Studies On Morphology, Cytology And Molecular Phylogenetics In The Genus Of Leymus

Leymus Hochst.is a genus of perennial grass in the tribe Triticeae(Poaceae). Hochstetter(1848)separated it from traditional Elymus L.,with Leymus arenarius(L.) Hochst.as the type species.There are about 34 species and 19 subspecies in Leymus,and all the species are polyploids with the chromosome numbers ranging from 2n=4x=28 to 2n=12x=84(L(?)ve,1984).Phytogeographically,they are distributed in the temperate regions of Eurasia,North and South America,extending to the subtropic and the tropic alpine regions.The large numbers of them are found mainly on the mountains of central Asia and North America(Tzvelev,1976;Dewey,1984).Despite decades of intensive efforts,there are still many unsolved questions to be answered,such as the definition, origin,geographical differentiation,migration,precise taxonomic ranks and the origin of Xm genome of Leymus species.In this study,we systematically evaluated the phylogeny and geographical differentiation of Leymus on morphology,cytology,and molecular phylogenetic reconstruction and network analysis.The phylogeny and network analysis of Leymus were explored using the sequences of three DNA fragments including nrDNA ITS, one single-copy nuclear gene DMC1(disrupted meiotic cDNA),and one chloroplast trnL-F.The main results showed as follows:1.A cladistic analysis based on morphology is presented from 34 Leymus species.The results indicate that:(1)L.arenarius is closely related to L.racemosus;(2)there are several morphological homologies between the Leymus species distributed in Qinghai-Tibetan Plateau and other Eurasian Leymus species;(3)the North America Leymus species differed morphologically from the Eurasian Leymus species;(4)there is a closely relationship among L.duthiei,L.duthiei ssp.longearistatus,and L.coreanus.2.The karyotypes of 7 Leymus species were reported.The karyotype formulate were as follows:L.alaicus 2n=4x=28=20m+8sm;L.cinereus 2n=8x=56=42m(2SAT)+14sm;L. shanxiensis 2n=4x=28=22m+6sm;L.racemosus 2n=4x=28 =22m+6sm;L.ovatus 2n=4x=28 =24m+4sm(2SAT);L.yiwuensis 2n=4x=28=22m +6sm(2SAT);L.crassiusculus 2n=4x=28=24m +4sm.3.The sequences of the nuclear rDNA internal transcribed spacer region(ITS)were analyzed for 34 Leymus accessions representing 25 species,together with three Pasthyrostachys species,two Pseudoroegneria(St genome)species,Lophopyrum elongatum(E~e genome),and Thinopyrum bessarabicum(E~b genome).The ITS RNA secondary structure of Leymus species were compared with that of their putative diploid donor.It is suggested that:(1)Leymus distributed in North and Eurasian is heterogeneous geographically;(2)L.coreanus,L.duthiei,L.duthiei var.longearistatus and L.komarovii are closely related to other Leymus species,and it is reasonable to transfer these species from the genus Hystrix to Leymus;(3)the different Leymus species and different distribution of a species derived their Ns genome from different Psathyrostachys species; (4)the ITS sequences of Leymus are evolutionarily distinct;(5)there is a close relationship among Leymus,Pseudoroegneria,Lophopyrum,and Thinopyrum.4.The DMC1 gene separated 18 Leymus species distributed in China into two clades, one of which include those from Qinghai-Tibetan Plateau(Qinghai-Tibetan Plateau cluster), the other clade contain those from Xinjiang,Neimenggu,and Heilongjiang(Xin-Nei-Hei cluster).Therefore,the DMC1 data revealed the geographical pattern of Leymus distributed in China.5.The sequences of the DMC1 gene were analyzed for 32 Leymus accessions,together with samples representing 17 diploid genera in the tribe Triticeae.It is suggested that:(1) some Leymus species showed multiple origin and experienced recurrent hybridization,and the different Leymus species and different distribution of a species derived their Ns genome from different Psathyrostachys species;(2)L.arenarius has the same origin as L. racemosus,and tetraploid L.arenarius and L.racemosus might be related to the speciation of octoploid L.racemosus;(3)the involvement of Pseudoroegneria into L.alaicus,L. alaicus ssp.karataviensis,L.condensatus,L.leptostachys,and L.secalinus(Y040)is a result of introgression;(4)the Xm genome differed obviously from the Ns genome, indicating that Leymus species have its allopolyploidy origin;(5)the Leymus species distributed in America originated from the ancestral taxa of central Asia.6.The trnL-F sequences were analyzed for 31 Leymus accessions,together with samples representing 16 diploid genera in the tribe Triticeae.It is suggested that:(1)the maternal donor of most Leymus species from Eurasia is Psathyrostachys,while the unknown genome Xm served as the maternal donor of L.coreanus,L.komarovii(East Asia),L.condensatus,L.erianthus,L.cinereus,L.triticoides,L.salinus,L.innovatus (North America);(2)the Leymus species with distinct morphological characteristic have a common maternal origin,while those with overall morphological similarity have different maternal origin;(3)the Leymus distributed in North America species are far from the Eurasian Leymus species;(4)the involvement of Pseudoroegneria into L.alaicus,L. alaicus ssp.karataviensis,L.condensatus is a result of introgression;(5)the Xm genome is closely related to the P genome of Agropyron and the F genome of Eremopyrum.7.Morphological characteristic and the sequence(ITS,DMC1,and trnL-F)data allowed the reconstruction of intrageneric migration routes of Leymus species distributed in America.Leymus evolved in central Asia and spread into northeast Asia and Qinghai-Tibetan Plateau.It also spread into northeast Asia from Qinghai-Tibetan Plateau. After northeast Asia was reached,it further migrates by two routes.One spread into Japan, while the other spread into North America and South America via Bering Strait.