Impaired DNA Repair and Oxidative Stress Imbalance Drive UV-C Sensitivity in fas1

Ultraviolet (UV-C) irradiation induces severe DNA damage, oxidative stress, and chloroplast dysfunction in plants. Here, we show that the Arabidopsis thaliana mutant fas1, defective in the CAF-1 histone chaperone complex that deposits histones H3.1/ H4 during DNA replication and repair, displays profound hypersensitivity to UV-C. Analysis of differentially expressed genes revealed that fas1 mutants show deregulation of redox homeostasis genes together with altered oxidative stress response. These findings demonstrate that CAF-1 is required to coordinate DNA repair, ROS balance, and chloroplast stability during UV-induced genotoxic stress.