Isolation and characterisation of genes encoding rye prolamins containing a highly repetitive sequence motif.
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Amino Acid Sequence↗
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A moderately repeated DNA sequence of wheat and rye genomes.
A 371 base pair segment (bordered by Hind III and Eco RI cutting sites) of wheat embryo nuclear DNA has been cloned and sequenced. It is AT-rich (68%), shares some sequence features with autonomously replicating sequence (ARS) elements, and occurs in approximately 7600 copies per haploid genome. When used as probe for blot hybridization to Hind III-digested wheat DNA, it gives an irregular series of hybridization bands. Essentially the same hybridization pattern was observed for rye DNA. It is concluded that this segment is distributed irregularly but, apparently, according to the same rule in both wheat and rye genomes.
Base Sequence↗
Fine structure and evolution of the rDNA intergenic spacer in rice and other cereals.
The intergenic spacer of a rice ribosomal RNA gene repeating unit has been completely sequenced. The spacer contains three imperfect, direct repeated regions of 264-253 bp, followed by a related but more highly divergent region. Detailed analysis of the sequence allows the presentation of an evolutionary scenario in which the 264-253-bp repeats are derived from an ancestral 150-bp sequence by deletion and amplification. Comparison of the rice sequence with those of maize, wheat, and rye shows that, despite considerable divergence from the ancestral sequence, several regions have been highly conserved, suggesting that they may play an important role in the structure and/or expression of the ribosomal genes.
Base Sequence↗
The K+ channel in the plasma membrane of rye roots has a multiple ion residency pore.
The permeation of K+ and Na+ through the pore of a K+ channel from the plasma membrane of rye roots was studied in planar 1-palmitoyl-2-oleoyl phosphatidylethanolamine bilayers. The pore contains at least two ion-binding sites which can be occupied simultaneously. This was indicated by: (i) biphasic relationships with increasing cation concentration of both channel conductance at the zero-current (reversal) potential of the channel (Erev) and unitary-current at a specified voltage and (ii) a decline in Erev in the presence of equimolar Na+ (cis):K+ (trans) as the cation concentration was increased. To determine the spatial characteristics and energy profiles for K+ and Na+ permeation, unitary-current/voltage data for the channel were fitted to a three energy-barrier, two ion-binding site (3B2S) model. The model allowed for simultaneous occupancy of binding sites and ionic repulsion within the pore, as well as surface potential effects. Results suggested that energy peaks and energy wells (ion binding sites) were situated asymmetrically within the electrical distance of the pore, the trans energy-well being closer to the center of the pore than its cis counterpart; that the energy profile for K+ permeation differed significantly from that of Na+ in having a higher cis energy peak and a deeper cis energy well; that cations repelled each other within the pore and that vestibule surface charge was negligible. The model successfully simulated various aspects of K+ and Na+ permeation including: (i) the complexities in current rectification of a wide range of contrasting ionic conditions; (ii) the biphasic relationships with increasing cation concentration of both channel conductance at Erev and unitary-current at a specified voltage; (iii) the decline in Erev in equimolar Na+ (cis):K+ (trans) as cation concentrations were increased and (iv) the complex relationships between mole fraction and Erev at total cation concentrations of 100 and 300 mM.
Cell Membrane↗
Evolutionary variations in DNA sequences transferred from chloroplast genomes to mitochondrial genomes in the Gramineae.
The transfer of fragments of DNA from chloroplast genomes to mitochondrial genomes is considered to be a general phenomenon in higher plants. In the present study, Southern hybridization, together with amplification by PCR and DNA sequencing techniques, was used to examine the regions homologous to chloroplast rps19 in the mitochondrial genomes of several gramineous plants. In all the mitochondrial DNAs from the gramineous plants examined, except for that from wheat, the transferred fragments of chloroplast DNA were found to be maintained and the same junctions of mitochondrion-specific and chloroplast-like sequences were found at one terminus. This finding indicates that the transfer of the chloroplast sequence occurred in the distant past during the evolution of gramineous plants. Subsequent analysis revealed that the fragments had been variously rearranged among species with respect to the other terminus. Considering the current diversity of this one particular transferred fragment of chloroplast DNA, we propose that chloroplast-derived DNA sequences that have lost their original functions tend to be rearranged during evolution in mitochondrial genomes.
