Biosystematics studies on Elymus breviaristatus and Elymus sinosubmuticus (Poaceae: Triticeae).

BACKGROUND: Elymus breviaristatus and Elymus sinosubmuticus are perennial herbs, not only morphologically similar but also sympatric distribution. The genome composition of E. sinosubmuticus has not been reported, and the relationship between E. sinosubmuticus and E. breviaristatus is still controversial. We performed artificial hybridization, genomic in situ hybridization, and phylogenetic analyses to clarify whether the two taxa were the same species. RESULTS: The high frequency bivalent (with an average of 20.62 bivalents per cell) at metaphase I of pollen mother cells of the artificial hybrids of E. breviaristatus (StYH) × E. sinosubmuticus was observed. It illustrated that E. sinosubmuticus was closely related to E. breviaristatus. Based on genomic in situ hybridization results, we confirmed that E. sinosubmuticus was an allohexaploid, and the genomic constitution was StYH. Phylogenetic analysis results also supported that this species contained St, Y, and H genomes. In their F1 hybrids, pollen activity was 53.90%, and the seed setting rate was 22.46%. Those indicated that the relationship between E. sinosubmuticus and E. breviaristatus is intersubspecific rather than interspecific, and it is reasonable to treated E. sinosubmuticus as the subspecies of E. breviaristatus. CONCLUSIONS: In all, the genomic constitutions of E. sinosubmuticus and E. breviaristatus were StYH, and they are species in the genus Campeiostachys. Because E. breviaristatus was treated as Campeistachys breviaristata, Elymus sinosubmuticus should be renamed Campeiostachys breviaristata (Keng) Y. H. Zhou, H. Q. Zhang et C. R. Yang subsp. sinosubmuticus (S. L. Chen) Y. H. Zhou, H. Q. Zhang et L. Tan.

Construction of the first high-density genetic linkage map and identification of seed yield-related QTLs and candidate genes in Elymus sibiricus, an important forage grass in Qinghai-Tibet Plateau.

BACKGROUND: Elymus sibiricus is an ecologically and economically important perennial, self-pollinated, and allotetraploid (StStHH) grass, widely used for forage production and animal husbandry in Western and Northern China. However, it has low seed yield mainly caused by seed shattering, which makes seed production difficult for this species. The goals of this study were to construct the high-density genetic linkage map, and to identify QTLs and candidate genes for seed-yield related traits. RESULTS: An F2 mapping population of 200 individuals was developed from a cross between single genotype from "Y1005" and "ZhN06". Specific-locus amplified fragment sequencing (SLAF-seq) was applied to construct the first genetic linkage map. The final genetic map included 1971 markers on the 14 linkage groups (LGs) and was 1866.35 cM in total. The length of each linkage group varied from 87.67 cM (LG7) to 183.45 cM (LG1), with an average distance of 1.66 cM between adjacent markers. The marker sequences of E. sibiricus were compared to two grass genomes and showed 1556 (79%) markers mapped to wheat, 1380 (70%) to barley. Phenotypic data of eight seed-related traits (2016-2018) were used for QTL identification. A total of 29 QTLs were detected for eight seed-related traits on 14 linkage groups, of which 16 QTLs could be consistently detected for two or three years. A total of 6 QTLs were associated with seed shattering. Based on annotation with wheat and barley genome and transcriptome data of abscission zone in E. sibiricus, we identified 30 candidate genes for seed shattering, of which 15, 7, 6 and 2 genes were involved in plant hormone signal transcription, transcription factor, hydrolase activity and lignin biosynthetic pathway, respectively. CONCLUSION: This study constructed the first high-density genetic linkage map and identified QTLs and candidate genes for seed-related traits in E. sibiricus. Results of this study will not only serve as genome-wide resources for gene/QTL fine mapping, but also provide a genetic framework for anchoring sequence scaffolds on chromosomes in future genome sequence assembly of E. sibiricus.

EST-SSR marker development based on RNA-sequencing of E. sibiricus and its application for phylogenetic relationships analysis of seventeen Elymus species.

