Studies On Whole Genome Duplication And Species Differentiation In Rehmannia

Genome sequencing has demonstrated that besides frequent small-scale duplications,large-scale duplication events such as whole genome duplication(WGD)are found on many branches of the evolutionary tree of life.Most flowering plants have been shown to be ancient polyploidy that have undergone one or more whole genome duplications early in their evolution.Genome duplication has been proposed as an accelerator for evolution.Recent studies suggest that polyploidy species have a higher adaptability and increased tolerance to different environmental conditions.It is still not clear whether the Rehmannia has occurred WGD in evolutionary history.In this research work,the phylogenetic relationships and divergence times of 14 angiosperms were estimated.The Ks values were used to analyze the existence of WGD events in 5 species of Rehmannia.In present studies our results show that the genus has experienced two WGD events in the evolutionary history.These ages of two WGD events correspond to the ? hexaploidization shared by all core eudicots(about 116.07?128.28 mya)and the key period of global transition from greenhouse to the modern icehouse conditions at Middle-Late Eocene(about 42.76?48.87 mya),respectively.The duplication genes produced by multiple paleopolyploidization events have an important influence on the functional evolution of the Rehmannia.Increase and decrease of gene families after duplication may accelerated the differentiation of species.Therefore,we want to explore the level of genetic diversity of the positively selected genes undergoing polyploidization in the evolution of species and wonder whether these genes promote the differentiation and adaptation of Rehmannia.The five Rehmannia species have different geographical distributions and ecological environments.The differences in geographic habitats often lead to differences in the intensity of natural selection at intra-specific and inter-specific levels.With the reduction of sequencing costs and the development of bioinformatics technology,evolutionary history and environmental adaption would be identified through high-throughput transcriptome sequencing.In order to explore the ecological adaptability of the Rehmannia,we screened out the single-copy positively selected genes shared by five species used the transcriptome data of the Rehmannia,and performed the GO and KEGG annotations to find out the functions and metabolic pathways.Our results can imply for the development the regulation of metabolic pathways and the adaptive evolution of the Rehmannia.On this basis,Reduced-Representation Sequencing on 32 individuals were collected from the natural geographical distribution area of the Rehmannia.The shared positively selected single copy genes were assembled and annotated.Then these nuclear gene fragments were used for nucleotide diversity,neutrality assay and haplotype pedigree analysis to explain the interspecies relationships.The results showed that 10 ? 29 haplotypes were obtained from nine nuclear gene fragments in genus of Rehmannia.The average haplotype diversity was 0.879,and the average nucleotide diversity was 0.03366.It showed that the Rehmannia has higher levels of genetic diversity and greater adaptability to the environment,which were consistent with our findings on the metabolic pathways and gene function annotations.The positive selected nuclear genes have propelled the process of adaptive evolution of the Rehmannia.Neutrality analysis found that most of the data were indistinctive negative values.Finally,phylogenetic analysis with haplotype network map and the ML(maximum likelihood)tree were discussed to explore the evolutionary history and the origin of the Rehmannia.