Complete Chloroplast Genomes of Anthurium huixtlense and Pothos scandens (Pothoideae, Araceae): Unique Inverted Repeat Expansion and Contraction Affect Rate of Evolution

Plastid genome data provide new insights into the dynamic evolution of the tribe Ampelopsideae (Vitaceae)

BACKGROUND

Ampelopsideae J. Wen & Z.L. Nie is a small-sized tribe of Vitaceae Juss., including ca. 47 species from four genera showing a disjunct distribution worldwide across all the continents except Antarctica. There are numerous species from the tribe that are commonly used as medicinal plants with immune-modulating, antimicrobial, and anti-hypertensive properties. The tribe is usually recognized into three clades, i.e., Ampelopsis Michx., Nekemias Raf., and the Southern Hemisphere clade. However, the relationships of the three clades differ greatly between the nuclear and the plastid topologies. There has been limited exploration of the chloroplast phylogenetic relationships within Ampelopsideae, and studies on the chloroplast genome structure of this tribe are only available for a few individuals. In this study, we aimed to investigate the evolutionary characteristics of plastid genomes of the tribe, including their genome structure and evolutionary insights.

RESULTS

We sequenced, assembled, and annotated plastid genomes of 36 species from the tribe and related taxa in the family. Three main clades were recognized within Ampelopsideae, corresponding to Ampelopsis, Nekemias, and the Southern Hemisphere lineage, respectively, and all with 100% bootstrap supports. The genome sequences and content of the tribe are highly conserved. However, comparative analyses suggested that the plastomes of Nekemias demonstrate a contraction in the large single copy region and an expansion in the inverted repeat region, and possess a high number of forward and palindromic repeat sequences distinct from both Ampelopsis and the Southern Hemisphere taxa.

CONCLUSIONS

Our results highlighted plastome variations in genome length, expansion or contraction of the inverted repeat region, codon usage bias, and repeat sequences, are corresponding to the three lineages of the tribe, which probably faced with different environmental selection pressures and evolutionary history. This study provides valuable insights into understanding the evolutionary patterns of plastid genomes within the Ampelopsideae of Vitaceae.

The evolution of ephemeral flora in Xinjiang, China: insights from plastid phylogenomic analyses of Brassicaceae

BACKGROUND

The ephemeral flora of northern Xinjiang, China, plays an important role in the desert ecosystems. However, the evolutionary history of this flora remains unclear. To gain new insights into its origin and evolutionary dynamics, we comprehensively sampled ephemeral plants of Brassicaceae, one of the essential plant groups of the ephemeral flora.

RESULTS

We reconstructed a phylogenetic tree using plastid genomes and estimated their divergence times. Our results indicate that ephemeral species began to colonize the arid areas in north Xinjiang during the Early Miocene and there was a greater dispersal of ephemeral species from the surrounding areas into the ephemeral community of north Xinjiang during the Middle and Late Miocene, in contrast to the Early Miocene or Pliocene periods.

CONCLUSIONS

Our findings, together with previous studies, suggest that the ephemeral flora originated in the Early Miocene, and species assembly became rapid from the Middle Miocene onwards, possibly attributable to global climate changes and regional geological events.

Comparatively analyzing of chloroplast genome and new insights into phylogenetic relationships regarding the genus Stephania

The medicinal plant of the genus Stephania holds significant economic importance in the pharmaceutical industry. However, accurately classifying and subdividing this genus remains a challenge. Herein, the chloroplast (cp) genomes of Stephania and Cyclea were sequenced, and the primary characteristics, repeat sequences, inverted repeats regions, simple sequence repeats, and codon usage bias of 17 species were comparatively analyzed. Twelve markers were identified through genome alignment and sliding window analysis. Moreover, a molecular clock analysis revealed the divergence between subgenus (subg.) Botryodiscia and the combined Cyclea, subg. Stephania and Tuberiphania during the early Oligocene epoch. Notably, the raceme-type inflorescence represents the ancestral state of the Stephania and Cyclea. The genetic relationships inferred from the cp genome and protein-coding genes exhibited similar topologies. Additionally, the paraphyletic relationship between the genera Cyclea and Stephania was confirmed. Bayesian inference, maximum likelihood, and neighbor-joining trees consistently showed that section Tuberiphania and Transcostula were non-monophyletic. In conclusion, this research provides valuable insights for further investigations into species identification, evolution, and phylogenetics within the Stephania genus.

The complete chloroplast genome sequence of Amorphophallus konjac (Araceae) from Yunnan, China and its phylogenetic analysis in the family Araceae

This work determined and analyzed the complete chloroplast genome sequence of Amorphophallus konjac K. Koch ex N.E.Br 1858 from Yunnan, China. The genome size was 167,470 bp, of which contains a large single-copy region (LSC 93,443 bp), a small single-copy region (SSC 21,575 bp), and a pair of inverted repeat regions (IR 26,226 bp). The chloroplast genome has 131 genes, including 86 protein-coding genes, 37 tRNAs, and eight rRNAs. A previous study reported deletion of accD, psbE, and trnG-GCC genes in the A. konjac chloroplast genome. Our study supports the conservative structure of A. konjac and does not support the gene deletion mentioned above. Phylogenetic analysis indicated that A. konjac shares a close relationship with another A. konjac (collected from Guizhou) and A. titanium by forming a clade in the genus Amorphophallus. Our results provide some useful information to the evolution of the family Araceae.

