Mahelka V., Kopecký D.
MOLECULAR BIOLOGY AND EVOLUTION
27(6):
1370–1390,
2010
Keywords:
Elymus repens, internal transcribed spacer, GBSSI, in situ hybridization, Triticeae, Panicoideae
Abstract:
Four accessions of hexaploid Elymus repens from its native Central European distribution area were analyzed using
sequencing of multicopy (internal transcribed spacer, ITS) and single-copy (granule-bound starch synthase I, GBSSI) DNA
in concert with genomic and fluorescent in situ hybridization (GISH and FISH) to disentangle its allopolyploid origin.
Despite extensive ITS homogenization, nrDNA in E. repens allowed us to identify at least four distinct lineages. Apart from
Pseudoroegneria and Hordeum, representing the major genome constituents, the presence of further unexpected alien
genetic material, originating from species outside the Triticeae and close to Panicum (Paniceae) and Bromus (Bromeae),
was revealed. GBSSI sequences provided information complementary to the ITS. Apart from Pseudoroegneria and
Hordeum, two additional gene variants from within the Triticeae were discovered: One was Taeniatherum-like, but the
other did not have a close relationship with any of the diploids sampled. GISH results were largely congruent with the
sequence-based markers. GISH clearly confirmed Pseudoroegneria and Hordeum as major genome constituents and further
showed the presence of a small chromosome segment corresponding to Panicum. It resided in the Hordeum subgenome
and probably represents an old acquisition of a Hordeum progenitor. Spotty hybridization signals across all chromosomes
after GISH with Taeniatherum and Bromus probes suggested that gene acquisition from these species is more likely due to
common ancestry of the grasses or early introgression than to recent hybridization or allopolyploid origin of E. repens.
Physical mapping of rDNA loci using FISH revealed that all rDNA loci except one minor were located on Pseudoroegneriaderived
chromosomes, which suggests the loss of all Hordeum-derived loci but one. Because homogenization mechanisms
seem to operate effectively among Pseudoroegneria-like copies in this species, incomplete ITS homogenization in our samples
is probably due to an interstitial position of an individual minor rDNA locus located within the Hordeum-derived subgenome.
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IEB authors: David Kopecký
