Résumé des résultats (Abstract)
(Anglais)
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'Genetic engineering of carotenoid metabolism: a novel route to vitamins, colours and aromas for the European market.'
Subtask 3.1:
Production of beta-carotene in rice
Vitamin A-deficiency affects the health of ca 400 million youth and is, after iron deficiency, the second most important human malnutrition. The goal of the project is to provide with a genetically engineered rice, the most important staple food of the world, especially in developing countries, where vitamin A-deficiency is the major problem, the basis for a daily diet rich in provitamin A as a measure against this health problem.
Milled rice does not contain any provitamin a (b-carotene) and the pathway ends with GGPP. The experimental approach was using endosperm-specific expression of the transgenes missing to complete the biochemical pathway. These are phytoene synthase, phytoene desaturase, ..-carotene desaturase, and lycopene cyclase (all isolated from Narcissus pseudonarcissus), or alternatively to the second and third gene the double-desaturase from Ervinia. Transgenic rice plants were produced for all these genes by biolistic transformation and gene combinations established by sexual crossing. However, due to complicated insertion patterns and subsequent silencing this approach never led to completion of the pathway.
The breakthrough was achieved when Agrobacterium-mediated co-transformation was used to recover transgenic lines which contained all necessary genes at a simple integration pattern. A series of plants could be regenerated which produced rice grains with a yellow endosperm. Biochemical analysis revealed that the yellow colour was due to the presence of b-carotene plus additional terpenoids.
A manuscript has been prepared and will be submitted soon:
Engineering the complete provitamin A (b-carotene) biosynthetic pathway into (carotenoid-free) rice endosperm by Xudong Ye, Salim Al.Babili, Andreas Klöti, Jing Zhang, Peter Beyer and Ingo Potrykus.
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