The complete chloroplast genome assembly of Amorphophallus krausei Engler, Pflanzenr 1911 (Araceae) from southwestern China

Plants in the genus Amorphophallus, many of which possess high konjac glucomannan content, are considered important cash crops in many Asian countries. Wild relatives of cultivated Amorphophallus species are valuable resources for the genetic improvement of these crops. To aid in future genetic research of wild germplasm resources of Amorphophallus, a single individual of Amorphophallus krausei Engler, Pflanzenr 1911 was collected from southwestern China, and its chloroplast genome was sequenced using next-generation sequencing technologies. The assembled chloroplast genome was 172,418 bp in length with a GC content of 35.23% (GenBank accession no. OR416863). A typical quadripartite structure was found in the genome, which was comprised of one large single-copy (LSC), one small single-copy (SSC), and two inverted repeats (IRs), with lengths of 91,983 bp, 15,591 bp, 32,422 bp, and 32,422 bp, respectively. A total of 132 genes were annotated in the genome, including 86 protein-coding genes, 38 tRNAs, and 8 rRNAs. A maximum likelihood (ML) tree of A. krausei and 17 other species in the family Araceae suggested that all Amorphophallus species formed a single monophyletic clade. A close relationship among A. konjac, A. albus, and A. krausei was also revealed by the phylogenetic tree. The newly sequenced chloroplast genome of A. krausei will support future genetic studies, particularly the assessment of genetic diversity, resource conservation, and phylogeographic research.

IRplus: An Augmented Tool to Detect Inverted Repeats in Plastid Genomes

High-throughput sequencing methods have increased the accessibility of plastid genomes, which are crucial for clarifying phylogenetic relationships. Current large sequencing efforts require software tools for routine display of their distinctive quadripartite structure, which is denoted by four junction sites. By concentrating on these junctions and their close vicinity, IRscope has emerged as the standard tool for detection of this structure and creating simplified comparative graphical maps of plastid genomes. Here, we provide an augmented version (IRplus) that encompasses a novel set of functions such as integrated error detection, flexible color schemes, and an upgraded method to detect inverted repeats in genomic sequences. Spanning across the plant tree of life, IRplus allows the quick visualization of various sets of plastid genomes and features, next to smooth interoperability with other widely used annotation file formats and platforms. The IRplus can be accessed at https://irscope.shinyapps.io/IRplus/, and source codes are freely available at https://github.com/AmiryousefiLab/IRplus.

Comparative plastome genomics, taxonomic delimitation and evolutionary divergences of Tetraena hamiensis var. qatarensis and Tetraena simplex (Zygophyllaceae)

The Zygophyllum and Tetraena genera are intriguingly important ecologically and medicinally. Based on morphological characteristics, T. hamiensis var. qatarensis, and T. simplex were transferred from Zygophyllum to Tetraena with the least genomic datasets available. Hence, we sequenced the T. hamiensis and T. simplex and performed in-depth comparative genomics, phylogenetic analysis, and estimated time divergences. The complete plastomes ranged between 106,720 and 106,446 bp-typically smaller than angiosperms plastomes. The plastome circular genomes are divided into large single-copy regions (~ 80,964 bp), small single-copy regions (~ 17,416 bp), and two inverted repeats regions (~ 4170 bp) in both Tetraena species. An unusual shrinkage of IR regions 16-24 kb was identified. This resulted in the loss of 16 genes, including 11 ndh genes which encode the NADH dehydrogenase subunits, and a significant size reduction of Tetraena plastomes compared to other angiosperms. The inter-species variations and similarities were identified using genome-wide comparisons. Phylogenetic trees generated by analyzing the whole plastomes, protein-coding genes, matK, rbcL, and cssA genes exhibited identical topologies, indicating that both species are sisters to the genus Tetraena and may not belong to Zygophyllum. Similarly, based on the entire plastome and proteins coding genes datasets, the time divergence of Zygophyllum and Tetraena was 36.6 Ma and 34.4 Ma, respectively. Tetraena stem ages were 31.7 and 18.2 Ma based on full plastome and protein-coding genes. The current study presents the plastome as a distinguishing and identification feature among the closely related Tetraena and Zygophyllum species. It can be potentially used as a universal super-barcode for identifying plants.

The complete chloroplast genome sequence of Anthurium andraeanum Linden (Araceae; Pothoideae)

The chloroplast genome of Anthurium andraeanum Linden 1877 was assembled and analyzed in this study. The genome size is 162,560 bp, of which contains a large single-copy (LSC) region with 88,814 bp, a small single-copy (SSC) region with 22,856 bp, and two inverted repeat regions (IRA and IRB) with 25,445 bp, respectively. The plastome contains 124 genes, including 80 protein-coding genes, 37 tRNAs, six rRNAs and one pseudogene. Phylogenetic analysis indicated that A. andraeanum is a member of Pothoideae and sister to A. huixtlense.

