The molecular biology of plant mitochondria

Advances in molecular biology and cell culture techniques have provided impetus to investigations of plant mitochondria. The organization of mitochondrial genomes has been intensely studied in maize, wheat, Oenothera, petunia, Brassica, and a few other species. These investigations have disclosed an unusually large and plastic genome, a unique organization based on a master chromosome and subgenomic chromosomes, and extra mitochondrial elements. The structural RNAs of plant mitochondria have furnished several new and exciting discoveries; they include the import of tRNAs into the mitochondria, editing of mRNAs, and the 'relaxed' nature of mitochondrial gene promoters. Cytoplasmic male sterility (CMS) is the most common mitochondrial gene mutation; it has therefore received extraordinary attention. Several mitochondrial gene mutations have been implicated in causing CMS, and attention is now focusing on the mechanism that causes pollen sterility, and how nuclear restorer genes interact with CMS genes to suppress sterility. Recently, a few other mitochondrial genes have been identified and characterized, which affect important mitochondrial fusions. Mitochondrial polypeptides, both nuclear and mitochondrial, are being studied to learn how they interact to form functional complexes, and how proteins are imported into the mitochondria. Protoplasm fusion experiments have provided a new and exciting means of recombining mtDNA that have generated interesting mutants, including CMS. Mitochondrial DNA replication is focusing on plasmid-like DNA and their origins of replication. Together, these studies have furnished insights into the origin of plant mitochondrial genomes and the relationships among plant species. This volume describes these many new and exciting findings on plant mitochondria.