The Complete Chloroplast Genome of Catha edulis: A Comparative Analysis of Genome Features with Related Species

Comparative analysis the chloroplast genomes of Celastrus (Celastraceae) species: Provide insights into molecular evolution, species identification and phylogenetic relationships

BACKGROUND

The genus Celastrus is an important medicinal plant resource. The similarity of morphology and the lack of complete chloroplast genome analysis have significantly impeded the exploration of species identification, molecular evolution and phylogeny of Celastrus.

PURPOSE

In order to resolve the phylogenic controversy of Celastrus species, the chloroplast genome comparative analysis was performed to provide genetic evidence.

METHODS

In this study, we collected and sequenced ten chloroplast genomes of Celastrus species from China and downloaded three chloroplast genomes from the databases. The chloroplast genomes were compared and analyzed to explore their characteristics and evolution. Furthermore, the phylogenetic relationships of Celastrus species were inferred based on the whole chloroplast genomes and protein-coding genes.

RESULTS

All the 13 Celastrus species chloroplast genomes showed a typical quadripartite structure with genome sizes ranging from 155,113 to 157,366 bp. The intron loss of the rps16 gene occurred in all the 13 Celastrus species. The GC content, gene sequence, repeat types and codon bias pattern were highly conserved. Ten highly variation regions were identified, which can be used as potential DNA markers in molecular identification of Celastrus species. Eight genes, including accD, atp4, ndhB, rpoC1, rbcL, rpl2, rpl20 and ycf1, were detected to experience positive selection. Phylogenetic analysis showed that Celastrus was a monophyletic group and Tripterygium was the closest sister-group. Noteworthy, C. gemmatus Loes. and C. orbiculatus Thunb. can be discriminated using the chloroplast genome as a super barcode. The comparative and phylogenetic analysis results proposed that C. tonkinensis Pitard. was the synonym of C. hindsii Benth.

CONCLUSION

The comparative analysis of the Celastrus chloroplast genomes can provide comprehensive genetic evidence for molecular evolution, species identification and phylogenetic relationships.

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.

Structural Diversities and Phylogenetic Signals in Plastomes of the Early-Divergent Angiosperms: A Case Study in Saxifragales

As representative of the early-divergent groups of angiosperms, Saxifragales is extremely divergent in morphology, comprising 15 families. Within this order, our previous case studies observed significant structural diversities among the plastomes of several lineages, suggesting a possible role in elucidating their deep phylogenetic relationships. Here, we collected 208 available plastomes from 11 constituent families to explore the evolutionary patterns among Saxifragales. With thorough comparisons, the losses of two genes and three introns were found in several groups. Notably, 432 indel events have been observed from the introns of all 17 plastomic intron-containing genes, which could well play an important role in family barcoding. Moreover, numerous heterogeneities and strong intrafamilial phylogenetic implications were revealed in pttRNA (plastomic tRNA) structures, and the unique structural patterns were also determined for five families. Most importantly, based on the well-supported phylogenetic trees, evident phylogenetic signals were detected in combinations with the identified pttRNAs features and intron indels, demonstrating abundant lineage-specific characteristics for Saxifragales. Collectively, the results reported here could not only provide a deeper understanding into the evolutionary patterns of Saxifragales, but also provide a case study for exploring the plastome evolution at a high taxonomic level of angiosperms.

Complete Chloroplast Genome Features of Dendrocalamusfarinosus and Its Comparison and Evolutionary Analysis with Other Bambusoideae Species

Dendrocalamus farinosus is one of the essential bamboo species mainly used for food and timber in the southwestern region of China. In this study, the complete chloroplast (cp) genome of D. farinosus is sequenced, assembled, and the phylogenetic relationship analyzed. The cp genome has a circular and quadripartite structure, has a total length of 139,499 bp and contains 132 genes: 89 protein-coding genes, eight rRNAs and 35 tRNAs. The repeat analyses showed that three types of repeats (palindromic, forward and reverse) are present in the genome. A total of 51 simple sequence repeats are identified in the cp genome. The comparative analysis between different species belonging to Dendrocalamus revealed that although the cp genomes are conserved, many differences exist between the genomes. The analysis shows that the non-coding regions were more divergent than the coding regions, and the inverted repeat regions are more conserved than the single-copy regions. Moreover, these results also indicate that rpoC2 may be used to distinguish between different bamboo species. Phylogenetic analysis results supported that D. farinosus was closely related to D. latiflorus. Furthermore, these bamboo species’ geographical distribution and rhizome types indicate two evolutionary pathways: one is from the tropics to the alpine zone, and the other is from the tropics to the warm temperate zone. Our study will be helpful in the determination of the cp genome sequences of D. farinosus, and provides new molecular data to understand the Bambusoideae evolution.

