Comparative chloroplast genomics: analyses including new sequences from the angiosperms Nuphar advena and Ranunculus macranthus

Comparative genomics and phylogenetic analysis of six Malvaceae species based on chloroplast genomes

The Malvaceae family, comprising 9 subfamilies and 4,225 species, includes economically significant taxa, such as Ceiba pentandra, Gossypium ekmanianum, Gossypium stephensii, Kokia drynarioides, Talipariti hamabo, and Durio zibethinus. Chloroplast (cp) genome research is crucial for elucidating the evolutionary divergence and species identification within this family. In this study, we assembled and annotated cp genomes of six Malvaceae species, conducting comprehensive comparative genomic and phylogenomic analyses. The assembled genomes range from 160,495 to 163,970 bp in size, with 125-129 genes annotated. Notable differences were observed in the IR (inverted repeat) regions, and SSR analysis revealed that Durio zibethinus has the highest number of specific variation sites. Among the six species, Talipariti hamabo uniquely exhibits more palindromic repeats than forward repeats. Seven highly mutated regions were identified, offering potential markers for species identification. Phylogenetic reconstruction using the maximum likelihood method revealed two primary clades within Malvaceae: Byttneriina and Malvadendrina. Within Malvadendrina, the subfamily Helicteroideae represents the earliest divergence, followed by Sterculioideae. This study provides a robust phylogenetic framework and valuable insights into the classification and evolutionary history of Malvaceae species.

The complete chloroplast genome of Illicium verum and comparative analysis with related species from Magnoliaceae and Illiciaceae

Illicium verum (Illiciaceae), an ecologically significant endemic plant, predominantly grows in Guangxi, China, which is the primary region for its cultivation. This area accounts for more than 80% of the total cultivation and yield in China. Despite its importance, comprehensive studies on the chloroplast (cp) genome of I. verum are limited. In our research, we sequenced and analyzed the complete cp genome of I. verum and conducted a comparative analysis with nine related species from the families Magnoliaceae, Schisandraceae, and Illiciaceae. The cp genome of I. verum spans 143,187 base pairs (bp), comprising a large single copy (LSC) region of 100,868 bp, a small single copy (SSC) region of 20,235 bp, and two inverted repeats (IR) regions, each 11,042 bp in length. We identified 81 simple sequence repeats (SSRs) within this genome. The chloroplast genome contains 78 protein-coding genes, 8 ribosomal RNA (rRNA) genes, and 35 transfer RNA (tRNA) genes. Structurally, the IR regions exhibit greater similarity across different genera of Magnoliaceae and Illiciaceae compared to the LSC and SSC regions. Phylogenetic analysis revealed high homology between the cp genome of I. verum and those of Illicium burmanicum, Illicium simonsii, and Illicium anisatum. These findings suggest that the cp genome of I. verum may serve as a valuable genomic resource for elucidating the phylogenetic positions and relationships within the Illiciaceae family. This information will be instrumental for future taxonomic research on Illicium species and for advancing genomic studies of these plants.

Complete chloroplast genomes of three Polygala species and indel marker development for identification of authentic polygalae radix (Polygala tenuifolia)

BACKGROUND

In Korea, only Polygala tenuifolia is registered as Polygalae Radix in the pharmacopoeia, while in China, both P. tenuifolia and P. sibirica are used equally. Accurate identification of herbal medicines is crucial for their safety and efficacy, but commercial products are typically sold in dried form, making morphological distinction difficult. Therefore, a quick and accurate method to distinguish P. tenuifolia is necessary for proper utilization of medicinal herb.

OBJECTIVE

We aimed to identify specific molecular markers for P. tenuifolia to avoid confusion regarding its pharmacological efficacy and to evaluate the classification of Polygala using plastid phylogenetic data.

METHODS

We analyzed the sequences of three species distributed in Korea, P. tenuifolia, P. japonica, and P. sibirica, and assembled their chloroplast genome sequences. Comparative analysis revealed regions of local divergence, and six molecular markers were developed from these hotspots. Additionally, a phylogenetic tree was constructed to determine the phylogenetic positions of the three Polygala species.

RESULTS

The marker successfully identified the three Polygala species, and all commercial products and breeding lines tested were confirmed to be P. tenuifolia and recognized as authentic. Phylogenetic analysis revealed that P. tenuifolia forms a distinct cluster from P. sibirica and P. japonica.

CONCLUSIONS

We determined the chloroplast genomes of the three Polygala species and performed phylogenetic tree analysis and marker development. Indel markers were developed to identify the critical herbal species, P. tenuifolia. This comprehensive study of the Polygala chloroplast genome provides useful information for P. tenuifolia identification.

Comparative analysis of chloroplast genomes in ten holly (Ilex) species: insights into phylogenetics and genome evolution

In order to clarify the chloroplast genomes and structural features of ten Ilex species and provide insights into the phylogeny and genome evolution of the genus Ilex, we conducted a comparative analysis of chloroplast genomes using bioinformatics methods. The chloroplast genomes of ten Ilex species were obtained, and their structural features and variations were compared. The results indicated that all chloroplast genomes in the genus Ilex exhibit a double-stranded circular structure, with sizes ranging from 157,356 to 158,018 bp, showing minimal differences in size. The chloroplast genomes of the ten Ilex species have a relatively conservative gene count, with a total of 134 to 135 genes, including 88 or 89 protein-coding genes, and a conserved number of 8 rRNA genes. Each chloroplast genome contains 3 to 123 SSR (Simple Sequence Repeat) sites, predominantly composed of mononucleotide and trinucleotide repeats, with no detection of pentanucleotide or hexanucleotide repeats. The variation in dispersed repeat sequences among Ilex species is minimal, with a total repeat sequence number ranging from 1 to 14, concentrated in the length range of 30 to 42 base pairs. The expansion and contraction of chloroplast genome boundaries among Ilex species are relatively stable, with only minor variations observed in individual species. Variations in non-coding regions are more pronounced than those in coding regions, with the variability in the Large Single Copy region (LSC) being the highest, while the variability in the Inverted Repeat region A (IRa) is the lowest. The divergence time among Ilex species was estimated using the MCMC-tree module, revealing the evolutionary relationships among these species, their common ancestors, and their differentiation throughout the evolutionary process. The research findings provide a valuable reference for the systematic study and molecular marker development of Ilex plants.

The adaptive evolution of Quercus section Ilex using the chloroplast genomes of two threatened species

Chloroplast (cp) genome sequences have been extensively used for phylogenetic and evolutionary analyses, as many have been sequenced in recent years. Identification of Quercus is challenging because many species overlap phenotypically owing to interspecific hybridization, introgression, and incomplete lineage sorting. Therefore, we wanted to gain a better understanding of this genus at the level of the maternally inherited chloroplast genome. Here, we sequenced, assembled, and annotated the cp genomes of the threatened Quercus marlipoensis (160,995 bp) and Q. kingiana (161,167 bp), and mined these genomes for repeat sequences and codon usage bias. Comparative genomic analyses, phylogenomics, and selection pressure analysis were also performed in these two threatened species along with other species of Quercus. We found that the guanine and cytosine content of the two cp genomes were similar. All 131 annotated genes, including 86 protein-coding genes, 37 transfer RNA genes, and 8 ribosomal RNA genes, had the same order in the two species. A strong A/T bias was detected in the base composition of simple sequence repeats. Among the 59 synonymous codons, the codon usage pattern of the cp genomes in these two species was more inclined toward the A/U ending. Comparative genomic analyses indicated that the cp genomes of Quercus section Ilex are highly conserved. We detected eight highly variable regions that could be used as molecular markers for species identification. The cp genome structure was consistent and different within and among the sections of Quercus. The phylogenetic analysis showed that section Ilex was not monophyletic and was divided into two groups, which were respectively nested with section Cerris and section Cyclobalanopsis. The two threatened species sequenced in this study were grouped into the section Cyclobalanopsis. In conclusion, the analyses of cp genomes of Q. marlipoensis and Q. kingiana promote further study of the taxonomy, phylogeny and evolution of these two threatened species and Quercus.

Comparative plastome analyses and evolutionary relationships of 25 East Asian species within the medicinal plant genus Scrophularia (Scrophulariaceae)

Backgroud

Scrophularia L., a genus of the Scrophulariaceae, is a group of important medicinal plants used for eliminating heat and detoxifying. East Asia has an abundance of potentially medicinal Scrophularia species, and it serves as a secondary diversity center of the genus. However, the genomic resources available for germplasm identification and pharmaceutical exploration of East Asian Scrophularia are insufficient, hindering its commercial and industrial development. Additionally, the interspecific relationships of most East Asian Scrophularia species remain unclear.

Methods

In this study, we sequenced the leaves of 25 East Asian species of the genus Scrophularia, assembled and annotated the complete chloroplast genomes, and subsequently performed comparative and phylogenetic analyses on these genomes.

Results and discussion

The conserved plastome length of these 25 species ranged from 151,582 bp to 153,239 bp, containing a total of 132 coding genes, including 18 duplicated genes and 114 unique genes. Through genome alignment of these 25 species, 38-53 repeated sequences and 7 shared SSRs were identified, along with regions with high nucleotide polymorphism (Pi), which could potentially serve as molecular markers for species identification. The genome structure, gene content, and arrangement showed conservation, while variations were observed in the IR boundary regions and IGS. Phylogenetic inferences based on whole plastomes or on coding sequences (CDS) only yielded congruent results. We categorized the 25 East Asian Scrophularia species into six distinct clades and further explored their interspecies relationships using morphological characteristics, such as flower color, the relative position of stamens and corolla, and plant height. This could lay a genetic basis for future resource development of Scrophularia in East Asia.

