Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 10/1/1998
Publication Date: N/A
Citation: Interpretive Summary: Hybrid vigor, heterosis, in higher plants is a major factor in much of the world's production of horticultural and field crops. To exploit heterosis, efficient methods are needed to produce male-sterile plants as seed parents for the production of F1 hybrid seed. In this chapter we review current knowledge of nuclear and cytoplasmic genes that cause male sterility. A large number of nuclear genes are involved in the development of anthers and pollen, and mutants of these genes often confer male sterility. Several are under development as potentially useful in hybrid seed production. Cytoplasmic male sterility (cms) is associated with unusual mitochondrial genes, which in most cases result from recombinational events. Recent data indicate that cms-associated genes can share substantial sequence similarity, within Brassica species, or even between sorghum and rice. Nuclear fertility restorer genes, required to produce fertile F1 hybrid plants, can be tightly linked to normal genes that influence mitochondrial gene expression, or could be normal counterparts of defective genes, i.e., alleles. Transgenic approaches to engineering male sterility and fertility restoration system are under development, utilizing anther or pollen-specific promoters for expression only during pollen formation. The chapter should be of value to breeders, geneticists, and biologists concerned with nuclear-mitochondrial interactions.
Technical Abstract: Under normal conditions, plants undergo a life cycle that consists of an alternating vegetative sporophytic generation and a much reduced sexual gametophytic generation. During these cycles, seeds germinate, the mature plant organs differentiate and finally vegetative growth terminates in flower formation, which in principle leads to sepals, petals, anthers and carpels. Male sterile mutants which cannot produce fertile pollen or functional anthers can often be observed in higher plant species. In this review we differentiate between nuclear and cytoplasmic-nuclear male sterility (CMS); the latter is particularly useful for production of hybrid seed. While nuclear male sterility is solely based on mutations which occur in nuclear genes, CMS is maternally inherited and based on changes in mitochondrial gene expression as influenced by nuclear genes. Importantly, the CMS phenotype may be corrected by nuclear fertility restoration (RF) genes. In the first section, we discuss anther and pollen development and present recent molecular data as well. In the second part, some of the most important CMS systems are presented. Finally, approaches to genetically engineer male sterility in higher plants are discussed.