Comparative Analysis of the Complete Chloroplast Genomes of Eight Ficus Species and Insights into the Phylogenetic Relationships of Ficus

The genus Ficus is an evergreen plant, the most numerous species in the family Moraceae, and is often used as a food and pharmacy source. The phylogenetic relationships of the genus Ficus have been debated for many years due to the overlapping phenotypic characters and morphological similarities between the genera. In this study, the eight Ficus species (Ficus altissima, Ficus auriculata, Ficus benjamina, Ficus curtipes, Ficus heteromorpha, Ficus lyrata, Ficus microcarpa, and Ficus virens) complete chloroplast (cp) genomes were successfully sequenced and phylogenetic analyses were made with other Ficus species. The result showed that the eight Ficus cp genomes ranged from 160,333 bp (F. heteromorpha) to 160,772 bp (F. curtipes), with a typical quadripartite structure. It was found that the eight Ficus cp genomes had similar genome structures, containing 127 unique genes. The cp genomes of the eight Ficus species contained 89−104 SSR loci, which were dominated by mono-nucleotides repeats. Moreover, we identified eight hypervariable regions (trnS-GCU_trnG-UCC, trnT-GGU_psbD, trnV-UAC_trnM-CAU, clpP_psbB, ndhF_trnL-UAG, trnL-UAG_ccsA, ndhD_psaC, and ycf1). Phylogenetic analyses have shown that the subgenus Ficus and subgenus Synoecia exhibit close affinities and based on the results, we prefer to merge the subgenus Synoecia into the subgenus Ficus. At the same time, new insights into the subgeneric classification of the Ficus macrophylla were provided. Overall, these results provide useful data for further studies on the molecular identification, phylogeny, species identification and population genetics of speciation in the Ficus genus.

Plastid genomes reveal evolutionary shifts in elevational range and flowering time of Osmanthus (Oleaceae)

Species of Osmanthus are economically important ornamental trees, yet information regarding their plastid genomes (plastomes) have rarely been reported, thus hindering taxonomic and evolutionary studies of this small but enigmatic genus. Here, we performed comparative genomics and evolutionary analyses on plastomes of 16 of the 28 currently accepted species, with 11 plastomes newly sequenced. Phylogenetic studies identified four main lineages within the genus that are here designated the: “Caucasian Osmanthus” (corresponding to O. decorus), “Siphosmanthus” (corresponding to O. sect. Siphosmanthus), “O. serrulatus + O. yunnanensis,” and “Core Osmanthus: (corresponding to O. sect. Osmanthus + O. sect. Linocieroides). Molecular clock analysis suggested that Osmanthus split from its sister clade c. 15.83 Ma. The estimated crown ages of the lineages were the following: genus Osmanthus at 12.66 Ma; “Siphosmanthus” clade at 5.85 Ma; “O. serrulatus + O. yunnanensis” at 4.89 Ma; and “Core Osmanthus: clade at 6.2 Ma. Ancestral state reconstructions and trait mapping showed that ancestors of Osmanthus were spring flowering and originated at lower elevations. Phylogenetic principal component analysis clearly distinguished spring‐flowering species from autumn‐flowering species, suggesting that flowering time differentiation is related to the difference in ecological niches. Nucleotide substitution rates of 80 common genes showed slow evolutionary pace and low nucleotide variations, all genes being subjected to purifying selection.

Complete Chloroplast Genomes and Comparative Analyses of Three Ornamental Impatiens Species

Impatiens L., the largest genus in the family Balsaminaceae with approximately 1,000 species, is a controversial genus. Due to the conflict of morphological features and insufficient genomic resources, the studies of systematic evolution and understanding of taxonomic identification are considered to be very limited. Hence, we have sequenced the complete chloroplast genomes of three ornamental species (Impatiens balsamina, I. hawkeri, and I. walleriana), and compared them with previously published wild species data. We performed a detailed comparison of a highly similar basic structure, size, GC content, gene number, order, and functional array among them. Similarly, most divergent genes were detected from previous work in the literature. The mutational regions containing highly variable nucleotide hotspots were identified and may be used as potential markers for species identification and taxonomy. Furthermore, using whole chloroplast genome data to analysis the phylogenetic relationship of the Balsaminaceae species, we found that they were all part of a single clade. The three phenotypically different ornamental species were clustered together, suggesting that they were very likely to be closely related. We achieved and characterized the plastid genome structure, identified the divergence hotspots, and determined the phylogenetic and taxonomic positions of the three cultivated species in the Impatiens genus. The results may show that the chloroplast genome can be used to solve phylogenetic problems in or between the Impatiens genus and also provide genomic resources for the study of the Balsaminaceae family’s systematics and evolution.

Disjunction and Vicariance Between East and West Asia: A Case Study on Euonymus sect. Uniloculares Based on Plastid Genome Analysis

Scientists have long been captivated by biogeographic disjunctions, and disjunctions between East Asia and North America have been particularly well-studied at the genus and family levels. By contrast, disjunctions between eastern and western Asia have received less attention. Euonymus L. is taxonomically divided into two sections based on the number of cells in anthers as follows: E. sect. Uniloculares has one-celled anthers and occurs mainly in Asia, whereas E. sect. Biloculares has two-celled anthers and is distributed globally. We used Illumina sequencing to investigate the genomes of four species in sect. Uniloculares. The chloroplast (cp) genomes are highly conserved (157,290-158,094 bp). Pseudogenisation of ndhF and intron loss in rps16 was detected. Based on the cp genomes of the four species of E. sect. Uniloculares, we propose a novel hypothesis of disjunction between eastern and western Asia. Biogeographic reconstruction and molecular dating revealed that sect. Uniloculares separated from its sect. Biloculares forebears 4.0 Mya during the Pliocene era. The radial diversification of sect. Uniloculares from East Asia and the establishment of the western Asian clade during the Pleistocene era (1.9 Mya) were the results of both dispersal and vicariance, making the section the youngest diverged clade conforming to age estimation. The centre of origin of sect. Uniloculares was determined to be in East Asia. Disjunctions and diversification between eastern and western Asia in sect. Uniloculares are thought to have been caused by changes in monsoon patterns, temperature variations, and the emergence of the Gobi Desert.

