Ser-Gln sites of SOG1 are rapidly hyperphosphorylated in response to DNA double-strand breaks.

The DNA damage response system (DDR) is crucial in addressing DNA double-strand breaks (DSBs), which pose a severe threat to genomic integrity. The SOG1 transcription factor is a master regulator of the Arabidopsis thaliana DDR. We previously showed that hyperphosphorylation of five Ser-Gln sites of SOG1 is the molecular switch to activate the DDR. In this study, we determined that SOG1 is hyperphosphorylated within 20 minutes following DSB-inducing treatment, followed by activation of several SOG1 target genes. Using SOG1 phosphorylation mutants, we demonstrated that although the hyperphosphorylation sites remain unchanged over time, the amount of hyperphosphorylation gradually increases. These observations suggest that rapid SOG1 hyperphosphorylation is limited by the amount of active kinases.