title: Linking chlorophyll biosynthesis to a dynamic plastoquinone pool.
abstract: Chlorophylls are essential cofactors in photosynthesis. All steps in the chlorophyll pathway are well characterized except for the cyclase reaction in which the fifth ring of the chlorophyll molecule is formed during conversion of Mg-protoporphyrin IX monomethyl ester into Protochlorophyllide. The only subunit of the cyclase identified so far, is AcsF (Xantha-l in barley and Chl27 in Arabidopsis). This subunit contains a typical consensus di-iron-binding sequence and belongs to a subgroup of di-iron proteins, such as the plastid terminal oxidase (PTOX) in the chloroplast and the alternative oxidase (AOX) found in mitochondria. In order to complete the catalytic cycle, the irons of these proteins need to be reduced from Fe(3+) to Fe(2+) and either a reductase or another form of reductant is required. It has been reported that the alternative oxidase (AOX) and the plastid terminal oxidase (PTOX) utilize the di-iron center to oxidise ubiquinol and plastoquinol, respectively. In this paper, we have used a specific inhibitor of di-iron proteins as well as Arabidopsis and barley mutants affected in regulation of photosynthetic electron flow, to show that the cyclase step indeed is directly coupled to the plastoquinone pool. Thus, plastoquinol might act as an electron donor for the cyclase reaction and thereby fulfil the role of a cyclase reductase. That would provide a functional connection between the redox status of the thylakoids and the biosynthesis of chlorophyll.
authors.affiliation: Copenhagen Plant Science Center, VILLUM Research Center "Plant Plasticity", Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871, Frederiksberg C, Denmark.
authors.forename: Verdiana
authors.initials: V
authors.lastname: Steccanella
authors.affiliation: Department of Biology, Lund University, Sölvgaten 35, 22100, Lund, Sweden.
authors.forename: Mats
authors.initials: M
authors.lastname: Hansson
authors.affiliation: Copenhagen Plant Science Center, VILLUM Research Center "Plant Plasticity", Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871, Frederiksberg C, Denmark. Electronic address: peje@plen.ku.dk.
authors.forename: Poul Erik
authors.initials: PE
authors.lastname: Jensen
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D053898:Biosynthetic Pathways / Q000187:drug effects; D002734:Chlorophyll / Q000096:biosynthesis* / Q000737:chemistry; D005453:Fluorescence; D005707:Gallic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006706:Homeostasis / Q000187:drug effects; D001467:Hordeum / Q000187:drug effects / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D010084:Oxidation-Reduction / Q000187:drug effects; D045332:Photosystem II Protein Complex / Q000378:metabolism; D010971:Plastoquinone / Q000737:chemistry / Q000378:metabolism*; D011521:Protochlorophyllide / Q000378:metabolism; D011524:Protoporphyrins / Q000494:pharmacology; D036226:Seedlings / Q000187:drug effects / Q000378:metabolism; D013379:Substrate Specificity / Q000187:drug effects; D020524:Thylakoids / Q000187:drug effects / Q000378:metabolism
chemical_list: D045332:Photosystem II Protein Complex; D011524:Protoporphyrins; C016627:octyl gallate; D002734:Chlorophyll; C033434:protoporphyrin IX monomethyl ester; D011521:Protochlorophyllide; D005707:Gallic Acid; D010971:Plastoquinone
keywords: Chlorophyll biosynthesis; Cyclase; Di-iron enzymes; Plastoquinol; Reductase