Kessler, Félix

2011, Infanger, Sibylle, Bischof, Sylvain, Hiltbrunner, Andreas, Agne, Birgit, Baginsky, Sacha, Kessler, Félix

2010, Agne, Birgit, Andres, Charles, Montandon, Cyril, Christ, Bastien, Ertan, Anouk, Jung, Friederike, Infanger, Sibylle, Bischof, Sylvain, Baginsky, Sacha, Kessler, Félix

2009, Agne, Birgit, Infanger, Sibylle, Wang, Fei, Hofstetter, Valère, Rahim, Gwendoline, Martin, Meryll, Lee, Dong Wook, Hwang, Inhwan, Schnell, Danny, Kessler, Félix

The heterotrimeric Toc core complex of the chloroplast protein import apparatus contains two GTPases, Toc159 and Toc34, together with the protein-conducting channel Toc75. Toc159 and Toc34 are exposed at the chloroplast surface and function in preprotein recognition. Together, they have been shown to facilitate the import of photosynthetic proteins into chloroplasts in Arabidopsis. Consequently, the ppi2 mutant lacking at Toc159 has a non-photosynthetic albino phenotype. Previous mutations in the conserved G1 and G3 GTPase motifs abolished the function of Toc159 in vivo by disrupting targeting of the receptor to chloroplasts. Here, we demonstrate that a mutant in a conserved G1 lysine (atToc159 K868R) defective in GTP binding and hydrolysis can target and assemble into Toc complexes. We show that atToc159 K868R can support protein import into isolated chloroplasts, albeit at lower preprotein binding and import efficiencies compared with the wild-type receptor. Considering the absence of measurable GTPase activity in the K868R mutant, we conclude that GTP hydrolysis at atToc159 is not strictly required for preprotein translocation. The data also indicate that preprotein import requires at least one additional GTPase other than Toc159.

2009, Agne, Birgit, Kessler, Félix

2011, Andres, Charles, Agne, Birgit, Kessler, Félix

2010, Aronsson, Henrik, Combe, Jonathan, Patel, Ramesh, Agne, Birgit, Martin, Meryll, Kessler, Félix, Jarvis, Paul

2009, Rahim, Gwendoline, Bischof, Sylvain, Kessler, Félix, Agne, Birgit

The GTPases atToc33 and atToc159 are pre-protein receptor components of the translocon complex at the outer chloroplast membrane in Arabidopsis. Despite their participation in the same complex in vivo, evidence for their interaction is still lacking. Here, a split-ubiquitin system is engineered for use in plants, and the in vivo interaction of the Toc GTPases in Arabidopsis and tobacco protoplasts is shown. Using the same method, the self-interaction of the peroxisomal membrane protein atPex11e is demonstrated. The finding suggests a more general suitability of the split-ubiquitin system as a plant in vivo interaction assay.

2010, Agne, Birgit, Kessler, Félix

2010, Andres, Charles, Agne, Birgit, Kessler, Félix

2009, Schelbert, Silvia, Aubry, Sylvain, Burla, Bo, Agne, Birgit, Kessler, Félix, Krupinska, Karin, Hörtensteiner, Stefan

During leaf senescence, chlorophyll is removed from thylakoid membranes and converted in a multistep pathway to colorless breakdown products that are stored in vacuoles. Dephytylation, an early step of this pathway, increases water solubility of the breakdown products. It is widely accepted that chlorophyll is converted into pheophorbide via chlorophyllide. However, chlorophyllase, which converts chlorophyll to chlorophyllide, was found not to be essential for dephytylation in Arabidopsis thaliana. Here, we identify pheophytinase (PPH), a chloroplast-located and senescence-induced hydrolase widely distributed in algae and land plants. In vitro, Arabidopsis PPH specifically dephytylates the Mg-free chlorophyll pigment, pheophytin (phein), yielding pheophorbide. An Arabidopsis mutant deficient in PPH (pph-1) is unable to degrade chlorophyll during senescence and therefore exhibits a stay-green phenotype. Furthermore, pph-1 accumulates phein during senescence. Therefore, PPH is an important component of the chlorophyll breakdown machinery of senescent leaves, and we propose that the sequence of early chlorophyll catabolic reactions be revised. Removal of Mg most likely precedes dephytylation, resulting in the following order of early breakdown intermediates: chlorophyll → pheophytin → pheophorbide. Chlorophyllide, the last precursor of chlorophyll biosynthesis, is most likely not an intermediate of breakdown. Thus, chlorophyll anabolic and catabolic reactions are metabolically separated.