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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.

Maize is the predominant food source for the world population, but lack of lysine and tryptophan in maize endosperm cannot fulfill the nutritional requirements of humans. Hence, the improvement of lysine and tryptophan content is the ultimate goal of maize biofortification programs. In the present study, the marker-assisted backcross (MABC) breeding strategy was used to enhance the lysine and tryptophan content of the elite maize inbred line UMI1230 by introgressing opaque 2 (o2) gene from the VQL1. During the transfer of the gene into UMI1230, SSR marker umc1066 tightly associated with o2 used for foreground selection. Background recovery was estimated using 168 SSR markers. Phenotype screening for morphological traits was adopted to choose plants parallel to UMI1230. As a result, four BC 2 F 3 improved lines (DBT5-1-14/25-5/25-8/25-8/25, DBT5-1-14/25-5/25-8/25-7/25, DBT5-1-14/25-5/25-8/25-10/25 and DBT5-1-14/25-5/25-8/25-12/25) with o2 were developed. The improved line's background genome recovery varied between 90.60 and 94.80%. Also, the improved lines had better agronomic performance along with increased lysine (0.311-0.331%) and tryptophan (0.040-0.048%) contents. In summary, the MABC breeding strategy has successfully improved the levels of lysine and tryptophan in UMI1230 without affecting agronomic performance. The improved line's hold great potential as donors in biofortification programs in maize., (© Prof. H.S. Srivastava Foundation for Science and Society 2020.)