HOMEODOMAIN GLABROUS 4 promotes DNA damage-induced stem cell death in Arabidopsis thaliana roots

Maintenance of genomic integrity is essential for sustained cell proliferation in plant meristems. In Arabidopsis thaliana, the DNA damage response is controlled by the transcription factor SUPPRESSOR OF GAMMA RESPONSE 1 (SOG1), which regulates the expression of genes involved in DNA repair, cell cycle arrest, and stem cell death. However, the mechanisms underlying the correlation between DNA damage signaling and the regulation of stem cell death remain incompletely understood. In this study, we identified HOMEODOMAIN GLABROUS 4 (HDG4), a member of the homeodomain leucine zipper class IV transcription factor family, as a factor promoting DNA damage-induced stem cell death in the root meristem. Reporter analyses revealed that HDG4 expression is strongly induced in the root meristem following DNA damage. Moreover, genetic analysis revealed that DNA damage-induced stem cell death was significantly suppressed in the hdg4 mutant. The DNA damage-associated repression of auxin efflux carriers, PIN-FORMED (PIN), was partially alleviated in the hdg4 mutant. Consistent with this observation, the reduction in the auxin response in the root tip after DNA damage was attenuated in the hdg4 mutant. These results indicate that HDG4 contributes to the suppression of auxin transport toward the root tip during DNA damage response, and reveal a transcriptional mechanism linking genome integrity surveillance with hormonal regulation of stem cell death.