PULSED-FIELD GEL MAPPING OF MAIZE MITOCHONDRIAL CHROMOSOMES

Pulsed-field gel electrophoresis (PFGE) in combination with infrequent ly cutting restriction enzymes was used to investigate the structure o f the mitochondrial (mt) genome of the maize variety Black Mexican Swe et (EMS). The mt genome of this variety was found to resemble that of the closely related B37N variety, with one recombination and five inse rtion/deletion events being sufficient to account for the differences observed between the two genomes. The majority of the EMS genome is or ganized as a number of subgenomic chromosomes with circular restrictio n maps. Several large repeated sequences are found in the EMS mt genom e, but not all appear to be in recombinational equilibrium. No molecul es large enough to contain the entire mt genome were discernible using these techniques. The mapping approach described here provides a mean s of quickly analyzing the large and complex mt genomes of plants.