title: A Role for TIC55 as a Hydroxylase of Phyllobilins, the Products of Chlorophyll Breakdown during Plant Senescence.
abstract: Chlorophyll degradation is the most obvious hallmark of leaf senescence. Phyllobilins, linear tetrapyrroles that are derived from opening of the chlorin macrocycle by the Rieske-type oxygenase PHEOPHORBIDE a OXYGENASE (PAO), are the end products of chlorophyll degradation. Phyllobilins carry defined modifications at several peripheral positions within the tetrapyrrole backbone. While most of these modifications are species-specific, hydroxylation at the C32position is commonly found in all species analyzed to date. We demonstrate that this hydroxylation occurs in senescent chloroplasts of Arabidopsis thaliana. Using bell pepper (Capsicum annuum) chromoplasts, we establish that phyllobilin hydroxylation is catalyzed by a membrane-bound, molecular oxygen-dependent, and ferredoxin-dependent activity. As these features resemble the requirements of PAO, we considered membrane-bound Rieske-type oxygenases as potential candidates. Analysis of mutants of the two Arabidopsis Rieske-type oxygenases (besides PAO) uncovered that phyllobilin hydroxylation depends on TRANSLOCON AT THE INNER CHLOROPLAST ENVELOPE55 (TIC55). Our work demonstrates a catalytic activity for TIC55, which in the past has been considered as a redox sensor of protein import into plastids. Given the wide evolutionary distribution of both PAO and TIC55, we consider that chlorophyll degradation likely coevolved with land plants.
authors.affiliation: Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland.
authors.forename: Mareike
authors.identifier: 0000-0002-0044-0490
authors.initials: M
authors.lastname: Hauenstein
authors.affiliation: Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland.
authors.forename: Bastien
authors.initials: B
authors.lastname: Christ
authors.affiliation: Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland.
authors.forename: Aditi
authors.initials: A
authors.lastname: Das
authors.affiliation: Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland.
authors.forename: Sylvain
authors.identifier: 0000-0002-7598-3609
authors.initials: S
authors.lastname: Aubry
authors.affiliation: Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland shorten@botinst.uzh.ch.
authors.forename: Stefan
authors.initials: S
authors.lastname: Hörtensteiner
mesh_terms: D000375:Aging / Q000235:genetics / Q000502:physiology; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D002734:Chlorophyll