Horizontal gene transfer from chloroplast to mitochondria of seagrasses in the yellow-Bohai seas

Seagrasses are ideal for studying plant adaptation to marine environments. In this study, the mitochondrial (mt) and chloroplast (cp) genomes of Ruppia sinensis were sequenced. The results showed an extensive gene loss in seagrasses, including a complete loss of cp-rpl19 genes in Zosteraceae, most cp-ndh genes in Hydrocharitaceae, and mt-rpl and mt-rps genes in all seagrasses, except for the mt-rpl16 gene in Phyllospadix iwatensis. Notably, most ribosomal protein genes were lost in the mt and cp genomes. The deleted cp genes were not transferred to the mt genomes through horizontal gene transfer. Additionally, a significant DNA transfer between seagrass organelles was found, with the mt genomes of Zostera containing numerous sequences from the cp genome. Rearrangement analyses revealed an unreported inversion of the cp genome in R. sinensis. Moreover, four positively selected genes (atp8, nad5, atp4, and ccmFn) and five variable regions (matR, atp4, atp8, rps7, and ccmFn) were identified.

Plastome structure and phylogenetic relationships of genus Hydrocotyle (apiales): provide insights into the plastome evolution of Hydrocotyle

BACKGROUND

The genus Hydrocotyle Tourn. ex L. is a key group for further study on the evolution of Apiales, comprising around 170 species globally. Previous studies mainly focused on separate sections and provided much information about this genus, but its infrageneric relationships are still confusing. In addition, the genetic basis of its adaptive evolution remains poorly understood. To investigate the phylogeny and evolution of the genus, we selected ten representative species covering two of three diversity distribution centers and exhibiting rich morphology diversity. Comparative plastome analysis was conducted to clarify the structural character of Hydrocotyle plastomes. Positive selection analyses were implemented to assess the evolution of the genus. Phylogenetic inferences with protein-coding sequences (CDS) of Hydrocotyle and 17 related species were also performed.

RESULTS

Plastomes within Hydrocotyle were generally conservative in structure, gene order, and size. A total of 14 regions (rps16-trnK, trnQ-rps16, atpI-atpH, trnC-petN-psbM, ycf3-trnS, accD-psaI-ycf4, petA-psbJ, rps12-rpl20, rpl16 intron, rps3-rpl16 intron, rps9-rpl22, ndhF-rpl32, ndhA intron, and ycf1a) were recognized as hotspot regions within the genus, which suggested to be promising DNA barcodes for global phylogenetic analysis of Hydrocotyle. The ycf15 gene was suggested to be a protein-coding gene for Hydrocotyle species, and it could be used as a DNA barcode to identify Hydrocotyle. In phylogenetic analysis, three monophyletic clades (Clade I, II, III) were identified with evidence of rapid radiation speciation within Clade I. The selective pressure analysis detected that six CDS genes (ycf1b, matK, atpF, accD, rps14, and psbB) of Hydrocotyle species were under positive selection. Within the genus, the last four genes were conservative, suggesting a relation to the unique evolution of the genus in Apiales. Seven genes (atpE, matK, psbH, ycf1a, ycf1b, rpoA, and ycf2) were detected to be under some degree of positive selection in different taxa within the genus Hydrocotyle, indicating their role in the adaptive evolution of species.

CONCLUSIONS

Our study offers new insights into the phylogeny and adaptive evolution of Hydrocotyle. The plastome sequences could significantly enhance phylogenetic resolution and provide genomic resources and potential DNA markers useful for future studies of the genus.

Exploring the Evolutionary History and Phylogenetic Relationships of Giant Reed (Arundo donax) through Comprehensive Analysis of Its Chloroplast Genome

Giant reed (Arundo donax) is widely distributed across the globe and is considered an important energy crop. This study presents the first comprehensive analysis of the chloroplast genome of giant reed, revealing detailed characteristics of this species' chloroplast genome. The chloroplast genome has a total length of 137,153 bp, containing 84 protein-coding genes, 38 tRNA genes, and 8 rRNA genes, with a GC content of 39%. Functional analysis indicates that a total of 45 photosynthesis-related genes and 78 self-replication-related genes were identified, which may be closely associated with its adaptability and growth characteristics. Phylogenetic analysis confirmed that Arundo donax cv. Lvzhou No.1 belongs to the Arundionideae clade and occupies a distinct evolutionary position compared to other Arundo species. The findings of this study not only enhance our understanding of the giant reed genome but also provide valuable genetic resources for its application in biotechnology, bioenergy crop development, and ecological restoration.

Complete plastome genomes of three medicinal heliotropiaceae species: comparative analyses and phylogenetic relationships

BACKGROUND

Heliotropiaceae is a family of the order Boraginales and has over 450 species. The members of the family Heliotropiaceae have been widely reported to be used in traditional medicine Over time, the classification of Heliotropiaceae has remained uncertain and has moved from family to subfamily, or conversely.

RESULTS

In the present study, we sequenced, analyzed, and compared the complete plastomes of Euploca strigosa, Heliotropium arbainense, and Heliotropium longiflorum with the genomes of related taxa. The lengths of the plastomes of E. strigosa, H. arbainense, and H. longiflorum were 155,174 bp, 154,709 bp, and 154,496 bp, respectively. Each plastome consisted of 114 genes: 80 protein-coding genes, 4 ribosomal RNA genes, and 30 transfer RNA genes. The long repeats analysis indicated that reverse, palindromic, complement and forward repeats were all found in the three plastomes. The simple repeats analysis showed that the plastomes of E. strigosa, H. arbainense, and H. longiflorum contained 158, 165, and 151 microsatellites, respectively. The phylogenetic analysis confirmed two major clades in the Boraginales: clade I comprised Boraginaceae, while clade II included Heliotropiaceae, Ehretiaceae, Lennoaceae, and Cordiaceae. Inside the family Heliotropiaceae, E. strigosa is nested within the Heliotropium genus.

CONCLUSIONS

This study expands our knowledge of the evolutionary relationships within Heliotropiaceae and offers useful genetic resources.

Genetic characterization and phylogenetic analysis of the Nigella sativa (black seed) plastome

In this study, the complete plastome sequence of Nigella sativa (black seed), was analyzed for the first time. The plastome spans approximately 154,120 bp, comprising four sections: the Large Single-Copy (LSC) (85,538 bp), the Small Single-Copy (SSC) (17,984 bp), and two Inverted Repeat (IR) regions (25,299 bp). A comparative study of N. sativa's plastome with ten other species from various genera in the Ranunculaceae family reveals substantial structural variations. The contraction of the inverted repeat region in N. sativa influences the boundaries of single-copy regions, resulting in a shorter plastome size than other species. When comparing the plastome of N. sativa with those of its related species, significant divergence is observed, particularly except for N. damascena. Among these, the plastome of A. glaucifolium displays the highest average pairwise sequence divergence (0.2851) with N. sativa, followed by A. raddeana (0.2290) and A. coerulea (0.1222). Furthermore, the study identified 12 distinct hotspot regions characterized by elevated Pi values (> 0.1). These regions include trnH-GUG-psbA, matK-trnQ-UUG, psbK-trnR-UCU, atpF-atpI, rpoB-psbD, ycf3-ndhJ, ndhC-cemA, petA-psaJ, trnN-GUU-ndhF, trnV-GAC-rps12, ycf2-trnI-CAU, and ndhA-ycf1. Approximately, 24 tandem and 48 palindromic and forward repeats were detected in N. sativa plastome. The analysis revealed 32 microsatellites with the majority being mononucleotide repeats. In the N. sativa plastome, phenylalanine had the highest number of codons (1982 codons), while alanine was the least common amino acid with 260 codons. A phylogenetic tree, constructed using protein-coding genes, revealed a distinct monophyletic clade comprising N. sativa and N. damascene, closely aligned with the Cimicifugeae tribe and exhibiting robust support. This plastome provides valuable genetic information for precise species identification, phylogenetic resolution, and evolutionary studies of N. sativa.

Complete chloroplast genome structural characterization of two Aerides (Orchidaceae) species with a focus on phylogenetic position of Aerides flabellata

BACKGROUND

The disputed phylogenetic position of Aerides flabellata Rolfe ex Downie, due to morphological overlaps with related species, was investigated based on evidence of complete chloroplast (cp) genomes. The structural characterization of complete cp genomes of A. flabellata and A. rosea Lodd. ex Lindl. & Paxton were analyzed and compared with those of six related species in "Vanda-Aerides alliance" to provide genomic information on taxonomy and phylogeny.

RESULTS

The cp genomes of A. flabellata and A. rosea exhibited conserved quadripartite structures, 148,145 bp and 147,925 bp in length, with similar GC content (36.7 ~ 36.8%). Gene annotations revealed 110 single-copy genes, 18 duplicated in inverted regions, and ten with introns. Comparative analysis across related species confirmed stable sequence identity and higher variation in single-copy regions. However, there are notable differences in the IR regions between two Aerides Lour. species and the other six related species. The phylogenetic analysis based on CDS from complete cp genomes indicated that Aerides species except A. flabellata formed a monophyletic clade nested in the subtribe Aeridinae, being a sister group to Renanthera Lour., consistent with previous studies. Meanwhile, a separate clade consisted of A. flabellata and six Vanda R. Br. species was formed, as a sister taxon to Holcoglossum Schltr.

CONCLUSIONS

This research was the first report on the complete cp genomes of A. flabellata. The results provided insights into understanding of plastome evolution and phylogenetic relationships of Aerides. The phylogenetic analysis based on complete cp genomes showed that A. flabellata should be placed in Vanda rather than in Aerides.