BACKGROUND: Elymus L. is the largest genus in the tribe Triticeae Dumort., encompassing approximately 150 polyploid perennial species widely distributed in the temperate regions of the world. It is considered to be an important gene pool for improving cereal crops. However, a shortage of molecular marker limits the efficiency and accuracy of genetic breeding for Elymus species. High-throughput transcriptome sequencing data is essential for gene discovery and molecular marker development. RESULTS: We obtained the transcriptome dataset of E. sibiricus, the type species of the genus Elymus, and identified a total of 8871 putative EST-SSRs from 6685 unigenes. Trinucleotides were the dominant repeat motif (4760, 53.66%), followed by dinucleotides (1993, 22.47%) and mononucleotides (1876, 21.15%). The most dominant trinucleotide repeat motif was CCG/CGG (1119, 23.5%). Sequencing of PCR products showed that the sequenced alleles from different Elymus species were homologous to the original SSR locus from which the primer was designed. Different types of tri-repeats as abundant SSR motifs were observed in repeat regions. Two hundred EST-SSR primer pairs were designed and selected to amplify ten DNA samples of Elymus species. Eighty-seven pairs of primer (43.5%) generated clear and reproducible bands with expected size, and showed good transferability across different Elymus species. Finally, thirty primer pairs successfully amplified ninety-five accessions of seventeen Elymus species, and detected significant amounts of polymorphism. In general, hexaploid Elymus species with genomes StStHHYY had a relatively higher level of genetic diversity (H = 0.219, I = 0.330, %P = 63.7), while tetraploid Elymus species with genomes StStYY had low level of genetic diversity (H = 0.182, I = 0.272, %P = 50.4) in the study. The cluster analysis showed that all ninety-five accessions were clustered into three major clusters. The accessions were grouped mainly according to their genomic components and origins. CONCLUSIONS: This study demonstrated that transcriptome sequencing is a fast and cost-effective approach to molecular marker development. These EST-SSR markers developed in this study are valuable tools for genetic diversity, evolutionary, and molecular breeding in E. sibiricus, and other Elymus species.

Assessing and Broadening Genetic Diversity of Elymus sibiricus Germplasm for the Improvement of Seed Shattering.

Siberian wild rye (Elymus sibiricus L.) is an important native grass in the Qinghai-Tibet Plateau of China. It is difficult to grow for commercial seed production, since seed shattering causes yield losses during harvest. Assessing the genetic diversity and relationships among germplasm from its primary distribution area contributes to evaluating the potential for its utilization as a gene pool to improve the desired agronomic traits. In the study, 40 EST-SSR primers were used to assess the genetic diversity and population structure of 36 E. sibiricus accessions with variation of seed shattering. A total of 380 bands were generated, with an average of 9.5 bands per primer. The polymorphic information content (PIC) ranged from 0.23 to 0.50. The percentage of polymorphic bands (P) for the species was 87.11%, suggesting a high degree of genetic diversity. Based on population structure analysis, four groups were formed, similar to results of principal coordinate analysis (PCoA). The molecular variance analysis (AMOVA) revealed the majority of genetic variation occurred within geographical regions (83.40%). Two genotypes from Y1005 and ZhN06 were used to generate seven F1 hybrids. The molecular and morphological diversity analysis of F1 population revealed rich genetic variation and high level of seed shattering variation in F1 population, resulting in significant improvement of the genetic base and desired agronomic traits.

Phylogenetic analysis of Elymus (Poaceae) in western China.

