Phylogenetic Analysis Of Betulaceae Plastomes

Betulaceae is a well-defined family of Fagales,including six living genera and more than 160 modern species.In this study,we analyzed the chloroplast genomes(plastomes)of 24 Betulaceae species from the six genera by comparative genomics.Then,the phylogenetic analysis was carried out using the plastomes and ITS sequences respectively.It would improve our understanding of the evolutionary history,as well as the development and utilization of Betulaceae.All of 24 plastomes were relatively conservative,with ~158-161 kb in length and 111 genes in the same order,and consisting of a large single-copy region(LSC),a small single-copy region(SSC)and a pair of inverted repeat regions(IRs)A and B.However,there are also some variations,including the extension of inverted repeat regions in the species of Corylus,the different location of boundaries of the four regions,the degree of variation in sequences and protein coding regions.Phylogenetic analysis of all available plastomes showed that each of the six genera of Betulaceae is monophyletic regarding the sampled species.However,Ostrya was nested in Carpinus,forming a complexed cluster in the ITS tree.Further incongruence was also detected within some genera between species,which indicated that incomplete lineage sorting(ILS)and/or hybridization,introgression may be widespread during the evolutionary history of the family.Our data analyses based on protein coding sequences of plastomes and four fossils calibration confirmed that Betulaceae started to diversify in the upper Cretaceous-early Palaeocene(63.7-74.9 Mya),and sampled species of the each genus in this study began to differentiate one another from mid-to late-Miocence(6.4-17.3 Mya).