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, ß-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.

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.

Environmental impact of phytic acid in Maize (Zea mays. L) genotypes for the identification of stable inbreds for low phytic acid.

Phytic acid is a ubiquitous compound that chelates the micronutrients in food and hinder their absorption. Hence, breeding for low phytate content for producing stable low phytic acid (lpa) hybrids is essential. Phytic acid content in maize grains has been found to vary across environments and its stable expression has yet to be explored. In a view of this, forty inbreds were screened with two checks viz., CO-6 and CO-H(M)-8 across three locations. Twenty morphological and three quality traits were observed to identify the stable lines for low phytic acid with higher free inorganic phosphorous and starch. Among all the lines, UMI-467, LPA-2-285, LPA-2-395 and UMI-447 recorded a stable performance in both AMMI and GGE biplot analysis for low phytic acid (2.52-3.32 mg/g). These lines also had a higher free inorganic phosphorous, ensuring its bioavailability (1.78-1.88 mg/g). There were perturbations in yield, starch and seed characteristics of the stable low phytic acid lines due to their lower phytic acid concentrations. This stated the role of phytic acid in plant physiology and established the constraints to be faced in breeding for low phytic acid in maize. Among the lpa lines, LPA-2-285 (57.83%) and UMI-447 (55.78%) had the highest average starch content. The lowest stable phytic acid content was observed in UMI-467 (2.52 mg/g) and this line had severe reductions in yield parameters. Considering the seed and yield characteristics, LPA-2-285, LPA-2-395 and UMI-447 performed better than UMI-467. Although these four stable lines were poor in their adaptability among all the genotypes, they could be utilised as promising stable donors to facilitate the development of stable lpa hybrids.

Enumerating the phytic acid content in maize germplasm and formulation of reference set to enhance the breeding for low phytic acid.

Phytic acid (Myoinositol 1, 2, 3, 4, 5, 6 hexakisphosphate) is a ubiquitous compound present in plants. It is an important constituent in seed reducing the bioavailability of phosphorous and mineral nutrients when fed to monogastric animals like swine, poultry, fish etc. Hence, identification of maize germplasm with reduced phytic acid content is imperative to formulate the breeding programs to evolve low phytate lines. Towards this, three hundred and thirty-eight maize germplasm accessions available at Department of Millets, TNAU, were raised and screened for phytic acid content which varied from 2.77 to 16.70 mg/g of seed. Based on the variability present, a reference set with fifty-eight genotypes for phytic acid was formulated. The reference set was formed with random genotypes selected from the base population to follow a normal distribution (skewness; 0.17, kurtosis; 0.61 and K-S test for normality Dn = 0.70) for phytic acid. The non-significant difference between the means of the base and the reference ensured the entire representation of the base in the formulated reference for phytic acid. Among all the lines in the reference set, the lowest phytic acid content were observed in the lines UMI-113 (2.77 mg/g) followed by UMI-300-1 (3.17 mg/g), UMI-467 (5.50 mg/g) and UMI-158 (6.58 mg/g) could be used as donors for low phytic acid in breeding programs. The principal component analysis for studying the extent of variability in the reference, revealed six major principal components that exhibited 80.40% of variation with flowering traits, ear height and phytic acid as a major contributor for variability. The characters namely plant stand, germination percentage, kernel yield, ear length, ear diameter and number of kernels per row were found to be positively correlated with the phytic acid and this emphasizes the negative pleiotropic effects of low phytic acid lines in germination and seed set. Thus this formulated reference set enables the breeders to handle minimum population for further grouping the genotypes to analyse their heterotic potential combined with low phytic acid.