showed a high protein content (14.86 g/100 g) among paddy landraces. Ogla-I and Phapra-I showed high contents of protein (14.80 g/100 g) and flavonoids (20.50 mg/g) among buckwheat landraces, respectively, followed by Nei-I, which exhibited the highest protein content (15.66 g/100 g) among naked barley landraces. Most of the target traits varied significantly (p < 0.05) among evaluated samples, except those associated with finger millet landraces. The grouping pattern obtained by principal component analysis (PCA) and multidimensional scaling (MDS) was congruent with the geographical relationship among the crop landraces. This study led to the identification of elite crop landraces having useful variations that could be exploited in plant breeding programs and biofortification strategies for future crop improvement. Our endeavor would aid in conserving the depleting Himalayan agro-biodiversity and promoting versatile traditional crops toward mainstream agriculture vis-à-vis future nutritional security.

Altering the localization and toxicity of arsenic in rice grain

Previous work has shown that inorganic As localizes in rice bran whereas DMA localizes in the endosperm, but less is known about co-localization of As and S species and how they are affected by growing conditions. We used high-resolution synchrotron X-ray fluorescence imaging to image As and S species in rice grain from plants grown to maturity in soil (field and pot) and hydroponically (DMA or arsenite dosed) at field-relevant As concentrations. In hydroponics, arsenite was localized in the ovular vascular trace (OVT) and the bran while DMA permeated the endosperm and was absent from the OVT in all grains analyzed, and As species had no affect on S species. In pot studies, soil amended with Si-rich rice husk with higher DMA shifted grain As into the endosperm for both japonica and indica ecotypes. In field-grown rice from low-As soil, As localized in the OVT as arsenite glutathione, arsenite, and DMA. Results support a circumferential model of grain filling for arsenite and DMA and show Si-rich soil amendments alter grain As localization, potentially lessening risk to rice consumers.

Potential of engineering the myo-inositol oxidation pathway to increase stress resilience in plants

Myo-inositol is one of the most abundant form of inositol. The myo-inositol (MI) serves as substrate to diverse biosynthesis pathways and hence it is conserved across life forms. The biosynthesis of MI is well studied in animals. Beyond biosynthesis pathway, implications of MI pathway and enzymes hold potential implications in plant physiology and crop improvement. Myo-inositol oxygenase (MIOX) enzyme catabolize MI into D-glucuronic acid (D-GlcUA). The MIOX enzyme family is well studied across few plants. More recently, the MI associated pathway's crosstalk with other important biosynthesis and stress responsive pathways in plants has drawn attention. The overall outcome from different plant species studied so far are very suggestive that MI derivatives and associated pathways could open new directions to explore stress responsive novel metabolic networks. There are evidences for upregulation of MI metabolic pathway genes, specially MIOX under different stress condition. We also found MIOX genes getting differentially expressed according to developmental and stress signals in Arabidopsis and wheat. In this review we try to highlight the missing links and put forward a tailored view over myo-inositol oxidation pathway and MIOX proteins.

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.

Polyester sulfur-coated urea (PSCU) application enhances brown rice iron concentrations in two alkaline soils

BACKGROUND

In neutral or alkaline soils, iron (Fe) easily forms insoluble complexes, which makes it difficult for plants to utilize Fe in the soil for nutrition. Polyester sulfur-coated urea (PSCU) is a novel controlled-release fertilizer widely used in China and some foreign countries, and it has been proven that sulfur film from controlled-release fertilizers can significantly improve the activation of Fe and other elements in the soil. However, few studies have focused on the effects of PSCU application on Fe accumulation in rice grain in alkaline soils.

RESULTS

Both our field and pot experiments proved that PSCU application could significantly improve rice grain yield and Fe concentration in brown rice in alkaline soil. This effect differs with different types of alkaline soils (i.e. medium-saline, sandy soil and/or silt soil). PSCU is released slowly, and the release rate is different in different alkaline soils. Rice shoot nitrogen (N) uptake was significantly enhanced with PSCU application.

