Multiple origins of allopolyploid wheatgrass Elymus caninus revealed by RPB2, PepC and TrnD/T genes

We examined evolutionary mechanisms in the tetraploid Elymus caninus by comparing the phylogenetic relationships of 21 accessions suggested by sequence data from two single copy nuclear genes, the largest subunit of RNA polymerase II (RPB2) and phosphoenolpyruvate carboxylase (pepC), and one non-coding chloroplast region, TrnD/T. Elymus caninus is known combining two different genomes, an St genome and an H genome. Data from two single copy nuclear genes showed that there are two versions of the St genome in the species, St1 and St2. Most accessions combined one of these versions with an H genome version but two accessions had both versions of the St sequence for RPB2. This suggests that the RPB2 gene may have been duplicated without chromosome doubling, possibly induced by transposable element. Our data also indicate that the H genome sequences in E. caninus have multiple origins, and a close phylogenetic relationship between Hordeum bogdanii and H sequences in some accessions of E. caninus. Thus, it is more likely that H. bogdanii is one of the major donors of the H copy in E. caninus. The maternal origin of E. caninus is the St genome species. There was no correlation between the geographic origin of the accessions and their sequence divergence.

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► The data indicated that the St genome in E. caninus has two distinct origins in either St1 and/or St2.
► H10404 and H2009 possessed three distinct copies of RPB2 sequences, St1, St2 and H sequences.
► PepC data showed that these two accessions each contain two copies of PepC sequences, St and H genome sequences.
► Three copies of RPB2 gene in the tetraploids might have been caused by segmental duplication.
► Our study indicated multiple origins of the H genome in E. caninus.