Insights into the regulation of reproductive development in Arabidopsis thaliana by the chromatin protein EBS

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Biología. Fecha de lectura: 06-11-2018Esta tesis tiene embargado el acceso al texto completo hasta el 06-05-2020Plant development progresses through distinct phases including embryonic, vegetative, and reproductive, eventually followed by seed set and senescence. These developmental stages are characterized by specific spatiotemporal patterns of gene expression so that selective activation or silencing of genes enables differentiation of characteristic cell types for each developmental stage. The developmental switch from vegetative to reproductive growth is one of the most dramatic changes in plant’s life, as successful reproduction requires not only the formation of the flowers, but also the change of plant architecture traits like internode elongation and branching to ensure the balance between optimal number of flowers and production of resources through photosynthesis. For that reason, the different phases of plant reproductive development are tightly regulated. Chromatin organization is a key element in the regulation of gene expression and is responsible for on/off transcriptional states of genes in eukaryotic organisms. The Arabidopsis locus EARLY BOLTING IN SHORT DAYS (EBS) encodes a transcriptional regulator that is required for repression of the floral integrator gene FT. In addition, EBS specifically recognizes H3K4me2/3 marks through the PHD domain, and mutations in the EBS gene cause an increase in the levels of histone H3 acetylation in the regulatory sequences of FT. Furthermore, EBS binds regulatory regions of this master gene of flowering and interacts with histone deacetylases such as HDA6. Altogether these observations indicate that EBS is crucial to maintain a transcriptionally inactive state in the chromatin of its target genes. In this work we have explored the role of EBS in the control of additional aspects of reproductive development in Arabidopsis. Following a detailed phenotypic analysis of the ebs mutant, we have unveiled the involvement of EBS in plant architecture control after bolting, floral meristem maintenance and function, as well as flower development and floral organ patterning. We have also characterized the impact of environmental conditions (temperature, photoperiod) on the expressivity of these traits. In addition, we have determined changes in Arabidopsis transcriptome that occur in the absence of a functional EBS protein, and propose FT, FLC, AGL24, LFY, TFL1 and SEP3 as candidate genes to mediate the phenotypic alterations observed in ebs. We have also analyzed the impact of EBS on chromatin features of these loci and concluded that the mechanism of FT repression mediated by EBS could also operate at least in some of these genes. However, additional mechanisms mediated by EBS regulating chromatin compaction and accessibility may occur. Finally, we have carried out genetic analyses to understand possible interactions between those candidates and EBS, making possible to elaborate working hypotheses to explain how these genes could mediate the effect of EBS on the control of inflorescence and flower production in Arabidopsis. Altogether, the data presented in this work reveal that EBS represents a central hub in the control of reproductive growth, orchestrating the expression of different genes that need to be coordinately expressed to enable successful completion of the Arabidopsis developmental plan and ensure adequate production of fruits and seeds to safeguard efficient transmission of genetic information to the following generatio