CONCLUSION

The results suggested that PSCU application in alkaline soils could significantly enhance brown rice Fe concentration and production. This effect differed with different kinds of alkaline soils. The study identified some efficient fertilizers to improve the Fe status in alkaline soils. © 2021 Society of Chemical Industry.

Metabolic Disturbance Induced by the Embryo Contributes to the Formation of Chalky Endosperm of a Notched-Belly Rice Mutant

Grain chalkiness is a key quality trait of the rice grain, whereas its underlying mechanism is still not thoroughly understood because of the complex genetic and environmental interactions. We identified a notched-belly (NB) mutant that has a notched-line on the belly of grains. The line dissects the endosperm into two distinct parts, the upper translucent part, and the bottom chalky part in the vicinity of the embryo. Using this mutant, our previous studies clued the negative influence of embryo on the biochemical makeup of the endosperm, suggesting the need for the in-depth study of the embryo effect on the metabolome of developing endosperm. This study continued to use the NB mutant to evolve a novel comparison method to clarify the role of embryo in the formation of a chalky endosperm. Grain samples of the wild-type (WT) and NB were harvested at 10, 20, and 30 days after fertilization (DAF), and then divided into subsamples of the embryo, the upper endosperm, and the bottom endosperm. Using non-targeted metabolomics and whole-genome RNA sequencing (RNA-seq), a nearly complete catalog of expressed metabolites and genes was generated. Results showed that the embryo impaired the storage of sucrose, amino acid, starch, and storage proteins in the bottom endosperm of NB by enhancing the expression of sugar, amino acids, and peptide transporters, and declining the expression of starch, prolamin, and glutelin synthesis-related genes. Importantly, the competitive advantage of the developing embryo in extracting the nutrients from the endosperm, transformed the bottom endosperm into an "exhaustive source" by diverting the carbon (C) and nitrogen (N) metabolism from synthetic storage to secondary pathways, resulting in impaired filling of the bottom endosperm and subsequently the formation of chalky tissue. In summary, this study reveals that embryo-induced metabolic shift in the endosperm is associated with the occurrence of grain chalkiness, which is of relevance to the development of high-quality rice by balancing the embryo-endosperm interaction.

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.

Engineering of thermostable phytase-xylanase for hydrolysis of complex biopolymers

Industrial processing of enzymes requires higher heating that affects the thermal stability of the enzyme and increases the production cost. In this study, xylanase-phytase (XP) fusion protein was generated via co-expression in a single vector with a cold-shock promoter, leading to improved activity at optimal pH, temperature and the thermal behaviour of the protein. Xylanase-phytase (XP) fusion and phytase proteins were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The XP fusion was thermally stable up to 124 °C, higher than phytase which was steady up to 113.5 °C. XP fusion exhibits higher stability at its thermal transition midpoint (T _m) 108 °C, higher than the T _m value of phytase which is 90 °C. Industrially efficient and environment-friendly proteins with low production cost and higher stability can be generated by 'fusion protein' technology.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02936-z.

Zinc in cereal grains: Concentration, distribution, speciation, bioavailability, and barriers to transport from roots to grains in wheat

Zinc (Zn) is an essential micro-nutrient for humans, and Zn deficiency is of global concern. In addition to inherited and pathological Zn deficiencies, insufficient dietary intake is leading cause, especially in those consuming cereal grains as a stable food, in which Zn concentration and bioavailability are relatively low. To improve Zn levels in the human body, it is important to understand the accumulation and bioavailability of Zn in cereal grains. In recent years, knowledge on the molecular mechanisms underlying Zn uptake, transport, homeostasis, and deposition within cereal crops has been accumulating, paving the way for a more targeted approach to improving the nutrient status of crop plants. In this paper, we briefly review existing studies on the distribution and transport pathways of Zn in major small-grained cereals, using wheat as a case study. The findings confirm that Zn transport in plants is a complex physiological process mainly governed by Zn transporters and metal chelators. This work reviews studies on Zn uptake, transport, and deposition in wheat plants, summarizes the possible barriers impairing Zn deposition in wheat grains, and describes strategies for increasing Zn concentration in wheat grains.

