Complete plastid genomes of Bupleurum chinense DC. and B. boissieuanum H. Wolff, with comparative and phylogenetic analyses of medicinal Bupleurum species / 药学学报

ABSTRACT

italic>Bupleurum L. (Apiaceae) is an economically important genus, in which many species are of medicinal value. In this study, the complete plastid genomes (plastomes) of B. chinense DC. and B. boissieuanum H. Wolff were sequenced and their characteristics were investigated. Comparative and phylogenetic analyses were conducted with other published Bupleurum plastomes. The complete plastomes of B. chinense and B. boissieuanum were 155 458 and 155 800 bp in length, and both exhibited the typical quadripartite circular structure consisting of a large single copy region (LSC, 85 343 and 85 804 bp), a small single copy region (SSC, 17 495 and 17 410 bp), and a pair of inverted repeat regions (IRa/b, 26 310 and 26 293 bp), respectively. A total of 129 genes, including 84 protein-coding genes, 37 transfer RNA (tRNA) genes, and eight ribosomal RNA (rRNA) genes were identified from each of the two plastomes. Repeat sequences detected were similar in types and distribution patterns, but the numbers were slightly different. Comparative analyses revealed that the Bupleurum plastomes were highly conserved in length, structure, the guanine and cytosine (GC) content, and gene content and order, both intraspecifically and interspecifically, and no obvious expansion or contraction of the inverted repeat regions occurred. Sequence variation was lower within the same species than among different species, noncoding sequences (including intergenic regions and introns) showed a higher divergence than the protein-coding sequences, and sequences in the LSC and SSC regions were more divergent than those in the IR regions. In addition, 11 sequences with higher nucleotide diversity among species were detected in the LSC and SSC regions. All studied Bupleurum species were inferred forming a monophyletic group with a 100% bootstrap value. Bupleurum chinense and B. boissieuanum were phylogenetically closest to B. commelynoideum and B. falcatum, separately, with all three B. chinense accessions clustered into a distinct clade. These results provide genetic information for further species identification, phylogenetic resolution, and will assist in exploration and utilization of medicinal Bupleurum species.