Studies on the organelle genomes of sugarbeet with male-fertile and male-sterile cytoplasms

Summary

Chloroplast DNA (ctDNA) from male-fertile and cytoplasmically male-sterile (cms) sugarbeet has been investigated by restriction endonuclease digestion. Three enzymes (SalGI, BamHI and PstI) did not distinguish between the ctDNA from the two different types of plant. Another enzyme (EcoRI) revealed one variant fragment in one of the male-fertile lines examined, but this variant is not thought to be associated with the cms trait. This situation contrasts with that for mitochondrial DNA (mtDNA) since it has previously been shown that mtDNA of cms sugarbeet differs considerably from that of male-fertile sugarbeet. The presently used form of cms in sugarbeet was discovered in the variety ‘US1’. Individual plants of this variety were examined to determine which types of mtDNA they contained. Some plants contained mtDNA typical of male-fertile plants and some mtDNA typical of cms plants. These results suggest that the cms trait in sugarbeet is encoded by mtDNA and not ctDNA. The small, circular DNA species previously found in mitochondria were cloned and used in hybridization experiments to determine their homologies to the other mtDNA molecules. The small DNA species showed no homology to the main band of high molecular weight DNA, but they did hybridize to molecules which were apparently their own dimers, tetramers, octamers, etc. If a small DNA species was absent from a particular sugarbeet line then no hybridization to any mtDNA of that line was detected.