Nuclear and mitochondrial revertants of a mitochondrial mutant with a defect in the ATP synthetase complex

Summary Yeast strain 990 carries a mutation mapping to the oli1 locus of the mitochondrial genome, the gene encoding ATPase subunit 9. DNA sequence analysis indicated a substitution of valine for alanine at residue 22 of the protein. The strain failed to grow on nonfermentable carbon sources such as glycerol at low temperature (20°C). At 28°C the strain grew on nonfermentable carbon sources and was resistant to the antibiotic oligomycin. ATPase activity in mitochondria isolated from 990 was reduced relative to the wild-type strain from which it was derived, but the residual activity was oligomycin resistant. Subunit 9 (the DCCD-binding proteolipid) from the mutant strain exhibited reduced mobility in SDS-polyacrylamide gels relative to the wild-type proteolipid. Ten revertant strains of 990 were analyzed. All restored the ability to grow on glycerol at 20°C. Mitotic segregation data showed that eight of the ten revertants were attributable to mitochondrial genetic events and two were caused by nuclear events since they appeared to be recessive nuclear suppressors. These nuclear mutations retained partial resistance to oligomycin and did not alter the electrophoretic behavior of subunit 9 or any other ATPase subunit. When mitochondrial DNA from each of the revertant strains was hybridized with an oligonucleotide probe covering the oli1 mutation, seven of the mitochondrial revertants were found to be true revertants and one a second mutation at the site of the original 990 mutation. The oli1 gene from this strain contained a substitution of glycine for valine at residue 22. The proteolipid isolated from this strain had increased electrophoretic mobility relative to the wild-type proteolipid.Abbreviations DCCD dicyclohexylcarbodiimide - SDS sodium dodecyl sulfate - PMSF phenylmethylsulfonyl fluoride - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulfonate - SMP submitochondrial particles - mit^- mitochondrial point mutant     

Genetic determination of ubiquinol-cytochromec reductase

Summary In order to find new genetic loci on the yeast mitochondrial DNA, especially mutations affecting the structure and function of ubiquinol-cytochrome c reductase, 45 independently arisen mutants resistant to mucidin have been isolated after MnCl₂ mutagenesis. The majority of the mutants exhibited increased sensitivity to chloramphenicol, diuron and antimycin A, respectively. it was shown by several criteria that all mutants resulted from mutations localized on the mitochondrial DNA.The allelism tests revealed that these mutations fall into three distinct loci muc1, muc2 and muc3. Mutations at a new locus muc3 were correlated with the changes in the binding or inhibitory sites on the inner mitochondrial membrane. Multifactorial crosses involving the mucidin resistance mutations and mitochondrial mutations conferring resistance to chloramphenicol, erythromycin, oligomycin and diuron revealed that the studied mutations at the loci muc1, muc2 and muc3 did not significantly influence the process of mitochondrial recombination and its control by the mitochondrial locus . The locus muc1 was found to be allelic to the locus diu2. The locus muc2 which was found to be allelic to cob1 locus appears to be linked to the locus oli1 but unlinked to the loci , cap1, ery1 and muc1. The new locus muc3 appears to be weakly linked to the locus diu1 but unlinked to the loci , cap1, ery1, oli1 and muc1.The results are consistent with the gene order oli1-muc2-muc3-diu1-muc1-oli2 and suggest the participation of at least three mucidin resistance loci and one diuron resistance locus in the biogenesis of the bc ₁ complex of the mitochondrial respiratory chain.     

Assembly of the mitochondrial membrane system: mutations in the pho2 locus of the mitochondrial genome of Saccharomyces cerevisiae.

