E2Fb and E2Fa transcription factors independently regulate the DNA damage response after UV-B exposure in Arabidopsis.

UV-B radiation affects plant growth inhibiting cell proliferation. This inhibition is in part controlled by the activity of transcription factors from the E2F family. In particular, the participation of E2Fc and E2Fe in UV-B responses in Arabidopsis plants was previously reported. However, E2Fa and E2Fb contribution to these processes has not been yet investigated. Thus, in this work, we provide evidence that, in Arabidopsis, both E2Fa and E2Fb control leaf size under UV-B conditions without participating in the repair of cyclobutane pyrimidine dimers in the DNA. Nevertheless, in UV-B exposed seedlings, E2Fa, but not E2Fb, regulates primary root elongation, cell proliferation and programmed cell death in the meristematic zone. Using e2fa mutants that overexpress E2Fb, we here demonstrate that the role of E2Fa in the roots cannot be replaced by E2Fb. Finally, our results show that E2Fa and E2Fb differentially regulate the expression of genes that activate the DNA damage response and cell cycle progression, both under conditions without UV-B and after exposure. Together, we here demonstrate that both E2Fa and E2Fb have different and non-redundant roles in developmental and DNA damage responses in Arabidopsis plants exposed to UV-B.