Genome constitution and evolution of Elymus atratus (Poaceae: Triticeae) inferred from cytogenetic and phylogenetic analysis.

BACKGROUND: Elymus atratus (Nevski) Hand.-Mazz. is perennial hexaploid wheatgrass. It was assigned to the genus Elymus L. sensu stricto based on morphological characters. Its genome constitution has not been disentangled yet. OBJECTIVE: To identify the genome constitution and origin of E. atratus. METHODS: In this study, genomic in situ hybridization and fluorescence in situ hybridization, and phylogenetic analysis based on the Acc1, DMC1 and matK sequences were performed. RESULTS: Genomic in situ hybridization and fluorescence in situ hybridization results reveal that E. atratus 2n = 6x = 42 is composed of 14 St genome chromosomes, 14 H genome chromosomes, and 14 Y genome chromosomes including two H-Y type translocation chromosomes, suggesting that the genome formula of E. atratus is StStYYHH. The phylogenetic analysis based on Acc1 and DMC1 sequences not only shows that the Y genome originated in a separate diploid, but also suggests that Pseudoroegneria (St), Hordeum (H), and a diploid species with Y genome were the potential donors of E. atratus. Data from chloroplast DNA showed that the maternal donor of E. atratus contains the St genome. CONCLUSION: Elymus atratus is an allohexaploid species with StYH genome, which may have originated through the hybridization between an allotetraploid Roegneria (StY) species as the maternal donor and a diploid Hordeum (H) species as the paternal donor.

Comparative physiological and root transcriptome analysis of two annual ryegrass cultivars under drought stress.

Annual ryegrass is a widely cultivated forage grass with rapid growth and high productivity. However, drought is one of the abiotic stresses affecting ryegrass growth and quality. In this study, we compared the physiological and transcriptome responses of Chuansi No.1 (drought-tolerant, DT) and Double Barrel (drought-sensitive, DS) under drought stress simulated by PEG-6000 for 7 days. The results showed that Chuansi No. 1 had stronger physiological and biochemical parameters such as root properties, water content, osmotic adjustment ability and antioxidant ability. In addition, RNA-seq was used to elucidate the molecular mechanism of root drought resistance. We identified 8588 differentially expressed genes related to drought tolerance in root, which were mainly enriched in oxidation-reduction process, carbohydrate metabolic process, apoplast, arginine and proline metabolism, and phenylpropanoid biosynthesis pathways. The expression levels of DEGs were consistent with physiological changes of ryegrass under drought stress. We found that genes related to sucrose and starch synthesis, root development, osmotic adjustment, ABA signal regulation and specifically up-regulated transcription factors such as WRKY41, WRKY51, ERF7, ERF109, ERF110, NAC43, NAC68, bHLH162 and bHLH148 in Chuansi No. 1 may be the reason for its higher drought tolerance. This study revealed the underlying physiological and molecular mechanisms of root response to drought stress in ryegrass and provided some new candidate genes for breeding rye drought tolerant varieties.

Evolutionary patterns of plastome resolve multiple origins of the Ns-containing polyploid species in Triticeae.

Tracing evolutionary history proves challenging for polyploid groups that have evolved rapidly, especially if an ancestor of a polyploid is extinct. The Ns-containing polyploids are recognized as the NsXm and StHNsXm genomic constitutions in Triticeae. The Ns originated from Psathyrostachys, while the Xm represented a genome of unknown origin. Here, we use genetic information in plastome to trace the complex lineage history of the Ns-containing polyploid species by sampling 26 polyploids and 90 diploid taxa representing 23 basic genomes in Triticeae. Phylogenetic reconstruction, cluster plot of genetic distance matrix, and migration event demonstrated that (1) the Ns plastome originated from different Psathyrostachys species, and the Xm plastome may originate from an ancestral lineage of Henrardia, Agropyron, and Eremopyrum; (2) the Ns, Xm, and St genome donors separately served as the maternal parents during the speciation of the Ns-containing polyploid species, resulting in a maternal haplotype polymorphism; (3) North AmericanLeymusspecies might originate from colonization during late Miocene via the Bering land bridge and were the paternal donor of the StHNsXm genome Pascopyrum species. Our results shed new light on our understanding of the rich diversity and ecological adaptation of the Ns-containing polyploid species.

