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Valimareanu, Sergiu

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Valimareanu, Sergiu
Affiliation principale
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https://libra.unine.ch/handle/123456789/775

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  • Publication
    Accès libre
    ABC1K1/PGR6 kinase: a regulatory link between photosynthetic activity and chloroplast metabolism
    Martinis, Jacopo
    ;
    Glauser, Gaétan
    ;
    Valimareanu, Sergiu 
    ;
    Stettler, Michaela
    ;
    Zeeman, Samuel C
    ;
    Yamamoto, Hiroshi
    ;
    Shikanai, Toshiharu
    ;
    Kessler, Félix 
    Arabidopsis proton gradient regulation (pgr) mutants have high chlorophyll fluorescence and reduced non-photochemical quenching (NPQ) caused by defects in photosynthetic electron transport. Here, we identify PGR6 as the chloroplast lipid droplet (plastoglobule, PG) kinase ABC1K1 (activity of bc1 complex kinase 1). The members of the ABC1/ADCK/UbiB family of atypical kinases regulate ubiquinone synthesis in bacteria and mitochondria, and impact various metabolic pathways in plant chloroplasts. Here, we demonstrate that abc1k1 has a unique photosynthetic and metabolic phenotype that is distinct from that of the abc1k3 homolog. The abc1k1/pgr6 single mutant is specifically deficient in the electron carrier plastoquinone, as well as in ß–carotene and the xanthophyll lutein, and is defective in membrane antioxidant tocopherol metabolism. After 2 days of continuous high light stress, abc1k1/pgr6 plants suffer extensive photosynthetic and metabolic perturbations, strongly affecting carbohydrate metabolism. Remarkably, however, the mutant acclimates to high light after 7 days together with a recovery of carotenoid levels and a drastic alteration in the starch-to-sucrose ratio. Moreover, ABC1K1 behaves as an active kinase and phosphorylates VTE1, a key enzyme of tocopherol (vitamin E) metabolism in vitro. Our results indicate that the ABC1K1 kinase constitutes a new type of regulatory link between photosynthetic activity and chloroplast metabolism.
  • Publication
    Accès libre
    A Chloroplast ABC1-like Kinase Regulates Vitamin E Metabolism in Arabidopsis
    Martinis, Jacopo
    ;
    Glauser, Gaétan
    ;
    Valimareanu, Sergiu 
    ;
    Kessler, Félix 
    In bacteria and mitochondria, ABC1 (for Activity of bc1 complex)-like kinases regulate ubiquinone synthesis, mutations causing severe respiration defects, including neurological disorders in humans. Little is known about plant ABC1-like kinases; in Arabidopsis (Arabidopsis thaliana), five are predicted in mitochondria but, surprisingly, six are located at lipid droplets in chloroplasts. These are a known site of prenylquinone (including tocopherol [vitamin E], phylloquinone [vitamin K] and plastoquinone) metabolism and contain a large proportion of the tocopherol cyclase (VTE1) required for vitamin E synthesis and recycling. Therefore, ABC1-like kinases may be involved in the regulation of chloroplast prenylquinone metabolism. Using a nontargeted lipidomics approach, we demonstrate that plants lacking the plastoglobule ABC1-like kinase ABC1K3 are defective both for the production of plastochromanol-8 (a plastoquinone-derived lipid antioxidant) and the redox recycling of a-tocopherol, whereas tocopherol production is not affected. All of these pathways require VTE1 activity. However, in the abc1k3 mutant, VTE1 levels are strongly reduced posttranscriptionally. We provide evidence that the ABC1-like kinase ABC1K3 phosphorylates VTE1, possibly stabilizing it at plastoglobules. However, ABC1K3 may also have other targets and be involved in a wider chloroplast regulatory network.