Two mutants of Saccharomyces cerevisiae which show a loss of mitochondrial rutamycin-sensitive ATPase activity are described. Although phenotypically similar to mutants of the mitochondrial locus pho1 [F. Foury and A. Tzagoloff (1976) Eur. J. Biochem. 68, 113-119], these mutants define a second ATPase locus on the mitochondrial DNA (designated pho2), which is genetically unlinked to pho1. Analysis of recombination in crosses involving multiple antibiotic resistance markers indicates that the locus is in the segment of the genome between ery1 and oli2, very close to oli1. In fact it is proposed that the oli1 and pho2 mutations are in the same gene. Supporting evidence for this proposal includes: 1. The analysis of marker retention in petite mutants shows that the oli1 and pho2 loci were either retained or lost together in all cases. 2. Recombination frequencies of 0.05% or less are observed in crosses between the oli1 and pho2 loci. 3. When rho+ revertants are isolated from the pho2 mutants they frequently are oligomycin resistant. 4. pho2 mutants have an altered subunit 9 of the ATPase complex.     

Mapping of ornithine aminotransferase gene sequences to mouse Chromosomes 7, X,and 3

Ornithine aminotransferase (OAT), a mitochondrial matrix enzyme, is deficient in patients with gyrate atrophy of the choroid and retina. In human, the OAT structural gene maps to Chromosome (Chr) 10q26 and several OAT-related sequences, some of which are known to be processed pseudogenes, which map to Xp11.3–11.21. Here, we report chromosomal localization in the mouse of the OAT gene and related sequences. Genomic DNA blot analysis of a well-characterized panel of Chinese hamster x mouse somatic cell hybrids using a human OAT probe revealed two murine loci, one on mouse Chr 7 and the other on Chr X. In addition, segregation of restriction fragment length polymorphisms (RFLPs) detected by the OAT probe in recombinant inbred (RI) strains detected a third locus on Chr 3 and positioned the X locus near Cf-8 and Rsvp. Progeny of an intersubspecific backcross were used to map the Chr 7 locus between Tyr and Int-2, near Cyp2e-1.     

Genetic control and linkage relations of additional isozyme markers in chick-pea

Summary Allozyme polymorphisms of nine enzymes — aspartate aminotransferase (AAT), diaphorase (DIA), esterase (EST), formate dehydrogenase (FDH), -galactosidase (GAL), -glucosidase (GLU), malate dehydrogenase (MDH), malic enzyme (ME), and peroxidase (PRX) — were described in chick-pea (Cicer L.). Thirteen isozyme loci, Aat-c, Dia-4, Est-2, Est-4, Est-10, Fdh, Gal-2, Gal-3, Gal-4, Glu-3, Mdh-2, Me-2, and Prx-2, were genetically defined. Alleles of each of these isozyme loci expressed codominantly in heterozygotes and exhibited a codominant, single-locus segregation ratio in F₂. The loci Est-2, Mdh-2, and Me-1 were expressed only in flower. Linkage relations were determined for these 13 and several previously defined isozyme loci. The following new genetic linkages were identified: Pgm-p (locus for plastid phosphoglucomutase) — Est-10; Ald-p1 (one of the duplicate loci for plastid aldolase) — Glu-3 — Gal-2 — Est-2,3; Gal-3 — Aco-m (locus for mitochondrial aconitase) — Prx-2,3; Gpi-c (locus for cytosolic glucosephosphate isomerase) — Fdh; and Est-4 — Me-1. This study provides further confirmation on the existence of several conserved linkage groups among Cicer, Pisum, and Lens.     

Inheritance of restriction fragment length polymorphisms and random amplified polymorphic DNAs in coastal Douglas-fir

A total of 225 new genetic loci [151 restriction fragment length polymorphisms (RFLP) and 74 random amplified polymorphic DNAs (RAPD)] in coastal Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco var. menziesii] have been identified using a three-generation outbred pedigree. The Mendelian inheritance of 16 RFLP loci and 29 RAPD loci was demonstrated based on single-locus segregation in a sample of F₂ progeny. One RFLP locus, PtIFG2025, showed segregation distortion. Probe pPtIFG2025 is a loblolly pine cDNA probe encoding for rbcS. The 16 RFLP loci and 23 allozyme loci were also assayed in a sample of 16 Douglas-fir seed-orchard clones. Allelism was determined at 11 of the 16 RFLP loci. RFLPs were able to detect slightly more variation (4.0 alleles per locus) than allozymes (3.1 alleles per locus). The inheritance of an additional 80 RAPD loci was determined based on haploid segregation analysis of megagametophytes from parent tree 013-1. Once 200–300 markers are identified and placed on a genetic map, quantitative trait loci affecting bud phenology will be mapped.     