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.

Confirmation of Natural Hybridization between Kengyilia (StStYYPP) and Campeiostachys (StStYYHH) (Triticeae: Poaceae) Based on Morphological and Molecular Cytogenetic Analyses.

Natural hybridization has been frequently observed in Triticeae; however, few studies have investigated the origin of natural intergeneric Triticeae hybrids. In the present study, we discovered three putative hybrid Triticeae plants in the Western Sichuan Plateau of China. Morphologically, the putative hybrids were intermediate between Kengyilia melanthera (2n = 6x = 42; StStYYPP) and Campeiostachys dahurica var. tangutorum (2n = 6x = 42; StStYYHH) with greater plant height and tiller number. Cytological analyses demonstrated that the hybrids were hexaploid with 42 chromosomes (2n = 6x = 42). At metaphase I, 12.10-12.58 bivalents and 13.81-14.18 univalents per cell were observed in the hybrid plants. Genomic in situ hybridization demonstrated that the hybrids had StStYYHP genomes. Phylogenetic analysis of Acc1 sequences indicated that the hybrids were closely related to K. melanthera and C. dahurica var. tangutorum. Our morphological, cytological, and molecular analyses indicate that these hexaploid natural hybrid plants may be hybrids of K. melanthera and C. dahurica var. tangutorum.

Variation in Plastome Sizes Accompanied by Evolutionary History in Monogenomic Triticeae (Poaceae: Triticeae).

To investigate the pattern of chloroplast genome variation in Triticeae, we comprehensively analyzed the indels in protein-coding genes and intergenic sequence, gene loss/pseudonization, intron variation, expansion/contraction in inverted repeat regions, and the relationship between sequence characteristics and chloroplast genome size in 34 monogenomic Triticeae plants. Ancestral genome reconstruction suggests that major length variations occurred in four-stem branches of monogenomic Triticeae followed by independent changes in each genus. It was shown that the chloroplast genome sizes of monogenomic Triticeae were highly variable. The chloroplast genome of Pseudoroegneria, Dasypyrum, Lophopyrum, Thinopyrum, Eremopyrum, Agropyron, Australopyrum, and Henradia in Triticeae had evolved toward size reduction largely because of pseudogenes elimination events and length deletion fragments in intergenic. The Aegilops/Triticum complex, Taeniatherum, Secale, Crithopsis, Herteranthelium, and Hordeum in Triticeae had a larger chloroplast genome size. The large size variation in major lineages and their subclades are most likely consequences of adaptive processes since these variations were significantly correlated with divergence time and historical climatic changes. We also found that several intergenic regions, such as petN-trnC and psbE-petL containing unique genetic information, which can be used as important tools to identify the maternal relationship among Triticeae species. Our results contribute to the novel knowledge of plastid genome evolution in Triticeae.

Evolutionary patterns of plastome uncover diploid-polyploid maternal relationships in Triticeae.

To investigate the diploid-polyploid relationships and the role of maternal progenitors in establishment of polyploid richness in Triticeae, 35 polyploids representing almost all genomic constitutions together with 48 diploid taxa representing 20 basic genomes in the tribe were analyzed. Phylogenomic reconstruction, genetic distance matrix, and nucleotide diversity patterns of plastome sequences indicated that (1) The maternal donor of the annual polyploid species with the U- and D-genome are related to extant Ae. umbellulata and Ae. tauschii, respectively. The maternal donor to the annual polyploid species with the S-, G-, and B-genome originated from the species of Sitopsis section of the genus Aegilops. The annual species with the Xe-containing polyploids were donated by Eremopyrum as the female parent; (2) Pseudoroegneria and Psathyrostachys were the maternal donor of perennial species with the St- and Ns-containing polyploids, respectively; (3) The Lophopyrum, Thinopyrum and Dasypyrum genomes contributed cytoplasm genome to Pseudoroegneria species as a result of incomplete lineage sorting and/or chloroplast captures, and these lineages were genetically transmitted to the St-containing polyploid species via polyploidization; (4) There is a reticulate relationship among the St-containing polyploid species. It can be suggested that genetic heterogeneity might associate with the richness of the polyploids in Triticeae.

Complete structure and variation of the chloroplast genome of Agropyron cristatum (L.) Gaertn.

