Studies on the meristematic and e2f-dependent gene expression in Arabidopsis thaliana plants

This thesis focuses on two studies concerning some aspects of cell proliferation and development in plants. The first part describes additional results completing the characterization of the three AtDRTS genes of Arabidopsis thaliana, which code for bifunctional dihydrofolate reductase/thymidylate synthase enzymes whose activity is fundamental in proliferating cells. These analyses allowed the identification of different AtDRTS isoforms, some of which are expected to encode monofunctional dihydrofolate reductases, and revealed common and distinctive patterns of expressions that suggest redundant as well as specific roles of the three genes. The characterization of the AtDRTS promoters revealed distinctive features and an E2F-dependent repression of both AtDRTS2 and AtDRTS3. Moreover, evidence has been obtained that the first intron of AtDRTS2 and the intragenic region containing the second intron of AtDRTS1 play crucial roles in the control of promoter activity in the root meristems. Moreover, analyses conducted within this thesis revealed that the first intron of AtDRTS2 is able to confer strong activity in root apical meristem to a non-meristematic plant promoter. The second part of this thesis describes studies conducted to evaluate the regulation in planta of a synthetic promoter, named E2F-Minimal-35S (EM35S), that is expected to be specifically activated by E2F factors, important regulators of cell cycle progression in both plants and animals. Transgenic Arabidopsis plants harboring a construct in which the synthetic promoter drives the expression of the GUS reporter allowed the detection of the E2F-dependent transcriptional activation in different tissues. Moreover, these plants have been used to investigate the cell cycle-dependent regulation of the EM35S promoter activity as well as the effects of epigenetic mechanisms and phosphorylation/dephosphorylation events.