Comparative plastomic analysis and insights into the phylogeny of Salvia (Lamiaceae)

Cytotoxic diterpenoids from Salvia glutinosa and comparison with the tanshinone profile of danshen (Salvia miltiorrhiza)

The roots of Salvia miltiorrhiza are the source of the traditional Chinese medicine danshen and the class of tanshinones, particular quinoid nor-diterpenoids of the abietane type. Of these compounds, cryptotanshinone, dihydrotanshinone I, tanshinone I, and tanshinone IIA, have been extensively studied for their anticancer potential, not only but as well because of their high abundance in S. miltiorrhiza and their thus easy availability. However, also additional Salvia species are known to contain tanshinones, mainly such of the subgenus Glutinaria, of which S. glutinosa is the only species widely occurring in Europe. Using UHPLC-DAD-MS, the tanshinone profile of S. glutinosa roots collected from two different locations was compared to the profile in S. miltiorrhiza roots. In addition, tanshinone IIA and another six diterpenoids from S. glutinosa were investigated for their antiproliferative and cytotoxic potential against MDA-MB-231 and HL-60 cells. Apart from dihydrotanshinone I, which has been previously characterized due to its anticancer properties, we determined danshenol A as a highly antiproliferative and cytotoxic agent, significantly surpassing the effects of dihydrotanshinone I. With regard to the diterpenoid profile, S. miltiorrhiza showed a higher concentration for most of the tanshinones, except for (+)-danshexinkun A, which was present in comparable amounts in both species. Danshenol A, in contrast, was only present in S. glutinosa as were dehydroabietic acid and (+)-pisiferic acid. The results of our study underlines the long traditional use of danshen due to its high amount on tanshinones, but also demonstrates the potential value of investigating closely related species for the discovery of new biologically active lead compounds.

Comparative analysis of chloroplast genome and new insights into phylogenetic relationships of Ajuga and common adulterants

Introduction

The potential contamination of herbal medicinal products poses a significant concern for consumer health. Given the limited availability of genetic information concerning Ajuga species, it becomes imperative to incorporate supplementary molecular markers to enhance and ensure accurate species identification.

Methods

In this study, the chloroplast (cp) genomes of seven species of the genus Ajuag were sequenced, de novo assembled and characterized.

Results

exhibiting lengths ranging from 150,342 bp to 150,472 bp, encompassing 86 - 88 protein-coding genes (PCGs), 35 - 37 transfer RNA, and eight ribosomal RNA. The repetitive sequences, codon uses, and cp genomes of seven species were highly conserved, and PCGs were the reliable molecular markers for investigating the phylogenetic relationship within the Ajuga genus. Moreover, four mutation hotspot regions (accD-psaI, atpH-atpI, ndhC-trnV(UAC), and ndhF-rpl23) were identified within cp genomes of Ajuga, which could help distinguish A. bracteosa and its contaminants. Based on cp genomes and PCGs, the phylogenetic tree preliminary confirmed the position of Ajuga within the Lamiaceae family. It strongly supported a sister relationship between Subsect. Genevense and Subsect. Biflorae, suggesting the merger of Subsect. Biflorae and Subsect. Genevenses into one group rather than maintaining separate categorizations. Additionally, molecular clock analysis estimated the divergence time of Ajuga to be around 7.78 million years ago.

Discussion

The species authentication, phylogeny, and evolution analyses of the Ajuga species may benefit from the above findings.

Comparative Analysis of Plastomes in Elsholtzieae: Phylogenetic Relationships and Potential Molecular Markers

