title: Integration of carbon assimilation modes with photosynthetic light capture in the green alga Chlamydomonas reinhardtii.
abstract: The unicellular green alga Chlamydomonas reinhardtii is capable of using organic and inorganic carbon sources simultaneously, which requires the adjustment of photosynthetic activity to the prevailing mode of carbon assimilation. We obtained novel insights into the regulation of light-harvesting at photosystem II (PSII) following altered carbon source availability. In C. reinhardtii, synthesis of PSII-associated light-harvesting proteins (LHCBMs) is controlled by the cytosolic RNA-binding protein NAB1, which represses translation of particular LHCBM isoform transcripts. This mechanism is fine-tuned via regulation of the nuclear NAB1 promoter, which is activated when linear photosynthetic electron flow is restricted by CO(2)-limitation in a photoheterotrophic context. In the wild-type, accumulation of NAB1 reduces the functional PSII antenna size, thus preventing a harmful overexcited state of PSII, as observed in a NAB1-less mutant. We further demonstrate that translation control as a newly identified long-term response to prolonged CO(2)-limitation replaces LHCII state transitions as a fast response to PSII over-excitation. Intriguingly, activation of the long-term response is perturbed in state transition mutant stt7, suggesting a regulatory link between the long- and short-term response. We depict a regulatory circuit operating on distinct timescales and in different cellular compartments to fine-tune light-harvesting in photoheterotrophic eukaryotes.
authors.affiliation: a Bielefeld University, Faculty of Biology, Center for Biotechnology (CeBiTec), Universitätsstrasse 27, 33615, Bielefeld, Germany.
authors.forename: Hanna
authors.initials: H
authors.lastname: Berger
authors.affiliation: a Bielefeld University, Faculty of Biology, Center for Biotechnology (CeBiTec), Universitätsstrasse 27, 33615, Bielefeld, Germany.
authors.forename: Olga
authors.initials: O
authors.lastname: Blifernez-Klassen
authors.affiliation: b Universita degli Studi di Verona, Department of Biotechnology, strada Le Grazie 15, 37134, Verona, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Ballottari
authors.affiliation: b Universita degli Studi di Verona, Department of Biotechnology, strada Le Grazie 15, 37134, Verona, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Bassi
authors.affiliation: a Bielefeld University, Faculty of Biology, Center for Biotechnology (CeBiTec), Universitätsstrasse 27, 33615, Bielefeld, Germany.
authors.forename: Lutz
authors.initials: L
authors.lastname: Wobbe
authors.affiliation: a Bielefeld University, Faculty of Biology, Center for Biotechnology (CeBiTec), Universitätsstrasse 27, 33615, Bielefeld, Germany olaf.kruse@uni-bielefeld.de.
authors.forename: Olaf
authors.initials: O
authors.lastname: Kruse
mesh_terms: D000064:Acclimatization / Q000187:drug effects / Q000528:radiation effects; D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism; D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism / Q000494:pharmacology; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D016825:Chlamydomonas reinhardtii / Q000187:drug effects / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects*; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D008954:Models, Biological; D010788:Photosynthesis / Q000187:drug effects / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D014176:Protein Biosynthesis / Q000187:drug effects / Q000528:radiation effects; D014158:Transcription, Genetic / Q000187:drug effects / Q000528:radiation effects
chemical_list: D020418:Algal Proteins; D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D002245:Carbon Dioxide; D002244:Carbon
keywords: Chlamydomonas reinhardtii; NAB1; carbon metabolism; light-harvesting antenna; state transitions; translation control