NpgRJ_Nbt_1082 1..6

‘Golden Rice’ is a variety of rice engineered to produce bcarotene (pro-vitamin A) to help combat vitamin A deficiency1, and it has been predicted that its contribution to alleviating vitamin A deficiency would be substantially improved through even higher b-carotene content2. We hypothesized that the daffodil gene encoding phytoene synthase (psy), one of the two genes used to develop Golden Rice, was the limiting step in b-carotene accumulation. Through systematic testing of other plant psys, we identified a psy from maize that substantially increased carotenoid accumulation in a model plant system. We went on to develop ‘Golden Rice 2’ introducing this psy in combination with the Erwinia uredovora carotene desaturase (crtI) used to generate the original Golden Rice1. We observed an increase in total carotenoids of up to 23-fold (maximum 37 lg/g) compared to the original Golden Rice and a preferential accumulation of b-carotene. Carotenoids are a group of plant pigments important in the human diet as the only precursors of vitamin A. Certain carotenoids, most importantly b-carotene, are cleaved to vitamin A within the body and are referred to as pro-vitamin A3. Vitamin A deficiency, a major problem in parts of the developing world, can result in permanent blindness and increase the incidence and severity of infectious diseases4. In Asia, vitamin A deficiency is associated with the povertyrelated predominant consumption of rice, which lacks pro-vitamin A in the edible part of the grain (endosperm). Providing pro-vitamin A in a staple food such as rice could be a simple and effective complement to supplementation programs5 because, through farming, it would be ubiquitous and self-sustaining. Golden Rice is the name coined to describe the genetically modified rice1 that produces carotenoids in the endosperm of the grain, giving rise to a characteristic yellow color. In this pioneering work, a maximum level of 1.6 mg/g total carotenoids was achieved and has