Mitochondrial Genes and Cytoplasmically Inherited Variation in Higher Plants

Abstract

Eukaryotic cells contain interdependent genetic and protein-synthesizing systems in the nucleus and cytoplasm and in mitochondria. Green plants are unique in that they contain, in addition, a third such system in the plastids. In the case of the chloroplast genome, detailed restriction maps of chloroplast DNA from several plant species are available, and the locations and sequences of chloroplast-specific rRNAs, tRNAs, and several of the major protein-coding genes are known (Bedbrook and Koldner 1979).

In contrast, we know little of the organization, information content, and function of mtDNA in green plants. In recent years, however, there has been renewed interest in the role of cytoplasmic genes in plant development and crop improvement. This is perhaps not surprising, since the mitochondrion and chloroplast are the major sites of energy conversion and presumably play a vital role in determining the vigor and productivity of the whole plant.

Our detailed knowledge of the mitochondrial genetic system has been acquired mainly from studies with ascomycete and animal mitochondria. Genetic analysis of the mtDNA in higher plants is much more difficult than in yeast, where the impressive progress in mapping genes localized in mtDNA has in large part been made possible by the availability of a wide variety of mutants whose characteristic phenotypes results from mutations in mtDNA. This, coupled with the unique ability of yeast to survive without functional mitochondria, has allowed the study of mutations that interfere with mitochondrial biogenesis and function. In contrast, many mutations in plant mtDNA may be lethal, and...