Regulates DNA damage response (DDR) synergistically with ATM (PubMed:28262819). Together with ATM, involved in the splicing of the ND2/NAD2 mRNA (PubMed:21623974, PubMed:28262819). Required for the accumulation of mitochondrial respiratory chain complex I (PubMed:21623974). Negative regulator of plant responses to abscisic acid (ABA) (PubMed:28613105). May have a pivotal role in vegetative growth and the phase transition from vegetative to reproductive growth (PubMed:28262819). Interacts with ATM. Mostly expressed in roots and rosette leaves of young seedlings, and, to a lower extent, in the flowers and siliques of mature plants. Preferentially expressed in the vascular tissues. Reduced by methyl methanesulfonate (MMS) treatment. Delayed development including late seed germination and cotyledon greening as well as delayed flowering time, short roots and mildly curled rosette leaves in long-day conditions, thus leading to extended life span (PubMed:21623974, PubMed:28262819). Reduced root length is associated with a smaller size of the root apical meristem (RAM) due to a decreased cortical cell number (PubMed:28262819). Reduced mitochondrial complex I abundance and activity. Lower levels of complex I subunits NAD9 and FRO1, but induced expression of the alternative oxidase (AOX) (PubMed:21623974). Reduced splicing efficiencies for both the trans-spliced intron 2 and the cis-spliced intron 3 of ND2/NAD2 mRNA (PubMed:21623974, PubMed:28262819). Increased capacities for import of nucleus-encoded mitochondrial proteins into the organelle and moderately increased mitochondrial transcript levels (PubMed:21623974). Increased plant responses to abscisic acid (ABA) during seed germination and post-germinative growth (PubMed:28613105). Augmented DNA damage response (DDR) associated with increased intracellular reactive oxygen species (ROS) levels and cell cycle arrest at the G2/M checkpoint in the root apical meristem (RAM), thus leading to root growth retardation (PubMed:28262819).