Comparative analysis of the complete chloroplast genome sequences in psammophytic Haloxylon species (Amaranthaceae)

Chloroplast Genome Comparison and Phylogenetic Analysis of the Commercial Variety Actinidia chinensis 'Hongyang'

Actinidia chinensis 'Hongyang', also known as red yangtao (red heart kiwifruit), is a vine fruit tree native to China possessing significant nutritional and economic value. However, information on its genetic diversity and phylogeny is still very limited. The first chloroplast (cp) genome of A. chinensis 'Hongyang' cultivated in China was sequenced using de novo technology in this study. A. chinensis 'Hongyang' possesses a cp genome that spans 156,267 base pairs (bp), exhibiting an overall GC content of 37.20%. There were 132 genes that were annotated, with 85 of them being protein-coding genes, 39 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. A total of 49 microsatellite sequences (SSRs) were detected, mainly single nucleotide repeats, mostly consisting of A or T base repeats. Compared with 14 other species, the cp genomes of A. chinensis 'Hongyang' were biased towards the use of codons containing A/U, and the non-protein coding regions in the A. chinensis 'Hongyang' cpDNA showed greater variation than the coding regions. The nucleotide polymorphism analysis (Pi) yielded nine highly variable region hotspots, most in the large single copy (LSC) region. The cp genome boundary analysis revealed a conservative order of gene arrangement in the inverted repeats (IRs) region of the cp genomes of 15 Actinidia plants, with small expansions and contractions of the boundaries. Furthermore, phylogenetic tree indicated that A. chinensis 'Hongyang' was the closest relative to A. indochinensis. This research provides a useful basis for future genetic and evolutionary studies of A. chinensis 'Hongyang', and enriches the biological information of Actinidia species.

Analysis of Complete Chloroplast Genome: Structure, Phylogenetic Relationships of Galega orientalis and Evolutionary Inference of Galegeae

Galega orientalis, a leguminous herb in the Fabaceae family, is an ecologically and economically important species widely cultivated for its strong stress resistance and high protein content. However, genomic information of Galega orientalis has not been reported, which limiting its evolutionary analysis. The small genome size makes chloroplast relatively easy to obtain genomic sequence for phylogenetic studies and molecular marker development. Here, the chloroplast genome of Galega orientalis was sequenced and annotated. The results showed that the chloroplast genome of G. orientalis is 125,280 bp in length with GC content of 34.11%. A total of 107 genes were identified, including 74 protein-coding genes, 29 tRNAs and four rRNAs. One inverted repeat (IR) region was lost in the chloroplast genome of G. orientalis. In addition, five genes (rpl22, ycf2, rps16, trnE-UUC and pbf1) were lost compared with the chloroplast genome of its related species G. officinalis. A total of 84 long repeats and 68 simple sequence repeats were detected, which could be used as potential markers in the genetic studies of G. orientalis and related species. We found that the Ka/Ks values of three genes petL, rpl20, and ycf4 were higher than one in the pairwise comparation of G. officinalis and other three Galegeae species (Calophaca sinica, Caragana jubata, Caragana korshinskii), which indicated those three genes were under positive selection. A comparative genomic analysis of 15 Galegeae species showed that most conserved non-coding sequence regions and two genic regions (ycf1 and clpP) were highly divergent, which could be used as DNA barcodes for rapid and accurate species identification. Phylogenetic trees constructed based on the ycf1 and clpP genes confirmed the evolutionary relationships among Galegeae species. In addition, among the 15 Galegeae species analyzed, Galega orientalis had a unique 30-bp intron in the ycf1 gene and Tibetia liangshanensis lacked two introns in the clpP gene, which is contrary to existing conclusion that only Glycyrrhiza species in the IR lacking clade (IRLC) lack two introns. In conclusion, for the first time, the complete chloroplast genome of G. orientalis was determined and annotated, which could provide insights into the unsolved evolutionary relationships within the genus Galegeae.

Complete chloroplast genome sequences of Phlomis fruticosa and Phlomoides strigosa and comparative analysis of the genus Phlomis sensu lato (Lamiaceae)

The taxonomic terms "Phlomis" and "Phlomoides" had been used to describe two sections within the genus Phlomis belonging to the Lamiaceae family. Recently, phylogenetic analyses using molecular markers showed that Phlomis and Phlomoides formed two monophyletic clades, and thus they are generally accepted as separate genera. In this study, we assembled the complete chloroplast genome of Phlomis fruticosa, which is the first reported chloroplast genome belonging to Phlomis genus, as well as the complete chloroplast genome of Phlomoides strigosa belonging to Phlomoides genus. The results showed that the length of chloroplast genome was 151,639 bp (Phlomis fruticosa) and 152,432 bp (Phlomoides strigosa), with conserved large single copy regions, small single copy regions, and inverted repeat regions. 121 genes in Phlomis fruticosa and 120 genes in Phlomoides strigosa were annotated. The chloroplast genomes of Phlomis fruticosa, Phlomoides strigosa, and three reported Phlomoides species, as well as those of 51 species from the Lamiaceae family, which covered 12 subfamilies, were subjected to phylogenetic analyses. The Phlomis and Phlomoides species were split into two groups, which were well supported by both maximum likelihood and Bayesian inference tree analyses. Our study provided further evidence to recognize Phlomis and Phlomoides as independent genera.

Comparative chloroplast genome and phylogenetic analyses of Chinese Polyspora

Polyspora Sweet (Theaceae) are winter ornamental landscape plants native to southern and southeastern Asia, some of which have medicinal value. The chloroplast (cp) genome data of Polyspora are scarce, and the gene evolution and interspecific relationship are still unclear. In this study, we sequenced and annotated Polyspora chrysandra cp genome and combined it with previously published genomes for other Chinese Polyspora species. The results showed that cp genomes of six Chinese Polyspora varied in length between 156,452 bp (P. chrysandra) and 157,066 bp (P. speciosa), but all contained 132 genes, with GC content of 37.3%, and highly similar genes distribution and codon usage. A total of eleven intergenic spacer regions were found having the highest levels of divergence, and eight divergence hotspots were identified as molecular markers for Phylogeography and genetic diversity studies in Polyspora. Gene selection pressure suggested that five genes were subjected to positive selection. Phylogenetic relationships among Polyspora species based on the complete cp genomes were supported strongly, indicating that the cp genomes have the potential to be used as super barcodes for further analysis of the phylogeny of the entire genus. The cp genomes of Chinese Polyspora species will provide valuable information for species identification, molecular breeding and evolutionary analysis of genus Polyspora.

The complete chloroplast genome and phylogenetic relationship of Apocynum pictum (Apocynaceae), a Central Asian shrub and second-class national protected species of western China

Apocynum pictum of the dogbane family, Apocynaceae, is a perennial semi-shrub species of ecological, medicinal, and economic value. It is mainly distributed in semi-arid, saline-alkaline, and desert regions of Xinjiang, Qinghai, and Gansu of western China and adjacent regions from Kazakhstan and Mongolia. Here, we reported the complete chloroplast (cp) genome of A. pictum for the first time, and we found that it had a circular structure with an estimated length of 150,749 bp and a GC content of 38.3%. The cp genome was composed of a large single copy (LSC), a single small single copy (SSC), and two inverted repeat (IR) regions, which were 81,888 bp, 17,251 bp and 25,805 bp long, respectively. The cp genome of A. pictum encoded 134 genes and contained 66 simple sequence repeats (SSRs). A comparative analysis with other cp genomes from Apocynaceae indicated that the cp genome of A. pictum was very conserved, except for subtle differences occurring in the protein-coding genes accD, ndhF, rpl22, rpl32, rpoC2, ycf1 and ycf2. A phylogenetic reconstruction showed that A. pictum and A. venetum were sister species, forming a strongly supported clade with Trachelospermum. Interestingly, nucleotide substitution ratios (Ka/Ks) between A. pictum and A. venetum on accD and ndhF were >1.0, suggesting positive selective pressure on these genes. Our result enriches the genomic resources for the diverse dogbane family and provides critical molecular resources to develop future studies on ecological adaptation to desert habitats in Apocynum.