Chloroplast genome analysis and evolutionary insights in the versatile medicinal plant Calendula officinalis L

Calendula officinalis L.is a versatile medicinal plant with numerous applications in various fields. However, its chloroplast genome structure, features, phylogeny, and patterns of evolution and mutation remain largely unexplored. This study examines the chloroplast genome, phylogeny, codon usage bias, and divergence time of C. officinalis, enhancing our understanding of its evolution and adaptation. The chloroplast genome of C. officinalis is a 150,465 bp circular molecule with a G + C content of 37.75% and comprises 131 genes. Phylogenetic analysis revealed a close relationship between C. officinalis, C. arvensis, and Osteospermum ecklonis. A key finding is the similarity in codon usage bias among these species, which, coupled with the divergence time analysis, supports their close phylogenetic proximity. This similarity in codon preference and divergence times underscores a parallel evolutionary adaptation journey for these species, highlighting the intricate interplay between genetic evolution and environmental adaptation in the Asteraceae family. Moreover unique evolutionary features in C. officinalis, possibly associated with certain genes were identified, laying a foundation for future research into the genetic diversity and medicinal value of C. officinalis.

Sequence characteristics, genetic diversity and phylogenetic analysis of the Cucurbita ficifolia (Cucurbitaceae) chloroplasts genome

BACKGROUND

Curcubita ficifolia Bouché (Cucurbitaceae) has high value as a food crop and medicinal plant, and also has horticultural value as rootstock for other melon species. China is home to many different cultivars, but the genetic diversity of these resources and the evolutionary relationships among them, as well as the differences between C. ficifolia and other Cucurbita species, remain unclear.

RESULTS

We investigated the chloroplast (cp) genomes of 160 C. ficifolia individuals from 31 populations in Yunnan, a major C. ficifolia production area in China. We found that the cp genome of C. ficifolia is ~151 kb and contains 128 genes, of which 86 are protein coding genes, 34 encode tRNA, and eight encode rRNAs. We also identified 64 SSRs, mainly AT repeats. The cp genome was found to contain a total of 204 SNP and 57 indels, and a total of 21 haplotypes were found in the 160 study individuals. The reverse repeat (IR) region of C. ficifolia contained a few differences compared with this region in the six other Cucurbita species. Sequence difference analysis demonstrated that most of the variable regions were concentrated in the single copy (SC) region. Moreover, the sequences of the coding regions were found to be more similar among species than those of the non-coding regions. The phylogenies reconstructed from the cp genomes of 61 representative species of Cucurbitaceae reflected the currently accepted classification, in which C. ficifolia is sister to the other Cucurbita species, however, different interspecific relationships were found between Cucurbita species.

CONCLUSIONS

These results will be valuable in the classification of C. ficifolia genetic resources and will contribute to our understanding of evolutionary relationships within the genus Cucurbita.

Phylogeny and Taxonomic Revision of the Genus Melanosciadium (Apiaceae), Based on Plastid Genomes and Morphological Evidence

Melanosciadium is considered a monotypic genus and is also endemic to the southwest of China. No detailed phylogenetic studies or plastid genomes have been identified in Melanosciadium. In this study, the plastid genome sequence and nrDNA sequence were used for the phylogenetic analysis of Melanosciadium and its related groups. Angelica tsinlingensis was previously considered a synonym of Hansenia forbesii. Similarly, Ligusticum angelicifolium was previously thought to be the genus Angelica or Ligusticopsis. Through field observations and morphological evidence, we believe that the two species are more similar to M. pimpinelloideum in leaves, umbel rays, and fruits. Meanwhile, we found a new species from Anhui Province (eastern China) that is similar to M. pimpinelloideum and have named it M. Jinzhaiensis. We sequenced and assembled the complete plastid genomes of these species and another three Angelica species. The genome comparison results show that M. pimpinelloideum, A. tsinlingensis, Ligusticum angelicifolium, and M. jinzhaiensis have similarities to each other in the plastid genome size, gene number, and length of the LSC and IR regions; the plastid genomes of these species are distinct from those of the Angelica species. In addition, we reconstruct the phylogenetic relationships using both plastid genome sequences and nrDNA sequences. The phylogenetic analysis revealed that A. tsinlingensis, M. pimpinelloideum, L. angelicifolium, and M. jinzhaiensis are closely related to each other and form a monophyletic group with strong support within the Selineae clade. Consequently, A. tsinlingensis and L. angelicifolium should be classified as members of the genus Melanosciadium, and suitable taxonomical treatments have been proposed. Meanwhile, a comprehensive description of the new species, M. jinzhaiensis, is presented, encompassing its habitat environment and detailed morphological traits.

Complete chloroplast genome and comparison of herbicides toxicity on Aeschynomene indica (Leguminosae) in upland direct-seeding paddy field

BACKGROUND

Indian jointvetch (Aeschynomene indica) is a common and pernicious weed found in the upland direct-seeding rice fields in the lower reaches of the Yangtze River in China. However, there are few reports on the degree of harm, genetic characteristics, and management methods of this weed. The purpose of this study is to clarify the harm of Indian jointvetch to upland direct-seeding rice, analyze the genetic characteristics of this weed based on chloroplast genomics and identify its related species, and screen herbicides that are effective in managing this weed in upland direct-seeding rice fields.

RESULTS

In a field investigation in upland direct-seeding rice paddies in Shanghai and Jiangsu, we determined that the plant height and maximum lateral distance of Indian jointvetch reached approximately 134.2 cm and 57.9 cm, respectively. With Indian jointvetch present at a density of 4/m2 and 8/m2, the yield of rice decreased by approximately 50% and 70%, respectively. We further obtained the first assembly of the complete chloroplast (cp.) genome sequence of Indian jointvetch (163,613 bp). There were 161 simple sequence repeats, 166 long repeats, and 83 protein-encoding genes. The phylogenetic tree and inverted repeat region expansion and contraction analysis based on cp. genomes demonstrated that species with closer affinity to A. indica included Glycine soja, Glycine max, and Sesbania cannabina. Moreover, a total of 3281, 3840, and 3838 single nucleotide polymorphisms were detected in the coding sequence regions of the cp. genomes of S. cannabina voucher IBSC, G. soja, and G. max compared with the A. indica sequence, respectively. A greenhouse pot experiment indicated that two pre-emergence herbicides, saflufenacil and oxyfluorfen, and two post-emergence herbicides, florpyrauxifen-benzyl and penoxsulam, can more effectively manage Indian jointvetch than other common herbicides in paddy fields. The combination of these two types of herbicides is recommended for managing Indian jointvetch throughout the entire growth period of upland direct-seeding rice.

CONCLUSIONS

This study provides molecular resources for future research focusing on the identification of the infrageneric taxa, phylogenetic resolution, and biodiversity of Leguminosae plants, along with recommendations for reliable management methods to control Indian jointvetch.

The complete plastome sequences of invasive weed Parthenium hysterophorus: genome organization, evolutionary significance, structural features, and comparative analysis

Parthenium hysterophorus, a globally widespread weed, poses a significant threat to agricultural ecosystems due to its invasive nature. We investigated the chloroplast genome of P. hysterophorus in this study. Our analysis revealed that the chloroplast genome of P. hysterophorus spans a length of 151,881 base pairs (bp). It exhibits typical quadripartite structure commonly found in chloroplast genomes, including inverted repeat regions (IR) of 25,085 bp, a small single copy (SSC) region of 18,052 bp, and a large single copy (LSC) region of 83,588 bp. A total of 129 unique genes were identified in P. hysterophorus chloroplast genomes, including 85 protein-coding genes, 36 tRNAs, and eight rRNAs genes. Comparative analysis of the P. hysterophorus plastome with those of related species from the tribe Heliantheae revealed both conserved structures and intriguing variations. While many structural elements were shared among the species, we identified a rearrangement in the large single-copy region of P. hysterophorus. Moreover, our study highlighted notable gene divergence in several specific genes, namely matK, ndhF, clpP, rps16, ndhA, rps3, and ndhD. Phylogenetic analysis based on the 72 shared genes placed P. hysterophorus in a distinct clade alongside another species, P. argentatum. Additionally, the estimated divergence time between the Parthenium genus and Helianthus (sunflowers) was approximately 15.1 million years ago (Mya). These findings provide valuable insights into the evolutionary history and genetic relationships of P. hysterophorus, shedding light on its divergence and adaptation over time.

Complete plastid genome structure of 13 Asian Justicia (Acanthaceae) species: comparative genomics and phylogenetic analyses

BACKGROUND

Justicia L. is the largest genus in Acanthaceae Juss. and widely distributed in tropical and subtropical regions of the world. Previous phylogenetic studies have proposed a general phylogenetic framework for Justicia based on several molecular markers. However, their studies were mainly focused on resolution of phylogenetic issues of Justicia in Africa, Australia and South America due to limited sampling from Asia. Additionally, although Justicia plants are of high medical and ornamental values, little research on its genetics was reported. Therefore, to improve the understanding of its genomic structure and relationships among Asian Justicia plants, we sequenced complete chloroplast (cp.) genomes of 12 Asian plants and combined with the previously published cp. genome of Justicia leptostachya Hemsl. for further comparative genomics and phylogenetic analyses.

RESULTS

All the cp. genomes exhibit a typical quadripartite structure without genomic rearrangement and gene loss. Their sizes range from 148,374 to 151,739 bp, including a large single copy (LSC, 81,434-83,676 bp), a small single copy (SSC, 16,833-17,507 bp) and two inverted repeats (IR, 24,947-25,549 bp). GC contents range from 38.1 to 38.4%. All the plastomes contain 114 genes, including 80 protein-coding genes, 30 tRNAs and 4 rRNAs. IR variation and repetitive sequences analyses both indicated that Justicia grossa C. B. Clarke is different from other Justicia species because its lengths of ndhF and ycf1 in IRs are shorter than others and it is richest in SSRs and dispersed repeats. The ycf1 gene was identified as the candidate DNA barcode for the genus Justicia. Our phylogenetic results showed that Justicia is a polyphyletic group, which is consistent with previous studies. Among them, J. grossa belongs to subtribe Tetramerinae of tribe Justicieae while the other Justicia members belong to subtribe Justiciinae. Therefore, based on morphological and molecular evidence, J. grossa should be undoubtedly recognized as a new genus. Interestingly, the evolutionary history of Justicia was discovered to be congruent with the morphology evolution.

