title: Metabolic flux analysis of plastidic isoprenoid biosynthesis in poplar leaves emitting and nonemitting isoprene.
abstract: The plastidic 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway is one of the most important pathways in plants and produces a large variety of essential isoprenoids. Its regulation, however, is still not well understood. Using the stable isotope 13C-labeling technique, we analyzed the carbon fluxes through the MEP pathway and into the major plastidic isoprenoid products in isoprene-emitting and transgenic isoprene-nonemitting (NE) gray poplar (Populus×canescens). We assessed the dependence on temperature, light intensity, and atmospheric [CO2]. Isoprene biosynthesis was by far (99%) the main carbon sink of MEP pathway intermediates in mature gray poplar leaves, and its production required severalfold higher carbon fluxes compared with NE leaves with almost zero isoprene emission. To compensate for the much lower demand for carbon, NE leaves drastically reduced the overall carbon flux within the MEP pathway. Feedback inhibition of 1-deoxy-D-xylulose-5-phosphate synthase activity by accumulated plastidic dimethylallyl diphosphate almost completely explained this reduction in carbon flux. Our data demonstrate that short-term biochemical feedback regulation of 1-deoxy-d-xylulose-5-phosphate synthase activity by plastidic dimethylallyl diphosphate is an important regulatory mechanism of the MEP pathway. Despite being relieved from the large carbon demand of isoprene biosynthesis, NE plants redirected only approximately 0.5% of this saved carbon toward essential nonvolatile isoprenoids, i.e. β-carotene and lutein, most probably to compensate for the absence of isoprene and its antioxidant properties.
authors.affiliation: Research Unit Environmental Simulation, Institute of Biochemical Plant Pathology, Helmholtz Zentrum München, 85764 Neuherberg, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Ghirardo
authors.forename: Louwrance Peter
authors.initials: LP
authors.lastname: Wright
authors.forename: Zhen
authors.initials: Z
authors.lastname: Bi
authors.forename: Maaria
authors.initials: M
authors.lastname: Rosenkranz
authors.forename: Pablo
authors.initials: P
authors.lastname: Pulido
authors.forename: Manuel
authors.initials: M
authors.lastname: Rodríguez-Concepción
authors.forename: Ülo
authors.initials: Ü
authors.lastname: Niinemets
authors.forename: Nicolas
authors.initials: N
authors.lastname: Brüggemann
authors.forename: Jonathan
authors.initials: J
authors.lastname: Gershenzon
authors.forename: Jörg-Peter
authors.initials: JP
authors.lastname: Schnitzler
mesh_terms: D002070:Butadienes; D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D002247:Carbon Isotopes; D015536:Down-Regulation / Q000528:radiation effects; D004896:Erythritol / Q000031:analogs & derivatives / Q000378:metabolism; D045782:Hemiterpenes / Q000096:biosynthesis* / Q000378:metabolism; D007553:Isotope Labeling; D008027:Light; D064688:Metabolic Flux Analysis / Q000379:methods*; D008954:Models, Biological; D009943:Organophosphorus Compounds / Q000378:metabolism; D010420:Pentanes; D010860:Pigments, Biological / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism* / Q000528:radiation effects; D018087:Plastids / Q000201:enzymology / Q000378:metabolism* / Q000528:radiation effects; D032107:Populus / Q000378:metabolism* / Q000528:radiation effects; D013403:Sugar Phosphates / Q000378:metabolism; D013696:Temperature; D014166:Transferases / Q000378:metabolism
chemical_list: C114232:2-C-methylerythritol 4-phosphate; D002070:Butadienes; D002247:Carbon Isotopes; D045782:Hemiterpenes; D009943:Organophosphorus Compounds; D010420:Pentanes; D010860:Pigments, Biological; D013403:Sugar Phosphates; C005059:isoprene; D002245:Carbon Dioxide; C043060:3,3-dimethylallyl pyrophosphate; D002244:Carbon; D014166:Transferases; C109461:deoxyxylulose-5-phosphate synthase; D004896:Erythritol