The Research On The Speciation Of The Akebia Longeracemosa By Using Transcriptome Data

Akebia Decne is a genus of Lardizabalaceae(Ranales),with high value of medicinal,nutritional and ornamental.However,the interspecific relationship within the genus is not clear.And A.longeracemosa is found to be consistent with the A.trifoliata in its leaf shape,while the long-inflorescence of A.longeracemosa equivalent to that of A.quinata.So,we propose the scientific hypothesis that the origin of the A.longeracemosa may be the hybrid of A.trifoliata and A.quinata,and after a long period of evolution,it has evolved into an independent species.With the development of sequencing technology,transcriptomes are increasingly used in phylogeny and hybrid speciation studies.In this dissertation,transcriptome sequencing was performed on the four species of A.trifoliata subsp.australis,A.longeracemosa,A.quinata and Archakebia apetala.A series of analyses based on the measured transcriptome data,such as orthologous inference,construction of species tree,testing of gene flow,and calculating of Ka/Ks for screeeing positive selection genes were performed to study the speciation of the A.longeracemosa.The major results were summarized as follows.1.After assembling of the transcriptomes of the four species,more than 50,000 Unigenes were obtained,and the number of CDSs per species was more than 48,000.After the gene annotation,we found A.trifoliata transcriptomes are most similar with Nelumbo nucifera genome,followed by the Vitis vinitera.2.In this study,4161 common core-orthologous genes were inferred from four taxa.A phylogenetic tree was constructed by the above core-orthologous genes.The results shows that the genetic relationship is most closely between A.longeracemosa and A.quinata,the second is A.trifoliata subsp.australis,the last is Archakebia apetala.3.In order to detect positive selection genes between different taxa,Ka/Ks ratio of each ortholog was calculated,and a total of 175 positive selection genes were screened.Then positive selection genes were annotated by software Blast2 go,and there are 145 genes were successfully annotated.4.For testing whether or not the introgression between species,this research used the Archakebia apetala as an outgroup to calculate the Patterson's D-statistic values between A.trifoliata subsp.australis,A.longeracemosa and A.quinata.And the results further proved that there is a remarkable introgression between them.According to the constructed species tree,the genetic relationship between A.longeracemosa and A.quinata is closer,while it is relatively far from the A.trifoliata subsp.australis.Patterson's D-statistic values are calculated to show that there is relatively little genetic exchange between A.longeracemosa and A.quinata.Combined with their geographic distribution,the A.longeracemosa is relatively far from A.quinata,there is geographical isolation between them.We speculated that theA.longeracemosa might be the hybrid between A.trifoliata and A.quinata,and formed an independent species.The results showed that the functional enrichment of positive selection genes yielded is mainly related to catalytic activity and banding,and enrichment of biological process yielded is mainly related to metabolism and cell metabolism.Further analysis revealed that some of positive selection genes play an important role in the length of the inflorescence,and some are related to the normal growth and development of plants,the repair of biofilms,and the response to stress.Therefore,these genes may be related to adaptive evolution.