Comparative Chloroplast Genome Analysis of Wax Gourd (Benincasa hispida) with Three Benincaseae Species, Revealing Evolutionary Dynamic Patterns and Phylogenetic Implications

Benincasa hispida (wax gourd) is an important Cucurbitaceae crop, with enormous economic and medicinal importance. Here, we report the de novo assembly and annotation of the complete chloroplast genome of wax gourd with 156,758 bp in total. The quadripartite structure of the chloroplast genome comprises a large single-copy (LSC) region with 86,538 bp and a small single-copy (SSC) region with 18,060 bp, separated by a pair of inverted repeats (IRa and IRb) with 26,080 bp each. Comparison analyses among B. hispida and three other species from Benincaseae presented a significant conversion regarding nucleotide content, genome structure, codon usage, synonymous and non-synonymous substitutions, putative RNA editing sites, microsatellites, and oligonucleotide repeats. The LSC and SSC regions were found to be much more varied than the IR regions through a divergent analysis of the species within Benincaseae. Notable IR contractions and expansions were observed, suggesting a difference in genome size, gene duplication and deletion, and the presence of pseudogenes. Intronic gene sequences, such as trnR-UCU–atpA and atpH–atpI, were observed as highly divergent regions. Two types of phylogenetic analysis based on the complete cp genome and 72 genes suggested sister relationships between B. hispida with the Citrullus, Lagenaria, and Cucumis. Variations and consistency with previous studies regarding phylogenetic relationships are discussed. The cp genome of B. hispida provides valuable genetic information for the detection of molecular markers, research on taxonomic discrepancies, and the inference of the phylogenetic relationships of Cucurbitaceae.

The complete chloroplast genome sequencing analysis revealed an unusual IRs reduction in three species of subfamily Zygophylloideae

Tetraena mongolica, Zygophyllum xanthoxylon, and Z. fabago are three typical dryland plants with important ecological values in subfamily Zygophylloideae of Zygophyllaceae. Studies on the chloroplast genomes of them are favorable for understanding the diversity and phylogeny of Zygophyllaceae. Here, we sequenced and assembled the whole chloroplast genomes of T. mongolica, Z. xanthoxylon, and Z. fabago, and performed comparative genomic and phylogenetic analysis. The total size, structure, gene content and orders of these three chloroplast genomes were similar, and the three chloroplast genomes exhibited a typical quadripartite structure with a large single-copy region (LSC; 79,696–80,291 bp), a small single-copy region (SSC; 16,462–17,162 bp), and two inverted repeats (IRs; 4,288–4,413 bp). A total of 107 unique genes were identified from the three chloroplast genomes, including 70 protein-coding genes, 33 tRNAs, and 4 rRNAs. Compared with other angiosperms, the three chloroplast genomes were significantly reduced in overall length due to an unusual 16–24 kb shrinkage of IR regions and loss of the 11 genes which encoded subunits of NADH dehydrogenase. Genome-wide comparisons revealed similarities and variations between the three species and others. Phylogenetic analysis based on the three chloroplast genomes supported the opinion that Zygophyllaceae belonged to Zygophyllales in Fabids, and Z. xanthoxylon and Z. fabago belonged to Zygophyllum. The genome-wide comparisons revealed the similarity and variations between the chloroplast genomes of the three Zygophylloideae species and other plant species. This study provides a valuable molecular biology evidence for further studies of phylogenetic status of Zygophyllaceae.

The impact of catha edulis (vahl) forssk. ex endl. (celestraceae) (khat) on pharmacokinetics of clinically used drugs

INTRODUCTION

Catha edulis (Vahl) Forssk. ex Endl. (Celestraceae) is used as a recreational drug on daily basis for its euphoric and psychostimulant effects. It is also chewed by individuals who are on medications, raising the possibility of drug-khat interaction. However, limited data are available in the literature, although clinically significant interactions are expected, as khat contains a complex mixture of pharmacologically active constituents.

AREAS COVERED

It provides an overview of the phytochemistry, pharmacokinetics, pharmacodynamics, and pharmacogenetics of khat based on the literature mined from PubMed, Google Scholar, and Cochrane databases. It also presents a detailed account of drug-khat interactions with specific examples and their clinical significance. The interactions mainly occur at the pharmacokinetics level and particular attention is paid for the phases of absorption and cytochrome P450 enzyme-mediated metabolism.

EXPERT OPINION

Despite the increasing trend of khat chewing with medications among the populace and the potential risk for the occurrence of clinically significant interactions, there is paucity of data in the literature demonstrating the magnitude of the risk. The available data, however, clearly demonstrate that the consequence of drug-khat interaction is dependent on genotype. Genotyping, where feasible, could be used to improve clinical outcome and minimize adverse reactions.

Comparative chloroplast genome analysis of Impatiens species (Balsaminaceae) in the karst area of China: insights into genome evolution and phylogenomic implications

BACKGROUND

Impatiens L. is a genus of complex taxonomy that belongs to the family Balsaminaceae (Ericales) and contains approximately 1000 species. The genus is well known for its economic, medicinal, ornamental, and horticultural value. However, knowledge about its germplasm identification, molecular phylogeny, and chloroplast genomics is limited, and taxonomic uncertainties still exist due to overlapping morphological features and insufficient genomic resources.

