title: Differential expression of two isopentenyl pyrophosphate isomerases and enhanced carotenoid accumulation in a unicellular chlorophyte.
abstract: The enzyme isopentenyl pyrophosphate (IPP) isomerase catalyzes the reversible isomerization of IPP to produce dimethylallyl pyrophosphate, the initial substrate leading to the biosynthesis of carotenoids and many other long-chain isoprenoids. Expression of IPP isomerase, and of two enzymes specific to the carotenoid pathway (lycopene beta-cyclase and beta-carotene-C-4-oxygenase), was followed in the green unicellular alga Haematococcus pluvialis after exposure to high illumination. This alga uniquely accumulates carotenoids in the cytoplasm and in late developmental stages turns deep-red in color because of accumulation of ketocarotenoids in the cytosol. The carotenoid/chlorophyll ratio increased 3-fold in wild type and 6-fold in a precocious carotenoid-accumulating mutant (Car-3) within 24 h after increasing the illumination from 20 to 150 micromol photon m-2.s-1. Two cDNAs encoding IPP isomerase in Haematococcus, ipiHp1 and ipiHp2, were identified. Although otherwise highly similar (95% identity overall), the predicted sequence of ipiHp1 contained a 12-aa region not found in that of ipiHp2. This was reflected by a size difference between two polypeptides of 34 and 32.5 kDa, both of which reacted with an antibody to the product of ipiHp1. We suggest that the 32.5-kDa form is involved with the carotenoid accumulation in the cytoplasm, since the 32.5-kDa polypeptide was preferentially up-regulated by high light preceding the carotenoid increase and only this form was detected in red cysts.
authors.affiliation: Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Sun
authors.forename: F X
authors.initials: FX
authors.lastname: Cunningham
authors.forename: E
authors.initials: E
authors.lastname: Gantt
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019748:Carbon-Carbon Double Bond Isomerases / Q000737:chemistry*; D002338:Carotenoids / Q000096:biosynthesis*; D002734:Chlorophyll / Q000378:metabolism; D000460:Chlorophyta / Q000201:enzymology*; D003001:Cloning, Molecular; D018507:Gene Expression Regulation, Developmental / Q000235:genetics; D045782:Hemiterpenes; D019753:Intramolecular Lyases / Q000032:analysis; D007527:Isoenzymes / Q000378:metabolism; D008027:Light; D008969:Molecular Sequence Data; D016296:Mutagenesis / Q000235:genetics; D009154:Mutation / Q000235:genetics; D009943:Organophosphorus Compounds / Q000378:metabolism; D010860:Pigments, Biological / Q000737:chemistry; D012333:RNA, Messenger / Q000378:metabolism; D016415:Sequence Alignment; D017421:Sequence Analysis
chemical_list: D045782:Hemiterpenes; D007527:Isoenzymes; D009943:Organophosphorus Compounds; D010860:Pigments, Biological; D012333:RNA, Messenger; D002734:Chlorophyll; C004809:isopentenyl pyrophosphate; D002338:Carotenoids; D019748:Carbon-Carbon Double Bond Isomerases; C021453:isopentenyldiphosphate delta-isomerase; D019753:Intramolecular Lyases; C070925:lycopene cyclase-isomerase