Exploring the Roles of DPa and DPb Proteins after UV-B exposure in Arabidopsis thaliana plants

LUCIO SIMONELLI; MARIA LUJAN SHERIDAN; PAULA CASATI

Congreso; XXXIV Reunión Argentina de Fisiología Vegetal; 2023

Plants are exposed to UV-B radiation, which at high intensities can damage lipids, proteins, and DNA, leading to growth inhibition. The G1/S transition is a critical checkpoint in cell division, this transition is regulated by the Retinoblastoma (Rb) protein and E2F transcription factors (TFs). Arabidopsis have 6 E2Fs, 3 (E2Fa-c) require DP proteins for their activity, while E2Fd-f act independently of these proteins. Previous studies using e2fa-c mutants demonstrated that these TF have important roles in various responses to UV-B radiation; these mutants showed altered cell division, DNA repair, and differentiation pathways after irradiation.Despite the participation of the typical E2F TFs in the responses to UV-B were previously described, the roles of DPa and DPb in these responses have not been analyzed. Thus, we used simple and double dpa and/or dpb mutants to understand their role in DNA damage accumulation and cell proliferation in plants exposed to UV-B. The single and double mutants showed no significant difference in root development compared to the wild type (WT) under control and UV-B conditions, with all irradiated seedlings showing a similar decrease in primary root elongation after exposure. Confocal microscopy showed that both dpa2 and dpb1 mutants exhibited a similar primary root meristematic zone (MZ) as WT seedlings, both under control conditions and after UV-B irradiation, while root meristems from dpa2xdpb1 mutants had a larger meristematic zone with longer and more cells than those from WT seedlings. Together, these results suggest that, in the double mutants, the increase in the MZ size could be compensated by a decrease in the elongation and/or differentiation zones, as primary roots from all lines had a similar length.Furthermore, all mutants exhibited a lower number of dead cells in the primary roots after a UV-B treatment than roots from WT plants, demonstrating the importance of DPa and DPb proteins regulating programmed cell death. Finally, DNA damage accumulation in UV-B exposed plants was studied. While dpa2 and dpb1 single mutants showed similar DNA damage as WT plants, dpa2xdpb1 exhibited increased damage. These results suggest that there is functional redundancy between DPa and DPb during DNA repair.In conclusion, both DPa and DPb participate in UV-B responses in Arabidopsis. Both proteins play redundant roles in DNA damage accumulation, and they are also involved in cell proliferation, plant growth, and programmed cell death in response to UV-B exposure.