DIFFERENTIAL SCREENING OF MITOCHONDRIAL CDNA LIBRARIES FROM MALE-FERTILE AND CYTOPLASMIC MALE-STERILE SUGAR-BEET REVEALS GENOME REARRANGEMENTS AT ATP6 AND ATPA LOCI

As part of a strategy to define differences in genome organization and expression between cytoplasmic male-sterile (CMS) and male-fertile (M F) sugar-beet mitochondria, cDNA libraries from both mitochondrial gen otypes were constructed. Preliminary screening with ribosomal RNA gene probes identified candidate cDNA clones corresponding to structural g enes. In addition, reciprocal hybridization experiments were performed using labelled first-strand cDNA to identify uniquely transcribed seq uences. One cDNA clone (pYC700) is unique to CM S mitochondria and is located upstream of the FoF1-ATPase subunit 6 gene (atp6). Another cDN A clone (pYC130), when used as a probe in northern hybridization analy sis, revealed novel transcript profiles in CMS sugar-beet mitochondria . Sequence analysis of this cDNA showed strong homology with the FoF1- ATPase subunit alpha (atpA) coding sequences from several higher plant s. The atp6 and atpA loci from each genotype were cloned and the genom ic organization, DNA sequence and transcription of each locus was stud ied. Differences in the transcript profiles of each gene are a consequ ence of genomic rearrangements 5' to the coding sequence.