RESULTS

We sequenced the chloroplast genomes of six different species (Impatiens chlorosepala, Impatiens fanjingshanica, Impatiens guizhouensis, Impatiens linearisepala, Impatiens loulanensis, and Impatiens stenosepala) in the karst area of China and compared them with those of six previously published Balsaminaceae species. We contrasted genomic features and repeat sequences, assessed sequence divergence and constructed phylogenetic relationships. Except for those of I. alpicola, I. pritzelii and I. glandulifera, the complete chloroplast genomes ranging in size from 151,366 bp (I. alpicola) to 154,189 bp (Hydrocera triflora) encoded 115 distinct genes [81 protein-coding, 30 transfer RNA (tRNA), and 4 ribosomal RNA (rRNA) genes]. Moreover, the characteristics of the long repeat sequences and simple sequence repeats (SSRs) were determined. psbK-psbI, trnT-GGU-psbD, rpl36-rps8, rpoB-trnC-GCA, trnK-UUU-rps16, trnQ-UUG, trnP-UGG-psaJ, trnT-UGU-trnL-UAA, and ycf4-cemA were identified as divergence hotspot regions and thus might be suitable for species identification and phylogenetic studies. Additionally, the phylogenetic relationships based on Maximum likelihood (ML) and Bayesian inference (BI) of the whole chloroplast genomes showed that the chloroplast genome structure of I. guizhouensis represents the ancestral state of the Balsaminaceae family.

CONCLUSION

Our study provided detailed information about nucleotide diversity hotspots and the types of repeats, which can be used to develop molecular markers applicable to Balsaminaceae species. We also reconstructed and analyzed the relationships of some Impatiens species and assessed their taxonomic statuses based on the complete chloroplast genomes. Together, the findings of the current study might provide valuable genomic resources for systematic evolution of the Balsaminaceae species.

Repeats in mitochondrial and chloroplast genomes characterize the ecotypes of the Oryza

Mitochondria and chloroplast are very important organelles for organism, participating in basic life activity. Their genomes contain many repeats which can lead to a variation of genome structure. Oryza is an important genus for human beings' nutrition. Several mitochondrial and chloroplast genomes of Oryza have been sequenced, which help us to insight the distribution and evolution of the repeats in Oryza species. In this paper, we compared six mitochondrial and 13 chloroplast genomes of Oryza and found that the structures of mitochondrial genomes were more diverse than chloroplast genomes. Since repeats can change the structure of the genome, resulting in the structural diversity of the genome, we analyzed all repeats and found 31 repeats in mitochondrial and 13 repeats in chloroplast genomes. Further, we developed 21 pairs of MRS molecular markers and 12 pairs of CRS molecular markers based on mitochondrial repeats and chloroplast repeats, respectively. These molecular markers can be used to detect the repeat-mediated recombination in Oryza mitochondrial and chloroplast genomes by PCR or fluorescence quantification.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-020-01198-6.

The complete chloroplast genome of Amana baohuaensis (Liliaceae)

Amana baohuaensis is a new species that was just named in 2019. Here, we obtained the complete chloroplast (cp) genome of A. baohuaensis using the Illumina paired-end sequencing technology. The cp genome has a typical quadripartite structure with 150,757 bp in length, containing a large single-copy (LSC) region of 81,757 bp, a small single-copy (SSC) region of 16,962 bp, and two inverted repeat (IR) regions of 26,019 bp. The total GC content is 36.73%, of which, the GC content of LSC, SSC and IR regions are 34.63%, 30.11% and 42.20%, respectively. The cp genome of A. baohuaensis contains 111 unique genes, including 78 protein-coding genes, 29 tRNA genes, and four rRNA genes. The Maximum Parsimony (MP) phylogenetic analysis suggested that A. baohuaensis had the closest relationship with A. wanzhensis, and all Amana species grouped together with high bootstrap support.

The complete chloroplast genome of the rare species Epimedium tianmenshanensis and comparative analysis with related species

Epimedium tianmenshanensis is a rare perennial herb distributed in China, and it is also an important medicinal plant. Here, we used illumina paired-end sequencing technology to obtain the complete chloroplast genome of E. tianmenshanensis, and compared analysis with related species. The length of the complete chloroplast genome of E. tianmenshanensis is 156,956 bp, which is a relatively conserved quadripartite structure including a large single copy (LSC) region of 88,409 bp, a small single copy (SSC) region of 17,448 bp, and a pair of inverted repeat (IRa/IRb) regions of 25,550 bp. The whole genome contains 132 unique genes, including 85 protein-coding genes, 38 tRNA genes, eight rRNA genes and one pseudogene. 87 simple sequence repeats (SSRs) were identified, and most of them were found to be composed of A/T. In addition, 22,923 codons were detected in 78 protein-coding genes of E. tianmenshanensis, and the overall codon bias pattern in the genome tended to use A/U ending codons. Phylogenetic analysis demonstrated that all the Epimedium species formed a monophyletic clade, and E. tianmenshanensis had the closest relationship to E. dolichostemon. The results of this study provided useful molecular information about the evolution and molecular biology of E. tianmenshanensis.

