Improving the nutritional value of Golden Rice through increased pro-vitamin A content

Abstract

"Golden Rice" is a variety of rice engineered to produce beta-carotene (pro-vitamin A) to help combat vitamin A deficiency, and it has been predicted that its contribution to alleviating vitamin A deficiency would be substantially improved through even higher beta-carotene content. 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 beta-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 Rice. We observed an increase in total carotenoids of up to 23-fold (maximum 37 microg/g) compared to the original Golden Rice and a preferential accumulation of beta-carotene.

Golden Rice – five years on the road – five years to go?

“…Thus, neither the flux of carbon into prenyllipid synthesis nor the efficiency of CRTI is the rate-limiting step in carotenoid synthesis in GR. This is corroborated by results obtained by Syngenta scientists who focused on optimizing the expression of PSY [8]. A side-by-side comparison of PSYs from different plants was carried out in a maize tissue culture model system, which revealed substantial differences in carotenoid accumulation.…”

“…Given the high degree of homology between plant PSYs, subtle but effective differences in primary structure are expected to govern the adaptation of the enzyme to its biochemical surroundings. Perhaps not surprisingly, the two best-performing PSY proteins (from rice and maize) were more similar to each other than to any of the other PSYs used [8]. Adaptations can be related to specific biochemical microenvironments affecting protein expression or enzymatic kinetics.…”

“…The conversion factor for b-carotene from a mixed diet is 12. Using this conversion factor and a conservative estimation of only 24 mg/g of provitamin A, 72 g of dry GR2 polished rice would provide 50% of the RDA for children [8]. It is therefore expected that GR2 will be able to contribute to alleviating VAD.…”

“…com), and Mogen (formerly), as well as Syngenta. In addition, Syngenta scientists during the past years have contributed substantially to the improvement of the technology [8] as well as to product development and regulatory expertise and advice.…”

Biofortified crops to alleviate micronutrient malnutrition

“…A case in point is Golden Rice, in which the carotenoid biosynthetic pathway has been reconstituted in non-carotenogenic endosperm tissue, as a means to deliver provitamin A [30][31][32]. Reconstitution of the pathway in other crops depends on the metabolic bottleneck, as illustrated by canola, tomato and potato [33][34][35][36][37].…”