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Cytoplasmic male sterility (CMS) is a mitochondrial-encoded trait that confers reproductive defects in males but not in females or any vegetative function. Why CMS is so often found in plants should be investigated from the viewpoint of mitochondrial phylogeny. Beta vulgaris, including the wild subspecies maritima and cultivated subspecies vulgaris (e.g., sugar beet), is known to be mitochondrially polymorphic, from which multiple CMS mitochondria have been found, but their evolutionary relationship has been obscure. We first refined the B. vulgaris reference mitochondrial genome to conduct a more accurate phylogenetic study. We identified mitochondrial single-nucleotide polymorphic sites from 600 B. vulgaris accessions. Principal component analysis, hierarchical clustering analysis, and creation of a phylogenetic tree consistently suggested that B. vulgaris mitochondria can be classified into several groups whose geographical distribution tends to be biased toward either the Atlantic or Mediterranean coasts. We examined the distribution of CMS-associated mitochondrial genes from Owen, E- and G-type CMS mitochondria. About one-third of cultivated beets had Owen-type CMS, which reflects the prevalence of using Owen-type CMS in hybrid breeding. Occurrence frequencies for each of the three CMS genes in wild beet were less than 4%. CMS genes were tightly associated with specific mitochondrial groups that are phylogenetically distinct, suggesting their independent origin. However, homologous sequences of the Owen type CMS gene occurred in several different mitochondrial groups, for which an intricate explanation is necessary. Whereas the origin of cultivated beet had been presumed to be Greece, we found an absence of Owen-type mitochondria in Greek accessions. [ABSTRACT FROM AUTHOR]

Introns may be considered as optional because they are removed from mRNA molecules, but introns are fairly preserved for unknown reasons. Previously, the mitochondrial rps3 gene of sugar beet (Beta vulgaris L., Caryophyllales) was shown to represent a unique example of an intron loss. We have determined the distribution of the rps3 intron in 19 Caryophyllalean species. The intron was absent from the Amaranthaceae and the Achatocarpaceae. In the Caryophyllaceae, Dianthus japonicus rps3 was pseudogenized, but the intronic sequence was retained. Intact intron-bearing rps3 copies were cloned from Portulaca grandiflora and Myrtillocactus geometrizans, members of the sister clade of the Amaranthaceae-- Achatocarpaceae-Caryophyllaceae clade. Most of the C-to-U RNA-editing sites in P. grandiflora and M. geometrizans rps3 transcripts were homologous in the two species, as well as in the sugar beet rps3, which, unlike the other 12 rps3 transcripts, lacks editing in the exonic regions around the intron. Provided that the loss of editing preceded the loss of rps3 intron, it appears conceivable that a requirement for editing could have prevented the loss of group II introns retained in angiosperm mitochondrial genomes. This interpretation is an alternative to the conventional one that views the loss of editing as a mere trace of RNA-mediated gene conversion. Key words: plant mitochondria, mitochondrial genome, evolution, Caryophyllales, Amaranthaceae, group II intron, retroprocessing. Il est possible de considerer les introns comme etant optionnels puisqu'ils sont retires des molecules d'ARN, mais les introns sont relativement conserves pour des raisons qui demeurent inconnues. Precedemment, il a ete montre que le gene mitochondrial rps3 de la betterave a sucre (Beta vulgaris L., Caryophyllales) representait un exemple unique de la perte d'un intron. Les auteurs ont determine la distribution de l'intron rps3 chez 19 especes au sein de l'ordre des Caryophyllales. L'intron etait absent chez les Amarenthaceae et les Achatocarpaceae. Au sein des Caryophyllaceae, le gene rps3 chez le Dianthus japonicus etait devenu un pseudogene au sein duquel l'intron est conserve. Des copies intactes de rps3 possedant l'intron ont ete clonees chez le Portulaca grandiflora et le Myrtillocactus geometrizans, deux membres d'un clade apparente au clade forme par les Amaranthaceae-Achatacarpaceae-Caryophyllaceae. La plupart des sites d'edition C-U au sein des transcrits rps3 chez P. grandiflora et M. geometrizans etaient conserves chez les deux especes, de meme que chez le rps3 de la betterave a sucre qui, contrairement a 12 autres transcrits rps3, est depourvu de sites d'edition dans les regions exoniques bordant l'intron. En supposant que la perte de l'edition precede la perte de l'intron rps3, il semble concevable que la necessite de l'edition pourrait prevenir la perte d'introns du groupe II qui sont conserves au sein des genomes mitochondriaux chez les angiospermes. Cette interpretation est une alternative a l'interpretation conventionnelle selon laquelle la perte de l'edition est consequence de la conversion genique due a l'ARN. Mots-cles : mitochondries chez les plantes, genome mitochondrial, evolution, Caryophyllales, Amaranthaceae, introns du groupe II, retro-traitement. [Traduit par la Redaction], Unlike in animals, introns are prevalent in land plant mitochondrial genes (Knoop 2004; Bonen 2008). In angiosperms, there are ~25 known group I and group II mitochondrial introns that interrupt [...]