CONCLUSION

Our study not only elucidates basic features of Justicia whole plastomes, but also sheds light on interspecific relationships of Asian Justicia plants for the first time.

The complete chloroplast genome of Ranunculus ternatus (Ranunculaceae)

Ranunculus ternatus Thunb. 1784 is a plant with important medicinal values. Here we report its chloroplast genome. This chloroplast genome was 156,003 bp in length with a GC content of 37.86%. It is composed of a large single copy (LSC) of 85,397 bp and a small single copy (SSC) of 19,856 bp, which are separated by a pair of inverted repeats (IR) of 25,375 bp each. The chloroplast genome contained 110 unique genes, including 77 protein-coding genes, 4 rRNA genes, and 29 tRNA genes. Phylogenetic analysis indicated that R. ternatus was closely related to R. cassubicifolius. This chloroplast genome not only enriches the genome information of Ranunculus but also will be useful for the evolution study of the family Ranunculaceae.

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

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

Characterization and Comparative Analysis of the Complete Plastomes of Five Epidendrum (Epidendreae, Orchidaceae) Species

Epidendrum, one of the three largest genera of Orchidaceae, exhibits significant horticultural and ornamental value and serves as an important research model in conservation, ecology, and evolutionary biology. Given the ambiguous identification of germplasm and complex evolutionary relationships within the genus, the complete plastome of this genus (including five species) were firstly sequenced and assembled to explore their characterizations. The plastomes exhibited a typical quadripartite structure. The lengths of the plastomes ranged from 147,902 bp to 150,986 bp, with a GC content of 37.16% to 37.33%. Gene annotation revealed the presence of 78-82 protein-coding genes, 38 tRNAs, and 8 rRNAs. A total of 25-38 long repeats and 130-149 SSRs were detected. Analysis of relative synonymous codon usage (RSCU) indicated that leucine (Leu) was the most and cysteine (Cys) was the least. The consistent and robust phylogenetic relationships of Epidendrum and its closely related taxa were established using a total of 43 plastid genomes from the tribe Epidendreae. The genus Epidendrum was supported as a monophyletic group and as a sister to Cattleya. Meanwhile, four mutational hotspots (trnCGCA-petN, trnDGUC-trnYGUA, trnSGCU-trnGUCC, and rpl32-trnLUAG) were identified for further phylogenetic studies. Our analysis demonstrates the promising utility of plastomes in inferring the phylogenetic relationships of Epidendrum.

Comparative Plastomes of Curcuma alismatifolia (Zingiberaceae) Reveal Diversified Patterns among 56 Different Cut-Flower Cultivars

Curcuma alismatifolia (Zingiberaceae) is an ornamental species with high economic value due to its recent rise in popularity among floriculturists. Cultivars within this species have mixed genetic backgrounds from multiple hybridization events and can be difficult to distinguish via morphological and histological methods alone. Given the need to improve identification resources, we carried out the first systematic study using plastomic data wherein genomic evolution and phylogenetic relationships from 56 accessions of C. alismatifolia were analyzed. The newly assembled plastomes were highly conserved and ranged from 162,139 bp to 164,111 bp, including 79 genes that code for proteins, 30 tRNA genes, and 4 rRNA genes. The A/T motif was the most common of SSRs in the assembled genomes. The Ka/Ks values of most genes were less than 1, and only two genes had Ka/Ks values above 1, which were rps15 (1.15), and ndhl (1.13) with petA equal to 1. The sequence divergence between different varieties of C. alismatifolia was large, and the percentage of variation in coding regions was lower than that in the non-coding regions. Such data will improve cultivar identification, marker assisted breeding, and preservation of germplasm resources.

Comparative Phylogenetic Analysis for Aerides (Aeridinae, Orchidaceae) Based on Six Complete Plastid Genomes

Aerides Lour. (Orchidaceae, Aeridinae) is a group of epiphytic orchids with high ornamental value, mainly distributed in tropical and subtropical forests, that comprises approximately 20 species. The species are of great value in floriculture and garden designing because of their beautiful flower shapes and colors. Although the morphological boundaries of Aerides are clearly defined, the relationship between Aerides and other closely related genera is still ambiguous in terms of phylogeny. To better understand their phylogenetic relationships, this study used next-generation sequencing technology to investigate the phylogeny and DNA barcoding of this taxonomic unit using genetic information from six Aerides plastid genomes. The quadripartite-structure plastomes ranged from 147,244 bp to 148,391 bp and included 120 genes. Among them, 74 were protein coding genes, 38 were tRNA genes and 8 were rRNA genes, while the ndh genes were pseudogenized or lost. Four non-coding mutational hotspots (rpl20-rpl33, psbM, petB, rpoB-trnCGCA, Pi > 0.06) were identified. A total of 71-77 SSRs and 19-46 long repeats (>30 bp) were recognized in Aerides plastomes, which were mostly located in the large single-copy region. Phylogenetic analysis indicated that Aerides was monophylic and sister to Renanthera. Moreover, our results confirmed that six Aerides species can be divided into three major clades. These findings provide assistance for species identification and DNA barcoding investigation in Aerides, as well as contributes to future research on the phylogenomics of Orchidaceae.

Phylogeny of Leontopodium (Asteraceae) in China-with a reference to plastid genome and nuclear ribosomal DNA

The infrageneric taxonomy system, species delimitation, and interspecies systematic relationships of Leontopodium remain controversial and complex. However, only a few studies have focused on the molecular phylogeny of this genus. In this study, the characteristics of 43 chloroplast genomes of Leontopodium and its closely related genera were analyzed. Phylogenetic relationships were inferred based on chloroplast genomes and nuclear ribosomal DNA (nrDNA). Finally, together with the morphological characteristics, the relationships within Leontopodium were identified and discussed. The results showed that the chloroplast genomes of Filago, Gamochaeta, and Leontopodium were well-conserved in terms of gene number, gene order, and GC content. The most remarkable differences among the three genera were the length of the complete chloroplast genome, large single-copy region, small single-copy region, and inverted repeat region. In addition, the chloroplast genome structure of Leontopodium exhibited high consistency and was obviously different from that of Filago and Gamochaeta in some regions, such as matk, trnK (UUU)-rps16, petN-psbM, and trnE (UUC)-rpoB. All the phylogenetic trees indicated that Leontopodium was monophyletic. Except for the subgeneric level, our molecular phylogenetic results were inconsistent with the previous taxonomic system, which was based on morphological characteristics. Nevertheless, we found that the characteristics of the leaf base, stem types, and carpopodium base were phylogenetically correlated and may have potential value in the taxonomic study of Leontopodium. In the phylogenetic trees inferred using complete chloroplast genomes, the subgen. Leontopodium was divided into two clades (Clades 1 and 2), with most species in Clade 1 having herbaceous stems, amplexicaul, or sheathed leaves, and constricted carpopodium; most species in Clade 2 had woody stems, not amplexicaul and sheathed leaves, and not constricted carpopodium.

Complete Chloroplast Genomes and Comparative Analyses of Three Paraphalaenopsis (Aeridinae, Orchidaceae) Species

Paraphalaenopsis, a genus of perennial herbs from the family Orchidaceae, contains a number of ornamental species. However, there is no information on the chloroplast genomes of Paraphalaenopsis, which limits our studies of this genus. In this study, we reported the chloroplast genomes of three species of Paraphalaenopsis (P. labukensis, P. denevel, and P. laycockii 'Semi-alba') and performed comprehensive comparative analysis. These three chloroplast genomes showed a typical quadripartile structure. Their lengths ranged from 147,311 bp to 149,240 bp. Each genome contained 120 unique genes, including 74 protein-coding genes, 38 tRNA genes, and 8 rRNA genes. Comparative analysis revealed major differences in sequence divergence in the three chloroplast genomes. In addition, six hypervariable regions were identified (psbM-trnD^GUC, psbB, ccsA, trnK^UUU, trnS^GCU-trnG^UCC, rps16-trnQ^UUG) that can be used as DNA molecular markers. Phylogenetic relationships were determined using the chloroplast genomes of 28 species from 12 genera of Aeridinae. Results suggested that Paraphalaenopsis was a clade of Aeridinae that was sister to the Holcoglossum-Vanda clade, with 100% bootstrap support within Aeridinae. The findings of this study provided the foundation for future studies on the phylogenetic analysis of Aeridinae.