Enhancing health benefits of milled rice: current status and future perspectives

Milled rice is an essential part of the regular diet for approximately half of the world's population. Its remarkable commercial value and consumer acceptance are mostly due to its promising cooking qualities, appealing sensory properties, and longer shelf life. However, the significant loss of the nutrient-rich bran layer during milling makes it less nutritious than the whole grain. Thus, enhancing the nutritive value of milled rice is vital in improving the health and wellbeing of rice consumers, particularly for those residing in the low-economic zones where rice is the primary source of calories and nutrition. This article provides a critical review on multiple frontiers of recent interventions, such as (1) infusing the genetic diversity to enrich amylose and resistant starch to reduce glycaemic index, (2) enhancing the minerals and vitamins through complementary fortification and biofortification as short and long-term interventions, and (3) developing transgenic solutions to improve the nutrient levels of milled rice. Additionally, the review highlights the benefits of functional ingredients of milled rice to human health and the potential of enhancing them in rice to address the triple burden of malnutrition. The potential merit of milled rice concerning food safety is also reviewed in this article.

Biofortification and bioavailability of Zn, Fe and Se in wheat: present status and future prospects

Knowledge of genetic variation, genetics, physiology/molecular basis and breeding (including biotechnological approaches) for biofortification and bioavailability for Zn, Fe and Se will help in developing nutritionally improved wheat. Biofortification of wheat cultivars for micronutrients is a priority research area for wheat geneticists and breeders. It is known that during breeding of wheat cultivars for productivity and quality, a loss of grain micronutrient contents occurred, leading to decline in nutritional quality of wheat grain. Keeping this in view, major efforts have been made during the last two decades for achieving biofortification and bioavailability of wheat grain for micronutrients including Zn, Fe and Se. The studies conducted so far included evaluation of gene pools for contents of not only grain micronutrients as above, but also for phytic acid (PA) or phytate and phytase, so that, while breeding for the micronutrients, bioavailability is also improved. For this purpose, QTL interval mapping and GWAS were carried out to identify QTLs/genes and associated markers that were subsequently used for marker-assisted selection (MAS) during breeding for biofortification. Studies have also been conducted to understand the physiology and molecular basis of biofortification, which also allowed identification of genes for uptake, transport and storage of micronutrients. Transgenics using transgenes have also been produced. The breeding efforts led to the development of at least a dozen cultivars with improved contents of grain micronutrients, although land area occupied by these biofortified cultivars is still marginal. In this review, the available information on different aspects of biofortification and bioavailability of micronutrients including Zn, Fe and Se in wheat has been reviewed for the benefit of those, who plan to start work or already conducting research in this area.

Phytic Acid in Brown Rice Can Be Reduced by Increasing Soaking Temperature

Phytic acid (PA) is a storage form of phosphorus in seeds. Phytase enzyme is activated at germination and hydrolyses PA into myo-inositol and inorganic phosphate. PA inhibits the absorption of minerals in the human intestine by chelation. Its degradation, therefore, is a key factor to improve mineral bioavailability in rice. Germinated brown rice (GBR) is favoured because it improves the availability of nutrients, and thus have a positive effect on health. In this study, we show the effects of soaking temperature on phytase activity and PA content in GBR. Rice phytase showed thermostability and its activity peaked at 50 °C. After 36 h of soaking, phytase activity was significantly increased at 50 °C and PA content was significantly decreased, compared to that at 30 °C. Zinc (Zn) analysis revealed that there was no significant difference in Zn content among different temperature treatments. Calculated total daily absorbed Zn (TAZ) was significantly higher in GBR compared with non-soaked seeds. Moreover, brown rice grains germinated at 50 °C showed a higher TAZ value than that at 30 °C. Seed germination and seed water soaking at high temperatures reduce PA content in brown rice showing a potentially effective way to improve mineral bioavailability in brown rice.

