Molecular Phylogenetic And Cytological Studies On The Species With StH Genome In The Tribe Triticeae

The tribe Triticeae, including about 350-450 species distributed in the temperate and subtropical and tropic regions, is of enormous important group in Poaceae. Triticeae includes about 20 basic genomes (Ns, H, P, St, Y, W, E).These basic genomes in various combinations constitute numerous polyploid speceis, such as StP, StY, StH, NsXm, StYW, StYP species, leading to 70%～75% of Triticeae species are of polyploidy origin. One important group of polyploids in Triticeae is the species with StH genomes, which orignated from hybridization between the species from Pseudoroegneria and Hordeum. They are distributed from the Arctic, to temperate and subtropical regions, and occurred on grassland, semi-desert, mountain slopes, valleys, and forest regions. Most species with StH genomes are fine herbages, and some species have disease resistance, insect resistance and stress tolerance, which are precious germplasm resources in crop improvement and forage breeding.The species with StH genomes, including about 20 allotetraploids (2n=4x=28)and allohexaploids (2n=6x=42),was constituted by the St and H genomes in various combinations in tribe Triticeae. Morphologically, the species with StH genomes exhibit different variations with one (Elymus caninus L.)to two (Elymus sibiricus L.)to three (Elymus canadensis L.)spikelets per node, and narrow and long (Elymus elymoides (Raf.) Swezey) to reduced (Elymus hystrix L.)glumes.All the species with StH genomes were in the inter-continental disjunction between Eurasian and North American. Despite the similarity of genomic constitution, different species with StH genomes have different morphological characters, distribution and habits. In addition, the taxonomic treatment and phylogenetic relationships of the species with StH genomes are still in dispute. The StH genome species were once included in Elymus, Hystrix, Sitanion and Elytrigia, and many species were treated as the type species. The sectional delimitation of the species with StH genomes has been proposed by different scholars, which increase the uncertainties regarding the phylogenetic relationships among these species.In this study, we carried out the phylogenetic analysis of the species with StH genomes based on multiple-copy nuclear ITS,single-copy nuclear Accl and DMC1, chloplastid trnL-F and mitochondrial CoxII sequences.Data from these molecular phylogenetic evidences were analysed together with the endosperm cytological structures and meiotic pairing in hybrids.The objectives were:(1)to elucidate the phylogenetic relationships of the species with StH genomes;(2)to investigate whether the phylogenetic relationships of the StH-genome species are linked with the inter-continental disjunction between Eurasian and North American; (3)to reveal the origin of the genome in the species with StH genomes;(4) to identify the maternal genome donor to the species with StH genomes; (5) to examine the level of nucleotide polymorphism in St and H genome from the species with StH genomes;(6) to document geographic diversification patterns of the species with StH genomes.The main results are as follows:1.Based on nrITS sequences, phylogenetic analysis was performed on sixteen species with StH genome, five Pseudoroegneria (St) species and three Hordeum (H) species in the tribe Triticeae. Phylogenetic analysis suggests that:(1)Sitanion jubatum,Sitanion hystrix and Hystrix patula were closely related to the species of Elymus, and should be included in the genus Elymus; (2) the StH-genome species from the same areas or neighboring geographic regions are closely related to each other;(3)the ITS sequence of the StH-genome species distributed in North and Eurasian is heterogeneous geographically; (4) the ITS sequence of the St and H genome species were evolutionarily distinct; (5)why the variation and differentiation occurred in the species with StH genome were also discussed.2.The chloroplast trnL-F sequences and mitochondria CoxⅡintron and the combined data set of 16 StH-genome species and the related diploid species were analyzed using Maximum Parsimony (ML),Bayesian Inference (BI) and Median-joining (MJ)network approaches.Phylogenetic analysis and MJ network analysis suggest that:(1)the StH-genome species were clustered with diploid Pseudoroegneria species, indicating the St genome served as the maternal parent to the species with StH genome; (2)the StH-genome species have different maternal lineages and Pseudoroegneria spicata or its ancestry was the most possible maternal donor of some species; (3)the degree of differentiation occurred the diploid species with St genome and polyploid species with StH genome; (4)Hystrix patula and Sitanion hystrix and Sitanion jubatum were clustered with Elymus species, which is reasonable to transfer them to Elymus;(5)Elytrigia repens is different from Elymus species and its taxonomic rank is still ambiguous.3.Twenty-nine haplotyps of the Accl gene were isolated from fifteen StH-genome species.These haplotypes were analysis together with the haplotypes from five Pseudoroegneria and three Hordeum taxa. The results suggested that:(1)the Accl sequences from Elymus virginicus (H-copy) and E. hystrix (H-copy) had a 173 bp insertion; (2) the Accl sequence of the StH-genome species from Eurasian were evolutionarily distinct from those from North America;(3)different Pseudoroegneria species might sever as the donor during the speciation of StH-genome species; (4) the StH-genome species are closely related to the Hordeum species from the same areas or neighboring geographic regions; (5) nucleotide sequence diversity in the StH-genome species was higher than that in the St genome of diploid Pseudoroegneria and the H genome of diploid Hordeum.4.Thirty-one haplotyps of the DMC1 gene were isolated from 16 StH-genome species. These haplotypes were analysed together with the haplotypes from four Pseudoroegneria and three Hordeum taxa. The results suggested that:(1)the DMC1 sequences of the StH-genome species from Eurasian were evolutionarily distinct from those from North America; (2) different Pseudoroegneria species might serve as donor during the speciation of StH-genome species;(3)the StH-genome species might experience recurrent hybridization with different donor of Hordeum species; (4) the ratio of parsimony-informative sites were higher in the DMC1 sequences than that in the Accl sequences.5.The endosperm cytological structures of 16 Triticeae species with StH, St or H genomes were observed. The results showed that significant variations existed in the size, forms and quantity of endosperm cells in those species. The differences in genera are smaller than those in species, indicating that the characters of endosperm cells have less value in the systematic studies of those genera than in the studies of those species in Triticeae.6.To evaluate the genomic differentiation among the StH-genome species and to study the relationships between the StH-genome species and the species of the genus Pseudoroegneria and Hordeum,interspecific and intergeneric hybridizations were carried out among the 16 StH-genome species and between the StH-genome species and the diploid donor of Pseudoroegneria (Pseudoroegneria libanotica, Pse. cognata,Pse. tauri, Pse. spicata, Pse. strigosa and Pse. stipifolia) and Hordeum(Hordeum bogdanii, H. brevisubulatum, H. chilense and H. stenostachys).In the previous study, four intergeneric hybridizations of E. wawawaiensis and E. Hystrix were successfully carried out with Pseudoroegneria species in Asia. The fertility and chromosome pairing behavior in meiosis of the parents and their hybrids F1 were investigated. The results showed that:(1)a high homology existed in the St genome donored by Pseudoroegneria species from the middle East and central Asia, and a low homology existed in the St genome donored by Pseudoroegneria species from the middle East and North America, indicating the differentiation among the St genome; (2) a high homology existed between the North America Elymus hystrix and Elymus wawawaiensis, and a low homology existed between the North America Elymus hystrix and Asia Elymus sibiricus, which is indicative of the differentiation of StH-genome species distributed between North America and Asia.