title: Chloroplast protein translocon components atToc159 and atToc33 are not essential for chloroplast biogenesis in guard cells and root cells.
abstract: Protein import into chloroplasts is mediated by a protein import apparatus located in the chloroplast envelope. Previous results indicate that there may be multiple import complexes in Arabidopsis. To gain further insight into the nature of this multiplicity, we analyzed the Arabidopsis ppi1 and ppi2 mutants, which are null mutants of the atToc33 and atToc159 translocon proteins, respectively. In the ppi2 mutant, in contrast to the extremely defective plastids in mesophyll cells, chloroplasts in guard cells still contained starch granules and thylakoid membranes. The morphology of root plastids in both mutants was similar to that in wild type. After prolonged light treatments, root plastids of both mutants and the wild type differentiated into chloroplasts. Enzymatic assays indicated that the activity of a plastid enzyme was reduced only in leaves but not in roots. These results indicated that both the ppi1 and ppi2 mutants had functional root and guard cell plastids. Therefore, we propose that import complexes are cell type specific rather than substrate or plastid specific.
authors.affiliation: Institute of Molecular Biology, Academia Sinica, Taipei 11529, Taiwan.
authors.forename: T S
authors.initials: TS
authors.lastname: Yu
authors.forename: H
authors.initials: H
authors.lastname: Li
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D029681:Arabidopsis Proteins; D001692:Biological Transport; D002454:Cell Differentiation; D002736:Chloroplasts / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000502:physiology*; D066298:In Vitro Techniques; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D009154:Mutation; D009928:Organ Specificity; D019441:Plant Epidermis / Q000166:cytology / Q000648:ultrastructure; D018515:Plant Leaves / Q000166:cytology / Q000648:ultrastructure; D010940:Plant Proteins; D018517:Plant Roots / Q000166:cytology / Q000648:ultrastructure; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013213:Starch / Q000096:biosynthesis
chemical_list: D029681:Arabidopsis Proteins; D008565:Membrane Proteins; D010940:Plant Proteins; C403444:TOC159 protein, Arabidopsis; C114786:Toc33 protein, Arabidopsis; D013213:Starch; D020558:GTP Phosphohydrolases