We found a number of male-sterile plants in a wild beet (Bern vulgaris L. subsp. mariiima) accession line, FR4-31. The inheritance study of the male sterility indicated the trait to be of the cytoplasmic type. The mitochondrial genome of FR4-31 proved to lack the male-sterility-associated genes preSatp6 and orf129, which are characteristic of the Owen CMS and I-12CMS(3) cytoplasms of beets, respectively. Instead, the truncated cox2 gene involved in G CMS originating from wild beets was present in the FR4-31 mitochondrial genome. In Southern hybridization using four mitochondrial gene probes, the FR4-31 cytoplasm showed patterns similar to those typical of the G cytoplasm. It is thus likely that the FR4-31 cytoplasm has a different CMS mechanism from both Owen CMS and I-12CMS(3), and that the FR4-31 and G cytoplasms resemble each other closely. A restriction map of the FR4-31 mitochondrial DNA was generated and aligned with those published for the Owen and normal fertile cytoplasms. The FR4-31 mitochondrial genome was revealed to differ extensively in arrangement from the Owen and normal genomes, and the male-sterile Owen and FR4-31 genomes seem to be derived independently from an ancestral genome. Key words: sugar beet, cytoplasmic male sterility, plant mitochondria, mitochondrial genome. Les auteurs ont trouve plusieurs plantes males steriles chez l'aceession FR4-31 de la betterave maritime (Beta vulgaris L. subsp. maritima), L'elude de l'heredite de cette sterilite male a montre que le caraclere etait cytoplasmique. Le genome mitochondrial de FR4-31 s'est avere depourvu de deux genes associes a la sterilite male, preSatp6 el orfl29, lesquels sont respectivement caracteristiques des cytoplasmes CMS Owen et I-12CMS(3) chez les betteraves. Au lieu, un gene cox2 tronque. implique dans la CMS G chez les betteraves maritimes. etait present dans le genome mitochondrial de FR4-31. Lors d'hybridations Southern realisees a l'aide de quatre sondes geniques mitochondriales. le cytoplasme FR4-31 s'est montre semblable a celui du cytoplasme G. Il est ainsi vraisemblable que le cytoplasme FR4-31 possede un mecanisme CMS different de celui present chez la CMS Owen et I-12CMS(3), et que les cytoplasmes FR4-31 et G se ressemblent beaucoup. Une carte de restriction de l'ADN mitochondrial de FR4-31 a ete generee et alignee avec celles publiees pour les cytoplasmes Owen et normaux fertiles. Le genome mitochondrial de FR4-31 a presente de nombreuses differences dans son organisation relativement aux genomes Owen et normal. Par contre, les genomes males steriles Owen et FR4-31 semblent derives independamment d'un genome ancestral. Mots-cles : betterave sucriere, sterilite male cytoplasmique, mitoehondries vegetales, genome mitochondrial. [Traduit par la Redaction], Introduction The discovery by Owen (1942, 1945) of cytoplasmic male sterility (CMS) in sugar beet (Beta vulgaris subsp. vulgaris) and the subsequent identification and development of slerility-maintainer lines resulted in [...]

Cytoplasmic male sterility (CMS), the maternally inherited failure to produce functional pollen, has been used in the breeding of sugar beet (Beta vulgaris ssp. vulgaris). At least three different sources of CMS can be distinguished from one another as well as from normal fertile cytoplasm by polymorphisms in their mitochondrial genomes. Here we analyzed 50 accessions of cultivated and wild beets to investigate the phylogenetic relationships among male-sterility-inducing and normal cytoplasms. The haplotypes were characterized by the nucleotide sequence of the mitochondrial cox2-cox1 spacer region and mitochondrial minisatellite loci. The results indicated that (1) a normal cytoplasm line, cv. TK81-O, was situated at the major core node of the haplotype network, and (2) the three sterilizing cytoplasms in question derived independently from the core haplotype. The evolutionary pathway was investigated by physical mapping study of the mitochondrial genome of a wild beet (B. vulgaris ssp. orientalis) accession BGRC56777 which shared the same mitochondrial haplotype with TK81-O, but was not identical to TK81-O for the RFLP profiles of mitochondrial DNA. Interestingly, three sets of inverted repeated sequences appeared to have been involved in a series of recombination events during the course of evolution between the BGRC56777 and the TK81-O mitochondrial genomes.