Comparative Analyses of Five Complete Chloroplast Genomes from the Genus Pterocarpus (Fabacaeae)

Pterocarpus is a genus of trees mainly distributed in tropical Asia, Africa, and South America. Some species of Pterocarpus are rosewood tree species, having important economic value for timber, and for some species, medicinal value as well. Up to now, information about this genus with regard to the genomic characteristics of the chloroplasts has been limited. Based on a combination of next-generation sequencing (Illumina Hiseq) and long-read sequencing (PacBio), the whole chloroplast genomes (cp genomes) of five species (rosewoods) in Pterocarpus (Pterocarpus macrocarpus, P. santalinus, P. indicus, P. pedatus, P. marsupium) have been assembled. The cp genomes of five species in Pterocarpus have similar structural characteristics, gene content, and sequence to other flowering plants. The cp genomes have a typical four-part structure, containing 110 unique genes (77 protein coding genes, 4 rRNAs, 29 tRNAs). Through comparative genomic analysis, abundant simple sequence repeat (SSR)loci (333-349) were detected in Pterocarpus, among which A /T single nucleotide repeats accounted for the highest proportion (72.8-76.4%). In the five cp genomes of Pterocarpus, eight hypervariable regions, including trnH-GUG_psbA, trnS-UGA_psbC, accD-psaI, ndhI-exon2_ndhI-exon1, ndhG_ndhi-exon2, rpoC2-exon2, ccsA, and trnfM-CAU, are proposed for use as DNA barcode regions. In the comparison of gene selection pressures (P. santalinus as the reference genome), purifying selection was inferred as the primary mode of selection in maintaining important biological functions. Phylogenetic analysis shows that Pterocarpus is a monophyletic group. The species P. tinctorius is resolved as early diverging in the genus. Pterocarpus was resolved as sister to the genus Tipuana.

Comparative Analysis of the Complete Plastid Genome of Five Bupleurum Species and New Insights into DNA Barcoding and Phylogenetic Relationship

Bupleurum L. (Apiaceae) is a perennial and herbal genus, most species of which have high medicinal value. However, few studies have been performed using plastome data in this genus, and the phylogenetic relationships have always been controversial. In this study, the plastid genomes of Bupleurum chinense and Bupleurum commelynoideum were sequenced, and their gene content, order, and structure were counted and analyzed. The only three published Bupleurum species (B. boissieuanum, B. falcatum, and B. latissimum) and other fifteen allied species were selected to conduct a series of comparative and phylogenetic analyses. The genomes of B. chinense and B. commelynoideum were 155,869 and 155,629 bp in length, respectively, both of which had a typical quadripartite structure. The genome length, structure, guanine and cytosine (GC) content, and gene distribution were highly similar to the other three Bupleurum species. The five Bupleurum species had nearly the same codon usages, and eight regions (petN-psbM, rbcL-accD, ccsA-ndhD, trnK(UUU)-rps16, rpl32-trnL(UAG)-ccsA, petA-psbJ, ndhF-rpl32, and trnP(UGG)-psaJ-rpl33) were found to possess relatively higher nucleotide diversity, which may be the promising DNA barcodes in Bupleurum. Phylogenetic analysis revealed that all Bupleurum species clustered into a monophyletic clade with high bootstrap support and diverged after the Chamaesium clade. Overall, our study provides new insights into DNA barcoding and phylogenetic relationship between Bupleurum and its related genera, and will facilitate the population genomics, conservation genetics, and phylogenetics of Bupleurum in Apiaceae.

Comparative analyses of chloroplast genomes from 13 Lagerstroemia (Lythraceae) species: identification of highly divergent regions and inference of phylogenetic relationships

Seven divergence hotspots as plastid markers for DNA barcoding was selected, and the phylogeny of 13 Lagerstroemia species based on the cp genome data was reconstructed within Myrtales. The Lagerstroemia species used in this study originated in China and have high economic and ecological value. The shared interspecific morphological characteristics and intraspecific morphological variation resulting from hybridization among Lagerstroemia taxa have made resolving their classification problems and phylogenetic relationships difficult. Systematic comparative genomic analysis has been shown to resolve phylogenetic relationships. We sequenced and annotated 6 Lagerstroemia cp genomes (Lagerstroemia excelsa, Lagerstroemia limii, Lagerstroemia siamica, Lagerstroemia tomentosa, Lagerstroemia venusta, and Lagerstroemia calyculata) for the first time and combined them with previously published genomes for Lagerstroemia species. Bioinformatics was used to analyse the 13 cp genomes in terms of gene structure and organization, codon usage, contraction and expansion of inverted repeat regions, repeat structure, divergence hotspots, species pairwise Ka/Ks ratios and phylogenetic relationships. The length varied between 152,049 bp in Lagerstroemia subcostata and 152,521 bp in L. venusta. We selected seven divergence hotspots in the cp genomes that had the potential to act as plastid markers to distinguish Lagerstroemia species. The phylogenetic relationships within Myrtales inferred from the cp genomes of 13 Lagerstroemia species and 27 other Myrtales species were highly supported, which illustrated several novel relationships within Myrtales. Taken together, our results provide comprehensive chloroplast genomic resources, which can be used further for species identification and molecular breeding of Lagerstroemia species.

Chloroplast genomic comparison of two sister species Allium macranthum and A. fasciculatum provides valuable insights into adaptive evolution

BACKGROUND

Allium macranthum and Allium fasciculatum are two sister species and their natural populations are separated by high mountains and deep valleys with exact opposite habitat. The chloroplast genome in angiosperms has showed useful for investigating plant evolution and systematic studies.

OBJECTIVE

Comparative analysis of these genomes revealed potential markers and phylogenetic analysis, and discuss the influence of positive selected sites on adaptive evolution.

METHODS

Here, we sequenced the complete chloroplast genomes of these two species and analyzed the repeat sequences components, nucleotide diversity, selection pressure and the phylogeny relationships with related species.

