title: Cytochrome P450 CYP89A9 is involved in the formation of major chlorophyll catabolites during leaf senescence in Arabidopsis.
abstract: Nonfluorescent chlorophyll catabolites (NCCs) were described as products of chlorophyll breakdown in Arabidopsis thaliana. NCCs are formyloxobilin-type catabolites derived from chlorophyll by oxygenolytic opening of the chlorin macrocycle. These linear tetrapyrroles are generated from their fluorescent chlorophyll catabolite (FCC) precursors by a nonenzymatic isomerization inside the vacuole of senescing cells. Here, we identified a group of distinct dioxobilin-type chlorophyll catabolites (DCCs) as the major breakdown products in wild-type Arabidopsis, representing more than 90% of the chlorophyll of green leaves. The molecular constitution of the most abundant nonfluorescent DCC (NDCC), At-NDCC-1, was determined. We further identified cytochrome P450 monooxygenase CYP89A9 as being responsible for NDCC accumulation in wild-type Arabidopsis; cyp89a9 mutants that are deficient in CYP89A9 function were devoid of NDCCs but accumulated proportionally higher amounts of NCCs. CYP89A9 localized outside the chloroplasts, implying that FCCs occurring in the cytosol might be its natural substrate. Using recombinant CYP89A9, we confirm FCC specificity and show that fluorescent DCCs are the products of the CYP89A9 reaction. Fluorescent DCCs, formed by this enzyme, isomerize to the respective NDCCs in weakly acidic medium, as found in vacuoles. We conclude that CYP89A9 is involved in the formation of dioxobilin-type catabolites of chlorophyll in Arabidopsis.
authors.affiliation: Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland.
authors.forename: Bastien
authors.initials: B
authors.lastname: Christ
authors.forename: Iris
authors.initials: I
authors.lastname: Süssenbacher
authors.forename: Simone
authors.initials: S
authors.lastname: Moser
authors.forename: Nicole
authors.initials: N
authors.lastname: Bichsel
authors.forename: Aurelie
authors.initials: A
authors.lastname: Egert
authors.forename: Thomas
authors.initials: T
authors.lastname: Müller
authors.forename: Bernhard
authors.initials: B
authors.lastname: Kräutler
authors.forename: Stefan
authors.initials: S
authors.lastname: Hörtensteiner
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000378:metabolism; D005453:Fluorescence; D018506:Gene Expression Regulation, Plant; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D058503:Mesophyll Cells / Q000378:metabolism; D018613:Microscopy, Confocal; D015394:Molecular Structure; D016254:Mutagenesis, Insertional; D018515:Plant Leaves / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D030821:Plants, Genetically Modified; D020133:Reverse Transcriptase Polymerase Chain Reaction; D021241:Spectrometry, Mass, Electrospray Ionization; D013053:Spectrophotometry
chemical_list: D029681:Arabidopsis Proteins; C585921:CYP89A9 protein, Arabidopsis; D002734:Chlorophyll; D049452:Green Fluorescent Proteins; D003577:Cytochrome P-450 Enzyme System