The analysis of mitochondrial mutations has been informative in several organisms, including yeast, fungi and humans. The genetic analysis of plant mitochondrial genomes has been limited due to the fact that only a few mutations with known progenitors have been described. We have focused on a set of lethal maize mutations (Nonchromosomal stripe; NCS) that survive in heteroplasmic plants. Different NCS mutants are associated with distinct phenotypes and the mutations have been shown to be deletions affecting the expression of a least three different mitochondrial genes (cox2, nad4 and the co-transcribed S3 and L16 ribosomal protein genes.) The major goal of this proposal is to elucidate the mechanisms by which the NCS lesions cause altered gene expression. We will analyze the mutant and normal transcripts in NCS2 and NCS3 plants and generate antibodies to determine whether the transcripts affected by NCS mutations are translated within nonmutant plant mitochondria. The long-term objective of this project is to understand the effects of individual plant mitochondrial genes on organelle biogenesis and overall cellular function. The proposed studies should clarify aspects of transcriptional and post-transcriptional regulation in plant mitochondria. A second goal of this proposal is to attempt to develop a system for demonstrating maize mitochondrial transformation using the NCS6 mutant, which carries a partial deletion of the well-characterized cox2 gene. The availability of a transformation system should facilitate studies of putative regulatory sequences in plant mitochondria.*** //
