Characterization of barley albina and xanthia mutants and analysis of gene expression associated with chloroplast development and cold acclimation

Chloroplasts are the light-harvesting, carbon-fixing, oxygen-producing energy source of the photosynthetic eukaryotic cells. The chloroplast has a central role for plant life therefore the study of chloroplast functioning and chloroplast dependent metabolism is fundamental. Plastids, having their own genomes, code only for a little part of the chloroplast localized proteins, thus depend, for their functioning, from nuclear codified genes. Moreover higher plants, during their life cycle, have to grow, develop and cope with both abiotic and biotic stress. This means that, during normal growth and as an environmental factor occur, a coordinated expression of nuclear and chloroplast genome is necessary for the assembling, functioning and reprogramming of the organelles and, consequently of the whole cell. Photosynthesis is primarily affected by environmental changes such as light intensity and quality or temperature mediated changes in membrane fluidity. Cold stress is a major environmental factor limiting plants geographical distribution and productivity; exposure to cold in presence of light leads to an excess of adsorbed energy. Photosynthesis itself functions as a sensor of the imbalance between available light and metabolic activity, and regulates the photophysical, photochemical and metabolic process of the chloroplast. It is thus clear that photosynthesis interacts with other processes during cold acclimation involving cross-talk between photosynthetic redox, cold acclimation and sugar signaling pathways to regulate plant acclimation to low temperature. External and internal signals, thus, flow in from various pathways and contribute to modulate gene expression, shaping the downstream response and modifying the plant performance to best exploit environmental conditions. The objective of this thesis was to evaluate the influence of the chloroplast on nuclear gene expression and its role in modifying the cell metabolism either during normal growth condition or during cold acclimation. To this purpose four barley albina/xantha mutants, having plastids blocked at subsequent stages of chloroplast development, were analyzed. Furthermore a study on some cold responsive mechanisms whose expression is independent from the chloroplast was also carried on. The oncoming of whole transcriptome approach, based on array technology, coupled to the use of mutants and accompanied with a deeper investigation of keys metabolic pathways resulted in a new insight of chloroplast effects on nuclear genome.