CPJSdraw: analysis and visualization of junction sites of chloroplast genomes

Background

Chloroplast genomes are usually circular molecules, and most of them are tetrad structures with two inverted repeat (IR) regions, a large single-copy region, and a small single-copy region. IR contraction and expansion are among the genetic diversities during the evolution of plant chloroplast genomes. The only previously released tool for the visualization of junction sites of the regions does not consider the diversity of the starting point of genomes, which leads to incorrect results or even no results for the examination of IR contraction and expansion.

Results

In this work, a new tool named CPJSdraw was developed for visualizing the junction sites of chloroplast genomes. CPJSdraw can format the starting point of the irregular linearized genome, correct the junction sites of IR and single-copy regions, display the tetrad structure, visualize the junction sites of any number (≥1) of chloroplast genomes, show the transcription direction of genes adjacent to junction sites, and indicate the IR expansion or contraction of chloroplast genomes.

Conclusions

CPJSdraw is a software that is universal and reliable in analysis and visualization of IR expansion or contraction of chloroplast genomes. CPJSdraw has more accurate analysis and more complete functions when compared with previously released tool. CPJSdraw as a perl package and tested data are available at http://dx.doi.org/10.5281/zenodo.7669480 for English users. In addition, an online version with a Chinese interface is available at http://cloud.genepioneer.com:9929/#/tool/alltool/detail/335.

Characterization of the Complete Chloroplast Genome and Phylogenetic Implications of Euonymus microcarpus (Oliv.) Sprague

Euonymus microcarpus (Oliv.) Sprague, is a species of evergreen shrub of the genus Euonymus, family Celastraceae. Here, we extracted the genomic DNA from the leaves of E. microcarpus and constructed a paired-end library. The chloroplast genome of E. microcarpus was generated with the high-throughput sequencing by the illumina Hiseq X Ten platform and de novo assembly. The chloroplast genome had a quadripartite structure, containing a long single copy region with a size of 85,386 bp and a short single copy region with a size of 18,456 bp, separated by two inverted repeat regions of 26,850 bp. The chloroplast genome contained 133 genes identified in total, including 87 potential protein-coding genes, 38 transfer RNA genes, and eight ribosomal RNA genes. A total of 282 simple sequence repeats and 63 long repeats were found. Furthermore, the phylogenetic relationships inferred that E. microcarpus is sister to E. japonicus and E. schensianus. A comparison of the structure of the chloroplast genomes of eight Euonymus species suggests a nucleotide variability of the junction sites and a higher divergence of non-coding regions, compared to the coding regions. The original findings of the study serves as a good reference for chloroplast genome assembly and a valuable foundation for the genetic diversity and evolution of E. microcarpus.

A Large Intergenic Spacer Leads to the Increase in Genome Size and Sequential Gene Movement around IR/SC Boundaries in the Chloroplast Genome of Adiantum malesianum (Pteridaceae)

Expansion and contraction (ebb and flow events) of inverted repeat (IR) boundaries occur and are generally considered to be major factors affecting chloroplast (cp) genome size changes. Nonetheless, the Adiantum malesianum cp genome does not seem to follow this pattern. We sequenced, assembled and corrected the A. flabellulatum and A. malesianum cp genomes using the Illumina NovaSeq6000 platform, and we performed a comparative genome analysis of six Adiantum species. The results revealed differences in the IR/SC boundaries of A. malesianum caused by a 6876 bp long rpoB-trnD-GUC intergenic spacer (IGS) in the LSC. This IGS may create topological tension towards the LSC/IRb boundary in the cp genome, resulting in a sequential movement of the LSC genes. Consequently, this leads to changes of the IR/SC boundaries and may even destroy the integrity of trnT-UGU, which is located in IRs. This study provides evidence showing that it is the large rpoB-trnD-GUC IGS that leads to A. malesianum cp genome size change, rather than ebb and flow events. Then, the study provides a model to explain how the rpoB-trnD-GUC IGS in LSC affects A. malesianum IR/SC boundaries. Moreover, this study also provides useful data for dissecting the evolution of cp genomes of Adiantum. In future research, we can expand the sample to Pteridaceae to test whether this phenomenon is universal in Pteridaceae.

Comparative chloroplast genomics provides insights into the genealogical relationships of endangered Tetraena mongolica and the chloroplast genome evolution of related Zygophyllaceae species

A comprehensive understanding of genetic background for rare species will provide an important theoretical basis for the future species management, monitoring and conservation. Tetraena mongolica is restrictedly distributed in the western Ordos plateau of China and has been listed as a national protected plant. We generated 13 chloroplast (cp) genomes of T. mongolica (size range of 106,062-106,230 bp) and conducted a series of comparative analyses of six Zygophyllaceae cp genomes. T. mongolica cp genome exhibited a quadripartite structure with drastically reduced inverted repeats (IRs, 4,315 bp) and undergone the loss of a suit of ndh genes and a copy of rRNAs. Furthermore, all the T. mongolica populations were divided into two genetic groups based on complete cp phylogenomics. In addition, notably variable genome size, gene order and structural changes had been observed among the six Zygophyllaceae cp genomes. Overall, our findings provide insights into the cp genome evolution mode and intraspecific relationships of T. mongolica, and provide a molecular basis for scientific conservation of this endangered plant.

