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Combinatorial genetic transformation generates a library of metabolic phenotypes for the carotenoid pathway in maize

Zhu, Changfu, Naqvi, Shaista, Breitenbach, Jürgen, Sandmann, Gerhard, Christou, Paul, Capell, Teresa
Proceedings of the National Academy of Sciences of the United States of America 2008 v.105 no.47 pp. 18232-18237
genetic transformation, gene transfer, Zea mays, biosynthesis, recombinant DNA, transgenic plants, corn, beta-carotene, endosperm, genes, promoter regions
Combinatorial nuclear transformation is a novel method for the rapid production of multiplex-transgenic plants, which we have used to dissect and modify a complex metabolic pathway. To demonstrate the principle, we transferred 5 carotenogenic genes controlled by different endosperm-specific promoters into a white maize variety deficient for endosperm carotenoid synthesis. We recovered a diverse population of transgenic plants expressing different enzyme combinations and showing distinct metabolic phenotypes that allowed us to identify and complement rate-limiting steps in the pathway and to demonstrate competition between β-carotene hydroxylase and bacterial β-carotene ketolase for substrates in 4 sequential steps of the extended pathway. Importantly, this process allowed us to generate plants with extraordinary levels of β-carotene and other carotenoids, including complex mixtures of hydroxycarotenoids and ketocarotenoids. Combinatorial transformation is a versatile approach that could be used to modify any metabolic pathway and pathways controlling other biochemical, physiological, or developmental processes.