Chloroplast Genome Evolution and Species Identification of Styrax (Styracaceae)

The genus Styrax L. consists of approximately 130 species distributed in the Americas, eastern Asia, and the Mediterranean region. The phylogeny and evolutionary history of this genus are not clear. Knowledge of the phylogenetic relationships and the method for species identification will be critical for the evolution of this genus. In this study, we sequenced the chloroplast genome of 17 Styrax samples and added 17 additional chloroplast genome sequences from GenBank. The data were used to investigate chloroplast genome evolution, infer phylogenetic relationships, and access the species identification rate within Styrax. The Styrax chloroplast genome contains typical quadripartite structures, ranging from 157,641 bp to 159,333 bp. The chloroplast genome contains 114 unique genes. The P distance among the Styrax species ranged from 0.0003 to 0.00611. Seventeen small inversions and SSR sites were discovered in the Styrax chloroplast genome. By comparing with the chloroplast genome sequences, six mutation hotspots were identified, and the markers ycf1b and trnT-trnL were identified as the best Styrax-specific DNA barcodes. The specific barcodes and superbarcode exhibited higher discriminatory power than universal barcodes. Chloroplast phylogenomic results improved the resolution of the phylogenetic relationships of Styrax compared to previous analyses.

Structural characterization of Platanthera ussuriensis chloroplast genome and comparative analyses with other species of Orchidaceae

BACKGROUND

The genus Tulotis has been classified into the genus Platanthera in the present taxonomic studies since the morphological characteristics of this genus is very similar to that of Platanthera. Platanthera ussuriensis, formerly named as Tulotis ussuriensis, is a small terrestrial orchid species and has been listed as wild plant under State protection (category II) in China. An improved understanding of the genomic information will enable future applications of conservation strategy as well as phylogenetic studies for this rare orchid species. The objective of this research was to characterize and compare the chloroplast genome of P. ussuriensis with other closely related species of Orchidaceae.

RESULTS

The chloroplast genome sequence of P. ussuriensis is 155,016 bp in length, which included a pair of inverted repeats (IRs) of 26,548 bp that separated a large single copy (LSC) region of 83,984 bp and a small single copy (SSC) region of 17,936 bp. The annotation contained a total of 132 genes, including 86 protein-coding genes, 38 tRNA genes and 8 rRNA genes. The simple sequence repeat (SSR) analysis showed that there were 104 SSRs in the chloroplast genome of P. ussuriensis. RNA editing sites recognition indicated 72 RNA editing events occurred, and all codon changes were C to T conversions. Comparative genomics showed that the chloroplast sequence of Platanthera related species were relatively conserved, while there were still some high variation regions that could be used as molecular markers. Moreover, Platanthera related species showed similar IR/SSC and IR/LSC borders. The phylogenetic analysis suggested that P. ussuriensis had a closer evolutionary relationship with P. japonica followed by the remaining Platanthera species.

CONCLUSION

Orchidaceae is a key group of biodiversity protection and also a hot spot group in the plant taxonomy and evolution studies due to their characteristics of high specialization and rapid evolution. This research determined the complete chloroplast genome of P. ussuriensis for the first time, and compared the sequence with other closely related orchid species. These results provide a foundation for future genomic and molecular evolution of the Orchidaceae species, and provide insights into the development of conservation strategy for Platanthera species.

Maxent Modeling for Identifying the Nature Reserve of Cistanche deserticola Ma under Effects of the Host (Haloxylon Bunge) Forest and Climate Changes in Xinjiang, China

Cistanche deserticola Ma is a traditional Chinese medicinal plant exclusively parasitizing on the roots of Haloxylon ammodendron (C. A. Mey.) Bunge and H. Persicum Bunge ex Boiss and the primary cultivated crop of the desert economy. Its wild resources became scarce due to over-exploitation and poaching for economic benefits. To protect the biological diversity of the desert Haloxylon–Cistanche community forest, the optimal combination of desert ecology and economy industry, and their future survival, this paper examines the conservation areas of wild C. deserticola from the perspective of hosts’ effects and climate changes. To identify conservation areas, the potential distributions generated by MaxEnt in two strategies (AH: abiotic and hosts factors; HO: hosts factors only) compare the model’s performance, the niche range overlap, and the changing trend in climate changes. The results show the following: (1) The HO strategy is more suitable for prediction and identifying the core conservation areas in hosts and climate changes (indirectly affected by host distributions) for C. deserticola. (2) The low-suitable habitat and the medium-suitable habitat are both sensitive to the climate changes; the reduction reaches 48.2% (SSP585, 2081–2100) and 26.6%(SSP370, 2081–2100), respectively. The highly suitable habitat is always in growth, with growth reaching 27.3% (SSP585, 2081–2100). (3) Core conservation areas and agriculture and education areas are 317,315.118 km2 and 319,489.874 km2, respectively. This study developed a predictive model for Maxent under climate change scenarios by limiting host and abiotic factors and inverted the natural habitat of C. deserticola to provide scientific zoning for biodiversity conservation in desert Haloxylon–Cistanche community forests systems, providing an effective reference for decision makers.

Primer Design for the Analysis of Closely Related Species: Application of Noncoding mtDNA and cpDNA Sequences

Noncoding regions of the chloroplast (cpDNA) and mitochondrial (mtDNA) genomes are commonly used in plant phylogenetic and population studies. Consensus primers, which are homologous to most coding regions, but amplify variable noncoding regions, are very useful for this purpose. However, high genetic diversity of plants poses a problem in developing molecular methods that require conserved DNA sequences between species.This chapter describes the protocol for designing PCR primers suitable for analysis of closely related plant species. As an example, we used PCR primer design for cpDNA noncoding regions of the rye (Secale).

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.

The complete chloroplast genome sequence of Rubus hirsutus Thunb. and a comparative analysis within Rubus species

Rubus hirsutus is a type of tonifying kidney-essence herb that belongs to the Rosaceae family, and has been commonly used to treat multiple diseases, such as polyuria, impotence, and infertility. In this study, we determined the complete chloroplast sequence of R. hirsutus and conduced a comparative analysis within the genus Rubus. The assembled chloroplast (cp.) genome is 156,380 bp in length with a GC content of 37.0% and shares a conserved quadripartite structure within the other cp. genomes in this genus. A total of 132 unique genes were annotated in the cp. genome of R. hirsutus, which contained 87 protein-coding genes, 37 tRNAs, and eight rRNAs. Seventeen duplicated genes were identified in the inverted repeats region. Furthermore, 70 simple sequence repeats and 35 long repeats were detected in total in the R. hirsutus chloroplast genome. Eight mutational hotspots were identified in the cp. genome of this species with higher nucleotide variations in non-coding regions than those of coding regions. Furthermore, the gene order, codon usage, and repeat sequence distribution were highly consistent in Rubus according to the results of a comparative analysis. A phylogenetic analysis indicated that there was a sister relationship between R. hirsutus and R. chingii. Overall, the complete chloroplast genome of R. hirsutus and the comparative analysis will help to further the evolutionary study, conservation, phylogenetic reconstruction, and development of molecular barcodes for the genus Rubus.

