The regulation of protein turnover by the ubiquitin proteasome system (UPS) is a major posttranslational mechanism in eukaryotes. One of the key components of the UPS, the COP9 signalosome (CSN), regulates 'culli...The regulation of protein turnover by the ubiquitin proteasome system (UPS) is a major posttranslational mechanism in eukaryotes. One of the key components of the UPS, the COP9 signalosome (CSN), regulates 'cullin-ring' E3 ubiquitin ligases. In plants, CSN participates in diverse cellular and developmental processes, ranging from light signaling to cell cycle control. In this work, we isolated a new plant-specific CSN-interacting F-box protein, which we denominated CFK1 (COP9 INTERACTING F-BOX KELCH 1). We show that, in Arabidopsis thaliana, CFK1 is a component of a functional ubiquitin ligase complex. We also show that CFK1 stability is regulated by CSN and by proteasome-dependent proteoly- sis, and that light induces accumulation of the CFK1 transcript in the hypocotyl. Analysis of CFK1 knockdown, mutant, and overexpressing seedlings indicates that CFK1 promotes hypocotyl elongation by increasing cell size. Reduction of CSN levels enhances the short hypocotyl phenotype of CFKl-depleted seedlings, while complete loss of CSN activity sup- presses the Iong-hypocotyl phenotype of CFKl-overexpressing seedlings. We propose that CFK1 (and its regulation by CSN) is a novel component of the cellular mechanisms controlling hypocotyl elongation.展开更多
The shoot apical meristem (SAM) is a population of undifferentiated cells at the tip of the shoot axis that establishes early during plant embryogenesis and gives rise to all shoot organs throughout the plant's lif...The shoot apical meristem (SAM) is a population of undifferentiated cells at the tip of the shoot axis that establishes early during plant embryogenesis and gives rise to all shoot organs throughout the plant's life. A plethora of different families of transcription factors (TFs) play a key role in establishing the equilibrium between cell differentiation and stem cell maintenance in the SAM. Fine tuning of these regulatory proteins is crucial for a proper and fast SAM response to environmental and hormonal cues, and for development progression. One effective way to rapidly inactivate TFs involves regulated proteolysis by the ubiquitin/26S proteasome system (UPS). However, a possible role of UPS-dependent protein degradation in the regulation of key SAM TFs has not been thoroughly investigated. Here, we summarize recent evidence supporting a role for the UPS in SAM maintenance and function. We integrate this survey with an in silico analysis of publicly-available microarray databases which identified ubiquitin ligases that are expressed in specific areas within the SAM, suggesting that they may regulate or act downstream of meristem-specific factors.展开更多
When it was discovered in the 1970s as a ubiquitous protein, ubiquitin, a 76-aminoacid peptide, had no assigned function. It was not until later that ubiquitin was found to be a necessary cofactor in a vital cellular ...When it was discovered in the 1970s as a ubiquitous protein, ubiquitin, a 76-aminoacid peptide, had no assigned function. It was not until later that ubiquitin was found to be a necessary cofactor in a vital cellular process: the degradation of proteins. Work by Avram Hershko, Aaron Ciechanover, and Irwin Rose (for which they received the 2004 Nobel Prize in Chemistry) showed that the covalent attachment of ubiquitin provide pro-teins with a tag that dispatches them to the proteasome, the main cell degradation machinery (Ciechanover 2012). Subsequent work, has revealed that ubiquitin belongs to a broader family of ubiquitin-like proteins that can modify not only protein stability, but also subcellular localization and function.展开更多
Cullin-RING E3 ligases (CRLs) regulate different aspects of plant development and are activated by modification of their cullin subunit with the ubiquitin-like protein NEDD8 (NEural precursor cell expressed Develop...Cullin-RING E3 ligases (CRLs) regulate different aspects of plant development and are activated by modification of their cullin subunit with the ubiquitin-like protein NEDD8 (NEural precursor cell expressed Developmentally Down-regulated 8) (neddylation) and deactivated by NEDD8 removal (deneddylation). The CONSTITUTIVELY PHOTOMORPHOGENIC9 (COP9) signalosome (CSN) acts as a molecular switch of CRLs activity by reverting their neddylation status, but its contribution to embryonic and early seedling development remains poorly characterized. Here, we analyzed the phenotypic defects of csn mutants and monitored the cullin deneddylation/neddylation ratio during embryonic and early seedling development. We show that while csn mutants can complete embryogenesis (albeit at a slower pace than wildtype) and are able to germinate (albeit at a reduced rate), they progressively lose meristem activity upon germination until they become unable to sustain growth. We also show that the majority of cullin proteins are progressively neddylated during the late stages of seed maturation and become deneddylated upon seed germination. This developmentally regulated shift in the cullin neddylation status is absent in csn mutants. We conclude that the CSN and its cullin deneddylation activity are required to sustain postembryonic meristem function in Arabidopsis.展开更多
Since its discovery about 50 years ago,the ubiquitin-proteasome system(UPS)has not stopped to surprise us for its level of sophistication and complexity in achieving substrate-specific protein degradation(Vierstra,200...Since its discovery about 50 years ago,the ubiquitin-proteasome system(UPS)has not stopped to surprise us for its level of sophistication and complexity in achieving substrate-specific protein degradation(Vierstra,2009).At the heart of this system lies the concerted activity of three major classes of enzymes:ubiquitin activators(E1),ubiquitin conjugators(E2),and ubiquitin ligases(or E3).E3s,together with selected E2s,are responsible for promoting the formation of a ubiquitin chain on a specific protein substrate.展开更多
文摘The regulation of protein turnover by the ubiquitin proteasome system (UPS) is a major posttranslational mechanism in eukaryotes. One of the key components of the UPS, the COP9 signalosome (CSN), regulates 'cullin-ring' E3 ubiquitin ligases. In plants, CSN participates in diverse cellular and developmental processes, ranging from light signaling to cell cycle control. In this work, we isolated a new plant-specific CSN-interacting F-box protein, which we denominated CFK1 (COP9 INTERACTING F-BOX KELCH 1). We show that, in Arabidopsis thaliana, CFK1 is a component of a functional ubiquitin ligase complex. We also show that CFK1 stability is regulated by CSN and by proteasome-dependent proteoly- sis, and that light induces accumulation of the CFK1 transcript in the hypocotyl. Analysis of CFK1 knockdown, mutant, and overexpressing seedlings indicates that CFK1 promotes hypocotyl elongation by increasing cell size. Reduction of CSN levels enhances the short hypocotyl phenotype of CFKl-depleted seedlings, while complete loss of CSN activity sup- presses the Iong-hypocotyl phenotype of CFKl-overexpressing seedlings. We propose that CFK1 (and its regulation by CSN) is a novel component of the cellular mechanisms controlling hypocotyl elongation.
