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R Appels

Publications and source records attributed to R Appels.

At least 37 records · Page 2Linked to original sources
PubMed1997

A complex arrangement of genes at a starch branching enzyme I locus in the D-genome donor of wheat.

Genomic DNA fragments from Triticum tauschii (D-genome donor to wheat) carrying starch branching enzyme I (SBE I) type genes have been characterized. One fragment contains one complete gene and two partial genes in 16 kb of DNA. One of the partial genes is oriented in the opposite strand to the other two. The gene that is complete was sequenced. Its structure corresponds closely to that of rice in that exons 3-8 are retained at similar sizes and spacings. A cDNA closely corresponding to the complete gene was isolated and characterized; it codes for a putative protein that represents a novel type of SBE I, as it is shorter at the 3' end than the forms reported so far in other plants. A second genomic fragment contains a different SBE I gene. There appear to be approximately 10 copies of SBE I type genes in wheat (approximately 5 in T. tauschii) and most of them have been assigned to group 7 chromosomes. In situ hybridization indicates that a major locus for the genes is located at the distal end of the short arm of chromosome 7D.

1,4-alpha-Glucan Branching Enzyme↗
PubMed1997

Map-based cloning of a gene sequence encoding a nucleotide-binding domain and a leucine-rich region at the Cre3 nematode resistance locus of wheat.

The Cre3 gene confers a high level of resistance to the root endoparasitic nematode Heterodera avenae in wheat. A DNA marker cosegregating with H. avenae resistance was used as an entry point for map-based cloning of a disease resistance gene family at the Cre3 locus. Two related gene sequences have been analysed at the Cre3 locus. One, identified as a cDNA clone, encodes a polypeptide with a nucleotide binding site (NBS) and a leucine-rich region; this member of the disease resistance gene family is expressed in roots. A second Cre3 gene sequence, cloned as genomic DNA, appears to be a pseudogene, with a frame shift caused by a deletion event. These two genes, related to members of the cytoplasmic NBS-leucine rich repeat class of plant disease resistance genes were physically mapped to the distal 0.06 fragment of the long arm of wheat chromosome 2D and cosegregated with nematode resistance.

Amino Acid Sequence↗
PubMed1996

The Sec-1 locus on the short arm of chromosome 1R of rye (Secale cereale).

This paper describes a detailed sequence analysis of the omega-secalin gene array at the Sec-1 locus on the short arm of chromosome 1 of rye. The analysis shows that the genes are separated by 8 kb of spacer sequence and that the gene/spacer units are arranged in a head to tail fashion. The boundaries of the array are identified, and a fragment containing the majority of the genes in the array is separated by PFG analysis. The sequence data of one 9.2 kb gene unit have been determined, and because of the similarity of the gene units within the array these data provide a detailed sequence analysis of 140 kb of the Sec-1 locus. Fluorescence in situ hybridization, using lambda clones isolated for the structural analysis, identifies the position of the array on the rye chromosomes relative to the 5S rRNA genes.

Cloning, Molecular↗
PubMed1995

Intraspecific and interspecific variation in 5S RNA genes are decoupled in diploid wheat relatives.

5S RNAs form part of the ribosome in most organisms. In some, e.g., prokaryotes and some fungi, the genes are part of the ribosomal operon, but in most eukaryotes they are in tandem arrays of hundreds to thousands of copies separate from the main ribosomal array. 5S RNA genes can be aligned across kingdoms. We were therefore surprised to find that, for 28 diploid species of the wheat tribe (Triticeae), nucleotide diversity within an array is up to 6.2% in the genes, not significantly different from that of the nontranscribed spacers. Rates of concerted evolution must therefore be insufficient to homogenize the entire array. Between species, there are significantly fewer fixed differences in the gene than would be expected, given the high within-species variation. In contrast, the amount of variation between species in the spacer is the same as or greater than that within individuals. This leads to a paradox. High variation within an individual suggests that there is little selection on any particular gene within an array. But conservation of the gene across species implies that polymorphisms are periodically eliminated at a rate approximately equal to or greater than that of speciation. Levels of intraspecific polymorphism and interspecific divergence are thus decoupled. This implies that selective mechanisms exist to eliminate mutations in the gene without also affecting the spacer.