Elymus L. is often planted in temperate and subtropical regions as forage. Species in the genus have 5 allopolyploid genomes that are found in the grass tribe Triticeae. To determine the phylogenetic relationships in Elymus species from western China, we estimated phylogenetic trees using sequences from the nuclear ribosomal internal transcribed spacer and non-coding chloroplast DNA sequences from 56 accessions (871 samples) of 9 polyploid Elymus species and 42 accessions from GenBank. Tetraploid and hexaploid Elymus species from western China had independent origins, and Elymus species from the same area or neighboring geographic regions were the most closely related. Based on the phylogenetic tree topology, the St- and Y-genomes were not derived from the same donor and Y-genome likely originated from the H-genome of Hordeum species, or they shared the same origin or underwent introgression. The maternal genome of tetraploid and hexaploid Elymus species originated from species of Hordeum or Pseudoroegneria. Additionally, Elymus species in western China began diverging 17-8.5 million years ago, during a period of increased aridification as a consequence of the Messinian salinity crisis. Elymus species adapted to drought and high salinity may have developed based on the environmental conditions during this period. Elymus evolution in western China may have been affected by the uplift of the Qinghai-Tibetan Plateau (5 million years ago), when Elymus seeds were dispersed by gravity or wind into a newly heterogeneous habitat, resulting in isolation.

Molecular phylogeny revealed distinct origin of the Y and St genome in Elymus longearistatus (Triticeae: Poaceae).

Cytogenetic data has indicated the presence of St and Y genome in Elymus longearistatus (Boiss.) Tzvelev. However, a random amplified polymorphic DNA (RAPD) based sequence tagged site (STS) study suggested one accession of Pseudoroegneria spicata (Pursh) Á Löve (St genome) as a potential Y genome donor candidate in tetraploid E. longearistatus. To examine the origin of Y genome in and the phylogeny of tetraploid E. longearistatus, sequences of cpDNA (RPS16 and TrnD/T intergenic spacer) and single copy nuclear genes (EF-G and HTL) from eight accessions of E. longearistatus, six StY genomic Elymus species and 62 accessions of diploid in Triticeae were analyzed. The cpDNA data suggested that P. stipifolia (St) is the most likely maternal donor of these six Iranian accessions of E. longearistatus, although P. strigosa could not be excluded. Two nuclear gene data convincingly showed that tetraploid E. longearistatus contains two distinct genomes, St and Y genome. The phylogenetic analyses from both the EF-G and HTL rejected the previous suggestion that accession PI232134 of Pseudoroegneria spicata (Pursh) Á Löve (St genome) was potential Y genome donor to E. longearistatus. Phylogenetic analyses revealed a separation of the Y genome sequences in Iranian accessions of E. longearistatus from the sequences in the Pakistan accession, indicating that geographic isolation might influence the evolution of the Y genome in E. longearistatus.

Phylogeny and molecular evolution of the Acc1 gene within the StH genome species in Triticeae (Poaceae).

To estimate the phylogeny and molecular evolution of a single-copy gene encoding plastid acetyl-CoA carboxylase (Acc1) within the StH genome species, two Acc1 homoeologous sequences were isolated from nearly all the sampled StH genome species and were analyzed with those from 35 diploid taxa representing 19 basic genomes in Triticeae. Sequence diversity patterns and genealogical analysis suggested that (1) the StH genome species from the same areas or neighboring geographic regions are closely related to each other; (2) the Acc1 gene sequences of the StH genome species from North America and Eurasia are evolutionarily distinct; (3) Dasypyrum has contributed to the nuclear genome of Elymus repens and Elymus mutabilis; (4) the StH genome polyploids have higher levels of sequence diversity in the H genome homoeolog than the St genome homoeolog; and (5) the Acc1 sequence may evolve faster in the polyploid species than in the diploids. Our result provides some insight on evolutionary dynamics of duplicate Acc1 gene, the polyploidy speciation and phylogeny of the StH genome species.

Phylogenetic relationships and Y genome origin in Elymus L. sensu lato (Triticeae; Poaceae) based on single-copy nuclear Acc1 and Pgk1 gene sequences.

