Co-suppression of synthesis of major α-kafirin sub-class together with γ-kafirin-1 and γ-kafirin-2 required for substantially improved protein digestibility in transgenic sorghum

Manifestation of agronomically valuable traits in the progeny of a sorghum mutant carrying the genetic construct for RNA silencing of the γ-kafirin gene

Improving the nutritional value of grain sorghum, a drought- and heat-tolerant grain crop, is an important task in the context of global warming. One of the reasons for the low nutritional value of sorghum grain is the resistance of its storage proteins (kafirins) to proteolytic digestion, which is due, among other things, to the structural organization of protein bodies, in which γ-kafirin, the most resistant to proteases, is located on the periphery, encapsulating more easily digested α-kafirins. The introduction of genetic constructs capable of inducing RNA silencing of the γ-kafirin (gKAF1) gene opens up prospects for solving this problem. Using Agrobacterium-mediated genetic transformation of immature embryos of the grain sorghum cv. Avans we have obtained a mutant with improved digestibility of endosperm proteins (up to 92 %) carrying a genetic construct for RNA silencing of the gKAF1 gene. The goal of this work was to study the stability of inheritance of the introduced genetic construct in T2-T4 generations, to identify the number of its copies, as well as to trace the manifestation of agronomically valuable traits in the offspring of the mutant. The mutant lines were grown in experimental plots in three randomized blocks. The studied lines were characterized by improved digestibility of kafirins, a modified type of endosperm, completely or partially devoid of the vitreous layer, an increased percentage of lysine (by 75 %), reduced plant height, peduncle length, 1000-grains weight, and grain yield from the panicle. In T2, a line with monogenic control of GA resistance was selected. qPCR analysis showed that in different T3 and T4 plants, the genetic construct was present in 2-4 copies. In T3, a line with a high digestibility of endosperm proteins (81 %) and a minimal decrease in agronomically valuable traits (by 5-7 %) was selected.

Large and stable genome edits at the sorghum alpha kafirin locus result in changes in chromatin accessibility and globally increased expression of genes encoding lysine enrichment

INTRODUCTION

Sorghum is a resilient and widely cultivated grain crop used for feed and food. However, it's grain is deficient in lysine, an essential amino acid. This is due to the primary seed storage proteins, the alpha-kafirins, lacking lysine. It has been observed that reductions in alpha-kafirin protein results in rebalancing of the seed proteome and a corresponding increase in non-kafirin proteins which leads to an increased lysine content. However, the mechanisms underlying proteome rebalancing are unclear. This study characterizes a previously developed gene edited sorghum line, with deletions at the alpha kafirin locus.

METHODS

A single consensus guide RNA leads to tandem deletion of multiple members of the gene family in addition to the small target site mutations in remaining genes. RNA-seq and ATAC-seq were utilized to identify changes in gene expression and chromatin accessibility in developing kernels in the absence of most alpha-kafirin expression.

RESULTS

Several differentially accessible chromatin regions and differentially expressed genes were identified. Additionally, several genes upregulated in the edited sorghum line were common with their syntenic orthologues differentially expressed in maize prolamin mutants. ATAC-seq showed enrichment of the binding motif for ZmOPAQUE 11, perhaps indicating the transcription factor's involvement in the kernel response to reduced prolamins.

DISCUSSION

Overall, this study provides a resource of genes and chromosomal regions which may be involved in sorghum's response to reduced seed storage proteins and the process of proteome rebalancing.

Prospects of microgreens as budding living functional food: Breeding and biofortification through OMICS and other approaches for nutritional security

Nutrient deficiency has resulted in impaired growth and development of the population globally. Microgreens are considered immature greens (required light for photosynthesis and growing medium) and developed from the seeds of vegetables, legumes, herbs, and cereals. These are considered "living superfood/functional food" due to the presence of chlorophyll, beta carotene, lutein, and minerals like magnesium (Mg), Potassium (K), Phosphorus (P), and Calcium (Ca). Microgreens are rich at the nutritional level and contain several phytoactive compounds (carotenoids, phenols, glucosinolates, polysterols) that are helpful for human health on Earth and in space due to their anti-microbial, anti-inflammatory, antioxidant, and anti-carcinogenic properties. Microgreens can be used as plant-based nutritive vegetarian foods that will be fruitful as a nourishing constituent in the food industryfor garnish purposes, complement flavor, texture, and color to salads, soups, flat-breads, pizzas, and sandwiches (substitute to lettuce in tacos, sandwich, burger). Good handling practices may enhance microgreens'stability, storage, and shelf-life under appropriate conditions, including light, temperature, nutrients, humidity, and substrate. Moreover, the substrate may be a nutritive liquid solution (hydroponic system) or solid medium (coco peat, coconut fiber, coir dust and husks, sand, vermicompost, sugarcane filter cake, etc.) based on a variety of microgreens. However integrated multiomics approaches alongwith nutriomics and foodomics may be explored and utilized to identify and breed most potential microgreen genotypes, biofortify including increasing the nutritional content (macro-elements:K, Ca and Mg; oligo-elements: Fe and Zn and antioxidant activity) and microgreens related other traits viz., fast growth, good nutritional values, high germination percentage, and appropriate shelf-life through the implementation of integrated approaches includes genomics, transcriptomics, sequencing-based approaches, molecular breeding, machine learning, nanoparticles, and seed priming strategiesetc.

