Abstract 9406055 A long-term objective of this project is to understand the effects of individual plant mitochondrial genes on organelle biogenesis and overall cellular function. 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 at least three different mitochondrial genes (cox2, nad4 and the co-transcribed S3 an L16 ribosomal protein genes. The major goal of the current proposal is to transform mitochondria that are homoplasmic for a deletion of the 5' end and promoter sequences of cytochrome oxidase subunit 2 with a distinguishable, functional copy of cox2. This would open up higher plant mitochondria to genetic manipulations that cannot otherwise be performed. Normal and mutant promoter constructs will be tested in vivo. We propose to continue our analyses of new mitochondrial mutations, particularly the partially characterized NCS4 mutation. The NCS4 mutant rearrangement involves S2-plasmid sequences that have incorporated into the mitochondrial genome. Finally, we propose to continue our genetic approach to analyzing the roles of mitochondria during plant development. The mutants in different steps of oxidative phosphorylation have distinguishable effects on chlorophyll levels and the production of nuclear-coded products for chloroplast function. We will also use the mutants to determine when mitochondrial function is essential for the survival of cells, tissues and organs. %%% The long-term objective of this project is to understand the effects of individual plant mitochondrial genes on organelle biogenesis and overall cellular function. During the tenure of this award, the focus will be on: (1) devel oping procedures for transforming higher plant mitochondria (2) continuing the analysis of existing mitochondrial mutations and (3) continuing to genetically analyze the role(s) of mitochondria during plant development. ***
