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  • Brassica  (4)
  • Cell & Developmental Biology  (2)
  • 1
    ISSN: 1573-5028
    Keywords: Brassica ; cultured cells ; mitochondrial DNA ; mitochondrial DNA instability ; heterogeneity ; sublimon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We previously showed that the mitochondrial DNA (mtDNA) of a Brassica campestris callus culture had undergone extensive rearrangements (i.e. large inversions and a duplication) relative to DNA of the control plant [54]. In this study we observed that after continued growth, the mtDNA of this culture continues to change, with rearranged forms amplifying and diminishing to varying proportions. Strikingly similar changes were detected in the mtDNA profiles of a variety of other long- and short-term callus and cell suspension lines. However, the proportions of parental (‘unrearranged’) and novel (‘rearranged’) forms varied in different cultured cell mtDNAs. To address the source of this heterogeneity, we compared the mtDNA organization of 28 individual plants from the parental seed stock. With the exception of one plant containing high levels of a novel plasmid-like mtDNA molecule, no significant variation was detected among individual plants and therefore source plant variation is unlikely to have contributed to the diversity of mitochondrial genomes observed in cultured cells. The source of this culture-induced heterogeneity was also investigated in 16 clones derived from single protoplasts. A mixed population of unrearranged and rearranged mtDNA molecules was apprent in each protoclone, suggesting that the observed heterogeneity in various cultures might reflect the genomic composition of each individual cell; however, the induction of an intercellular heterogeneity subsequent to the protoplast isolation was not tested and therefore cannot be ruled out. The results of this study support our earlier model that the rapid structural alteration of B. campestris mtDNA in vitro results from preferential amplification and reassortment of minor pre-existing forms of the genome rather than de novo rearrangement. Infrequent recombination between short dispersed repeated elements is proposed as the underlying mechanism for the formation of these minor mtDNA molecules.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    BioEssays 2 (1985), S. 263-267 
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The small, relatively constant size and conservative evolution of chloroplast DNA (cpDNA) make it an ideal molecule for tracing the evolutionary history of plant species. At lower taxonomic levels, cpDNA variation is easily and conveniently assayed by comparing restriction patterns and maps, while at higher taxonomic levels, DNA sequencing and inversion analysis are the methods of choice for comparing chloroplast genomes. The study of cpDNA variation has already yielded important new insights into the origin and evolution of many agriculturally important crop plants, and promises to significantly enhance our phylogenetic understanding of the major lines of descent among land plants and algae.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    BioEssays 17 (1995), S. 1005-1008 
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The most common form of the CO2-fixing enzyme rubisco is a form I enzyme, heretofore found universally in oxygenic phototrophs (cyanobacteria and plastids) and widely in proteobacteria. Two groups(1-4), however, now report that in dinoflagellate plastids the usual form I rubisco has been replaced by the distantly related form II enzyme, known previously only from anaerobic proteobacteria. This raises the important question of how such an oxygensensitive rubisco could function in an aerobic organism. Moreover, the dinoflagellate rubisco has unusual molecular properties: it is encoded as a polyprotein, by nuclear (rather than plastid) genes, and these genes contain noncanonical spliceosomal introns. The nuclear location and alphaproteobacterial affinity of dinoflagellate rubisco genes hint at a possible mitochondrial origin and highlight the extraordinary richness of lateral gene transfers, both between and within organisms, that have occurred during rubisco evolution.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-1432
    Keywords: Genome evolution ; Rearrangement ; Inversion ; Brassica ; Base substitution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We examined the tempo and mode of mitochondrial DNA (mtDNA) evolution in six species of crucifers from two genera,Brassica andRaphanus. The six mtDNAs have undergone numerous internal rearrangements and therefore differ dramatically with respect to the sizes of their subgenomic circular chromosomes. Between 3 and 14 inversions must be postulated to account for the structural differences found between any two species. In contrast, these mtDNAs are extremely similar in primary sequence, differing at only 1–8 out of every 1000 bp. The point mutation rate in these plant mtDNAs is roughly 4 times slower than in land plant chloroplast DNA (cpDNA) and 100 times slower than in animal mtDNA. Conversely, the rate of rearrangements is extraordinarily faster in plant mtDNA than in cpDNA and animal mtDNA.
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  • 5
    ISSN: 1432-0983
    Keywords: Brassica ; Mitochondrial DNA ; Cytoplasmic male sterility ; Recombination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The gene coxI, encoding subunit I of mitochondrial cytochrome c oxidase, has been characterized from the normal (fertile) and Ogura (male-sterile) cytoplasms of radish to determine if a previously identified mitochondrial DNA rearrangement, and its associated transcriptional differences, could play a role in Ogura cytoplasmic male sterility (CMS). The normal and Ogura loci are virtually identical for 2.8 kb, including a 527-codon open reading frame whose product is approximately 95% identical to other plant COXI polypeptides. A rearrangement 120 bp 5′ to the coding region results in different 5′ transcript termini for the two genes. A comparison of several crucifer mitochondrial DNAs indicates that this rearrangement also occurs in the normal radish cytoplasm and is, therefore, not involved in Ogura CMS. Sequences present at the coxI locus belong to at least two different dispersed repeat families, members of which are also associated with other rearranged genes in radish.
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  • 6
    ISSN: 1432-0983
    Keywords: Brassica ; Mitochondrial DNA ; nad4 ; Group II introns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The gene nad4, encoding subunit four of the mitochondrial NADH dehydrogenase complex I, has been isolated and characterized from turnip, Brassica campestris. The 8 kb turnip nad4 gene contains four exons, which potentially encode a NAD4 polypeptide of 495 amino acids, and three large group II introns. Northern analysis identifies an abundant 2 kb transcript that most likely serves as the nad4 mRNA, while several larger transcripts (putative splicing intermediates) are also detected. Analysis of the nad4 locus in three distantly related dicotyledons indicates that introns 2 and 3 are optional. Mung bean has the same nad4 organization as turnip, whereas spinach nad4 contains introns 1 and 3, and lettuce nad4 has intron 1 only. We infer that all three group II introns were present in the nad4 gene of an angiosperm common ancestor and have persisted in certain lineages for over 200 million years, with two of the introns having been lost in other lineages.
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