The chloroplast genome of Amygdalus L. (Rosaceae) reveals the phylogenetic relationship and divergence time

Background

Limited access to genetic information has greatly hindered our understanding of the molecular evolution, phylogeny, and differentiation time of subg. Amygdalus. This study reported complete chloroplast (cp) genome sequences of subg. Amygdalus, which further enriched the available valuable resources of complete cp genomes of higher plants and deepened our understanding of the divergence time and phylogenetic relationships of subg. Amygdalus.

Results

The results showed that subg. Amygdalus species exhibited a tetrad structure with sizes ranging from 157,736 bp (P. kansuensis) to 158,971 bp (P. davidiana), a pair of inverted repeat regions (IRa/IRb) that ranged from 26,137–26,467 bp, a large single-copy region that ranged from 85,757–86,608 bp, and a small single-copy region that ranged from 19,020–19,133 bp. The average GC content of the complete cp genomes in the 12 species was 36.80%. We found that the structure of the subg. Amygdalus complete cp genomes was highly conserved, and the 12 subg. Amygdalus species had an rps19 pseudogene. There was not rearrangement of the complete cp genome in the 12 subg. Amygdalus species. All 12 subg. Amygdalus species clustered into one clade based on both Bayesian inference and maximum likelihood. The divergence time analyses based on the complete cp genome sequences showed that subg. Amygdalus species diverged approximately 15.65 Mya.

Conclusion

Our results provide data on the genomic structure of subg. Amygdalus and elucidates their phylogenetic relationships and divergence time.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07968-6.

Phylogeny and Comparative Analysis for the Plastid Genomes of Five Tulipa (Liliaceae)

Species of Tulipa (Liliaceae) are of great horticultural importance and are distributed across Europe, North Africa, and Asia. The Tien Shan Mountain is one of the primary diversity centres of Tulipa, but the molecular studies of Tulipa species from this location are lacking. In our study, we assembled four Tulipa plastid genomes from the Tien Shan Mountains, T. altaica, T. iliensis, T. patens, and T. thianschanica, combined with the plastid genome of T. sylvestris to compare against other Liliaceae plastid genomes. We focussed on the species diversity and evolution of their plastid genomes. The five Tulipa plastid genomes proved highly similar in overall size (151,691-152,088 bp), structure, gene order, and content. With comparative analysis, we chose 7 mononucleotide SSRs from the Tulipa species that could be used in further population studies. Phylogenetic analyses based on 24 plastid genomes robustly supported the monophyly of Tulipa and the sister relationship between Tulipa and Amana, Erythronium. T. iliensis, T. thianschanica, and T. altaica were clustered together, and T. patens was clustered with T. sylvestris, with our results clearly demonstrating the relationships between these five Tulipa species. Our results provide a more comprehensive understanding of the phylogenomics and comparative genomics of Tulipa.

The Comparative Analyses of Six Complete Chloroplast Genomes of Morphologically Diverse Chenopodium album L. (Amaranthaceae) Collected in Korea

Chenopodium album sensu stricto belonging to C. album aggregate is an annual cosmopolitan weed displaying the diversity of morphologies. We completed the six chloroplast genomes of C. album s. str. collected in Korea to understand the relationship between the diversity of chloroplast genomes and their morphological variations. All six C. album chloroplast genomes have a typical quadripartite structure with length ranging from 151,906 bp to 152,199 bp, similar to the previously sequenced C. album chloroplast genome (NC_034950). In total, 56 single nucleotide polymorphisms (SNPs) and 26 insertion and deletion (INDEL) regions (308 bp in total) were identified from the six chloroplast genomes, presenting a low level of intraspecific variations in comparison to the other angiosperm species. 376 normal simple sequence repeats were identified in all seven C. album chloroplast genomes. The phylogenetic analysis based on all available complete Amaranthaceae chloroplast genomes presents phylogenetic positions of six C. album samples as well as correlation with one of C. album morphological features. Our results provide the way to investigate intraspecific features of C. album chloroplast genomes and also the insights of understanding various intraspecific characteristics including morphological features.

Phylogenomic and evolutionary dynamics of inverted repeats across Angelica plastomes

BACKGROUND

Angelica L. (family Apiaceae) is an economically important genus comprising ca. One hundred ten species. Angelica species are found on all continents of the Northern Hemisphere, and East Asia hosts the highest number of species. Morphological characters such as fruit anatomy, leaf morphology and subterranean structures of Angelica species show extreme diversity. Consequently, the taxonomic classification of Angelica species is complex and remains controversial, as the classifications proposed by previous studies based on morphological data and molecular data are highly discordant. In addition, the phylogenetic relationships of major clades in the Angelica group, particularly in the Angelica s. s. clade, remain unclear. Chloroplast (cp) genome sequences have been widely used in phylogenetic studies and for evaluating genetic diversity.

RESULTS

In this study, we sequenced and assembled 28 complete cp genomes from 22 species, two varieties and two cultivars of Angelica. Combined with 36 available cp genomes in GenBank from representative clades of the subfamily Apioideae, the characteristics and evolutionary patterns of Angelica cp genomes were studied, and the phylogenetic relationships of Angelica species were resolved. The Angelica cp genomes had the typical quadripartite structure including a pair of inverted repeats (IRs: 5836-34,706 bp) separated by a large single-copy region (LSC: 76,657-103,161 bp) and a small single-copy region (SSC: 17,433-21,794 bp). Extensive expansion and contraction of the IR region were observed among cp genomes of Angelica species, and the pattern of the diversification of cp genomes showed high consistency with the phylogenetic placement of Angelica species. Species of Angelica were grouped into two major clades, with most species grouped in the Angelica group and A. omeiensis and A. sinensis grouped in the Sinodielsia with Ligusticum tenuissimum.

CONCLUSIONS

Our results further demonstrate the power of plastid phylogenomics in enhancing the phylogenetic reconstructions of complex genera and provide new insights into plastome evolution across Angelica L.

SPInDel Analysis of the Non-Coding Regions of cpDNA as a More Useful Tool for the Identification of Rye (Poaceae: Secale) Species

Secale is a small but very diverse genus from the tribe Triticeae (family Poaceae), which includes annual, perennial, self-pollinating and open-pollinating, cultivated, weedy and wild species of various phenotypes. Despite its high economic importance, classification of this genus, comprising 3–8 species, is inconsistent. This has resulted in significantly reduced progress in the breeding of rye which could be enriched with functional traits derived from wild rye species. Our previous research has suggested the utility of non-coding sequences of chloroplast and mitochondrial DNA in studies on closely related species of the genus Secale. Here we applied the SPInDel (Species Identification by Insertions/Deletions) approach, which targets hypervariable genomic regions containing multiple insertions/deletions (indels) and exhibiting extensive length variability. We analysed a total of 140 and 210 non-coding sequences from cpDNA and mtDNA, respectively. The resulting data highlight regions which may represent useful molecular markers with respect to closely related species of the genus Secale, however, we found the chloroplast genome to be more informative. These molecular markers include non-coding regions of chloroplast DNA: atpB-rbcL and trnT-trnL and non-coding regions of mitochondrial DNA: nad1B-nad1C and rrn5/rrn18. Our results demonstrate the utility of the SPInDel concept for the characterisation of Secale species.

