The complete plastid genome sequence of Panax notoginseng, a famous traditional Chinese medicinal plant of the family Araliaceae

Plastid genome and composition analysis of two medical ferns: Dryopteris crassirhizoma Nakai and Osmunda japonica Thunb

Background

Dryopteris crassirhizoma Nakai and Osmunda japonica Thunb. are ferns that are popularly used for medicine, as recorded by the Chinese pharmacopoeia, and are distributed in different regions of China. However, O. japonica is not record in the Standards of Chinese Herbal Medicines in Hong Kong. Research on identification methods of D. crassirhizoma and O. japonica is necessary and the phylogenetic position of the two species should be identified. The plastid genome is structurally highly conserved, providing valuable sources of genetic markers for phylogenetic analyses and development of molecule makers for identification.

Methods

The plastid genome DNA was extracted from both fern species and then sequenced on the Illumina Hiseq 4000. Sequences were assembled into contigs by SOAPdenovo2.04, aligned to the reference genome using BLAST, and then manually corrected. Genome annotation was performed by the online DOGMA tool. General characteristics of the plastid genomes of the two species were analyzed and compared with closely related species. Additionally, phylogenetical trees were reconstructed by maximum likelihood methods. The content of dryocrassin of the two species were determined according to the Standards of Chinese Herbal Medicines in Hong Kong.

Results

The genome structures of D. crassirhizoma and O. japonica have different characteristics including the genome size, the size of each area, gene location, and types. Moreover, the (simple sequence repeats) SSRs of the plastid genomes were more similar to other species in the same genera. Compared with D. fragrans, D. crassirhizoma shows an inversion (approximately 1.6 kb), and O. japonica shows two inversions (1.9 kb and 216 bp). The nucleotide diversity (polymorphism information, Pi) analysis showed that the psbK gene and rpl14-rpl16 region have the highest Pi value in Dryopteris, and the ycf2-CDS3 and rpl14-rpl16 regions show the highest Pi vale in O. japonica. Phylogenetic analyses showed that the two species were grouped in two separate clades from each other, with both individually located with other members of their genus. The marker content of dryocrassin is not found in O. japonica.

Conclusions

The study is the first to identify plastid genome features of D. crassirhizoma and O. japonica. The results may provide a theoretical basis for the identification and the application of the two medically important fern species.

Electronic supplementary material

The online version of this article (10.1186/s13020-019-0230-4) contains supplementary material, which is available to authorized users.

The complete plastome of Panax stipuleanatus: Comparative and phylogenetic analyses of the genus Panax (Araliaceae)

Panax stipuleanatus (Araliaceae) is an endangered and medicinally important plant endemic to China. However, phylogenetic relationships within the genus Panax have remained unclear. In this study, we sequenced the complete plastome of P. stipuleanatus and included previously reported Panax plastomes to better understand the relationships between species and plastome evolution within the genus Panax. The plastome of P. stipuleanatus is 156,069 base pairs (bp) in length, consisting of a pair of inverted repeats (IRs, each 25,887 bp) that divide the plastome into a large single copy region (LSC, 86,126 bp) and a small single copy region (SSC, 8169 bp). The plastome contains 114 unigenes (80 protein-coding genes, 30 tRNA genes, and 4 rRNA genes). Comparative analyses indicated that the plastome gene content and order, as well as the expansion/contraction of the IR regions, are all highly conserved within Panax. No significant positive selection in the plastid protein-coding genes was observed across the eight Panax species, suggesting the Panax plastomes may have undergone a strong purifying selection. Our phylogenomic analyses resulted in a phylogeny with high resolution and supports for Panax. Nine protein-coding genes and 10 non-coding regions presented high sequence divergence, which could be useful for identifying different Panax species.

Positive Selection Driving Cytoplasmic Genome Evolution of the Medicinally Important Ginseng Plant Genus Panax

Panax L. (the ginseng genus) is a shade-demanding group within the family Araliaceae and all of its species are of crucial significance in traditional Chinese medicine. Phylogenetic and biogeographic analyses demonstrated that two rounds of whole genome duplications accompanying with geographic and ecological isolations promoted the diversification of Panax species. However, contributions of the cytoplasmic genomes to the adaptive evolution of Panax species remained largely uninvestigated. In this study, we sequenced the chloroplast and mitochondrial genomes of 11 accessions belonging to seven Panax species. Our results show that heterogeneity in nucleotide substitution rate is abundant in both of the two cytoplasmic genomes, with the mitochondrial genome possessing more variants at the total level but the chloroplast showing higher sequence polymorphisms at the genic regions. Genome-wide scanning of positive selection identified five and 12 genes from the chloroplast and mitochondrial genomes, respectively. Functional analyses further revealed that these selected genes play important roles in plant development, cellular metabolism and adaptation. We therefore conclude that positive selection might be one of the potential evolutionary forces that shaped nucleotide variation pattern of these Panax species. In particular, the mitochondrial genes evolved under stronger selective pressure compared to the chloroplast genes.