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

Abstract

The genus Elymus L. in the tribe Triticeae (Poaceae) includes economically and ecologically important forage grasses. The genus contains the pivotal St genome from Pseudoroegneria in combination with other genomes in the tribe. Many Elymus species 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, genome in situ hybridization, and molecular studies, we hypothesized an endoallopolyploidy origin of the StY-genome species from the autotetraploid Pseudoroegneria species. 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; and Waxy) from Elymus, Pseudoroegneria, and Hordeum species. The phylogenetic trees constructed based on the sequencing analyses of all genes indicated that diploid and autotetraploid Pseudoroegneria species were closely related, although with considerable genetic variation in tetraploids. In addition, the StY-genome Elymus species tended to have a close relationship with the diploid and autotetraploid Pseudoroegneria species, 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 in Pseudoroegneria in 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 some Elymus species.

Molecular cytogenetic study on the plants of Elymus nutans with varying fertility on the Qinghai-Tibet Plateau

“…The concept of nucleocytoplasmic interaction (NCI) hypothesizes that specific chromosome rearrangement plays an important role in restoring fertility and nucleocytoplasmic compatibility for the genetic stabilization of newly formed hybrids and polyploids ( Gill, 1991 ; Jiang and Gill 1994 ). In E. nutans , heteroplasmy and variation in mitochondrial genes have been identified among individuals ( Liu et al., 2020 ). Whether the fertility of the heterozygote is affected by NCI still requires further investigation in E. nutans.…”

Meiotic Chromosomal Abnormality Detected in a Heterozygote of Elymus nutans

“…E. nutans is an allopolyploid with a genome constitution of StStHHYY (2 n = 6 x = 42). The St genome originates from the genus Pseudoroegneria , the H genome from Hordeum , and the Y genome’s origin is unknown and still on debating ( Wang et al, 1994 ; Lei et al, 2022 ; Liu et al, 2022 ). E. nutans distributed on the Qinghai-Tibet Plateau show highly divergent adaptation, growing on grassland, bushland, wetland, mountain slopes, and swales, at altitudes from 1,000 to 5,000 m, and is tolerant to various environmental stresses associated with high altitudes, such as cold and drought.…”

Roegneria yenchiana: A new species in the Triticeae (Poaceae) from the Hengduan Mountain region

“…Dewey ( 1984 ) considered that the Y genome has its origin in Central Asia or the Himalaya region, and may be extinct. Extensive cytogenetic and molecular studies have suggested that the St ( Pseudoroegneria ), W [ Australopyrum (Tzvelev) Á. Löve], V [ Dasypyrum villosum (L.) Candargy], and Xp [ Peridictyon O. Seberg, S. Frederiksen & C. Baden] genomes are potential donors of the Y genome (Fan et al., 2013 ; Lei et al., 2022 ; Liu et al., 2006 , 2022 ; Sun & Komatsuda, 2010 ).…”

“…The tetraploid species Roegneria alashanica Keng was found to have the StSt Y genome constitution (Wang & Jensen, 2017), suggesting that the Y genome might derive from St through StY. Dewey (1984) (Fan et al, 2013;Lei et al, 2022;Liu et al, 2006Liu et al, , 2022Sun & Komatsuda, 2010).…”