Evolution of the S-Genomes in Triticum-Aegilops Alliance: Evidences From Chromosome Analysis

Abstract

Five diploid Aegilops species of the Sitopsis section: Ae. speltoides, Ae. longissima, Ae. sharonensis, Ae. searsii, and Ae. bicornis, two tetraploid species Ae. peregrina (= Ae. variabilis) and Ae. kotschyi (Aegilops section) and hexaploid Ae. vavilovii (Vertebrata section) carry the S-genomes. The B- and G-genomes of polyploid wheat are also the derivatives of the S-genome. Evolution of the S-genome species was studied using Giemsa C-banding and fluorescence in situ hybridization (FISH) with DNA probes representing 5S (pTa794) and 18S-5.8S-26S (pTa71) rDNAs as well as nine tandem repeats: pSc119.2, pAesp_SAT86, Spelt-1, Spelt-52, pAs1, pTa-535, and pTa-s53. To correlate the C-banding and FISH patterns we used the microsatellites (CTT)10 and (GTT)9, which are major components of the C-banding positive heterochromatin in wheat. According to the results obtained, diploid species split into two groups corresponding to Emarginata and Truncata sub-sections, which differ in the C-banding patterns, distribution of rDNA and other repeats. The B- and G-genomes of polyploid wheat are most closely related to the S-genome of Ae. speltoides. The genomes of allopolyploid wheat have been evolved as a result of different species-specific chromosome translocations, sequence amplification, elimination and re-patterning of repetitive DNA sequences. These events occurred independently in different wheat species and in Ae. speltoides. The 5S rDNA locus of chromosome 1S was probably lost in ancient Ae. speltoides prior to formation of Timopheevii wheat, but after the emergence of ancient emmer. Evolution of Emarginata species was associated with an increase of C-banding and (CTT)10-positive heterochromatin, amplification of Spelt-52, re-pattering of the pAesp_SAT86, and a gradual decrease in the amount of the D-genome-specific repeats pAs1, pTa-535, and pTa-s53. The emergence of Ae. peregrina and Ae. kotschyi did not lead to significant changes of the S*-genomes. However, partial elimination of 45S rDNA repeats from 5S* and 6S* chromosomes and alterations of C-banding and FISH-patterns have been detected. Similarity of the Sv-genome of Ae. vavilovii with the Ss genome of diploid Ae. searsii confirmed the origin of this hexaploid. A model of the S-genome evolution is suggested.

Genome-Wide Distribution of Novel Ta-3A1 Mini-Satellite Repeats and Its Use for Chromosome Identification in Wheat and Related Species

“…Moreover, Ae. speltoides is cytogenetically distinct from the S genomes of other diploid and polyploid Aegilops species based on C-banding and FISH [59,60]. We also showed that the FISH patterns of Ta-3A1 appeared on the long arm of 5S in Ae.…”

Chromosome restructuring among hybridizing wild wheats

“…The genome composition of each species is indicated in between brackets and the reticulation event between species of the A‐ and the B‐genome lineages at the origin of the D‐genome lineage is shown as dotted lines following Huynh et al (), with mean node ages and 95% credibility intervals in Myr ago (Ma). Chromosomes were labelled with the A/D‐genome‐specific repeat pAs1 (green) and the B/S‐genome‐specific repeat pSc119.2 (red), and fluorescence in situ hybridization (FISH) karyotypes following Badaeva et al (, , ) and Ruban & Badaeva () show progenitor species from the A‐genome ( T. monococcum here shown) and B‐genome ( Ae. speltoides here shown) lineages together with selected karyotypes from the three clades nested within the hybrid D‐genome lineage: (1) Aegilops tauschii shows the A‐like karyotype of the tauschii clade (also see Fig.…”

“…speltoides and Ae. mutica indeed are the only outcrossing wild wheats that also distinctively possess B‐chromosomes (Ohta, ) and present very similar karyotype structure showing similar major 45S rDNA loci and large clusters of GTT n microsatellite sequences in pericentromeric regions (Badaeva et al , ; Ruban & Badaeva, ). Accordingly, phylogenies based on either fully parameterized multispecies networks vs topology or single nucleotide polymorphism (SNP) approaches present rather shallow discrepancies due to ancestral population structure (see discussion in Huynh et al , ).…”

“… Abundance of tandem repeats Spelt52 (Sp52), Spelt1 (Sp1), pTa‐535 (Ta), pAs1 (As), pSc119.2 (Sc) characterized in Badaeva et al () and Ruban & Badaeva () and summarized here as absent (0), low (+), medium (++), high (+++) or not available (na) based on their correlation between abundance in genomes and intensity of FISH signals. …”

A flow cytometry-based analysis to establish a cell cycle synchronization protocol for Saccharum spp.

“…To reduce this complexity, the sugarcane genome can be dissected into single chromosomes using flow cytometry. Since this approach requires sufficient numbers of metaphase chromosomes, a stable and efficient cell cycle synchronization (CCS) method for sugarcane is needed.The eukaryotic cell cycle is typically divided into four phases: G 1 phase, in which the cell grows and duplicates organelles; S phase, in which DNA synthesis occurs; G 2 phase, in which the cell prepares to divide after replication; M phase, during which the chromosomes precisely separate and form two daughter nuclei along the mitotic spindle, and cytokinesis when the actual cell division occurs [5][6][7] . Cells in each of these cell cycle phases have a distinct nuclear DNA content, which can be exploited for sorting by flow cytometry 8 .…”