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Phylogenetic relationships among Secale species revealed by amplified fragment length polymorphisms.

Amplified fragment length polymorphism (AFLP) data were utilized to analyze the phylogenetic relationships among 29 accessions representing 14 of the most commonly recognized ranked species or subspecies in the genus Secale. We observed 789 AFLP markers of 1130 fragments utilizing 18 P-/M- and E-/M- primer combinations. All polymorphic fragments were used to construct phenetic and phylogenetic trees. The resulting phenogram and cladogram had similar tree topologies. Cluster analysis showed that Secale sylvestre was the most distantly related to all other ryes. Annual forms were grouped together, and the perennial forms appeared more closely related to each other. This suggested that life cycle could have played an important role in determining the relationships among Secale species. Secale sylvestre was considered to be the most ancient species, whereas Secale cereale was the most recently evolved species. Amplified fragment length polymorphism analysis clearly separated all Secale species into only 3 major species groups, within the genus Secale: S. sylvestre, Secale montanum (syn. Secale strictum) for perennial forms, and S. cereale for annual forms. This study demonstrated that the AFLP approach is a useful tool for discriminating species differences, and also gave a much better resolution in discerning genetic relationships among Secale species as compared with previous studies using other approaches.

Edible Grain↗

An empirical test of the treatment of indels during optimization alignment based on the phylogeny of the genus Secale (Poaceae).

The ability of the program POY, implementing optimization alignment, to deal with major indels is explored and discussed in connection with a phylogenetic analysis of the genus Secale based on partial Adh1 sequences. The Adh1 sequences used span exon 2-4. Nearly all variation is found in intron 2 and intron 3, which form the basis for the phylogenetic analyses. Both in some ingroup and outgroup taxa intron 3 has a major duplication. Previous phylogenetic analyses have repeatedly confirmed monophyly of both Secale and Hordeum, the latter being part of the outgroup. However, optimization alignment only recovers both genera as monophyletic when knowledge of the duplication is incorporated in the analysis. The phylogenetic relationships within Secale are not clearly resolved. Subspecific taxa of Secale strictum have identical sequences and they are confined to a monophyletic group. However, the two subspecific taxa of Secale cereale do not form a monophyletic group, and the position of Secale sylvestre is uncertain.

Algorithms↗

Evolutionary trends of different repetitive DNA sequences during speciation in the genus secale.

The presence and distribution of two simple sequence repeats (SSRs), three highly repetitive sequences from rye, and the 5S rDNA have been investigated in 3 rye cultivars and 10 wild-related species of the genus SECALE: The following conclusions can be drawn in addition to detailed knowledge of the sequence content of chromatin in each accession studied: (1) Every species is unique in either or both the complement and chromosomal distribution of the six repeated sequences analyzed. (2) These sequences reveal multiple landmarks along all the rye chromosomes arms. (3) High polymorphism as well as heterozygosity between homologues in the distribution of the (AAG)(5) and (AAC)(5) was revealed in the outbreeding species of the Secale strictum complex. (4) It is possible to deduce trends in the complexity of repetitive DNA during the evolution of the genus. A possible evolutionary pathway that accounts for the present-day Secale species is presented.

DNA, Plant↗

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↗

Polymorphism for ribosomal RNA gene arrangement in the mitochondrial genome of fall rye (Secale cereale L.).

A restriction-fragment-length polymorphism (RFLP) in mitochondrial DNA (mtDNA) was detected between varieties of fall rye (Secale cereale L.) by Southern hybridization with rrn18, the gene encoding the mitochondrial 18S ribosomal RNA. Restriction mapping showed that the RFLP is based on differing numbers of genomic contexts (one vs three) for a recombining-repeat element (the "18S/5S repeat"). From examination of other Secale species, we conclude that the one-context state arose relatively recently, putatively by deletion of two of an ancestral set of three distinct genomic loci containing the mitochondrial 18S/5S repeat. This is consistent with our earlier conclusion that the 18S/5S repeat has probably existed in at least two genomic copies throughout much of the history of the grass family (at least 40 million years). Interestingly, the intervarietal difference in the number of distinct rrn18 loci is not accompanied by a major difference in the number of rrn18 copies per unit mass of mtDNA. This suggests the existence of a mechanism that can compensate rather precisely for differences in mitochondrial gene dosage, perhaps by over-replication or stabilization of specific subgenomic molecules.