To estimate the origin and genomic relationships of the polyploid species within Elymus L. sensu lato, two unlinked single-copy nuclear gene (Acc1 and Pgk1) sequences of eighteen tetraploids (StH and StY genomes) and fourteen hexaploids (StStH, StYP, StYH, and StYW genomes) were analyzed with those of 35 diploid taxa representing 18 basic genomes in Triticeae. Sequence and phylogenetic analysis suggested that: (1) the St, H, W, and P genomes were donated by Pseudoroegneria, Hordeum, Australopyrum, and Agropyron, respectively, while the Y genome is closely related to the Xp genome in Peridictyon sanctum; (2) different hexaploid Elymus s.l. species may derived their StY genome from different StY genome tetraploid species via independent origins; (3) due to incomplete lineage sorting and/or hybridization events, the genealogical conflict between the two gene trees suggest introgression involving some Elymus s.l. species, Pseudoroegneria, Agropyron and Aegilops/Triticum; (4) it is reasonable to recognize the StH genome species as Elymus sensu stricto, the StY genome species as Roegneria, the StYW genome species as Anthosachne, the StYH genome species as Campeiostachys, and the StYP genome species as Kengyilia. The occurrence of multiple origin and introgression could account for the rich diversity and ecological adaptation of Elymus s.l. species.

Phylogenetic analysis revealed reticulate evolution of allotetraploid Elymus ciliaris.

Increasing evidence has shown the complex and dynamic nature of polyploids. Two single copy nuclear genes were used to explore genome evolutionary dynamics and the origin of tetraploid E. ciliaris: the phosphoglycerate kinase (PGK1) and the second largest subunit of RNA polymerase II (RPB2) together with a chloroplast gene encoding ribosomal protein S16 (RPS16). RPS16 data confirmed that the maternal origin of E. ciliaris is the St genome species. Both RPB2 and PGK1 data supported that E. ciliairs has multiple origins, and originated from the Pseudorogneria (St) and unknown donor (Y) diploids. The St genome in E. ciliaris species has a complex evolutionary history. Both RPB2 and PGK1 data suggested the absence of St genome in accession PI 377532 of E. ciliaris. However, cpDNA RPS16 clearly indicated that its maternal origin is the same as other E. ciliaris accessions, and is St genomic diploid species. Results suggest that there are two lineages of St genome present in E. ciliaris species; one is grouped with Pseudoroegneria diploid species, the other is grouped with Hordeum (H) species (named St?). The Japanese accession PI 377532 might have introgression either from HordeumH genome species or from ElymusStH genome species with replacement of at least some nuclear St-loci by H-loci. The correlation between genome differentiation and geographical distribution is also discussed.

Untangling nucleotide diversity and evolution of the H genome in polyploid Hordeum and Elymus species based on the single copy of nuclear gene DMC1.

Numerous hybrid and polypoid species are found within the Triticeae. It has been suggested that the H subgenome of allopolyploid Elymus (wheatgrass) species originated from diploid Hordeum (barley) species, but the role of hybridization between polyploid Elymus and Hordeum has not been studied. It is not clear whether gene flow across polyploid Hordeum and Elymus species has occurred following polyploid speciation. Answering these questions will provide new insights into the formation of these polyploid species, and the potential role of gene flow among polyploid species during polyploid evolution. In order to address these questions, disrupted meiotic cDNA1 (DMC1) data from the allopolyploid StH Elymus are analyzed together with diploid and polyploid Hordeum species. Phylogenetic analysis revealed that the H copies of DMC1 sequence in some Elymus are very close to the H copies of DMC1 sequence in some polyploid Hordeum species, indicating either that the H genome in theses Elymus and polyploid Hordeum species originated from same diploid donor or that gene flow has occurred among them. Our analysis also suggested that the H genomes in Elymus species originated from limited gene pool, while H genomes in Hordeum polyploids have originated from broad gene pools. Nucleotide diversity (π) of the DMC1 sequences on H genome from polyploid species (π = 0.02083 in Elymus, π = 0.01680 in polyploid Hordeum) is higher than that in diploid Hordeum (π = 0.01488). The estimates of Tajima's D were significantly departure from the equilibrium neutral model at this locus in diploid Hordeum species (P<0.05), suggesting an excess of rare variants in diploid species which may not contribute to the origination of polyploids. Nucleotide diversity (π) of the DMC1 sequences in Elymus polyploid species (π = 0.02083) is higher than that in polyploid Hordeum (π = 0.01680), suggesting that the degree of relationships between two parents of a polyploid might be a factor affecting nucleotide diversity in allopolyploids.

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 RPB2gene 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.

