title: Pheophytin pheophorbide hydrolase (pheophytinase) is involved in chlorophyll breakdown during leaf senescence in Arabidopsis.
abstract: During leaf senescence, chlorophyll is removed from thylakoid membranes and converted in a multistep pathway to colorless breakdown products that are stored in vacuoles. Dephytylation, an early step of this pathway, increases water solubility of the breakdown products. It is widely accepted that chlorophyll is converted into pheophorbide via chlorophyllide. However, chlorophyllase, which converts chlorophyll to chlorophyllide, was found not to be essential for dephytylation in Arabidopsis thaliana. Here, we identify pheophytinase (PPH), a chloroplast-located and senescence-induced hydrolase widely distributed in algae and land plants. In vitro, Arabidopsis PPH specifically dephytylates the Mg-free chlorophyll pigment, pheophytin (phein), yielding pheophorbide. An Arabidopsis mutant deficient in PPH (pph-1) is unable to degrade chlorophyll during senescence and therefore exhibits a stay-green phenotype. Furthermore, pph-1 accumulates phein during senescence. Therefore, PPH is an important component of the chlorophyll breakdown machinery of senescent leaves, and we propose that the sequence of early chlorophyll catabolic reactions be revised. Removal of Mg most likely precedes dephytylation, resulting in the following order of early breakdown intermediates: chlorophyll --> pheophytin --> pheophorbide. Chlorophyllide, the last precursor of chlorophyll biosynthesis, is most likely not an intermediate of breakdown. Thus, chlorophyll anabolic and catabolic reactions are metabolically separated.
authors.affiliation: Institute of Plant Biology, University of Zürich, CH-8008 Zurich, Switzerland.
authors.forename: Silvia
authors.initials: S
authors.lastname: Schelbert
authors.forename: Sylvain
authors.initials: S
authors.lastname: Aubry
authors.forename: Bo
authors.initials: B
authors.lastname: Burla
authors.forename: Birgit
authors.initials: B
authors.lastname: Agne
authors.forename: Felix
authors.initials: F
authors.lastname: Kessler
authors.forename: Karin
authors.initials: K
authors.lastname: Krupinska
authors.forename: Stefan
authors.initials: S
authors.lastname: Hörtensteiner
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000033:anatomy & histology / Q000502:physiology; D029681:Arabidopsis Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D016922:Cellular Senescence / Q000502:physiology*; D002734:Chlorophyll / Q000378:metabolism*; D002736:Chloroplasts / Q000201:enzymology; D006867:Hydrolases / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D010674:Pheophytins / Q000235:genetics / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology; D010802:Phylogeny; D010836:Phytol / Q000378:metabolism; D018515:Plant Leaves / Q000166:cytology / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D029681:Arabidopsis Proteins; D008565:Membrane Proteins; D010674:Pheophytins; D011993:Recombinant Fusion Proteins; C499578:Tic110 protein, Arabidopsis; D002734:Chlorophyll; D010836:Phytol; C061694:pheophytin a; D006867:Hydrolases