The Elsholtzieae, comprising ca. 7 genera and 70 species, is a small tribe of Lamiaceae (mint family). Members of Elsholtzieae are of high medicinal, aromatic, culinary, and ornamentals value. Despite the rich diversity and value of Elsholtzieae, few molecular markers or plastomes are available for phylogenetics. In the present study, we employed high-throughput sequencing to assemble two Mosla plastomes, M. dianthera and M. scabra, for the first time, and compared with other plastomes of Elsholtzieae. The plastomes of Elsholtzieae exhibited a quadripartite structure, ranging in size from 148,288 bp to 152,602 bp. Excepting the absence of the pseudogene rps19 in Elsholtzia densa, the exhaustive tally revealed the presence of 132 genes (113 unique genes). Among these, 85 protein-coding genes (CDS), 37 tRNA genes, 8 rRNA genes, and 2 pseudogenes (rps19 and ycf1) were annotated. Comparative analyses showed that the plastomes of these species have minor variations at the gene level. Notably, the E. eriostchya plastid genome exhibited increased GC content regions in the LSC and SSC, resulting in an increased overall GC content of the entire plastid genome. The E. densa plastid genome displayed modified boundaries due to inverted repeat (IR) contraction. The sequences of CDS and intergenic regions (IGS) with elevated variability were identified as potential molecular markers for taxonomic inquiries within Elsholtzieae. Phylogenetic analysis indicated that four genera formed monophyletic entities, with Mosla and Perilla forming a sister clade. This clade was, in turn, sister to Collinsonia, collectively forming a sister group to Elsholtzia. Both CDS, and CDS + IGS could construct a phylogenetic tree with stronger support. These findings facilitate species identification and DNA barcoding investigations in Elsholtzieae and provide a foundation for further exploration and resource utilization within this tribe.

Comparative and phylogenetic analysis of complete chloroplast genome sequences of Salvia regarding its worldwide distribution

Salvia is widely used as medicine, food, and ornamental plants all over the world, with three main distribution centers, the Central and western Asia/Mediterranean (CAM), the East Aisa (EA), and the Central and South America (CASA). Along with its large number of species and world-wide distribution, Salvia is paraphyletic with multiple diversity. Chloroplast genomes (CPs) are useful tools for analyzing the phylogeny of plants at lower taxonomic levels. In this study, we reported chloroplast genomes of five species of Salvia and performed phylogenetic analysis with current available CPs of Salvia. Repeated sequence analysis and comparative analysis of Salvia CPs were also performed with representative species from different distribution centers. The results showed that the genetic characters of the CPs are related to the geographic distribution of plants. Species from CAM diverged first to form a separate group, followed by species from EA, and finally species from CASA. Larger variations of CPs were observed in species from CAM, whereas more deficient sequences and less repeated sequences in the CPs were observed in species from CASA. These results provide valuable information on the development and utilization of the worldwide genetic resources of Salvia.

Molecular phylogeny and inflorescence evolution of Prunus (Rosaceae) based on RAD-seq and genome skimming analyses

Prunus is an economically important genus widely distributed in the temperate Northern Hemisphere. Previous studies on the genus using a variety of loci yielded conflicting phylogenetic hypotheses. Here, we generated nuclear reduced representation sequencing data and plastid genomes for 36 Prunus individuals and two outgroups. Both nuclear and plastome data recovered a well-resolved phylogeny. The species were divided into three main clades corresponding to their inflorescence types, - the racemose group, the solitary-flower group and the corymbose group - with the latter two sister to one another. Prunus was inferred to have diversified initially in the Late Cretaceous around 67.32 million years ago. The diversification of the three major clades began between the Paleocene and Miocene, suggesting that paleoclimatic events were an important driving force for Prunus diversification. Ancestral state reconstructions revealed that the most recent common ancestor of Prunus had racemose inflorescences, and the solitary-flower and corymb inflorescence types were derived by reduction of flower number and suppression of the rachis, respectively. We also tested the hybrid origin hypothesis of the racemose group proposed in previous studies. Prunus has undergone extensive hybridization events, although it is difficult to identify conclusively specific instances of hybridization when using SNP data, especially deep in the phylogeny. Our study provides well-resolved nuclear and plastid phylogenies of Prunus, reveals substantial cytonuclear discord at shallow scales, and sheds new light on inflorescence evolution in this economically important lineage.