基金supported by the Executive Programme of Scientific and Technological Cooperation between Italy and China(2010-2012)of the Italian Ministry of Foreign Affairs(MAE),Direzione Generale per la Promozione e la Co-operazione Culturale,with the contribution of the Ministero dell'Istruzione dell'Università e della Ricerca(MIUR)Project:Control of substrate degradation in plant development and environmental responseby the Agri-food CNR strategic project(AG.P01.003):Genetic,Physiological and Molecular Basis of Development and Differentiation of Model and Crop Species of Interest to Agri-food in response to endogenous and environmental cues
文摘The shoot apical meristem (SAM) is a population of undifferentiated cells at the tip of the shoot axis that establishes early during plant embryogenesis and gives rise to all shoot organs throughout the plant's life. A plethora of different families of transcription factors (TFs) play a key role in establishing the equilibrium between cell differentiation and stem cell maintenance in the SAM. Fine tuning of these regulatory proteins is crucial for a proper and fast SAM response to environmental and hormonal cues, and for development progression. One effective way to rapidly inactivate TFs involves regulated proteolysis by the ubiquitin/26S proteasome system (UPS). However, a possible role of UPS-dependent protein degradation in the regulation of key SAM TFs has not been thoroughly investigated. Here, we summarize recent evidence supporting a role for the UPS in SAM maintenance and function. We integrate this survey with an in silico analysis of publicly-available microarray databases which identified ubiquitin ligases that are expressed in specific areas within the SAM, suggesting that they may regulate or act downstream of meristem-specific factors.
基金supported by an Executive Programme of Scientific and Technological Cooperation between Italy and China 2010-2012the National Science Foundation of China 31030047
文摘When it was discovered in the 1970s as a ubiquitous protein, ubiquitin, a 76-aminoacid peptide, had no assigned function. It was not until later that ubiquitin was found to be a necessary cofactor in a vital cellular process: the degradation of proteins. Work by Avram Hershko, Aaron Ciechanover, and Irwin Rose (for which they received the 2004 Nobel Prize in Chemistry) showed that the covalent attachment of ubiquitin provide pro-teins with a tag that dispatches them to the proteasome, the main cell degradation machinery (Ciechanover 2012). Subsequent work, has revealed that ubiquitin belongs to a broader family of ubiquitin-like proteins that can modify not only protein stability, but also subcellular localization and function.
文摘Cullin-RING E3 ligases (CRLs) regulate different aspects of plant development and are activated by modification of their cullin subunit with the ubiquitin-like protein NEDD8 (NEural precursor cell expressed Developmentally Down-regulated 8) (neddylation) and deactivated by NEDD8 removal (deneddylation). The CONSTITUTIVELY PHOTOMORPHOGENIC9 (COP9) signalosome (CSN) acts as a molecular switch of CRLs activity by reverting their neddylation status, but its contribution to embryonic and early seedling development remains poorly characterized. Here, we analyzed the phenotypic defects of csn mutants and monitored the cullin deneddylation/neddylation ratio during embryonic and early seedling development. We show that while csn mutants can complete embryogenesis (albeit at a slower pace than wildtype) and are able to germinate (albeit at a reduced rate), they progressively lose meristem activity upon germination until they become unable to sustain growth. We also show that the majority of cullin proteins are progressively neddylated during the late stages of seed maturation and become deneddylated upon seed germination. This developmentally regulated shift in the cullin neddylation status is absent in csn mutants. We conclude that the CSN and its cullin deneddylation activity are required to sustain postembryonic meristem function in Arabidopsis.
文摘Since its discovery about 50 years ago,the ubiquitin-proteasome system(UPS)has not stopped to surprise us for its level of sophistication and complexity in achieving substrate-specific protein degradation(Vierstra,2009).At the heart of this system lies the concerted activity of three major classes of enzymes:ubiquitin activators(E1),ubiquitin conjugators(E2),and ubiquitin ligases(or E3).E3s,together with selected E2s,are responsible for promoting the formation of a ubiquitin chain on a specific protein substrate.