Target destabilization and chromatin remodelling are coordinated by CRL4-CDDD E3 ubiquitin ligases to repress photomorphogenesis in "Arabidopsis thaliana" (L.)

• Autores: Amr Abdelmotagaly Nassrallah
• Directores de la Tesis: Vicente Rubio Muñoz (dir. tes.)
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2017
• Idioma: español
• Número de páginas: 134
• Tribunal Calificador de la Tesis: Crisanto Gutiérrez Armenta (presid.), Cristina Ortega Villasante (secret.), Salomé Prat (voc.), Frédy Barneche (voc.), José Antonio Jarillo Quiroga (voc.)
• Enlaces
  • Tesis en acceso abierto en: Biblos-e Archivo
• Resumen

  • Plants adapt their growth and development according to the environmental light information. Light signals are perceived, processed and integrated through highly structured intracellular networks. These rely on tight transcription coordination, achieved by chromatin remodeling synchronized with transcription factor binding to DNA, and precise control of their activity and abundance. Control of transcription factor levels is mediated, in many cases, by specific ubiquitination and degradation at the 26S proteasome. Protein target ubiquitination is mediated, among others, by Cullin 4 RING E3 ubiquitin Ligases (CRL4s) associated to COP10-DDB1-DET1-DDA1 (CDDD) complexes. Recently, we have characterized DDA1 as a novel type of substrate adaptor for CRL4-CDDD (Irigoyen et al., 2014). In a yeast two hybrid screening, we found SGF11 as a DDA1 interactor. SGF11 is a member of the deubiquitination module (DUBm), which in yeast and animals has been shown to be part of the SAGA (SPT-ADA-GCN5-Acetyltransferase) complex. The role of DUBm on H2Bub (ubiquitinated histone 2B) deubiquitination to promote transcription elongation is well described in yeast, Drosophila and mammals. However, in plants, the function of DUBm remains unexplored.

    In this study, we show that the Arabidopsis DUBm is composed of at least three subunits: SGF11, ENY2 and UBP22, with UBP22 as the H2B ubiquitin‐specific protease. According to their predicted function, loss of SGF11 or UBP22 function increased the abundance of H2Bub. DUBm function is likely controlled by the light conditions since all three components were destabilized under dark conditions. We demonstrate that SGF11 degradation involves DET1 function, suggesting that upon recognition of SGF11 by DDA1, CRL4-CDDD E3 ligases promote its ubiquitination and proteasomal degradation. In agreement with this notion, CRL4-CDDD function alters global H2Bub abundance.

    Phenotypic characterization of sgf11 and ubp22 mutants showed that the DUBm also plays a role in the control of plant responses to light. Thus, both sgf11 and ubp22 mutations synergistically enhanced the detiolated phenotype of det1-1 plants under dark conditions, whereas SGF11 overexpression ameliorated det1-1 photomorphogenic defects. Photomorphogenic defects correlated, respectively, with increased or reduced abundance of HY5, a positive regulator of light responses whose accumulation is repressed by CRL4-CDDD E3 ligases. Altogether, our findings indicate that the DUBm acts as a negative regulator of photomorphogenesis, and point to a role for H2B deubiquitination in this process. We propose a model in which de DUBm facilitates recruitment of CRL4-CDDD complexes to light responsive promoter regions in order to increase recognition and targeted degradation of HY5 to repress photomorphogenic developmen