Abstract:

Objective: China's wild peony has been regarded as precious germplasm resources at home and abroad. Wild Paeonia jishanensis is considered as one of the most important ancestral species of cultivated tree peonies. The analysis of chloroplast genome (cp DNA) characteristics of Paeonia, including P. jishanensis, has important theoretical and practical values for elucidating the phylogeny of Paeonia and developing improved varieties. Method: Chloroplast data of P. jishanensis were obtained by high-throughput sequencing. The cp DNA data of P. ostii, P. ludlowii, P. delavayi, P. veitchii and P. obovata were downloaded from NCBI database. Comparative analysis of the six peony cp DNA was performed using Geneious 8.0 and EMBOSS 6.4.0. Result: The cp DNA sequence of P. jishanensis was 152 628 bp with 112 genes, 25 988 codons encoding 78 proteins. There are 19 genes (including 4 rRNA, 7 tRNA, 8 protein coding genes) repeat in the IR (Inverse Repeat) region. A total of 143 SSR loci were searched, the mononucleotide repeat are the most common (116, accounting for 81.12%), and there was no hexanucleotide repeat motif. Although the chloroplast genome of Paeonia is conservative, there are still some changes in the boundary of IR and LSC(large single-copy) between different species. The rpl2 gene of P. ostii extends 718 bp to the LSC region, while that of other species are completely located in the IR region. Conclusion: Paeonia cp DNA genome size and gene content are highly conserved. The cp DNA of P. obovata and P. delavayi was the largest (152 698 bp), and that of P. ostii was the smallest (152 153 bp). The codons of cp DNA protein coding genes and the base composition of SSR loci in P. jishanensis prefer to use A/T. Among 143 SSR loci, 134 loci were A/T loci. The distribution of cp DNA SSRs in P. jishanensis has heterogeneity, 14 SSR loci were located in IR region, 103 in LSC region and 26 in SSC region. Analysis showed that boundary change of LSC/IRb was the main reason for the expansion or contraction of IR region in Paeonia. The results provide a basis for the studies of phylogeny and origin of cultivation, and for the development of molecular markers and the breeding of elite cultivars of Paeonia plants.

Key words: Paeonia, Paeonia jishanensis, high-throughput sequencing, chloroplast genome, SSR loci, IR boundary analysis