Molecular Phylogeny Of The Species With St Genome And Evolution Of The St Genome In Tribe Triticeae

Hybridization and polyploidization is a major mechanism in plant evolution and speciation.Polyploidization by itself has many consequences for genome evolution,particularly for gene expression and gene organization.These changes may result in full fertility and stabilization of the hybrid condition and assist in establishing the phenotype in nature,which allows polyploids to adapt to new ecological niches or to be competitively superior to the parental donor.The wheat tribe Triticeae(Poaceae)includes many different auto-and allopolyploid taxa,and has received considerable study of its systematics,genetics and speciation.One example of a polyploid complex within that tribe Triticeae is the complex with St genome.It includes the traditional species of Elymus L.,Roegneria C.Koch,Douglasdeweya C.Yen,J.L.Yang&B.R.Baum,Kengyilia C.Yen et J.L.Yang,Campeiostachys Drob.,Anthosachne Steud.,Trichopyrum(Host.)Love,and Pascopyrum A.Love.The species in above genera are allopolyploids that share a common St genome from Pseudoroegneria in different combinations with H,Y,P,Ns,and W genomes.But how the St genome evolved in those allopolyploids during the hybridization and polyploidization events remains unclear.We used chloroplast,mitochondrial and nuclear DNA-based phylogenetic analyses to shed some light on this process.In the present study,we analyzed the Pseudoroegneria species,allotetraploids with St genome and other realted diploids using internal transcribed spacer region of nuclear(nrDNA ITS)gene,chalcone synthase(CHS)gene and three chloroplast genes(rbcL,matK and the intergenic region of trnH-psbA).The objectives of this study are:1)to elucidate the phylogenetic relationships of polyploid species with St genome;2)to examine the genetic differentiation of St genome in Pseudoroegneria;3)to investigate the genetic differentiation of St genome in polyploidy relative to each other and Pseudoroegneria;4)to compare the nucleotide diversity of the St-genome sequences between Pseudoroegneria species and allotetraploids with St genome.1.Based on the the results from the chloroplast encoding rbcL,matK fragment,and non-encoding trnH-psbA sequence,molecular phylogenetic and the maternal donor of the tetraploid,hexaploid Triticeae species containing St genome were analysised,and the differentiation pattern of St genome after polyploidization was also inferred.The results showed that:1)Pseudoroegneria(St genome donor)should be the maternal donor of the tetraploid,hexaploid Triticeae species containing St genome;2)There is geographical differentiation in the genara of Pseudoroegneria.Pseudoroegneria strigosa is from Eastern Europe.Pseudoroegneria spicata is from North America.Pseudoroegneria stipifolia,Pse.libanotica and Pse.strigosa ssp.aegilopoides is from Eurasia.These Pseudoroegneria species,which has different sources,were clustered with part of the tetraploid,hexaploid Triticeae species in different evolutionary branches.This indicated that tetraploid,hexaploid Triticeae species evolved in parallel with Pseudoroegneria species.They may be originated from Eurasia,and then spread to North America after hybridization and polyploidization events;3)We infered that Pseudoroegneria containing St genome were closed to Dasypyrum containing V genome and Lophopyrum containing E genome base on the chloroplast gene sequences;4)The non-encoding cpDNA sequence(trnH-psbA)provideing more the evolution of information than encoding cpDNA sequence(rbcL and matK),can more clearly reveal the differentiation of St genome in tetraploid,hexaploid Triticeae species.2.Mitochondrial CoxⅡ gene intron sequences were used to do the molecular phylogenetic and the maternal donor analysis of of hexaploid,octoploid Triticeae species containing St genome,and the differentiation pattern of St genome after polyploidization.The results showed that:1)Pseudoroegneria containing St genome would be the maternal donor of the hexaploid Campeiostachys,Anthosachne,Trichopyrum species and octoploid Pascopyrum species we used in this study;2)In this study,Campeiostachys species mainly come from Asia.Anthosachne Steud.species come from Australia.Trichopyrum species mainly come from Eurasia and North America.Pascopyrum species mainly come from North america.Diploid Pseudoroegneria spicata(PI232131)from the North American and Pseudoroegneria strigosa(PI499493)from East Asia were clustered with hexaploid and octoploid from Eurasia and North America.This indicated that the local St genome containing diploids are involved in the process of formation of polyploid species in Eurasia and North America;3)Pseudoroegneria libanotica(PI228392)and Pseudoroegneria stipifolia(PI325181)from West Asia and Central Asia,is located at the base of the phylogenetic tree,indicating Pseudoroegneria from West Asia and Central Asia are more likely primitive than those from East Asia and North America.3.Based on molecular phylogenetic and the maternal donor analysis of nrITS sequence of tetraploid,hexaploid Triticeae species containing St genome and differentiation pattern of St genome after polyploidization,the results showed that:1)an intermediate type was isolated from the nrITS sequence,representing a mixture of the nrITS sequences of the two ancestor(St and St-Y).Pseudoroegneria derived from Central Asia may play an ancestral role in the hybridization of Roegneria(StY,Central Asia),making it possible to reconstruct the sequence.This is a typical evolutionary pattern of parental nrITS sequence recombination in polyploid;2)the polymorphism of the St genome in the tetraploid StY species is higher than that of the St genome in the hexaploid(StYW and StYH)species.That is because,the distribution of StYW and StYP species is narrower than those of StY species,and the number of StYH species is rare;(3)StY genome species might be a hybrid ancestor to form the allopolyploid containing StYH,StYP and StYW genome species.Combing with the cytogenetic evidence,a large ammount of the Roegneria species with StY genome and no diploid donor Y was found so far,StY genome species may be the immediate donor of species with StYH,StYP and StYW genome in allopolyploid formation process.These results also suggested that the multiple origins of some polyploid species arise from independent origin;(4)Elymus tangutorum and E.breviaristatus has been considered to Elymus composed of St,Y and H genome.Combing with the morphological evidence,E.tangutorum and E.breviaristatus are more similar with Campeiostachys species,they contain the same length of the palea and lemma.Although there are tiny morphological differences in these species,it is suggested that genus should be classified according to its composition and morphology at the same time.Therefore,this study supports that E.tangutorum and E.breviaristatus belong to Campeiostachys.4.Molecular phylogenetic analysis of CHS gene fragment of dioploid,tetraploid,hexaploid,octoploid Triticeae species containing St genome showed that:(1)Pseudoroegneria to participate the formation process of tetraploid Elymus species,Roegneria species,hexaploid Campeiostachys,Anthosachne,Trichopyrum species and octoploid Pascopyrum species in this study in different extent;(2)phylogenetic analysis showed close relationship among Dewey species and Kengyilia species.Because of Dewey,containing StP genome,formed from Pseudoroegneria and Agropyron by natural hybridization,and Kengyilia,containing StYP genome,formed from Roegneria tetraploid and Agropyron diploid by natural hybridization;(3)St genome is close to V,W,Q genome because of the participation of the E genome in polyploidization and the process of differentiation of St genome.It can be concluded that the St genome is gradually differentiated in the process of polyploidization,and is affected by the obvious network evolution and gene introgression.(4)Y genome has a close relationship with St,W and Q genome.