Base Sequence↗
PubMed1994

Amplification of DNA sequences in wheat and its relatives: the Dgas44 and R350 families of repetitive sequences.

The sequence of a Triticum tauschii genomic clone representing a family of D-genome amplified DNA sequences, designated Dgas44, is reported. The Dgas44 sequence occurs on all chromosomes of the D genome of wheat, Triticum aestivum, and in situ hybridization revealed it to be evenly dispersed on all seven chromosome pairs. An internal HindIII fragment of Dgas44, designated Dgas44-3, defines the highly amplified region that is specific to the D genome. The polymerase chain reaction was used to amplify a 236-bp fragment within Dgas44-3 from chromosomes 1D, 2D, 3D, 4D, 5D, and 7D, and identical copies of this region of the Dgas44-3 sequence were found among the isolates from each of the chromosomes. The Dgas44-3 sequence population from specific chromosomes differed on average by 0.22% from the original Dgas44 sequence. The Dgas44 sequence was found to differentiate between the D genome present in T. aestivum, T. tauschii, hexaploid T. crassum, T. cylindricum, T. ventricosum, in which the sequence was present in a highly amplified form and T. juvenale, T. syriacum, and tetraploid T. crassum where the sequence family was difficult to detect. Another class of amplified sequences previously considered to be rye "specific." R350, was isolated from tetraploid wheat and its dispersed distribution on chromosomes was similar to the Dgas44 family in T. tauschii. In contrast with the Dgas44 sequence family, genome specificity for the remnant R350 sequence family was not evident since it was present on all wheat chromosomes.

Base Sequence↗
PubMed1991

The cytogenetic and molecular architecture of chromosome 1R--one of the most widely utilized sources of alien chromatin in wheat varieties.

Chromosome 1R of rye (Secale cereale) is one of the most intensively used sources of alien chromatin in bread wheat. It provides a source of valuable disease resistance genes and its widespread use has stimulated the development of genetic maps incorporating protein and DNA markers. Published data as well as new mapping data were combined into a consensus map by using common markers in the different mapping studies to orient the various data sets relative to each other. The consensus map provides a tentative order, and relative distances, between the genetic markers. A summary of the dispersed repetitive sequences that are now available for the detection and characterization of chromosome 1R segments in wheat is also provided.

Base Sequence↗
PubMed1990

New Secale cereale (rye) DNA derivatives for the detection of rye chromosome segments in wheat.

Subcloning of a clone of the 120-bp family of rye, pSc119, has produced two extremely useful probes. pSc119.1 assays rye-specific dispersed repetitive sequence families. It is present on all seven rye chromosomes and hybridizes to the entire length of each chromosome, with the exception of some telomeres and the nucleolar organiser region. pSc119.2, in contrast, hybridizes predominantly to the telomeric regions of rye chromosomes, with some interstitial sites. Unlike pSc119.1, it assays similar repetitive sequence families in both wheat and rye chromosomes.

Chromosomes↗
PubMed1989

The molecular-cytogenetic analysis of grasses and its application to studying relationships among species of the Triticeae.

An analysis of four species from the genus Secale, including the study of different accessions, has shown that the properties of DNA clones of monomer units from three repeated sequence loci, namely, Ter, Nor, and 5S DNA, proved to be representative of the entire loci from which they were isolated. This finding in Secale species, including the discovery of a new locus for 5S DNA on chromosome 5R, has been used to interpret information on the Ter, Nor, and 5S DNA loci from 15 species in the Triticeae complex. The evolutionary relationship among species suggested by the DNA sequence data has shown many consistencies with a number of other characters such as those used in classical systematics, as well as geographical distribution data and isozyme and chromosome-pairing studies. Apparent inconsistencies such as a close relationship between the R and P genomes at the Ter loci are interpreted in terms of amplification-deletion phenomena known to occur at repetitive sequence loci. In addition, this study included species endemic to Australia and thus provided a broad time span in which to consider some features of repeated sequence family evolution, such as the conservation of certain parts of 5S DNA spacer regions.

