RUG3 and ATM synergistically regulate the alternative splicing of mitochondrial nad2 and the DNA damage response in Arabidopsis thaliana

The root apical meristem (RAM) determines both RAM activity and the growth of roots. Plant roots are constantly exposed to adverse environmental stresses that can cause DNA damage or cell cycle arrest in the RAM; however, the mechanism linking root meristematic activity and RAM size to the DNA damage response (DDR) is unclear. Here, we demonstrate that a loss of function in RCC1/UVR8/GEF-Like 3 (RUG3) substantially augmented the DDR and produced a cell cycle arrest in the RAM in rug3 mutant, leading to root growth retardation. Furthermore, the mutation of RUG3 caused increased intracellular reactive oxygen species (ROS) levels, and ROS scavengers improved the observed cell cycle arrest and reduced RAM activity level in rug3 plants. Most importantly, we detected a physical interaction between RUG3 and ataxia telangiectasia mutated (ATM), a key regulator of the DDR, suggesting that they synergistically modulated the alternative splicing of nad2. Our findings reveal a novel synergistic effect of RUG3 and ATM on the regulation of mitochondrial function, redox homeostasis, and the DDR in the RAM, and outline a protective mechanism for DNA damage repair and the restoration of mitochondrial function that involves RUG3-mediated mitochondrial retrograde signaling and the activation of an ATM-mediated DDR pathway.