Proteasome-mediated turnover of arabidopsis MED25 is coupled to the activation of FLOWERING LOCUS T transcription

• Autores: Iñigo, S.; Giraldez, A.N.; Chory, J.; Cerdán, P.D.
• Año de publicación: 2012
• Idioma: inglés
• Tipo de recurso: artículo
• Fuente: Plant Physiol. 2012;160(3):1662-1673
• Materia: Arabidopsis protein; FT protein, Arabidopsis; nuclear protein; PFT1 protein, Arabidopsis; proteasome; ubiquitin protein ligase; amino acid sequence; Arabidopsis; article; chemistry; flower; gene expression regulation; gene silencing; genetic transcription; genetics; metabolism; molecular genetics; mutation; physiology; protein binding; protein degradation; protein stability; protein tertiary structure; Amino Acid Sequence; Arabidopsis; Arabidopsis Proteins; Flowers; Gene Expression Regulation, Plant; Gene Knockdown Techniques; Molecular Sequence Data; Mutation; Nuclear Proteins; Proteasome Endopeptidase Complex; Protein Binding; Protein Stability; Protein Structure, Tertiary; Proteolysis; Transcription, Genetic; Ubiquitin-Protein Ligases; Arabidopsis; Arabidopsis thaliana; Eukaryota; Saccharomyces cerevisiae
• Institución: Universidad Nacional de Buenos Aires. Facultad de Ciencias Exactas y Naturales

The Mediator complex is a greater than 1-megadalton complex, composed of about 30 subunits and found in most eukaryotes, whose main role is to transmit signals from DNA-bound transcription factors to RNA Polymerase II. The proteasome is emerging as an important regulator of transcription during both initiation and elongation. It is increasing the number of cases where the proteolysis of transcriptional activators by the proteasome activates their function. This counterintuitive phenomenon was called "activation by destruction." Here, we show that, in Arabidopsis (Arabidopsis thaliana), PHYTOCHROME AND FLOWERING TIME1 (PFT1), the MEDIATOR25 (MED25) subunit of the plant Mediator complex, is degraded by the proteasome and that proteasome-mediated PFT1 turnover is coupled to its role in stimulating the transcription of FLOWERING LOCUS T, the plant florigen, which is involved in the process of flowering induction. We further identify two novel RING-H2 proteins that target PFT1 for degradation. We show that MED25-BINDING RING-H2 PROTEIN1 (MBR1) and MBR2 bind to PFT1 in yeast (Saccharomyces cerevisiae) and in vitro, and they promote PFT1 degradation in vivo, in a RING-H2- dependent way, typical of E3 ubiquitin ligases. We further show that both MBR1 and MBR2 also promote flowering by PFT1- dependent and -independent mechanisms. Our findings extend the phenomenon of activation by destruction to a Mediator subunit, adding a new mechanism by which Mediator subunits may regulate downstream genes in specific pathways. Furthermore, we show that two novel RING-H2 proteins are involved in the destruction of PFT1, adding new players to this process in plants. © 2012 American Society of Plant Biologists.
Fil:Cerdán, P.D. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.