Base Sequence↗
PubMed1989

Phylogenetic relationships of Triticum tauschii, the D-genome donor to hexaploid wheat. 4. Variation and chromosomal location of 5S DNA.

The 5S DNA sequences in Triticum tauschii are organised in large clusters containing units that are primarily either 420 ("short") or 490 base pairs (bp) in length ("long"). The main cluster of short units was shown to be located on chromosome 1D in hexaploid wheat and is designated 5SDna-D1, while the cluster of long units was shown to be on chromosome 5D and is designated 5SDna-D2. The chromosomal locations in hexaploid wheat most likely correspond to those in T. tauschii and this could be shown directly for the 5SDna-D2 locus by using a T. tauschii 5D substitution in 'Chinese Spring' wheat. The sequence alignment of units derived from 5SDna-D1 and 5SDna-D2 revealed three apparent deletions in the noncoding spacer region, which were fixed in units from 5SDna-D1, and one deletion, which was fixed in units from 5SDna-D2. A minor size class, 400 bp long and closely related to the units from 5SDna-D1, was found in 2 of 415 accessions surveyed. A continuous range of quantitative changes in the number of 5S DNA units at the two loci was evident with up to a 10-fold relative abundance level of units being found in some accessions. Triticum tauschii var. typica was particularly noteworthy in that many accessions showed more units at 5SDna-D2 relative to 5SDna-D1. Partial thermal dissociation experiments with radioactive probes, synthesized from either the short or long 5S DNA units, hybridized to genomic DNA showed that the population of units at the respective loci were relatively homogeneous and clearly distinct from each other.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1989

A second locus for the 5S multigene family in Secale L.: sequence divergence in two lineages of the family.

The 5S RNA genes in Secale sp. are arranged as tandem arrays of a 460- and 480-bp repeating sequence. These size classes were initially discovered by restriction endonuclease analysis using BamHI and subsequently by DNA sequencing of cloned units. The length variation between short and long units originated from major deletion-insertion events in the noncoding spacer region of the 5S DNA repeat units. In situ hybridization with [3H]cRNA and biotin-labelled probes synthesized from both the short and long 5S DNA units of S. cereale localized the sites on chromosome 1R and a new site on a chromosome identified as 5R. We propose that the chromosome 1R locus, which has been mapped previously, be named 5SDna-R1 and the second locus, reported in the present paper, be referred to as 5SDna-R2. A preferential hybridization of a probe from the long unit to the 5SDna-R2 locus and of a probe from the short unit to the 5SDna-R1 locus is reported. The clustering of long units in the 5SDna-R2 locus was confirmed by restriction endonuclease digestion of DNA from rye chromosome 5R additions to wheat. Nucleotide sequence alignment of 5S DNA repeat units from a number of Secale species, using both phenetic and cladistic computer programmes, demonstrated that two clear lineages corresponding to the long and short units existed in this genus. The different Secale species could not be unambiguously differentiated using the 5S DNA sequences.

Base Sequence↗
PubMed1986

The heterochromatin of grasshoppers from the Caledia captiva species complex. I. Sequence evolution and conservation in a highly repeated DNA family.

