title: Spontaneous dominant mutations in chlamydomonas highlight ongoing evolution by gene diversification.
abstract: We characterized two spontaneous and dominant nuclear mutations in the unicellular alga Chlamydomonas reinhardtii, ncc1 and ncc2 (for nuclear control of chloroplast gene expression), which affect two octotricopeptide repeat (OPR) proteins encoded in a cluster of paralogous genes on chromosome 15. Both mutations cause a single amino acid substitution in one OPR repeat. As a result, the mutated NCC1 and NCC2 proteins now recognize new targets that we identified in the coding sequences of the chloroplast atpA and petA genes, respectively. Interaction of the mutated proteins with these targets leads to transcript degradation; however, in contrast to the ncc1 mutation, the ncc2 mutation requires on-going translation to promote the decay of the petA mRNA. Thus, these mutants reveal a mechanism by which nuclear factors act on chloroplast mRNAs in Chlamydomonas. They illustrate how diversifying selection can allow cells to adapt the nuclear control of organelle gene expression to environmental changes. We discuss these data in the wider context of the evolution of regulation by helical repeat proteins.
authors: Unité Mixte de Recherche 7141, CNRS/UPMC, Institut de Biologie Physico-Chimique, F-75005 Paris, France.
authors: Alix
authors: A
authors: Boulouis
authors: Unité Mixte de Recherche 7141, CNRS/UPMC, Institut de Biologie Physico-Chimique, F-75005 Paris, France.
authors: Dominique
authors: http://orcid.org/0000-0002-0418-8931
authors: D
authors: Drapier
authors: Unité Mixte de Recherche 7141, CNRS/UPMC, Institut de Biologie Physico-Chimique, F-75005 Paris, France.
authors: Hélène
authors: http://orcid.org/0000-0003-4291-6351
authors: H
authors: Razafimanantsoa
authors: Unité Mixte de Recherche 7141, CNRS/UPMC, Institut de Biologie Physico-Chimique, F-75005 Paris, France.
authors: Katia
authors: http://orcid.org/0000-0002-5358-9117
authors: K
authors: Wostrikoff
authors: Unité Mixte de Recherche 7141, CNRS/UPMC, Institut de Biologie Physico-Chimique, F-75005 Paris, France.
authors: Nicolas J
authors: NJ
authors: Tourasse
authors: Unité Mixte de Recherche 7141, CNRS/UPMC, Institut de Biologie Physico-Chimique, F-75005 Paris, France.
authors: Kevin
authors: K
authors: Pascal
authors: Unité Mixte de Recherche 7141, CNRS/UPMC, Institut de Biologie Physico-Chimique, F-75005 Paris, France.
authors: Jacqueline
authors: J
authors: Girard-Bascou
authors: Unité Mixte de Recherche 7141, CNRS/UPMC, Institut de Biologie Physico-Chimique, F-75005 Paris, France.
authors: Olivier
authors: O
authors: Vallon
authors: Unité Mixte de Recherche 7141, CNRS/UPMC, Institut de Biologie Physico-Chimique, F-75005 Paris, France.
authors: Francis-André
authors: http://orcid.org/0000-0003-2638-7840
authors: FA
authors: Wollman
authors: Unité Mixte de Recherche 7141, CNRS/UPMC, Institut de Biologie Physico-Chimique, F-75005 Paris, France choquet@ibpc.fr.
authors: Yves
authors: http://orcid.org/0000-0003-4760-3397
authors: Y
authors: Choquet
mesh_terms: D002696:Chlamydomonas / Q000235:genetics* / Q000378:metabolism*; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000378:metabolism; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology; D009154:Mutation; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics
chemical_list: D010940:Plant Proteins; D012333:RNA, Messenger