https://phys.org/news/2018-06-micronutrients-efficiently.html

To achieve this enrichment, Bhullar and her team incorporated a genetic construct expressing a combination of three additional genes into the rice plants. One of these genes facilitates mobilisation of iron stored in the plant vacuoles, another encodes for an iron-storing protein Ferritin, and the third promotes efficient iron and zinc uptake by the roots.

Last year, the same team of researchers established a proof of concept in combining three nutritionally relevant traits in one rice line, namely iron, zinc and β-carotene were increased simultaneously in the rice grains.