The restriction enzyme TaqI digests 0.2% of the genomic DNA from the grasshopper Caledia captiva to a family of sequences 168 bp in length (length of consensus sequence). The sequence variation of this "Taq family" of repeat units was examined among four races from C. captiva to assay the pattern of evolution within this highly repeated DNA. The Taq-family repeats are located in C-banded heterochromatin on at least one member of each homologous pair of chromosomes; the locations range from centromeric to telomeric. Thirty-nine cloned repeats isolated from two population 1A individuals along with 11 clones from seven populations taken from three of the races demonstrated sequence variation at 72 positions. Pairwise comparisons of the cloned repeats, both within an individual and between different races, indicate that levels of intraspecific divergence, as measured by reproductive incompatibility, do not correlate with sequence divergence among the 168-bp repeats. A number of subsequences within the repeat remain unchanged among all 50 clones; the longest of these is 18 bp. That the same 18-bp subsequence is present in all clones examined is a finding that departs significantly (P less than 0.01) from what would be expected to occur at random. Two other cloned repeats, from a reproductively isolated race of C. captiva, have sequences that show 56% identity with this 18-bp conserved region. An analysis showed that the frequency of occurrence of an RsaI recognition site within the 168-bp repeat in the entire Taq family agreed with that found in the cloned sequences. These data, along with a partial sequence for the entire Taq family obtained by sequencing uncloned repeats, suggest that the consensus sequence from the cloned copies is representative of this highly repeated family and is not a biased sample resulting from the cloning procedure. The 18-bp conserved sequence is part of a 42-bp sequence that possesses dyad symmetry typical of protein-binding sites. We speculate that this may be significant in the evolution of the Taq family of sequences.

Animals↗
PubMed1982

Pleiotropic effects associated with the deletion of heterochromatin surrounding rDNA on the X chromosome of Drosophila.

In Drosophila melanogaster X chromosome heterochromatin (Xh) constitutes the proximal 40% of the X chromosome DNA and contains a number of genetic elements with homologous sites on the Y chromosome, one of which is well defined, namely, the bobbed locus, the repetitive structural locus for the 18S and 28S rRNAs. This report presents the localisation of specific repeated DNA sequences within Xh and the employment of this sequence map in constructing new chromosomes to analyse the nature of the heterochromatin surrounding the rDNA region. Repeated sequences were located relative to inversion breakpoints which differentiate Xh cytogenetically. When the rDNA region was manipulated to be in a position in the chromosome so that it was without the Xh which normally surrounds it, the following observations were made. (i) The rDNA region of Xh is intrinsically heterochromatic, remaining genetically active and yet possessing major heterochromatic properties even in the absence of the flanking heterochromatin regions. (ii) The size of the deletion removing the portion of Xh normally located distal to the rDNA region affected the dominance relationship between the X and Y nucleolar organizers (activity/endoreduplication assayed in male salivary glands). The X rDNA without any flanking heterochromatin was dominant over Y rDNA while the presence of some Xh allowed both the X and Y rDNA to be utilized. (iii) Enhancement of the position effect variegation on the white locus was demonstrated to occur as a result of the Xh deletions generated. EMS mutagenesis studies argue that the regions of Xh flanking the rDNA region contain no vital loci despite the fact that they strongly effect gene expression in some genotypes. This is consistent with early studies using X-ray mutagenesis (Lindsley et al., 1960). The pleiotropic effects of deleting specific regions of Xh is discussed in relation to the possible influence of heterochromatin on the organisation of the functional interphase nucleus.

Animals↗
PubMed1981

The distribution of two highly repeated DNA sequences within Drosophila melanogaster chromosomes.

In situ hybridization using 3H-RNA probes has been used to localize the sequences found in two satellites of density 1.705 g/cc and 1.672 g/cc to specific sites within the chromosomal complement. A detailed analysis of the sites on the S chromosome was carried out using the acute series of inversions to relate the heterochromatic breakpoint relative to the location of the sequence on this chromosome. It has also been possible to establish the order of arrangement of 1.705 and 1.672 DNA at the heterochromatic-euchromatic junction on chromosome 3(R). A mitotic map is provided. The Tm of hybrids formed in situ showed that the hybrids were representative of the sequences being analyzed. The two satellites also were traced through a number of purification procedures to show that a covalent linkage may be likely between the 1.705 g/cc and 1.672 g/cc satellite as predicted from in situ hybridization analyses.

Animals↗