How was golden rice engineered to produce more beta-carotene?

Golden rice was engineered to produce beta-carotene by modifying the rice genome to include genes from other organisms, as beta-carotene does not naturally occur in rice grains. Because the production of beta-carotene is a complex biochemical process regulated by several genes, scientists introduced specific genetic material to enable its synthesis in the rice endosperm, the edible part of the plant.12

The original modification involved adding a gene from the daffodil (Narcissus pseudonarcissus) that produces the enzyme phytoene synthase, along with a gene from a bacterium (such as Pantoea ananatis or Erwinia uredovora) that produces the enzyme phytoene desaturase. Later versions of the crop also incorporated genes from corn. These additions allowed the rice to accumulate beta-carotene, which the human body can convert into vitamin A. In 2004, researchers further improved the model by creating "Golden Rice 2," which achieved a 23-fold increase in carotenoid production compared with the original variety.12