A Phylogenetic Study Of Ulmaceae Based On Chloroplast Genomes

Ulmaceae is a well defined family of Urticales,including 15 genera and more than220 species.In China,Ulmaceae contains 8 genera,46 species and 10 varietas.Species of Ulmaceae in China are all woody plants.Ulmaceae in China shows strong ecological adaptability,giving it great ecological and economic value.We sequenced,accembled and annotated chloroplast genomes in 16 species of Ulmaceae by Illumina Hi Seq2500,including 6 species of Ulmus,6 species in Celtis and4 species of Trema.Two samples from different location were sequenced both in T.cannabia and T.tomentosa.Eventually,we got 18 complete chloroplast genomes of Ulmaceae.The length of these genomes is from 157 kb to 160 kb,GC content is from35.5% to 36.4%.Each genome possessed the typical angiosperm quadripartite structure(Large Single-Copy region,LSC;Small Single-Copy region,SSC;Inverted-Repeat regions,IR)and contained a total of 114 or 115 genes in the same order.The structure of these genomes contains difference,such as the expansion and contraction of IR in Pteroceltis and Gironniera.Pseudogenization and gene loss is found in some species,inf A in Aphananthe,Gironniera and Hemiptelea,and ycf15 in some species of Celtis.There are long-standing controversies over the circumscription and phylogenetic position of Ulmaceae.Such as the monophyly of Ulmaceae,the phylogeny among the genera of Ulmaceae,and the Phylogeny among Ulmaceae,Moraceae,Urticaceae and Cannabaceae.In this research,we reconstructed the phylogenetic tree of Ulmaceae based on chloroplast genome and the CDS sequences respectively.The phylogenetic tree shows that:(1)Each genus in this research is monophyletic.(2)There are two clade in Ulmaceae.One is known as Ulmoideae,including Ulmus,Zelkova and Hemiptelea,the other is known as Celtidoideae,including Aphananthe,Gironniera,Celtis,Chaetachme,Pteroceltis and Trema.(3)Zelkova is belong to Ulmoideae.Hemiptelea is the basal taxon of Ulmoideae. Gironniera and Aphananthe are basal taxa of Celtidoideae.(4)Celtidoideae is more related to Moraceae and Urticaceae than Ulmoideae.(5)Based on chloroplast genome,the phylogeny in genus can be well supported,while it shows difficult using CDS sequences.The availability of these chloroplast genomes provides valuable genetic information for accurately identifying species,clarifying taxonomy and reconstructing the intergeneric phylogeny of Ulmaceae.