Diverse role of phytic acid in plants and approaches to develop low-phytate grains to enhance bioavailability of micronutrients

Natural or synthetic compounds that interfere with the bioavailability of nutrients are called antinutrients. Phytic acid (PA) is one of the major antinutrients present in the grains and acts as a chelator of micronutrients. The presence of six reactive phosphate groups in PA hinders the absorption of micronutrients in the gut of non-ruminants. Consumption of PA-rich diet leads to deficiency of minerals such as iron and zinc among human population. On the contrary, PA is a natural antioxidant, and PA-derived molecules function in various signal transduction pathways. Therefore, optimal concentration of PA needs to be maintained in plants to avoid adverse pleiotropic effects, as well as to ensure micronutrient bioavailability in the diets. Given this, the chapter enumerates the structure, biosynthesis, and accumulation of PA in food grains followed by their roles in growth, development, and stress responses. Further, the chapter elaborates on the antinutritional properties of PA and explains the conventional breeding and transgene-based approaches deployed to develop low-PA varieties. Studies have shown that conventional breeding methods could develop low-PA lines; however, the pleiotropic effects of these methods viz. reduced yield, embryo abnormalities, and poor seed quality hinder the use of breeding strategies. Overexpression of phytase in the endosperm and RNAi-mediated silencing of genes involved in myo-inositol biosynthesis overcome these constraints. Next-generation genome editing approaches, including CRISPR-Cas9 enable the manipulation of more than one gene involved in PA biosynthesis pathway through multiplex editing, and scope exists to deploy such tools in developing varieties with optimal PA levels.

Nutrition and antioxidant profiling in the unpolished and polished grains of eleven indigenous aromatic rice cultivars

The present study emphasized on the yet-unexplored exhaustive analyses of nutritional and antioxidant parameters in the unpolished and polished grains of eleven indigenous aromatic rice varieties. Tulaipanji appeared to be a highly demanding variety by virtue of having sufficient levels of micronutrients like Fe, Zn and Cu (linked with higher expression of fer2, ZIP and NAS3), inorganic phosphorus, hexose sugars, total amino acids and lysine (correlated with higher expression of glutelin and RLRH1), tocopherol (due to higher HGGT expression), total phenolic content, flavonoids, anthocyanins (concomitant with higher expression of PPO, PAL and ANS), LOX activity and LOX1 gene expression, and overall higher total antioxidant capacity, particularly in the polished grains. The importance of IET-21261, with regard to higher content of phytic acid and total phosphorus (with high IPK1 expression), β-carotene (with high PSY expression) and tocopherol (with high HGGT expression), and of Kalonunia, with respect to cysteine and γ-oryzanol in the polished grains, was also significant. Lower α-amylase enzyme activity and α-amylase expression led to considerable starch accumulation, with lower sucrose content, in the unpolished grains of Radhunipagal and polished grains of Pusa Basmati-1. Paramanya registered the highest content of thiamine and TH1 expression, together with minimum methylglyoxal level (low TPI expression). Paramanya and Radhunipagal maintained a higher pool of majority of the nutritional and antioxidant components in their unpolished grains. The polished grains of all the genotypes showed strikingly lower nutritional constituents, as compared to unpolished grains. The knowledge gained from this study will largely provide a road map to the farmers and rice consumers for making proper choice of the aromatic genotypes for large-scale cultivation and dietary consumption to derive maximum nutritional benefits.