Base Sequence↗
The mitochondrial atpA/atp9 co-transcript in wheat and triticale: RNA processing depends on the nuclear genotype.
The gene region coding for subunits alpha and 9 of the mitochondrial ATP synthase exhibit an identical DNA sequence in wheat, rye, and the intergeneric hybrid triticale (xTriticosecale Wittmack). However, co-transcripts containing both genes show different sizes depending on the nuclear genotype. To investigate nuclear-mitochondrial interactions leading to this variation, we performed a comparative transcript analysis with various lines carrying defined nuclear and cytoplasmic genotypes. Northern analyses showed that all wheat lines investigated possess a single atpA/atp9 mRNA of 2.6kb, whereas in rye and five independent triticale lines an additional transcript of 2.35kb appeared. Primer-extension and RNase-protection analyses indicate that the co-transcripts of this gene have staggered 5' termini in some lines, whereas the 3' termini seem to be similar in wheat, rye, and triticale. Transcription is initiated at position -338/-339 upstream of the atpA gene in all lines investigated, giving rise to a 2.6-kb mRNA. In rye and triticale, staggered 5' termini were observed closer to the translational start. The DNA sequences upstream of these termini exhibit homology to plant mitochondrial-processing sites, therefore the proximal 5' ends are most probably generated by RNA processing. As the processing event occurs more frequently in triticale carrying the Triticum timopheevi cytoplasm, trans-acting factors from rye are likely to interact with other cytoplasmic factors resulting in the observed RNA modification. Most interestingly, the T. timopheevi cytoplasm inducing male sterility in alloplasmic wheat, fails to generate the CMS phenotype in triticale. The data support our hypothesis that nuclear factors affect mitochondrial gene expression and thus control sexual fertility in wheat and triticale.
Arabidopsis Proteins↗
Non-random distribution of chiasmata in rye, Crotalaria and coffe.
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Chromosomes↗
Meiotic pairing in wheat-rye derivatives detected by genomic in situ hybridization and C-banding--A comparative analysis.
Meiosis of triticalextetraploid rye hybrids (genome constitution ABRRR) was analysed by genomic in situ hybridization (GISH) and C-banding. The results obtained reveal a considerable difference between these techniques with regard to their efficiency in detecting any type of pairing, either homologous or homoeologous. Thus the percentage of pollen mother cells containing wheat/rye homoeologous associations determined by C-banding and GISH was 2.5 and 9.2, respectively. Such a discrepancy can be ascribed to a certain proportion of wheat/rye associations not being identified by C-banding. The potential and limitations of the two techniques for meiotic analysis are discussed.
Chimera↗
Physical mapping of 5S rDNA reveals a new locus on 3R and unexpected complexity in a rye translocation used in chromosome mapping.
Using fluorescence in situ hybridization (FISH) with probe pScT7, three different 5S rDNA loci were detected in the satellite of rye chromosome 1R (5SDna-R1) and in the short arms of chromosomes 3R (5SDna-R3) and 5R (5SDna-R2) respectively. All three loci showed polymorphism for the hybridization signal intensity. In order to determine the localization of these rye 5S rDNA multigene loci with higher precision within the corresponding chromosome arms, the probe pScT7 was physically mapped by FISH in relation to the following five translocations (Wageningen Tester Set): T850W (1RS/4RL), T248W (1RS/6RS), T273W (1RS/5RL), T305W (2RS/5RS) and T240W (3RS/5RL). Accurate physical maps of the translocation breakpoints had previously been made using electron microscope analysis of spread pachytene synaptonemal complexes of heterozygotes for the different translocations. The results indicate that locus 5SDna-R3 is located between the breakpoint of translocation T240W and the telomere, whereas locus 5SDna-R2 is located between the breakpoint of translocation T305W and the centromere, the hybridization of probe pScT7 on T305W translocated chromosomes demonstrating the complex nature of this translocation. On the other hand, the simultaneous detection of probes pScT7 and pTA71 (18S-5.8S-26S rDNA) with two different fluorochromes, indicated that the breakpoints of translocations T850W and T248W are located between loci Nor-R1 and 5SDna-R1.
