Comparative and phylogenetic analyses of the chloroplast genomes of species of Paeoniaceae

Plants belonging to family Paeoniaceae are not only economically important ornamental plants but also medicinal plants used as an important source of traditional Chinese medicine. Owing to the complex network evolution and polyploidy evolution of this family, its systematics and taxonomy are controversial and require a detailed investigation. In this study, three complete chloroplast genomes of sect. Paeonia, one of the sections of Paeonia, were sequenced and then analysed together with 16 other published chloroplast genomes of Paeoniaceae species. The total lengths of the chloroplast genomes of these species were 152,153-154,405 bp. A total of 82-87 protein-coding genes, 31-40 tRNA genes and 8 rRNA genes were annotated. Bioinformatics analysis revealed 61-74 simple sequence repeats (SSRs) in the chloroplast genomes, most of which have A/T base preference. Codon usage analysis showed that A/U-ending codons were more positive than C/G-ending codons, and a slight bias in codon usage was observed in these species. A comparative analysis of these 19 species of Paeoniaceae was then conducted. Fourteen highly variable regions were selected for species relationship study. Phylogenetic analysis revealed that the species of sect. Paeonia gathered in one branch and then divided into different small branches. P. lactiflora, P. anomala, P. anomala subsp. veitchii and P. mairei clustered together. P. intermedia was related to P. obovata and P. obovata subsp. willmottiae. P. emodi was the sister to all other species in the sect. Paeonia.