Prediction of available energy and amino acid digestibility of Chinese sorghum fed to growing-finishing pigs

Two experiments were conducted to determine digestible energy (DE), metabolizable energy (ME), as well as the standardized ileal digestibility (SID) of crude protein (CP) and amino acids (AA) in 10 sorghum samples fed to pigs. In experiment 1, 22 crossbred barrows (Duroc × Yorkshire × Landrace, Initial body weight [BW]: 70.0 ± 1.8 kg) were selected and allotted to a replicated 11 × 3 incomplete Latin square design, including a basal diet and 10 sorghum energy diets and three consecutive periods. Each period had 7 d adaptation and 5 d total feces and urine collection. The DE and ME were determined by the total collection and the difference method. In experiment 2, 22 crossbred barrows (Duroc × Yorkshire × Landrace, Initial BW: 41.3 ± 1.2 kg) that had a T-cannula installed in the distal ileum were assigned to a replicated 11 × 3 incomplete Latin square design, including an N-free diet and 10 sorghum diets. Each period had 5 d adaptation and 2 d ileal digesta collection. The basal endogenous N losses were measured by the N-free diet method. All diets in experiment 2 were added 0.30% titanium dioxide as an indigestible marker for calculating the ileal CP and AA digestibility. On an as-fed basis, the DE and ME contents in sorghum were 3,410 kcal/kg (2,826 to 3,794 kcal/kg) and 3,379 kcal/kg (2,785 to 3,709 kcal/kg), respectively. The best-fit prediction equation for DE and ME were DE = 6,267.945 - (1,271.154 × % tannin) - (1,109.720 × % ash) (R2 = 0.803) and ME = 51.263 + (0.976 × DE) (R2 = 0.994), respectively. The SID of CP, Lys, Met, Thr, and Trp (SIDCP, SIDLys, SIDMet, SIDThr, and SIDTrp) in 10 sorghum samples were 78.48% (69.56% to 84.23%), 74.27% (61.11% to 90.60%), 92.07% (85.16% to 95.40%), 75.46% (66.39% to 80.80%) and 87.99% (84.21% to 92.37%), respectively. The best prediction equations for SID of CP and the first four limiting AAs were as following: SIDCP = 93.404 - (21.026 × % tannin) (R2 = 0.593), SIDCP = 42.922 - (4.011 × % EE) + (151.774 × % Met) (R2 = 0.696), SIDLys = 129.947 - (670.760 × % Trp) (R2 = 0.821), SIDMet = 111.347 - (232.298 × % Trp) (R2 = 0.647), SIDThr = 55.187 + (3.851 × % ADF) (R2 = 0.609) and SIDTrp = 95.676 - (10.824 × % tannin) (R2 = 0.523), respectively. Overall, tannin and ash are the first and second predictors of DE and ME values of sorghum, respectively, and the tannin, EE, Trp, ash, CF, and ADF can be used as the key predictors for SID of CP and first four limiting AAs.

Progress and challenges in sorghum biotechnology, a multipurpose feedstock for the bioeconomy

Sorghum [Sorghum bicolor (L.) Moench] is the fifth most important cereal crop globally by harvested area and production. Its drought and heat tolerance allow high yields with minimal input. It is a promising biomass crop for the production of biofuels and bioproducts. In addition, as an annual diploid with a relatively small genome compared with other C4 grasses, and excellent germplasm diversity, sorghum is an excellent research species for other C4 crops such as maize. As a result, an increasing number of researchers are looking to test the transferability of findings from other organisms such as Arabidopsis thaliana and Brachypodium distachyon to sorghum, as well as to engineer new biomass sorghum varieties. Here, we provide an overview of sorghum as a multipurpose feedstock crop which can support the growing bioeconomy, and as a monocot research model system. We review what makes sorghum such a successful crop and identify some key traits for future improvement. We assess recent progress in sorghum transformation and highlight how transformation limitations still restrict its widespread adoption. Finally, we summarize available sorghum genetic, genomic, and bioinformatics resources. This review is intended for researchers new to sorghum research, as well as those wishing to include non-food and forage applications in their research.

