Genetic Differentiation Between Quercus Mongolica And Quercus Wutaishancia

Quercus wutaishanica and Quercus mongolica are important forest and economic tree species widely distributed in northern China,and also the two most important forage tree species used for Antheraea pernyi larvae.Due to the similarity in morphology,high overlap in distribution range,and the existence of a large number of interspecific hybridization,the taxonomic relationship between Q.wutaishanica and Q.mongolica has been controversial since the establishment of Q.wutaishanica in 1912.Some scholars believed that Q.wutaishanica should be classified as a subspecies of Q.mongolica,and others maintained that Q.wutaishanica and Q.mongolica are two distinct species.In this paper,several individuals of Q.wutaishanica and Q.mongolica were selected from wide distribution range in China,and the genetic differentiation within and between species were evaluated based on the chloroplast genome and ITS sequence.The main results are as follows:1.The ITS sequences of 18 Q.wutaishanica and Q.mongolica individuals from multiple regions were obtained.These sequences were found to be highly consistent in length(392 bp or 393 bp),with 36 variation loci.In the phylogenetic tree,individuals of Q.wutaishanica and Q.mongolica did not group together according to its taxonomic species.2.The chloroplast genomes of six individuals of Q.wutaishanica and Q.mongolica were assembled and annotated,and the nucleotide polymorphisms and phylogenetic relationships of chloroplast genomes of Q.wutaishanica and Q.mongolica were analyzed in combination with the chloroplast genomes of nine individuals published by other research groups.The results showed that the chloroplast genomes of Q.wutaishanica and Q.mongolica ranged in size from 161,182-161,317 bp,and their structure and gene composition were almost identical.IR boundary changes occurred in some individuals.The chloroplast genome sequences of Q.wutaishanica and Q.mongolica were highly conserved with very low nucleotide polymorphisms(Pi =0.00051),but a hot spot of variation was identified between rbcl-acc D and acc D(Pi =0.0156).Phylogenetic analysis also showed that individuals of Q.wutaishanica and Q.mongolica did not cluster according to its taxonomic relationship.3.Our results showed that there was no significant genetic differentiation between Q.wutaishanica and Q.mongolica at the chloroplast genome and ITS sequence level,which was consistent with the previous finding for Q.variabilis,Q.acutissima and Q.chenii.These results presented in this study based on the chloroplast genome and ITS sequence and previously reported studies based on morphological characters and population genetics analyses support the view that Q.wutaishanica and Q.mongolica are two independent species,but still in the early stage of differentiation.