Evolutionary Dynamics Of The Triticeae(poaceae)based On Single-copy Nuclear Acc1 And GBSSI Gene Data

The tribe Triticeae,distributed all over the world,is of enormous important group in Poaceae.Triticeae includes some of the world's most important cereal wheat and a significant number of important forage grasses.A clear picture of phylogenetic relationships would pointto wild taxa that may serve as sources of novel gene pool,focus efforts at conservation of germplasm,and help set priorities for preservation of grassland habitats.Gene duplication plays an important role in the process of biological evolution,besides it is an important driving force for the differentiation of genome and genetic system.Polyploidy(or whole genome duplication)has always been considered as a major contributor to species formation and genome evolution.Molecular phylogenetic analysis is a widely used method to study the evolution of biological origin,various of DNA sequences have been used nowadays.But many factors such as hybridization,introgression,pedigree separation,horizontal transfer,recombination,gene duplication,sites interaction and coevolution,the evolution of single genetic locus has its special evolutionary course.Therefore,the construction of gene tree based on single genetic site DNA fragment is not necessarily true.The combination of different genes for phylogenetic reconstruction was widly used to phylogenetic research,which made the results of molecular phylogenetic more reliable.In this study,we selected 364 Acc1 and 242 GBSSI 135 of Triticeae species to analysis phylogenetic reconstructions,speciation and evolutionary dynamics.The following results are obtained:1.Based on Acc1 sequences of 135 species and GBSSI sequences of 104 species,the phylogenetic reconstructions of 25 genomes represented by Triticeae were built,and the result suggested that:(1)Pseudoroegneria,Psathyrostachys,Thinopyrum,Lophopyrum,Hordeum,Australopyrum and Agropyron were the donor of St,Ns,E~b,W and P genomes,respectively;(2)Triticum,Aegilops,Taeniatherum(Ta)and Thinopyrum(E~b)have a close relationship;(3)Y genome may have close relationship with St and V;(4)The genome of Xm may have common origin with Eremopyrum(F),Agropyron(P)and Psathyrostachys(Ns);2.According to the phylogenetic reconstructions Acc1 sequences and GBSSI sequences,Roegneria(StY)may be the donor of hexaploid includes StYH,StYW,StYP;Polyploid species of Elymus,Leymus,Anthosachne and Kengyilia have multiple origins.3.Based on nucleotide polymorphism analysis and selective pressure analysis of Acc1sequences,nucleotide polymorphism of A?H?P?Ns and St genomes increased with polyploidy,but that of Xm and D genomes were reverse,which may enhance the environmental adaptability.Selective pressure of Ns and Xm genomes decreased with polyploidy,which may improve implementation of gene expression enhancements.The decrease of nucleotide polymorphisms between hexaploid Triticum(ABD),Anthosachne(StYW)and their tetraploid donor species may be caused by artificial domestication and geographical isolation.4.Based on nucleotide polymorphism analysis and selective pressure analysis of GBSSI sequences,nucleotide polymorphism of A?Ns and St genomes increased with polyploidy,but that of Xm and D genomes were reverse.Selective pressure of H and Ns genomes decreased with polyploidy,which may improve implementation of gene expression enhancements.Selective pressure of Xm and St genomes increased with polyploidy,which may enhance the adaptability to environment.5.According to the analysis of phylogenetic reconstructions and volutionary dynamics with Acc1 sequences and GBSSI sequences,two gene trees have some conflict on clades.The reason for the conflict may be the genetic communication between the wheat species,which leads to complexity of its evolutionary history.The evolutionary dynamics of Ns,Xm,H and St genomes on Acc1 and GBSSI genes are different,which may caused by the different gene functions.