title: On the complexity of chloroplast RNA metabolism: psaA trans-splicing can be bypassed in chlamydomonas.
abstract: In the chloroplast, the posttranscriptional steps of gene expression are remarkably complex. RNA maturation and translation rely on a large cohort of nucleus-encoded proteins that act specifically on a single target transcript or a small set of targets. For example in the chloroplast of Chlamydomonas, trans-splicing of the two split introns of psaA requires at least 14 nucleus-encoded proteins. To investigate the functional significance of this complex trans-splicing pathway, we have introduced an intron-less copy of psaA in the chloroplast genomes of three mutants deficient in trans-splicing and of the wild type. We find that the intron-less psaA gene rescues the mutant phenotypes. The growth of strains with the intron-less psaA is indistinguishable from the wild type under the set of different experimental conditions that were investigated. Thus, the trans-splicing factors do not appear to have any other essential function and trans-splicing of psaA can be bypassed. We discuss how these observations support the hypothesis that complex RNA metabolism in the chloroplast may in part be the result of a nonadaptive evolutionary ratchet. Genetic drift may lead to the accumulation of chloroplast mutations and the recruitment of compensatory nuclear suppressors from large preexisting pools of genes encoding RNA-binding proteins.
authors: Department of Botany and Plant Biology and Department of Molecular Biology, University of Geneva, Geneva, Switzerland.
authors: Linnka
authors: L
authors: Lefebvre-Legendre
authors: Department of Botany and Plant Biology and Department of Molecular Biology, University of Geneva, Geneva, Switzerland.
authors: Livia
authors: L
authors: Merendino
authors: Department of Botany and Plant Biology and Department of Molecular Biology, University of Geneva, Geneva, Switzerland.
authors: Cristian
authors: C
authors: Rivier
authors: Department of Botany and Plant Biology and Department of Molecular Biology, University of Geneva, Geneva, Switzerland michel.goldschmidt-clermont@unige.ch.
authors: Michel
authors: M
authors: Goldschmidt-Clermont
mesh_terms: D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D040961:Genetic Drift; D007438:Introns; D007501:Iron / Q000378:metabolism; D009154:Mutation; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018747:RNA, Chloroplast / Q000235:genetics / Q000378:metabolism*; D017423:Sequence Analysis, RNA; D020040:Trans-Splicing
chemical_list: D010940:Plant Proteins; D018747:RNA, Chloroplast; D007501:Iron
keywords: Chlamydomonas; RNA processing; chloroplast; constructive neutral evolution; splicing; synthetic biology