title: Different mechanisms are responsible for chlorophyll dephytylation during fruit ripening and leaf senescence in tomato.
abstract: Chlorophyll breakdown occurs in different green plant tissues (e.g. during leaf senescence and in ripening fruits). For different plant species, the PHEOPHORBIDE A OXYGENASE (PAO)/phyllobilin pathway has been described to be the major chlorophyll catabolic pathway. In this pathway, pheophorbide (i.e. magnesium- and phytol-free chlorophyll) occurs as a core intermediate. Most of the enzymes involved in the PAO/phyllobilin pathway are known; however, the mechanism of dephytylation remains uncertain. During Arabidopsis (Arabidopsis thaliana) leaf senescence, phytol hydrolysis is catalyzed by PHEOPHYTINASE (PPH), which is specific for pheophytin (i.e. magnesium-free chlorophyll). By contrast, in fruits of different Citrus spp., chlorophyllase, hydrolyzing phytol from chlorophyll, was shown to be active. Here, we enlighten the process of chlorophyll breakdown in tomato (Solanum lycopersicum), both in leaves and fruits. We demonstrate the activity of the PAO/phyllobilin pathway and identify tomato PPH (SlPPH), which, like its Arabidopsis ortholog, was specifically active on pheophytin. SlPPH localized to chloroplasts and was transcriptionally up-regulated during leaf senescence and fruit ripening. SlPPH-silencing tomato lines were impaired in chlorophyll breakdown and accumulated pheophytin during leaf senescence. However, although pheophytin transiently accumulated in ripening fruits of SlPPH-silencing lines, ultimately these fruits were able to degrade chlorophyll like the wild type. We conclude that PPH is the core phytol-hydrolytic enzyme during leaf senescence in different plant species; however, fruit ripening involves other hydrolases, which are active in parallel to PPH or are the core hydrolases in fruits. These hydrolases remain unidentified, and we discuss the question of whether chlorophyllases might be involved.
authors.affiliation: Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland (L.G., S.S.H., B.C., S.H.); andDepartemento de Botânica, Instituto de Biociências, Universidade de São Paulo, CEP05508-090 Sao Paulo, Brazil (B.S.L., M.R.).
authors.forename: Luzia
authors.initials: L
authors.lastname: Guyer
authors.affiliation: Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland (L.G., S.S.H., B.C., S.H.); andDepartemento de Botânica, Instituto de Biociências, Universidade de São Paulo, CEP05508-090 Sao Paulo, Brazil (B.S.L., M.R.).
authors.forename: Silvia Schelbert
authors.initials: SS
authors.lastname: Hofstetter
authors.affiliation: Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland (L.G., S.S.H., B.C., S.H.); andDepartemento de Botânica, Instituto de Biociências, Universidade de São Paulo, CEP05508-090 Sao Paulo, Brazil (B.S.L., M.R.).
authors.forename: Bastien
authors.initials: B
authors.lastname: Christ
authors.affiliation: Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland (L.G., S.S.H., B.C., S.H.); andDepartemento de Botânica, Instituto de Biociências, Universidade de São Paulo, CEP05508-090 Sao Paulo, Brazil (B.S.L., M.R.).
authors.forename: Bruno Silvestre
authors.initials: BS
authors.lastname: Lira
authors.affiliation: Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland (L.G., S.S.H., B.C., S.H.); andDepartemento de Botânica, Instituto de Biociências, Universidade de São Paulo, CEP05508-090 Sao Paulo, Brazil (B.S.L., M.R.).
authors.forename: Magdalena
authors.initials: M
authors.lastname: Rossi
authors.affiliation: Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland (L.G., S.S.H., B.C., S.H.); andDepartemento de Botânica, Instituto de Biociências, Universidade de São Paulo, CEP05508-090 Sao Paulo, Brazil (B.S.L., M.R.) shorten@botinst.uzh.ch.
authors.forename: Stefan
authors.initials: S
authors.lastname: Hörtensteiner
mesh_terms: D000595:Amino Acid Sequence; D002736:Chloroplasts / Q000201:enzymology*; D005638:Fruit / Q000502:physiology*; D018551:Solanum lycopersicum / Q000502:physiology*; D008969:Molecular Sequence Data; D010105:Oxygenases / Q000378:metabolism; D010674:Pheophytins / Q000378:metabolism*; D010836:Phytol / Q000378:metabolism; D018515:Plant Leaves / Q000502:physiology*; D010940:Plant Proteins / Q000378:metabolism
chemical_list: D010674:Pheophytins; D010940:Plant Proteins; D010836:Phytol; D010105:Oxygenases; C112915:pheide a oxygenase