RESULTS

A typical quadripartite structure was detected with a genome size changed from 152,148 to 152,931 bp. We identified 67 and 79 simple sequence repeats in A. macranthum and A. fasciculatum, in which the mono-nucleotide repeats A/T possess the highest percentage. Three mutational hotspots (rpl32, rps16 and matK) at the SSC and LSC regions were observed, which showed remarkably higher Pi value (> 0.03). Additionally, eight genes (rpoA, atpF, cemA, rps4, ccsA, rpoC2, rpl14 and clpP) exhibited elevated pairwise Ka/Ks ratios in alpine species. Phylogenetic analyses based on the CDS sequences and the whole complete genomes showed same topologies with high support, and A. macranthum was closely clustered with A. fasciculatum within the fourteen Amaryllidaceae species.

CONCLUSION

Their coding proteins of these genes often functioned in chloroplast protein synthesis, gene transcription, energy transformation and regulation and photosynthesis. These results provide valuable insights into the alpine species adaptation and evolution.

-Complete plastid genome sequences of two species of the Neotropical genus Brunellia (Brunelliaceae)

Here we present the first two complete plastid genomes for Brunelliaceae, a Neotropical family with a single genus, Brunellia. We surveyed the entire plastid genome in order to find variable cpDNA regions for further phylogenetic analyses across the family. We sampled morphologically different species, B. antioquensis and B. trianae, and found that the plastid genomes are 157,685 and 157,775 bp in length and display the typical quadripartite structure found in angiosperms. Despite the clear morphological distinction between both species, the molecular data show a very low level of divergence. The amount of nucleotide substitutions per site is one of the lowest reported to date among published congeneric studies (π = 0.00025). The plastid genomes have gene order and content coincident with other COM (Celastrales, Oxalidales, Malpighiales) relatives. Phylogenetic analyses of selected superrosid representatives show high bootstrap support for the ((C,M)O) topology. The N-fixing clade appears as the sister group of the COM clade and Zygophyllales as the sister to the rest of the fabids group.

Analysis of complete chloroplast genomes of Curcuma and the contribution to phylogeny and adaptive evolution

Curcuma is an important member of Zingiberaceae. Many species of this genus are widely used in traditional medicine and have important cultural value in East Asia. Among them, C. longa is considered to be the main source of curcumin and has a very wide range of uses. The rapid development of molecular phylogeny has deepened our understanding of taxonomy and evolution of Curcuma. However, little is known about the chloroplast genome phylogeny and the genetic bases of adaptative evolution. In this work, we sequenced the complete chloroplast genome of 4 Curcuma species. Curcuma chloroplast genomes showed highly conserved structures and the length ranged from 159,423 bp to 152,723 bp. A total of 133 genes were observed. Multiple repeats and simple sequence repeats (SSRs) were detected. By comparing with related species, 7 highly variable regions were identified as potential specific DNA barcodes for species identification. Phylogenetic analysis of complete plastome sequences and specific data sets revealed discordance with expected genus boundary. Chloroplast phylogenetic relationships were better predicted by geography than by morphological and nuclear DNA, indicating a substantial existence of introgression. 9 genes were proved to have high posteriori probability in positive selection analysis, and 4 of them (psbA, psbD, PetA and rbcL) closely related to photosynthesis, implying that chloroplast genes may had undergone positive selection pressure in evolution. These results are of great significance for us to understand the genetic basis, phylogeny and adaptive evolution of Curcuma chloroplast.

Comparative Analyses of Euonymus Chloroplast Genomes: Genetic Structure, Screening for Loci With Suitable Polymorphism, Positive Selection Genes, and Phylogenetic Relationships Within Celastrineae

In this study, we assembled and annotated the chloroplast (cp) genome of the Euonymus species Euonymus fortunei, Euonymus phellomanus, and Euonymus maackii, and performed a series of analyses to investigate gene structure, GC content, sequence alignment, and nucleic acid diversity, with the objectives of identifying positive selection genes and understanding evolutionary relationships. The results indicated that the Euonymus cp genome was 156,860-157,611bp in length and exhibited a typical circular tetrad structure. Similar to the majority of angiosperm chloroplast genomes, the results yielded a large single-copy region (LSC) (85,826-86,299bp) and a small single-copy region (SSC) (18,319-18,536bp), separated by a pair of sequences (IRA and IRB; 26,341-26,700bp) with the same encoding but in opposite directions. The chloroplast genome was annotated to 130-131 genes, including 85-86 protein coding genes, 37 tRNA genes, and eight rRNA genes, with GC contents of 37.26-37.31%. The GC content was variable among regions and was highest in the inverted repeat (IR) region. The IR boundary of Euonymus happened expanding resulting that the rps19 entered into IR region and doubled completely. Such fluctuations at the border positions might be helpful in determining evolutionary relationships among Euonymus. The simple-sequence repeats (SSRs) of Euonymus species were composed primarily of single nucleotides (A)n and (T)n, and were mostly 10-12bp in length, with an obvious A/T bias. We identified several loci with suitable polymorphism with the potential use as molecular markers for inferring the phylogeny within the genus Euonymus. Signatures of positive selection were seen in rpoB protein encoding genes. Based on data from the whole chloroplast genome, common single copy genes, and the LSC, SSC, and IR regions, we constructed an evolutionary tree of Euonymus and related species, the results of which were consistent with traditional taxonomic classifications. It showed that E. fortunei sister to the Euonymus japonicus, whereby E. maackii appeared as sister to Euonymus hamiltonianus. Our study provides important genetic information to support further investigations into the phylogenetic development and adaptive evolution of Euonymus species.