Moving pictures of DNA released upon lysis from bacteria,chloroplasts, and mitochondria

Summary Cells and organelles suspended in gelled agarose agarose were lysed with detergent and protease, stained with ethidium bromide and their DNA was observed by fluorescence microscopy. The migration of individual DNA molecules during electrophoresis on a microscope slide was recorded on video tape so that moving pictures could be analyzed. The DNA from lysed bacteria (Escherichia coli andAgrobacterium tumefaciens) appeared as a rosette of at least twenty loops of varying size, whereas that from bacterial spheroplasts (E. coli andPseudomonas aeruginosa) appeared as circular forms or rods with many fine filaments of RNA extending toward the anode. The DNA from chloroplasts of watermelon (Citrullus vulgaris) and pea (Pisum sativum) did not appear as a rosette of loops. Many or most of the chloroplast DNA molecules per lysed chloroplast were immobile in the electric field, as if in circular form hooked on agarose fibers. The amount of DNA-fluorescence per watermelon mitochondrial particle was much less than that found for either chloroplasts or bacteria. The appearance of the mitochondrial DNA during electrophoresis was that of linear molecules, no obviously circular forms were evident and no rosette structures were observed.Abbreviations cpDNA chloroplast DNA - DAPI 4,6-diamidino-2-phenylindole - kb kilobase pairs - mtDNA mitochondrial DNA - PFGE pulsed-field gel electrophoresis     

Mitochondrial resistance to miconazole in Saccharomyces cerevisiae

Summary One mutant of mitochondrial origin resistant to miconazole has been isolated and characterized in S. cerevisiae. The mutation is linked to the locus oli1, the structural gene for subunit 9 of ATPase on mitochondrial DNA. Miconazole inhibited the mitochondrial ATPase of the wild type while the enzyme of the resistant mutant was insensitive to this effect. Levels of ATP decreased to one-third of the control in the wild type in the presence of miconazole, while they were unaffected in the mutant.Abbreviations MNNG N-methyl-N-nitrosoguanidine - Mic^s/Mic^r phenotypic sensitivity/resistance to miconazole - M ₁ ^R mitochondrial locus conferring miconazole resistance - rho⁺/rho^- grand/cytoplasmic petite - rho^o cytoplasmic petite deleted of all mitochondrial DNA - w⁺ mitochondrial locus conferring polarity of recombination     

Organellar segregation,rearrangement and recombination in protoplast fusion-derived Brassica oleracea calli

Summary Cauliflower protoplasts were fused to determine the effect of protoplast source and pretreatment on organellar segregation in fusion products. Mitochondrial and chloroplast type were determined for over 250 calli from eight fusions between iodoacetate-treated or -irradiated leaf or hypocotyl protoplasts with fertile or Ogura cytoplasms. Organelles in fusion-derived calli were identified with five mitochondrial probes and one chloroplast probe. Mitochondrial and chloroplast segregation were independent but biased. Most calli had B. oleracea chloroplasts, but more calli had Ogura mitochondria than B. oleracea ones. Neither protoplast source nor pretreatment alone affected organelle segregation. However, iodoacetate treatment of hypocotyl protoplasts reduced their mitochondrial contribution to the fusion products although it did not affect chloroplast segregation. Over half of the calli had mitochondrial genomes distinct from those of either fusion partner; many of these contained the complete mitochondrial genome of one partner along with some mitochondrial DNA from the other. Out of 258 calli, 83 showed evidence of mitochondrial recombination, most commonly by formation of a novel 11-kb PstI fragment near the atp9 region.     

