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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Current genetics 11 (1987), S. 565-570 
    ISSN: 1432-0983
    Keywords: Restriction map ; Circular chromosome ; Recombination repeat ; Inversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Restriction mapping studies reveal that the mitochondrial genome of white mustard (Brassica hirta) exists in the form of a single circular 208 kb chromosome. The B. hirta genome has only one copy of the two sequences which, in several related Brassica species, are duplicated and undergo intramolecular recombination. This first report of a plant mitochondrial DNA that does not exist in a multipartite structure indicates that high frequency intramolecular recombination is not an obligatory feature of plant mitochondrial genomes. Heterologous filter hybridizatios reveal that the mitochondrial genomes of B. hirta and B. campestris have diverged radically in sequence arrangement, as the result of approximately 10 large inversions. At the same time, however, the two genomes are similar in size, sequence content, and primary sequence.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0983
    Keywords: Restriction maps ; Gene organization ; Chloroplast DNA ; Inversion ; Asteraceae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have cloned into plasmids 17 of 18 lettuce chloroplast DNA SacI fragments covering 96% of the genome. The cloned fragments were used to construct cleavage maps for 10 restriction enzymes for the chloroplast genomes of lettuce (Lactuca sativa) and Barnadesia caryophylla, two distantly related species in the sunflower family (Asteraceae). Both genomes are approximately 151 kb in size and contain a 25 kb inverted repeat. We also mapped the position and orientation of 37 chloroplast DNA genes. The mapping studies reveal that chloroplast DNAs of lettuce and Barnadesia differ by a 22 kb inversion in the large single copy region. Barnadesia has retained the primitive land plant genome arrangement, while the inversion has occurred in a lettuce lineage. The endpoints of the derived lettuce inversion were located by comparison to the well-characterized spinach and tobacco genomes. Both endpoints are located in intergenic spacers within tRNA gene clusters; one cluster being located downstream from the atpA gene and the other upstream from the psbD gene. The endpoint near the atpA gene is very close to one endpoint of a 20 kb inversion in wheat (Howe et al. 1983; Quigley and Weil 1985). Comparison of the restriction site maps gives an estimated sequence divergence of 3.7% for the lettuce and Barnadesia genomes. This value is relatively low compared to previous estimates for other angiosperm groups, suggesting a high degree of sequence conservation in the Asteraceae.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0983
    Keywords: Chloroplast genome evolution ; Inverted repeat ; Inversion ; Repeated sequence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have compared the sequence organization of four previously uncharacterized legume chloroplast DNAs - from alfalfa, lupine, wisteria and subclover — to that of legume chloroplast DNAs that either retain a large, ribosomal RNA-encoding inverted repeat (mung bean) or have deleted one half of this repeat (broad bean). The circular, 126 kilobase pair (kb) alfalfa chloroplast genome, like those of broad bean and pea, lacks any detectable repeated sequences and contains only a single set of ribosomal RNA genes. However, in contrast to broad bean and pea, alfalfa chloroplast DNA is unrearranged (except for the deletion of one segment of the inverted repeat) relative to chloroplast DNA from mung bean. Together with other findings reported here, these results allow us to determine which of the four possible inverted repeat configurations was deleted in the alfalfa-pea-broad bean lineage, and to show how the present-day broad bean genome may have been derived from an alfalfa-like ancestral genome by two major sequence inversions. The 147 kb lupine chloroplast genome contains a 22 kb inverted repeat and has essentially complete colinearity with the mung bean genome. In contrast, the 130 kb wisteria genome has deleted one half of the inverted repeat and appears colinear with the alfalfa genome. The 140 kb subclover genome has been extensively rearranged and contains a family of at least five dispersed repetitive sequence elements, each several hundred by in size; this is the first report of dispersed repeats of this size in a land plant chloroplast genome. We conclude that the inverted repeat has been lost only once among legumes and that this loss occurred prior to all the other rearrangements observed in subclover, broad bean and pea. Of those lineages that lack the inverted repeat, some are stable and unrearranged, other have undergone a moderate amount of rearrangement, while still others have sustained a complex series of rearrangement either with or without major sequence duplications and transpositions.
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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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