Inheritance of the genetic construct for RNA-silencing of the γ-kafirin gene (gKAF1) in the progeny of transgenic sorghum plants

Sorghum is one of the most important cereal crops in drought regions of the Globe. However, a number of constrains, such as poor nutritional value compared to other cereals, which is caused by resistance of its grain storage proteins (kafirins) to protease digestion, makes it less popular. The use of modern genetic technologies, such as RNA interference, opens up prospects for solving this problem. In this paper, we describe the inheritance of the genetic construct for RNAi silencing of the γ-kafirin gene (gKAF1) in the progeny of the mutant Avans-1/18, that we obtained previously by Agrobacterium-mediated genetic transformation of immature embryos of commercial cv. Avans. Inheritance of the genetic construct was traced by PCR-analysis to the nos-promoter governing expression of the marker gene bar and to the ubi1-intron, which is part of the genetic construct for silencing. It was found that the genetic construct inherited in T1 and T2 generations of the mutant grown both in the growth chamber and in the field plot, and in the F1 hybrids of the mutant with CMS-lines A2 KVV-181, A2 KVV-114, A2 O-1237, and fertile lines Volzhskoe-4v, Volzhskoe-615, O-1237. The studied plants from T1 and T2 generations had significantly higher in vitro protein digestibility than original non-transgenic cv. Avans. The vitreous endosperm in these plants was reduced either completely or manifested a faint layer. These data demonstrated that genetic construct for gKAF1 silencing was not only stably integrated in genome of the mutant plants but also expressed and improved the digestibility of endosperm proteins. In addition, in T1 progeny we found the plant, PCR positive for nos-promoter but PCR-negative for ubi1-intron, that had vitreous endosperm and was characterized by poor in vitro protein digestibility. These data are an example of instability of the genetic construct for RNAi-silencing in genome of some transgenic plants; they show close correlation of the floury endosperm type and high in vitro protein digestibility.

Fractional composition of grain sorghum proteins depending on the variety

14 varieties of grain sorghum bred by the Federal State Budgetary Scientific Institution RosNIISK Rossorgo were studied. The amount of protein in grain and its fractions was experimentally determined: albumin, globulins, glutelins and prolamins, a comparative analysis was carried out within each fraction and a conclusion was made about the highest biological value among the studied varieties. The results showed that sorghum seeds contain all four protein fractions, the highest content of which is albumin and glutel. The highest nutritional value was noted in the variety of sorghum Zhemchug, which contained the highest amount of albumin, characterized by a complete amino acid composition, and the lowest content of prolamins, which have a low balance of amino acids. In the varieties Kamelik and Locus, there was an insufficient content of complete proteins that make up the water-soluble and salt-soluble fractions in the grain of these plants. Grain sorghum varieties with the highest amount of protein (Pomegranate, Locus, Pearl and Bachelor) were characterized by a low level of alcohol-soluble protein fraction.

Effect of the nixtamalization process on the protein bioaccessibility of white and red sorghum flours during in vitro gastrointestinal digestion

Protein bioaccessibility is a major concern in sorghum (Sorghum bicolor L. Moench) due to potential interactions with tannins affecting its nutritional value. Technological treatments such as boiling or alkaline cooking have been proposed to address this problem by reducing tannin-protein interactions. This research aimed to evaluate the impact of nixtamalization in the protein bioaccessibility from two sorghum varieties (red and white sorghum) during in vitro gastrointestinal digestion. Nixtamalization increased protein bioaccessibility in the non-digestible fraction (NDF) (5.26 and 26.31% for red and white sorghum, respectively). However, cooking showed a higher permeation speed of protein from red sorghum flours at the end of the intestinal incubation (9.42%). The SDS-PAGE profile of the digested fraction (DF) at 90 min of intestinal incubation indicated that, for red sorghum, cooking allows the formation of α and γ-kafirins while nixtamalization increase α-kafirin release. Principal Components Analysis (PCA) showed the association between nixtamalization and dissociation of δα kafirin complexes and increased protein content in the digestible fraction. In silico interactions indicated the highest biding energies for (+)-catechin and kafirin fractions (β-kafirin: -7.0 kcal/mol; γ-kafirin: -5.8 kcal/mol, and δ-kafirin: -6.8 kcal/mol), suggesting a minor influence of depolymerized proanthocyanidin fractions with sorghum proteins as a result of the nixtamalization process. In conclusion, nixtamalization increased the bioaccessibility of sorghum proteins, depolymerizing condensed tannins, and breaking protein-tannin complexes. Such technological process improves the nutrimental value of sorghum, supporting its inclusion in the human diet.

