title: Two novel proteins, MRL7 and its paralog MRL7-L, have essential but functionally distinct roles in chloroplast development and are involved in plastid gene expression regulation in Arabidopsis.
abstract: Chloroplast development requires the coordinated action of various proteins, many of which remain to be identified. Here, we report two novel genes, Mesophyll-cell RNAi Library line 7 (MRL7) and MRL7-Like (MRL7-L), that are involved in this process. An Arabidopsis knock-down transgenic plant (MRL7-RNAi) with delayed-greening phenotype was isolated from an RNA interference (RNAi) transformant library. Cotyledons and young leaves of MRL7-RNAi were pale in seedlings and gradually greened as the plant matured, while a knock-out in the MRL7 gene was seedling lethal. The MRL7 protein was shown to co-localize with a marker protein for nucleoids in chloroplasts, indicative of a role for the protein in chloroplast nucleic acid metabolism. Accordingly, chloroplast development was arrested upon loss of MRL7 function and the expression of plastid-encoded genes transcribed by plastid-encoded RNA polymerase (PEP) was significantly reduced in MRL7 knock-down and knock-out plants. A paralog of MRL7 (MRL7-L) was identified in the Arabidopsis genome. Both MRL7 and MRL7-L are only found in land plants and encode previously uncharacterized proteins without any known conserved domain. Like MRL7, knock-down of MRL7-L also resulted in a virescent phenotype, and a similar effect on plastid gene expression. However, the MRL7-L protein was localized to the chloroplast stroma. Taken together, our data indicate that the two paralogous proteins MRL7 and MRL7-L have essential but distinct roles during early chloroplast development and are involved in regulation of plastid gene expression.
authors.affiliation: National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan, PR China.
authors.forename: Jiangwei
authors.initials: J
authors.lastname: Qiao
authors.forename: Chonglie
authors.initials: C
authors.lastname: Ma
authors.forename: Matthias
authors.initials: M
authors.lastname: Wimmelbacher
authors.forename: Frederik
authors.initials: F
authors.lastname: Börnke
authors.forename: Meizhong
authors.initials: M
authors.lastname: Luo
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D018548:Cotyledon / Q000254:growth & development / Q000378:metabolism; D012321:DNA-Directed RNA Polymerases / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D055785:Gene Knockdown Techniques; D055786:Gene Knockout Techniques; D005804:Genes, Lethal; D005838:Genotype; D008856:Microscopy, Fluorescence; D010641:Phenotype; D010802:Phylogeny; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure; D034622:RNA Interference; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic
chemical_list: D029681:Arabidopsis Proteins; D012321:DNA-Directed RNA Polymerases