Evaluation of 11 single‐locus and seven multilocus DNA barcodes in Lamium L. (Lamiaceae)

The aim of this work was to evaluate the suitability of selected DNA regions in the barcoding of plants, based on the species belonging to the genus Lamium (Lamiaceae). For this purpose, nine chloroplast barcodes, that is, accD, matK, rbcL, rpoA, rpoB, rpoC1, rpoC2, trnH‐psbA, trnL‐trnF, as well as ITS nuclear region, and intron of mitochondrial nad5 gene were tested. Among the single‐locus barcodes, most effective in the identification of Lamium species was the trnH‐psbA spacer and matK gene. The high level of variability and resolving power was also observed in the case of rpoA and rpoC2 genes. Despite the high interspecies variability of ITS region, it turned out to be inapplicable in Lamium identification. An important disadvantage of ITS as a barcode is a limitation of its use in polyploid plants, samples contaminated with fungal material or samples with partially degraded DNA. We have also evaluated five‐two‐locus and two‐three‐locus barcode regions created from a combination of most effective single loci. The best‐performing barcode combinations were matK + trnH‐psbA and matK + rpoA. Both of them had equally high discriminative power to identify Lamium species.     

Bacteriophage ?29 infection of Bacillus subtilis minicells

Summary Labelled chloroplast rRNAs from Spinacia oleracea were hybridized to restriction endonuclease digests of chloroplast DNA from Oenothera hookeri and Euglena gracilis, to mitochondrial DNA of Acanthamoeba castellanii, and to DNA of the E. coli rrn B operon in the transducing phage lambda rif^d18. The degree of homology is greatest for the 16S rRNA gene. Greater than 90% occurs between the two higher plant genes, 80% homology to the lower plant gene, 60%–70% homology to the bacterial gene, and 20% homology to the mitochondrial gene. The degree of hybridization varied considerably for the 23S and the 5S rRNA genes. Very high homology exists between the two higher plant genes, only about 50% homology for both the Euglena and bacterial genes, and no significant homology for the mitochondrial genes. These results show that any chloroplast (or E. coli) rRNA may be used as a probe to identify rRNA genes in other ctDNAs.Two RNA populations, each enriched for a different ctDNA-encoded mRNA, proved useful in the location of these genes on both higher plant ctDNAs. No significant hybridization was obtained using these probes to the Euglena ctDNA which seems to be too distantly related.Abbreviations Md megadalton, 10⁶ dalton - bp, kbp base pair, kilo base pair - SSC Standard saline citrate, 1 times SSC is 0.15M sodium, chloride, 0.015 M trisodium citrate, pH, 6.8 - mtDNA mitochondrial DNA - ctDNA chloroplast DNA - ctrRNA chloroplast ribosomal RNA     

Inheritance of Organelle DNA in Rye (Secale cereale L.) with Triticale (×Triticale Thch.) Hybrids

The mode of inheritance of chloroplast and mitochondrial DNA (mtDNA) in rye × triticale intergeneric hybrids has been studied with the use of specific PCR markers for loci 18S/5S and 3rbcL in organelle DNA. In rye × triticale BC₁, mtDNA copies of two types, paternal and maternal, have been found; in BC₂ plants, only paternal mtDNA and chloroplast DNA (cpDNA) have been detected. Mechanisms determining the inheritance and/or differential amplification of organelles of a specific type are discussed.     

Mutants in yeast affecting ethidium bromide induced rho- formation and their effects on transmission and recombination of mitochondrial genes.

