Endo‐allopolyploidy of autopolyploids and recurrent hybridization—A possible mechanism to explain the unresolved Y‐genome donor in polyploidElymusspecies (Triticeae: Poaceae)

This is the authors' abstract. We don't add key points for this paper.

The genusElymusL. in the tribe Triticeae (Poaceae) includes economically and ecologically important forage grasses. The genus contains the pivotal St genome fromPseudoroegneriain combination with other genomes in the tribe. ManyElymusspecies are tetraploids containing the StY genomes. It is thought that polyploidization characterizes the speciation of the genus in which the Y is considered as another key genome. Based on data from cytological, genomein situhybridization, and molecular studies, we hypothesized an endo‐allopolyploidy origin of the StY‐genome species from the autotetraploidPseudoroegneriaspecies. To test this hypothesis, we amplified, cloned, and sequenced five single‐copy nuclear genes (i.e., alcohol dehydrogenase 1–3,Adh1–Adh3, RNA polymerase II,Rpb2; andWaxy) fromElymus, Pseudoroegneria, andHordeumspecies. The phylogenetic trees constructed based on the sequencing analyses of all genes indicated that diploid and autotetraploidPseudoroegneriaspecies were closely related, although with considerable genetic variation in tetraploids. In addition, the StY‐genomeElymusspecies tended to have a close relationship with the diploid and autotetraploidPseudoroegneriaspecies, although different phylogenetic relationships among the gene trees were detected. These results indicated that the StY‐genome species may have an autotetraploid origin and experienced recurrent hybridization. The complex St genomes inPseudoroegneriain the polyploid state may gain more opportunities for within‐species differentiation and recurrent hybridization. As a result, series modified versions of St genomes evolved into the StY genomes in someElymusspecies.