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  • 1
    ISSN: 1432-0983
    Keywords: Chlamydomonas eugametos ; Chlamydomonas moewusii ; Hybrid backcrosses ; Mitochondrial DNA polymorphism ; Chloroplast genetic markers ; Inheritance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Southern blot analysis of AvaI-digested total cellular DNA from the interfertile species Chlamydomonas eugametos and Chlamydomonas moewusii with a coxI mitochondrial gene probe from Chlamydomonas reinhardtii revealed single hybridizing fragments of 5.0 and 3.5 kb, respectively. The transmission of these mitochondrial DNA physical markers along with that of chloroplast genetic markers for resistance to streptomycin and resistance to erythromycin was studied in the fourth backcrosses of F1 hybrids to one or the other parent. Viability in these backcrosses is high in contrast to the cross C. eugametos x C. moewusii and its reciprocal which are associated with considerable meiotic product lethality. The resulting zygospores were found to transmit the mitochondrial and chloroplast genome markers uniparentally or preferentially from the mating-type-plus parent. Thus the species pair C. eugametos and C. moewusii differs from the pair Chlamydomonas reinhardtii and Chlamydomonas smithii in which mitochondrial genome markers are transmitted uniparentally by the mating-type minus parent, while the chloroplast genome markers are transmitted uniparentally by the opposite parental mating-type (Boynton et al. 1987).
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  • 2
    ISSN: 1432-0983
    Keywords: Chlamydomonas ; Gene mapping ; Mitochondrial genome ; Evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We report the cloning and physical mapping of the mitochondrial genome of Chlamydomonas eugametos together with a comparison of the overall sequence structure of this DNA with the mitochondrial genome of Chlamydomonas moewusii, its closely related and interfertile relative. The C. eugametos mitochondrial DNA (mtDNA) has a 24 kb circular map and is thus 2 kb larger than the 22 kb circular mitochondrial genome of C. moewusii. Restriction mapping and heterologous fragment hybridization experiments indicate that the C. eugametos and C. moewusii mtDNAs are colinear. Nine cross-hybridizing restriction fragments common to the C. eugametos and C. moewusii mtDNAs, and spanning the entirety of these genomes, show length differences between homologous fragments which vary from 0.1 to 2.3 kb. A 600 bp subfragment of C. moewusii mtDNA, within one of these conserved fragments, showed no hybridization with the C. eugametos mtDNA. Of the 73 restriction sites identified in the C. eugametos and C. moewusii mtDNAs, five are specific to C. moewusii, eight are specific to C. eugametos and 30 are common to both species. Hybridization experiments with gene probes derived from protein-coding and ribosomal RNA-coding regions of wheat and Chlamydomonas reinhardtii mtDNAs support the view that the small and large subunit ribosomal RNA-coding regions of the C. eugametos and C. moewusii mtDNAs are interrupted and interspersed with each other and with protein-coding regions, as are the ribosomal RNA-coding regions of C. reinhardtii mtDNA; however, the specific arrangement of these coding elements in the C. eugametos and C. moewusii mtDNAs appears different from that of C. reinhardtii mtDNA.
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  • 3
    ISSN: 1432-0983
    Keywords: Chlamydomonas ; Chloroplast DNA WRecombination WRestriction analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Differences in the restriction endonuclease fragmentation patterns of chloroplast DNA (cpDNA) from C. eugametos and C. moewusii have been used to study the inheritance of these DNAs in interspecific hybrids. Analysis of the cpDNAs from ten randomly selected F1 hybrids, in each case revealed cpDNA to be recombinant for AvaI and BstEII restriction sites, although fragments characteristic of C. eugametos, the mt+ parent, were typically found in excess of those for C. moewusii, the mt− parent. In backcrosses between an F 1 mt+ hybrid and C. moewusii mt−, seven randomly selected B1 hybrids showed cpDNA restriction patterns either identical to or highly similar to that of the mt+ parent. We propose that cpDNA molecules are predominantly transmitted by the mt+ parent in both F1 and B1 generations but that selection favors survival of F1 progeny with recombinant chloroplast genomes which avoid interspecific incompatibilities. On the surface, the inheritance of recombinant cpDNA contrasts with the simultaneous uniparental inheritance of two putative chloroplast markers (sr-2 and er-nM1 +). However, it may be that these two markers are by chance associated with cpDNA sequences of the mt+ parent which were selected in all F1 hybrids.
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  • 4
    ISSN: 1432-0983
    Keywords: Key wordsChlamydomonas eugametos/ Chlamydomonas moewusii ; Chloroplast DNA polymorphisms ; Mobile elements ; Gene conversion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Unlike most polymorphic markers in the Chlamydomonas eugametos and Chlamydomonas moewusii chloroplast DNAs (cpDNAs), the C. moewusii 6- and 21-kb extra sequences and the C. eugametos-specific CeLSU ⋅ 5 intron are transmitted to all of the few viable progeny in reciprocal crosses between the two green algae. To determine whether this unidirectional transmission pattern is due to gene conversion or to selection for F1 hybrid survival, we followed the inheritance of the parental alleles at the loci featuring these three deletions/additions and at several other polymorphic cpDNA loci in zygospore clones derived from high-viability crosses. The great majority of the zygospore clones examined inherited exclusively the long alleles from the mt – parent at the loci containing the three optional cpDNA elements, but as expected, they preferentially inherited the markers from the mt + parent at most other loci. Our results therefore indicate that all three optional cpDNA sequences propagate themselves very efficiently by gene conversion in crosses between strains differing by the presence of these elements. The co-conversion tracts associated with these sequences are longer (〉3 kb) than those previously reported for mobile elements spreading by gene conversion. Our results also revealed that less efficient gene conversion events occurred at two other cpDNA loci.