Base Sequence↗

Fluorescent in situ hybridization and C-banding analyses of highly repetitive DNA sequences in the heterochromatin of rye (Secale montanum Guss.) and wheat incorporating S. montanum chromosome segments.

The molecular characterization of C-banded regions of Secale montanum Guss. by means of in situ hybridization was performed in order to provide new information about their chromosome structure relative to cultivated rye, Secale cereale L. Accurate identification of individual chromosomes was achieved using simultaneous and (or) successive fluorescent in situ hybridization (FISH) and C-banding. FISH identification was performed using total rye DNA, three highly repetitive rye DNA sequences (pSc119.2, pSc74, and pSc34), and the ribosomal RNA probes pTa71 (18S, 5.8S, and 26S rDNA) and pTa794 (5S rDNA). FISH was also used to identify the chromosome segment involved in two spontaneous translocation lines recovered from a 'Chinese Spring'--S. montanum wheat-rye addition line. FISH analysis revealed the exact translocation breakpoints and allowed the identification of the transferred rye segments. The value of this type of analysis is discussed.

Chromosome Banding↗

Distribution of highly repeated DNA sequences in species of the genus Secale.

The presence and distribution of the most important highly repetitive DNA sequences of rye in cultivated and wild species of the genus Secale were investigated using fluorescence in situ hybridization. Accurate identification of individual chromosomes in the most commonly recognized species or subspecies of the genus Secale (S. cereale, S. ancestrale, S. segetale, S. afghanicum, S. dighoricum, S. montanum, S. montanum ssp. kuprijanovii, S. africanum, S. anatolicum, S. vavilovii, and S. silvestre) was achieved using three highly repetitive rye DNA sequences (probes pSc119.2, pSc74, and pSc34) and the 5S ribosomal DNA sequence pTa794. It is difficult to superimpose trends in the complexity of repetitive DNA during the evolution of the genus on conclusions from other cytogenetic and morphological assays. However, there are two clear groups. The first comprises the self-pollinated annuals S. silvestre and S. vavilovii that have few repeated nucleotide sequences of the main families of 120 and 480 bp. The second group presents amplification and interstitialization of the repeated nucleotide sequences and includes the perennials S. montanum, S. anatolicum, S. africanum, and S. kuprijanovii, as well as the annual and open-pollinated species S. cereale and its related weedy forms. The appearance of a new locus for 5S rRNA in S. cereale and S. ancestrale suggests that cultivated ryes evolved from this wild weedy species.

Biological Evolution↗

Production and morphology of the hybrids Aegilops kotschyi x Secale cereale and Ae. biuncialis x S. cereale.

Hybrids between Aegilops kotschyi and Ae. biuncialis with Secale cereale were synthesized. Five Ae. kotschyi and four Ae. biuncialis accessions, as well as one inbred and four self-compatible forms of Secale cereale were used for crossing. The hybrids were produced directly from cultured embryos or through embryo callus culture. Sixty hybrids, 11 involving Ae. kotschyi and 49 Ae. biuncialis, had a stable somatic chromosome number 2n = 3x = 21. The plants showed good vegetative vigour and tillering capacity. Morphologically the hybrids were intermediate between their parents and completely sterile. In vitro propagation of Ae. kotschyi and Ae. biuncialis x S. cereale hybrids revealed that their capacity for callus production and plantlet regeneration - varies.

Body Constitution↗

Hordeum and Secale mitotic genomes lie apart in a hybrid.

In both unpretreated root tip metaphases and pretreated mitoses of Hordeum vulgare L. cv. Sultan x Secale africanum Stapf F1 hybrids, Hordeum chromosomes tended to be nearer the centre of the mitosis than Secale chromosomes. This was clear in 4 serially sectioned cells examined in the electron microscope. In Feulgen squashes of 38 of 40 cells studied in the light microscope, the mean distances in each cell from the mean centromere position for the cell was less for Hordeum centromeres than for Scale centromeres. Such spatial separation of parent genomes might prevent pairing of homoeologues in hybrids.

Centromere↗

The complete chloroplast genome of Secale strictum ssp. strictum provides insights into Triticeae evolution and breeding.