Phylogeny of Trigonotis in China-with a special reference to its nutlet morphology and plastid genome

The genus Trigonotis comprises nearly 60 species mainly distributed in East and Southeast Asia. China has the largest number of Trigonotis species in the world, with a total of 44 species, of which 38 are endemic. Nutlet morphology is useful for the taxonomic delimitation of Trigonotis. However, there are still controversial circumscriptions of nutlet shape in some species. In previous studies, interspecies phylogenetic relationships were inferred using few DNA markers and very few taxa, which possibly led to erroneous or incomplete conclusions. In this study, the nutlet morphology of 39 Trigonotis taxa and the characteristics of 34 complete chloroplast genomes (29 taxa) were investigated and analyzed. Then, the phylogenetic relationships were discussed within this genus based on complete chloroplast genomes. To the best of our knowledge, this study is the first comprehensive analysis of nutlet morphology and complete chloroplast genome of Trigonotis. Based on nutlet morphology, Trigonotis can be divided into two groups: Group 1, hemispherical or oblique tetrahedron with carpopodiums, and Group 2, inverted tetrahedron without carpopodiums. The chloroplast genome of Trigonotis exhibited a typical quadripartite structure, including 84-86 protein-coding, 37 transfer RNA, and 8 ribosomal RNA genes, with a total length of 147,247-148,986 bp. Genes in the junctions were well conserved in Trigonotis, similar to those in other Boraginaceae s.str. species. Furthermore, Trigonotis chloroplast genomes showed relatively high diversity, with more conserved genic regions than intergenic regions; in addition, we detected 14 hot spots (Pi > 0.005) in non-coding regions. Phylogenetic analyses based on chloroplast genome data identified highly resolved relationships between Trigonotis species. Specifically, Trigonotis was divided into two clades with strong support: one clade included species with hemispherical or oblique tetrahedron nutlets with carpopodiums and bracts, whereas the other clade included species with inverted tetrahedron nutlets without carpopodiums or bracts. Our results may inform future taxonomic, phylogenetic, and evolutionary studies on Boraginaceae.

Complete Chloroplast Genome Determination of Ranunculus sceleratus from Republic of Korea (Ranunculaceae) and Comparative Chloroplast Genomes of the Members of the Ranunculus Genus

Ranunculus sceleratus (family: Ranunculaceae) is a medicinally and economically important plant; however, gaps in taxonomic and species identification limit its practical applicability. This study aimed to sequence the chloroplast genome of R. sceleratus from Republic of Korea. Chloroplast sequences were compared and analyzed among Ranunculus species. The chloroplast genome was assembled from Illumina HiSeq 2500 sequencing raw data. The genome was 156,329 bp and had a typical quadripartite structure comprising a small single-copy region, a large single-copy region, and two inverted repeats. Fifty-three simple sequence repeats were identified in the four quadrant structural regions. The region between the ndhC and trnV-UAC genes could be useful as a genetic marker to distinguish between R. sceleratus populations from Republic of Korea and China. The Ranunculus species formed a single lineage. To differentiate between Ranunculus species, we identified 16 hotspot regions and confirmed their potential using specific barcodes based on phylogenetic tree and BLAST-based analyses. The ndhE, ndhF, rpl23, atpF, rps4, and rpoA genes had a high posterior probability of codon sites in positive selection, while the amino acid site varied between Ranunculus species and other genera. Comparison of the Ranunculus genomes provides useful information regarding species identification and evolution that could guide future phylogenetic analyses.

Chloroplast genome analysis of three Acanthus species reveal the adaptation of mangrove to intertidal habitats

Acanthus is a distinctive genus that covers three species with different ecological niches including Acanthus mollis (arid terrestrial), Acanthus leucostachyus (damp forest) and Acanthus ilicifolius (coastal intertidal). It is an intriguing question how these species evolved from terrestrial to coastal intertidal. In the present study, we assembled chloroplast genomes of A. ilicifolius, A. leucostachyus and A. mollis, which exhibited typical quadripartite structures. The sizes were 150,758, 154,686 and 150,339 bp that comprised a large single copy (LSC, 82,963, 86,461 and 82,612 bp), a small single copy (SSC, 17,191, 17,511 and 17,019 bp), and a pair of inverted repeats (IRs, 25,302, 25,357 and 25,354 bp), respectively. Gene annotation revealed that A. ilicifolius, A. leucostachyus and A. mollis contained 113, 112 and 108 unique genes, each of which contained 79, 79 and 74 protein-coding genes, 30, 29 and 30 tRNAs, and 4 rRNA genes, respectively. Differential gene analysis revealed plenty of ndhs gene deletions in the terrestrial plant A. mollis. Nucleotide diversity analysis showed that the psbK, ycf1, ndhG, and rpl22 have the highest nucleotide variability. Compared to A. leucostachyus and A. mollis, seven genes in A. ilicifolius underwent positive selection. Among them, the atpF gene showed a strong positive selection throughout terrestrial to marine evolution and was important for adaptation to coastal intertidal habitats. Phylogenetic analysis indicated that A. ilicifolius has a closer genetic relationship with A. leucostachyus than A. mollis which further confirmed the evolutionary direction of Acanthus going from terrestrial to coastal intertidal zones.

The First Complete Chloroplast Genome of Cordia monoica: Structure and Comparative Analysis

Cordia monoica is a member of the Boraginaceae family. This plant is widely distributed in tropical regions and has a great deal of medical value as well as economic importance. In the current study, the complete chloroplast (cp) genome of C. monoica was sequenced, assembled, annotated, and reported. This circular chloroplast genome had a size of 148,711 bp, with a quadripartite structure alternating between a pair of repeated inverted regions (26,897-26,901 bp) and a single copy region (77,893 bp). Among the 134 genes encoded by the cp genome, there were 89 protein-coding genes, 37 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. A total of 1387 tandem repeats were detected, with the hexanucleotides class making up 28 percent of the repeats. Cordia monoica has 26,303 codons in its protein-coding regions, and leucine amino acid was the most frequently encoded amino acid in contrast to cysteine. In addition, 12 of the 89 protein-coding genes were found to be under positive selection. The phyloplastomic taxonomical clustering of the Boraginaceae species provides further evidence that chloroplast genome data are reliable not only at family level but also in deciphering the phylogeny at genus level (e.g., Cordia).

A Comparative Analysis of the Chloroplast Genomes of Three Lonicera Medicinal Plants

Both Lonicerae japonicae flos and Lonicerae similis flos are important components in traditional Chinese medicine (TCM) with precious medicinal value. However, the absence of studies on their chloroplast genomes and chromatography has considerably hindered the study of their evolutionary and phylogenetic relationships. In this study, the complete chloroplast (cp) genomes of Lonicera acuminata Wall. and Lonicera similis Hemsl. were sequenced using the Illumina sequencing platform and compared with that of Lonicera japonica Thunb., which has been previously reported. Furthermore, the chromatographic fingerprints of the three plants were constructed using HPLC and the content of quality marker (Q-Marker) was calculated. The annotation results showed that the two chloroplast genomes were typical quadripartite structures with lengths of 155,330 bp (L. acuminata) and 155,207 bp (L. similis). A total of 126 different genes were annotated, containing 82 protein-coding genes, 36 tRNA genes, and 8 rRNA genes. The expansion and contraction of the inverted repeat (IR) regions suggested that the boundary regions of IR/SC were comparatively conserved in the three species, and six regions (trnH-GUG-psbA, rps2-rpoC2, rbcL-psaI, trnN-GUU-ndhF, rps15-ycf1, and infA) with nucleotide diversity values (Pi) of variable sites higher than 1% were identified. Phylogenetic relation indicated that L. similis had a closer genetic relationship with L. japonica than L. acuminata. Additionally, the chromatographic fingerprints showed that the characteristic peaks of the three medicinal plants were similar, including Neochlorogenic acid, Chlorogenic acid, 4-Dicaffeoylquinic acid, Sweroside, Secoxyloganin, Luteoloside, Isochlorogenic acid A, Isochlorogenic acid B, and Isochlorogenic acid C. The content of chlorogenic acid and total phenolic acid in L. acuminata (7.4633 ± 0.4461%, 14.8953 ± 0.0728%) and L. similis (14.1055 ± 0.2566%, 21.9782 ± 0.1331%) was much higher than that of L. japonica (3.9729 ± 0.0928%, 6.0964 ± 0.1228%), respectively. This study provides appropriate information for species identification, phylogeny, quality assessment, and rational use of three medicinal plants of the genus Lonicera.

The complete chloroplast genome of Hibiscus syriacus using long-read sequencing: Comparative analysis to examine the evolution of the tribe Hibisceae

Hibiscus syriacus, a member of the tribe Hibisceae, is considered an important ornamental and medicinal plant in east Asian countries. Here, we sequenced and assembled the complete chloroplast genome of H. syriacus var. Baekdansim using the PacBio long-read sequencing platform. A quadripartite structure with 161,026 base pairs was obtained, consisting of a pair of inverted repeats (IRA and IRB) with 25,745 base pairs, separated by a large single-copy region of 89,705 base pairs and a short single-copy region of 19,831 base pairs. This chloroplast genome had 79 protein-coding genes, 30 transfer RNA genes, 4 ribosomal RNA genes, and 109 simple sequence repeat regions. Among them, ndhD and rpoC1, containing traces of RNA-editing events associated with adaptive evolution, were identified by analysis of putative RNA-editing sites. Codon usage analysis revealed a preference for A/U-terminated codons. Furthermore, the codon usage pattern had a clustering tendency similar to that of the phylogenetic analysis of the tribe Hibisceae. This study provides clues for understanding the relationships and refining the taxonomy of the tribe Hibisceae.

Assembly, annotation, and comparative analysis of Ipomoea chloroplast genomes provide insights into the parasitic characteristics of Cuscuta species

In the Convolvulaceae family, around 1650 species belonging to 60 genera are widely distributed globally, mainly in the tropical and subtropical regions of America and Asia. Although a series of chloroplast genomes in Convolvulaceae were reported and investigated, the evolutionary and genetic relationships among the chloroplast genomes of the Convolvulaceae family have not been extensively elucidated till now. In this study, we first reported the complete chloroplast genome sequence of Ipomoea pes-caprae, a widely distributed coastal plant with medical values. The chloroplast genome of I. pes-caprae is 161667 bp in length, and the GC content is 37.56%. The chloroplastic DNA molecule of I. pes-caprae is a circular structure composed of LSC (large-single-copy), SSC (small-single-copy), and IR (inverted repeat) regions, with the size of the three regions being 88210 bp, 12117 bp, and 30670 bp, respectively. The chloroplast genome of I. pes-caprae contains 141 genes, and 35 SSRs are identified in the chloroplast genome. Our research results provide important genomic information for the molecular phylogeny of I. pes-caprae. The Phylogenetic analysis of 28 Convolvulaceae chloroplast genomes showed that the relationship of I. pes-caprae with I. involucrata or I. obscura was much closer than that with other Convolvulaccae species. Further comparative analyses between the Ipomoea species and Cuscuta species revealed the mechanism underlying the formation of parasitic characteristics of Cuscuta species from the perspective of the chloroplast genome.

