STRUCTURE AND FUNCTION OF THE HIGHER-PLANT MITOCHONDRIAL GENOME

This chapter reviews structure and function of the higher plant mitochondrial genomes. The high frequency of recombination is considered the most unique feature of higher plant mitochondrial genomes. The three mutant phenotypes attributed to mitochondrial genomes include male sterility, sensitivity to a fungal toxin, and abnormal growth with striping of leaves. Mitochondrial mutations causing male sterility are relatively benign defects, resulting primarily in the prevention of normal reproductive development. The first two mitochondrial loci, which encode cytoplasmic male sterility (CMS), were in maize CMS-T and in Petunia. Both these loci contain abnormal genes derived from multiple recombination events. in both the cases, the abnormal genes are upstream of apparently normal mitochondrial genes. Early characterization of plant mtDNA by physical methods reveals that the buoyant density of mtDNA and therefore the G+C values are relatively constant in widely divergent species. The similarity in GC content is in contrast to the kinetic complexity of mitochondrial genomes. Relatively abundant small nucleic acid molecules (linear and circular DNA and double-stranded RNAs) have been observed in mitochondria of several plant species. © 1992 Academic Press Inc.