Agropyron cristatum (L.) Gaertner, a perennial grass in the tribe Triticeae (Poaceae), is a wild relative of cereal crops that is suitable for genetic improvement. In this study, we first sequenced the complete chloroplast (cp) genome of Ag. cristatum using Hiseq4000 PE150. The Ag. cristatum chloroplast genome is 135,554bp in length, has a typical quadripartite structure and contains 76 protein-coding genes, 29 tRNA genes and four rRNA genes. The cp genome of Ag. cristatum was used for comparison with other seven Triticeae species. One large variable region (800bp), which primarily contained the rpl23 (non-reciprocally translocated from IRs) and accD genes, was detected between rbcL gene and psaI gene within LSC region. The deletion of the accD and translocated rpl23 genes in Ag. cristatum indicated an independent gene-loss events or an additional divergence in Triticeae. Analyses of the dn/ds ratio and K2-P's genetic distance for 76 protein-coding genes showed that genes with evolutionary divergence might suffer from the effect of sequence regional constraints or gene functional constraints in Triticeae species. Our research will generally contribute to the knowledge of plastid genome evolution in Triticeae.

Phylogeny and maternal donors of Elytrigia Desv. sensu lato (Triticeae; Poaceae) inferred from nuclear internal-transcribed spacer and trnL-F sequences.

BACKGROUND: Elytrigia Desv. is a genus with a varied array of morphology, cytology, ecology, and distribution in Triticeae. Classification and systematic position of Elytrigia remain controversial. We used nuclear internal-transcribed spacer (nrITS) sequences and chloroplast trnL-F region to study the relationships of phylogenetic and maternal genome donor of Elytrigia Desv. sensu lato. RESULTS: (1) E, F, P, St, and W genomes bear close relationship with one another and are distant from H and Ns genomes. Ee and Eb are homoeologous. (2) In ESt genome species, E genome is the origin of diploid Elytrigia species with E genome, St genome is the origin of Pseudoroegneria. (3) Diploid species Et. elongata were differentiated. (4) Et. stipifolia and Et. varnensis sequences are diverse based on nrITS data. (5) Et. lolioides contains St and H genomes and belongs to Elymus s. l. (6) E genome diploid species in Elytrigia serve as maternal donors of E genome for Et. nodosa (PI547344), Et. farcta, Et. pontica, Et. pycnantha, Et. scirpea, and Et. scythica. At least two species act as maternal donor of allopolyploids (ESt and EStP genomes). CONCLUSIONS: Our results suggested that Elytrigia s. l. species contain different genomes, which should be divided into different genera. However, the genomes of Elytrigia species had close relationships with one another. Diploid species were differentiated, because of introgression and different geographical sources. The results also suggested that the same species and the same genomes of different species have different maternal donor. Further study of molecular biology and cytology could facilitate the evaluation of our results of phylogenetic in a more specific and accurate way.

Contrasting evolutionary patterns of multiple loci uncover new aspects in the genome origin and evolutionary history of Leymus (Triticeae; Poaceae).

Leymus Hochst. (Triticeae: Poaceae), a group of allopolyploid species with the NsXm genomes, is a perennial genus with diversity in morphology, cytology, ecology, and distribution in the Triticeae. To investigate the genome origin and evolutionary history of Leymus, three unlinked low-copy nuclear genes (Acc1, Pgk1, and GBSSI) and three chloroplast regions (trnL-F, matK, and rbcL) of 32 Leymus species were analyzed with those of 36 diploid species representing 18 basic genomes in the Triticeae. The phylogenetic relationships were reconstructed using Bayesian inference, Maximum parsimony, and NeighborNet methods. A time-calibrated phylogeny was generated to estimate the evolutionary history of Leymus. The results suggest that reticulate evolution has occurred in Leymus species, with several distinct progenitors contributing to the Leymus. The molecular data in resolution of the Xm-genome lineage resulted in two apparently contradictory results, with one placing the Xm-genome lineage as closely related to the P/F genome and the other splitting the Xm-genome lineage as sister to the Ns-genome donor. Our results suggested that (1) the Ns genome of Leymus was donated by Psathyrostachys, and additional Ns-containing alleles may be introgressed into some Leymus polyploids by recurrent hybridization; (2) The phylogenetic incongruence regarding the resolution of the Xm-genome lineage suggested that the Xm genome of Leymus was closely related to the P genome of Agropyron; (3) Both Ns- and Xm-genome lineages served as the maternal donor during the speciation of Leymus species; (4) The Pseudoroegneria, Lophopyrum and Australopyrum genomes contributed to some Leymus species.

