title: Involvement of a Putative Bipartite Transit Peptide in Targeting Rice Pheophorbide a Oxygenase into Chloroplasts for Chlorophyll Degradation during Leaf Senescence.
abstract: Leaf senescence is one of the major factors contributing to the productivity and the grain quality in crops. The regulatory mechanism of leaf senescence remains largely unknown. Here, we report the identification and characterization of a rice early senescence 1 (eas1) mutant, which displayed an early leaf senescence phenotype, accompanying by dwarfism and reduced tiller number, eventually leading to the reduction of grain yield. Map-based cloning revealed that the nuclear gene EAS1 encodes a pheophorbide a oxygenase (PaO), a key enzyme for chlorophyll breakdown. A highly conserved Thr residue of PaO was mutated into Ile in the eas1 mutant. Phylogenetic analysis indicates that PaO is an evolutionarily conserved protein, and EAS1 is 68% identical to the Arabidopsis ACCERLERATED CELL DEATH (ACD1) protein. Unlike ACD1 that contains a single transit peptide, EAS1 contains two putative transit peptides at its N-terminus, which are essential for its functionality, suggesting that targeting of EAS1 to the chloroplast is likely mediated by a putative bipartite transit peptide. Consistently, only a short version of EAS1 lacking the first putative transit peptide, but not the full-length EAS1, was capable of rescuing the Arabidopsis acd1 mutant phenotype. These results suggest that rice EAS1 represents a functional PaO, which is involved in chlorophyll degradation and may utilize a unique mechanism for its import into the chloroplast.
authors.affiliation: State Key Laboratory of Plant Genomics and National Plant Gene Research Center, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China; The University of Chinese Academy of Sciences, Beijing 100049, China; State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, South China Agricultural University, Guangzhou 510642, China.
authors.forename: Qingjun
authors.initials: Q
authors.lastname: Xie
authors.affiliation: State Key Laboratory of Plant Genomics and National Plant Gene Research Center, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Liang
authors.affiliation: State Key Laboratory of Plant Genomics and National Plant Gene Research Center, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Plant Genomics and National Plant Gene Research Center, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China; The University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Huakun
authors.initials: H
authors.lastname: Zheng
authors.affiliation: State Key Laboratory of Rice Biology, China National Rice Research Institute, Chinese Academy of Agricultural Sciences, Hangzhou 310006, China.
authors.forename: Guojun
authors.initials: G
authors.lastname: Dong
authors.affiliation: State Key Laboratory of Rice Biology, China National Rice Research Institute, Chinese Academy of Agricultural Sciences, Hangzhou 310006, China. Electronic address: qianqian188@hotmail.com.
authors.forename: Qian
authors.initials: Q
authors.lastname: Qian
authors.affiliation: State Key Laboratory of Plant Genomics and National Plant Gene Research Center, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China. Electronic address: jrzuo@genetics.ac.cn.
authors.forename: Jianru
authors.initials: J
authors.lastname: Zuo
mesh_terms: D002734:Chlorophyll / Q000378:metabolism*; D060365:Chloroplast Proteins / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D003001:Cloning, Molecular; D009154:Mutation; D012275:Oryza / Q000166:cytology / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D010105:Oxygenases / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism*; D021382:Protein Sorting Signals
chemical_list: D060365:Chloroplast Proteins; D021382:Protein Sorting Signals; C078737:chloroplast transit peptides; D002734:Chlorophyll; D010105:Oxygenases; C112915:pheide a oxygenase
keywords: Leaf senescence; Pheophorbide a oxygenase; Rice; Targeting; Transit peptide