[Application of ITS2 secondary structure phylogenetic information in DNA barcode identification of Chrysanthemum indicum and its related plants].

By exploring additional phylogenetic information hidden in ITS2 secondary structure,the possibility of identifying Chrysanthemum indicum and its related species with DNA barcode of ITS2 nucleic acid sequence and its structure information were discussed.The genomic DNA was extracted from 12 samples. The ITS2 fragments were amplified by PCR and sequenced bidirectionally to obtain ITS2 sequence information. 28 sequences of related species for Ch. indicum were downloaded from Gen Bank. Until all 40 ITS2 sequences were aligned,ITS2 secondary structure prediction and structure comparison were finished. Then ITS2 secondary structure information was coded. After comparing ITS2 structure information and nucleic acid information,MP phylogenetic trees were built. The results showed that the secondary structures of ITS2 shared the same structure model--a four-fingered hand. They not only have the common characteristics of ITS2 secondary structures in plants,but also have many other conservative sequences,and their overall conservativeness is high. Among all species used in this study,their ITS2 secondary structures had obvious difference. In addition,the number of mutation sites in the joint matrix compared with the nucleic acid sequences increased by nearly 90%,which greatly enriched the number of mutation sites. This method of information analysis distinguished Ch. indicum from its related species. At the same time,the support rate of the branches of evolutionary trees and the identification rate of species were significantly improved. Although there was no distinction between Ch. zawadskii and Ch. morifolium,it effectively distinguished the three species,namely,Ch. hypargyrum,Ch.oreastrum,and Ch. dichrum. Therefore,the authors suggest that the ITS2 sequence combined with its structural data information should be applied to the identification of Ch. indicum and its related species,and be widely applied to DNA barcode research.