Complete chloroplast genome sequence of Eranthis byunsanensis B.Y. Sun (Ranunculaceae), an endemic species in Korea

The Korean endemic Eranthis byunsanensis B.Y. Sun, 1993 (Ranunculaceae) is a rare plant distributed in the southwestern part of the Korean Peninsula. The complete chloroplast (cp) genome of E. byunsanensis was sequenced by next-generation sequencing (NGS) using an Illumina HiSeq X platform. The cp genome of E. byunsanensis is 160,324 bp in length with 37.9% GC content. It showed a typical quadripartite structure consisting of a pair of inverted repeats (IRs; 28,356 bp), a large single-copy region (LSC; 87,671 bp), and a small single-copy region (SSC; 15,941 bp). The cp genome comprises 130 genes including 85 protein-coding genes (PCGs), 37 tRNA genes, and eight rRNA genes. The molecular phylogenetic analysis indicates that E. byunsanensis is closely related to Eranthis stellata, both of which belong to the genus Eranthis.

Complete chloroplast genome sequences of Myristicaceae species with the comparative chloroplast genomics and phylogenetic relationships among them

BACKGROUND

Myristicaceae was widly distributed from tropical Asia to Oceania, Africa, and tropical America. There are 3 genera and 10 species of Myristicaceae present in China, mainly distributed in the south of Yunnan Province. Most research on this family focuses on fatty acids, medicine, and morphology. Based on the morphology, fatty acid chemotaxonomy, and a few of molecular data, the phylogenetic position of Horsfieldia pandurifolia Hu was controversial.

RESULTS

In this study, the chloroplast genomes of two Knema species, Knema globularia (Lam.) Warb. and Knema cinerea (Poir.) Warb., were characterized. Comparing the genome structure of these two species with those of other eight published species, including three Horsfieldia species, four Knema species, and one Myristica species, it was found that the chloroplast genomes of these species were relatively conserved, retaining the same gene order. Through sequence divergence analysis, there were 11 genes and 18 intergenic spacers were subject to positive selection, which can be used to analyze the population genetic structure of this family. Phylogenetic analysis showed that all Knema species were clustered in the same group and formed a sister clade with Myristica species support by both high maximum likelihood bootstrap values and Bayesian posterior probabilities; among Horsfieldia species, Horsfieldia amygdalina (Wall.) Warb., Horsfieldia kingii (Hook.f.) Warb., Horsfieldia hainanensis Merr. and Horsfieldia tetratepala C.Y.Wu. were grouped together, but H. pandurifolia formed a single group and formed a sister clade with genus Myristica and Knema. Through the phylogenetic analysis, we support de Wilde' view that the H. pandurifolia should be separated from Horsfieldia and placed in the genus Endocomia, namely Endocomia macrocoma subsp. prainii (King) W.J.de Wilde.

CONCLUSION

The findings of this study provide a novel genetic resources for future research in Myristicaceae and provide a molecular evidence for the taxonomic classification of Myristicaceae.

Chloroplast gene expression level is negatively correlated with evolutionary rates and selective pressure while positively with codon usage bias in Ophioglossum vulgatum L

BACKGROUND

Characterization of the key factors determining gene expression level has been of significant interest. Previous studies on the relationship among evolutionary rates, codon usage bias, and expression level mostly focused on either nuclear genes or unicellular/multicellular organisms but few in chloroplast (cp) genes. Ophioglossum vulgatum is a unique fern and has important scientific and medicinal values. In this study, we sequenced its cp genome and transcriptome to estimate the evolutionary rates (dN and dS), selective pressure (dN/dS), gene expression level, codon usage bias, and their correlations.

RESULTS

The correlation coefficients between dN, dS, and dN/dS, and Transcripts Per Million (TPM) average values were -0.278 (P = 0.027 < 0.05), -0.331 (P = 0.008 < 0.05), and -0.311 (P = 0.013 < 0.05), respectively. The codon adaptation index (CAI) and tRNA adaptation index (tAI) were significantly positively correlated with TPM average values (P < 0.05).

CONCLUSIONS

Our results indicated that when the gene expression level was higher, the evolutionary rates and selective pressure were lower, but the codon usage bias was stronger. We provided evidence from cp gene data which supported the E-R (E stands for gene expression level and R stands for evolutionary rate) anti-correlation.

The Complete Chloroplast Genome of Hypoestes forskaolii (Vahl) R.Br: Insights into Comparative and Phylogenetic Analyses within the Tribe Justiceae

Hypoestes forskaolii is one of the most important species of the family Acanthaceae, known for its high economic and medicinal importance. It is well distributed in the Arab region as well as on the African continent. Previous studies on ethnomedicine have reported that H. forskaolii has an anti-parasitic effect as well as antimalarial and anthelmintic activities. Previous studies mainly focused on the ethnomedicinal properties, hence, there is no information on the genomic architecture and phylogenetic positions of the species within the tribe Justiceae. The tribe Justicieae is the most taxonomically difficult taxon in Acanthoideae due to its unresolved infratribal classification. Therefore, by sequencing the complete chloroplast genome (cp genome) of H. forskaolii, we explored the evolutionary patterns of the cp genome and reconstructed the phylogeny of Justiceae. The cp genome is quadripartite and circular in structure and has a length of 151,142 bp. There are 130 genes (86 coding for protein, 36 coding for tRNA and 8 coding for rRNA) present in the plastome. Analyses of long repeats showed only three types of repeats: forward, palindromic and reverse were present in the genome. Microsatellites analysis revealed 134 microsatellites in the cp genome with mononucleotides having the highest frequency. Comparative analyses within Justiceae showed that genomes structure and gene contents were highly conserved but there is a slight distinction in the location of the genes in the inverted repeat and single copy junctions. Additionally, it was discovered that the cp genome includes variable hotspots that can be utilized as DNA barcodes and tools for determining evolutionary relationships in the Justiceae. These regions include: atpH-atpI, trnK-rps16, atpB-rbcL, trnT-trnL, psbI-trnS, matK, trnH-psbA, and ndhD. The Bayesian inference phylogenetic tree showed that H. forskaolii is a sister to the Dicliptra clade and belongs to Diclipterinae. The result also confirms the polyphyly of Justicia and inclusion of Diclipterinae within justicioid. This research has revealed the phylogenetic position of H. forskaolii and also reported the resources that can be used for evolutionary and phylogenetic studies of the species and the Justicieae.

Characterization of the Evolutionary Pressure on Anisodus tanguticus Maxim. with Complete Chloroplast Genome Sequence

Anisodus tanguticus Maxim. (Solanaceae), a traditional endangered Tibetan herb, is endemic to the Qinghai-Tibet Plateau. Here, we report the de novo assembled chloroplast (cp) genome sequences of A. tanguticus (155,765 bp). The cp contains a pair of inverted repeated (IRa and IRb) regions of 25,881 bp that are separated by a large single copy (LSC) region (86,516 bp) and a small single copy SSC (17,487 bp) region. A total of 132 functional genes were annotated in the cp genome, including 87 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. Moreover, 199 simple sequence repeats (SSR) and 65 repeat structures were detected. Comparative plastome analyses revealed a conserved gene order and high similarity of protein-coding sequences. The A. tanguticus cp genome exhibits contraction and expansion, which differs from Przewalskia tangutica and other related Solanaceae species. We identified 30 highly polymorphic regions, mostly belonging to intergenic spacer regions (IGS), which may be suitable for the development of robust and cost-effective markers for inferring the phylogeny of the genus Anisodus and family Solanaceae. Analysis of the Ka/Ks ratios of the Hyoscyameae tribe revealed significant positive selection exerted on the cemA, rpoC2, and clpP genes, which suggests that protein metabolism may be an important strategy for A. tanguticus and other species in Hyoscyameae in adapting to the adverse environment on the Qinghai-Tibetan Plateau. Phylogenetic analysis revealed that A. tanguticus clustered closer with Hyoscyamus niger than P. tangutica. Our results provide reliable genetic information for future exploration of the taxonomy and phylogenetic evolution of the Hyoscyameae tribe and related species.

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

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

Comparative Analysis of Whole Chloroplast Genomes of Three Common Species of Echinochloa (Gramineae) in Paddy Fields

Echinochloa crus-galli var. crus-galli, E. crus-galli var. zelayensis, and E. glabrescens, morphologically similar at the seedling stage, are the most pernicious barnyard grass species in paddy fields worldwide. Chloroplast (cp) genomes could be conducive to their identification. In this study, we assembled the complete cp genome sequences of Echinochloa crus-galli var. crus-galli (139,856 bp), E. crus-galli var. zelayensis (139,874 bp), and E. glabrescens (139,874 bp), which exhibited a typical circular tetramerous structure, large and small single-copy regions, and a pair of inverted repeats. In Echinochloa crus-galli var. crus-galli, there were 136 simple sequence (SSRs) and 62 long (LRs) repeats, and in the other two species, 139 SSRs and 68 LRs. Each cp genome contains 92 protein-encoding genes. In Echinochloa crus-galli var. crus-galli and E. glabrescens, 321 and 1 single-nucleotide polymorphisms were detected compared to Echinochloa crus-galli var. zelayensis. IR expansion and contraction revealed small differences between the three species. The phylogenetic tree based on cp genomes demonstrated the phylogenetic relationship between ten barnyard grass species and other common Gramineae plants, showing new genetic relationships of the genus Echinochloa. This study provides valuable information on cp genomes, useful for identifying and classifying the genus Echinochloa and studying its phylogenetic relationships and evolution.

