AUTHOR=Ruban Alevtina S. , Badaeva Ekaterina D. 

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

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.01756

DOI=10.3389/fpls.2018.01756

ISSN=1664-462X

ABSTRACT=<p>Five diploid <italic>Aegilops</italic> species of the <italic>Sitopsis</italic> section: <italic>Ae. speltoides, Ae. longissima, Ae. sharonensis, Ae. searsii</italic>, and <italic>Ae. bicornis</italic>, two tetraploid species <italic>Ae. peregrina</italic> (= <italic>Ae. variabilis</italic>) and <italic>Ae. kotschyi</italic> (<italic>Aegilops</italic> section) and hexaploid <italic>Ae. vavilovii</italic> (<italic>Vertebrata</italic> 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 <italic>in situ</italic> 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)<sub>10</sub> and (GTT)<sub>9</sub>, 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 <italic>Emarginata</italic> and <italic>Truncata</italic> 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 <italic>Ae. speltoides</italic>. 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 <italic>Ae. speltoides</italic><sub>.</sub> The 5S rDNA locus of chromosome 1S was probably lost in ancient <italic>Ae. speltoides</italic> prior to formation of Timopheevii wheat, but after the emergence of ancient emmer. Evolution of <italic>Emarginata</italic> species was associated with an increase of C-banding and (CTT)<sub>10</sub>-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 <italic>Ae. peregrina</italic> and <italic>Ae. kotschyi</italic> did not lead to significant changes of the S<sup>*</sup>-genomes. However, partial elimination of 45S rDNA repeats from 5S<sup>*</sup> and 6S<sup>*</sup> chromosomes and alterations of C-banding and FISH-patterns have been detected. Similarity of the S<sup>v</sup>-genome of <italic>Ae. vavilovii</italic> with the S<sup>s</sup> genome of diploid <italic>Ae. searsii</italic> confirmed the origin of this hexaploid. A model of the S-genome evolution is suggested.</p>