Abstract
BackgroundHybridization and polyploidization can be major mechanisms for plant evolution and speciation. Thus, the process of polyploidization and evolutionary history of polyploids is of widespread interest. The species in Elymus L. sensu lato are allopolyploids that share a common St genome from Pseudoroegneria in different combinations with H, Y, P, and W genomes. But how the St genome evolved in the Elymus s. l. during the hybridization and polyploidization events remains unclear. We used nuclear and chloroplast DNA-based phylogenetic analyses to shed some light on this process.ResultsThe Maximum likelihood (ML) tree based on nuclear ribosomal internal transcribed spacer region (nrITS) data showed that the Pseudoroegneria, Hordeum and Agropyron species served as the St, H and P genome diploid ancestors, respectively, for the Elymus s. l. polyploids. The ML tree for the chloroplast genes (matK and the intergenic region of trnH-psbA) suggests that the Pseudoroegneria served as the maternal donor of the St genome for Elymus s. l. Furthermore, it suggested that Pseudoroegneria species from Central Asia and Europe were more ancient than those from North America. The molecular evolution in the St genome appeared to be non-random following the polyploidy event with a departure from the equilibrium neutral model due to a genetic bottleneck caused by recent polyploidization.ConclusionOur results suggest the ancient common maternal ancestral genome in Elymus s. l. is the St genome from Pseudoroegneria. The evolutionary differentiation of the St genome in Elymus s. l. after rise of this group may have multiple causes, including hybridization and polyploidization. They also suggest that E. tangutorum should be treated as C. dahurica var. tangutorum, and E. breviaristatus should be transferred into Campeiostachys. We hypothesized that the Elymus s. l. species origined in Central Asia and Europe, then spread to North America. Further study of intraspecific variation may help us evaluate our phylogenetic results in greater detail and with more certainty.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0517-2) contains supplementary material, which is available to authorized users.
Highlights
Hybridization and polyploidization can be major mechanisms for plant evolution and speciation
E. tangutorum should be treated as C. dahurica var. tangutorum and E. breviaristatus should be transferred into Campeiostachys
In this study, the nuclear ribosomal internal transcribed spacer region (nrITS) sequence analysis in different Elymus s. l. species showed a clear linkage between nrITS sequences of polyploid Elymus s. l. species and those of their diploid ancestors
Summary
Hybridization and polyploidization can be major mechanisms for plant evolution and speciation. Evolution under polyploidization alone and/or hybridization and polyploidization together can give rise to a complex of lineages whose phylogenetic relationships are unclear. For such groups, molecular genetic analysis is often necessary to elucidate the genome evolution patterns and the phylogenetic relationships among taxa [8]. One example of a polyploid complex within that tribe Triticeae is the genus Elymus L. sensu lato delimited by Löve [12]; it is an important perennial genus with approximately 150 species worldwide. It includes the traditional species of Elymus L., Roegneria C.
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