Assessment of worldwide genetic diversity of Siberian wild rye (Elymus sibiricus L.) germplasm based on gliadin analysis.

E. sibiricus L., the type species of the genus Elymus, is a perennial, self-pollinating and allotetraploid grass indigenous to Northern Asia, which in some countries can be cultivated as an important forage grass. In the present study, eighty-six Elymus sibiricus accessions, mostly from different parts of Asia, were assayed by gliadin markers based on Acid Polyacrylamide Gel Electrophoresis to differentiate and explore their genetic relationships. The genetic similarity matrix was calculated by 47 polymorphic bands, which ranged from 0.108 to 0.952 with an average of 0.373. The total Shannon diversity index (H(o)) and the Simpson index (H(e)) was 0.460 and 0.302, respectively. Cluster analysis showed a clear demarcation between accessions from Qinghai-Tibetan Plateau, China and the others as separate groups. The clustering pattern was probably dependent on geographic origin and ecological adaptability of the accessions. The population structure analysis based on Shannon indices showed that the proportion of variance within and among the five geographic regions of the Northern Hemisphere was 55.9 and 44.1%, respectively, or 63.4 and 36.6% within and among six Chinese provinces. This distinct geographical divergence was perhaps depended on ecogeographical conditions such as climate difference and mountain distribution. The results of gladin analysis in this study are useful for the collection and preservation of E. sibiricus germplasm resources.

A molecular genetic linkage map identifying the St and H subgenomes of Elymus (Poaceae: Triticeae) wheatgrass.

Elymus L. is the largest and most complex genus in the Triticeae tribe of grasses with approximately 150 polyploid perennial species occurring worldwide. We report here the first genetic linkage map for Elymus. Backcross mapping populations were created by crossing caespitose Elymus wawawaiensis (EW) (Snake River wheatgrass) and rhizomatous Elymus lanceolatus (EL) (thickspike wheatgrass) to produce F(1) interspecific hybrids that were then backcrossed to the same EL male to generate progeny with segregating phenotypes. EW and EL are both allotetraploid species (n = 14) containing the St (Pseudoroegneria) and H (Hordeum) genomes. A total of 387 backcross progeny from four populations were genotyped using 399 AFLP and 116 EST-based SSR and STS markers. The resulting consensus map was 2574 cM in length apportioned among the expected number of 14 linkage groups. EST-based SSR and STS markers with homology to rice genome sequences were used to identify Elymus linkage groups homoeologous to chromosomes 1-7 of wheat. The frequency of St-derived genome markers on each linkage group was used to assign genome designations to all linkage groups, resulting in the identification of the seven St and seven H linkage groups of Elymus. This map also confirms the alloploidy and disomic chromosome pairing and segregation of Elymus and will be useful in identifying QTLs controlling perennial grass traits in this genus.

Origin of the H genome in StH-genomic Elymus species based on the single-copy nuclear gene DMC1.

Previous studies have suggested that the H haplome in Elymus could originate from different diploid Hordeum species, however, which diploid species best represent the parental species remains unanswered. The focus of this study seeks to pinpoint the origin of the H genome in Elymus. Allopolyploid Elymus species that contain the StH genome were analyzed together with diploid Hordeum species and a broad sample of diploid genera in the tribe Triticeae using DMC1 sequences. Both parsimony and maximum likelihood analyses well separated the American Hordeum species, except Hordeum brachyantherum subsp. californicum, from the H genome of polyploid Elymus species. The Elymus H-genomic sequences were formed into different groups. Our data suggested that the American Horedeum species, except H. brachyantherum subsp. californicum, are not the H-genomic donor to the Elymus species. Hordeum brevisubulatum subsp. violaceum was the progenitor species to Elymus virescens, Elymus confusus, Elymus lanceolatus, Elymus wawawaiensis, and Elymus caninus. Furthermore, North American H. brachyantherum subsp. californicum was a progenitor of the H genome to Elymus hystrix and Elymus cordilleranus. The H genomes in Elymus canadensis, Elymus sibiricus, and Elymus multisetus were highly differentiated from the H genome in Hordeum and other Elymus species. The H genome in both North American and Eurasian Elymus species was contributed by different Hordeum species.