Gene editing of three BnITPK genes in tetraploid oilseed rape leads to significant reduction of phytic acid in seeds

Commercialization of Brassica napus. L (oilseed rape) meal as protein diet is gaining more attention due to its well-balanced amino acid and protein contents. Phytic acid (PA) is a major source of phosphorus in plants but is considered as anti-nutritive for monogastric animals including humans due to its adverse effects on essential mineral absorption. The undigested PA causes eutrophication, which potentially threatens aquatic life. PA accounts to 2-5% in mature seeds of oilseed rape and is synthesized by complex pathways involving multiple enzymes. Breeding polyploids for recessive traits is challenging as gene functions are encoded by several paralogs. Gene redundancy often requires to knock out several gene copies to study their underlying effects. Therefore, we adopted CRISPR-Cas9 mutagenesis to knock out three functional paralogs of BnITPK. We obtained low PA mutants with an increase of free phosphorus in the canola grade spring cultivar Haydn. These mutants could mark an important milestone in rapeseed breeding with an increase in protein value and no adverse effects on oil contents.

Retention of Zn, Fe and phytic acid in parboiled biofortified and non-biofortified rice

Biofortified rice with high Zn concentration could reduce Zn deficiency in South Asia. This population frequently parboils rice. True retention (TR) of Zn, Fe and phytic acid after parboiling and milling was evaluated in biofortified and non-biofortified rice. TR in milled non-parboiled rice was 63.8-89.6% for Zn, 21.1-44.5% for Fe and 16.4-40.3% for phytic acid, whereas in milled parboiled rice TR was 49.8-72.2% for Zn, 23.4-36.7% for Fe and 22.0-33.3% for phytic acid. Milled parboiled rice resulted in lower Zn TR compared to milled non-parboiled. These results suggest that Zn moves from the inner endosperm towards the outer layers during parboiling, regardless of initial Zn concentration, consequently, once milled, the potential impact of Zn intake on Zn deficiency from parboiled rice is less than non-parboiled rice. Despite Zn losses during processing, biofortified rice could provide over 50% of the Zn EAR for children.

Phosphorus toxicity disrupts Rubisco activation and reactive oxygen species defence systems by phytic acid accumulation in leaves

Phosphorus (P) is an essential mineral nutrient for plants. Nevertheless, excessive P accumulation in leaf mesophyll cells causes necrotic symptoms in land plants; this phenomenon is termed P toxicity. However, the detailed mechanisms underlying P toxicity in plants have not yet been elucidated. This study aimed to investigate the molecular mechanism of P toxicity in rice. We found that under excessive inorganic P (Pi) application, Rubisco activation decreased and photosynthesis was inhibited, leading to lipid peroxidation. Although the defence systems against reactive oxygen species accumulation were activated under excessive Pi application conditions, the Cu/Zn-type superoxide dismutase activities were inhibited. A metabolic analysis revealed that excessive Pi application led to an increase in the cytosolic sugar phosphate concentration and the activation of phytic acid synthesis. These conditions induced mRNA expression of genes that are activated under metal-deficient conditions, although metals did accumulate. These results suggest that P toxicity is triggered by the attenuation of both photosynthesis and metal availability within cells mediated by phytic acid accumulation. Here, we discuss the whole phenomenon of P toxicity, beginning from the accumulation of Pi within cells to death in land plants.

Genetic Manipulation for Improved Nutritional Quality in Rice

Food with higher nutritional value is always desired for human health. Rice is the prime staple food in more than thirty developing countries, providing at least 20% of dietary protein, 3% of dietary fat and other essential nutrients. Several factors influence the nutrient content of rice which includes agricultural practices, post-harvest processing, cultivar type as well as manipulations followed by selection through breeding and genetic means. In addition to mutation breeding, genetic engineering approach also contributed significantly for the generation of nutrition added varieties of rice in the last decade or so. In the present review, we summarize the research update on improving the nutritional characteristics of rice by using genetic engineering and mutation breeding approach. We also compare the conventional breeding techniques of rice with modern molecular breeding techniques toward the generation of nutritionally improved rice variety as compared to other cereals in areas of micronutrients and availability of essential nutrients such as folate and iron. In addition to biofortification, our focus will be on the efforts to generate low phytate in seeds, increase in essential fatty acids or addition of vitamins (as in golden rice) all leading to the achievements in rice nutrition science. The superiority of biotechnology over conventional breeding being already established, it is essential to ascertain that there are no serious negative agronomic consequences for consumers with any difference in grain size or color or texture, when a nutritionally improved variety of rice is generated through genetic engineering technology.

