Study On Molecular Phylogeny And Chromosome Differentiation In Wheatgrass Genus Thinopyrum

Thinopyrum is a perennial genus of the Triticeae family of Poaceae,of which there are about 50 species in the world,mainly in frigid and temperate zones in Asia and Europe.There are about 6 species in China.The Thinopyrum genus is one of the wild relatives of Triticum.Among them,many species have excellent traits such as lush growth,disease resistance,cold resistance,drought resistance and salt tolerance.It is a foreign gene donor with important value in wheat genetic improvement.As an important third-level gene source for the current and future wheat genetic improvement,the research of genus Thinopyrumum has great potential value for wheat development and great significance to improve the genetic variation basis in wheat.However,there is still a great deal of controversy about the origin,interspecific relationship,system status and species boundaries in genus Thinopyrum.In this study,we used a variety of Thinopyrum grasses from different regions collected by American National Germplasm Resources to do research about the characteristics of genome and chromosome differentiation for polyploidy of Thinopyrum by cytology,fluorescence in situ hybridization(FISH)and molecular phylogenetics.The genomic structure and the genome origin of polyploidy,the molecular phylogeny of the genus Thinopyrum,and the chromosome karyotype of the genus Thinopyrum were studied in detail.The main results are as follows:1.On the 184 accessions of Thinopyrum,The chromosome number in root tip cell was analyzed to distinguish the different ploidy of the material,which provided the basis for the selection of the next experimental material.The results showed that Th.bessarabicum had diploid and decaploid.No report for decaploid in Th.Bessarabicum was found so far in our Baidu search.Th.caespitosum had tetraploid and hexploid.Th.elongatum had the kind of diploid,tetraploid,hexaploid,octoploid,decaploid in accessions.In addition,the materials whose chromosome number was not a multiple of 7 were found in Th.elongatum.2.Based on the fragment sequences of the single copy nuclear gene Pgk1 and PepC encoding phosphoglycerate kinase as well as phosphoenolpyruvate carboxylase,the different diploid wild species of wheat and 14 materials of three species(Th.bessarbicum,Th.caespitosum,Th.elongatum)were studied for phylogenetic relationship and chromosome constitution.The results showed that:(1)There are Ee,Eb,St and unknown genome in genus Thinopyrum.The unknown genome could be formed by infiltrating E group from the other genomic groups(such as M,Am,Ta,etc.)(2)Eb genome of Th.bessarabicum and Ee genome of Th.elongatum have evolved significantly in chromosome differentiation during the evolution.(3)The genus Thinopyrum has a close genetic relationship with Pseudoroegneria,and the St genome in genus Thinopyrum is derived from the genus Pseudoroegneria.(4)According to the phylogenetic tree,it was suggested that St,Ee and Eb genome were contained in the decaploidy Th.bessarabicum and Th.elongatum.The results shown that St genome exist in tetraploid,hexaploiu of Th.caespitosum,Ee,Eb genome exist in the tetraploidy Th.elongatum.The hexaploidy Th.Elongatum had St,Ee,Eb genome and the octoploid of Th.elongatum had St,Ee genome.3.The five kinds of ploidy of Thinopyrum genus and different diploid accession in Th.elongatum and Th.bessarabicum were used to do no-denaturing FISH by the oligonucleotide sequence and 45s rDNA probes.The results showed that:(1)The number of 45S rDNA loci did not necessarily increase with the ploidy of Thinopyrum genus during the evolution,and the main location of 45S rDNA was moved to terminal of chromosome short arm from the middle or proximal terminal of chromosome short arm along with the increasement of ploidy.(2)The FISH karyotypes of different diploid accession in Th elongatum are almost same with each other.However,there are some small differences in the FISH karyotype for different diploid accession.The reasons are relative with the different geographical location leading to chromosome differentiation.The FISH karyotypes of diploid Th elongatum are different with diploid Th.bessarabicum.