Towards a global perspective for Salvia L.: Phylogeny, diversification and floral evolution

Salvia is the most species-rich genus in Lamiaceae, encompassing approximately 1000 species distributed all over the world. We sought a new evolutionary perspective for Salvia by employing macroevolutionary analyses to address the tempo and mode of diversification. To study the association of floral traits with speciation and extinction, we modelled and explored the evolution of corolla length and the lever-mechanism pollination system across our Salvia phylogeny. We reconstructed a multigene phylogeny for 366 species of Salvia in the broad sense including all major recognized lineages and 50 species from Iran, a region previously overlooked in studies of the genus. Our comprehensive sampling of Iranian species of Salvia provides higher phylogenetic resolution for southwestern Asian species than obtained in previous studies. Our phylogenetic data in combination with divergence time estimates were used to examine the evolution of corolla length, woody versus herbaceous habit, and presence versus absence of a lever mechanism. We investigated the timing and dependence of Salvia diversification related to corolla length evolution through a disparity test and BAMM analysis. A HiSSE model was used to evaluate the dependency of diversification on the lever-mechanism pollination system in Salvia. A medium corolla length (15-18 mm) was reconstructed as the ancestral state for Salvia with multiple shifts to shorter and longer corollas. Macroevolutionary model analyses indicate that corolla length disparity is high throughout Salvia evolution, significantly different from expectations under a Brownian motion model during the last 28 million years of evolution. Our analyses show evidence of a higher diversification rate of corolla length for some Andean species of Salvia compared to other members of the genus. Based on our tests of diversification models, we reject the hypothesis of a direct effect of the lever mechanism on Salvia diversification. Therefore, we suggest caution in considering the lever-mechanism pollination system as one of the main drivers of speciation in Salvia.

Comparison of Boraginales Plastomes: Insights into Codon Usage Bias, Adaptive Evolution, and Phylogenetic Relationships

The Boraginales (Boraginaceae a.l.) comprise more than 2450 species worldwide. However, little knowledge exists of the characteristics of the complete plastid genome. In this study, three new sequences representing the first pt genome of Heliotropiaceae and Cordiaceae were assembled and compared with other Boraginales species. The pt genome sizes of Cordia dichotoma, Heliotropium arborescens, and Tournefortia montana were 151,990 bp, 156,243 bp, and 155,891 bp, respectively. Multiple optimal codons were identified, which may provide meaningful information for enhancing the gene expression of Boraginales species. Furthermore, codon usage bias analyses revealed that natural selection and other factors may dominate codon usage patterns in the Boraginales species. The boundaries of the IR/LSC and IR/SSC regions were significantly different, and we also found a signal of obvious IR region expansion in the pt genome of Nonea vesicaria and Arnebia euchroma. Genes with high nucleic acid diversity (pi) values were also calculated, which may be used as potential DNA barcodes to investigate the phylogenetic relationships in Boraginales. psaI, rpl33, rpl36, and rps19 were found to be under positive selection, and these genes play an important role in our understanding of the adaptive evolution of the Boraginales species. Phylogenetic analyses implied that Boraginales can be divided into two groups. The existence of two subfamilies (Lithospermeae and Boragineae) in Boraginaceae is also strongly supported. Our study provides valuable information on pt genome evolution and phylogenetic relationships in the Boraginales species.

Comparative Analysis of the Chloroplast Genome of Cardamine hupingshanensis and Phylogenetic Study of Cardamine

Cardamine hupingshanensis (K. M. Liu, L. B. Chen, H. F. Bai and L. H. Liu) is a perennial herbal species endemic to China with narrow distribution. It is known as an important plant for investigating the metabolism of selenium in plants because of its ability to accumulate selenium. However, the phylogenetic position of this particular species in Cardamine remains unclear. In this study, we reported the chloroplast genome (cp genome) for the species C. hupingshanensis and analyzed its position within Cardamine. The cp genome of C. hupingshanensis is 155,226 bp in length and exhibits a typical quadripartite structure: one large single copy region (LSC, 84,287 bp), one small single copy region (17,943 bp) and a pair of inverted repeat regions (IRs, 26,498 bp). Guanine-Cytosine (GC) content makes up 36.3% of the total content. The cp genome contains 111 unique genes, including 78 protein-coding genes, 29 tRNA genes and 4 rRNA genes. A total of 115 simple sequences repeats (SSRs) and 49 long repeats were identified in the genome. Comparative analyses among 17 Cardamine species identified the five most variable regions (trnH-GUG-psbA, ndhK-ndhC, trnW-CCA-trnP-UGG, rps11-rpl36 and rpl32-trnL-UAG), which could be used as molecular markers for the classification and phylogenetic analyses of various Cardamine species. Phylogenetic analyses based on 79 protein coding genes revealed that the species C. hupingshanensis is more closely related to the species C. circaeoides. This relationship is supported by their shared morphological characteristics.

