title: Reconstruction of the astaxanthin biosynthesis pathway in rice endosperm reveals a metabolic bottleneck at the level of endogenous β-carotene hydroxylase activity.
abstract: Astaxanthin is a high-value ketocarotenoid rarely found in plants. It is derived from β-carotene by the 3-hydroxylation and 4-ketolation of both ionone end groups, in reactions catalyzed by β-carotene hydroxylase and β-carotene ketolase, respectively. We investigated the feasibility of introducing an extended carotenoid biosynthesis pathway into rice endosperm to achieve the production of astaxanthin. This allowed us to identify potential metabolic bottlenecks that have thus far prevented the accumulation of this valuable compound in storage tissues such as cereal grains. Rice endosperm does not usually accumulate carotenoids because phytoene synthase, the enzyme responsible for the first committed step in the pathway, is not present in this tissue. We therefore expressed maize phytoene synthase 1 (ZmPSY1), Pantoea ananatis phytoene desaturase (PaCRTI) and a synthetic Chlamydomonas reinhardtii β-carotene ketolase (sCrBKT) in transgenic rice plants under the control of endosperm-specific promoters. The resulting grains predominantly accumulated the diketocarotenoids canthaxanthin, adonirubin and astaxanthin as well as low levels of monoketocarotenoids. The predominance of canthaxanthin and adonirubin indicated the presence of a hydroxylation bottleneck in the ketocarotenoid pathway. This final rate-limiting step must therefore be overcome to maximize the accumulation of astaxanthin, the end product of the pathway.
authors: Department of Plant Production and Forestry Science, ETSEA, University of Lleida-Agrotecnio Center, Avenida Alcalde Rovira Roure, 191, 25198, Lleida, Spain.
authors: Chao
authors: C
authors: Bai
authors: Department of Plant Production and Forestry Science, ETSEA, University of Lleida-Agrotecnio Center, Avenida Alcalde Rovira Roure, 191, 25198, Lleida, Spain.
authors: Judit
authors: J
authors: Berman
authors: Department of Plant Production and Forestry Science, ETSEA, University of Lleida-Agrotecnio Center, Avenida Alcalde Rovira Roure, 191, 25198, Lleida, Spain.
authors: Gemma
authors: G
authors: Farre
authors: Department of Plant Production and Forestry Science, ETSEA, University of Lleida-Agrotecnio Center, Avenida Alcalde Rovira Roure, 191, 25198, Lleida, Spain.
authors: Teresa
authors: T
authors: Capell
authors: Institute of Molecular Bioscience, J. W. Goethe University, Max von Laue Str. 9, 60438, Frankfurt am Main, Germany.
authors: Gerhard
authors: G
authors: Sandmann
authors: Department of Plant Production and Forestry Science, ETSEA, University of Lleida-Agrotecnio Center, Avenida Alcalde Rovira Roure, 191, 25198, Lleida, Spain.|ICREA, Catalan Institute for Research and Advanced Studies, Passeig Lluís Companys 23, 08010, Barcelona, Spain.
authors: Paul
authors: P
authors: Christou
authors: Department of Plant Production and Forestry Science, ETSEA, University of Lleida-Agrotecnio Center, Avenida Alcalde Rovira Roure, 191, 25198, Lleida, Spain. zhu@pvcf.udl.cat.
authors: Changfu
authors: C
authors: Zhu
mesh_terms: D016825:Chlamydomonas reinhardtii / Q000201:enzymology; D056625:Endosperm / Q000235:genetics / Q000378:metabolism; D005818:Genetic Engineering; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase / Q000235:genetics*; D060847:Metabolic Engineering / Q000379:methods; D053858:Metabolic Networks and Pathways / Q000235:genetics; D006899:Mixed Function Oxygenases / Q000235:genetics; D012275:Oryza / Q000235:genetics / Q000254:growth & development; D010088:Oxidoreductases / Q000235:genetics*; D010105:Oxygenases / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D024341:Xanthophylls / Q000096:biosynthesis / Q000235:genetics; D003313:Zea mays / Q000201:enzymology; D019207:beta Carotene / Q000096:biosynthesis / Q000235:genetics
chemical_list: D024341:Xanthophylls; D019207:beta Carotene; C005948:astaxanthine; D006899:Mixed Function Oxygenases; D010088:Oxidoreductases; D010105:Oxygenases; C093259:beta-carotene ketolase; C079232:beta-carotene hydroxylase; C022398:phytoene dehydrogenase; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase
keywords: Astaxanthin; Carotenoids; Ketocarotenoids; Multigene transformation; Rice (Oryza sativa L.); β-carotene ketolase