A Nucleus-Encoded Chloroplast Phosphoprotein Governs Expression of the Photosystem I Subunit PsaC in Chlamydomonas reinhardtii.
The nucleo-cytoplasmic compartment exerts anterograde control on chloroplast gene expression through numerous proteins that intervene at posttranscriptional steps. Here, we show that the maturation of psaC mutant (mac1) of Chlamydomonas reinhardtii is defective in photosystem I and fails to accumulate psaC mRNA. The MAC1 locus encodes a member of the Half-A-Tetratricopeptide (HAT) family of super-helical repeat proteins, some of which are involved in RNA transactions. The Mac1 protein localizes to the chloroplast in the soluble fraction. MAC1 acts through the 5' untranslated region of psaC transcripts and is required for their stability. Small RNAs that map to the 5'end of psaC RNA in the wild type but not in the mac1 mutant are inferred to represent footprints of MAC1-dependent protein binding, and Mac1 expressed in bacteria binds RNA in vitro. A coordinate response to iron deficiency, which leads to dismantling of the photosynthetic electron transfer chain and in particular of photosystem I, also causes a decrease of Mac1. Overexpression of Mac1 leads to a parallel increase in psaC mRNA but not in PsaC protein, suggesting that Mac1 may be limiting for psaC mRNA accumulation but that other processes regulate protein accumulation. Furthermore, Mac 1 is differentially phosphorylated in response to iron availability and to conditions that alter the redox balance of the electron transfer chain.
Department of Botany and Plant Biology and Department of Molecular Biology, University of Geneva, 1211 Geneva 4, Switzerland.
Damien
0000-0002-6155-9153
D
Douchi
Institute of Biology, Molecular Genetics, Humboldt University of Berlin, D-10115 Berlin, Germany.
Yujiao
0000-0002-9030-3528
Y
Qu
Department of Botany and Plant Biology and Department of Molecular Biology, University of Geneva, 1211 Geneva 4, Switzerland.
Paolo
0000-0003-0587-7621
P
Longoni
Department of Botany and Plant Biology and Department of Molecular Biology, University of Geneva, 1211 Geneva 4, Switzerland.
Linnka
L
Legendre-Lefebvre
Unité Mixte de Recherche 7141, CNRS/Université Pierre et Marie Curie, Institut de Biologie Physico-Chimique, 75005 Paris, France.
Xenie
X
Johnson
Institute of Biology, Molecular Genetics, Humboldt University of Berlin, D-10115 Berlin, Germany.
Christian
C
Schmitz-Linneweber
Department of Botany and Plant Biology and Department of Molecular Biology, University of Geneva, 1211 Geneva 4, Switzerland michel.goldschmidt-clermont@unige.ch.
Michel
0000-0003-1224-5868
M
Goldschmidt-Clermont
D002467:Cell Nucleus / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000235:genetics*; D010788:Photosynthesis / Q000235:genetics; D045331:Photosystem I Protein Complex / Q000235:genetics* / Q000378:metabolism; D011485:Protein Binding
D045331:Photosystem I Protein Complex