http://hdl.handle.net/10362/3393 2013-05-22T03:31:43Z http://hdl.handle.net/10362/8584 Title: Insights into the role of almond CBF transcription factors in the environmental control of cold acclimation and dormancy break Authors: Barros, Pedro Miguel Abstract: Cold is an important environmental factor that may influence plant survival and productivity. It also plays a crucial role in the seasonal development of perennial plants by regulating the extent of (winter) dormancy and that of vegetative and reproductive growth periods. This aspect is particularly relevant in fruit trees, since it may directly impact fruit production. The Prunus genus includes economically relevant species, and the almond (Prunus dulcis Mill.) stands out for its high range of genetic variability, thus being an interesting model to study specific traits of agricultural interest. Considering that low temperature signalling pathways are still poorly understood in Prunus spp., this study aimed to identify and elucidate, in almonds, the function of members of the C-repeat Binding Factor (CBF) family of transcription factors (TFs) which are known to be relevant in the response to cold. Therefore, two CBF genes (PrdCBF1 and - 2) and their corresponding regulatory regions were cloned and sequenced in this species. Southern-blot analysis and further comparisons to the recently available peach genome revealed that the almond CBF family is composed of at least five members, located in close proximity in chromosome 5. In addition, a mapping analysis suggested an association between PrdCBFs and PrdDehydrin1 (PrdDHN1, a putative CBF target gene, involved in cold acclimation) to recently reported QTLs controlling chilling requirements and blooming time. However, further analyses are necessary to confirm this association.(...) Description: Dissertation presented to obtain the Ph.D degree in Biology 2012-03-01T00:00:00Z http://hdl.handle.net/10362/8560 Title: Novel transcription factors regulating the expression of the rice gene OsDREB1B Authors: Figueiredo, Duarte Dionísio Abstract: Environmental stresses are responsible for major losses in crop production worldwide. Due to an increasing world population, there is a higher demand for food, feed and fuel, which requires the development of new plant varieties with an increased yield, particularly under adverse environmental conditions. Transcription Factors (TFs) are promising candidates for plant improvement, since a single TF can modulate the expression of several genes. The AP2/ERF family of transcriptional regulators and, namely, the TFs belonging to the DREB1/CBF sub-family were described as major regulators of plant responses to abiotic stresses. Nevertheless, the transcriptional regulation of the genes coding for these TFs is still poorly understood. We focused our research on the rice gene OsDREB1B, whose gene expression had been previously described as responsive to abiotic stress, namely cold. Using semi-quantitative RT-PCR, we confirmed the cold-induction of this gene, but also observed that its response is different depending on the severity of the stress. Moreover, we observed that this gene is highly induced in response to drought stress in roots, and also in response to mechanical stress. Using the Yeast One-Hybrid system and the promoter of OsDREB1B as bait, we have screened a rice cold-induced cDNA expression library. Thereby we identified eight TFs as binding to OsDREB1B promoter: seven Zinc Finger TFs, of which three C2H2-type and four Zn Finger-Homeodomain (ZF-HD) TFs, as well as one bHLH TF, predicted as a putative Phytochrome Interacting Factor (PIF).(...) Description: Dissertation presented to obtain the Ph.D degree in Biology 2011-10-01T00:00:00Z http://hdl.handle.net/10362/6847 Title: Chromatin dynamics in Arbidopsis development: a live cell imaging approach Authors: Rosa, Stefanie Abstract: The proper development of multicellular organisms demands the distinct specification of a variety of specialized cell types. While this is one of the oldest statements of developmental genetics, how different patterns of gene expression are established in genetically identical cells and maintained during somatic cell divisions is still an active topic of research. Chromatin structure is now recognized to regulate gene activity playing a crucial role in cell differentiation and development. Chromatin is not simply a packaging tool but a dynamic entity that reflects the regulatory cues necessary to program appropriate cellular pathways. There are several ways by which chromatin structure can be remodelled. These mechanisms include DNA-methylation, post-translational modifications of histone proteins, histone variants and, nuclear localization. While the dynamic nature of chromatin structure has been previously described its biological function and repercussions on development are only now beginning to be revealed. In this work we used in vivo microscopy techniques to assess how different aspects of chromatin organization play a role on various aspects of development.(...) Description: Dissertation presented to obtain the Ph.D degree in Biology 2011-10-01T00:00:00Z http://hdl.handle.net/10362/6185 Title: Biochemistry of grape berries: post-genomics approaches to uncover the effects of water deficits on ripening Authors: Franscisco, Rita Abstract: Grapevine (Vitis vinifera L.) is one of the most important fruit crops worldwide. In Europe, high-quality wine producing areas are traditionally non-irrigated. However, irrigation has become a wide-spread agronomical practice to overcome the deleterious effects of drought, high temperature and high evaporative demand that vines can be exposed to during the growing season. This is particularly true in the Mediterranean area, where the foreseen scenario predicts that water deficit may become a limiting factor in wine production and quality. Paradoxically, the imposition of mild to moderate water deficit (WD) via e.g. water deficit irrigation has been regarded as an agronomical tool that manipulates berry sensory characteristics, while maintaining yield. Grape berries, which are described as non-climacteric fruits, undergo a complex biochemical suite of alterations during development and ripening that remain poorly understood, including the molecular events that control the onset of ripening. At harvest, grape berry quality is largely dependent on the sugar/acids balance within the berry flesh, and on phenolic compounds (e.g. flavonoids) in the grape skin, which contribute to wine colour, aroma and flavour.(...) Description: Dissertation presented to obtain the Ph.D degree in Biochemistry, Plant Physiology 2011-07-01T00:00:00Z