The Complete Chloroplast Genome of Arabidopsis thaliana Isolated in Korea (Brassicaceae): An Investigation of Intraspecific Variations of the Chloroplast Genome of Korean A. thaliana

Arabidopsis thaliana (L.) Heynh. is a model organism of plant molecular biology. More than 1,700 whole genome sequences have been sequenced, but no Korean isolate genomes have been sequenced thus far despite the fact that many A. thaliana isolated in Japan and China have been sequenced. To understand the genetic background of Korean natural A. thaliana (named as 180404IB4), we presented its complete chloroplast genome, which is 154,464 bp long and has four subregions: 85,164 bp of large single copy (LSC) and 17,781 bp of small single copy (SSC) regions are separated by 26,257 bp of inverted repeat (IRs) regions including 130 genes (85 protein-coding genes, eight rRNAs, and 37 tRNAs). Fifty single nucleotide polymorphisms (SNPs) and 14 insertion and deletions (INDELs) are identified between 180404IB4 and Col0. In addition, 101 SSRs and 42 extendedSSRs were identified on the Korean A. thaliana chloroplast genome, indicating a similar number of SSRs on the rest five chloroplast genomes with a preference of sequence variations toward the SSR region. A nucleotide diversity analysis revealed two highly variable regions on A. thaliana chloroplast genomes. Phylogenetic trees with three more chloroplast genomes of East Asian natural isolates show that Korean and Chinese natural isolates are clustered together, whereas two Japanese isolates are not clustered, suggesting the need for additional investigations of the chloroplast genomes of East Asian isolates.

Methods of analysis of chloroplast genomes of C3, Kranz type C4 and Single Cell C4 photosynthetic members of Chenopodiaceae

BACKGROUND

Chloroplast genome information is critical to understanding forms of photosynthesis in the plant kingdom. During the evolutionary process, plants have developed different photosynthetic strategies that are accompanied by complementary biochemical and anatomical features. Members of family Chenopodiaceae have species with C3 photosynthesis, and variations of C4 photosynthesis in which photorespiration is reduced by concentrating CO2 around Rubisco through dual coordinated functioning of dimorphic chloroplasts. Among dicots, the family has the largest number of C4 species, and greatest structural and biochemical diversity in forms of C4 including the canonical dual-cell Kranz anatomy, and the recently identified single cell C4 with the presence of dimorphic chloroplasts separated by a vacuole. This is the first comparative analysis of chloroplast genomes in species representative of photosynthetic types in the family.

RESULTS

Methodology with high throughput sequencing complemented with Sanger sequencing of selected loci provided high quality and complete chloroplast genomes of seven species in the family and one species in the closely related Amaranthaceae family, representing C3, Kranz type C4 and single cell C4 (SSC4) photosynthesis six of the eight chloroplast genomes are new, while two are improved versions of previously published genomes. The depth of coverage obtained using high-throughput sequencing complemented with targeted resequencing of certain loci enabled superior resolution of the border junctions, directionality and repeat region sequences. Comparison of the chloroplast genomes with previously sequenced plastid genomes revealed similar genome organization, gene order and content with a few revisions. High-quality complete chloroplast genome sequences resulted in correcting the orientation the LSC region of the published Bienertia sinuspersici chloroplast genome, identification of stop codons in the rpl23 gene in B. sinuspersici and B. cycloptera, and identifying an instance of IR expansion in the Haloxylon ammodendron inverted repeat sequence. The rare observation of a mitochondria-to-chloroplast inter-organellar gene transfer event was identified in family Chenopodiaceae.

CONCLUSIONS

This study reports complete chloroplast genomes from seven Chenopodiaceae and one Amaranthaceae species. The depth of coverage obtained using high-throughput sequencing complemented with targeted resequencing of certain loci enabled superior resolution of the border junctions, directionality, and repeat region sequences. Therefore, the use of high throughput and Sanger sequencing, in a hybrid method, reaffirms to be rapid, efficient, and reliable for chloroplast genome sequencing.

Evolutionary directions of single nucleotide substitutions and structural mutations in the chloroplast genomes of the family Calycanthaceae

BACKGROUND

Chloroplast genome sequence data is very useful in studying/addressing the phylogeny of plants at various taxonomic ranks. However, there are no empirical observations on the patterns, directions, and mutation rates, which are the key topics in chloroplast genome evolution. In this study, we used Calycanthaceae as a model to investigate the evolutionary patterns, directions and rates of both nucleotide substitutions and structural mutations at different taxonomic ranks.

RESULTS

There were 2861 polymorphic nucleotide sites on the five chloroplast genomes, and 98% of polymorphic sites were biallelic. There was a single-nucleotide substitution bias in chloroplast genomes. A → T or T → A (2.84%) and G → C or C → G (3.65%) were found to occur significantly less frequently than the other four transversion mutation types. Synonymous mutations kept balanced pace with nonsynonymous mutations, whereas biased directions appeared between transition and transversion mutations and among transversion mutations. Of the structural mutations, indels and repeats had obvious directions, but microsatellites and inversions were non-directional. Structural mutations increased the single nucleotide mutations rates. The mutation rates per site per year were estimated to be 0.14-0.34 × 10- 9 for nucleotide substitution at different taxonomic ranks, 0.64 × 10- 11 for indels and 1.0 × 10- 11 for repeats.

CONCLUSIONS

Our direct counts of chloroplast genome evolution events provide raw data for correctly modeling the evolution of sequence data for phylogenetic inferences.

The complete chloroplast genome sequence of the medicinal plant Sophora tonkinensis

Sophora tonkinensis belongs to genus Sophora of the Fabaceae family. It is mainly distributed in the ridge and peak regions of limestone areas in western China and has high medicinal value and important ecological functions. Wild populations of S. tonkinensis are in danger and need urgent conservation. Furthermore, wild S. tonkinensis resources are very limited relative to the needs of the market, and many adulterants are present on the market. Therefore, a method for authenticating S. tonkinensis and its adulterants at the molecular level is needed. Chloroplast genomes are valuable sources of genetic markers for phylogenetic analyses, genetic diversity evaluation, and plant molecular identification. In this study, we report the complete chloroplast genome of S. tonkinensis. The circular complete chloroplast genome was 154,644 bp in length, containing an 85,810 bp long single-copy (LSC) region, an 18,321 bp short single-copy (SSC) region and two inverted repeat (IR) regions of 50,513 bp. The S. tonkinensis chloroplast genome comprised 129 genes, including 83 protein-coding genes, 38 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. The structure, gene order and guanine and cytosine (GC) content of the S. tonkinensis chloroplast genome were similar to those of the Sophora alopecuroides and Sophora flavescens chloroplast genomes. A total of 1,760 simple sequence repeats (SSRs) were identified in the chloroplast genome of S. tonkinensis, and most of them (93.1%) were mononucleotides. Moreover, the identified SSRs were mainly distributed in the LSC region, accounting for 60% of the total number of SSRs, while 316 (18%) and 383 (22%) were located in the SSC and IR regions, respectively. Only one complete copy of the rpl2 gene was present at the LSC/IRB boundary, while another copy was absent from the IRA region because of the incomplete structure caused by IR region expansion and contraction. The phylogenetic analysis placed S. tonkinensis in Papilionoideae, sister to S. flavescens, and the genera Sophora and Ammopiptanthus were closely related. The complete genome sequencing and chloroplast genome comparative analysis of S. tonkinensis and its closely related species presented in this paper will help formulate effective conservation and management strategies as well as molecular identification approaches for this important medicinal plant.