Plastome characteristics and species identification of Chinese medicinal wintergreens (Gaultheria, Ericaceae)

Wintergreen oil is a folk medicine widely used in foods, pesticides, cosmetics and drugs. In China, nine out of 47 species within Gaultheria (Ericaceae) are traditionally used as Chinese medicinal wintergreens; however, phylogenetic approaches currently used to discriminating these species remain unsatisfactory. In this study, we sequenced and characterized plastomes from nine Chinese wintergreen species and identified candidate DNA barcoding regions for Gaultheria. Each Gaultheria plastome contained 110 unique genes (76 protein-coding, 30 tRNA, and four rRNA genes). Duplication of trnfM, rps14, and rpl23 genes were detected, while all plastomes lacked ycf1 and ycf2 genes. Gaultheria plastomes shared substantially contracted SSC regions that contained only the ndhF gene. Moreover, plastomes of Gaultheria leucocarpa var. yunnanensis contained an inversion in the LSC region and an IR expansion to cover the ndhF gene. Multiple rearrangement events apparently occurred between the Gaultheria plastomes and those from several previously reported families in Ericales. Our phylogenetic reconstruction using 42 plastomes revealed well-supported relationships within all nine Gaultheria species. Additionally, seven mutational hotspot regions were identified as potential DNA barcodes for Chinese medicinal wintergreens. Our study is the first to generate complete plastomes and describe the structural variations of the complicated genus Gaultheria. In addition, our findings provide important resources for identification of Chinese medicinal wintergreens.

Integration of Repeatomic and Cytogenetic Data on Satellite DNA for the Genome Analysis in the Genus Salvia (Lamiaceae)

Within the complicated and controversial taxonomy of cosmopolitan genus Salvia L. (Lamiaceae) are valuable species Salvia officinalis L. and Salvia sclarea L., which are important for the pharmaceutical, ornamental horticulture, food, and perfume industries. Genome organization and chromosome structure of these essential oil species remain insufficiently studied. For the first time, the comparative repeatome analysis of S. officinalis and S. sclarea was performed using the obtained NGS data, RepeatExplorer/TAREAN pipelines and FISH-based chromosome mapping of the revealed satellite DNA families (satDNAs). In repeatomes of these species, LTR retrotransposons made up the majority of their repetitive DNA. Interspecific variations in genome abundance of Class I and Class II transposable elements, ribosomal DNA, and satellite DNA were revealed. Four (S. sclarea) and twelve (S. officinalis) putative satDNAs were identified. Based on patterns of chromosomal distribution of 45S rDNA; 5S rDNA and the revealed satDNAs, karyograms of S. officinalis and S. sclarea were constructed. Promising satDNAs which can be further used as chromosome markers to assess inter- and intraspecific chromosome variability in Salvia karyotypes were determined. The specific localization of homologous satDNA and 45S rDNA on chromosomes of the studied Salvia species confirmed their common origin, which is consistent with previously reported molecular phylogenetic data.

