Mitochondrial Ribosomal RNAs of Triticum aestivum (Wheat): Sequence Analysis and Gene Organization

Abstract

The complicated restriction patterns of plant mtDNA suggest that it is unusually large and complex and possesses a type of sequence heterogeneity not found in the mtDNAs of other eukaryotes (Leaver and Gray 1982). As a result, our knowledge of the genetic function and organization of this important organelle genome is much less advanced than in the case of animal and fungal mtDNAs. As one approach to improving this situation, we are identifying and characterizing large restriction fragments encoding specific plant mitochondrial genes. Our work has centered on the mtDNA of wheat, Triticum aestivum, and has focused particularly on the rRNA genes.

DISCUSSION
Novel Arrangement of rRNA Genes in Wheat mtDNA
The mitochondrial 26S and 18S rRNAs of wheat differ from their cytosol counterparts in physicochemical properties (Cunningham and Gray 1977), T1 oligonucleotide fingerprints (Cunningham et al. 1976), and (in the case of the 18S rRNAs) T1 oligonucleotide catalogs (Bonen et al. 1977). Wheat mitochondrial 5S rRNA is also a distinct molecular species, as demonstrated by oligonucleotide cataloging (Cunningham et al. 1976) and, more recently, by determination of its complete primary sequence (Spencer et al. 1981).

Using Southern hybridization, we found that bulk mtRNA from wheat is specifically encoded by wheat mtDNA and shares no detectable sequence homology with wheat cytosol RNA (Bonen and Gray 1980). We also identified restriction fragments encoding the individual 26S, 18S, and 5S wheat mitochondrial rRNAs, as well as the mitochondrial tRNAs (Fig. 1). These represent the first documented plant mitochondrial genes. In view of...