Summary A series of mutants called ebi, less inducible by ethidium bromide than the parental strain for the ^+– mutation have been isolated after E.M.S. mutagenesis. Some of the ebi mutants also show an important accumulation of ^– cells, in the absence of ethidium bromide. Ebi mutations are nuclearly inherited as shown by meiotic segregation. The effects of these mutants on the transmission and recombination of mitochondrial genes among the diploid progeny of crosses have been studied. Some of the ebi mutants show a non coordinated transmission of the oli1 mitochondrial marker with respect to other mitochondrial markers unexpected for homosexual crosses. This bias which is independent from will be discussed in relation to the segregation and recombination. No significant decrease of the frequency of recombinants has been detected.Abbreviations E.B. Ethidium bromide - E.M.S. Ethyl méthane sulfonate - C^S/C^R Allelic forms of the rib 1 locus conferring chloramphenicol sensitivity/resistance - E^S/E^R Allelic forms of the rib 3 locus conferring erythromycine sensitivity/resistance - O^R/O^R Allelic forms of the oli 1 locus conferring oligomycin sensitivity/resistance - P^S/P^R Allelic forms of the par 1 locus conferring paromomycine sensitivity/resistance - D^S/D^R Allelic forms of the diu 1 or diu 2 loci conferring diuron sensitivity/resistance - C^S/C^R Allelic forms of the mitochondrial locus - ⁺ grande or respiratory competent cells - ^– petite or cytoplasmic respiratory deficient cells     

Biogenesis of mitochondria 49 identification and mapping of a new mitochondrial locus (tsr1) which maps within polar region of yeast mitochondrial genome.

Summary An enrichment procedure which facilitates the isolation of conditional respiratory-deficient mutants of Saccharomyces cerevisiae is reported. Detailed genetic analysis of one mutant which exhibits a respiratory deficient phenotype at low temperature (18°C) is also presented. The phenotype is due to a single lesion at a new locus, tsr1, located on the mitochondrial DNA. By analysis of locus retention patterns in a set of physically characterized petite strains, the tsr1 mutation has been mapped within the segment 0–5 map units on the physical map of the yeast mitochondrial genome. This segment of the mitochondrial DNA also contains the cap1 and ery1 loci and the cistron for the mitochondrial 21S rRNA. Studies of the frequencies of co-retention of markers in petite populations, and of the frequencies of recombination of markers in non-polar crosses (⁺ × ⁺), demonstrate linkage of the tsr1 locus to both the cap1 and ery1 loci. The degree of linkage indicates that tsr1 is closer to the ery1 locus. Comparison of pairwise recombination frequencies for these three markers indicate the order cap1-tsr1-ery1. The tsr1 locus lies within the segment of the mitochondrial genome which is influenced by the polarity locus , and analysis of transmission and recombination frequencies and polarities in a polar (⁺ × ^-) cross show that the behaviour of the tsr1 locus is similar to that of ery1. However striking features of this cross are that the recombination frequency between tsr1 and ery1 is comparable to that observed in non-polar crosses, and that the polarity for recombination between tsr1 and cap1 or ery1 is extremely low.     

The phylogenetic utility of chloroplast and nuclear DNA markers and the phylogeny of the Rubiaceae tribe Spermacoceae

The phylogenetic utility of chloroplast (atpB-rbcL, petD, rps16, trnL-F) and nuclear (ETS, ITS) DNA regions was investigated for the tribe Spermacoceae of the coffee family (Rubiaceae). ITS was, despite often raised cautions of its utility at higher taxonomic levels, shown to provide the highest number of parsimony informative characters, in partitioned Bayesian analyses it yielded the fewest trees in the 95% credible set, it resolved the highest proportion of well resolved clades, and was the most accurate region as measured by the partition metric and the proportion of correctly resolved clades (well supported clades retrieved from a combined analysis regarded as “true”). For Hedyotis, the nuclear 5S-NTS was shown to be potentially as useful as ITS, despite its shorter sequence length. The chloroplast region being the most phylogenetically informative was the petD group II intron.We also present a phylogeny of Spermacoceae based on a Bayesian analysis of the four chloroplast regions, ITS, and ETS combined. Spermacoceae are shown to be monophyletic. Clades supported by high posterior probabilities are discussed, especially in respect to the current generic classification. Notably, Oldenlandia is polyphyletic, the two subgenera of Kohautia are not sister taxa, and Hedyotis should be treated in a narrow sense to include only Asian species.     

