title: Cell growth defect factor 1 is crucial for the plastid import of NADPH:protochlorophyllide oxidoreductase A in Arabidopsis thaliana.
abstract: Tetrapyrroles such as chlorophyll, heme, and bacteriochlorophyll play fundamental roles in the energy absorption and transduction of all photosynthetic organisms. They are synthesized via a complex pathway taking place in chloroplasts. Chlorophyll biosynthesis in angiosperms involves 16 steps of which only one is light-requiring and driven by the NADPH:protochlorophyllide oxidoreductase (POR). Three POR isoforms have been identified in Arabidopsis thaliana--designated PORA, PORB, and PORC--that are differentially expressed in etiolated, light-exposed, and light-adapted plants. All three isoforms are encoded by nuclear genes, are synthesized as larger precursors in the cytosol (pPORs), and are imported posttranslationally into the plastid compartment. Import of the precursor to the dark-specific isoform PORA (pPORA) is protochlorophyllide (Pchlide)-dependent and due to the operation of a unique translocon complex dubbed PTC (Pchlide-dependent translocon complex) in the plastid envelope. Here, we identified a ∼30-kDa protein that participates in pPORA import. The ∼30-kDa protein is identical to the previously identified CELL GROWTH DEFECT FACTOR 1 (CDF1) in Arabidopsis that is conserved in higher plants and Synechocystis. CDF1 operates in pPORA import and stabilization and hereby acts as a chaperone for PORA protein translocation. CDF1 permits tight interactions between Pchlide synthesized in the plastid envelope and the importing PORA polypeptide chain such that no photoexcitative damage occurs through the generation of singlet oxygen operating as a cell death inducer. Together, our results identify an ancient mechanism dating back to the endosymbiotic origin of chloroplasts as a key element of Pchlide-dependent pPORA import.
authors.affiliation: Biologie Environnementale et Systémique (BEeSy), Université Joseph Fourier, F-38041 Grenoble Cedex 9, France; diter@wsu.edu steffen.reinbothe@ujf-grenoble.fr.
authors.forename: Steffen
authors.initials: S
authors.lastname: Reinbothe
authors.affiliation: Department of Biological Sciences, University of Toledo, Toledo, OH 43606; and.
authors.forename: John
authors.initials: J
authors.lastname: Gray
authors.affiliation: Department of Crop and Soil Sciences, School of Molecular Biosciences, Center for Reproductive Biology, Washington State University, Pullman, WA 99164-6420.
authors.forename: Sachin
authors.initials: S
authors.lastname: Rustgi
authors.affiliation: Department of Crop and Soil Sciences, School of Molecular Biosciences, Center for Reproductive Biology, Washington State University, Pullman, WA 99164-6420 diter@wsu.edu steffen.reinbothe@ujf-grenoble.fr.
authors.forename: Diter
authors.initials: D
authors.lastname: von Wettstein
authors.affiliation: Biologie Environnementale et Systémique (BEeSy), Université Joseph Fourier, F-38041 Grenoble Cedex 9, France;
authors.forename: Christiane
authors.initials: C
authors.lastname: Reinbothe
mesh_terms: D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins / Q000502:physiology*; D001692:Biological Transport; D002352:Carrier Proteins / Q000502:physiology*; D002734:Chlorophyll / Q000737:chemistry*; D002736:Chloroplasts / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006706:Homeostasis; D010088:Oxidoreductases / Q000378:metabolism*; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000378:metabolism*; D010100:Oxygen / Q000737:chemistry; D010641:Phenotype; D010788:Photosynthesis; D010858:Pigmentation; D018087:Plastids / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D011521:Protochlorophyllide / Q000378:metabolism; D012639:Seeds / Q000378:metabolism; D026082:Singlet Oxygen / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D046939:Synechocystis / Q000378:metabolism; D013696:Temperature
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; C000592515:cell growth defect factor-1, Arabidopsis; D002734:Chlorophyll; D049452:Green Fluorescent Proteins; D026082:Singlet Oxygen; D011521:Protochlorophyllide; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; C023886:protochlorophyllide reductase; D010100:Oxygen
keywords: chaperone action; chloroplast biogenesis; membrane transport; photoprotection; protein translocation