Cytogenetic study and stripe rust response of the derivatives from a wheat - Thinopyrum intermedium - Psathyrostachys huashanica trigeneric hybrid.

To transfer multiple desirable alien genes into common wheat, we previously reported a new trigeneric hybrid synthesized by crossing a wheat - Thinopyrum intermedium partial amphiploid with wheat - Psathyrostachys huashanica amphiploid. Here, the meiotic behavior, chromosome constitution, and stripe rust resistance of F5 derivatives from the wheat - Th. intermedium - P. huashanica trigeneric hybrid were studied. Cytological analysis indicated the F5 progenies had chromosome numbers of 42-50 (average 44.96). The mean meiotic configuration was 1.28 univalents, 21.74 bivalents, 0.04 trivalents, and 0.02 tetravalents per pollen mother cell. In 2n = 42 lines, the average pairing configuration was 0.05 I + 19.91 II (ring) + 1.06 II (rod) + 0.003 IV, suggesting these lines were cytologically stable. Most lines with 2n = 43, 44, 46, 48, or 50, bearing a high frequency of univalents or multivalents, showed abnormal meiotic behavior. Genomic in situ hybridization karyotyping results revealed that 25 lines contained 1-7 Th. intermedium chromosomes, but no P. huashanica chromosomes were found among the 27 self-pollinated progenies. At meiosis, univalents (1-5) possessing Th. intermedium hybridization signals were detected in 19 lines. Bivalents (1-3) expressing fluorescence signals were observed in 12 lines. Importantly, 21 lines harbored wheat - Th. intermedium chromosomal translocations with various alien translocation types. Additionally, two homozygous lines, K13-668-10 and K13-682-12, possessed a pair of wheat - Th. intermedium small fragmental translocations. Compared with the recurrent parent Zhong 3, most lines showed high resistance to the stripe rust (Puccinia striiformis f. sp. tritici) pathogens prevalent in China, including race V26/Gui22. This paper reports a highly efficient technical method for inducing alien translocation between wheat and Th. intermedium by trigeneric hybridization. These lines might be potentially valuable germplasm resources for further wheat improvement.

Genome origin, historical hybridization and genetic differentiation in Anthosachne australasica (Triticeae; Poaceae), inferred from chloroplast rbcL, trnH-psbA and nuclear Acc1 gene sequences.

BACKGROUND AND AIMS: Anthosachne Steudel is a group of allopolyploid species that was derived from hexaploidization between the Asian StY genome Roegneria entity and the Australasia W genome Australopyrum species. Polyploidization and apomixis contribute to taxonomic complexity in Anthosachne Here, a study is presented on the phylogeny and evolutionary history of Anthosachne australasica The aims are to demonstrate the process of polyploidization events and to explore the differentiation patterns of the St genome following geographic isolation. METHODS: Chloroplast rbcL and trnH-psbA and nuclear Acc1 gene sequences of 60 Anthosachne taxa and nine Roegneria species were analysed with those of 33 diploid taxa representing 20 basic genomes in Triticeae. The phylogenetic relationships were reconstructed. A time-calibrated phylogeny was generated to estimate the evolutionary history of A. australasica Nucleotide diversity patterns were used to assess the divergence within A. australasica and between Anthosachne and its putative progenitors. KEY RESULTS: Three homoeologous copies of the Acc1 sequences from Anthosachne were grouped with the Acc1 sequences from Roegneria, Pseudoroegneria, Australopyrum, Dasypyrum and Peridictyon The chloroplast sequences of Anthosachne were clustered with those from Roegneria and Pseudoroegneria Divergence time for Anthosachne was dated to 4·66 million years ago (MYA). The level of nucleotide diversity in Australasian Anthosachne was higher than that in continental Roegneria A low level of genetic differentiation within the A. australasica complex was found. CONCLUSIONS: Anthosachne originated from historical hybridization between Australopyrum species and a Roegneria entity colonized from Asia to Australasia via South-east Asia during the late Miocene. The St lineage served as the maternal donor during the speciation of Anthosachne A contrasting pattern of population genetic structure exists in the A. australasica complex. Greater diversity in island Anthosachne compared with continental Roegneria might be associated with mutation, polyploidization, apomixis and expansion. It is reasonable to consider that A. australasica var. scabra and A. australasica var. plurinervisa should be included in the A. australasica complex.

