|M.Sc Student||Yael Volovik|
|Subject||Identification and Characterization of USP Gene and its|
Products in Arabidopsis Plants
|Department||Department of Biology||Supervisor||Professor Emeritus Gepstein Shimon|
|Full Thesis text - in Hebrew|
Plant senescence is a highly regulated age-dependent deteriorative process at the cellular, tissue, organ, or organismal level, leading to death. Abiotic and biotic stresses can trigger and affect senescence to various extents. A comparison of gene expression patterns between stress responses and leaf senescence indicates that considerable crosstalk exists between these processes. Suppression subtractive hybridization carried out between senescing and mature leaves, revealed the up-regulation of gene that encodes to Universal stress protein (Usp) in Arabidopsis thaliana. In prokaryotic cells Usp mediates survival of cells starved for a wide variety of nutrients, exposed to toxic chemicals, and exposed to osmotic stress or UV light damage. Therefore the plant Usp protein is predicted to take part in stress responses similar to the bacterial Usp protein. However, no direct evidence is available regarding the regulatory role of the plant Usp in the context of stress tolerance. The bioinformatics analysis of amino acid sequence predicts binding of ATP to Arabidopsis Usp, the active structure is probably a homodimer and the gene promoter contains an ethylene responsive element. In this study, we identified and characterized the Universal stress protein gene and its products in Arabidopsis plants. We examined the phenotype and the altered development of different Usp mutants and wt plants during different abiotic stresses. Surprisingly, wt and Usp knock-out plants show high similarity during development and only slight difference in the senescence syndrome under most of the studied stress conditions. However, under cold treatment early inflorescence development in the knock-out plants was observed. The young Usp over-expression plants showed a delayed inflorescence development while the mature plants showed accelerated senescence under cold, dark and soil limitation treatments. Furthermore, Usp over-expressing plants produced relatively low biomass and twofold shorter roots as compared to wt and knock-out plants during growth on limited amount of soil. Usp gene expression in wt plants was strongly induced by cold treatment and under limited soil availability. GFP was used as a reporter gene, for monitoring promoter activity. Usp promoter activation was detected during all developmental stages and found to be restricted to photosynthetic tissues. Sub-cellular localization analysis revealed the cytosolic location of the Usp protein. Our results indicate that Usp protein might be involved in several processes related to the interactions of plant responses to different abiotic stresses and plant senescence. Our results may suggest similar regulatory role of the plant Usp to the prokariotic counterpart.