Mapping of chloroplast mutations conferring resistance to antibiotics in Chlamydomonas: Evidence for a novel site of streptomycin resistance in the small subunit rRNA

Summary A major obstacle to out understanding of the mechanisms governing the inheritance, recombination and segregation of chloroplast genes in Chlamydomonas is that the majority of antibiotic resistance mutations that have been used to gain insights into such mechanisms have not been physically localized on the chloroplast genome. We report here the physical mapping of two chloroplast antibiotic resistance mutations: one conferring cross-resistance to erythromycin and spiramycin in Chlamydomonas moewusii (er-nM1) and the other conferring resistance to streptomycin in the interfertile species C. eugametos (sr-2). The er-nM1 mutation results from a C to G transversion at a well-known site of macrolide resistance within the peptidyl transferase loop region of the large subunit rRNA gene. This locus, designated rib-2 in yeast mitochondrial DNA, corresponds to residue C-2611 in the 23 S rRNA of Escherichia coli. The sr-2 locus maps within the small subunit (SSU) rRNA gene at a site that has not been described previously. The mutation results from an A to C transversion at a position equivalent to residue A-523 in the E. coli 16 S rRNA. Although this region of the E. coli SSU rRNA has no binding affinity for streptomycin, it binds to ribosomal protein S4, a protein that has long been associated with the response of bacterial cells to this antibiotic. We propose that the sr-2 mutation indirectly affects the nearest streptomycin binding site through an altered interaction between a ribosomal protein and the SSU rRNA.     

Analysis of chloroplast and mitochondrial segregation in three different combinations of somatic hybrids produced within Brassicaceae

Summary Mitochondrial and chloroplast DNA were characterized in three different combinations of somatic hybrids produced between different species within Brassicaceae. The fusions were made between B. campestris and B. oleracea, B. napus and B. nigra and between B. napus and Eruca sativa. The combinations represent interspecific hybridizations, but the phylogenetic distance between the species used in each instance is different. Whereas the B. campestris (+) B. oleracea and the B. napus (+)B. nigra hybrids are both examples of intrageneric hybrids, B. campestris is more closely related to B. oleracea than B. napus is to B. nigra. The fusion of B. napus and E. sativa represents an intergeneric hybridization. Since hybrids were produced with reproducible and uniform fusion and culture methods, a comparison of chloroplast and mitochondrial segregation and mitochondrial DNA (mt-DNA) rearrangements could be made between the combinations. The segregation of both chloroplasts and mitochondria was biased in the B. napus (+)B. nigra and the B. napus (+)E. sativa combination. The nonrandom segregation of chloroplasts and mitochondria could be due to the different ploidy levels of the fusion partners and/or reflect differences in organelle replication rate. Furthermore, segregation of mitochondria was correlated to the differences in phylogenetic distance between the species used in the fusions. However, mitochondrial segregation, in contrast to chloroplast segregation, could in all combinations also have been affected by the cell type used as protoplast source in the fusions. All different chloroplast types could be established within each combination. Hybrids containing chloroplast from one parent together with mitochondria from the other parent were found in two of the combinations, although the majority of the hybrids had mt-DNA that was altered compared to the parental species. The rearranged mt-DNA found in most hybrids was an effect of the heteroplasmic state following protoplast fusion rather than of the tissue culture methods, since no mt-DNA rearrangements were found in B. napus plants regenerated from protoplast culture. The mtDNA restriction patterns of the hybrids with rearranged mt-DNA indicated that specific regions of the mt-DNA were involved in the rearrangements following protoplast fusion.     

