title: Identification of the 7-hydroxymethyl chlorophyll a reductase of the chlorophyll cycle in Arabidopsis.
abstract: The interconversion of chlorophyll a and chlorophyll b, referred to as the chlorophyll cycle, plays a crucial role in the processes of greening, acclimation to light intensity, and senescence. The chlorophyll cycle consists of three reactions: the conversions of chlorophyll a to chlorophyll b by chlorophyllide a oxygenase, chlorophyll b to 7-hydroxymethyl chlorophyll a by chlorophyll b reductase, and 7-hydroxymethyl chlorophyll a to chlorophyll a by 7-hydroxymethyl chlorophyll a reductase. We identified 7-hydroxymethyl chlorophyll a reductase, which is the last remaining unidentified enzyme of the chlorophyll cycle, from Arabidopsis thaliana by genetic and biochemical methods. Recombinant 7-hydroxymethyl chlorophyll a reductase converted 7-hydroxymethyl chlorophyll a to chlorophyll a using ferredoxin. Both sequence and biochemical analyses showed that 7-hydroxymethyl chlorophyll a reductase contains flavin adenine dinucleotide and an iron-sulfur center. In addition, a phylogenetic analysis elucidated the evolution of 7-hydroxymethyl chlorophyll a reductase from divinyl chlorophyllide vinyl reductase. A mutant lacking 7-hydroxymethyl chlorophyll a reductase was found to accumulate 7-hydroxymethyl chlorophyll a and pheophorbide a. Furthermore, this accumulation of pheophorbide a in the mutant was rescued by the inactivation of the chlorophyll b reductase gene. The downregulation of pheophorbide a oxygenase activity is discussed in relation to 7-hydroxymethyl chlorophyll a accumulation.
authors.affiliation: Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan.
authors.forename: Miki
authors.initials: M
authors.lastname: Meguro
authors.forename: Hisashi
authors.initials: H
authors.lastname: Ito
authors.forename: Atsushi
authors.initials: A
authors.lastname: Takabayashi
authors.forename: Ryouichi
authors.initials: R
authors.lastname: Tanaka
authors.forename: Ayumi
authors.initials: A
authors.lastname: Tanaka
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002734:Chlorophyll / Q000031:analogs & derivatives* / Q000378:metabolism; D000077194:Chlorophyll A; D005288:Ferredoxins / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D007506:Iron-Sulfur Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D016415:Sequence Alignment
chemical_list: C098029:7-hydroxymethyl chlorophyll; D029681:Arabidopsis Proteins; D005288:Ferredoxins; D007506:Iron-Sulfur Proteins; D002734:Chlorophyll; C581015:7-hydroxymethyl chlorophyll a reductase, Arabidopsis; D010088:Oxidoreductases; D000077194:Chlorophyll A