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Hummel M.,University Utrecht | Hummel M.,University of California at Riverside | Dobrenel T.,Umea University | Dobrenel T.,French National Institute for Agricultural Research | And 10 more authors.
Journal of Proteomics | Year: 2015

Arabidopsis thaliana cytosolic ribosomes are large complexes containing eighty-one distinct ribosomal proteins (r-proteins), four ribosomal RNAs (rRNA) and a plethora of associated (non-ribosomal) proteins. In plants, r-proteins of cytosolic ribosomes are each encoded by two to seven different expressed and similar genes, forming an r-protein family. Distinctions in the r-protein coding sequences of gene family members are a source of variation between ribosomes. We performed proteomic investigation of actively translating cytosolic ribosomes purified using both immunopurification and a classic sucrose cushion centrifugation-based protocol from plants of different developmental stages. Both 1D and 2D LC-MSE with data-independent acquisition as well as conventional data-dependent MS/MS procedures were applied. This approach provided detailed identification of 165 r-protein paralogs with high coverage based on proteotypic peptides. The detected r-proteins were the products of the majority (68%) of the 242 cytosolic r-protein genes encoded by the genome. A total of 70 distinct r-proteins were identified. Based on these results and information from DNA microarray and ribosome footprint profiling studies a re-annotation of Arabidopsis r-proteins and genes is proposed. This compendium of the cytosolic r-protein proteome will serve as a template for future investigations on the dynamic structure and function of plant ribosomes. Biological significance: Translation is one of the most energy demanding processes in a living cell and is therefore carefully regulated. Translational activity is tightly linked to growth control and growth regulating mechanism. Recently established translational profiling technologies, including the profiling of mRNAs associated with polysomes and the mapping of ribosome footprints on mRNAs, have revealed that the expression of gene expression is often fine-tuned by differential translation of gene transcripts. The eukaryotic ribosome, the hub of these important processes, consists of close to eighty different proteins (depending on species) and four large RNAs assembled into two highly conserved subunits. In plants and to lesser extent in yeast, the r-proteins are encoded by more than one actively transcribed gene. As r-protein gene paralogs frequently do not encode identical proteins and are regulated by growth conditions and development, in vivo ribosomes are heterogeneous in their protein content. The regulatory and physiological importance of this heterogeneity is unknown. Here, an improved annotation of the more than two hundred r-protein genes of Arabidopsis is presented that combines proteomic and advanced mRNA expression data. This proteomic investigation and re-annotation of Arabidopsis ribosomes establish a base for future investigations of translational control in plants. © 2015 Elsevier B.V.

Boex-Fontvieille E.,University Paris - Sud | Daventure M.,Plateforme PAPPSO | Jossier M.,University Paris - Sud | Zivy M.,Plateforme PAPPSO | And 3 more authors.
PLoS ONE | Year: 2013

Photosynthetic CO2 assimilation is the carbon source for plant anabolism, including amino acid production and protein synthesis. The biosynthesis of leaf proteins is known for decades to correlate with photosynthetic activity but the mechanisms controlling this effect are not documented. The cornerstone of the regulation of protein synthesis is believed to be translation initiation, which involves multiple phosphorylation events in Eukaryotes. We took advantage of phosphoproteomic methods applied to Arabidopsis thaliana rosettes harvested under controlled photosynthetic gas-exchange conditions to characterize the phosphorylation pattern of ribosomal proteins (RPs) and eukaryotic initiation factors (eIFs). The analyses detected 14 and 11 new RP and eIF phosphorylation sites, respectively, revealed significant CO2-dependent and/or light/dark phosphorylation patterns and showed concerted changes in 13 eIF phosphorylation sites and 9 ribosomal phosphorylation sites. In addition to the well-recognized role of the ribosomal small subunit protein RPS6, our data indicate the involvement of eIF3, eIF4A, eIF4B, eIF4G and eIF5 phosphorylation in controlling translation initiation when photosynthesis varies. The response of protein biosynthesis to the photosynthetic input thus appears to be the result of a complex regulation network involving both stimulating (e.g. RPS6, eIF4B phosphorylation) and inhibiting (e.g. eIF4G phosphorylation) molecular events. © 2013 Boex-Fontvieille et al.

Boex-Fontvieille E.,University Paris - Sud | Davanture M.,Plateforme PAPPSO | Jossier M.,University Paris - Sud | Zivy M.,Plateforme PAPPSO | And 3 more authors.
Journal of Experimental Botany | Year: 2014

Cellulose is one of the most important organic compounds in terrestrial ecosystems and represents a major plant structural polymer. However, knowledge of the regulation of cellulose biosynthesis is still rather limited. Recent studies have shown that the phosphorylation of cellulose synthases (CESAs) may represent a key regulatory event in cellulose production. However, the impact of environmental conditions on the carbon flux of cellulose deposition and on phosphorylation levels of CESAs has not been fully elucidated. Here, we took advantage of gas exchange measurements, isotopic techniques, metabolomics, and quantitative phosphoproteomics to investigate the regulation of cellulose production in Arabidopsis rosette leaves in different photosynthetic contexts (different CO2 mole fractions) or upon light/dark transition. We show that the carbon flux to cellulose production increased with photosynthesis, but not proportionally. The phosphorylation level of several phosphopeptides associated with CESA1 and 3, and several enzymes of sugar metabolism was higher in the light and/or increased with photosynthesis. By contrast, a phosphopeptide (Ser126) associated with CESA5 seemed to be more phosphorylated in the dark. Our data suggest that photosynthetic activity affects cellulose deposition through the control of both sucrose metabolism and cellulose synthesis complexes themselves by protein phosphorylation. © The Author 2014. Published by Oxford University Press on behalf of the Society for Experimental Biology.

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