Expression of mitochondrial genes in fertile and sterile sugar beet cytoplasms with different nuclear fertility restorer genes.

Variations in mitochondrial genome organization and in its expression between fertile, sterile sugar beet lines and fertile nuclear-restored plants were studied. Southern blot hybridization with COXI, COXII, COB and atpA mitochondrial genes as probes showed that changes in the mitochondrial genome organization of sterile lines are associated with variations in the location of COB, atpA and COXII, but not COXI. When the COXII and atpA genes were used as hybridization probes, differences in the primary structure of mitochondrial DNAs from sterile lines of different origin were revealed. Differences in the transcriptional patterns of the three mitochondrial genes (COXI, COXII and atpA) were observed between fertile and sterile sugar beet lines; COB was the only mitochondrial gene whose transcription was identical in both fertile and sterile cytoplasms. The dominant nuclear fertility restorer genes altered the transcriptional patterns of the COB and atpA without affecting those of the COXI and COXII genes; atp A expression was identical in fertile plants and nuclear-restored plants with sterile cytoplasm.