Similar but different: unveiling the roles of atypical E2Fd/DEL2 and E2Ff/DEL3 transcription factors during the DNA damage response after UV-B exposure in Arabidopsis.

Ultraviolet-B (UV-B) radiation is the most energetic part of the solar spectra, and at high intensities inhibits plant growth by repressing cell proliferation. Inhibition of cell division after DNA damage is partly controlled by transcription factors (TFs) from the E2F family. We have previously shown that canonical E2F TFs regulate UV-B responses, and the role of the non-canonical DEL1/E2Fe in these responses was also demonstrated. Nevertheless, the contribution of the atypical DEL2/E2Fd and DEL3/E2Ff in the DNA damage response (DDR) after UV-B exposure in Arabidopsis plants has not been investigated. Therefore, in this work, we show that, despite having high sequence similarities, E2Fd and E2Ff show differences in expression patterns depending on the developmental stage and organ of the plants. Besides, E2Fd, but not E2Ff, controls leaf size under UV-B conditions and regulates DNA damage accumulation in UV-B exposed leaves by controlling the expression of the UVR2 photolyase. However, in UV-B-exposed seedlings, neither E2Fd nor E2Ff regulate primary root elongation or programmed cell death in the meristematic zone. Finally, we here show that E2Fd differentially controls the expression of DDR and cell cycle genes, either or both under conditions without UV-B and after exposure. Together, we provide evidence that E2Fd, but not E2Ff, participates in DDRs in leaves of Arabidopsis plants exposed to UV-B, while neither of them has a role in DDR in the roots.