Cytogenetic Behavior of Trigeneric Hybrid Progeny Involving Wheat, Rye and Psathyrostachys huashanica.

Trigeneric hybrids are commonly used as bridges to transfer genes from some wild species to cultivated wheat and to measure the genomic interaction between donor species. We previously reported that trigeneric germplasms were produced by crossing wheat-Psathyrostachys huashanica amphiploids (PHW-SA, 2n = 8x = 56, AABBDDNsNs) with hexaploid triticale (Zhongsi 828, 2n = 6x = 42, AABBRR). In the present study, chromosome pairing behavior and the genome constitution of the F4 progenies of wheat-rye-P. huashanica trigeneric hybrids were studied. Cytological analysis showed that the chromosome number of F4 progenies ranged from 39 to 46, and 57.5% of them had 42 chromosomes. The mean meiotic configuration of F4 lines was 1.71 univalents, 20.26 bivalents, 0.04 trivalents, and 0.001 quadrivalents per pollen mother cell. Among the lines with 2n = 42, the average pairing configuration was 1.21 univalents, 16.22 ring bivalents, 4.16 rod bivalents, and 0.01 trivalents. This result indicated that these lines were cytologically stable. Other lines with 2n = 39, 40, 41, 43, 44, 45, and 46, bearing a high number of univalents or multivalents, showed abnormal meiotic behavior. Genomic in situ hybridization (GISH) revealed that all F4 lines had 11-14 rye chromosomes, but no P. huashanica chromosomes. The complete set of 14 rye chromosomes was found in 19 lines. At meiosis, GISH detected 1-6 univalents with hybridization signals of rye in 13 lines. Bivalents with fluorescence signals were identified in each line, ranging from 3 to 7. A quadrivalent with hybridization signals was observed in only 1 line, K13-714-8. Lagging chromosomes, chromosome bridges, micronuclei, and chromosome fragments hybridizing with the probe were not discovered in any of the lines. These results inferred that the behavior of rye chromosomes was normal during meiosis. In addition, 21 lines of 2n = 42 (91.3%) with 12 or 14 rye chromosomes, always contained 6 or 7 bivalents bearing fluorescence signals. This suggested that the rye chromosomes exhibiting complete pairing in these lines were cytologically stable during meiosis and may therefore be considered as new hexaploid triticales. Thus, these lines might be potential materials for further hexaploid triticale improvement.

Characterization of wheat - Psathyrostachys huashanica small segment translocation line with enhanced kernels per spike and stripe rust resistance.

Psathyrostachys huashanica Keng (2n = 2x = 14, NsNs), a distant wild relative of common wheat, possesses rich potentially valuable traits, such as disease resistance and more spikelets and kernels per spike, that could be useful for wheat genetic improvement. Development of wheat - P. huashanica translocation lines will facilitate its practical utilization in wheat breeding. In the present study, a wheat - P. huashanica small segmental translocation line, K-13-835-3, was isolated and characterized from the BC1F5 population of a cross between wheat - P. huashanica amphiploid PHW-SA and wheat cultivar CN16. Cytological studies showed that the mean chromosome configuration of K-13-835-3 at meiosis was 2n = 42 = 0.10 I + 19.43 II (ring) + 1.52 II (rod). GISH analyses indicated that chromosome composition of K-13-835-3 included 40 wheat chromosomes and a pair of wheat - P. huashanica translocation chromosomes. FISH results demonstrated that the small segment from an unidentified P. huashanica chromosome was translocated into wheat chromosome arm 5DS, proximal to the centromere region of 5DS. Compared with the cultivar wheat parent CN16, K-13-835-3 was highly resistant to stripe rust pathogens prevalent in China. Furthermore, spikelets and kernels per spike in K-13-835-3 were significantly higher than those of CN16 in two growing seasons. These results suggest that the desirable genes from P. huashanica were successfully transferred into CN16 background. This translocation line could be used as novel germplasm for high-yield and, eventually, resistant cultivar breeding.