Cold Resistance of Euonymus japonicus Beihaidao Leaves and Its Chloroplast Genome Structure and Comparison with Celastraceae Species

Euonymus japonicus Beihaidao is one of the most economically important ornamental species of the Euonymus genus. There are approximately 97 genera and 1194 species of plants worldwide in this family (Celastraceae). Using E. japonicus Beihaidao, we conducted a preliminary study of the cold resistance of this species, evaluated its performance during winter, assembled and annotated its chloroplast genome, and performed a series of analyses to investigate its gene structure GC content, sequence alignment, and nucleic acid diversity. Our objectives were to understand the evolutionary relationships of the genus and to identify positive selection genes that may be related to adaptations to environmental change. The results indicated that E. japonicus Beihaidao leaves have certain cold resistance and can maintain their viability during wintering. Moreover, the chloroplast genome of E. japonicus Beihaidao is a typical double-linked ring tetrad structure, which is similar to that of the other four Euonymus species, E. hamiltonianus, E. phellomanus, E. schensianus, and E. szechuanensis, in terms of gene structure, gene species, gene number, and GC content. Compared to other Celastraceae species, the variation in the chloroplast genome sequence was lower, and the gene structure was more stable. The phylogenetic relationships of 37 species inferred that members of the Euonymus genus do not form a clade and that E. japonicus Beihaidao is closely related to E. japonicus and E. fortunei. A total of 11 functional positive selected genes were identified, which may have played an important role in the process of Celastraceae species adapting to environmental changes. Our study provides important genetic information to support further investigations into the phylogenetic development and adaptive evolution of Celastraceae species.

Comparative chloroplast genomes and phylogenetic relationships of Aglaonema modestum and five variegated cultivars of Aglaonema

Aglaonema, commonly called Chinese evergreens, are widely used for ornamental purposes. However, attempts to identify Aglaonema species and cultivars based on leaf morphology have been challenging. In the present study, chloroplast sequences were used to elucidate the phylogenetic relationships of cultivated Aglaonema in South China. The chloroplast genomes of one green species and five variegated cultivars of Aglaonema, Aglaonema modestum, ‘Red Valentine’, ‘Lady Valentine’, ‘Hong Yan’, ‘Hong Jian’, and ‘Red Vein’, were sequenced for comparative and phylogenetic analyses. The six chloroplast genomes of Aglaonema had typical quadripartite structures, comprising a large single copy (LSC) region (91,092–91,769 bp), a small single copy (SSC) region (20,816–26,501 bp), and a pair of inverted repeat (IR) regions (21,703–26,732 bp). The genomes contained 112 different genes, including 79–80 protein coding genes, 28–29 tRNAs and 4 rRNAs. The molecular structure, gene order, content, codon usage, long repeats, and simple sequence repeats (SSRs) were generally conserved among the six sequenced genomes, but the IR-SSC boundary regions were significantly different, and ‘Red Vein’ had a distinct long repeat number and type frequency. For comparative and phylogenetic analyses, Aglaonema costatum was included; it was obtained from the GenBank database. Single-nucleotide polymorphisms (SNPs) and insertions/deletions (indels) were determined among the seven Aglaonema genomes studied. Nine divergent hotspots were identified: trnH-GUG-CDS1_psbA, trnS-GCU_trnS-CGA-CDS1, rps4-trnT-UGU, trnF-GAA-ndhJ, petD-CDS2-rpoA, ycf1-ndhF, rps15-ycf1-D2, ccsA-ndhD, and trnY-GUA-trnE-UUC. Additionally, positive selection was found for rpl2, rps2, rps3, ycf1 and ycf2 based on the analyses of Ka/Ks ratios among 16 Araceae chloroplast genomes. The phylogenetic tree based on whole chloroplast genomes strongly supported monophyletic Aglaonema and clear relationships among Aroideae, Lasioideae, Lemnoideae, Monsteroideae, Orontioideae, Pothoideae and Zamioculcadoideae in the family Araceae. By contrast, protein coding gene phylogenies were poorly to strongly supported and incongruent with the whole chloroplast genome phylogenetic tree. This study provided valuable genome resources and helped identify Aglaonema species and cultivars.

Comparative chloroplast genomes and phylogenetic analyses of Pinellia

Background

Pinellia Tenore (Araceae) is a genus of perennial herbaceous plants, all of which have medicinal value. The chloroplast (cp) genome data of Pinellia are scarce, and the phylogenetic relationship and gene evolution remain unclear.

Methods and results

We sequenced and annotated the Pinellia pedatisecta cp genome and combined it with previously published genomes for other Pinellia species. We used bioinformatics methods to analyse the genomic structure, repetitive sequences, interspecific variation, divergence hotspots, phylogenetic relationships, divergence time estimation and selective pressure of four Pinellia plastomes. Results showed that the cp genomes of Pinellia varied in length between 168,178 (P. pedatisecta MN046890) and 164,013 bp (P. ternata KR270823). A total of 68–111 SSR loci were identified as candidate molecular markers for further genetic diversity study. Eight mutational hotspot regions were determined, including psbI-trnG-UCC, psbM-rpoB, ndhJ-trnT-UGU, trnP-UGG-trnW-CCA, ndhF-trnN-GUU, ndhG-ndhE, ycf1-rps15 and trnR-ycf1. Gene selection pressure suggested that four genes were subjected to positive selection. Phylogenetic inferences based on the complete cp genomes revealed a sister relationship between Pinellia and Arisaema plants whose divergence was estimated to occur around 22.48 million years ago. All Pinellia species formed a monophyletic evolutionary clade in which P. peltata, rather than P. pedatisecta, earlier diverged, indicating that P. pedatisecta is not the basal taxon of Pinellia but P. peltata may be.