Biolistic DNA Delivery and Its Applications in Sorghum bicolor

Biolistic DNA delivery has been considered a universal tool for genetic manipulation to transfer exotic genes to cells or tissues due to its simplicity, versatility, and high efficiency. It has been a preferred method for investigating plant gene function in most monocot crops. The first transgenic sorghum plants were successfully regenerated through biolistic DNA delivery in 1993, with a relatively low transformation efficiency of 0.3%. Since then, tremendous progress has been made in recent years where the highest transformation efficiency was reported at 46.6%. Overall, the successful biolistic DNA delivery system is credited to three fundamental cornerstones: robust tissue culture system, effective gene expression in sorghum, and optimal parameters of DNA delivery. In this chapter, the history, application, and current development of biolistic DNA delivery in sorghum are reviewed, and the prospect of sorghum genetic engineering is discussed.

The effect of genotype and traditional food processing methods on in-vitro protein digestibility and micronutrient profile of sorghum cooked products

Sorghum (Sorghum bicolor (L.) Moench) is one of the principal staple for millions of people in sub-Saharan Africa serving as the main sources of protein. However, protein digestibility is low in sorghum and this may be affected by processing methods. In this study 15 sorghum cultivars and one variety each of maize (Zea maize) and tef (Eragrostis tef) all of Ethiopian origin were investigated for in-vitro protein digestibility (IVPD), activity and concentration of anti-nutritional factors and micro nutrient profile in raw flour and various cooked food samples. Kafirin composition content and composition was also determined from raw flour samples of the sorghum cultivars. IVPD was significantly different between genotypes with both maize and tef superior to sorghum both in cooked and uncooked state except for the high lysine genotype Wetet Be-gunchie. Cooking significantly reduced IVPD in all crops but had only minor effect in maize. Results revealed a highly significant interaction between genotype and food processing methods where, occasionally, genotypes with highest IVPD under one processing method ended up to be the lowest under another. Trypsin inhibitor levels had a significant and negative correlation with IVPD (r2 = 0.1), while changes in phytic acid concentration and intrinsic phytase levels during processing followed opposite trends to each other. Processing increased mineral levels by 20-44% for iron and 4-29% for zinc perhaps due to degradation of phytic acid. Results demonstrated that protein digestibility and the concentration of anti- nutritional factors varied widely depending on the food type. Identification of specific genotypes for a specific food product may help improve the nutritional quality of sorghum based foods.

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

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

A Comparative Study of Selected Physical and Biochemical Traits of Wild-Type and Transgenic Sorghum to Reveal Differences Relevant to Grain Quality

Transgenic sorghum featuring RNAi suppression of certain kafirins was developed recently, to address the problem of poor protein digestibility in the grain. However, it was not firmly established if other important quality parameters were adversely affected by this genetic intervention. In the present study several quality parameters were investigated by surveying several important physical and biochemical grain traits. Important differences in grain weight, density and endosperm texture were found that serve to differentiate the transgenic grains from their wild-type counterpart. In addition, ultrastructural analysis of the protein bodies revealed a changed morphology that is indicative of the effect of suppressed kafirins. Importantly, lysine was found to be significantly increased in one of the transgenic lines in comparison to wild-type; while no significant changes in anti-nutritional factors could be detected. The results have been insightful for demonstrating some of the corollary changes in transgenic sorghum grain, that emerge from imposed kafirin suppression.

Molecular Approaches to Understand Nutritional Potential of Coarse Cereals

Coarse grains are important group of crops that constitutes staple food for large population residing primarily in the arid and semi-arid regions of the world. Coarse grains are designated as nutri-cereals as they are rich in essential amino acids, minerals and vitamins. In spite of having several nutritional virtues in coarse grain as mentioned above, there is still scope for improvement in quality parameters such as cooking qualities, modulation of nutritional constituents and reduction or elimination of anti-nutritional factors. Besides its use in traditional cooking, coarse grains have been used mainly in the weaning food preparation and other malted food production. Improvement in quality parameters will certainly increase consumer's preference for coarse grains and increase their demand. The overall genetic gain in quality traits of economic importance in the cultivated varieties will enhance their industrial value and simultaneously increase income of farmers growing these varieties. The urgent step for improvement of quality traits in coarse grains requires a detailed understanding of molecular mechanisms responsible for varied level of different nutritional contents in different genotypes of these crops. In this review we have discussed the progresses made in understanding of coarse grain biology with various omics tool coupled with modern breeding approaches and the current status with regard to our effort towards dissecting traits related to improvement of quality and nutritional constituents of grains.