title: Hyper-accumulation of starch and oil in a Chlamydomonas mutant affected in a plant-specific DYRK kinase.
abstract: BACKGROUND
  Because of their high biomass productivity and their ability to accumulate high levels of energy-rich reserve compounds such as oils or starch, microalgae represent a promising feedstock for the production of biofuel. Accumulation of reserve compounds takes place when microalgae face adverse situations such as nutrient shortage, conditions which also provoke a stop in cell division, and down-regulation of photosynthesis. Despite growing interest in microalgal biofuels, little is known about molecular mechanisms controlling carbon reserve formation. In order to discover new regulatory mechanisms, and identify genes of interest to boost the potential of microalgae for biofuel production, we developed a forward genetic approach in the model microalga Chlamydomonas reinhardtii.
  
  
  RESULTS
  By screening an insertional mutant library on the ability of mutants to accumulate and re-mobilize reserve compounds, we isolated a Chlamydomonas mutant (starch degradation 1, std1) deficient for a dual-specificity tyrosine-phosphorylation-regulated kinase (DYRK). The std1 mutant accumulates higher levels of starch and oil than wild-type and maintains a higher photosynthetic activity under nitrogen starvation. Phylogenetic analysis revealed that this kinase (named DYRKP) belongs to a plant-specific subgroup of the evolutionarily conserved DYRK kinase family. Furthermore, hyper-accumulation of storage compounds occurs in std1 mostly under low light in photoautotrophic condition, suggesting that the kinase normally acts under conditions of low energy status to limit reserve accumulation.
  
  
  CONCLUSIONS
  The DYRKP kinase is proposed to act as a negative regulator of the sink capacity of photosynthetic cells that integrates nutrient and energy signals. Inactivation of the kinase strongly boosts accumulation of reserve compounds under photoautotrophic nitrogen deprivation and allows maintaining high photosynthetic activity. The DYRKP kinase therefore represents an attractive target for improving the energy density of microalgae or crop plants.
authors.affiliation: CEA, CNRS, Aix-Marseille Université, Institut de Biosciences et Biotechnologies Aix Marseille, Laboratoire de Bioénergétique et Biotechnologie des Bactéries et Microalgues, CEA Cadarache, 13108 Saint-Paul-lez-Durance, France ; CNRS, Biologie Végétale et Microbiologie Environnementale, UMR7265, 13108 Saint-Paul-lez-Durance, France ; Aix Marseille Université, Biologie Végétale et Microbiologie Environnementale, UMR7265, 13284 Marseille, France ; Molecular Biotechnology and Systems Biology, TU Kaiserslautern, Paul-Ehrlich-Straße 23, 67663 Kaiserslautern, Germany.
authors.forename: Miriam
authors.initials: M
authors.lastname: Schulz-Raffelt
authors.affiliation: CEA, CNRS, Aix-Marseille Université, Institut de Biosciences et Biotechnologies Aix Marseille, Laboratoire de Bioénergétique et Biotechnologie des Bactéries et Microalgues, CEA Cadarache, 13108 Saint-Paul-lez-Durance, France ; CNRS, Biologie Végétale et Microbiologie Environnementale, UMR7265, 13108 Saint-Paul-lez-Durance, France ; Aix Marseille Université, Biologie Végétale et Microbiologie Environnementale, UMR7265, 13284 Marseille, France ; Research School of Biology College of Medicine, Biology and Environment, Linneaus Building 134, The Australian National University, Canberra, ACT 2601 Australia.
authors.forename: Vincent
authors.initials: V
authors.lastname: Chochois
authors.affiliation: CEA, CNRS, Aix-Marseille Université, Institut de Biosciences et Biotechnologies Aix Marseille, Laboratoire de Bioénergétique et Biotechnologie des Bactéries et Microalgues, CEA Cadarache, 13108 Saint-Paul-lez-Durance, France ; CNRS, Biologie Végétale et Microbiologie Environnementale, UMR7265, 13108 Saint-Paul-lez-Durance, France ; Aix Marseille Université, Biologie Végétale et Microbiologie Environnementale, UMR7265, 13284 Marseille, France.
authors.forename: Pascaline
authors.initials: P
authors.lastname: Auroy
authors.affiliation: CEA, CNRS, Aix-Marseille Université, Institut de Biosciences et Biotechnologies Aix Marseille, Laboratoire de Bioénergétique et Biotechnologie des Bactéries et Microalgues, CEA Cadarache, 13108 Saint-Paul-lez-Durance, France ; CNRS, Biologie Végétale et Microbiologie Environnementale, UMR7265, 13108 Saint-Paul-lez-Durance, France ; Aix Marseille Université, Biologie Végétale et Microbiologie Environnementale, UMR7265, 13284 Marseille, France.
authors.forename: Stéphan
authors.initials: S
authors.lastname: Cuiné
authors.affiliation: CEA, CNRS, Aix-Marseille Université, Institut de Biosciences et Biotechnologies Aix Marseille, Laboratoire de Bioénergétique et Biotechnologie des Bactéries et Microalgues, CEA Cadarache, 13108 Saint-Paul-lez-Durance, France ; CNRS, Biologie Végétale et Microbiologie Environnementale, UMR7265, 13108 Saint-Paul-lez-Durance, France ; Aix Marseille Université, Biologie Végétale et Microbiologie Environnementale, UMR7265, 13284 Marseille, France.
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Billon
authors.affiliation: UMR8576, CNRS, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq, France.
authors.forename: David
authors.initials: D
authors.lastname: Dauvillée
authors.affiliation: CEA, CNRS, Aix-Marseille Université, Institut de Biosciences et Biotechnologies Aix Marseille, Laboratoire de Bioénergétique et Biotechnologie des Bactéries et Microalgues, CEA Cadarache, 13108 Saint-Paul-lez-Durance, France ; CNRS, Biologie Végétale et Microbiologie Environnementale, UMR7265, 13108 Saint-Paul-lez-Durance, France ; Aix Marseille Université, Biologie Végétale et Microbiologie Environnementale, UMR7265, 13284 Marseille, France.
authors.forename: Yonghua
authors.initials: Y
authors.lastname: Li-Beisson
authors.affiliation: CEA, CNRS, Aix-Marseille Université, Institut de Biosciences et Biotechnologies Aix Marseille, Laboratoire de Bioénergétique et Biotechnologie des Bactéries et Microalgues, CEA Cadarache, 13108 Saint-Paul-lez-Durance, France ; CNRS, Biologie Végétale et Microbiologie Environnementale, UMR7265, 13108 Saint-Paul-lez-Durance, France ; Aix Marseille Université, Biologie Végétale et Microbiologie Environnementale, UMR7265, 13284 Marseille, France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Peltier
keywords: Chlamydomonas; DYRK; Kinase; Microalgae; Nutrient deprivation; Oil; Photosynthesis; Starch