Organelle Heredity

The compartmentation of genetic information is a fundamental feature of the eukaryotic cell. The metabolic capacity of a eukaryotic (plant) cell and the steps leading to it are overwhelmingly an endeavour of a joint genetic cooperation between nucleus/cytosol, plastids, and mitochondria. Alter ation of the genetic material in anyone of these compartments or exchange of organelles between species can seriously affect harmoniously balanced growth of an organism. Although the biological significance of this genetic design has been vividly evident since the discovery of non-Mendelian inheritance by Baur and Correns at the beginning of this century, and became indisputable in principle after Renner's work on interspecific nuclear/plastid hybrids (summarized in his classical article in 1934), studies on the genetics of organelles have long suffered from the lack of respectabil ity. Non-Mendelian inheritance was considered a research sideline~ifnot a freak~by most geneticists, which becomes evident when one consults common textbooks. For instance, these have usually impeccable accounts of photosynthetic and respiratory energy conversion in chloroplasts and mitochondria, of metabolism and global circulation of the biological key elements C, N, and S, as well as of the organization, maintenance, and function of nuclear genetic information. In contrast, the heredity and molecular biology of organelles are generally treated as an adjunct, and neither goes as far as to describe the impact of the integrated genetic system.

Cytoplasmic Genes and Organelles is about cytoplasmic genes: what they are and what they do. It applies the concepts and methods of cytoplasmic genetics to the problems of cell and molecular biology to which they can uniquely contribute. It shows geneticists the many attractive problems in this area awaiting their attention; cell biologists and biochemists the usefulness of cytoplasmic genetic analysis in their endeavors; and students the potential power of an integrated experimental approach using cytoplasmic genes together with the more conventional tools of biochemistry and electron microscopy in the investigation of organelle biogenesis. The book treats the following aspects of cytoplasmic genetic systems: (1) the properties of cytoplasmic DNA; (2) the genetic analysis of cytoplasmic systems; and (3) the functions of cytoplasmic genes in organelle biogenesis. The opening chapter summarizes the principal findings to provide readers with a bird's eye view of the subject. Subsequent chapters cover topics such as cytoplastmic DNAs; cytoplasmic genes in Chlamydomonas; mitochondrial genetics of yeast; cytoplasmic genes in higher plants; the role of mitochondrial genes in mitochondrial biogenesis; and cytoplasmic genes and cell heredity.

Mitochondria and chloroplasts are eukaryotic organelles that evolved from bacterial ancestors and harbor their own genomes. The gene products of these genomes work in concert with those of the nuclear genome to ensure proper organelle metabolism and biogenesis. This book explores the forces that have shaped the evolution of organelle genomes and the expression of the genes encoded by them. Some striking examples of trends in organelle evolution explored here are the reduction in genome size and gene coding content observed in most lineages, the complete loss of organelle DNA in certain lineages, and the unusual modes of gene expression that have emerged, such as the extensive and essential mRNA editing that occurs in plant mitochondria and chloroplasts. This book places particular emphasis on the current techniques used to study the evolution of organelle genomes and gene expression.

Chloroplasts in photosynthetic organisms and mitochondria in a vast majority of eukaryotes, contain part of the genetic material of a eukaryotic cell. The organisation and inheritance patterns of this organellar DNA are quite different to that of nuclear DNA. Present-day chloroplast and mitochondrial genomes contain only a few dozen genes. Nevertheless, these organelles harbor several thousand proteins, the vast majority of them encoded by the nucleus. As a result, the expression of nuclear and organelle genomes has to be very precisely coordinated.

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These editors provide a stimulating survey of the ways in which mitochondria, plastids, and other cellular organelles replicate. The orderly division and segregation of these organelles is essential for the survival of all eukaryotes and is therefore a topic of importance to a wide range of biologists, from geneticists, via physiologists, to molecular biologists. The first part of the volume examines the mechanism, regulation, and consequences of organelle segregation and division as studied in plant and animal cells. The second part compares the replication of DNA in eukaryote organelles with bacterial processes. Reviews range from a comparative study of DNA polymerases to the possible mechanisms ensuring DNA segregation.