Evolutionary Pattern Of Single Copy Nuclear Gene DMC1 In Triticeae (Poaceae)

Gene duplication is an important feature of genome structure in polyploid plants.Whole-genome duplication,i.e.polyploidization,is a significant driving force for the evolution of organisms and the main way for plants to adapt to the natural environment.A large number of duplicate genes have been determined during the process of plant polyploidization,which provide a potential resource pool for plant evolution based on duplicate genes.Duplicate genes may disappear or be retained and spread in the population with the process of plant polyploidization.The different evolutionary directions of the duplicate genes may produce more abundant genetic diversity and greater survival competitiveness for polyploid plants.The recombinant meiotic protein encoded by DMC1 gene,found in eukaryotic organisms,is a homologous protein of RecA protein of E.coli.It plays an important role in homology search and DNA chains exchange during meiotic homology recombination.Analyses of genetic variation patterns of DMC1 gene help to understand the molecular evolutionary dynamics and causes in plant speciation and divergence.The tribe Triticeae,including about 30 genera and 465 species distributed in the temperate regions,is of enormous important group in Poaceae.Species of Triticeae can grow in the environment of hillsides,marshes and deserts s,and have complex origins.Because of the great variation in biological mechanism and genetic system and the clear source of genomic donors,Triticeae is ideal taxa in the study of speciation,taxonomy,phylogeny,molecular evolution and genetic diversity.A total of 382 single copy nuclear gene DMC1 sequences of 159 species,4 varieties and 26 subspecies in 25 genera in Triticeae were used to analyze the polymorphism of homologous loci,selection pressure and gene expression between polyploids and diploids,and to explore the evolutionary dynamics of DMC1 gene in Triticeae in this study.The main conclusions were as follows:1.There are significant differences in nucleotide polymorphisms of DMC1 gene between genus and species of direct origin in Triticeae.Natural hybridization leads to the loci polymorphisms in polyploids usually higher than their diploid donors,which indicates that DMC1 gene evolves faster in polyploids.2.Nucleotide polymorphisms in B genome of Triticum decreased afterpolyploidization.The evolutionary rate slowed down and genetic basis narrowed may result from the genetic bottlenecks that caused by long-term domestication of human beings.The decrease of nucleotide polymorphisms in the process of speciation in tetraploid species containing StSt genomes may be the result of population historical expansion.3.Analysis of selective pressure of the A,B,Ns,Xm,St,H and P genomes in Triticeae showed that dN/dS was less than 1,indicating that DMC1 gene had undergone purifying selection in the evolution process,and the selection pressure of these genomes was significantly different.The evolution of DMC1 gene was driven by the change of polyploidization.4.Branch-Site REL analysis showed that there were a few high proportions of neutral and positive selection loci of the genomes in Triticeae,suggesting that there may be potential pseudogenes or adaptive evolutionary characteristics of DMC1 gene in Triticeae.5.Real-time fluorescence quantitative experiment showed that the selective pressure dN/dS of DMC1 gene was negatively correlated with the gene expression level.When the selective pressure of DMC1 gene increased,the expression of DMC1 gene is restricted by more restricted function,whereas when the selection pressure decreases,the expression of DMC1 gene is reduced by more relaxed functional restriction.