Molecular cloning and function analysis of the stay green gene in rice

• Published in: The Plant journal : for cell and molecular biology Vol. 52; no. 2; pp. 197 - 209
• Main Authors: Jiang, Huawu, Li, Meiru, Liang, Naiting, Yan, Hongbo, Wei, Yubo, Xu, Xinlan, Liu, Jian, Xu, Zhifang, Chen, Fan, Wu, Guojiang
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.10.2007; Blackwell Publishing Ltd; Blackwell Science
• Subjects: Alleles; Amino Acid Sequence; Biological and medical sciences; Botany; Chl breakdown; Chlorophyll - metabolism; Chloroplasts - ultrastructure; Cloning; Cloning, Molecular; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Plant; Genes, Plant - genetics; Genes. Genome; Molecular and cellular biology; Molecular biology; Molecular genetics; Molecular Sequence Data; Mutation; Oryza - genetics; Oryza - metabolism; Oryza sativa; Oryza sativa L; Phylogeny; Plant Leaves; Plant Proteins - genetics; Plant Proteins - metabolism; Rice; senescence; stay green; thylakoid; Chlorophyll; Monocotyledones; Senescence; Oryza sativa L; Plant leaf; Thylakoid; Cytokinin; Chl breakdown; Oryza sativa; Gene; Gramineae; Angiospermae; Spermatophyta; Mutation; Photosynthesis; stay green; Chloroplast
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/j.1365-313x.2007.03221.x

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 γ-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.