Nuclear-encoded maturase required for splicing of group-II introns in mitochondria. Involved in NAD1 pre-mRNA processing and maturation of introns 1, 3 and 4. Necessary for mitochondrial biogenesis during early developmental stages. Essential for respiratory holocomplex I biogenesis in mitochondria. Altered mitochondrial morphology. Impaired seed germination (e.g. many dark and wrinkled seeds in siliques), seedling establishment and development (e.g. abnormal primary root elongation and vegetative growth). Defects in the processing and maturation of various mitochondrial NAD1 introns. Modified respiration phenotypes associated with complex I defects. Seed-specific deficiency in the regulation of carbohydrate metabolism. Small plants requiring sucrose-supplemented medium to survive. Belongs to the plant nuclear intron maturase (nMat) family.