Plastid phylogenomics contributes to the taxonomic revision of taxa within the genus Sanicula L. and acceptance of two new members of the genus

Introduction

The genus Sanicula L. is a taxonomically complicated taxa within Apiaceae, as its high variability in morphology. Although taxonomists have performed several taxonomic revisions for this genus, the interspecific relationships and species boundaries have not been satisfactorily resolved, especially for those endemic to China. This study mainly focused on S. giraldii var. ovicalycina, S. tienmuensis var. pauciflora, and S. orthacantha var. stolonifera and also described two new members of the genus.

Methods

We newly sequenced sixteen plastomes from nine Sanicula species. Combined with eleven plastomes previously reported by us and one plastome downloaded, we performed a comprehensively plastid phylogenomics analysis of 21 Sanicula taxa.

Results and Discussion

The comparative results showed that 21 Sanicula plastomes in their structure and features were highly conserved and further justified that two new species were indeed members of Sanicula. Nevertheless, eleven mutation hotspot regions were still identified. Phylogenetic analyses based on plastome data and the ITS sequences strongly supported that these three varieties were clearly distant from three type varieties. The results implied that these three varieties should be considered as three independent species, which were further justified by their multiple morphological characters. Therefore, revising these three varieties into three independent species was reasonable and convincing. Moreover, we also identified and described two new Sanicula species (S. hanyuanensis and S. langaoensis) from Sichuan and Shanxi, China, respectively. Based on their distinct morphological characteristics and molecular phylogenetic analysis, two new species were included in Sanicula. In summary, our study impelled the revisions of Sanicula members and improved the taxonomic system of the genus.

Phylogeny and diversification of genus Sanicula L. (Apiaceae): novel insights from plastid phylogenomic analyses

BACKGROUND

The genus Sanicula L. is a unique perennial herb that holds important medicinal values. Although the previous studies on Sanicula provided us with a good research basis, its taxonomic system and interspecific relationships have not been satisfactorily resolved, especially for those endemic to China. Moreover, the evolutionary history of this genus also remains inadequately understood. The plastid genomes possessing highly conserved structure and limited evolutionary rate have proved to be an effective tool for studying plant phylogeny and evolution.

RESULTS

In the current study, we newly sequenced and assembled fifteen Sanicula complete plastomes. Combined with two previously reported plastomes, we performed comprehensively plastid phylogenomics analyses to gain novel insights into the evolutionary history of this genus. The comparative results indicated that the seventeen plastomes exhibited a high degree of conservation and similarity in terms of their structure, size, GC content, gene order, IR borders, codon bias patterns and SSRs profiles. Such as all of them displayed a typical quadripartite structure, including a large single copy region (LSC: 85,074-86,197 bp), a small single copy region (SSC: 17,047-17,132 bp) separated by a pair of inverted repeat regions (IRs: 26,176-26,334 bp). And the seventeen plastomes had similar IR boundaries and the adjacent genes were identical. The rps19 gene was located at the junction of the LSC/IRa, the IRa/SSC junction region was located between the trnN gene and ndhF gene, the ycf1 gene appeared in the SSC/IRb junction and the IRb/LSC boundary was located between rpl12 gene and trnH gene. Twelve specific mutation hotspots (atpF, cemA, accD, rpl22, rbcL, matK, ycf1, trnH-psbA, ycf4-cemA, rbcL-accD, trnE-trnT and trnG-trnR) were identified that can serve as potential DNA barcodes for species identification within the genus Sanicula. Furthermore, the plastomes data and Internal Transcribed Spacer (ITS) sequences were performed to reconstruct the phylogeny of Sanicula. Although the tree topologies of them were incongruent, both provided strong evidence supporting the monophyly of Saniculoideae and Apioideae. In addition, the sister groups between Saniculoideae and Apioideae were strongly suggested. The Sanicula species involved in this study were clustered into a clade, and the Eryngium species were also clustered together. However, it was clearly observed that the sections of Sanicula involved in the current study were not respectively recovered as monophyletic group. Molecular dating analysis explored that the origin of this genus was occurred during the late Eocene period, approximately 37.84 Ma (95% HPD: 20.33-52.21 Ma) years ago and the diversification of the genus was occurred in early Miocene 18.38 Ma (95% HPD: 10.68-25.28 Ma).

CONCLUSION

The plastome-based tree and ITS-based tree generated incongruences, which may be attributed to the event of hybridization/introgression, incomplete lineage sorting (ILS) and chloroplast capture. Our study highlighted the power of plastome data to significantly improve the phylogenetic supports and resolutions, and to efficiently explore the evolutionary history of this genus. Molecular dating analysis explored that the diversification of the genus occurred in the early Miocene, which was largely influenced by the prevalence of the East Asian monsoon and the uplift of the Hengduan Mountains (HDM). In summary, our study provides novel insights into the plastome evolution, phylogenetic relationships, taxonomic framework and evolution of genus Sanicula.

Phylogeny and Evolution of Cocconeiopsis (Cocconeidaceae) as Revealed by Complete Chloroplast and Mitochondrial Genomes

The genus Cocconeiopsis was separated from Navicula, but its systematic position is in debate. We sequenced the complete chloroplast and mitochondrial genome of Cocconeidaceae for the first time with Cocconeiopsis kantsiensis and investigated its phylogeny and evolutionary history. Results showed that the plastid genome was 140,415 bp long with 167 genes. The mitochondrial genome was 43,732 bp long with 66 genes. Comparative analysis showed that the plastid genome structure of C. kantsiensis was most similar to those of three Navicula species and Halamphora americana, and its size was significantly smaller than that of a monoraphid species. Its mitochondrial genome was similar to that of related species except for Phaeodactylum tricornutum. The multigene phylogeny reconstruction showed that Cocconeiopsis was sister to Didymosphenia but distant from Naviculaceae. The two-gene phylogenetic analysis containing 255 species showed Cocconeiopsis was sister to Cocconeis, and distant from Naviculaceae as well. Divergence time estimation indicates the common ancestor of cocconeid species occurred about 62.8 Ma and Cocconeiopsis diverged with monoraphid Cocconeis about 58.9 Ma. Our results support the assignment of Cocconeiopsis to Cocconeidaceae and that monoraphid cocconeids were likely evolved from the lineage of Cocconeiopsis.