Effect of Rice Flour Fermentation with Lactobacillus spicheri DSM 15429 on the Nutritional Features of Gluten-Free Muffins

Lactobacillus Spicheri DSM 15429 strain was used to ferment rice flour, aiming at exploiting its influence on the amino-acids, minerals, lactic acid, total phenols, and antioxidant activity of the rice sourdough and gluten-free muffins. Gluten-free muffins were prepared by using 15% rice sourdough fermented with the above strain of lactic acid bacteria and compared with rice spontaneous fermentation. Methods like LC-MS (Liquid chromatography–mass spectrometry), AA (atomic absorption), HPLC (High-performance liquid chromatography), Folin–Ciocalteu, and 1,1-Diphenyl-2-picrylhydrazyl radical scavenging activity (DPPH) were used to fulfill the aim of the study. The addition of rice sourdough fermented with LAB was reflected in the chemical composition of the final baked good, improving its amount on bioactive compounds such as amino acids, mineral bioavailability, total phenols, and antioxidant activity. Total phenols and antioxidant activity increased their amount by 70.53% and 73.70%, respectively, meanwhile, lactic acid, minerals, and amino-acids increased their values at least twice. Thus, rice fermented with Lactobacilus spicheri DSM 15429 strain could be a tool to further increase the nutritional value of gluten-free baked products.

Interactions of Dimethylarsinic Acid, Total Arsenic and Zinc Affecting Rice Crop Management and Human Health in Cambodia

BACKGROUND

In parts of Cambodia and in many other parts of the world, irrigation of rice with groundwater results in arsenic (As) accumulation in soil and rice, leading to health concerns associated with rice consumption. At times, some As is present as relatively nontoxic, non-regulated, dimethylarsinic acid (DMA). Low levels of zinc (Zn) have been found in rice from Bangladesh, Cambodia, and China where As levels in rice are high. Furthermore, there have been claims that Zn deficiency is responsible for stunting the growth of children in Cambodia and elsewhere, however in rural Asia, rice is the major source of Zn. Current data are inadequate for both Zn and DMA in Cambodian rice.

OBJECTIVES

The present study aimed to provide a preliminary evaluation of the relationship between the content of Zn and DMA in rice grain in Preak Russey, an area with elevated levels of As in groundwater and to improve the management of Zn deficiency in rice.

METHODS

Rice agriculture was evaluated along the Mekong River in Cambodia. Analyses for metals, total As, and As species in rice and water were conducted by inductively coupled plasma mass spectrometry. Analysis of total Zn and As in soils and total Zn in rice were analyzed using X-ray fluorescence (XRF) spectrometry.

RESULTS

Rice in Preak Russey had Zn concentrations less than a third the level recommended by the United Nations World Food Programme. There was a significant (p < 0.05) negative correlation between the Zn content of rice and DMA in rice with the lowest Zn and highest DMA levels occurring near irrigation wells, the source of As.

CONCLUSIONS

The highest levels of DMA in rice were associated with Zn deficiency in rice.

COMPETING INTERESTS

The authors declare no competing financial interests.