Conclusions

The cp genomes of Pinellia will provide valuable information for species classification, identification, molecular breeding and evolutionary exploration of the genus Pinellia.

Supplementary Information

The online version of this article (10.1007/s11033-022-07617-5) contains supplementary material, which is available to authorized users.

Complete chloroplast genome sequences of three aroideae species (Araceae): lights into selective pressure, marker development and phylogenetic relationships

Background

Colocasia gigantea, Caladium bicolor and Xanthosoma sagittifolium are three worldwide famous ornamental and/or vegetable plants in the Araceae family, these species in the subfamily Aroideae are phylogenetically perplexing due to shared interspecific morphological traits and variation.

Result

This study, for the first time ever, assembled and analyzed complete chloroplast genomes of C. gigantea, C. bicolor and X. sagittifolium with genome sizes of 165,906 bp, 153,149 bp and 165,169 bp in length, respectively. The genomes were composed of conserved quadripartite circular structures with a total of 131 annotated genes, including 8 rRNA, 37 tRNA and 86 protein-coding genes. A comparison within Aroideae showed seven protein-coding genes (accD, ndhF, ndhK, rbcL, rpoC1, rpoC2 and matK) linked to environmental adaptation. Phylogenetic analysis confirmed a close relationship of C. gigantea with C. esculenta and S. colocasiifolia, and the C. bicolor with X. sagittifolium. Furthermore, three DNA barcodes (atpH-atpI + psaC-ndhE, atpH-atpI + trnS-trnG, atpH-atpI + psaC-ndhE + trnS-trnG) harbored highly variable regions to distinguish species in Aroideae subfamily.

Conclusion

These results would be beneficial for species identification, phylogenetic relationship, genetic diversity, and potential of germplasm resources in Aroideae.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08400-3.

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.

Phylogenomic and comparative analyses of Coffeeae alliance (Rubiaceae): deep insights into phylogenetic relationships and plastome evolution

BACKGROUND

The large and diverse Coffeeae alliance clade of subfamily Ixoroideae (Rubiaceae) consists of 10 tribes, > 90 genera, and > 2000 species. Previous molecular phylogenetics using limited numbers of markers were often unable to fully resolve the phylogenetic relationships at tribal and generic levels. Also, the structural variations of plastomes (PSVs) within the Coffeeae alliance tribes have been poorly investigated in previous studies. To fully understand the phylogenetic relationships and PSVs within the clade, highly reliable and sufficient sampling with superior next-generation analysis techniques is required. In this study, 71 plastomes (40 newly sequenced and assembled and the rest from the GenBank) were comparatively analyzed to decipher the PSVs and resolve the phylogenetic relationships of the Coffeeae alliance using four molecular data matrices.

RESULTS

All plastomes are typically quadripartite with the size ranging from 153,055 to 155,908 bp and contained 111 unique genes. The inverted repeat (IR) regions experienced multiple contraction and expansion; five repeat types were detected but the most abundant was SSR. The size of the Coffeeae alliance clade plastomes and its elements are affected by the IR boundary shifts and the repeat types. However, the emerging PSVs had no taxonomic and phylogenetic implications. Eight highly divergent regions were identified within the plastome regions ndhF, ccsA, ndhD, ndhA, ndhH, ycf1, rps16-trnQ-UUG, and psbM-trnD. These highly variable regions may be potential molecular markers for further species delimitation and population genetic analyses for the clade. Our plastome phylogenomic analyses yielded a well-resolved phylogeny tree with well-support at the tribal and generic levels within the Coffeeae alliance.

CONCLUSIONS

Plastome data could be indispensable in resolving the phylogenetic relationships of the Coffeeae alliance tribes. Therefore, this study provides deep insights into the PSVs and phylogenetic relationships of the Coffeeae alliance and the Rubiaceae family as a whole.

Comparison of Magnoliaceae Plastomes: Adding Neotropical Magnolia to the Discussion

Chloroplast genomes are considered to be highly conserved. Nevertheless, differences in their sequences are an important source of phylogenetically informative data. Chloroplast genomes are increasingly applied in evolutionary studies of angiosperms, including Magnoliaceae. Recent studies have focused on resolving the previously debated classification of the family using a phylogenomic approach and chloroplast genome data. However, most Neotropical clades and recently described species have not yet been included in molecular studies. We performed sequencing, assembly, and annotation of 15 chloroplast genomes from Neotropical Magnoliaceae species. We compared the newly assembled chloroplast genomes with 22 chloroplast genomes from across the family, including representatives from each genus and section. Family-wide, the chloroplast genomes presented a length of about 160 kb. The gene content in all species was constant, with 145 genes. The intergenic regions showed a higher level of nucleotide diversity than the coding regions. Differences were higher among genera than within genera. The phylogenetic analysis in Magnolia showed two main clades and corroborated that the current infrageneric classification does not represent natural groups. Although chloroplast genomes are highly conserved in Magnoliaceae, the high level of diversity of the intergenic regions still resulted in an important source of phylogenetically informative data, even for closely related taxa.