Phylogenetic position of Ligusticopsis (Apiaceae, Apioideae): evidence from molecular data and carpological characters

Ligusticopsis (Apiaceae, Apioideae) is now considered to have an East-Asia and Sino-Himalaya distribution. The genus was not recognized as a natural and separate genus and was treated as a synonym of Ligusticum both in Flora Reipublicae Popularis Sinicae and Flora of China since first established, though Pimenov et al. have made many taxonomic revisions to Ligusticopsis, phylogenetic relationships between Ligusticopsis and Ligusticum have been in dispute. Thirty-four plastomes and 35 nrITS from Apioideae were analysed by RAxML and MrBayes to reconstruct the phylogenetic relationships, along with carpology of 10 species and comparative analyses of 17 plastomes to investigate the evidence supporting the independence of Ligusticopsis. As a result, nine species suggested to be Ligusticopsis formed a highly supported monophyletic branch (Subclade A) inside Selineae both in maximum likelihood and Bayesian inference; the results of the comparative analyses further supported the monophyly of Subclade A, mainly in the location of genes at the IRa/LSC boundary, the sequence diversity exhibited by various genes (e.g. trnH-GUG-psbA and ycf2) and same codon biases in terminator TAA (relative synonymous codon usage = 1.75). Species in Subclade A also had shared characters in mericarps, combined with other characters of the plant, 'base clothed in fibrous remnant sheaths, pinnate bracts, pinnate bracteoles longer than rays of umbellule, mericarps strongly compressed dorsally, median and lateral ribs filiform or keeled, marginal ribs winged, and numerous vittae in commissure and each furrow' should be the most important and diagnostic characters of Ligusticopsis. Our phylogenetic trees and other analyses supported the previous taxonomic treatments of Pimenov et al. that Ligusticopsis should be a natural and separate genus rather than a synonym of Ligusticum.

Comparative Plastome Analysis of Three Amaryllidaceae Subfamilies: Insights into Variation of Genome Characteristics, Phylogeny, and Adaptive Evolution

In the latest APG IV classification system, Amaryllidaceae is placed under the order of Asparagus and includes three subfamilies: Agapanthoideae, Allioideae, and Amaryllidoideae, which include many economically important crops. With the development of molecular phylogeny, research on the phylogenetic relationship of Amaryllidaceae has become more convenient. However, the current comparative analysis of Amaryllidaceae at the whole chloroplast genome level is still lacking. In this study, we sequenced 18 Allioideae plastomes and combined them with publicly available data (a total of 41 plastomes), including 21 Allioideae species, 1 Agapanthoideae species, 14 Amaryllidoideae species, and 5 Asparagaceae species. Comparative analyses were performed including basic characteristics of genome structure, codon usage, repeat elements, IR boundary, and genome divergence. Phylogenetic relationships were detected using single-copy genes (SCGs) and ribosomal internal transcribed spacer sequences (ITS), and the branch-site model was also employed to conduct the positive selection analysis. The results indicated that all Amaryllidaceae species showed a highly conserved typical tetrad structure. The GC content and five codon usage indexes in Allioideae species were lower than those in the other two subfamilies. Comparison analysis of Bayesian and ML phylogeny based on SCGs strongly supports the monophyly of three subfamilies and the sisterhood among them. Besides, positively selected genes (PSGs) were detected in each of the three subfamilies. Almost all genes with significant posterior probabilities for codon sites were associated with self-replication and photosynthesis. Our study investigated the three subfamilies of Amaryllidaceae at the whole chloroplast genome level and suggested the key role of selective pressure in the adaptation and evolution of Amaryllidaceae.

Insights into the plateau adaptation of Salvia castanea by comparative genomic and WGCNA analyses

INTRODUCTION

Salvia castanea, a wild plant species is adapted to extreme Qinghai-Tibetan plateau (QTP) environments. It is also used for medicinal purposes due to high ingredient of tanshinone IIA (T-IIA). Despite its importance to Chinese medicinal industry, the mechanisms associated with secondary metabolites accumulation (i.e. T-IIA and rosmarinic acid (RA)) in this species have not been characterized. Also, the role of special underground tissues in QTP adaptation of S. castanea is still unknown.

OBJECTIVES

We explored the phenomenon of periderm-like structure in underground stem center of S. castanea with an aim to unravel the molecular evolutionary mechanisms of QTP adaptation in this species.

METHODS

Morphologic observation and full-length transcriptome of S. castanea plants were conducted. Comparative genomic analyses of S. castanea with other 14 representative species were used to reveal its phylogenetic position and molecular evolutionary mechanisms. RNA-seq and WGCNA analyses were applied to understand the mechanisms of high accumulations of T-IIA and RA in S. castanea tissues.

