Analysis of rice mitochondrial genome organization using pulsed-field gel electrophoresis

Most of the plant mitochondrial (mt) genomes that have been mapped are beli eved to be organized as master circle molecules from which sub-genomic mole cules arise through homologous recombination. We have evidence to suggest t hat a major part of the rice mt genome is organized as independent, sub-gen omic molecules or mt chromosomes, one of which has already been mapped. Thi s study is aimed at the identification of the other molecular entities that comprise the genome. Pulsed-field gel electrophoresis of the native rice mt DNA and Southern ana lysis with different mt gene probes have shown that in addition to the 117 kb mt chromosome, at least four more such molecules of sizes 130 kb, 95 kb, 70 kb and 56 kb account for most of the rice mt genome. A majority of the rice mt genes that encode products involved in oxidative phosphorylation ar e distributed among these five chromosomes. Partial restriction map of the 95 kb orf 25/cox 3 chromosome, indicating the sites for the enzymes Bg/II a nd HindIII has also been determined.