Identification of evolutionary relationships and DNA markers in the medicinally important genus Fritillaria based on chloroplast genomics

The genus Fritillaria has attracted great attention because of its medicinal and ornamental values. At least three reasons, including the accurate discrimination between various Fritillaria species, protection and sustainable development of rare Fritillaria resources as well as understanding of relationship of some perplexing species, have prompted phylogenetic analyses and development of molecular markers for Fritillaria species. Here we determined the complete chloroplast (CP) genomes for F. unibracteata, F. przewalskii, F. delavayi, and F. sinica through Illumina sequencing, followed by de novo assembly. The lengths of the genomes ranged from 151,076 in F. unibracteata to 152,043 in F. przewalskii. Those CP genomes displayed a typical quadripartite structure, all including a pair of inverted repeats (26,078 to 26,355 bp) separated by the large single-copy (81,383 to 81,804 bp) and small single-copy (17,537 to 17,569 bp) regions. Fritillaria przewalskii, F. delavayi, and F. sinica equivalently encoded 133 unique genes consisting of 38 transfer RNA genes, eight ribosomal RNA genes, and 87 protein coding genes, whereas F. unibracteata contained 132 unique genes due to absence of the rps16 gene. Subsequently, comparative analysis of the complete CP genomes revealed that ycf1, trnL, trnF, ndhD, trnN-trnR, trnE-trnT, trnN, psbM-trnD, atpI, and rps19 to be useful molecular markers in taxonomic studies owning to their interspecies variations. Based on the comprehensive CP genome data collected from 53 species in Fritillaria and Lilium genera, a phylogenomic study was carried out with three Cardiocrinum species and five Amana species as outgroups. The results of the phylogenetic analysis showed that Fritillaria was a sister to Lilium, and the interspecies relationships within subgenus Fritillaria were well resolved. Furthermore, phylogenetic analysis based on the CP genome was proved to be a promising method in selecting potential novel medicinal resources to substitute current medicinal species that are on the verge of extinction.

Comparative and Phylogenetic Analysis Based on the Chloroplast Genome of Coleanthus subtilis (Tratt.) Seidel, a Protected Rare Species of Monotypic Genus

Coleanthus subtilis (Tratt.) Seidel (Poaceae) is an ephemeral grass from the monotypic genus Coleanthus Seidl, which grows on wet muddy areas such as fishponds or reservoirs. As a rare species with strict habitat requirements, it is protected at international and national levels. In this study, we sequenced its whole chloroplast genome for the first time using the next-generation sequencing (NGS) technology on the Illumina platform, and performed a comparative and phylogenetic analysis with the related species in Poaceae. The complete chloroplast genome of C. subtilis is 135,915 bp in length, with a quadripartite structure having two 21,529 bp inverted repeat regions (IRs) dividing the entire circular genome into a large single copy region (LSC) of 80,100 bp and a small single copy region (SSC) of 12,757 bp. The overall GC content is 38.3%, while the GC contents in LSC, SSC, and IR regions are 36.3%, 32.4%, and 43.9%, respectively. A total of 129 genes were annotated in the chloroplast genome, including 83 protein-coding genes, 38 tRNA genes, and 8 rRNA genes. The accD gene and the introns of both clpP and rpoC1 genes were missing. In addition, the ycf1, ycf2, ycf15, and ycf68 were pseudogenes. Although the chloroplast genome structure of C. subtilis was found to be conserved and stable in general, 26 SSRs and 13 highly variable loci were detected, these regions have the potential to be developed as important molecular markers for the subfamily Pooideae. Phylogenetic analysis with species in Poaceae indicated that Coleanthus and Phippsia were sister groups, and provided new insights into the relationship between Coleanthus, Zingeria, and Colpodium. This study presents the initial chloroplast genome report of C. subtilis, which provides an essential data reference for further research on its origin.

Comparative Chloroplast Genome Analyses of the Winter-Blooming Eastern Asian Endemic Genus Chimonanthus (Calycanthaceae) With Implications For Its Phylogeny and Diversification

