Nuclear-encoded maturase required for splicing of group-II introns in mitochondria (PubMed:16621844, PubMed:22429648). Necessary for mitochondrial biogenesis during early developmental stages (PubMed:22429648). Involved in the splicing of mitochondrial NAD4 transcripts (PubMed:16621844). Required for trans-splicing of NAD1 intron 1 and also functions in cis-splicing of NAD2 intron 1 and NAD4 intron 2 (PubMed:22429648). Required for the regulation of fundamental metabolic pathways such as amino acid metabolism, triacylglycerol degradation and polysaccharide synthesis (cellulose and starch) during the early stage of plant growth (PubMed:16621844). Implicated in stress responses (PubMed:22429648). Expressed at low levels in seedlings and accumulates in adult plants. Slightly slower growth rate. Impaired splicing of mitochondrial group-II introns-containing NAD4 transcript and altered carbon metabolism. Altered fundamental metabolic pathways including amino acid metabolism, triacylglycerol degradation and polysaccharide synthesis (cellulose and starch) during the early stage of plant growth. Reduced sensitivity to 2,6-dichlorobenzonitrile (DCB) and isoxaben treatments, cellulose biosynthesis inhibitors. Increased sensitivity to sugar concentration of the medium (PubMed:16621844). Retarded growth and developmental phenotypes (e.g. reduced germination efficiency, altered primary root elongation and impaired vegetative growth and fertility) and modified respiration activities. Altered stress responses characterized by high levels accumulation of reactive oxygen species (ROS) and darker and reddish leaves. Abnormal mitochondrial morphology (PubMed:22429648). Belongs to the plant nuclear intron maturase (nMat) family.