Textural and Sensory Features Changes of Gluten Free Muffins Based on Rice Sourdough Fermented with Lactobacillus spicheri DSM 15429

Gluten free products available on the market have a low textural quality associated with high crumbly structure, low-flavor, aroma, poor mouthfeel, less appearance, in comparison with the conventional final baked products. The aim of this study was to assess the influence of rice sourdough fermented with Lactobacillus spicheri DSM 15429 strain on textural, volatile profile, and sensorial properties of gluten free muffins in order to obtain baked goods with improved quality characteristics. Lactobacillus spicheri is a novel strain isolated from industrial rice sourdough but unexploited for bakery products manufacturing. The results showed that Lactobacillus spicheri DSM 15429 was able to growth in the rice flour influencing the texture and the volatile profile of gluten free muffins as well as their sensory characteristics. Both, textural parameters and volatiles recorded significant differences comparing to muffins obtained with a spontaneously fermented rice sourdough. Hardness and cohesiveness decreased while springiness and resilience of gluten free muffins improved their values. The volatile profile of gluten free muffins was significantly improved by utilization of the rice sourdough fermented with Lactobacilus spicheri DSM 15429. 3-methylbutanal, 2-methylbutanal, acetophenone and limonene were the main volatile derivatives responsible for aroma and odor scores of sensory analysis.

Phytic acid content may affect starch digestibility and glycemic index value of rice (Oryza sativa L.)

BACKGROUND

Phytic acid (PA) is an anti-nutrient present in cereals and pulses. It is known to reduce mineral bioavailability and inhibit starch-digesting α-amylase (which requires calcium for activity) in the human gut. In principle, the greater the amount of PA, the lower is the rate of starch hydrolysis. It is reflected in the lower glycemic index (GI) value of food. People leading sedentary lifestyles and consuming rice as a staple food are likely to develop type 2 diabetes. Hence, this study was planned to understand how PA content of different rice varieties affects the GI.

RESULTS

Rice Khira and Mugai which had very low PA (0.30 and 0.36 g kg^-1 , respectively) had higher GI values and α-amylase activity, while Nua Dhusara and the pigmented rice Manipuri black rice (MBR) which had high PA (2.13 and 2.98 g kg^-1 , respectively) showed low α-amylase activity and GI values. This relationship was statistically significant, though a weak relationship was found for the pigmented rice. Expression levels of MIPSI, IPKI and GBSSI markedly increased in the middle stage of grain development in all of the six genotypes having contrasting PA and GI. Maximum expression of MIPSI and IPKI was observed in Nua Dhusara and MBR (which had high PA) while that of GBSSI was observed in Khira and Mugai (with higher GI) at middle stage showing a negative correlation between PA and GI.

CONCLUSIONS

The data indicate that high PA content in rice might have an adverse effect on starch digestibility resulting in slower starch digestion in the human gut and consequently low glycemic response. © 2019 Society of Chemical Industry.

Genotypic Differences in the Effect of P Fertilization on Phytic Acid Content in Rice Grain

Phytic acid (PA) prevents the absorption of minerals in the human intestine, and it is regarded as an antinutrient. Low PA rice is beneficial because of its higher Zn bioavailability and it is suggested that the gene expression level of myo-inositol 3-phosphate synthase 1 (INO1) in developing grain is a key factor to explain the genotypic difference in PA accumulation among natural variants of rice. P fertilization is also considered to affect the PA content, but it is not clear how it affects INO1 gene expression and the PA content in different genotypes. Here, we investigated the effect of P fertilization on the PA content in two contrasting rice genotypes, with low and high PA accumulation, respectively. Based on the results of the analysis of the PA content, inorganic P content, INO1 gene expression, and xylem sap inorganic P content, we concluded that the effect of P fertilization on PA accumulation in grain differed with the genotype, and it was regulated by multiple mechanisms.

