Novel transcription factors regulating the expression of the rice gene OsDREB1B

Dissertation presented to obtain the Ph.D degree in Biology

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).(...)

Financial support from Fundação para a Ciência e Tecnologia and Fundo Social Europeu in the scope of Quadro Comunitário de Apoio through the PhD fellowship SFRH/BD/29258/2006 and research projects POCI/BIA-BCM/56063/2004 and PTDC/BIA_BCM/099836/2008. Part of the in vitro co-immunoprecipitation work in Chapter 4 was funded by National Institutes of Health Grant GM-47475, Department of Energy Grant DEFG03-87ER13742, and USDA Agricultural Research Service Current Research Information System Grant 5335-21000-027-00D, through Peter H. Quail.