Plant Mitochondrial DNA: The Last Frontier

Abstract

“Unexpected, shocking, and true.”

P.P. Slonimski, May 17, 1981, describing the kind of results he hoped to see in mitochondrial research.

For most groups of organisms, we already have at least a fair understanding of the structure and information content of their genomes, even if we are only beginning to understand the way in which the information is expressed. Genes and sequences have been extensively characterized for the nucleus, chloroplast, and viruses in all types of eukaryotes, as well as for the chromosome, plasmids, and viruses of bacteria. The structure of the mitochondrial genome in some animals and fungi is known in exquisite detail; and for some protozoa, ciliates, and algae we think we know the relationship between genes and DNA molecules. The mitochondrial genome in plants is absurdly large (Table 1). Furthermore, there exists a sevenfold to eightfold variation in mitochondrial genome size within a single plant family, the cucurbits. (There is a nearly sixfold variation among yeasts [Clark-Walker et al. 1981], although the morphological and nutritional criteria used to designate a yeast may not assess true relatedness, whatever that really means.) Another puzzling feature of plant mtDNA in all species analyzed is that, when examined in the electron microscope (Kolodner and Tewari 1972; Synenki et al. 1978; Levings et al. 1979; Quetier and Vedel 1980; Sparks and Dale 1980), several to many different sizes of circular molecules are found, none of which even approaches 200 MD, the size of the smallest plant mitochondrial genome.

Why is the mitochondrial...