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  • 5
    ISSN: 1432-0983
    Keywords: Chlamydomonas ; Chloroplast ; DNA ; Genetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The density, molecular weight, and cellular repetition of DNA molecules associated with the β-DNA satellite of the interfertile algae Chlamydomonas eugametos and C. moewusii are reported. The similarities between these values and those for the chloroplast DNA (cpDNA) in the related alga Chlamydomonas reinhardtii indicate that these satellites represent cpDNA. The buoyant densities of C. eugametos and C. moewusii cpDNAs are indistinguishable from one another, as are those of their respective nuclear DNAs. These densities differ slightly from the densities of the homologous components of C. reinhardtii whole cell DNA. All three species differ with respect to additional minor satellite DNAs and low molecular weight DNAs of unknown cellular location. Differences in the Aval and Smal restriction endonuclease fragmentation patterns of C. eugametos and C. moewusii cpDNAs were employed to study the inheritance of cpDNA in an F1 hybrid which had inherited a non-Mendelian streptomycin resistance marker (sr-2) from the C. eugametos mating-type plus (mt +) parent and in two homoplasmic mitotic segregants from a B 1 hybrid (F1 × C. moewusii) which had been initially heteroplasmic for the resistance marker. Although the cpDNA patterns in the F1 hybrid were similar to those of the C. eugametos ml 1 parent, important differences were noted which suggest that recombination between C. eugametos and C. moewusii cpDNA had occurred. Homoplasmic streptomycin resistant and sensitive mitotic segregants recovered from the B1 hybrid product reveal Aval restriction patterns similar to those of the respective resistant and sensitive parents. These data are consistent with the hypothesis that the sr-2 marker is located in cpDNA and that C. eugametos and C. moewusii cpDNA sequences can coexist in the same chloroplast and, at least sometimes, segregate without extensive recombination. The transmission of low molecular weight DNAs characteristic of C. moewusii but of unknown cellular origin shows no direct correlation with the transmission of the sr-2 marker.
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  • 6
    ISSN: 1432-0983
    Keywords: Chlamydomonas ; Chloroplast DNA ; Density transfer ; Recombination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 15N-14N density transfer experiments with synchronized vegetative cultures of Chlamydomonas reinhardtii revealed a dispersive labelling of chloroplast DNA (cpDNA) while the labelling of nuclear DNA was consistent with semiconservative replication. The dispersive labelling of cpDNA was progressive and extensive as after less than two net doublings of this DNA in 14N-medium no significant amount of fully heavy, 15N-strands could be detected in denatured cpDNA preparations; the average size of DNA in these preparations corresponded to 6% of the intact chloroplast genome or about 12 kbp. The density shifts of native cpDNA samples were found to be consistent with the net amounts of cpDNA synthesized. This observation indicates that essentially all 15N atoms incorporated prior to the transfer were conserved and that metabolic turnover of cpDNA was probably absent. Our results are best explained by the exchange of homologous single-stranded segments between cpDNA molecules to form heteroduplex regions and by each DNA molecule undergoing several rounds of heteroduplex formation.
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  • 7
    ISSN: 1432-0983
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
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  • 8
    ISSN: 1432-0983
    Keywords: Chlamydomonas ; chloroplast DNA ; cell-cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The accumulation of chloroplast and nuclear DNAs during the 12 h light and 12 h dark synchronized vegetative cell-cycle of Chlamydomonas reinhardtii was monitored by the direct optical quantification of these DNAs in the analytical ultracentrifuge. Net synthesis of nuclear DNA was sharply discontinuous and this synthesis occurred during the first 6 h of the dark period. In contrast, the net synthesis of chloroplast DNA appeared continuous throughout the cell-cycle. The rate of this accumulation, however, was greatest in the dark period.
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  • 9
    ISSN: 1432-0983
    Keywords: Physical mapping ; Gene localization ; Chloroplast genome evolution ; Sequence rearrangement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The physical mapping of Aval, BstEII and EcoR1 restriction sites on the chloroplast genome of the green alga Chlamydomonas eugametos is presented. The circular map, with a size of 243 kilobase pairs, is the largest yet reported for a chloroplast genome. It features a large inverted repeat sequence, part of which encodes the 16S and 23S ribosomal RNAs (rRNAs), the large subunit of ribulose-1,5-bisphosphate carboxylase-oxygenase (rbcL) and the “32-kdodalton” thylakoid membrane protein (psbA). Such an rRNA-encoding inverted repeat sequence is also found in the chloroplast genomes of Chlamydomonas reinhardtii and most land plants. These genomes, however, differ from that of C. eugametos by the absence of the rbcL gene from the inverted repeat sequence of C. reinhardtii and by the absence of both the rbcL and psbA genes from the inverted repeat sequence of land plants. Possible evolutionary implications of these differences are discussed.
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  • 10
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In synchronized cultures of Chlamydomonas reinhardtii N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) was found to selectively mutate replicating forms of nuclear DNA. This conclusion was based on the 15- to 30-fold increase in the recovery of MNNG induced Mendelian streptomycin resistant mutants (sr-1) which was correlated with mutagenesis during the period of nuclear DNA replication. No concomitant increase in the recovery of non-Mendelian streptomycin resistant mutants (sr-2) occurred during this same period. Mutagenesis at the time of chloroplast DNA replication, however, resulted in a 1.5- to 1.6-fold increase in the recovery of both sr-1 and sr-2 induced mutants.
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