Chimonanthus of Calycanthaceae is a small endemic genus in China, with unusual winter-blooming sweet flowers widely cultivated for ornamentals and medicinal uses. The evolution of Chimonanthus plastomes and its phylogenetic relationships remain unresolved due to limited availability of genetic resources. Here, we report fully assembled and annotated chloroplast genomes of five Chimonanthus species. The chloroplast genomes of the genus (size range 153,010 – 153,299 bp) reveal high similarities in gene content, gene order, GC content, codon usage, amino acid frequency, simple sequence repeats, oligonucleotide repeats, synonymous and non-synonymous substitutions, and transition and transversion substitutions. Signatures of positive selection are detected in atpF and rpoB genes in C. campanulatus. The correlations among substitutions, InDels, and oligonucleotide repeats reveal weak to strong correlations in distantly related species at the intergeneric levels, and very weak to weak correlations among closely related Chimonanthus species. Chloroplast genomes are used to reconstruct a well-resolved phylogenetic tree, which supports the monophyly of Chimonanthus. Within Chimonanthus, C. praecox and C. campanulatus form one clade, while C. grammatus, C. salicifolius, C. zhejiangensis, and C. nitens constitute another clade. Chimonanthus nitens appears paraphyletic and is closely related to C. salicifolius and C. zhejiangensis, suggesting the need to reevaluate the species delimitation of C. nitens. Chimonanthus and Calycanthus diverged in mid-Oligocene; the radiation of extant Chimonanthus species was dated to the mid-Miocene, while C. grammatus diverged from other Chimonanthus species in the late Miocene. C. salicifolius, C. nitens(a), and C. zhejiangensis are inferred to have diverged in the Pleistocene of the Quaternary period, suggesting recent speciation of a relict lineage in the subtropical forest regions in eastern China. This study provides important insights into the chloroplast genome features and evolutionary history of Chimonanthus and family Calycanthaceae.

Lemnaceae and Orontiaceae Are Phylogenetically and Morphologically Distinct from Araceae

Duckweeds comprise a distinctive clade of pleustophytic monocots that traditionally has been classified as the family Lemnaceae. However, molecular evidence has called into question their phylogenetic independence, with some authors asserting instead that duckweeds should be reclassified as subfamily Lemnoideae of an expanded family Araceae. Although a close phylogenetic relationship of duckweeds with traditional Araceae has been supported by multiple studies, the taxonomic disposition of duckweeds must be evaluated more critically to promote nomenclatural stability and utility. Subsuming duckweeds as a morphologically incongruent lineage of Araceae effectively eliminates the family category of Lemnaceae that has been widely used for many years. Instead, we suggest that Araceae subfamily Orontioideae should be restored to family status as Orontiaceae, which thereby would enable the recognition of three morphologically and phylogenetically distinct lineages: Araceae, Lemnaceae, and Orontiaceae.

Comparative plastome analysis of Blumea, with implications for genome evolution and phylogeny of Asteroideae

The genus Blumea (Asteroideae, Asteraceae) comprises about 100 species, including herbs, shrubs, and small trees. Previous studies have been unable to resolve taxonomic issues and the phylogeny of the genus Blumea due to the low polymorphism of molecular markers. Therefore, suitable polymorphic regions need to be identified. Here, we de novo assembled plastomes of the three Blumea species B. oxyodonta, B. tenella, and B. balsamifera and compared them with 26 other species of Asteroideae after correction of annotations. These species have quadripartite plastomes with similar gene content, genome organization, and inverted repeat contraction and expansion comprising 113 genes, including 80 protein-coding, 29 transfer RNA, and 4 ribosomal RNA genes. The comparative analysis of codon usage, amino acid frequency, microsatellite repeats, oligonucleotide repeats, and transition and transversion substitutions has revealed high resemblance among the newly assembled species of Blumea. We identified 10 highly polymorphic regions with nucleotide diversity above 0.02, including rps16-trnQ, ycf1, ndhF-rpl32, petN-psbM, and rpl32-trnL, and they may be suitable for the development of robust, authentic, and cost-effective markers for barcoding and inference of the phylogeny of the genus Blumea. Among these highly polymorphic regions, five regions also co-occurred with oligonucleotide repeats and support use of repeats as a proxy for the identification of polymorphic loci. The phylogenetic analysis revealed a close relationship between Blumea and Pluchea within the tribe Inuleae. At tribe level, our phylogeny supports a sister relationship between Astereae and Anthemideae rooted as Gnaphalieae, Calenduleae, and Senecioneae. These results are contradictory to recent studies which reported a sister relationship between "Senecioneae and Anthemideae" and "Astereae and Gnaphalieae" or a sister relationship between Astereae and Gnaphalieae rooted as Calenduleae, Anthemideae, and then Senecioneae using nuclear genome sequences. The conflicting phylogenetic signals observed at the tribal level between plastidt and nuclear genome data require further investigation.

Mutational Dynamics of Aroid Chloroplast Genomes II

The co-occurrence among single nucleotide polymorphisms (SNPs), insertions-deletions (InDels), and oligonucleotide repeats has been reported in prokaryote, eukaryote, and chloroplast genomes. Correlations among SNPs, InDels, and repeats have been investigated in the plant family Araceae previously using pair-wise sequence alignments of the chloroplast genomes of two morphotypes of one species, Colocasia esculenta belonging to subfamily Aroideae (crown group), and four species from the subfamily Lemnoideae, a basal group. The family Araceae is a large family comprising 3,645 species in 144 genera, grouped into eight subfamilies. In the current study, we performed 34 comparisons using 27 species from 7 subfamilies of Araceae to determine correlation coefficients among the mutational events at the family, subfamily, and genus levels. We express strength of the correlations as: negligible or very weak (0.10–0.19), weak (0.20–0.29), moderate (0.30–0.39), strong (0.40–0.69), very strong (0.70–0.99), and perfect (1.00). We observed strong/very strong correlations in most comparisons, whereas a few comparisons showed moderate correlations. The average correlation coefficient was recorded as 0.66 between “SNPs and InDels,” 0.50 between “InDels and repeats,” and 0.42 between “SNPs and repeats.” In qualitative analyses, 95–100% of the repeats at family and sub-family level, while 36–86% of the repeats at genus level comparisons co-occurred with SNPs in the same bins. Our findings show that such correlations among mutational events exist throughout Araceae and support the hypothesis of distribution of oligonucleotide repeats as a proxy for mutational hotspots.