Phylogeny and differentiation of the St genome in Elymus L. sensu lato (Triticeae; Poaceae) based on one nuclear DNA and two chloroplast genes.

BACKGROUND: 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. RESULTS: 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. CONCLUSION: 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.

Evolutionary pattern of rDNA following polyploidy in Leymus (Triticeae: Poaceae).

Ribosomal ITS polymorphism and its ancestral genome origin of polyploid Leymus were examined to infer the evolutionary outcome of rDNA gene following allopolyploid speciation and to elucidate the geographic pattern of ITS variation. The results demonstrated that different polyploids have experienced varying fates, including maintenance or homogenization of divergent arrays, occurrence of chimeric repeats and potential pseudogenes. Our data suggested that (1) the Ns, P/F, and St genomic types in Leymus were originated from Psathyrostachys, Agropyron/Eremopyrum, and Pseudoroegneria, respectively; (2) the occurrence of a higher proportion of Leymus species with predominant uniparental rDNA type might associate with the segmental allopolyploid origin, nucleolar dominance of alloploids, and rapid radiation of Leymus; (3) maintenance of multiple parental ITS types in allopolyploid might result from long generation times associated to vegetative multiplication, number and chromosomal location of ribosomal loci and/or recurrent hybridization; (4) the rDNA genealogical structure of Leymus species might associate with the geographic origins; and (5) ITS sequence clade shared by Leymus species from Central Asia, North America, and Nordic might be an outcome of ancestral ITS homogenization. Our results shed new light on understanding evolutionary outcomes of rDNA following allopolyploid speciation and geographic isolation.

Evolutionary history of Triticum petropavlovskyi Udacz. et Migusch. inferred from the sequences of the 3-phosphoglycerate kinase gene.

Single- and low-copy genes are less likely to be subject to concerted evolution. Thus, they are appropriate tools to study the origin and evolution of polyploidy plant taxa. The plastid 3-phosphoglycerate kinase gene (Pgk-1) sequences from 44 accessions of Triticum and Aegilops, representing diploid, tetraploid, and hexaploid wheats, were used to estimate the origin of Triticum petropavlovskyi. Our phylogenetic analysis was carried out on exon+intron, exon and intron sequences, using maximum likelihood, Bayesian inference and haplotype networking. We found the D genome sequences of Pgk-1 genes from T. petropavlovskyi are similar to the D genome orthologs in T. aestivum, while their relationship with Ae. tauschii is more distant. The A genome sequences of T. petropavlovskyi group with those of T. polonicum, but its Pgk-1 B genome sequences to some extent diverge from those of other species of Triticum. Our data do not support for the origin of T. petropavlovskyi either as an independent allopolyploidization event between Ae. tauschii and T. polonicum, or as a monomendelian mutation in T. aestivum. We suggest that T. petropavlovskyi originated via spontaneous introgression from T. polonicum into T. aestivum. The dating of divergence among T. polonicum, T. petropavlovskyi, T. carthlicum, T. turgidum, and T. compactum indicates an age of 0.78 million years [corrected].

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.

Molecular evolution and diversity of dimeric alpha-amylase inhibitor gene in Kengyilia species (Triticeae: Poaceae).

Kengyilia Yen et J. L. Yang is a group of allohexaploid species with StYP genomic constitutions in the wheat tribe. To investigate the evolution and diversity of dimeric alpha-amylase inhibitor genes in the Kengyilia, forty-five homoeologous DAAI gene sequences were isolated from sampled Kengyilia species and analyzed together with those of its close relatives. These results suggested that (1) Kengyilia species from Central Asia and the Qinghai-Tibetan Plateau had different origins from those of the geographically differentiated P genome; (2) the St and P genomes of Kengyilia were donated by Pseudoroegneria and Agropyron, respectively, and the Y genome had an independent origin and showed an affinity with the St genome; (3) purifying selection dominated the DAAI gene members and the St-DAAI gene was evolving at faster rate than the P- and Y-DAAI genes in Kengyilia; and (4) natural selection was the main factor on the codon usage pattern of the DAAI gene in Kengyilia.

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.