Mediates abscisic acid (ABA) signal transduction through mitochondrial retrograde regulation involving ABI4 during seed germination and seedling growth, and leading to the production of reactive oxygen species (ROS) by the alternative respiratory pathway (PubMed:26163700). Required for the maintenance of mitochondrial structure (PubMed:26163700). Highly expressed in germinating seeds and developing seedlings (PubMed:26163700). Also present at low levels in seedlings, roots, leaves, stems and flowers, and barely in siliques (PubMed:26163700). Decreased abscisic acid (ABA) sensitivity during seed germination and seedling growth (PubMed:26163700). Abnormal mitochondria extensively internally vacuolated and characterized by a reduced ABA-stimulated reactive oxygen species (ROS) production associated with the inhibition of ABA-induced AOX1a and ABI4 gene expression (PubMed:26163700). Belongs to the RMD1/sif2 family.