Effect of storage period on provitamin‐A carotenoids retention in biofortified maize hybrids

Analysis of nutritional composition in opaque2- and crtRB1-based single- and double-biofortified super sweet corn

Sweet corn has emerged as a favorite food item worldwide owing to its kernel sweetness. However, traditional sweet corn cultivars are poor in provitamin-A (proA) and essential amino acids, viz., lysine and tryptophan. So far, no sweet corn hybrid with high nutritional qualities has been commercialized elsewhere. Here, we analyzed accumulation of provitamin-A (proA), lysine, and tryptophan in a set of mutant versions of (i) crtRB1-, (ii) o2-, and (iii) crtRB1 + o2-based sweet corn inbreds and hybrids with (iv) traditional sweet corn (wild-type: O2 + CrtRB1). The crtRB1- and crtRB1 + o2-based genotypes possessed significantly higher proA (17.31 ppm) over traditional sweet corn (2.83 ppm), while o2- and crtRB1 + o2-based genotypes possessed significantly higher lysine (0.345%) and tryptophan (0.080%) over traditional sweet corn (lysine 0.169%, tryptophan 0.036%). Late sowing favored high kernel lysine, proA, and green cob yield among hybrids. Sweetness (17.87%) among the improved inbreds and hybrids was comparable to the original sweetcorn genotypes (17.84%). Among the four genotypic classes, crtRB1 + o2-based improved genotypes showed stronger association among traits over genotypes with o2 and crtRB1 genes alone. Significant association was observed among (i) proA and BC (r = 0.99), (ii) proA and BCX (r = 0.93), (iii) lysine and tryptophan (r = 0.99), and (iv) green cob yield with fodder yield (r = 0.73) in sweet corn hybrids. The study demonstrated that combining crtRB1 and o2 genes did not pose any negative impact on nutritional, yield, and agronomic performance. Sweet corn with crtRB1 + o2 assumes significance for alleviating malnutrition through sustainable and cost-effective approach.

Quantitative trait loci and candidate genes for iron and zinc bio-fortification in genetically diverse germplasm of maize (Zea mays L): A systematic review

Genetically and economically, Maize plays a pivotal role in tackling Iron-Zinc mineral deficiency through the crop's biofortification approach to high-yielding cultivars. The objective of this study is to summarize quantitative trait loci (QTL) is useful for identifying novel genes of interest in diverse germplasm for understanding the exact genetic mechanism for Iron and zinc uptake, deposition, and biosynthesis in Zea mays L endosperm. various techniques like Germplasm Genetic Wide Association, QTL meta-analysis, and biparental linkage analysis are used by researchers in diverse germplasm of Maize for the gene of interest marking and are extracted as secondary information through a systematic review of scientific published sources in peer-reviewed sites. A literature review was focused on quantitative trait loci with candidate genes from different families like YS, NRAMP, ferritin, Cation efflux, etc., and cloned four phytase soluble genes which influence the concentration as well as bioavailability of Fe & Zn in the endosperm. More than 30 QTLs with 15-Fe, 17-Zn; 10 Meta QTLS are common and linked with micronutrient concentration as well 17 candidate genes from different families are responsible for the zinc-iron deposition on the endosperm. More than 46 Fe-Zn (20 + 26) SNPs and 22 SNPs (10 + 12) on nine different chromosomes play a significant role in the variation of the mineral value of inbreeds and Double haploid Bi-parental population of Zea mays L. In Rice and Maize, five different chromosomes are collinear for the uptake to deposition of these minerals in the endosperm. The success of marker-based biofortification depends upon the nature of germplasm, the gap between flanking marker and targeted genes, the selection of genotypes in each generation, and genotype-environment interaction which are the future area of study. This study can assist the breeders in fast-tracking Fe and Zn biofortification through frequency multiplication of these desired loci of Maize.

Marker-assisted pyramiding of lycopene-ε-cyclase, β-carotene hydroxylase1 and opaque2 genes for development of biofortified maize hybrids

Malnutrition affects growth and development in humans and causes socio-economic losses. Normal maize is deficient in essential amino acids, lysine and tryptophan; and vitamin-A. Crop biofortification is a sustainable and economical approach to alleviate micronutrient malnutrition. We combined favorable alleles of crtRB1 and lcyE genes into opaque2 (o2)-based four inbreds viz. QLM11, QLM12, QLM13, and QLM14 using marker-assisted backcross breeding. These are parents of quality protein maize versions of two elite hybrids viz. Buland and PMH1, grown in India. Gene-based SSRs for o2 and InDel markers for crtRB1 and lcyE were successfully employed for foreground selection in BC₁F₁, BC₂F₁, and BC₂F₂ generations. The recurrent parent genome recovery ranged from 88.9 to 96.0% among introgressed progenies. Kernels of pyramided lines possessed a high concentration of proA (7.14–9.63 ppm), compared to 1.05 to 1.41 ppm in the recurrent parents, while lysine and tryptophan ranged from 0.28–0.44% and 0.07–0.09%, respectively. The reconstituted hybrids (RBuland and RPMH1) showed significant enhancement of endosperm proA (6.97–9.82 ppm), tryptophan (0.07–0.09%), and lysine (0.29–0.43%), while grain yield was at par with their original versions. The dissemination of reconstituted hybrids holds significant promise to alleviate vitamin-A deficiency and protein-energy malnutrition in developing countries.

Low expression of carotenoids cleavage dioxygenase 1 (ccd1) gene improves the retention of provitamin-A in maize grains during storage

Provitamin-A (proA) is essentially required for vision in humans but its deficiency affects children and pregnant women especially in the developing world. Biofortified maize rich in proA provides new opportunity for sustainable and cost-effective solution to alleviate malnutrition, however, significant loss of carotenoids during storage reduces its efficacy. Here, we studied the role of carotenoid cleavage dioxygenase 1 (ccd1) gene on degradation of carotenoids in maize. A set of 24 maize inbreds was analyzed for retention of proA during storage. At harvest, crtRB1-based maize inbreds possessed significantly high proA (β-carotene: 12.30 µg/g, β-cryptoxanthin: 4.36 µg/g) than the traditional inbreds (β-carotene: 1.74 µg/g, β-cryptoxanthin: 1.28 µg/g). However, crtRB1-based inbreds experienced significant degradation of proA carotenoids (β-carotene: 20%, β-cryptoxanthin: 32% retention) following 5 months. Among the crtRB1-based genotypes, V335PV had the lowest retention of proA (β-carotene: 1.63 µg/g, β-cryptoxanthin: 0.82 µg/g), while HKI161PV had the highest retention of proA (β-carotene: 4.17 µg/g, β-cryptoxanthin: 2.32 µg/g). Periodical analysis revealed that ~ 60-70% of proA degraded during the first three months. Expression analysis revealed that high expression of ccd1 led to low retention of proA carotenoids in V335PV, whereas proA retention in HKI161PV was higher due to lower expression. Highest expression of ccd1 was observed during first 3 months of storage. Copy number of ccd1 gene varied among yellow maize (1-6 copies) and white maize (7-35 copies) while wild relatives contained 1-4 copies of ccd1 gene per genome. However, copy number of ccd1 gene did not exhibit any correlation with proA carotenoids. We concluded that lower expression of ccd1 gene increased the retention of proA during storage in maize. Favourable allele of ccd1 can be introgressed into elite maize inbreds for higher retention of proA during storage.