title: Chlorophyll breakdown: pheophorbide a oxygenase is a Rieske-type iron-sulfur protein, encoded by the accelerated cell death 1 gene.
abstract: Chlorophyll (chl) breakdown during senescence is an integral part of plant development and leads to the accumulation of colorless catabolites. The loss of green pigment is due to an oxygenolytic opening of the porphyrin macrocycle of pheophorbide (pheide) a followed by a reduction to yield a fluorescent chl catabolite. This step is comprised of the interaction of two enzymes, pheide a oxygenase (PaO) and red chl catabolite reductase. PaO activity is found only during senescence, hence PaO seems to be a key regulator of chl catabolism. Whereas red chl catabolite reductase has been cloned, the nature of PaO has remained elusive. Here we report on the identification of the PaO gene of Arabidopsis thaliana (AtPaO). AtPaO is a Rieske-type iron-sulfur cluster-containing enzyme that is identical to Arabidopsis accelerated cell death 1 and homologous to lethal leaf spot 1 (LLS1) of maize. Biochemical properties of recombinant AtPaO were identical to PaO isolated from a natural source. Production of fluorescent chl catabolite-1 required ferredoxin as an electron source and both substrates, pheide a and molecular oxygen. By using a maize lls1 mutant, the in vivo function of PaO, i.e., degradation of pheide a during senescence, could be confirmed. Thus, lls1 leaves stayed green during dark incubation and accumulated pheide a that caused a light-dependent lesion mimic phenotype. Whereas proteins were degraded similarly in wild type and lls1, a chl-binding protein was selectively retained in the mutant. PaO expression correlated positively with senescence, but the enzyme appeared to be post-translationally regulated as well.
authors.affiliation: Institute of Plant Sciences, University of Bern, Altenbergrain 21, CH-3013 Bern, Switzerland.
authors.forename: Adriana
authors.initials: A
authors.lastname: Pruzinská
authors.forename: Gaby
authors.initials: G
authors.lastname: Tanner
authors.forename: Iwona
authors.initials: I
authors.lastname: Anders
authors.forename: Maria
authors.initials: M
authors.lastname: Roca
authors.forename: Stefan
authors.initials: S
authors.lastname: Hörtensteiner
mesh_terms: D051017:Apoptosis Regulatory Proteins; D017360:Arabidopsis / Q000235:genetics; D029681:Arabidopsis Proteins / Q000737:chemistry; D016923:Cell Death; D016922:Cellular Senescence; D002734:Chlorophyll / Q000031:analogs & derivatives* / Q000737:chemistry*; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D014450:Electron Transport Complex III / Q000737:chemistry*; D004583:Electrons; D005288:Ferredoxins / Q000737:chemistry; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D008956:Models, Chemical; D009154:Mutation; D010088:Oxidoreductases / Q000737:chemistry; D010100:Oxygen / Q000378:metabolism; D010105:Oxygenases / Q000737:chemistry*; D010641:Phenotype; D018515:Plant Leaves / Q000378:metabolism; D014176:Protein Biosynthesis; D011994:Recombinant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D003313:Zea mays / Q000737:chemistry / Q000235:genetics
chemical_list: D051017:Apoptosis Regulatory Proteins; D029681:Arabidopsis Proteins; D018076:DNA, Complementary; D005288:Ferredoxins; D007506:Iron-Sulfur Proteins; D011994:Recombinant Proteins; C037989:Rieske iron-sulfur protein; D002734:Chlorophyll; D010088:Oxidoreductases; D010105:Oxygenases; C112915:pheide a oxygenase; C408689:ACD2 protein, Arabidopsis; D014450:Electron Transport Complex III; C032623:pheophorbide a; D010100:Oxygen