[Reproductive tillers phenotypic plasticity of Elymus excelsus population at different earring time in Songnen Plain of Northeast China].

The reproductive tillers of Elymus excelsus population in Songnen Plain were randomly marked with labels every other four days (five times in total) at early earring stage, and the marked tillers were harvested at dough stage, with the differences of their quantitative characteristics as well as the relationships between the quantitative characteristics and the shortened time of reproductive growth were analyzed. With the shortened time of reproductive growth, the quantitative characteristics of the reproductive tillers decreased gradually, which was not beneficial to the reproductive growth, reproductive allocation, and fruiting of reproductive tillers. The later the earring time, the larger the impact on fruiting and reproductive allocation was. When the reproductive growth time was shortened by 16 days, the grain biomass, setting penentage, reproductive allocation I , and reproductive allocation II decreased by 99.4%, 98.8%, 54.3%, and 99.2%, respectively. With the shortened time of reproductive growth, the tiller height decreased linearly, spike biomass, reproductive allocation I, and setting penentage decreased exponentially, tiller biomass, spike length, and floret number decreased powerly, and grain biomass, grain number, and reproductive allocation II decreased logarithmically.

Origin of the Y genome in Elymus and its relationship to other genomes in Triticeae based on evidence from elongation factor G (EF-G) gene sequences.

It is well known that Elymus arose through hybridization between representatives of different genera. Cytogenetic analyses show that all its members include the St genome in combination with one or more of four other genomes, the H, Y, P, and W genomes. The origins of the H, P, and W genomes are known, but not for the Y genome. We analyzed the single copy nuclear gene coding for elongation factor G (EF-G) from 28 accessions of polyploid Elymus species and 45 accessions of diploid Triticeae species in order to investigate origin of the Y genome and its relationship to other genomes in the tribe Triticeae. Sequence comparisons among the St, H, Y, P, W, and E genomes detected genome-specific polymorphisms at 66 nucleotide positions. The St and Y genomes are relatively dissimilar. The phylogeny of the Y genome sequences was investigated for the first time. They were most similar to the W genome sequences. The Y genome sequences were placed in two different groups. These two groups were included in an unresolved clade that included the W and E sequences as well as sequences from many annual species. The H genomes sequences were in a clade with the F, P, and Ns genome sequences as sister groups. These two clades were more closely related to each other and to the L and Xp genomes than they were to the St genome sequences. These data support the hypothesis that the Y genome evolved in a diploid species and has a different origin from the St genome.

A Y genome specific STS marker in Pseudoroegneria and Elymus species (Triticeae: Gramineae).

The tribe Triticeae Dumortier in the grass family (Poaceae) includes the most important cereal crops (e.g., wheat, barley, and rye) and some economically important forage grasses. Elymus L. is the largest and most complex genus in the Triticeae tribe with approximately 150 species occurring worldwide. The genomic constitutions of approximately 40% of Elymus species are unknown and some have unverified genomic combinations. Of those known for genome constitutions, Elymus species have a genomic formula of StH, StP, StY, StStY, StHY, StPY, or StWY. However, the origin of the Y genome is unknown because no diploid species have been identified as the Y genome donor. A putative Y genome specific random amplified polymorphic DNA (RAPD) marker was converted to a sequence tagged site (STS) marker. The reliability of this STS marker for confirming the presence of the Y genome was demonstrated using 42 accessions of Elymus. The STS-PCR for the Y genome marker was then assayed on 43 accessions of diploid Pseudoroegneria (Nevski) A. Löve species having the St genome to identify possible donors of the Y genome. A rare accession of Pseudoroegneria spicata (Pursh) A. Löve was found to possess sequences that most closely related to those from the tetraploid Elymus longearistatus (Boiss.) Tzvelev (StStYY), making P. spicata the most likely donor of the Y genome, although Pseudoroegneria libanotica (Heck.) D.R. Dewey or other Pseudoroegneria species could not be excluded. Our findings support the hypothesis that the Y genome in some Elymus species shares a progenitor genome (designated StY) with the St genome of Pseudoroegneria.