DNA barcoding of Gaultheria L. in China (Ericaceae: Vaccinioideae)

Abstract Four DNA barcoding loci, chloroplast loci rbcL, matK, trnH‐psbA, and nuclear locus internal transcribed spacer (ITS), were tested for the accurate discrimination of the Chinese species of Gaultheria by using intraspecific and interspecific pairwise P‐distance, Wilcoxon signed rank test, and tree‐based analyses. This study included 186 individuals from 89 populations representing 30 species. For all individuals, single locus markers showed high levels of sequencing universality but were ineffective for species resolvability. Polymerase chain reaction amplification and sequencing were successful for all four loci. Both ITS and matK showed significantly higher levels of interspecific species delimitation than rbcL and trnH‐psbA. A combination of matK and ITS was the most efficient DNA barcode among all studied regions, however, they do not represent an appropriate candidate barcode for Chinese Gaultheria, by which only 11 out of 30 species can be separated. Loci rbcL, matK, and trnH‐psbA, which were recently proposed as universal plant barcodes, have a very poor capacity for species separation for Chinese Gaultheria. DNA barcodes may be reliable tools to identify the evolutionary units of this group, so further studies are needed to develop more efficient DNA barcodes for Gaultheria and other genera with complicated evolutionary histories.     

Nucleoid organization in the radioresistant bacterium Deinococcus radiodurans

Processes favoring the exceptional resistance to genotoxic stress of Deinococcus radiodurans are not yet completely characterized. It was postulated that its nucleoid and chromosome(s) organization could participate in the DNA double strand break repair process. Here, we investigated the organization of chromosome 1 by localization of three chromosomal loci including oriC, Ter and a locus located in its left arm. For this purpose, we used a ParB‐parS system to visualize the position of the loci before and after exposure to γ‐rays. By comparing the number of fluorescent foci with the number of copies of the studied loci present in the cells measured by quantitative polymerase chain reaction (qPCR), we demonstrated that the 4–10 copies of chromosome 1 per cell are dispersed within the nucleoid before irradiation, indicating that the chromosome copies are not prealigned. Chromosome segregation is progressive but not co‐ordinated, allowing each locus to be paired with its sister during part of the cell cycle. After irradiation, the nucleoid organization is modified, involving a transient alignment of the loci in the late stage of DNA repair and a delay of segregation of the Ter locus. We discuss how these events can influence DNA double strand break repair.     

Microsatellites and microsynteny in the chloroplast genomes of Oryza and eight other Gramineae species

Primer pairs flanking ten chloroplast microsatellite loci, originally identified in Oryza sativa cv Nipponbare, were evaluated for amplification and allelic diversity using a panel of 13 diverse cultivars of rice (O. sativa), 19 accessions of wild rice (three O. officinalis, five O. latifolia, five O. minuta, four O. australiensis, one O. brachyantha and one O. ridleyi) and eight other Gramineae species (maize, teosinte, wheat, oat, barley, pearl millet, sorghum and sugarcane). Amplified products were obtained for all samples at nine out of ten loci. Among the rice cultivars, the number of alleles per locus ranged from one to four, with monomorphic patterns observed at five loci. The average polymorphism information content (PIC) value at the other five (polymorphic) loci was 0.54 among the 13 cultivars. When wild rice and the other Gramineae species were compared based on the proportion of shared alleles, their phylogenetic relationships were in agreement with previous studies using different types of markers; however, the magnitude of the differences based on chloroplast microsatellites underestimated the genetic distance separating these divergent species and genera. A sequence-based comparison of homologous regions of the rice and maize chloroplast genomes revealed that, while a high level of microsynteny is evident, the occurrence of actively evolving microsatellite motifs in specific regions of the rice chloroplast genome appears to be mainly a species or genome-specific phenomenon. Thus the chloroplast primer pairs used in this study bracketed mutationally active microsatellite motifs in rice but degenerate, interrupted motifs or highly conserved, mutationally inert motifs in distantly related genera. Received: 17 March 1999 / Accepted: 11 November 1999