The retinoblastoma homolog RBR1 mediates localization of the repair protein RAD51 to DNA lesions in Arabidopsis

This is the authors' abstract. We don't add key points for this paper.

The retinoblastoma protein (Rb), which typically functions as a transcriptional repressor of E2F‐regulated genes, represents a major control hub of the cell cycle. Here, we show that loss of the Arabidopsis Rb homolog RETINOBLASTOMA‐RELATED 1 (RBR1) leads to cell death, especially upon exposure to genotoxic drugs such as the environmental toxin aluminum. While cell death can be suppressed by reduced cell‐proliferation rates, rbr1 mutant cells exhibit elevated levels of DNA lesions, indicating a direct role of RBR1 in the DNA‐damage response (DDR). Consistent with its role as a transcriptional repressor, we find that RBR1 directly binds to and represses key DDR genes such as RADIATION SENSITIVE 51 (RAD51), leaving it unclear why rbr1 mutants are hypersensitive to DNA damage. However, we find that RBR1 is also required for RAD51 localization to DNA lesions. We further show that RBR1 is itself targeted to DNA break sites in a CDKB1 activity‐dependent manner and partially co‐localizes with RAD51 at damage sites. Taken together, these results implicate RBR1 in the assembly of DNA‐bound repair complexes, in addition to its canonical function as a transcriptional regulator. The conserved retinoblastoma protein (Rb) functions as a transcriptional repressor of cell cycle and DNA‐damage response (DDR) genes, affecting also cell survival and DNA repair. Surprisingly, the Arabidopsis homolog RBR1 has an additional direct role at DNA break sites. In plants, the conserved transcriptional repressor of cell cycle and DNA repair genes has a surprising additional function directly at DNA break sites.