Negative regulator of E2F transcription factors links cell cycle checkpoint and DNA damage repair.

DNA damage poses a serious threat to genome integrity and greatly affects growth and development. To maintain genome stability, all organisms have evolved elaborate DNA damage response mechanisms including activation of cell cycle checkpoints and DNA repair. Here, we show that the DNA repair protein SNI1, a subunit of the evolutionally conserved SMC5/6 complex, directly links these two processes in Arabidopsis SNI1 binds to the activation domains of E2F transcription factors, the key regulators of cell cycle progression, and represses their transcriptional activities. In turn, E2Fs activate the expression of SNI1, suggesting that E2Fs and SNI1 form a negative feedback loop. Genetically, overexpression of SNI1 suppresses the phenotypes of E2F-overexpressing plants, and loss of E2F function fully suppresses the sni1 mutant, indicating that SNI1 is necessary and sufficient to inhibit E2Fs. Altogether, our study revealed that SNI1 is a negative regulator of E2Fs and plays dual roles in DNA damage responses by linking cell cycle checkpoint and DNA repair.