The internal transcribed spacer region (ITS) of nuclear ribosomal DNA was sequenced from 195 representative species of Allium, two species of Nothoscordum, and one species each of lpheion, Dichelostemma, and Tulbaghia. Within the Allium species the lengths of the ITS regions were in a range from 612 to 661 base pairs and pairwise genetic distances reached up to 46%. The ITS data supported the inclusion of Nectaroscordum, Caloscordum, and Milula into Allium. Subgenera Rhizirideum and Allium, as well as sects.
Advanced resources for genome-assisted research in barley (Hordeum vulgare) including a whole-genome shotgun assembly and an integrated physical map have recently become available. These have made possible studies that aim to assess genetic diversity or to isolate single genes by whole-genome resequencing and in silico variant detection. However such an approach remains expensive given the 5 Gb size of the barley genome. Targeted sequencing of the mRNA-coding exome reduces barley genomic complexity more than 50-fold, thus dramatically reducing this heavy sequencing and analysis load. We have developed and employed an in-solution hybridization-based sequence capture platform to selectively enrich for a 61.6 megabase coding sequence target that includes predicted genes from the genome assembly of the cultivar Morex as well as publicly available full-length cDNAs and de novo assembled RNA-Seq consensus sequence contigs. The platform provides a highly specific capture with substantial and reproducible enrichment of targeted exons, both for cultivated barley and related species. We show that this exome capture platform provides a clear path towards a broader and deeper understanding of the natural variation residing in the mRNA-coding part of the barley genome and will thus constitute a valuable resource for applications such as mapping-by-sequencing and genetic diversity analyzes.
Sequences of the internal transcribed spacers (ITS) of the nuclear ribosomal DNA are important molecular markers in phylogenetic analyses. To obtain sequences from herbarium material in which DNA often is severely degraded, the ITS region has to be amplified in two steps. Two methods that reduce bench time and reagents used are described. (i) Separately amplified preparations of subunits ITS-1 and ITS-2 are combined before purification. The presence of two fragments in the sequencing reaction does not impair the quality of sequences. (ii) Newly designed internal primers amplify partly overlapping regions of the two subunits. A combination of these internal primers with the external primers in one PCR allows the amplification of the entire ITS region even when degraded DNAs are used. This recombinant PCR approach, taking into account the +A bases added by several Taq DNA polymerases, will also be useful with other marker regions used in molecular phylogenetics.
The Hordeum marinum species group consists of two annual grasses of western Eurasian saline meadows or marshes. The two grasses split in the Quaternary about two million years ago. Hordeum marinum and the diploid of Hordeum gussoneanum (2x) co-occur throughout the Mediterranean basin, while the autotetraploid cytotype of H. gussoneanum (4x) overlaps with its diploid progenitor geographically only in the utmost Eastern Mediterranean, extending from there eastwards into Asia. Using chloroplast sequences of the trnL-F region, six newly developed chloroplast microsatellite loci, ecological predictive models based on climate data, and the present geographical distribution of the two species we analysed differentiation processes in the H. marinum group. The chloroplast data indicated clear differences in the history of both species. For H. marinum we found a subdivision between genetically variable populations from the Iberian Peninsula and the more uniform populations from the remaining Mediterranean. As an explanation, we assume Pleistocene fragmentation of an earlier widespread population and survival in an Iberian and a Central Mediterranean glacial refuge. Chloroplast variation was completely absent within the cytotypes of H. gussoneanum, indicating a severe and recent genetic bottleneck. Due to this lack of chloroplast variation only the combination of ecological habitat modelling with molecular data analyses allowed conclusions about the history of this taxon. The distribution areas of the two cytotypes of H. gussoneanum overlap today in parts of Turkey, indicating an area with similar climate conditions during polyploid formation. However, after its origin the polyploid cytotype underwent a pronounced ecological shift, compared to its diploid progenitor, allowing it to colonize mountainous inland habitats between the Mediterranean basin and Afghanistan. The extant sympatric occurrence of H. marinum and H. gussoneanum 2x in the Mediterranean region is interpreted as a result of secondary contact after fast Holocene range expansion out of different ice age refugia.
During the last decade several phylogenetic studies of Hordeum were published using a multitude of loci from the chloroplast and nuclear genomes. In many studies taxon sampling was not representative and, thus, does not allow the inference of relationships among species. Generally, chloroplast data seem not suitable for reliable phylogenetic results, as far reaching incomplete lineage sorting result in nearly arbitrary species relationships within narrow species groups, depending on the individuals included in the analyses. Nuclear loci initially resulted at contradictory phylogenetic hypotheses. However, combining at least three nuclear loci in total evidence analyses finally provides consistent relationships among Hordeum species groups, and supports data from earlier cytological and karyological studies. Thus, recently published phylogenies agree on the monophyly of the four Hordeum genome groups (H, I, Xa, Xu), monophyly of the H/Xu and I/Xa groups, and separation between Asian and American members within the I-genome group. A new infrageneric classification of Hordeum is proposed, dividing the genus in subgenus Hordeum comprising sections Hordeum and Trichostachys, and subgenus Hordeastrum with sections Marina, Nodosa, and Stenostachys. The latter consists of two series reflecting the geographical distribution of the taxa, i.e. series Sibirica with Central Asian taxa and series Critesion comprising native taxa from the Americas. In section Nodosa all allopolyploid taxa are grouped, which are characterized by I/Xa genome combinations.
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