The complete chloroplast genome of Secale strictum ssp. strictum (Poaceae: Triticeae) was sequenced and analyzed to support its use in rye and wheat breeding. The genome is 137,063 bp long and includes a pair of inverted repeats (IRs; 21,580 bp each) that separate the small (SSC; 12,817 bp) and large (LSC; 81,086 bp) single-copy regions. It contains 113 genes: 74 protein-coding, 30 tRNA, four rRNA genes, and five conserved open reading frames. A total of 42 repeat sequences were identified, mainly in the LSC region, with direct repeats being most common. All mononucleotide SSRs consisted of A/T motifs. Seven highly variable regions were identified, offering potential as molecular markers for species identification and phylogenetic studies. Phylogenetic analysis based on 73 protein-coding genes confirmed the systematic placement of the species and showed that S. strictum ssp. strictum is closely related to S. cereale and other S. strictum accessions. This study presents the first complete plastome of S. strictum ssp. strictum, now available as a reference genome under GenBank accession number OL979486.

Genome, Chloroplast↗

A DNA-polymerase-related reading frame (pol-r) in the mtDNA of Secale cereale.

Mitochondrial (mt)DNA of Secale cereale contains an open reading frame (pol-r), the potential translation product of which shows significant homology to the type-B DNA polymerase encoded by the S1 plasmid of Zea mays; it contains the highly-conserved domains IIa to V of family B polymerases. The pol-r ORF is transcribed, as proven by RT-PCR, but the transcript is not edited. Upstream of the putative start codon a potential promoter motif was detected, fitting well into the postulated consensus sequence of the transcription initiation regions of Z. mays and Triticum aestivum. The pol-r ORF occurs in mtDNA of the fertile rye variety "Halo" and the cytoplasmic male-sterile (CMS) line "Pampa". Both ORFs are almost identical, apart from the 3' terminus; pol-r from Halo can code for 289 amino acids, pol-r from Pampa for 312 amino acids. Based on codon usage and the lack of editing, pol-r is considered to be a "young" gene, probably introduced in the mtDNA of rye by recombination with an mt plasmid.

Amino Acid Sequence↗

Molecular studies on genetic integrity of open-pollinating species rye (Secale cereale L.) after long-term genebank maintenance.

The genetic integrity of six accessions represented by 14 sub-populations of the open-pollinating species rye ( Secale cereale L.) was investigated. Seeds available from a herbarium collection (first regeneration) and from the cold store (most recent regeneration) were multiplied two to fourteen times and fingerprinted using microsatellite markers. Four accessions had significantly different allele frequencies. These were multiplied seven to thirteen times. Nearly 50% of the alleles discovered in the original samples were not found in the material present in the cold store. However alleles were detected in the most recently propagated sub-populations, that were not observed in the investigated plants of the original one. The change in allele frequencies is a continuous process. Reasons for the occurrence of genetic changes and consequences for managing open pollinating species maintained in ex situ genebanks are discussed.

Gene Frequency↗

Somatic embryogenesis and fertile green plant regeneration from suspension cell-derived protoplasts of rye ( Secale cereale L.).

A method for somatic embryogenesis and fertile green plant regeneration from suspension cell-derived protoplasts of rye (Secale cereale L. cv. Auvinen) was developed. Fast-growing and friable embryogenic calli with a high regeneration capacity were induced from immature rye inflorescences using modified MS medium. These friable embryogenic calli were used for suspension culture initiation in liquid AA medium. A high yield of protoplasts was obtained from suspension cell clumps after 3-5 days of subculture. Isolated protoplasts were cultured in KM8p medium. The frequency of protoplast cell divisions and colony formations in liquid culture medium were similar to those on agarose-solidified medium. Compact embryogenic calli were developed from protoplast-derived microcalli in growth medium mMS. Approximately 7% of the transferred embryogenic calli produced green shoots on N6 regeneration medium. Of 33 green plants, 28 were fertile with normal flowering and seed set. The ratio of green and albino plantlets was 1:4. Rye protoplast-derived green plants showed normal diploid characters as determined by flow cytometer analysis and chromosome counting.

Cell Division↗

Microdissection and microcloning of rye (Secale cereale L.) chromosome 1R.