RESULTS

Based on anatomical observations, we proposed a "trunk-branches" developmental model to explain periderm-like structure in the center of underground stem of S. castanea. Our study suggested that S. castanea branched off from cultivated Danshen around 16 million years ago. During the evolutionary process, significantly expanded orthologous gene groups, 24 species-specific and 64 positively selected genes contributed to morphogenesis and QTP adaptation in S. castanea. RNA-seq and WGCNA analyses unraveled underlying mechanisms of high accumulations of T-IIA and RA in S. castanea and identified NAC29 and TGA22 as key transcription factors.

CONCLUSION

We proposed a "trunk-branches" developmental model for the underground stem in S. castanea. Adaptations to extreme QTP environment in S. castanea are associated with accumulations of high secondary metabolites in this species.

Challenges in Medicinal and Aromatic Plants DNA Barcoding-Lessons from the Lamiaceae

The potential value of DNA barcoding for the identification of medicinal plants and authentication of traded plant materials has been widely recognized; however, a number of challenges remain before DNA methods are fully accepted as an essential quality control method by industry and regulatory authorities. The successes and limitations of conventional DNA barcoding are considered in relation to important members of the Lamiaceae. The mint family (Lamiaceae) contains over one thousand species recorded as having a medicinal use, with many more exploited in food and cosmetics for their aromatic properties. The family is characterized by a diversity of secondary products, most notably the essential oils (EOs) produced in external glandular structures on the aerial parts of the plant that typify well-known plants of the basil (Ocimum), lavender (Lavandula), mint (Mentha), thyme (Thymus), sage (Salvia) and related genera. This complex, species-rich family includes widely cultivated commercial hybrids and endangered wild-harvested traditional medicines, and examples of potential toxic adulterants within the family are explored in detail. The opportunities provided by next generation sequencing technologies to whole plastome barcoding and nuclear genome sequencing are also discussed with relevant examples.

Chloroplast genomic diversity in Bulbophyllum section Macrocaulia (Orchidaceae, Epidendroideae, Malaxideae): Insights into species divergence and adaptive evolution

Bulbophyllum is the largest genus in Orchidaceae with a pantropical distribution. Due to highly significant diversifications, it is considered to be one of the most taxonomically and phylogenetically complex taxa. The diversification pattern and evolutionary adaptation of chloroplast genomes are poorly understood in this species-rich genus, and suitable molecular markers are necessary for species determination and phylogenetic analysis. A natural Asian section Macrocaulia was selected to estimate the interspecific divergence of chloroplast genomes in this study. Here, we sequenced the complete chloroplast genome of four Bulbophyllum species, including three species from section Macrocaulia. The four chloroplast genomes had a typical quadripartite structure with a genome size ranged from 156,182 to 158,524 bp. The chloroplast genomes included 113 unique genes encoding 79 proteins, 30 tRNAs and 4 rRNAs. Comparison of the four chloroplast genomes showed that the three species from section Macrocaulia had similar structure and gene contents, and shared a number of indels, which mainly contribute to its monophyly. In addition, interspecific divergence level was also great. Several exclusive indels and polymorphism SSR loci might be used for taxonomical identification and determining interspecific polymorphisms. A total of 20 intergenic regions and three coding genes of the most variable hotspot regions were proposed as candidate effective molecular markers for future phylogenetic relationships at different taxonomical levels and species divergence in Bulbophyllum. All of chloroplast genes in four Bulbophyllum species were under purifying selection, while 13 sites within six genes exhibited site-specific selection. A whole chloroplast genome phylogenetic analysis based on Maximum Likelihood, Bayesian and Parsimony methods all supported the monophyly of section Macrocaulia and the genus of Bulbophyllum. Our findings provide valuable molecular markers to use in accurately identifying species, clarifying taxonomy, and resolving the phylogeny and evolution of the genus Bulbophyllum. The molecular markers developed in this study will also contribute to further research of conservation of Bulbophyllum species.