Complete chloroplast genome of Lens lamottei reveals intraspecies variation among with Lens culinaris

Lens lamottei is a member of the Fabaceae family and the second gene pool of the genus Lens. The environmental factors that drove the divergence among wild and cultivated species have been studied extensively. Recent research has focused on genomic signatures associated with various phenotypes with the acceleration of next-generation techniques in molecular profiling. Therefore, in this study, we provide the complete sequence of the chloroplast genome sequence in the wild Lens species L. lamottei with a deep coverage of 713 × next-generation sequencing (NGS) data for the first time. Compared to the cultivated species, Lens culinaris, we identified synonymous, and nonsynonymous changes in the protein-coding regions of the genes ndhB, ndhF, ndhH, petA, rpoA, rpoC2, rps3, and ycf2 in L. lamottei. Phylogenetic analysis of chloroplast genomes of various plants under Leguminosae revealed that L. lamottei and L. culinaris are closest to one another than to other species. The complete chloroplast genome of L. lamottei also allowed us to reanalyze previously published transcriptomic data, which showed high levels of gene expression for ATP-synthase, rubisco, and photosystem genes. Overall, this study provides a deeper insight into the diversity of Lens species and the agricultural importance of these plants through their chloroplast genomes.

Chloroplast genome characteristics and phylogeny of the sinodielsia clade (apiaceae: apioideae)

BACKGROUND

The Sinodielsia clade of the subfamily Apioideae (Apiacieae) was established in 2008, and it is composed of 37 species from 17 genera. Its circumscription is still poorly delimited and unstable, and interspecific relationships in the clade lack comprehensive analysis. Chloroplast (cp.) genomes provide valuable and informative data sources for evolutionary biology and have been widely used in studies on plant phylogeny. To infer the phylogenetic history of the Sinodielsia clade, we assembled complete cp. genomes of 39 species and then performed phylogenetic analysis based on these cp. genome sequence data combined with 66 published cp. genomes from 16 genera relative to the Sinodielsia clade.

RESULTS

These 39 newly assembled genomes had a typical quadripartite structure with two inverted repeat regions (IRs: 17,599-31,486 bp) separated by a large single-copy region (LSC: 82,048-94,046 bp) and a small single-copy region (SSC: 16,343-17,917 bp). The phylogenetic analysis showed that 19 species were clustered into the Sinodielsia clade, and they were divided into two subclades. Six mutation hotspot regions were detected from the whole cp. genomes among the Sinodielsia clade, namely, rbcL-accD, ycf4-cemA, petA-psbJ, ycf1-ndhF, ndhF-rpl32 and ycf1, and it was found that ndhF-rpl32 and ycf1 were highly variable in the 105 sampled cp. genomes.

CONCLUSION

The Sinodielsia clade was subdivided into two subclades relevant to geographical distributions, except for cultivated and introduced species. Six mutation hotspot regions, especially ndhF-rpl32 and ycf1, could be used as potential DNA markers in the identification and phylogenetic analyses of the Sinodielsia clade and Apioideae. Our study provided new insights into the phylogeny of the Sinodielsia clade and valuable information on cp. genome evolution in Apioideae.

The Complete Chloroplast Genome of Endangered Species Stemona parviflora: Insight into the Phylogenetic Relationship and Conservation Implications

Stemona parviflora is an endangered species, narrowly endemic to Hainan and Southwest Guangdong. The taxonomic classification of S. parviflora remains controversial. Moreover, studying endangered species is helpful for current management and conservation. In this study, the first complete chloroplast genome of S. parviflora was assembled and compared with other Stemona species. The chloroplast genome size of S. parviflora was 154,552 bp, consisting of 87 protein-coding genes, 38 tRNA genes, 8 rRNA genes, and one pseudogene. The ψycf1 gene was lost in the cp genome of S. sessilifolia, but it was detected in four other species of Stemona. The inverted repeats (IR) regions have a relatively lower length variation compared with the large single copy (LSC) and small single copy (SSC) regions. Long repeat sequences and simple sequence repeat (SSR) were detected, and most SSR were distributed in the LSC region. Codon usage bias analyses revealed that the RSCU value of the genus Stemona has almost no difference. As with most angiosperm chloroplast genomes, protein-coding regions were more conservative than the inter-gene spacer. Seven genes (atpI, ccsA, cemA, matK, ndhA, petA, and rpoC1) were detected under positive selection in different Stemona species, which may result from adaptive evolution to different habitats. Phylogenetic analyses show the Stemona cluster in two main groups; S. parviflora were closest to S. tuberosa. A highly suitable region of S. parviflora was simulated by Maxent in this study; it is worth noting that the whole territory of Taiwan has changed to a low fitness area and below in the 2050 s, which may not be suitable for the introduction and cultivation of S. parviflora. In addition, limited by the dispersal capacity of S. parviflora, it is necessary to carry out artificial grafts to expand the survival areas of S. parviflora. Our results provide valuable information on characteristics of the chloroplast genome, phylogenetic relationships, and potential distribution range of the endangered species S. parviflora.