Comparing and phylogenetic analysis chloroplast genome of three Achyranthes species

In this study, the chloroplast genome sequencing of the Achyranthes longifolia, Achyranthes bidentata and Achyranthes aspera were performed by Next-generation sequencing technology. The results revealed that there were a length of 151,520 bp (A. longifolia), 151,284 bp (A. bidentata), 151,486 bp (A. aspera), respectively. These chloroplast genome have a highly conserved structure with a pair of inverted repeat (IR) regions (25,150 bp; 25,145 bp; 25,150 bp), a large single copy (LSC) regions (83,732 bp; 83,933 bp; 83,966 bp) and a small single copy (SSC) regions (17,252 bp; 17,263 bp; 17,254 bp) in A. bidentate, A. aspera and A. longifolia. There were 127 genes were annotated, which including 8 rRNA genes, 37 tRNA genes and 82 functional genes. The phylogenetic analysis strongly revealed that Achyranthes is monophyletic, and A. bidentata was the closest relationship with A. aspera and A. longifolia. A. bidentata and A. longifolia were clustered together, the three Achyranthes species had the same origin, then the gunes of Achyranthes is the closest relative to Alternanthera, and that forms a group with Alternanthera philoxeroides. The research laid a foundation and provided relevant basis for the identification of germplasm resources in the future.

Comparative analysis of four Zantedeschia chloroplast genomes: expansion and contraction of the IR region, phylogenetic analyses and SSR genetic diversity assessment

The horticulturally important genus Zantedeschia (Araceae) comprises eight species of herbaceous perennials. We sequenced, assembled and analyzed the chloroplast (cp) genomes of four species of Zantedeschia (Z. aethiopica, Z. odorata, Z. elliottiana, and Z. rehmannii) to investigate the structure of the cp genome in the genus. According to our results, the cp genome of Zantedeschia ranges in size from 169,065 bp (Z. aethiopica) to 175,906 bp (Z. elliottiana). We identified a total of 112 unique genes, including 78 protein-coding genes, 30 transfer RNA (tRNA) genes and four ribosomal RNA (rRNA) genes. Comparison of our results with cp genomes from other species in the Araceae suggests that the relatively large sizes of the Zantedeschia cp genomes may result from inverted repeats (IR) region expansion. The sampled Zantedeschia species formed a monophylogenetic clade in our phylogenetic analysis. Furthermore, the long single copy (LSC) and short single copy (SSC) regions in Zantedeschia are more divergent than the IR regions in the same genus, and non-coding regions showed generally higher divergence than coding regions. We identified a total of 410 cpSSR sites from the four Zantedeschia species studied. Genetic diversity analyses based on four polymorphic SSR markers from 134 cultivars of Zantedeschia suggested that high genetic diversity (I = 0.934; Ne = 2.371) is present in the Zantedeschia cultivars. High genetic polymorphism from the cpSSR region suggests that cpSSR could be an effective tool for genetic diversity assessment and identification of Zantedeschia varieties.

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.

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.

Complete chloroplast genome sequence of Pueraria lobata (Willd.) Ohwi (Fabaceae): a traditional Chinese medicinal herb

Pueraria lobata is a traditional Chinese herb which has been used medically since ancient times. In this study, we sequenced the complete chloroplast genome of P. lobata based on next-generation sequencing and used the data to assess genomic resources. The chloroplast genome of P. lobata is 153,411 bp in length consisting of large and small single-copy regions of length 84,142 and 17,989 bp, separated by two IR regions of 25,640 bp. The overall GC content was 35.4%. De novo assembly and annotation showed the presence of 112 unique genes with 78 protein-coding genes, 30 tRNA genes, and four rRNA genes. A maximum-likelihood phylogenomic analysis showed that Pueraria was sister to Pediomelum + Glycine.

Comparison of different annotation tools for characterization of the complete chloroplast genome of Corylus avellana cv Tombul

BACKGROUND

Several bioinformatics tools have been designed for assembly and annotation of chloroplast (cp) genomes, making it difficult to decide which is most useful and applicable to a specific case. The increasing number of plant genomes provide an opportunity to accurately obtain cp genomes from whole genome shotgun (WGS) sequences. Due to the limited genetic information available for European hazelnut (Corylus avellana L.) and as part of a genome sequencing project, we analyzed the complete chloroplast genome of the cultivar 'Tombul' with multiple annotation tools.

RESULTS

Three different annotation strategies were tested, and the complete cp genome of C. avellana cv Tombul was constructed, which was 161,667 bp in length, and had a typical quadripartite structure. A large single copy (LSC) region of 90,198 bp and a small single copy (SSC) region of 18,733 bp were separated by a pair of inverted repeat (IR) regions of 26,368 bp. In total, 125 predicted functional genes were annotated, including 76 protein-coding, 25 tRNA, and 4 rRNA unique genes. Comparative genomics indicated that the cp genome sequences were relatively highly conserved in species belonging to the same order. However, there were still some variations, especially in intergenic regions, that could be used as molecular markers for analyses of phylogeny and plant identification. Simple sequence repeat (SSR) analysis showed that there were 83 SSRs in the cp genome of cv Tombul. Phylogenetic analysis suggested that C. avellana cv Tombul had a close affinity to the sister group of C. fargesii and C. chinensis, and then a closer evolutionary relationship with Betulaceae family than other species of Fagales.

CONCLUSION

In this study, the complete cp genome of Corylus avellana cv Tombul, the most widely cultivated variety in Turkey, was obtained and annotated, and additionally phylogenetic relationships were predicted among Fagales species. Our results suggest a very accurate assembly of chloroplast genome from next generation whole genome shotgun (WGS) sequences. Enhancement of taxon sampling in Corylus species provide genomic insights into phylogenetic analyses. The nucleotide sequences of cv Tombul cp genomes can provide comprehensive genetic insight into the evolution of genus Corylus.

Complete chloroplast genome sequence of Ligustrum quihoui (Oleaceae): genome structure and genomic resources

Ligustrum quihoui is popular as landscape plants used as hedges in gardens. In this study, we sequenced the complete chloroplast genome of L. quihoui based on next-generation sequencing and used the data to assess genomic resources. The chloroplast genome of L. quihoui is 163,575 bp in length consisting of large and small single-copy regions of length 88,072 and 11,493 bp, separated by two IR regions of 32,005 bp. De novo assembly and annotation showed the presence of 115 unique genes with 81 protein-coding genes, 30 tRNA genes, and four rRNA genes. A total of 62 perfect chloroplast simple sequence repeats were analyzed in the L. quihoui. A maximum-likelihood phylogenomic analysis showed that L. quihoui was sister to L. gracile.

Comparative analysis of the complete chloroplast genomes of seven Populus species: Insights into alternative female parents of Populus tomentosa

Populus tomentosa, of section Populus, is distributed mainly in northern China. This species has high resistance to many diseases and insects, and it plays key roles in shelterbelts and urban afforestation in northern China. It has long been suspected to be a hybrid, but its parents remain unknown. In the present study, we report four newly sequenced complete cp genomes from section Populus and comparative genomic analyses of these new sequences and three published cp genome sequences. The seven cp genomes ranged from 155,853 bp (P. tremula var. davidiana) to 156,746 bp (P. adenopoda) in length, and their gene orders, gene numbers and GC contents were similar. We analyzed SNPs, indels, SSRs and repeats among the seven cp genomes, and eight small inversions were detected in the ndhC-trnV, rbcL-accD, petA-psbJ, trnW-trnP, rpl16-rps3, trnL-ycf15, ycf15-trnL, and ndhF-trnL intergenic regions. Furthermore, seven divergent regions (trnH-psbA, matK, psbM-psbD, ndhC-trnV, ycf1, ndhF-ccsA and ccsA-ndhD) were found in more highly variable regions. The phylogenetic tree reveals that P. tomentosa is closely related to P. alba and P. alba var. pyramidalis. Hence, P. alba was involved in the formation of P. tomentosa.