Molecular phylogeny of RPB2 gene reveals multiple origin, geographic differentiation of H genome, and the relationship of the Y genome to other genomes in Elymus species.

It has been hypothesized from isozymic and cytological studies of Elymus species that the Old and New World taxa may be of separate origin of the H genome in the StH genome species. To test this hypothesis, and estimate the phylogenetic relationships of polyploid Elymus species within the Triticeae, the second largest subunit of RNA polymerase II (RPB2) sequence of 36 Elymus accessions containing StH or StY genomes was analyzed with those of Pseudoroegneria (St), Hordeum (H), Agropyron (P), Australopyrum (W), Lophopyrum(Ee), Thinopyrum(Eb) and Dasypyrum (V). Our data indicated that the H genome in Elymus species is differentiated in accordance with geographical origin, and that the Eurasian and American StH genome species have independent alloploid origins with different H-genome donors. Phylogenetic analysis of Y genome sequences with other genome donors (St, H, P, W) of Elymus revealed that W and P genomes are sister to Y genome with a 87% bootstrap support, and that StY and StH species group might have acquired their RPB2 St sequences from distinct Pseudoroegneria gene pools. Our data did not support the suggestion that the St and Y genomes have the same origin as put forward in a previous study using ITS data. Our result provides some insight on the origin of Y genome and its relationship to other genomes in Elymus.

Phylogenetic relationships in Leymus (Poaceae: Triticeae) revealed by the nuclear ribosomal internal transcribed spacer and chloroplast trnL-F sequences.

Using the nuclear ribosomal internal transcribed spacer (ITS) sequences and the chloroplasttrnL-F sequence, phylogeneic analysis was performed on 57 accessions of species in the tribe Triticeae including 13 Leymus species (N(s)) with different ploidy levels and 40 diploid species from 18 genera. The ITS sequences revealed that ployploid Leymus has close phylogentic relationships with Psathyrostachys and an undefined genus in Triticeae. The trnL-F tree demonstrated close relationships between certain Leymus species and Psathyrostachys, and other Leymus species distributed in North America were far from Psathyrostachys. Based on these results, it is unlikely that the unknown genome in Leymus species originated from one of the sampled diploid species in the present study. The maternal donor of all the Leymus species with a natural distribution in Eurasia were N(s) genome. Furthermore, Elymus californicus should be transferred from the genus Elymus to Leymus.

Molecular diversity and relationships among Elymus trachycaulus, E. subsecundus, E. virescens, E. violaceus, and E. hyperarcticus (Poaceae: Triticeae) as determined by amplified fragment length polymorphism.

Morphological similarity among E. trachycaulus, E. virescens, E. violaceus, and E. hyperarcticus has often been noted. Taxonomists have tried to discriminate among these taxa using morphological characters and a number of different relationships among them have been suggested. However, the genetic relationships among these taxa are still unknown. AFLP analysis was used to characterize the molecular diversity of these taxa and to examine genetic relationships among them. A high degree of genetic identity was apparent among 7 accessions of E. virescens. The similarity values ranged from 0.90 to 0.99 with an average of 0.94. The mean similarity values among 3 E. hyperarcticus and among 5 E. violaceus accessions were 0.84 (0.81-0.87) and 0.77 (0.66-0.90), respectively. The similarity values among 17 E. trachycaulus accessions ranged from 0.49 to 0.92 with an average of 0.75. The 5 accessions of E. subsecundus displayed high variation, with similarity values between 0.52 and 0.68 and a mean value of 0.59. Both maximum-parsimony (MP) and neighbor-joining (NJ) analyses showed that all 7 accessions of E. virescens formed a clade, indicating a monophyletic origin. On the other hand, Elymus trachycaulus, E. subsecundus, and E. violaceus were each paraphyletic and separated into different genetically distinct groups. Among these 5 taxa, E. virescens was genetically similar to E. trachycaulus, and E. violaceus was genetically similar to E. hyperarcticus.