Genome constitution and evolution of Elytrigia lolioides inferred from Acc1, EF-G, ITS, TrnL-F sequences and GISH

Abstract

<b>Background:</b> <i>Elytrigia lolioides</i> (Kar. et Kir.) Nevski, which is a perennial, cross-pollinating wheatgrass that is distributed in Russia and Kazakhstan, is classified into <i>Elytrigia</i>, <i>Elymus</i>, and <i>Lophopyrum</i> genera by taxonomists on the basis of different taxonomic classification systems. However, the genomic constitution of <i>E. lolioides</i> is still unknown. To identify the genome constitution and evolution of <i>E. lolioides</i>, we used single-copy nuclear genes acetyl-CoA carboxylase (<i>Acc1</i>) and elongation factor G (<i>EF-G</i>), multi-copy nuclear gene internal transcribed space (<i>ITS</i>), chloroplast gene <i>trnL-F</i> together with fluorescence and genomic in situ hybridization.<br>

<b>Results:</b> Despite the widespread homogenization of <i>ITS</i> sequences, two distinct lineages (genera <i>Pseudoroegneria</i> and <i>Hordeum</i>) were identified. <i>Acc1</i> and <i>EF-G</i> sequences suggested that in addition to <i>Pseudoroegneria</i> and <i>Hordeum</i>, unknown genome was the third potential donor of <i>E. lolioides</i>. Data from chloroplast DNA showed that <i>Pseudoroegneria</i> is the maternal donor of <i>E. lolioides</i>. Data from specific FISH marker for St genome indicated that <i>E. lolioides</i> has two sets of St genomes. Both genomic in situ hybridization (GISH) and fluorescence in situ hybridization (FISH) results confirmed the presence of <i>Hordeum</i> genome in this species. When E genome was used as the probe, no signal was found in 42 chromosomes. The E-like copy of <i>Acc1</i> sequences was detected in <i>E. lolioides</i> possibly due to the introgression from E genome species. One of the H chromosomes in the accession W6-26586 from Kazakhstan did not hybridize H genome signals but had St genome signals on the pericentromeric regions in the two-color GISH.<br> <b>Conclusions:</b> Phylogenetic and in situ hybridization indicated the presence of two sets of <i>Pseudoroegneria</i> and one set of <i>Hordeum</i> genome in <i>E. lolioides</i>. The genome formula of <i>E. lolioides</i> was designed as StStStStHH. <i>E. lolioides</i> may have originated through the hybridization between tetraploid <i>Elymus</i> (StH) and diploid <i>Pseudoroegneria</i> species. E and unknown genomes may participate in the speciation of <i>E. lolioides</i> through introgression. According to the genome classification system, <i>E. lolioides</i> should be transferred into <i>Elymus</i> L. and renamed as <i>Elymus lolioidus</i> (Kar. er Kir.) Meld.