The complete chloroplast genome sequences of three lilies: genome structure, comparative genomic and phylogenetic analyses

We sequenced and analyzed the complete chloroplast genomes of Lilium amoenum, Lilium souliei, and Nomocharis forrestii in detail, including the first sequence and structural comparison of Nomocharis forrestii. We found that the lengths and nucleotide composition of the three chloroplast genes showed little variation. The chloroplast genomes of the three Lilium species contain 87 protein coding genes (PCGs), 38 tRNAs, and 8 rRNA genes. The only difference is that Nomocharis forrestii had an additional infA pseudogene. In the sequence analysis of the Lilium chloroplast genomes, 216 SSRs, 143 pairs of long repeats, 571 SNPs, and 202 indels were detected. In addition, we identified seven hypervariable regions that can be used as potential molecular markers and DNA barcodes of Lilium through complete sequence alignment. The phylogenetic tree was constructed from the three chloroplast genome sequences of Lilium obtained here and 40 chloroplast genome sequences from the NCBI database (including 35 Lilium species, 4 Fritillaria species, and one species of Smilax). The analysis showed that the species clustering of the genus Lilium essentially conformed to the classical morphological classification system of Comber, but differences in the classification of individual species remained. In our report, we support the reclassification of Lilium henryi and Lilium rosthorniiy in the genus Lilium. In general, this study not only provides genome data for three Lilium species, but also provides a comparative analysis of the Lilium chloroplast genomes. These advances will help to identify Lilium species, clarify the phylogenetic analysis of the Lilium genus, and help to solve and improve the disputes and deficiencies in the traditional morphological classification.

Complete chloroplast genome sequencing and comparative analysis of threatened dragon trees Dracaena serrulata and Dracaena cinnabari

Dracaena (Asparagaceae family) tree is famous for producing "dragon blood"—a bioactive red-colored resin. Despite its long history of use in traditional medicine, little knowledge exists on the genomic architecture, phylogenetic position, or evolution. Hence, in this study, we sequenced the whole chloroplast (cp) genomes of D. serrulata and D. cinnabari and performed comparative genomics of nine genomes of the genus Dracaena. The results showed that the genome sizes range from 155,055 (D. elliptica) to 155,449 (D. cochinchinensis). The cp genomes of D. serrulata and D. cinnabari encode 131 genes, each including 85 and 84 protein-coding genes, respectively. However, the D. hokouensis had the highest number of genes (133), with 85 protein coding genes. Similarly, about 80 and 82 repeats were identified in the cp genomes of D. serrulata and D. cinnabari, respectively, while the highest repeats (103) were detected in the cp genome of D. terniflora. The number of simple sequence repeats (SSRs) was 176 and 159 in D. serrulata and D. cinnabari cp genomes, respectively. Furthermore, the comparative analysis of complete cp genomes revealed high sequence similarity. However, some sequence divergences were observed in accD, matK, rpl16, rpoC2, and ycf1 genes and some intergenic spacers. The phylogenomic analysis revealed that D. serrulata and D. cinnabari form a monophyletic clade, sister to the remaining Dracaena species sampled in this study, with high bootstrap values. In conclusion, this study provides valuable genetic information for studying the evolutionary relationships and population genetics of Dracaena, which is threatened in its conservation status.

Plastome structure, phylogenomic analyses and molecular dating of Arecaceae

Arecaceae is a species-rich clade of Arecales, while also being regarded as a morphologically diverse angiosperm family with numerous species having significant economic, medicinal, and ornamental value. Although in-depth studies focused on the chloroplast structure of Arecaceae, as well as inferring phylogenetic relationships using gene fragments, have been reported in recent years, a comprehensive analysis of the chloroplast structure of Arecaceae is still needed. Here we perform a comprehensive analysis of the structural features of the chloroplast genome of Arecaceae, compare the variability of gene sequences, infer phylogenetic relationships, estimate species divergence times, and reconstruct ancestral morphological traits. In this study, 74 chloroplast genomes of Arecaceae were obtained, covering five subfamilies. The results show that all chloroplast genomes possess a typical tetrad structure ranging in size between 153,806-160,122 bp, with a total of 130-137 genes, including 76-82 protein-coding genes, 29-32 tRNA genes, and 4 rRNA genes. Additionally, the total GC content was between 36.9-37.7%. Analysis of the SC/IR boundary indicated that the IR region underwent expansion or contraction. Phylogenetic relationships indicate that all five subfamilies in Arecaceae are monophyletic and that Ceroxyloideae and Arecoideae are sister groups (BS/PP = 100/1). The results of molecular dating indicate that the age of the crown group of Arecaceae is likely to be 96.60 [84.90-107.60] Ma, while the age of the stem group is 102.40 [93.44-111.17] Ma. Reconstruction of ancestral traits indicate that the ancestral characteristics of the family include monoecious plants, one seed, six stamens, and a smooth pericarp.

Comparative Analyses of Complete Chloroplast Genomes and Karyotypes of Allotetraploid Iris koreana and Its Putative Diploid Parental Species (Iris Series Chinenses, Iridaceae)

The Iris series Chinenses in Korea comprises four species (I. minutoaurea, I. odaesanensis, I. koreana, and I. rossii), and the group includes some endangered species, owing to their high ornamental, economic, and conservation values. Among them, the putative allotetraploid, Iris koreana (2n = 4x = 50), is hypothesized to have originated from the hybridization of the diploids I. minutoaurea (2n = 2x = 22) and I. odaesanensis (2n = 2x = 28) based on morphological characters, chromosome numbers, and genome size additivity. Despite extensive morphological and molecular phylogenetical studies on the genus Iris, little is known about Korean irises in terms of their complete chloroplast (cp) genomes and molecular cytogenetics that involve rDNA loci evolution based on fluorescence in situ hybridization (FISH). This study reports comparative analyses of the karyotypes of the three Iris species (I. koreana, I. odaesanensis, and I. minutoaurea), with an emphasis on the 5S and 35S rDNA loci number and localization using FISH together with the genome size and chromosome number. Moreover, the cp genomes of the same individuals were sequenced and assembled for comparative analysis. The rDNA loci numbers, which were localized consistently at the same position in all species, and the chromosome numbers and genome size values of tetraploid Iris koreana (four 5S and 35S loci; 2n = 50; 1C = 7.35 pg) were additively compared to its putative diploid progenitors, I. minutoaurea (two 5S and 35S loci; 2n = 22; 1C = 3.71 pg) and I. odaesanensis (two 5S and 35S loci; 2n = 28; 1C = 3.68 pg). The chloroplast genomes were 152,259–155,145 bp in length, and exhibited a conserved quadripartite structure. The Iris cp genomes were highly conserved and similar to other Iridaceae cp genomes. Nucleotide diversity analysis indicated that all three species had similar levels of genetic variation, but the cp genomes of I. koreana and I. minutoaurea were more similar to each other than to I. odaesanensis. Positive selection was inferred for psbK and ycf2 genes of the three Iris species. Phylogenetic analyses consistently recovered I. odaesanensis as a sister to a clade containing I. koreana and I. minutoaurea. Although the phylogenetic relationship, rDNA loci number, and localization, together with the genome size and chromosome number of the three species, allowed for the inference of I. minutoaurea as a putative maternal taxon and I. odaesanensis as a paternal taxon, further analyses involving species-specific molecular cytogenetic markers and genomic in situ hybridization are required to interpret the mechanisms involved in the origin of the chromosomal variation in Iris series Chinenses. This study contributes towards the genomic and chromosomal evolution of the genus Iris.

Comparative phylogenetic analysis of complete plastid genomes of Renanthera (Orchidaceae)

Owing to its attractive flower shape and color, Renanthera (Orchidaceae), comprising about 19 species, has significant ornamental value as a houseplant, in floral design and in landscape gardens. Two species of Renanthera are categorized as endangered and critically endangered in China’s Red List and international trade in these orchids is currently strictly monitored by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). This paper reports on the de novo assembled and annotated plastome of four species of Renanthera; R. citrina, R. coccinea, R. imschootiana, and R. philippinensis. The length of the plastome sequences ranged from 144,673 bp (R. imschootiana) to 149,007 bp (R. coccinea) with GC content of 36.6–36.7%. The plastomes showed a typical quadripartite structure, including a large single-copy (84,241–86,404 bp), a small single-copy (11,468–12,167 bp), and a pair of inverted repeats (24,482–25,715 bp) regions. Of the 120 genes detected, 74 were protein coding, 38 were tRNA, and eight were rRNA genes. The plastome of Renanthera is rather conserved, but nucleotide variations that could distinguish them apart are noticeable—the total number of tandem repeats ranged from 62 (in R. imschootiana) to 74 (in R. citrina); while the number of long repeats ranged from 21 (in R. imschootiana and R. philippinensis) to 43 (in R. citrina). Three hypervariable regions (psbI-trnS-GCU, trnG-GCC, rpl32) were identified. Phylogenetic analyses based on the CDS using maximum likelihood (ML) and Bayesian inference (BI) revealed that Renanthera is closely related to Holcoglossum, Neofinetia, Pendulorchis, and Vanda. The relationship between the four species of Renanthera was fully resolved; a monophyletic clade was formed and R. coccinea was recorded as the first to diverge from the rest. The genetic data obtained from this study could serve as a useful resource for species identification in Renanthera as well as contribute to future research on the phylogenomics of Orchidaceae.

