Heterogeneity of circular mitochondrial DNA molecules from sugar beet with normal and male sterile cytoplasms

Summary Mitochondrial (mt) DNAs from normal (N) and male sterile (S) cytoplasms of sugar been have been isolated and investigated by electron microscopy. The results showed that mtDNA was composed of a heterogeneous population of circular molecules. Their contour lengths varied from 0.28 to 51 m, but unlike in the case of maize, a large difference was not observed in the distribution of molecular classes greater than 1.0 m between N and S cytoplasms of sugar beet. On the other hand, N and S cytoplasms were shown to contain their own characteristic combinations of small circular mtDNA species with lengths between 0.28 m and 0.6 m. Mitochondrial DNAs from various sources of male-sterile cytoplasms were analyzed by agarose gel electrophoresis to determine the extent of cytoplasmic variation. Additional low molecular weight DNA bands appeared in all male-sterile lines examined, and as a result, three distinctive banding patterns were recognized. These data are in general agreement with those based upon restriction endonuclease digestion of mt and chloroplast DNAs and the genetic analysis of fertility restoration in test crosses.     

Molecular heterogeneity in mitochondrial and chloroplast DNAs from normal and male sterile cytoplasms in sugar beets

Summary Mitochondrial (mt) and chloroplast (ct) DNAs were prepared from normal (N) and male sterile (S) cytoplasmic lines of sugar beet. The DNAs were cleaved with BamHI, EcoRI, HindIII and SalI enzymes, and the resultant fragments were fractionated by agarose gel electrophoresis. The results showed that N and S cytoplasms contained distinct mtDNA. Although most of the DNA fragments were common to these two cytoplasms, each cytoplasm was readily characterized by bands specific to that cytoplasm. In addition, these distinctive cleavage patterns were invariant in different nuclear backgrounds. In contrast to the marked variation in mtDNA, restriction fragment analyses of ctDNA demonstrated little difference between both cytoplasms. Only HindIII digestion showed one band missing in the S genome. The data presented here provides circumstantial evidence for mitochondrial involvement in the inheritance of cytoplasmic male sterility in sugar beet.     

Novel mitochondrial genomes in Brassica napus somatic hybrids

Summary The mitochondrial genomes of nine male-fertile and two Ogura cytoplasmic male-sterile (cms) Brassica napus somatic hybrids were probed with 46 mitochondrial DNA fragments. The distribution of information obtained from each fusion partner was not random. Several regions, including the coxI gene and a major recombination repeat sequence, were always derived from the Brassica campestris fusion partner, and some regions were always derived from the Ogura mitochondrial genome. Novel fragments occurred in seven distinct regions. Some of the rearrangement breakpoints were located near the evolutionary breakpoints relating the mitochondrial genomes of the Brassica species. The sizes of the mitochondrial genomes in the somatic hybrids ranged from 224.8 to 285.3 kb. A direct correlation between a specific gene and the cms phenotype was not observed; however, a possible cms-associated region was identified. It corresponds to a region that was identified through analysis of fertile revertants from a cms B. napus cybrid.     

Properties and nucleotide sequence of a mitochondrial plasmid from sunflower

Summary The 1.413 circular supercoiled mitochondrial DNA plasmid P 1 from a fertile sunflower line was sequenced, and a series of 160 by tandemly repeated sequences was observed. The P1 plasmid was detected in both fertile and cytoplasmic male-sterile (CMS) lines, but in different quantities. Two other circular plasmids, P2 and P3, each 1.8 kbp in length, were shown to share common sequences with Pl. The mitochondrial plasmid P1 detected homologous sequences in the nuclear DNA of sunflower, but not in chloroplast DNA nor in main band mitochondrial DNA. RNA molecules of about 680 and 550 nucleotides were detected that were complementary to mt plasmid P1.     

A mitochondrial plasmid specifically associated with male sterility and its relation with other mitochondrial plasmids in Vicia faba L.

Summary Small supercoiled DNA molecules of Vicia faba were cloned and characterized by restriction mapping and molecular hybridization. The 1700 by S plasmid has been found to be specifically associated with the male sterile cytoplasms and exhibited large homologies with the other 1700 by F plasmid as shown by molecular cross hybridization. In one line bearing the male sterile 350 cytoplasm, a deleted mitochondrial plasmid of 1540 bp was observed and this plasmid derives from the 1700 bp S plasmid. Our results indicate therefore that three of the four plasmids analysed are closely related between each other.     

