title: Molecular cloning and function analysis of the stay green gene in rice.
abstract: Chloroplasts undergo drastic morphological and physiological changes during senescence with a visible symptom of chlorophyll (Chl) degradation. A stay green mutant was identified and then isolated from the japonica rice (Oryza sativa) cv. Huazhiwu by gamma-ray irradiation. The stay green mutant was characterized by Chl retention, stable Chl-protein complexes, and stable thylakoid membrane structures, but lost its photosynthetic competence during senescence. The gene, designated Stay Green Rice (SGR), was cloned by a positional cloning strategy encoding an ancient protein containing a putative chloroplast transit peptide. SGR protein was found in both soluble and thylakoid membranes in rice. SGR, like the gene for pheophorbide a oxygenase (PaO), was constitutively expressed, but was upregulated by dark-induced senescence in rice leaves. Senescence-induced expression of SGR and PaO was enhanced by ABA, but inhibited by cytokinin. Overexpression of SGR reduced the number of lamellae in the grana thylakoids and reduced the Chl content of normally growing leaves. This indicates that upregulation of SGR increases Chl breakdown during senescence in rice. A small quantity of chlorophyllide a accumulated in sgr leaves, but this also accumulated in wild-type rice leaves during senescence. Some pheophorbide a was detected in sgr leaves in the dark. According to these observations, we propose that SGR may be involved in regulating or taking part in the activity of PaO, and then may influence Chl breakdown and degradation of pigment-protein complex.
authors: South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China.
authors: Huawu
authors: H
authors: Jiang
authors: Meiru
authors: M
authors: Li
authors: Naiting
authors: N
authors: Liang
authors: Hongbo
authors: H
authors: Yan
authors: Yubo
authors: Y
authors: Wei
authors: Xinlan
authors: X
authors: Xu
authors: Jian
authors: J
authors: Liu
authors: Zhifang
authors: Z
authors: Xu
authors: Fan
authors: F
authors: Chen
authors: Guojiang
authors: G
authors: Wu
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000648:ultrastructure; D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D012275:Oryza / Q000235:genetics* / Q000378:metabolism*; D010802:Phylogeny; D018515:Plant Leaves; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D002734:Chlorophyll