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

Abstract

Background: Elytrigia lolioides (Kar. et Kir.) Nevski, which is a perennial, cross-pollinating wheatgrass that is distributed in Russia and Kazakhstan, is classified into Elytrigia, Elymus, and Lophopyrum genera by taxonomists on the basis of different taxonomic classification systems. However, the genomic constitution of E. lolioides is still unknown. To identify the genome constitution and evolution of E. lolioides, we used single-copy nuclear genes acetyl-CoA carboxylase (Acc1) and elongation factor G (EF-G), multi-copy nuclear gene internal transcribed space (ITS), chloroplast gene trnL-F together with fluorescence and genomic in situ hybridization. Results: Despite the widespread homogenization of ITS sequences, two distinct lineages (genera Pseudoroegneria and Hordeum) were identified. Acc1 and EF-G sequences suggested that in addition to Pseudoroegneria and Hordeum, unknown genome was the third potential donor of E. lolioides. Data from chloroplast DNA showed that Pseudoroegneria is the maternal donor of E. lolioides. Data from specific FISH marker for St genome indicated that E. lolioides has two sets of St genomes. Both genomic in situ hybridization (GISH) and fluorescence in situ hybridization (FISH) results confirmed the presence of Hordeum genome in this species. When E genome was used as the probe, no signal was found in 42 chromosomes. The E-like copy of Acc1 sequences was detected in E. lolioides 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. Conclusions: Phylogenetic and in situ hybridization indicated the presence of two sets of Pseudoroegneria and one set of Hordeum genome in E. lolioides. The genome formula of E. lolioides was designed as StStStStHH. E. lolioides may have originated through the hybridization between tetraploid Elymus (StH) and diploid Pseudoroegneria species. E and unknown genomes may participate in the speciation of E. lolioides through introgression. According to the genome classification system, E. lolioides should be transferred into Elymus L. and renamed as Elymus lolioidus (Kar. er Kir.) Meld.