Defective splicing of the first nad4 intron is associated with lack of several complex I subunits in the Nicotiana sylvestris NMS1 nuclear mutant

In this work, we provide evidence for the existence of a nuclear factor inv olved in the splicing of a specific mitochondrial intron in higher plants. In the Nicotiana sylvestris nuclear NMS1 mutant, defective in both vegetati ve and reproductive development, the first intron of the nad4 transcript en coding the complex I NAD4 subunit is not removed, whatever the tissue analy sed. Transcript patterns of other standard mitochondrial genes are not affe cted in NMS1. However, numerous polypeptides are missing in two-dimensional in organello mitochondrial protein synthesis patterns and several nuclear and mitochondrial complex I subunits are present in trace amounts. This ind icates that translational or post-translational steps in the synthesis of o ther mitochondrial proteins are affected. All of these defects co-segregate d with the abnormal phenotype in the offspring of a NMS1 x wild-type cross, showing that they are controlled by the same nuclear gene (MS1) or tightly linked loci. Such a complex situation has been described in chloroplasts a nd mitochondria of fungi, but never in higher plant mitochondria.