Chromosome Mapping↗
A case report on a minor contamination of nivalenol in cereals harvested in Canada.
An investigation for the occurrence of nivalenol (NIV), deoxynivalenol (DON) and zearalenone (ZEN) in cereals (ten wheat, one rye and one corn) harvested in Canada have been carried out using a procedure, which is rapid and sensitive for Fusarium mycotoxins. NIV, DON and ZEN were detected in 4, 9 and 9 out of ten wheat samples, and their average levels in the positives were 23 ng/g, 1257 ng/g and 9 ng/g, respectively. One rye and one corn were also contaminated with a minor amount of NIV. This is the first evidence for the natural occurrence of NIV in cereals grown in Canada, though its level was far less than DON.
Canada↗
A survey of the natural occurrence of Fusarium mycotoxins, deoxynivalenol, nivalenol and zearalenone, in cereals harvested in the Netherlands.
A survey for the natural occurrence of Fusarium mycotoxins, deoxynivalenol (DON), nivalenol (NIV) and zearalenone (ZEN), in Dutch cereals (totaling 29 samples) harvested in 1984/1985, showed that 90%, 79% and 62% of samples were contaminated with DON, NIV and ZEN, respectively. Average contents (ng/g) in the total of positive samples were 221 (DON), 123 (NIV) and 61 (ZEN). Among the cereals examined, the highest concentrations (ng/g) was 3198 (DON), 1875 (NIV) and 677 (ZEN) in a yellow corn sample for animal feed. The results of this survey show that Dutch cereals were relatively significantly contaminated with Fusarium mycotoxins.
Edible Grain↗
The relatedness and evolution of repeated nucleotide sequences in the genomes of some Gramineae species.
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Base Sequence↗
Cereal prolamin evolution and homology revealed by sequence analysis.
Prolamin mixtures were isolated from oats, rice, normal and high-lysine sorghum, two varieties of pearl millet, two strains of teosinte, and gamma grass and subjected to NH2-terminal amino acid sequence determinations. In each case (except for rice, whose prolamins apparently have blocked or unavailable NH2-terminal residues), primarily a single sequence was observed despite significant heterogeneity, suggesting that prolamin homology in each cereal arose through duplication and mutation of a single ancestral gene. Comparisons were then made to prolamin sequences previously determined for wheat, corn, barley, and rye. Within genera, different varieties or subspecies exhibited few differences, but more distantly related genera, subtribes, and tribes showed increasingly large differences. Within the subfamily Festucoideae, no homology was apparent between prolamins of oats and those of the subtribe Triticinae (including wheat, rye, and barley, for which prolamin homology was previously demonstrated). Within the subfamily Panicoideae, corn was shown to be closely related to teosinte but more distantly to Tripsacum. Sorghum was shown to have diverged less from corn than had millet. These comparisons demonstrate that prolamin sequence analyses can successfully predict and clarify evolutionary relationships of cereals.
Amino Acid Sequence↗
Genetic control of a novel series of trypsin inhibitors in wheat and its relatives.
The aneuploids of Chinese Spring wheat have been used to locate the genes (Ti-2) coding for a novel series of trypsin inhibitors to the long arms of the homoeologous group 5 chromosomes. Three allelic variants at the 5D locus were detected in a limited survey among wheat varieties, but no variation at the loci on either chromosome 5A or chromosome 5B was detected. Homoeoloci were found in a number of alien relatives, and in the majority of cases, these were present on the group 5 homoeologue. However, in Aegilops umbellulata, the Ti-U2 locus was located on a chromosome presumed to belong to homoeologous group 1. No Hordeum vulgare or H. chilense Ti-2 gene was expressed in a wheat background. This new marker will be especially useful as a screening mechanism for nullisomy of chromosome 5B in work aimed at introgression of alien chromatin into wheat.