Intramolecular recombination of a mitochondrial minicircular plasmid-like DNA of date-palm mediated by a set of short direct-repeat sequences

A molecular clone containing the complete sequence of a mitochondrial circular plasmid-like DNA (the R plasmid) isolated from the date-palm variety V3DP was used as a probe in Southern analyses of mitochondrial DNA prepared from other varieties. Another circular structure (the S plasmid) was detected in some of these varieties, and sequenced from variety V2DP. It appears that the R plasmid could have arisen from the S plasmid by an intermolecular recombination event at a set of 26-bp imperfect short direct repeats.     

The organization of mitochondrial atp6 gene region in male fertile and CMS lines of pepper (Capsicum annuum L.)

The mitochondrial atp6 gene in male fertile (N) and CMS (S) pepper has previously been compared and was found to be present in two copies (Kim et al. in J Kor Soc Hort Sci 42:121–127 2001). In the current study, these atp6 copies were amplified by an inverse PCR technique, and the coding region as well as the 5′ and 3′ flanking regions were sequenced. The atp6 copies in CMS pepper were detected as one intact gene and one pseudogene, truncated at the 3′ coding region. When the atp6 genes in pepper were compared to other plant species, pepper, potato, and petunia all possessed a sequence of 12 identical amino acids at the 3′ extended region, which was considered a hallmark of the Solanaceae family. Northern blot analysis showed differences in mRNA band patterns between CMS and restorer lines, indicating that atp6 gene is one of the candidates for CMS in pepper. GenBank accession number: DQ126682 (atp6-1 genomic sequence common to fertile and CMS pepper), DQ126681 (Fertile atp6-2 genomic sequence), DQ126680 (CMS pseudo-atp6-2 genomic sequence)     

The maize mitochondrial genome of the normal type and the cytoplasmic male sterile type T have very different organization

Summary The normal type (N) and cytoplasmic male sterile type T (cmsT) maize mitochondrial genomes are 570 kb and 540 kb in length respectively. Detailed hybridization studies have been undertaken to compare the sequence complexity and variation between the two genomes (genotype B37). They have approximately 500 kb of common sequences but there is considerable variation in sequence organization which can be accounted for by structural alterations from large and small permutations. The sequences not shared between the two genomes totaling 70 kb in N and 40 kb in cmsT can be accounted for by the presence of different repeated sequences, the absence of the integrated form of plasmids S1 and S2 in cmsT, the presence or absence of chloroplast sequences, and a number of sequences that are specific to N or to cmsT.     

Physical and gene organization of mitochondrial DNA from the fertile cytoplasm of sugarbeet (Beta vulgaris L.)

We have constructed a complete physical map of the mitochondrial genome from the male-fertile cytoplasm of sugarbeet. The entire sequence complexity can be represented on a single circular master chromosome of 358 kb. This master chromosome contains three copies of one recombinationally active repeat sequence, with two copies in direct orientation and the other in inverted orientation. The positions of the rRNA genes and of 23 polypeptide genes, determined by filter hybridization, are scattered throughout the genome, with triplicate rrn26 genes located partially or entirely within the recombination-repeat elements. Three ribosomal-protein genes (rps1A, rps14 and rps19) were found to be absent from sugarbeet mtDNA. Our results also reveal that at least six regions homologous with cpDNA are dispersed in the mitochondrial genome.     

Interaction between mitochondrial DNA and mitochondrial plasmids in Claviceps purpurea: analysis of plasmid-homologous sequences upstream of the IrRNA-gene

Homology of two linear, mitochondrial (mt) Claviceps purpurea plasmids, pC1K1 and pClT5, to the upstream region of the large ribosomal RNA gene in the mtDNA of three strains (W3, T5 and K) has been investigated in detail to explore the widespread phenomenon of homology between mt plasmids and mtDNA in C. purpurea. Sequence comparison indicates that recombination between free plasmids and mtDNA is the cause of the observed homology. The process is similar to the integration of the structurally related adenoviruses into the mammalian genome. As in other fungi, palindromic sequences seem to be involved in this mitochondrial recombination process.