Non-CG DNA Methylation Regulates Root Stem Cell Niche Maintenance, Auxin Signaling, and ROS Homeostasis in Arabidopsis Under Cadmium Stress

Non-CG DNA methylation plays a critical role in regulating root development and stress responses in Arabidopsis thaliana under cadmium (Cd2+) exposure. We compared wild type (WT) plants with the ddc triple mutant (deficient in DRM1, DRM2, and CMT3) to assess how epigenetic modifications affect the root apical meristem (RAM) under 100 µM and 150 µM CdCl2 treatments. Cd2+ exposure led to RAM disorganization, reduced cortical cell number, and quiescent center (QC) cell loss in WT roots, while ddc mutants maintained meristem integrity and exhibited QC cell expansion. Auxin signaling, assessed via pDR5::GFP, was disrupted in WT roots at high Cd2+ levels but remained stable in ddc mutants. Similarly, WT roots showed elevated reactive oxygen species accumulation under stress, whereas ddc mutants displayed a reduced oxidative response. These results suggest that non-CG DNA methylation suppresses key regulators of stem cell maintenance, hormonal balance, and redox homeostasis during heavy metal stress. Loss of this methylation in the ddc mutant confers enhanced resilience to Cd2+ toxicity, highlighting an epigenetic mechanism underlying root stress adaptation.