Complete chloroplast genome of Camellia japonica genome structures, comparative and phylogenetic analysis

Camellia is an economically, ecologically and phylogenetically valuable genus in the family Theaceae. The frequent interspecific hybridization and polyploidization makes this genus phylogenetically and taxonomically under controversial and require detailed investigation. Chloroplast (cp) genome sequences have been used for cpDNA marker development and genetic diversity evaluation. Our research newly sequenced the chloroplast genome of Camellia japonica using Illumina HiSeq X Ten platform, and retrieved five other chloroplast genomes of Camellia previously published for comparative analyses, thereby shedding lights on a deeper understanding of the applicability of chloroplast information. The chloroplast genome sizes ranged in length from 156,607 to 157,166 bp, and their gene structure resembled those of other higher plants. There were four categories of SSRs detected in six Camellia cpDNA sequences, with the lengths ranging from 10 to 17bp. The Camellia species exhibited different evolutionary routes that lhbA and orf188, followed by orf42 and psbZ, were readily lost during evolution. Obvious codon preferences were also shown in almost all protein-coding cpDNA and amino acid sequences. Selection pressure analysis revealed the influence of different environmental pressures on different Camellia chloroplast genomes during long-term evolution. All Camellia species, except C. crapnelliana, presented the identical rate of amplification in the IR region. The datasets obtained from the chloroplast genomes are highly supportive in inferring the phylogenetic relationships of the Camellia taxa, indicating that chloroplast genome can be used for classifying interspecific relationships in this genus.

Genetic diversity and relationship between cultivated, weedy and wild rye species as revealed by chloroplast and mitochondrial DNA non-coding regions analysis

The genus Secale is small but very diverse. Despite the high economic importance, phylogenetic relationships of rye species have not been fully determined, and they are extremely important for the process of breeding of new cultivars that can be enriched with functional traits derived from wild rye species. The study analyzed the degree of relationship of 35 accessions of the genus Secale, representing 13 most often distinguished species and subspecies, originating from various seed collections in the world, based on the analysis of non-coding regions of the chloroplast (cpDNA) and mitochondrial genome (mtDNA), widely used in phylogenetic and population plant studies, because of a higher rate of evolution than the coding regions. There was no clear genetic structure between different species and subspecies, which may indicated the introgression between these taxa. The obtained data confirmed that S. vavilovii was very similar to S. cereale, which confirmed the assumption that they might share a common ancestor. The results also confirmed the divergence of S. sylvestre from other species and subspecies of rye. Areas that may be useful molecular markers in studies on closely related species of the genus Secale were also indicated.

Comparative Chloroplast Genomics at Low Taxonomic Levels: A Case Study Using Amphilophium (Bignonieae, Bignoniaceae)

Chloroplast (cp) genome organization, gene order, and content have long been considered conserved among land plants. Despite that, the generation of thousands of complete plastomes through next-generation sequencing (NGS) has challenged their conserved nature. In this study, we analyze 11 new complete plastomes of Amphilophium (Bignonieae, Bignoniaceae), a diverse genus of Neotropical lianas, and that of Anemopaegma prostratum. We explored the structure and content of the assembled plastomes and performed comparative analyses within Amphilophium and among other plastomes available for Bignoniaceae. The overall gene content and orientation of plastomes is similar in all species studied. Plastomes are not conserved among Amphilophium, showing significant differences in length (155,262-164,786 bp), number of genes duplicated in the IRs (eight, 18, or 19), and location of the SC/IR boundaries (i.e., LSC/IRa junction between rps19 and rpl2 genes, within petD, or within petB). Length differences reflect expansions of the IRs and contractions of the LSC regions. The plastome of A. prostratum is 168,172 bp, includes 19 duplicated genes, and has the LSC/IRa boundary located within the petB gene. Amphilophium plastomes show high nucleotide diversity, with many hypervariable regions, and 16 genes with signatures of positive selection. Multiple SSRs and repeat regions were identified for Amphilophium and Anemopaegma prostratum. The differences in structure detected within Amphilophium plastomes in terms of LSC/IR and IR/SSC boundaries, number of duplicated genes, and genome sizes are mostly shared between taxa that belong to the same clade. Our results bring new insights into the evolution of plastomes at low taxonomic levels.

Interspecific chloroplast genome sequence diversity and genomic resources in Diospyros

BACKGROUND

Fruits of persimmon plants are traditional healthy food in China, Korea and Japan. However, due to the shortage of morphological and DNA markers, the development of persimmon industry has been heavily inhibited.

RESULTS

Chloroplast genomes of Diospyros cathayensis, D. virginiana, D. rhombifolia and D. deyangensis were newly sequenced. Comparative analyses of ten chloroplast genomes including six previously published chloroplast genomes of Diospyros provided new insights into the genome sequence diversity and genomic resources of the genus. Eight hyper-variable regions, trnH-psbA, rps16-trnQ, rpoB-trnC, rps4-trnT-trnL, ndhF, ndhF-rpl32-trnL, ycf1a, and ycf1b, were discovered and can be used as chloroplast DNA markers at/above species levels. The complete chloroplast genome sequences provided the best resolution at inter-specific level in comparison with different chloroplast DNA sequence datasets.

CONCLUSION

Diospyros oleifera, D. deyangensis, D. virginiana, D. glaucifolia, D. lotus and D. jinzaoshi are important wild species closely related to the cultivated persimmon D. kaki. The hyper-variable regions can be used as DNA markers for global genetic diversity detection of Diospyros. Deeper study on these taxa would be helpful for elucidating the origin of D. kaki.

First reported chloroplast genome sequence of Punica granatum (cultivar Helow) from Jabal Al-Akhdar, Oman: phylogenetic comparative assortment with Lagerstroemia

Pomegranate (Punica granatum L.) is one of the oldest known edible fruits. It has grown in popularity and is a profitable fruit crop due to its attractive features including a bright red appearance and its biological activities. Scientific exploration of the genetics and evolution of these beneficial traits has been hampered by limited genomic information. In this study, we sequenced the complete chloroplast (cp) genome of the native P. granatum (cultivar Helow) cultivated in the mountains of Jabal Al-Akhdar, Oman. The results revealed a P. granatum cp genome length of 158,630 bp, characterized by a relatively conserved structure containing 2 inverted repeat regions of 25,466 bp, an 18,686 bp small single copy regions, and an 89,015 bp large single copy region. The 86 protein-coding genes included 37 transfer RNA genes and 8 ribosomal RNA genes. Comparison of the P. granatum whole cp genome with seven Lagerstroemia species revealed an overall high degree of sequence similarity with divergence among intergenic spacers. The location, distribution, and divergence of repeat sequences and shared genes of the Punica and Lagerstroemia species were highly similar. Analyses of nucleotide substitution, insertion/deletions, and highly variable regions in these cp genomes identified potential plastid markers for taxonomic and phylogenetic studies in Myrtales. A phylogenetic study of the cp genomes and 76 shared coding regions generated similar cladograms. The complete cp genome of P. granatum will aid in taxonomical studies of the family Lythraceae.