Characterization of the Complete Chloroplast Genome of Acer truncatum Bunge (Sapindales: Aceraceae): A New Woody Oil Tree Species Producing Nervonic Acid

Acer truncatum, which is a new woody oil tree species, is an important ornamental and medicinal plant in China. To assess the genetic diversity and relationships of A. truncatum, we analyzed its complete chloroplast (cp) genome sequence. The A. truncatum cp genome comprises 156,492 bp, with the large single-copy, small single-copy, and inverted repeat (IR) regions consisting of 86,010, 18,050, and 26,216 bp, respectively. The A. truncatum cp genome contains 112 unique functional genes (i.e., 4 rRNA, 30 tRNA, and 78 protein-coding genes) as well as 78 simple sequence repeats, 9 forward repeats, 1 reverse repeat, 5 palindromic repeats, and 7 tandem repeats. We analyzed the expansion/contraction of the IR regions in the cp genomes of six Acer species. A comparison of these cp genomes indicated the noncoding regions were more diverse than the coding regions. A phylogenetic analysis revealed that A. truncatum is closely related to A. miaotaiense. Moreover, a novel ycf4-cemA indel marker was developed for distinguishing several Acer species (i.e., A. buergerianum, A. truncatum, A. henryi, A. negundo, A. ginnala, and A. tonkinense). The results of the current study provide valuable information for future evolutionary studies and the molecular barcoding of Acer species.

Comparative analyses of chloroplast genomes from 22 Lythraceae species: inferences for phylogenetic relationships and genome evolution within Myrtales

BACKGROUND

Lythraceae belongs to the order Myrtales, which is part of Archichlamydeae. The family has 31 genera containing approximately 620 species of herbs, shrubs and trees. Of these 31 genera, five large genera each possess 35 or more species. They are Lythrum, with 35; Rotala, with 45; Nesaea, with 50; Lagerstroemia, with 56; and Cuphea, with 275 species.

RESULTS

We reported six newly sequenced chloroplast (cp) genomes (Duabanga grandiflora, Trapa natans, Lythrum salicaria, Lawsonia inermis, Woodfordia fruticosa and Rotala rotundifolia) and compared them with 16 other cp genomes of Lythraceae species. The cp genomes of the 22 Lythraceae species ranged in length from 152,049 bp to 160,769 bp. In each Lythraceae species, the cp genome contained 112 genes consisting of 78 protein coding genes, four ribosomal RNAs and 30 transfer RNAs. Furthermore, we detected 211-332 simple sequence repeats (SSRs) in six categories and 7-27 long repeats in four categories. We selected ten divergent hotspots (ndhF, matK, ycf1, rpl22, rpl32, trnK-rps16, trnR-atpA, rpl32-trnL, trnH-psbA and trnG-trnR) among the 22 Lythraceae species to be potential molecular markers. We constructed phylogenetic trees from 42 Myrtales plants with 8 Geraniales plants as out groups. The relationships among the Myrtales species were effectively distinguished by maximum likelihood (ML), maximum parsimony (MP) and Bayesian inference (BI) trees constructed using 66 protein coding genes. Generally, the 22 Lythraceae species gathered into one clade, which was resolved as sister to the three Onagraceae species. Compared with Melastomataceae and Myrtaceae, Lythraceae and Onagraceae differentiated later within Myrtales.

CONCLUSIONS

The study provided ten potential molecular markers as candidate DNA barcodes and contributed cp genome resources within Myrtales for further study.

The complete chloroplast genome sequence of Alpinia oxyphylla Miq. and comparison analysis within the Zingiberaceae family

Alpinia oxyphylla Miq. (A. oxyphylla) is an important edible and traditional herbal medicine. In this study, the complete chloroplast genome of A. oxyphylla was sequenced, analysed, and compared to five species in the Zingiberaceae family. The size of the A. oxyphylla chloroplast genome was 161351 bp, which consisted of a large single-copy (LSC, 87248 bp) and small single-copy (SSC, 16175 bp) region separated by a pair of inverted repeats (IRa and IRb, 28964 bp each). The genome encoded 132 unique genes, including 87 protein-coding genes, 37 tRNAs and four rRNAs. The GC content of the genome was 36.17%. A total of 53 simple sequence repeats (SSRs) and 80 long repeats were identified in the A. oxyphylla chloroplast genome. The chloroplast genome of A. oxyphylla shared the highest sequence similarity of >90% with the chloroplast genome of A. zerumbet, and six chloroplast genomes in the Zingiberaceae family were compared by using CGView Comparison Tool (CCT). According to the phylogenetic tree, the Zingiberaceae family is divided into two categories, which coincide with the classification of the characteristics of sun-like and shade-like in plants. Our results reveal the phototrophic component of NADH-dehydrogenase (ndhB and ndhC), photosystem II (psbZ) and ATP synthase (atpE, atpF) exhibit adaptive evolution under different environments, and the strength of light is an important trigger for the adaptations at the chloroplast level.