Comparative Chloroplast Genomics of Sophora Species: Evolution and Phylogenetic Relationships in the Early-Diverging Legume Subfamily Papilionoideae (Fabaceae)

The taxonomy and evolutionary history of Sophora L., a genus with high economic and medicinal value, remain uncertain due to the absence of genetic resource (especially in China) and low polymorphism of molecular markers. Our aim was to elucidate the molecular evolution and phylogenetic relationships in chloroplast genomes of Sophora species in the early-diverging legume subfamily Papilionoideae (Fabaceae). We reported nine Sophora chloroplast genome from China using Illumina sequencing. We performed a series of analyses with previously published genomes of Sophora species to investigate their genomic characteristics, identified simple sequence repeats, large repeat sequences, tandem repeats, and highly polymorphic loci. The genomes were 152,953-158,087 bp in length, and contained 111-113 unique genes, including 76-78 protein coding, 31 tRNA, and 4 rRNA. The expansion of inverted repeat boundary of Sophora resulted in rps12 entering into the LSC region and loss of trnT-CGU gene in some species. Also, we found an approximately 23 kb inversion between trnC-GCA and trnF-GAA within the genus. In addition, we identified seven highly polymorphic loci (pi (π) > 0.035) suitable for inferring the phylogeny of Sophora species. Among these, three regions also co-occurred with large repeat sequences and support use of repeats as a proxy for the identification of polymorphic loci. Based on whole chloroplast genome and protein-coding sequences data-set, a well-supported phylogenetic tree of Sophora and related taxa showed that this genus is monophyletic, but sect. Disamaea and sect. Sophora, are incongruent with traditional taxonomic classifications based on fruit morphology. Our finding provides significant genetic resources to support further investigation into the phylogenetic relationship and evolution of the genus Sophora.

Chloroplast genomes elucidate diversity, phylogeny, and taxonomy of Pulsatilla (Ranunculaceae)

Pulsatilla (Ranunculaceae) consists of about 40 species, and many of them have horticultural and/or medicinal value. However, it is difficult to recognize and identify wild Pulsatilla species. Universal molecular markers have been used to identify these species, but insufficient phylogenetic signal was available. Here, we compared the complete chloroplast genomes of seven Pulsatilla species. The chloroplast genomes of Pulsatilla were very similar and their length ranges from 161,501 to 162,669 bp. Eight highly variable regions and potential sources of molecular markers such as simple sequence repeats, large repeat sequences, and single nucleotide polymorphisms were identified, which are valuable for studies of infra- and inter-specific genetic diversity. The SNP number differentiating any two Pulsatilla chloroplast genomes ranged from 112 to 1214, and provided sufficient data for species delimitation. Phylogenetic trees based on different data sets were consistent with one another, with the IR, SSC regions and the barcode combination rbcL + matK + trnH-psbA produced slightly different results. Phylogenetic relationships within Pulsatilla were certainly resolved using the complete cp genome sequences. Overall, this study provides plentiful chloroplast genomic resources, which will be helpful to identify members of this taxonomically challenging group in further investigation.

Comparison of Chloroplast Genomes among Species of Unisexual and Bisexual Clades of the Monocot Family Araceae

The chloroplast genome provides insight into the evolution of plant species. We de novo assembled and annotated chloroplast genomes of four genera representing three subfamilies of Araceae: Lasia spinosa (Lasioideae), Stylochaeton bogneri, Zamioculcas zamiifolia (Zamioculcadoideae), and Orontium aquaticum (Orontioideae), and performed comparative genomics using these chloroplast genomes. The sizes of the chloroplast genomes ranged from 163,770 bp to 169,982 bp. These genomes comprise 113 unique genes, including 79 protein-coding, 4 rRNA, and 30 tRNA genes. Among these genes, 17-18 genes are duplicated in the inverted repeat (IR) regions, comprising 6-7 protein-coding (including trans-splicing gene rps12), 4 rRNA, and 7 tRNA genes. The total number of genes ranged between 130 and 131. The infA gene was found to be a pseudogene in all four genomes reported here. These genomes exhibited high similarities in codon usage, amino acid frequency, RNA editing sites, and microsatellites. The oligonucleotide repeats and junctions JSB (IRb/SSC) and JSA (SSC/IRa) were highly variable among the genomes. The patterns of IR contraction and expansion were shown to be homoplasious, and therefore unsuitable for phylogenetic analyses. Signatures of positive selection were seen in three genes in S. bogneri, including ycf2, clpP, and rpl36. This study is a valuable addition to the evolutionary history of chloroplast genome structure in Araceae.

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.