Biofortification of wheat with enhanced provitamin a through metabolic engineering

Abstract:

Vitamin A deficiency affects an estimated 190 million pre-school children worldwide, yet the staple cereal that feeds most of them—wheat—is essentially devoid of provitamin A carotenoids in its endosperm. Metabolic engineering of the carotenoid biosynthetic pathway offers a way to accumulate β-carotene directly in wheat grain. This research introduced bacterial phytoene synthase (CrtB) and phytoene desaturase (CrtI) genes, driven by the endosperm-specific 1Dx5 promoter, into Indian bread wheat cultivar HD-2967 via Agrobacterium-mediated transformation. Twelve independent T₂ transgenic events were evaluated at Sri Venkateswara Veterinary and Agricultural University, Tirupati, during rabi 2022-23. Total carotenoid content in transgenic endosperm ranged from 2.6 to 9.4 μg/g dry weight (DW), compared with 1.8 μg/g in the wild type. The highest-performing line (T4-D) accumulated 9.4 μg/g total carotenoids, of which 7.1 μg/g was β-carotene—a 14.2-fold increase over the wild type. Lutein and zeaxanthin also increased by 2.8 and 3.7-fold, respectively. However, a negative correlation (r = −0.94) was observed between total carotenoid content and grain yield, with T4-D showing a 21.3 percent yield penalty compared to the wild type. HPLC profiling confirmed that β-carotene was the dominant carotenoid in all transgenic lines. Milling and cooking stability tests showed 82.6 percent β-carotene retention after chapati preparation. These results demonstrate that wheat endosperm can be engineered to produce meaningful levels of provitamin A, though yield drag in high-carotenoid lines needs to be addressed through further breeding.