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Descripción
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| During the first stages of post-embryonic development, the shoot apical meristem (SAM) gives rise to vegetative organs and once the SAM acquires competence, it undergoes the floral transition and begins the production of reproductive organs with specific patterns of cell differentiation. The timing of the floral transition is controlled by a combination of endogenous and environmental signals generating the characteristic plasticity that allows plant species to optimize their adaptation to the environment. Screens for flowering-time mutants in rapidflowering backgrounds have been effective in genetically defining several pathways that regulate flowering time, including the photoperiod, the autonomous and the vernalization pathways. In this work, we describe the isolation and molecular characterization of early in short days7-1 (esd7-1), a viable mutation displaying early flowering phenotype and pleiotropic defects in both vegetative and reproductive development. Thus, esd7-1 mutations causes early flowering independently of photoperiod, shortened inflorescence internodes and altered leaf and root development. Beside, the epidermal cells of leaves revealed that esd7 mutant possesses fewer cells than the wild type plants and the RAM were found to exhibit an altered disposition that might correlate with the abnormal expression pattern of marker genes. EARLY IN SHORT DAYS 7 (ESD7) gene encodes the catalytic subunit of the DNA polymerase epsilon (¿), AtPOL2a. This enzyme has been involved in other organisms in diverse processes such as DNA replication, DNA repair, chromatin remodelling and transcriptional silencing. esd7-1 was a hypomorphic allele whereas KO alleles displayed an embryo-lethal phenotype, suggesting that this gene is essential for the proper embryo development and viability. ESD7/AtPOL2a is expressed ubiquitously at low levels in all the tissues analyzed and its expression is upregulated by genotoxic stress. In fact, the mutant showed higher sensitivity to these agents than wild type plants and altered expression of genes involved in DNA repair mechanisms by homologous recombination such as RAD51, BRCA1, BRCA2 and GR1. esd7 early flowering phenotype requires functional FT and SOC1 proteins and might be related to the deregulation of AG and AG-like gene expression found in esd7. Loci involved in the modulation of the chromatin structure dynamic, such as TFL2 and EBS, which also negatively regulate FT expression, were found to interact genetically with ESD7. In fact, the carboxy terminus of ESD7 interacted with TFL2 in vitro. Moreover, fasciata2 (fas2) mutations suppressed esd7 early flowering phenotype and INCURVATA 2 (ICU2) was found to be epistatic to ESD7. Discrete regions of the chromatin of FT and AG loci were enriched in acetylated H3 and trimethylated H3K4 activating epigenetic marks in the esd7-1 mutant. We concluded that ESD7, in addition to its role in DNA replication and DNA repair mechanisms, serves a crucial function in chromatinmaintaining gene silencing in plants, and reinforce the involvement of chromatin remodelling in the floral transition control. | |
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Internacional
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Tipo de Tesis
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Doctoral |
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Calificación
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Sobresaliente cum laude |
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Fecha
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