Complete Chloroplast Genomes of 14 Subspecies of D. glomerata: Phylogenetic and Comparative Genomic Analyses

Orchardgrass (Dactylis glomerata L.) is a species in the Gramineae family that is highly important economically and valued for its role in ecology. However, the phylogeny and taxonomy of D. glomerata are still controversial based on current morphological and molecular evidence. The study of chloroplast (cp) genomes has developed into a powerful tool to develop molecular markers for related species and reveal the relationships between plant evolution and phylogenetics. In this study, we conducted comparative genomic analyses and phylogenetic inferences on 14 cp genomes of D. glomerata originating from the Mediterranean and Eurasia. The genome size ranged from 134,375 bp to 134,993 bp and exhibited synteny of gene organization and order. A total of 129–131 genes were identified, including 85–87 protein coding genes, 38 tRNA genes and 8 rRNA genes. The cp sequences were highly conserved, and key sequence variations were detected at the junctions of inverted repeats (IRs)/small single–copy (SSC) regions. Moreover, nine highly variable regions were identified among the subspecies based on a sequence divergence analysis. A total of 285 RNA editing sites were detected that were relevant to 52 genes, where rpoB exhibited the most abundant RNA editing sites. The phylogenetic analysis revealed that all Dactylis subspecies clustered into a monophyletic group and most branches provided a high support bootstrap. The main divergence time of D. glomerata was dated to the Miocene era, and this could have been due to changes in the climate. These findings will provide useful insights for further studies on phylogeny, the identification of subspecies and the development of hypotheses for the evolutionary history of the genus Dactylis and of the Gramineae family.

Complete chloroplast genome of the desert date (Balanites aegyptiaca (L.) Del. comparative analysis, and phylogenetic relationships among the members of Zygophyllaceae

BACKGROUND

Balanites aegyptiaca (L.) Delile, commonly known as desert date, is a thorny evergreen tree belonging to the family Zygophyllaceae and subfamily Tribuloideae that is widespread in arid and semiarid regions. This plant is an important source of food and medicines and plays an important role in conservation strategies for restoring degraded desert ecosystems.

RESULTS

In the present study, we sequenced the complete plastome of B. aegyptiaca. The chloroplast genome was 155,800 bp, with a typical four-region structure: a large single copy (LSC) region of 86,562 bp, a small single copy (SSC) region of 18,102 bp, and inverted repeat regions (IRa and IRb) of 25,568 bp each. The GC content was 35.5%. The chloroplast genome of B. aegyptiaca contains 107 genes, 75 of which coding proteins, 28 coding tRNA, and 4 coding rRNA. We did not observe a large loss in plastid genes or a reduction in the genome size in B. aegyptiaca, as found previously in some species belonging to the family Zygophyllaceae. However, we noticed a divergence in the location of certain genes at the IR-LSC and IR-SSC boundaries and loss of ndh genes relative to other species. Furthermore, the phylogenetic tree constructed from the complete chloroplast genome data broadly supported the taxonomic classification of B. aegyptiaca as belonging to the Zygophyllaceae family. The plastome of B. aegyptiaca was found to be rich in single sequence repeats (SSRs), with a total of 240 SSRs.

CONCLUSIONS

The genomic data available from this study could be useful for developing molecular markers to evaluate population structure, investigate genetic variation, and improve production programs for B. aegyptiaca. Furthermore, the current data will support future investigation of the evolution of the family Zygophyllaceae.

Complete chloroplast genomes and comparative analyses of Hippeastrum ‘milady’, Hippeastrum albertii and Hippeastrum reticulatum (Amaryllidaceae)

Hippeastrum is a genus of ornamental plants with large, brightly colored flowers. Due to the very high seed-setting rate of the hybridization of Hippeastrum, the large population of hybrid progeny and the existence of superparent inheritance, it is difficult to trace the origin of the varieties collected from the market during breeding. In this study, we analyzed the chloroplast genomes of Hippeastrum ‘Milady’, H. alberti, and H. reticulatum using the Illumina NovaSeq sequencing platform and generated full-length sequences of 158,067, 158,067, and 158,522 bp, respectively. All three genomes had the typical tetrad structure. The large single copy, small single copy, and inverted repeat regions of H. reticulatum were observed to be respectively 277, 138, and 20 bp longer than the corresponding regions of H. ‘Milady’ and H. alberti. The results of comparative analysis of simple sequence repeats (SSRs), Ka/Ks ratios, codon preferences, and complete sequences of chloroplasts of these three taxa and 14 other plant species were as follows. First, the chloroplast genomes of H. ‘Milady’, H. alberti, and H. reticulatum contain 209, 209, and 211 SSR sites, respectively, most of which (123, 123, and 122, respectively) are single nucleotide repeats. Second, leucine, arginine, and serine are the most frequently used amino acids in the three chloroplast genomes. Third, H. ‘Milady’, H. alberti, and H. reticulatum are more closely related to Lycoris and Narcissus than to Allium and Agapanthus. Our results will provide information on the study of origins or relatedness of native species, and the identification of cultivars.

Plastome structure of 8 Calanthe s.l. species (Orchidaceae): comparative genomics, phylogenetic analysis

Background

Calanthe (Epidendroideae, Orchidaceae) is a pantropical genus distributed in Asia and Africa. Its species are of great importance in terms of economic, ornamental and medicinal values. However, due to limited and confusing delimitation characters, the taxonomy of the Calanthe alliance (Calanthe, Cephalantheropsis, and Phaius) has not been sufficiently resolved. Additionally, the limited genomic information has shown incongruences in its systematics and phylogeny. In this study, we used illumina platform sequencing, performed a de novo assembly, and did a comparative analysis of 8 Calanthe group species' plastomes: 6 Calanthe and 2 Phaius species. Phylogenetic analyses were used to reconstruct the relationships of the species as well as with other species of the family Orchidaceae.

Results

The complete plastomes of the Calanthe group species have a quadripartite structure with varied sizes ranging between 150,105bp-158,714bp, including a large single-copy region (LSC; 83,364bp- 87,450bp), a small single-copy region (SSC; 16,297bp -18,586bp), and a pair of inverted repeat regions (IRs; 25,222bp - 26,430bp). The overall GC content of these plastomes ranged between 36.6-36.9%. These plastomes encoded 131-134 differential genes, which included 85-88 protein-coding genes, 37-38 tRNA genes, and 8 rRNA genes. Comparative analysis showed no significant variations in terms of their sequences, gene content, gene order, sequence repeats and the GC content hence highly conserved. However, some genes were lost in C. delavayi (P. delavayi), including ndhC, ndhF, and ndhK genes. Compared to the coding regions, the non-coding regions had more sequence repeats hence important for species DNA barcoding. Phylogenetic analysis revealed a paraphyletic relationship in the Calanthe group, and confirmed the position of Phaius delavayi in the genus Calanthe as opposed to its previous placement in Phaius.

Conclusion

This study provides a report on the complete plastomes of 6 Calanthe and 2 Phaius species and elucidates the structural characteristics of the plastomes. It also highlights the power of plastome data to resolve phylogenetic relationships and clarifies taxonomic disputes among closely related species to improve our understanding of their systematics and evolution. Furthermore, it also provides valuable genetic resources and a basis for studying evolutionary relationships and population genetics among orchid species.

Plastome structure of 8 Calanthe s.l. species (Orchidaceae): comparative genomics, phylogenetic analysis

BACKGROUND

Calanthe (Epidendroideae, Orchidaceae) is a pantropical genus distributed in Asia and Africa. Its species are of great importance in terms of economic, ornamental and medicinal values. However, due to limited and confusing delimitation characters, the taxonomy of the Calanthe alliance (Calanthe, Cephalantheropsis, and Phaius) has not been sufficiently resolved. Additionally, the limited genomic information has shown incongruences in its systematics and phylogeny. In this study, we used illumina platform sequencing, performed a de novo assembly, and did a comparative analysis of 8 Calanthe group species' plastomes: 6 Calanthe and 2 Phaius species. Phylogenetic analyses were used to reconstruct the relationships of the species as well as with other species of the family Orchidaceae.

RESULTS

The complete plastomes of the Calanthe group species have a quadripartite structure with varied sizes ranging between 150,105bp-158,714bp, including a large single-copy region (LSC; 83,364bp- 87,450bp), a small single-copy region (SSC; 16,297bp -18,586bp), and a pair of inverted repeat regions (IRs; 25,222bp - 26,430bp). The overall GC content of these plastomes ranged between 36.6-36.9%. These plastomes encoded 131-134 differential genes, which included 85-88 protein-coding genes, 37-38 tRNA genes, and 8 rRNA genes. Comparative analysis showed no significant variations in terms of their sequences, gene content, gene order, sequence repeats and the GC content hence highly conserved. However, some genes were lost in C. delavayi (P. delavayi), including ndhC, ndhF, and ndhK genes. Compared to the coding regions, the non-coding regions had more sequence repeats hence important for species DNA barcoding. Phylogenetic analysis revealed a paraphyletic relationship in the Calanthe group, and confirmed the position of Phaius delavayi in the genus Calanthe as opposed to its previous placement in Phaius.

CONCLUSION

This study provides a report on the complete plastomes of 6 Calanthe and 2 Phaius species and elucidates the structural characteristics of the plastomes. It also highlights the power of plastome data to resolve phylogenetic relationships and clarifies taxonomic disputes among closely related species to improve our understanding of their systematics and evolution. Furthermore, it also provides valuable genetic resources and a basis for studying evolutionary relationships and population genetics among orchid species.