Chromosome Mapping↗
Restriction fragment analysis of the secalin loci of rye.
Analyses of wheat/rye addition lines by Southern blotting confirmed the presence of sequences related to the Sec 1, Sec 2, and Sec 3 loci on chromosomes 1R and 2R. Comparison of the 1R and 2R addition lines allowed the identification of gamma-secalin genes at Sec 1 and Sec 2, respectively, while omega-secalin and gamma-secalin genes at Sec 1 were discriminated by comparative hybridization with three probes: omega-secalin, total gamma-secalin, and 3' gamma-secalin. The high molecular weight (HMW) secalin genes at Sec 3 were identified using a homologous HMW subunit probe from wheat. Gene copy numbers were estimated as about 40-60 for omega-scalins, 5-10 for gamma-secalins, and 2 for HMW secalins. Comparison of individual plants of cv. Gazelle showed a high degree of polymorphism, particularly for sequences related to omega-secalins and HMW secalins.
Amino Acid Sequence↗
Synaptic patterns of rye B chromosomes. I: The standard type.
Chromosome pairing of standard B chromosomes (Bs) in rye has been studied by synaptonemal complex surface spreading of pollen mother cells containing from one to eight Bs. The main characteristics exhibited by the Bs are: (i) They are often located peripherally in surface spread nuclei and do not show presynaptic alignment. (ii) The period of pairing is delayed relative to that of the A set. (iii) Bs undergo extensive non-homol-ogous pairing at pachytene. (iv) The frequency of trivalents and quadrivalents in plants with 3Bs and 4Bs is about 66% following the expectations on the basis of random pairing among the short and the long arms with a single distal pairing initiation site per arm. Some quadrivalents containing two partner switches were observed, but on the same basis of randomness there was a deficiency of pachytene multivalents in plants with 5-8 Bs. The possible causes of the discrepancy between these observations are discussed. (v) There is a reduction in the frequency of multivalents between pachytene and metaphase I.
Chromosome Banding↗
Analysis of rye B-chromosome structure using fluorescence in situ hybridization (FISH).
Fluorescence in situ hybridization (FISH) has been used to analyse the structure of the rye B chromosome. Genomic in situ hybridization (GISH) demonstrates the high level of overall similarity between A and B chromosomes of rye, as well as the presence of a number of specific sequences. The B-specific repeat families D1100 and E3900 have been analysed in terms of their physical location and possible contiguity. Rye Bs contain members of the rye-specific dispersed repetitive family R173, as well as centromeric regions similar to those of the As. The B chromosomes analysed in our study lack detectable rDNA sequences. Anomalous results have been obtained with a number of subtelomeric repetitive probes from rye. Bs usually lack these sequences, but evidence is presented that in some cases A-B translocation events may relocate such sequences from the As to the Bs. These data are discussed in the context of current models for the origin of the B chromosome.
Chromosomes↗
The influence of B chromosomes on rDNA organization in rye interphase nuclei.
Patterns of rye rDNA organization in interphase nuclei were studied through the use of in situ hybridization in spreads of root meristem cells from plants with and without B chromosomes (Bs). In cells from plants without Bs each rDNA locus is organized as a single perinucleolar knob of condensed chromatin with decondensed chromatin inside the nucleolus. In plants with Bs there is a marked modification of the pattern, found in more than 23% of nuclei, which involves several regions of condensed chromatin interspersed with decondensed chromatin inside the nucleolus. This B-induced alteration in rDNA interphase organization suggests a change in expression of the rRNA genes located on the A chromosomes probably related to the reduction in nuclear RNA observed previously in plants with Bs. The influence of the Bs on the expression of A chromosome genes, through rearrangement of interphase chromatin, could provide the basis of an explanation for some of the known phenotypic effects of B chromosomes in rye.
Cell Nucleus↗