Complete Chloroplast Genomes and Comparative Analysis of Sequences Evolution among Seven Aristolochia (Aristolochiaceae) Medicinal Species

Aristolochiaceae, comprising about 600 species, is a unique plant family containing aristolochic acids (AAs). In this study, we sequenced seven species of Aristolochia, and retrieved eleven chloroplast (cp) genomes published for comparative genomics analysis and phylogenetic constructions. The results show that the cp genomes had a typical quadripartite structure with conserved genome arrangement and moderate divergence. The cp genomes range from 159,308 bp to 160,520 bp in length and have a similar GC content of 38.5%–38.9%. A total number of 113 genes were identified, including 79 protein-coding genes, 30 tRNAs and four rRNAs. Although genomic structure and size were highly conserved, the IR-SC boundary regions were variable between these seven cp genomes. The trnH-GUG genes, are one of major differences between the plastomes of the two subgenera Siphisia and Aristolochia. We analyzed the features of nucleotide substitutions, distribution of repeat sequences and simple sequences repeats (SSRs), positive selections in the cp genomes, and identified 16 hotspot regions for genomes divergence that could be utilized as potential markers for phylogeny reconstruction. Phylogenetic relationships of the family Aristolochiaceae inferred from the 18 cp genome sequences were consistent and robust, using maximum parsimony (MP), maximum likelihood (ML), and Bayesian analysis (BI) methods.

Comparative Analysis of the Chloroplast Genomes of the Chinese Endemic Genus Urophysa and Their Contribution to Chloroplast Phylogeny and Adaptive Evolution

Urophysa is a Chinese endemic genus comprising two species, Urophysa rockii and Urophysa henryi. In this study, we sequenced the complete chloroplast (cp) genomes of these two species and of their relative Semiquilegia adoxoides. Illumina sequencing technology was used to compare sequences, elucidate the intra- and interspecies variations, and infer the phylogeny relationship with other Ranunculaceae family species. A typical quadripartite structure was detected, with a genome size from 158,473 to 158,512 bp, consisting of a pair of inverted repeats separated by a small single-copy region and a large single-copy region. We analyzed the nucleotide diversity and repeated sequences components and conducted a positive selection analysis by the codon-based substitution on single-copy coding sequence (CDS). Seven regions were found to possess relatively high nucleotide diversity, and numerous variable repeats and simple sequence repeats (SSR) markers were detected. Six single-copy genes (atpA, rpl20, psaA, atpB, ndhI, and rbcL) resulted to have high posterior probabilities of codon sites in the positive selection analysis, which means that the six genes may be under a great selection pressure. The visualization results of the six genes showed that the amino acid properties across each column of all species are variable in different genera. All these regions with high nucleotide diversity, abundant repeats, and under positive selection will provide potential plastid markers for further taxonomic, phylogenetic, and population genetics studies in Urophysa and its relatives. Phylogenetic analyses based on the 79 single-copy genes, the whole complete genome sequences, and all CDS sequences showed same topologies with high support, and U. rockii was closely clustered with U. henryi within the Urophysa genus, with S. adoxoides as their closest relative. Therefore, the complete cp genomes in Urophysa species provide interesting insights and valuable information that can be used to identify related species and reconstruct their phylogeny.

Comparative Analysis of the Complete Chloroplast Genomes of Four Aconitum Medicinal Species

Aconitum (Ranunculaceae) consists of approximately 400 species distributed in the temperate regions of the northern hemisphere. Many species are well-known herbs, mainly used for analgesia and anti-inflammatory purposes. This genus is well represented in China and has gained widespread attention for its toxicity and detoxification properties. In southwestern China, several Aconitum species, called ‘Dula’ in the Yi Nationality, were often used to control the poisonous effects of other Aconitum plants. In this study, the complete chloroplast (cp) genomes of these species were determined for the first time through Illumina paired-end sequencing. Our results indicate that their cp genomes ranged from 151,214 bp (A. episcopale) to 155,769 bp (A. delavayi) in length. A total of 111–112 unique genes were identified, including 85 protein-coding genes, 36–37 tRNA genes and eight ribosomal RNA genes (rRNA). We also analyzed codon usage, IR expansion or contraction and simple sequence repeats in the cp genomes. Eight variable regions were identified and these may potentially be useful as specific DNA barcodes for species identification of Aconitum. Phylogenetic analysis revealed that all five studied species formed a new clade and were resolved with 100% bootstrap support. This study will provide genomic resources and potential plastid markers for DNA barcoding, further taxonomy and germplasm exploration of Aconitum.

The Complete Chloroplast Genome of Heimia myrtifolia and Comparative Analysis within Myrtales

Heimia myrtifolia is an important medicinal plant with several pharmacologically active alkaloids and is also used as an ornamental landscape plant. The purpose of this study is to complete and characterize the chloroplast (cp) genome of H. myrtifolia and compare genomic features to other Myrtales species' cp genomes. The analysis showed that H. myrtifolia has a total length of 159,219 bp with a typical quadripartite structure containing two identical inverted repeats (IRs) of 25,643 bp isolated by one large single copy (LSC) of 88,571 bp and one small single copy (SSC) of 18,822 bp. The H. myrtifolia cp genome contains 129 genes with eight ribosomal RNAs, 30 transfer RNAs, and 78 protein coding genes, in which 17 genes are duplicated in two IR regions. The genome organization including gene type and number and guanine-cytosine (GC) content is analyzed among the 12 cp genomes in this study. Approximately 255 simple sequence repeats (SSRs) and 16 forward, two reverses, and two palindromic repeats were identified in the H. myrtifolia cp genome. By comparing the whole H. myrtifolia cp genome with 11 other Myrtales species, the results showed that the sequence similarity was high between coding regions while sequence divergence was high between intergenic regions. By employing the full cp genomes for phylogenetic analysis, structural and sequence differences were characterized between H. myrtifolia and 11 Myrtales species illustrating what patterns are common in the evolution of cp genomes within the Myrtales. The first entire cp genome in the genus Heimia provides a valuable resource for further studies in these medicinally and ornamentally important taxa.