Mutational Analysis of OsPLDα1 Reveals Its Involvement in Phytic Acid Biosynthesis in Rice Grains

Phospholipids and phytic acid are important phosphorus (P)-containing compounds in rice grains. Phytic acid is considered as a major antinutrient, because the negatively charged phytic acid chelates cations, including essential micronutrients, and decreases their bioavailability to human beings and monogastric animals. To gain an insight into the interplay of these two kinds of phosphorus-containing metabolites, we used the CRISPR/Cas9 system to generate mutants of a phospholipase D gene (OsPLDα1) and analyzed the mutational effect on metabolites, including phytic acid in rice grains. Metabolic profiling of two ospldα1 mutants revealed depletion in the phosphatidic acid production and lower accumulation of cytidine diphosphate diacylglycerol and phosphatidylinositol. The mutants also showed significantly reduced phytic acid content as compared to their wild-type parent, and the expression of the key genes involved in the phytic acid biosynthesis was altered in the mutants. These results demonstrate that OsPLDα1 not only plays an important role in phospholipid metabolism but also is involved in phytic acid biosynthesis, most probably through the lipid-dependent pathway, and thus revealed a potential new route to regulate phytic acid biosynthesis in rice.

Expression regulation of myo-inositol 3-phosphate synthase 1 (INO1) in determination of phytic acid accumulation in rice grain

Phytic acid (PA) is the primary phosphorus (P) storage compound in the seeds of cereals and legumes. Low PA crops, which are considered an effective way to improve grain nutrient availability and combat environmental issues relating to seed P have been developed using mutational and reverse genetics approaches. Here, we identify molecular mechanism regulating PA content among natural rice variants. First, we performed genome-wide association (GWA) mapping of world rice core collection (WRC) accessions to understand the genetic determinants underlying PA trait in rice. Further, a comparative study was undertaken to identify the differences in PA accumulation, protein profiles, and gene expression in low (WRC 5) and high PA (WRC 6) accessions. GWA results identified myo-inositol 3-phosphate synthase 1 (INO1) as being closely localized to a significant single nucleotide polymorphism. We found high rates of PA accumulation 10 days after flowering, and our results indicate that INO1 expression was significantly higher in WRC 6 than in WRC 5. Seed proteome assays found that the expression of INO1 was significantly higher in WRC 6. These results suggest that not only the gene itself but regulation of INO1 gene expression at early developmental stages is important in determining PA content in rice.

Novel allelic variant of Lpa1 gene associated with a significant reduction in seed phytic acid content in rice (Oryza sativa L.)

In plants, myo-inositol-1,2,3,4,5,6-hexakisphosphate (InsP₆), also known as phytic acid (PA), is a major component of organic phosphorus (P), and accounts for up to 85% of the total P in seeds. In rice (Oryza sativa L.), PA mainly accumulates in rice bran, and chelates mineral cations, resulting in mineral deficiencies among brown rice consumers. Therefore, considerable efforts have been focused on the development of low PA (LPA) rice cultivars. In this study, we performed genetic and molecular analyses of OsLpa1, a major PA biosynthesis gene, in Sanggol, a low PA mutant variety developed via chemical mutagenesis of Ilpum rice cultivar. Genetic segregation and sequencing analyses revealed that a recessive allele, lpa1-3, at the OsLpa1 locus (Os02g0819400) was responsible for a significant reduction in seed PA content in Sanggol. The lpa1-3 gene harboured a point mutation (C623T) in the fourth exon of the predicted coding region, resulting in threonine (Thr) to isoleucine (Ile) amino acidsubstitution at position 208 (Thr208Ile). Three-dimensional analysis of Lpa1 protein structure indicated that myo-inositol 3-monophosphate [Ins(3)P₁] could bind to the active site of Lpa1, with ATP as a cofactor for catalysis. Furthermore, the presence of Thr208 in the loop adjacent to the entry site of the binding pocket suggests that Thr208Ile substitution is involved in regulating enzyme activity via phosphorylation. Therefore, we propose that Thr208Ile substitution in lpa1-3 reduces Lpa1 enzyme activity in Sanggol, resulting in reduced PA biosynthesis.