title: Metabolic engineering of ketocarotenoid biosynthesis in higher plants.
abstract: Ketocarotenoids such as astaxanthin and canthaxanthin have important applications in the nutraceutical, cosmetic, food and feed industries. Astaxanthin is derived from beta-carotene by 3-hydroxylation and 4-ketolation at both ionone end groups. These reactions are catalyzed by beta-carotene hydroxylase and beta-carotene ketolase, respectively. The hydroxylation reaction is widespread in higher plants, but ketolation is restricted to a few bacteria, fungi, and some unicellular green algae. The recent cloning and characterization of beta-carotene ketolase genes in conjunction with the development of effective co-transformation strategies permitting facile co-integration of multiple transgenes in target plants provided essential resources and tools to produce ketocarotenoids in planta by genetic engineering. In this review, we discuss ketocarotenoid biosynthesis in general, and characteristics and functional properties of beta-carotene ketolases in particular. We also describe examples of ketocarotenoid engineering in plants and we conclude by discussing strategies to efficiently convert beta-carotene to astaxanthin in transgenic plants.
authors.affiliation: Departament de Producció Vegetal i Ciència Forestal, Universitat de Lleida, Av. Alcalde Rovira Roure, 191, Lleida 25198, Spain. zhu@pvcf.udl.cat
authors.forename: Changfu
authors.initials: C
authors.lastname: Zhu
authors.forename: Shaista
authors.initials: S
authors.lastname: Naqvi
authors.forename: Teresa
authors.initials: T
authors.lastname: Capell
authors.forename: Paul
authors.initials: P
authors.lastname: Christou
mesh_terms: D002338:Carotenoids / Q000096:biosynthesis*; D002384:Catalysis; D018556:Crops, Agricultural; D006900:Hydroxylation; D010105:Oxygenases / Q000235:genetics; D010944:Plants / Q000378:metabolism*; D019076:Transgenes
chemical_list: D002338:Carotenoids; D010105:Oxygenases; C093259:beta-carotene ketolase