title: Identification of the carotenoid isomerase provides insight into carotenoid biosynthesis, prolamellar body formation, and photomorphogenesis.
abstract: Carotenoids are essential photoprotective and antioxidant pigments synthesized by all photosynthetic organisms. Most carotenoid biosynthetic enzymes were thought to have evolved independently in bacteria and plants. For example, in bacteria, a single enzyme (CrtI) catalyzes the four desaturations leading from the colorless compound phytoene to the red compound lycopene, whereas plants require two desaturases (phytoene and zeta-carotene desaturases) that are unrelated to the bacterial enzyme. We have demonstrated that carotenoid desaturation in plants requires a third distinct enzyme activity, the carotenoid isomerase (CRTISO), which, unlike phytoene and zeta-carotene desaturases, apparently arose from a progenitor bacterial desaturase. The Arabidopsis CRTISO locus was identified by the partial inhibition of lutein synthesis in light-grown tissue and the accumulation of poly-cis-carotene precursors in dark-grown tissue of crtISO mutants. After positional cloning, enzymatic analysis of CRTISO expressed in Escherichia coli confirmed that the enzyme catalyzes the isomerization of poly-cis-carotenoids to all-trans-carotenoids. Etioplasts of dark-grown crtISO mutants accumulate acyclic poly-cis-carotenoids in place of cyclic all-trans-xanthophylls and also lack prolamellar bodies (PLBs), the lattice of tubular membranes that defines an etioplast. This demonstrates a requirement for carotenoid biosynthesis to form the PLB. The absence of PLBs in crtISO mutants demonstrates a function for this unique structure and carotenoids in facilitating chloroplast development during the first critical days of seedling germination and photomorphogenesis.
authors.affiliation: School of Biochemistry and Molecular Biology, Australian National University, Canberra, ACT 0200, Australia.
authors.forename: Hyoungshin
authors.initials: H
authors.lastname: Park
authors.forename: Sarah S
authors.initials: SS
authors.lastname: Kreunen
authors.forename: Abby J
authors.initials: AJ
authors.lastname: Cuttriss
authors.forename: Dean
authors.initials: D
authors.lastname: DellaPenna
authors.forename: Barry J
authors.initials: BJ
authors.lastname: Pogson
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000528:radiation effects; D029681:Arabidopsis Proteins; D002338:Carotenoids / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D003001:Cloning, Molecular; D003624:Darkness; D004926:Escherichia coli / Q000235:genetics; D005786:Gene Expression Regulation; D007536:Isomerism; D008027:Light; D014975:Lutein / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D000077276:Lycopene; D008854:Microscopy, Electron; D009154:Mutation; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D018520:Plant Shoots / Q000201:enzymology / Q000235:genetics / Q000528:radiation effects; D018087:Plastids / Q000378:metabolism / Q000648:ultrastructure; D019745:cis-trans-Isomerases / Q000235:genetics / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D002338:Carotenoids; C100185:(all-E) phytoene; D010088:Oxidoreductases; C022398:phytoene dehydrogenase; C099215:zeta-carotene desaturase; C444651:CRTISO protein, Arabidopsis; D019745:cis-trans-Isomerases; D000077276:Lycopene; D014975:Lutein