Chromosome 1R was microdissected and collected from mitotic metaphase spreads of rye (Secale cereale L.) by using glass needles. The isolated chromosomes were amplified in vitro by Sau3A linker adaptor-mediated polymerase chain reaction (PCR). After amplification, the presence of rye-specific DNA was verified by Southern hybridization. The second-round PCR products from five 1R chromosomes were cloned into a plasmid vector to create a chromosome-specific library, which produced approximately 220,000 recombinant clones. Characterization of the microclone library showed that the 172 clones evaluated ranged in size from 300-1800 bp with an average size of 950 bp, of which approximately 42% were medium/high copy and 58% were low/unique copy clones. Chromosome in situ hybridization confirmed that the PCR products from microdissected chromosomes originated from chromosome 1R, indicating that many chromosome 1R-specific sequences were present in the library.

Base Sequence↗

Increased capacity for synthesis of the D1 protein and of catalase at low temperature in leaves of cold-hardened winter rye (Secale cereale L.).

The effect of low temperature on protein synthesis, particularly the synthesis of the photolabile proteins D1 of photosystem II and catalase (EC 1.11.1.6), was compared in non-hardened leaves (NHL) and cold-hardened leaves (CHL) of winter rye (Secale cereale L.). At 4 degrees C, both the uptake of L-[(35)S]methionine into leaf sections and its incorporation into proteins were reduced, relative to 25 degrees C. However, much lower reductions were observed in CHL than in NHL. In particular, the proportion of the L-[(35)S]methionine uptake incorporated into membrane proteins at 4 degrees C was considerably higher in CHL than in NHL. At 25 degrees C, the incorporation of L-[(35)S]methionine into both the D1 protein and catalase was lower in CHL than in NHL, in accord with a slower light-induced turnover in CHL. At 4 degrees C, the incorporation into the D1 protein and catalase was, however, much higher in CHL than in NHL, indicating that their de novo synthesis was less suppressed by the low temperature. The results indicate that cold-acclimated leaves had an improved ability to repair the photolabile proteins D1 and catalase at low temperature, relative to NHL. mRNAs for the D1 protein and for leaf catalase were not increased in CHL, relative to NHL. The superior capacity of CHL for repair at low temperature must result from posttranscriptional mechanisms. The translational efficiency of the catalase mRNA was similarly increased in both NHL and CHL during 7-h exposures to high light at 4 degrees C, while the amounts of the catalase transcript declined under these conditions. However, during a recovery period at 22 degrees C, subsequent to an exposure of NHL to 4 degrees C and high light, transient increases of the D1 and catalase mRNAs were observed.

Adaptation, Physiological↗

Changes in gene expression during dehardening of cold-hardened winter rye (Secale cereale L.) leaves and potential role of a peptide methionine sulfoxide reductase in cold-acclimation.

Suppression subtractive hybridization and differential display polymerase chain reactions were used to identify genes that were differentially expressed in cold-hardened and dehardened leaves of winter rye (Secale cereale L.). The transcripts of nine genes declined during dehardening at 22 degrees C of cold-hardened 4 degrees C-grown leaves, indicating some role in cold-acclimation. Among the genes that were strongly expressed in cold-hardened leaves were five genes of photosynthetic metabolism, the gene of the antioxidative enzyme peptide methionine sulfoxide reductase (PMSR) and three genes of RNA and protein metabolism. Four genes were identified that were more strongly expressed during dehardening of cold-hardened leaves at 22 degrees C. A full-length cDNA for a presumed cytosolic PMSR (EC 1.8.4.6) of rye leaves was identified. After heterologous expression in Escherichia coli, an antiserum against the ScPMSR was produced. The content of the ScPMSR protein, visualized by immunoblotting, was much higher in cold-hardened than in non-hardened leaves and declined during dehardening. In non-hardened leaves the mRNA of ScPMSR increased only slowly during exposures to 4 degrees C in light and was not affected by exposure to 4 degrees C in darkness. However, the ScPMSR mRNA was also induced by prolonged exposure (48 h) to high light at 22 degrees C, or by treatment with 2 muM paraquat. Consequently, the induction of cytosolic ScPMSR is a late response to prolonged photooxidative stress conditions, as expected during growth at low temperature in light. In cold-hardened leaves, PMSR may protect proteins from photodamage and thus prevent their degradation and the need for repair.

Acclimatization↗