Characterization of the Chloroplast Genome Sequence of Acer miaotaiense: Comparative and Phylogenetic Analyses

Acer miaotaiense is an endangered species within the Aceraceae family, and has only a few small natural distributions in China's Qingling Mountains and Bashan Mountains. Comparative analyses of the complete chloroplast genome could provide useful knowledge on the diversity and evolution of this species in different environments. In this study, we sequenced and compared the chloroplast genome of Acer miaotaiense from five ecological regions in the Qingling and Mashan Regions of China. The size of the chloroplast genome ranged from 156,260 bp to 156,204 bp, including two inverted repeat regions, a small single-copy region, and a large single-copy region. Across the whole chloroplast genome, there were 130 genes in total, and 92 of them were protein-coding genes. We observed four genes with non-synonymous mutations involving post-transcriptional modification (matK), photosynthesis (atpI), and self-replication (rps4 and rpl20). A total of 415 microsatellite loci were identified, and the dominant microsatellite types were composed of dinucleotide and trinucleotide motifs. The dominant repeat units were AT and AG, accounting for 37.92% and 31.16% of the total microsatellite loci, respectively. A phylogenetic analysis showed that samples with the same altitude (Xunyangba, Ningshan country, and Zhangliangmiao, Liuba country) had a strong bootstrap value (88%), while the remaining ones shared a similar longitude. These results provided clues about the importance of longitude/altitude for the genetic diversity of Acer miaotaiense. This information will be useful for the conservation and improved management of this endangered species.

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.

The complete plastid genome of Suaeda malacosperma (Amaranthaceae/Chenopodiaceae), a vulnerable halophyte in coastal regions of Korea and Japan

Suaeda malacosperma has limited distribution in the coastal regions of Korea and Japan and is named as a vulnerable halophyte in the Red List of Japan. The complete plastid genome of S. malacosperma is 151,989 bp long, and is composed of large single-copy (83,492 bp) and small single-copy (18,121 bp) regions plus two inverted repeats (25,188 bp each). The plastid genome encodes 130 genes, including 8 rRNAs, 37 tRNAs, and 83 protein-coding genes. rpl23 is pseudogenized. Phylogenetic analysis showed a sister relationship between Suaeda and Bienertia. This complete plastid genome is the first reported in genus Suaeda.

Plastid Genome Evolution in the Early-Diverging Legume Subfamily Cercidoideae (Fabaceae)

The subfamily Cercidoideae is an early-branching legume lineage, which consists of 13 genera distributed in the tropical and warm temperate Northern Hemisphere. A previous study detected two plastid genomic variations in this subfamily, but the limited taxon sampling left the overall plastid genome (plastome) diversification across the subfamily unaddressed, and phylogenetic relationships within this clade remained unresolved. Here, we assembled eight plastomes from seven Cercidoideae genera and conducted phylogenomic-comparative analyses in a broad evolutionary framework across legumes. The plastomes of Cercidoideae all exhibited a typical quadripartite structure with a conserved gene content typical of most angiosperm plastomes. Plastome size ranged from 151,705 to 165,416 bp, mainly due to the expansion and contraction of inverted repeat (IR) regions. The order of genes varied due to the occurrence of several inversions. In Tylosema species, a plastome with a 29-bp IR-mediated inversion was found to coexist with a canonical-type plastome, and the abundance of the two arrangements of isomeric molecules differed between individuals. Complete plastome data were much more efficient at resolving intergeneric relationships of Cercidoideae than the previously used selection of only a few plastid or nuclear loci. In sum, our study revealed novel insights into the structural diversification of plastomes in an early-branching legume lineage, and, thus, into the evolutionary trajectories of legume plastomes in general.

Complete Chloroplast Genome Sequence and Phylogenetic Analysis of Paeonia ostii

Paeonia ostii, a common oil-tree peony, is important ornamentally and medicinally. However, there are few studies on the chloroplast genome of Paeonia ostii. We sequenced and analyzed the complete chloroplast genome of P. ostii. The size of the P. ostii chloroplast genome is 152,153 bp, including a large single-copy region (85,373 bp), a small single-copy region (17,054 bp), and a pair of inverted repeats regions (24,863 bp). The P. ostii chloroplast genome encodes 111 genes, including 77 protein-coding genes, four ribosomal RNA genes, and 30 transfer RNA genes. The genome contains forward repeats (22), palindromic repeats (28), and tandem repeats (24). The presence of rich simple-sequence repeat loci in the genome provides opportunities for future population genetics work for breeding new varieties. A phylogenetic analysis showed that P. ostii is more closely related to Paeonia delavayi and Paeonialudlowii than to Paeoniaobovata and Paeoniaveitchii. The results of this study provide an assembly of the whole chloroplast genome of P. ostii, which may be useful for future breeding and further biological discoveries. It will provide a theoretical basis for the improvement of peony yield and the determination of phylogenetic status.

Comparative Genomics and Phylogenetic Analysis Revealed the Chloroplast Genome Variation and Interspecific Relationships of Corylus (Betulaceae) Species

Corylus L. is an economically and phylogenetically important genus in the family Betulaceae. Taxonomic and phylogenetic relationships of Corylus species have long been controversial for lack of effective molecular markers. In this study, the complete chloroplast (cp) genomes of six Corylus species were assembled and characterized using next-generation sequencing. We compared the genome features, repeat sequences, sequence divergence, and constructed the phylogenetic relationships of the six Corylus species. The results indicated that Corylus cp genomes were typical of the standard double-stranded DNA molecule, ranging from 160,445 base pairs (bp) (C. ferox var. thibetca) to 161,621 bp (C. yunnanensis) in length. Each genome contained a pair of inverted repeats (IRs), a large single-copy (LSC) region and a small single-copy (SSC) region. Each of the six cp genomes possessed 113 unique genes arranged in the same order, including 80 protein-coding, 29 tRNA, and 4 rRNA genes. C. yunnanensis contained the highest number of repeat sequences, and the richest SSRs in six cp genomes were A/T mononucleotides. Comparative analyses of six Corylus cp genomes revealed four hotspot regions (trnH-psbA, rpoB-trnC, trnF-ndhJ, and rpl32-trnL) that could be used as potential molecular markers. Phylogenetic analyses of the complete chloroplast genomes and 80 protein-coding genes exhibited nearly identical topologies that strongly supported the monophyly of Corylus and simultaneously revealed the generic relationships among Betulaceae. The availability of these genomes can offer valuable genetic information for further taxonomy, phylogeny, and species delimitation in Corylus or even Betulaceae plants.

