Studies on the control of cell size homeostasis, programmed cell death and gene expression in plant meristems

Plant development relies on the control of proliferation and differentiation of meristematic stem cells. The E2F transcription factors are key components of the RB/E2F pathway, which regulates the G1/S transition of the cell cycle and coordinates stem cell maintenance and differentiation. The E2Fs act as activator or repressors of E2F-dependent genes and their interplay controls cell cycle progression as well as endoreduplication and DNA repair. This thesis investigated in A. thaliana the role of activating E2Fs in two processes that are important for plant development: the emergence of floral buds at the inflorescence meristem flanks and the programmed cell death (PCD) that occurs in root meristems upon DNA damage. Overexpression of AtE2Fa in floral meristems did not alter the coordination between cell growth and DNA synthesis, and the constitutive overexpression of AtE2Fa or AtE2Fb did not change the PCD pattern induced by DNA damage in root meristems. However, co-expression with the dimerizing partner AtDPa might be necessary to promote the cell cycle progression, and possibly affect stem cell homeostasis and/or PCD in plant meristems. Additional work for this thesis concerned also the study of regulatory elements promoting the meristematic expression of the AtDRTS2 gene, previously shown to be negatively regulated by E2F factors, that results to be upregulated by a HEX site in the promoter and by the intron in the 5’ untranslated region