title: 7-Hydroxymethyl chlorophyll a reductase functions in metabolic channeling of chlorophyll breakdown intermediates during leaf senescence.
abstract: During natural or dark-induced senescence, chlorophyll degradation causes leaf yellowing. Recent evidence indicates that chlorophyll catabolic enzymes (CCEs) interact with the photosynthetic apparatus; for example, five CCEs (NYC1, NOL, PPH, PAO and RCCR) interact with LHCII. STAY-GREEN (SGR) and CCEs interact with one another in senescing chloroplasts; this interaction may allow metabolic channeling of potentially phototoxic chlorophyll breakdown intermediates. 7-Hydroxymethyl chlorophyll a reductase (HCAR) also acts as a CCE, but HCAR functions during leaf senescence remain unclear. Here we show that in Arabidopsis, HCAR-overexpressing plants exhibited accelerated leaf yellowing and, conversely, hcar mutants stayed green during dark-induced senescence. Moreover, HCAR interacted with LHCII in in vivo pull-down assays, and with SGR, NYC1, NOL and RCCR in yeast two-hybrid assays, indicating that HCAR is a component of the proposed SGR-CCE-LHCII complex, which acts in chlorophyll breakdown. Notably, HCAR and NOL are expressed throughout leaf development and are drastically down-regulated during dark-induced senescence, in contrast with SGR, NYC1, PPH and PAO, which are up-regulated during dark-induced senescence. Moreover, HCAR and NOL are highly up-regulated during greening of etiolated seedlings, strongly suggesting a major role for NOL and HCAR in the chlorophyll cycle during vegetative stages, possibly in chlorophyll turnover.
authors.affiliation: Department of Plant Science, Plant Genomics and Breeding Institute, and Research Institute for Agriculture and Life Sciences, Seoul National University, Seoul 151-921, Republic of Korea.
authors.forename: Yasuhito
authors.initials: Y
authors.lastname: Sakuraba
authors.forename: Ye-Sol
authors.initials: YS
authors.lastname: Kim
authors.forename: Soo-Cheul
authors.initials: SC
authors.lastname: Yoo
authors.forename: Stefan
authors.initials: S
authors.lastname: Hörtensteiner
authors.forename: Nam-Chon
authors.initials: NC
authors.lastname: Paek
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002734:Chlorophyll / Q000031:analogs & derivatives* / Q000378:metabolism; D003624:Darkness; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D018515:Plant Leaves / Q000201:enzymology / Q000502:physiology*; D030821:Plants, Genetically Modified / Q000196:embryology / Q000235:genetics / Q000502:physiology
chemical_list: C098029:7-hydroxymethyl chlorophyll; D029681:Arabidopsis Proteins; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; C581015:7-hydroxymethyl chlorophyll a reductase, Arabidopsis; D010088:Oxidoreductases