Comparison of the organization and expression of mtDNA of fertile and male-sterile sugar beet varieties (Beta vulgaris L.).

Analysis of minicircle occurrence in different samples of sugar beet mitochondrial (mt) DNA invalidates the postulated relationship between cytoplasmic male sterility (CMS) phenotype and the absence of minicircle c and d. In high molecular weight mt DNA, two types of restriction patterns are found for fertile genomes and only one type for the CMS; in spite of the multiplicity of crosses carried out by plant breeders, all the CMS varieties analyzed seem to have derived from the original cytoplasm discovered by Owen in 1945. Southern hybridizations with mitochondrial genes coding for cytochrome oxidase subunits II and III, ATPase subunits α, 6 and 9 and 26S ribosomal RNA indicate that gene organization is different between fertile and sterile genomes but similar in all fertile genomes. Transcription analysis with the same genes indicate several differences between fertile and sterile varieties but also within some fertile varieties. These results suggest that the mt genome found in male-sterile sugar beet may originate not from modifications of the fertile mitochondrial genome but from a particular source of cytoplasm, of which a possible origin is discussed.