title: The senescence-induced staygreen protein regulates chlorophyll degradation.
abstract: Loss of green color in leaves results from chlorophyll (Chl) degradation in chloroplasts, but little is known about how Chl catabolism is regulated throughout leaf development. Using the staygreen (sgr) mutant in rice (Oryza sativa), which maintains greenness during leaf senescence, we identified Sgr, a senescence-associated gene encoding a novel chloroplast protein. Transgenic rice overexpressing Sgr produces yellowish-brown leaves, and Arabidopsis thaliana pheophorbide a oxygenase-impaired mutants exhibiting a stay-green phenotype during dark-induced senescence have reduced expression of Sgr homologs, indicating that Sgr regulates Chl degradation at the transcriptional level. We show that the leaf stay-greenness of the sgr mutant is associated with a failure in the destabilization of the light-harvesting chlorophyll binding protein (LHCP) complexes of the thylakoid membranes, which is a prerequisite event for the degradation of Chls and LHCPs during senescence. Transient overexpression of Sgr in Nicotiana benthamiana and an in vivo pull-down assay show that Sgr interacts with LHCPII, indicating that the Sgr-LHCPII complexes are formed in the thylakoid membranes. Thus, we propose that in senescing leaves, Sgr regulates Chl degradation by inducing LHCPII disassembly through direct interaction, leading to the degradation of Chls and Chl-free LHCPII by catabolic enzymes and proteases, respectively.
authors.affiliation: Department of Plant Science and Research Institute for Agriculture and Life Sciences, Seoul National University, Seoul 151-921, Korea.
authors.forename: So-Yon
authors.initials: SY
authors.lastname: Park
authors.forename: Jae-Woong
authors.initials: JW
authors.lastname: Yu
authors.forename: Jong-Sung
authors.initials: JS
authors.lastname: Park
authors.forename: Jinjie
authors.initials: J
authors.lastname: Li
authors.forename: Soo-Cheul
authors.initials: SC
authors.lastname: Yoo
authors.forename: Na-Yeoun
authors.initials: NY
authors.lastname: Lee
authors.forename: Sang-Kyu
authors.initials: SK
authors.lastname: Lee
authors.forename: Seok-Won
authors.initials: SW
authors.lastname: Jeong
authors.forename: Hak Soo
authors.initials: HS
authors.lastname: Seo
authors.forename: Hee-Jong
authors.initials: HJ
authors.lastname: Koh
authors.forename: Jong-Seong
authors.initials: JS
authors.lastname: Jeon
authors.forename: Youn-Il
authors.initials: YI
authors.lastname: Park
authors.forename: Nam-Chon
authors.initials: NC
authors.lastname: Paek
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000378:metabolism; D002265:Carboxylic Ester Hydrolases / Q000378:metabolism; D016922:Cellular Senescence; D002734:Chlorophyll / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003624:Darkness; D017343:Genes, Plant; D007425:Intracellular Membranes / Q000378:metabolism / Q000648:ultrastructure; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D012275:Oryza / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D010641:Phenotype; D018515:Plant Leaves / Q000166:cytology / Q000254:growth & development; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid; D013816:Thermodynamics; D020524:Thylakoids / Q000378:metabolism / Q000648:ultrastructure; D014026:Nicotiana / Q000378:metabolism
chemical_list: D045342:Light-Harvesting Protein Complexes; D010940:Plant Proteins; D002734:Chlorophyll; D002265:Carboxylic Ester Hydrolases; C019875:chlorophyllase