The Complete Chloroplast Genome Sequences of Aconitum pseudolaeve and Aconitum longecassidatum, and Development of Molecular Markers for Distinguishing Species in the Aconitum Subgenus Lycoctonum

Aconitum pseudolaeve Nakai and Aconitum longecassidatum Nakai, which belong to the Aconitum subgenus Lycoctonum, are distributed in East Asia and Korea. Aconitum species are used in herbal medicine and contain highly toxic components, including aconitine. A. pseudolaeve, an endemic species of Korea, is a commercially valuable material that has been used in the manufacture of cosmetics and perfumes. Although Aconitum species are important plant resources, they have not been extensively studied, and genomic information is limited. Within the subgenus Lycoctonum, which includes A. pseudolaeve and A. longecassidatum, a complete chloroplast (CP) genome is available for only one species, Aconitum barbatum Patrin ex Pers. Therefore, we sequenced the complete CP genomes of two Aconitum species, A. pseudolaeve and A. longecassidatum, which are 155,628 and 155,524 bp in length, respectively. Both genomes have a quadripartite structure consisting of a pair of inverted repeated regions (51,854 and 52,108 bp, respectively) separated by large single-copy (86,683 and 86,466 bp) and small single-copy (17,091 and 16,950 bp) regions similar to those in other Aconitum CP genomes. Both CP genomes consist of 112 unique genes, 78 protein-coding genes, 4 ribosomal RNA (rRNA) genes, and 30 transfer RNA (tRNA) genes. We identified 268 and 277 simple sequence repeats (SSRs) in A. pseudolaeve and A. longecassidatum, respectively. We also identified potential 36 species-specific SSRs, 53 indels, and 62 single-nucleotide polymorphisms (SNPs) between the two CP genomes. Furthermore, a comparison of the three Aconitum CP genomes from the subgenus Lycoctonum revealed highly divergent regions, including trnK-trnQ, ycf1-ndhF, and ycf4-cemA. Based on this finding, we developed indel markers using indel sequences in trnK-trnQ and ycf1-ndhF. A. pseudolaeve, A. longecassidatum, and A. barbatum could be clearly distinguished using the novel indel markers AcoTT (Aconitum trnK-trnQ) and AcoYN (Aconitum ycf1-ndhF). These two new complete CP genomes provide useful genomic information for species identification and evolutionary studies of the Aconitum subgenus Lycoctonum.

Chloroplast Genomic Resource of Paris for Species Discrimination

Paris is famous in China for its medicinal value and has been included in the Chinese Pharmacopoeia. Inaccurate identification of these species could confound their effective exploration, conservation, and domestication. Due to the plasticity of the morphological characteristics, correct identification among Paris species remains problematic. In this regard, we report the complete chloroplast genome of P. thibetica and P. rugosa to develop highly variable molecular markers. Comparing three chloroplast genomes, we sought out the most variable regions to develop the best cpDNA barcodes for Paris. The size of Paris chloroplast genome ranged from 162,708 to 163,200 bp. A total of 134 genes comprising 81 protein coding genes, 45 tRNA genes and 8 rRNA genes were observed in all three chloroplast genomes. Eight rapidly evolving regions were detected, as well as the difference of simple sequence repeats (SSR) and repeat sequence. Two regions of the coding gene ycf1, ycf1a and ycf1b, evolved the quickest and were proposed as core barcodes for Paris. The complete chloroplast genome sequences provide more integrated and adequate information for better understanding the phylogenetic pattern and improving efficient discrimination during species identification.

Completion of Eight Gynostemma BL. (Cucurbitaceae) Chloroplast Genomes: Characterization, Comparative Analysis, and Phylogenetic Relationships

Gynostemma BL., belonging to the family Cucurbitaceae, is a genus containing 17 creeping herbaceous species mainly distributed in East Asia. It can be divided into two subgenera based on different fruit morphology. Herein, we report eight complete chloroplast genome sequences of the genus Gynostemma, which were obtained by Illumina paired-end sequencing, assembly, and annotation. The length of the eight complete cp genomes ranged from 157,576 bp (G. pentaphyllum) to 158,273 bp (G. laxiflorum). Each encoded 133 genes, including 87 protein-coding genes, 37 tRNA genes, eight rRNA genes, and one pseudogene. The four types of repeated sequences had been discovered and indicated that the repeated structure for species in the Subgen. Triostellum was greater than that for species in the Subgen. Gynostemma. The percentage of variation of the eight cp genomes in different regions were calculated, which demonstrated that the coding and inverted repeats regions were highly conserved. Phylogenetic analysis based on Bayesian inference and maximum likelihood methods strongly supported the phylogenetic position of the genus Gynostemma as a member of family Cucurbitaceae. The phylogenetic relationships among the eight species were clearly resolved using the complete cp genome sequences in this study. It will also provide potential molecular markers and candidate DNA barcodes for future studies and enrich the valuable complete cp genome resources of Cucurbitaceae.

Phylogenetic Resolution in Juglans Based on Complete Chloroplast Genomes and Nuclear DNA Sequences

Walnuts (Juglans of the Juglandaceae) are well-known economically important resource plants for the edible nuts, high-quality wood, and medicinal use, with a distribution from tropical to temperate zones and from Asia to Europe and Americas. There are about 21 species in Juglans. Classification of Juglans at section level is problematic, because the phylogenetic position of Juglans cinerea is disputable. Lacking morphological and DNA markers severely inhibited the development of related researches. In this study, the complete chloroplast genomes and two nuclear DNA regions (the internal transcribed spacer and ubiquitin ligase gene) of 10 representative taxa of Juglans were used for comparative genomic analyses in order to deepen the understanding on the application value of genetic information for inferring the phylogenetic relationship of the genus. The Juglans chloroplast genomes possessed the typical quadripartite structure of angiosperms, consisting of a pair of inverted repeat regions separated by a large single-copy region and a small single-copy region. All the 10 chloroplast genomes possessed 112 unique genes arranged in the same order, including 78 protein-coding, 30 tRNA, and 4 rRNA genes. A combined sequence data set from two nuclear DNA regions revealed that Juglans plants could be classified into three branches: (1) section Juglans, (2) section Cardiocaryon including J. cinerea which is closer to J. mandshurica, and (3) section Rhysocaryon. However, three branches with a different phylogenetic topology were recognized in Juglans using the complete chloroplast genome sequences: (1) section Juglans, (2) section Cardiocaryon, and (3) section Rhysocaryon plus J. cinerea. The molecular taxonomy of Juglans is almost compatible to the morphological taxonomy except J. cinerea (section Trachycaryon). Based on the complete chloroplast genome sequence data, the divergence time between section Juglans and section Cardiocaryon was 44.77 Mya, while section Rhysocaryon diverged from other sections in the genus Juglans was 47.61 Mya. Eleven of the 12 small inversions in the chloroplast genomes provided valuable phylogenetic information for classification of walnut plants at section and species levels. Our results are valuable for future studies on Juglans genetic diversity and will enhance the understanding on the phylogenetic evolution of Juglandaceae.

Comparative Analysis of Six Lagerstroemia Complete Chloroplast Genomes

Crape myrtles are economically important ornamental trees of the genus Lagerstroemia L. (Lythraceae), with a distribution from tropical to northern temperate zones. They are positioned phylogenetically to a large subclade of rosids (in the eudicots) which contain more than 25% of all the angiosperms. They commonly bloom from summer till fall and are of significant value in city landscape and environmental protection. Morphological traits are shared inter-specifically among plants of Lagerstroemia to certain extent and are also influenced by environmental conditions and different developmental stages. Thus, classification of plants in Lagerstroemia at species and cultivar levels is still a challenging task. Chloroplast (cp) genome sequences have been proven to be an informative and valuable source of cp DNA markers for genetic diversity evaluation. In this study, the complete cp genomes of three Lagerstroemia species were newly sequenced, and three other published cp genome sequences of Lagerstroemia were retrieved for comparative analyses in order to obtain an upgraded understanding of the application value of genetic information from the cp genomes. The six cp genomes ranged from 152,049 bp (L. subcostata) to 152,526 bp (L. speciosa) in length. We analyzed nucleotide substitutions, insertions/deletions, and simple sequence repeats in the cp genomes, and discovered 12 relatively highly variable regions that will potentially provide plastid markers for further taxonomic, phylogenetic, and population genetics studies in Lagerstroemia. The phylogenetic relationships of the Lagerstroemia taxa inferred from the datasets from the cp genomes obtained high support, indicating that cp genome data may be useful in resolving relationships in this genus.