title: In vivo effects of NbSiR silencing on chloroplast development in Nicotiana benthamiana.
abstract: Sulfite reductase (SiR) performs dual functions, acting as a sulfur assimilation enzyme and as a chloroplast (cp-) nucleoid binding protein. In this study, we examined the in vivo effects of SiR deficiency on chloroplast development in Nicotiana benthamiana. Virus-induced gene silencing of NbSiR resulted in leaf yellowing and growth retardation phenotypes, which were not rescued by cysteine supplementation. NbSiR:GFP fusion protein was targeted to chloroplasts and colocalized with cp-nucleoids. Recombinant full-length NbSiR protein and the C-terminal half of NbSiR possessed cp-DNA compaction activities in vitro, and expression of full-length NbSiR in E. coli caused condensation of genomic DNA. NbSiR silencing differentially affected expression of plastid-encoded genes, inhibiting expression of several genes more severely than others. In the later stages, depletion of NbSiR resulted in chloroplast ablation. In NbSiR-silenced plants, enlarged cp-nucleoids containing an increased amount of cp-DNA were observed in the middle of the abnormal chloroplasts, and the cp-DNAs were predominantly of subgenomic sizes based on pulse field gel electrophoresis. The abnormal chloroplasts developed prolamellar body-like cubic lipid structures in the light without accumulating NADPH:protochlorophyllide oxidoreductase proteins. Our results suggest that NbSiR plays a role in cp-nucleoid metabolism, plastid gene expression, and thylakoid membrane development.
authors.affiliation: Department of Biology, Yonsei University, Seoul, 120-749, Korea.
authors.forename: Yong-Won
authors.initials: YW
authors.lastname: Kang
authors.forename: Jae-Yong
authors.initials: JY
authors.lastname: Lee
authors.forename: Young
authors.initials: Y
authors.lastname: Jeon
authors.forename: Gang-Won
authors.initials: GW
authors.lastname: Cheong
authors.forename: Moonil
authors.initials: M
authors.lastname: Kim
authors.forename: Hyun-Sook
authors.initials: HS
authors.lastname: Pai
mesh_terms: D002736:Chloroplasts / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D003545:Cysteine / Q000494:pharmacology; D018744:DNA, Plant / Q000378:metabolism; D020868:Gene Silencing; D049452:Green Fluorescent Proteins / Q000032:analysis; D007425:Intracellular Membranes / Q000378:metabolism / Q000648:ultrastructure; D008928:Mitochondria / Q000378:metabolism / Q000648:ultrastructure; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000235:genetics* / Q000502:physiology; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics* / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000032:analysis; D013025:Glycine max / Q000235:genetics; D014026:Nicotiana / Q000187:drug effects / Q000235:genetics* / Q000648:ultrastructure
chemical_list: D018744:DNA, Plant; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D050862:Oxidoreductases Acting on Sulfur Group Donors; D003545:Cysteine