title: Conditional repression of essential chloroplast genes: Evidence for new plastid signaling pathways.
abstract: The development of a repressible chloroplast gene expression system in Chlamydomonas reinhardtii has opened the door for studying the role of essential chloroplast genes. This approach has been used to analyze three chloroplast genes of this sort coding for the α subunit of RNA polymerase (rpoA), a ribosomal protein (rps12) and the catalytic subunit of the ATP-dependent ClpP protease (clpP1). Depletion of the three corresponding proteins leads to growth arrest and cell death. Shutdown of chloroplast transcription and translation increases the abundance of a set of plastid transcripts that includes mainly those involved in transcription, translation and proteolysis and reveals multiple regulatory feedback loops in the chloroplast gene circuitry. Depletion of ClpP profoundly affects plastid protein homeostasis and elicits an autophagy-like response with extensive cytoplasmic vacuolization of cells. It also triggers changes in chloroplast and nuclear gene expression resulting in increased abundance of chaperones, proteases, ubiquitin-related proteins and proteins involved in lipid trafficking and thylakoid biogenesis. These features are hallmarks of an unfolded protein response in the chloroplast and raise new questions on plastid protein homeostasis and plastid signaling. This article is part of a Special Issue entitled: Chloroplast Biogenesis.
authors.affiliation: Department of Molecular Biology, University of Geneva, 1211 Geneva, Switzerland; Department of Plant Biology, University of Geneva, 1211 Geneva, Switzerland. Electronic address: Jean-David.Rochaix@unige.ch.
authors.forename: Jean-David
authors.initials: JD
authors.lastname: Rochaix
authors.affiliation: Department of Molecular Biology, University of Geneva, 1211 Geneva, Switzerland; Department of Plant Biology, University of Geneva, 1211 Geneva, Switzerland.
authors.forename: Silvia
authors.initials: S
authors.lastname: Ramundo
mesh_terms: D001343:Autophagy; D060365:Chloroplast Proteins / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D061125:Genes, Chloroplast; D050356:Lipid Metabolism; D018087:Plastids / Q000502:physiology*; D011786:Quality Control; D015398:Signal Transduction
chemical_list: D060365:Chloroplast Proteins
keywords: Autophagy; Chaperone; Chloroplast; Plastid gene expression; Protein quality control; Unfolded protein response