Plant mitochondria, as subcellular compartments involved in energy metabolism, contain their own genetic information. The dynamic nature of the plant mitochondrial genome represents an important feature that distinguishes plants and animals. An understanding of the underlying genetic basis of this trait is important to developing an appreciation of its value to evolution and its amenability to manipulation. Two types of genetic exchange are characteristic of plant mitochondria: high frequency DNA exchange that occurs at "like" sequences found as large, interspersed repeats, and infrequent DNA exchange at "unlike" sites containing as little as six or seven shared nucleotides. Both appear to represent important sources of genetic variation in plants. The laboratory of the PI has cloned a gene in the model plant species Arabidopsis thaliana, designated MSH1, that is associated with mitochondrial DNA maintenance and possibly with DNA exchange activity. In this proposal, the function of MSH1 will be analyzed. As a corollary to these studies, mitochondrial DNA exchange activity dependent on the gene RecA will be investigated. The central hypothesis of the research is that RecA, together with interacting protein components, control recombination activity in higher plant mitochondria by mechanisms that are distinct from MSH1 activity. As tests of this hypothesis, proteins that demonstrate interaction with RecA will be isolated, as well as mitochondrial DNA sequences to which this putative protein complex binds. Functional analysis of RecA will involve mutation studies and plant transformations. Evidence for RecA and MSH1 functional and physical interaction will also be sought. The importance of the proposed study will be to identify and characterize components of a genetic network that appears to be uniquely adapted to plants, and to understand the role of recombination processes in plant mitochondrial genome maintenance and transmission. From a practical standpoint, an understanding of mitochondrial recombination activity is key to the development of mutations that cause male sterility, and hence the proposed research should be useful to the agricultural seed industry for hybrid seed. The project will also involve training opportunities for undergraduates, graduate students and postdoctoral fellows; recruitment of under-represented minorities will be a priority.
