Abstract
We previously isolated Arabidopsis sog1-1 (suppressor of gamma response) as a suppressor mutant capable of overcoming the ionizing radiation (IR)-sensitive phenotype of xpf-2 mutant plants. Although genes associated with cell-cycle progression are suppressed by IR in wild-type plants, this suppression was impaired in sog1-1 mutants, showing that cell-cycle is not correctly arrested in response to IR. Furthermore, genome instability was increased in sog1-1 mutants after IR treatment. These results suggest that SOG1 plays a role in DNA damage checkpoint.
SOG1 encodes a putative transcription factor belonging to the NAC protein family. Hundreds of genes are upregulated within 1.5 hr of IR treatment in wild-type Arabidopsis. Surprisingly, almost every gene was not induced in sog1-1 mutants, indicating that SOG1 is a master transcription factor that governs transcriptional response to IR. To understand the functional role of SOG1 in plant development, we examined its expression pattern using a SOG1-GUS fusion construct under the control of the SOG1 promoter. SOG1-GUS staining was observed in the apical meristems of shoots and roots, and in lateral root primordia, indicating that the function of SOG1 is important for actively dividing cells. These studies reveal a new aspect of the plant's damage checkpoint system, which is to direct the flow of information through a central regulatory transcription factor, SOG1, in response to genomic stress.
