Vignette d'image

Kessler, Félix

Nom
Kessler, Félix
Affiliation principale
Fonction
Professeur ordinaire
Email
felix.kessler@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/320

Résultat de la recherche

Filtres

3
3
Réinitialiser les filtres

Paramètres

Voici les éléments 1 - 3 sur 3
  • Publication
    Accès libre
    The Function and Diversity of Plastid Protein Import Pathways : A Multilane GTPase Highway into Plastids
    (2006)
    Kessler, Félix 
    ;
    Schnell, Danny J.
    The photosynthetic chloroplast is the hallmark organelle of green plants. During the endosymbiotic evolution of chloroplasts, the vast majority of genes from the original cyanobacterial endosymbiont were transferred to the host cell nucleus. Chloroplast biogenesis therefore requires the import of nucleus-encoded proteins from their site of synthesis in the cytosol. The majority of proteins are imported by the activity of Toc and Tic complexes located within the chloroplast envelope. In addition to chloroplasts, plants have evolved additional, non-photosynthetic plastid types that are essential components of all cells. Recent studies indicate that the biogenesis of various plastid types relies on distinct but homologous Toc–Tic import pathways that have specialized in the import of specific classes of substrates. These different import pathways appear to be necessary to balance the essential physiological role of plastids in cellular metabolism with the demands of cellular differentiation and plant development.
  • Publication
    Accès libre
    AtToc90, a New GTP-Binding Component of the Arabidopsis Chloroplast Protein Import Machinery
    (2004)
    Hiltbrunner, Andreas
    ;
    Grünig, Kathrin
    ;
    Alvarez-Huerta, Mayte
    ;
    Infanger, Sibylle
    ;
    Bauer, Jörg
    ;
    Kessler, Félix 
    AtToc159 is a GTP-binding chloroplast protein import receptor. In vivo, atToc159 is required for massive accumulation of photosynthetic proteins during chloroplast biogenesis. Yet, in mutants lacking atToc159 photosynthetic proteins still accumulate, but at strongly reduced levels whereas non-photosynthetic proteins are imported normally: This suggests a role for the homologues of atToc159 (atToc132, -120 and -90). Here, we show that atToc90 supports accumulation of photosynthetic proteins in plastids, but is not required for import of several constitutive proteins. Part of atToc90 associates with the chloroplast surface in vivo and with the Toc-complex core components (atToc75 and atToc33) in vitro suggesting a function in chloroplast protein import similar to that of atToc159. As both proteins specifically contribute to the accumulation of photosynthetic proteins in chloroplasts they may be components of the same import pathway.
  • Publication
    Accès libre
    Nucleotide binding and dimerization at the chloroplast pre-protein import receptor, atToc33, are not essential in vivo but do increase import efficiency
    Aronsson, Henrik
    ;
    Combe, Jonathan
    ;
    Patel, Ramesh
    ;
    Agne, Birgit
    ;
    Martin, Meryll
    ;
    Kessler, Félix 
    ;
    Jarvis, Paul
    The atToc33 protein is one of several pre-protein import receptors in the outer envelope of Arabidopsis chloroplasts. It is a GTPase with motifs characteristic of such proteins, and its loss in the plastid protein import 1 (ppi1) mutant interferes with the import of photosynthesis-related pre-proteins, causing a chlorotic phenotype in mutant plants. To assess the significance of GTPase cycling by atToc33, we generated several atToc33 point mutants with predicted effects on GTP binding (K49R, S50N and S50N/S51N), GTP hydrolysis (G45R, G45V, Q68A and N101A), both binding and hydrolysis (G45R/K49N/S50R), and dimerization or the functional interaction between dimeric partners (R125A, R130A and R130K). First, a selection of these mutants was assessed in vitro, or in yeast, to confirm that the mutations have the desired effects: in relation to nucleotide binding and dimerization, the mutants behaved as expected. Then, activities of selected mutants were tested in vivo, by assessing for complementation of ppi1 in transgenic plants. Remarkably, all tested mutants mediated high levels of complementation: complemented plants were similar to the wild type in growth rate, chlorophyll accumulation, photosynthetic performance, and chloroplast ultrastructure. Protein import into mutant chloroplasts was also complemented to >50% of the wild-type level. Overall, the data indicate that neither nucleotide binding nor dimerization at atToc33 is essential for chloroplast import (in plants that continue to express the other TOC receptors in native form), although both processes do increase import efficiency. Absence of atToc33 GTPase activity might somehow be compensated for by that of the Toc159 receptors. However, overexpression of atToc33 (or its close relative, atToc34) in Toc159-deficient plants did not mediate complementation, indicating that the receptors do not share functional redundancy in the conventional sense.