title: Quantitative proteomics of a chloroplast SRP54 sorting mutant and its genetic interactions with CLPC1 in Arabidopsis.
abstract: cpSRP54 (for chloroplast SIGNAL RECOGNITION PARTICLE54) is involved in cotranslational and posttranslational sorting of thylakoid proteins. The Arabidopsis (Arabidopsis thaliana) cpSRP54 null mutant, ffc1-2, is pale green with delayed development. Western-blot analysis of individual leaves showed that the SRP sorting pathway, but not the SecY/E translocon, was strongly down-regulated with progressive leaf development in both wild-type and ffc1-2 plants. To further understand the impact of cpSRP54 deletion, a quantitative comparison of ffc2-1 was carried out for total leaf proteomes of young seedlings and for chloroplast proteomes of fully developed leaves using stable isotope labeling (isobaric stable isotope labeling and isotope-coded affinity tags) and two-dimensional gels. This showed that cpSRP54 deletion led to a change in light-harvesting complex composition, an increase of PsbS, and a decreased photosystem I/II ratio. Moreover, the cpSRP54 deletion led in young leaves to up-regulation of thylakoid proteases and stromal chaperones, including ClpC. In contrast, the stromal protein homeostasis machinery returned to wild-type levels in mature leaves, consistent with the developmental down-regulation of the SRP pathway. A differential response between young and mature leaves was also found in carbon metabolism, with an up-regulation of the Calvin cycle and the photorespiratory pathway in peroxisomes and mitochondria in young leaves but not in old leaves. The Calvin cycle was down-regulated in mature leaves to adjust to the reduced capacity of the light reaction, while reactive oxygen species defense proteins were up-regulated. The significance of ClpC up-regulation was confirmed through the generation of an ffc2-1 clpc1 double mutant. This mutant was seedling lethal under autotrophic conditions but could be partially rescued under heterotrophic conditions.
authors.affiliation: Department of Plant Biology, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Heidi
authors.initials: H
authors.lastname: Rutschow
authors.forename: A Jimmy
authors.initials: AJ
authors.lastname: Ytterberg
authors.forename: Giulia
authors.initials: G
authors.lastname: Friso
authors.forename: Robert
authors.initials: R
authors.lastname: Nilsson
authors.forename: Klaas J
authors.initials: KJ
authors.lastname: van Wijk
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D060365:Chloroplast Proteins; D002736:Chloroplasts / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D049071:Endopeptidase Clp / Q000235:genetics / Q000378:metabolism*; D006706:Homeostasis; D007525:Isoelectric Focusing; D007554:Isotopes / Q000378:metabolism; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D013058:Mass Spectrometry; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism; D010940:Plant Proteins / Q000096:biosynthesis; D021381:Protein Transport; D040901:Proteomics; D036226:Seedlings / Q000254:growth & development / Q000378:metabolism; D018271:Signal Recognition Particle / Q000235:genetics / Q000378:metabolism*; D020524:Thylakoids / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D060365:Chloroplast Proteins; C083707:FFC protein, Arabidopsis; D007554:Isotopes; D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D018271:Signal Recognition Particle; D049071:Endopeptidase Clp; D009584:Nitrogen