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
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.
