Characterization of the complete chloroplast genome of Polygonatum franchetii Hua, a Chinese endemic medicinal species, and phylogenetic relationships of Polygonatum / 药学学报

ABSTRACT

italic>Polygonatum franchetii Hua is a medicinal plant endemic to China from Polygonatum Mill. The chloroplast genomes of two P. franchetii individuals sampled from two different habitats were sequenced by using the DNBSEQ-T7 high-throughput sequencing platform. After assembly and annotation, the two complete chloroplast genomes were characterized, and then comparative and phylogenetic analyses were performed with other published chloroplast genome sequences from Polygonatum. The whole chloroplast genomes of the two P. franchetii individuals were 155 942 and 155 962 bp in length, with a large single copy region (LSC, 84 670 and 84 722 bp), a small single copy region (SSC, 18 564 and 18 566 bp) and a pair of reverse repeats (IRa/IRb, 26 354 and 26 337 bp), respectively. Both of them contained 113 genes, including 79 protein-coding genes (PCGs), 30 transfer RNA (tRNA) genes, and 4 ribosomal RNA (rRNA) genes. Comparative analyses showed that the genome length, the guanine and cytosine (GC) content, genes content and order were highly conserved between the two P. franchetii individuals and among different Polygonatum species. The detected repeat sequences, including dispersed repeats, tandem repeats and simple sequence repeats (SSRs), were also relatively similar in types and positions, though showing a slightly difference in number. No significant expansion or contraction of the inverted repeat regions was found. Sequences variation between the two P. franchetii individuals was lower than that among different Polygonatum species. Besides, coding sequences (CDS) showed less divergence than noncoding sequences, and sequence divergence of IRs regions was lower than that of the LSC and SSC regions, both intraspecifically and interspecifically. Eight sequences with high nucleotide diversity among different species were screened, all of which were found located in the LSC and SSC regions. Phylogenetic inference showed that all Polygonatum species clustered into a monophyletic clade with a 100% bootstrap value, within which, species in section Verticillata formed a distinct group, section Sibirica and section Polygonatum were sister groups. The two P. franchetii individuals grouped together and showed the closest phylogenetic affinity to P. stenophyllum Maxim., belonging to the section Verticillata. The chloroplast genome of P. franchetii and its phylogenetic position in Polygonatum were comprehensively investigated and clearly elucidated in this study, the results may lay a foundation for the resource development and utilization of P. franchetii, as well as further molecular identification and phylogenetic studies of medicinal Polygonatum species.