Background: Single- and low- copy genes are less likely subject to concerted evolution, thus making themselves ideal tools for studying the origin and evolution of polyploid taxa.Leymusis a polyploid genus with a diverse array of morphology, ecology and distribution in Triticeae. The genomic constitution ofLeymuswas assigned as NsXm, where Ns was presumed to be originated fromPsathyrostachys, while Xm represented a genome of unknown origin. In addition, little is known about the evolutionary history ofLeymus. Here, we investigate the phylogenetic relationship, genome donor, and evolutionary history ofLeymusbased on a single-copy nuclearAcc1gene.Results: Two homoeologues of theAcc1gene were isolated from nearly all the sampledLeymusspecies using allele-specific primer and were analyzed with those from 35 diploid taxa representing 18 basic genomes in Triticeae. Sequence diversity patterns and genealogical analysis suggested that (1)Leymusis closely related toPsathyrostachys,Agropyron, andEremopyrum; (2)Psathyrostachys junceais an ancestral Ns-genome donor ofLeymusspecies; (3) the Xm genome inLeymusmay be originated from an ancestral lineage ofAgropyronandEremopyrum triticeum; (4) theAcc1sequences ofLeymusspecies from the Qinghai-Tibetan plateau are evolutionarily distinct; (5) North AmericaLeymusspecies might originate from colonization via the Bering land bridge; (6)Leymusoriginated about 11-12MYA in Eurasia, and adaptive radiation might have occurred inLeymusduring the period of 3.7-4.3 MYA and 1.7-2.1 MYA.Conclusion: Leymusspecies have allopolyploid origin. It is hypothesized that the adaptive radiation ofLeymusspecies might have been triggered by the recent upliftings of the Qinghai-Tibetan plateau and subsequent climatic oscillations. Adaptive radiation may have promoted the rapid speciation, as well as the fixation of unique morphological characters inLeymus. Our results shed new light on our understanding of the origin of Xm genome, the polyploidization events and evolutionary history ofLeymusthat could account for the rich diversity and ecological adaptation ofLeymusspecies.

Hybridization 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. The 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. Our 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.

Lisha Yi, Haiqin Zhang, Huihui Sun, Lu Zhou, Ying Chen, Liqian Xuan, Yuanxi Jiang, and Shuchang Xu. J Neurogastroenterol Motil 1999;0:. https://doi.org/10.5056/jnm16089

Background: The wheat dwarfing gene increases lodging resistance, the grain number per spike and harvest index. Dwarf Polish wheat (Triticum polonicum L., 2n = 4x = 28, AABB, DPW), initially collected from Tulufan, Xinjiang, China, carries a semi-dwarfing gene Rht-dp on chromosome 4BS. However, Rht-dp and its dwarfing mechanism are unknown. Results: Homologous cloning and mapping revealed that Rht-dp is the ‘Green Revolution’ gene Rht-B1b. A haplotype analysis in 59 tetraploid wheat accessions showed that Rht-B1b was only present in T. polonicum. Transcriptomic analysis of two pairs of near-isogenic lines (NILs) of DPW × Tall Polish wheat (Triticum polonicum L., 2n = 4x = 28, AABB, TPW) revealed 41 differentially expressed genes (DEGs) as potential dwarfism-related genes. Among them, 28 functionally annotated DEGs were classed into five sub-groups: hormone-related signalling transduction genes, transcription factor genes, cell wall structure-related genes, reactive oxygen-related genes, and nitrogen regulation-related genes. Conclusions: These results indicated that Rht-dp is Rht-B1b, which regulates pathways related to hormones, reactive oxygen species, and nitrogen assimilation to modify the cell wall structure, and then limits cell wall loosening and inhibits cell elongation, thereby causing dwarfism in DPW.