Comparative and phylogenetic analysis of chloroplast genomes from four species in Quercus section Cyclobalanopsis.

The Quercus L. species is widely recognized as a significant group in the broad-leaved evergreen forests of tropical and subtropical East Asia. These plants hold immense economic value for their use as firewood, furniture, and street trees. However, the identification of Quercus species is considered challenging, and the relationships between these species remain unclear. In this study, we sequenced and assembled the chloroplast (cp.) genomes of four Quercus section Cyclobalanopsis species (Quercus disciformis, Quercus dinghuensis, Quercus blackei, and Quercus hui). Additionally, we retrieved six published cp. genome sequences of Cyclobalanopsis species (Quercus fleuryi, Quercus pachyloma, Quercus ningangensis, Quercus litseoides, Quercus gilva, and Quercus myrsinifolia). Our aim was to perform comparative genomics and phylogenetic analyses of the cp. whole genome sequences of ten Quercus section Cyclobalanopsis species. The results revealed that: (1) Quercus species exhibit a typical tetrad structure, with the cp. genome lengths of the newly sequenced species (Q. disciformis, Q. dinghuensis, Q. blakei, and Q. hui) being 160,805 bp, 160,801 bp, 160,787 bp, and 160,806 bp, respectively; (2) 469 SSRs were detected, among which A/T base repeats were the most common; (3) no rearrangements or inversions were detected within the chloroplast genomes. Genes with high nucleotide polymorphism, such as rps14-psaB, ndhJ-ndhK, rbcL-accD, and rps19-rpl2_2, provided potential reference loci for molecular identification within the Cyclobalanopsis section; (4) phylogenetic analysis showed that the four sections of Cyclobalanopsis were grouped into sister taxa, with Q. hui being the first to diverge from the evolutionary branch and Q. disciformis being the most closely related to Q. blackei. The results of this study form the basis for future studies on taxonomy and phylogenetics.

The chloroplast genome inheritance pattern of the Deli-Nigerian prospection material (NPM) × Yangambi population of Elaeis guineensis Jacq.

Background: The chloroplast genome has the potential to be genetically engineered to enhance the agronomic value of major crops. As a crop plant with major economic value, it is important to understand every aspect of the genetic inheritance pattern among Elaeis guineensis individuals to ensure the traceability of agronomic traits. Methods: Two parental E. guineensis individuals and 23 of their F1 progenies were collected and sequenced using the next-generation sequencing (NGS) technique on the Illumina platform. Chloroplast genomes were assembled de novo from the cleaned raw reads and aligned to check for variations. The sequences were compared and analyzed with programming language scripting and relevant bioinformatic softwares. Simple sequence repeat (SSR) loci were determined from the chloroplast genome. Results: The chloroplast genome assembly resulted in 156,983 bp, 156,988 bp, 156,982 bp, and 156,984 bp. The gene content and arrangements were consistent with the reference genome published in the GenBank database. Seventy-eight SSRs were detected in the chloroplast genome, with most located in the intergenic spacer region.The chloroplast genomes of 17 F1 progenies were exact copies of the maternal parent, while six individuals showed a single variation in the sequence. Despite the significant variation displayed by the male parent, all the nucleotide variations were synonymous. This study show highly conserve gene content and sequence in Elaeis guineensis chloroplast genomes. Maternal inheritance of chloroplast genome among F1 progenies are robust with a low possibility of mutations over generations. The findings in this study can enlighten inheritance pattern of Elaeis guineensis chloroplast genome especially among crops' scientists who consider using chloroplast genome for agronomic trait modifications.

Complete Chloroplast Genome of Alternanthera sessilis and Comparative Analysis with Its Congeneric Invasive Weed Alternanthera philoxeroides.

Alternanthera sessilis is considered the closest relative to the invasive weed Alternanthera philoxeroides in China, making it an important native species for studying the invasive mechanisms and adaptations of A. philoxeroides. Chloroplasts play a crucial role in a plant's environmental adaptation, with their genomes being pivotal in the evolution and adaptation of both invasive and related species. However, the chloroplast genome of A. sessilis has remained unknown until now. In this study, we sequenced and assembled the complete chloroplast genome of A. sessilis using high-throughput sequencing. The A. sessilis chloroplast genome is 151,935 base pairs long, comprising two inverted repeat regions, a large single copy region, and a small single copy region. This chloroplast genome contains 128 genes, including 8 rRNA-coding genes, 37 tRNA-coding genes, 4 pseudogenes, and 83 protein-coding genes. When compared to the chloroplast genome of the invasive weed A. philoxeroides and other Amaranthaceae species, we observed significant variations in the ccsA, ycf1, and ycf2 regions in the A. sessilis chloroplast genome. Moreover, two genes, ccsA and accD, were found to be undergoing rapid evolution due to positive selection pressure. The phylogenetic trees were constructed for the Amaranthaceae family, estimating the time of independent species formation between A. philoxeroides and A. sessilis to be approximately 3.5186-8.8242 million years ago. These findings provide a foundation for understanding the population variation within invasive species among the Alternanthera genus.

Complete Chloroplast Genome Sequence Structure and Phylogenetic Analysis of Kohlrabi (Brassica oleracea var. gongylodes L.).

Kohlrabi is an important swollen-stem cabbage variety belonging to the Brassicaceae family. However, few complete chloroplast genome sequences of this genus have been reported. Here, a complete chloroplast genome with a quadripartite cycle of 153,364 bp was obtained. A total of 132 genes were identified, including 87 protein-coding genes, 37 transfer RNA genes and eight ribosomal RNA genes. The base composition analysis showed that the overall GC content was 36.36% of the complete chloroplast genome sequence. Relative synonymous codon usage frequency (RSCU) analysis showed that most codons with values greater than 1 ended with A or U, while most codons with values less than 1 ended with C or G. Thirty-five scattered repeats were identified and most of them were distributed in the large single-copy (LSC) region. A total of 290 simple sequence repeats (SSRs) were found and 188 of them were distributed in the LSC region. Phylogenetic relationship analysis showed that five Brassica oleracea subspecies were clustered into one group and the kohlrabi chloroplast genome was closely related to that of B. oleracea var. botrytis. Our results provide a basis for understanding chloroplast-dependent metabolic studies and provide new insight for understanding the polyploidization of Brassicaceae species.

Decoding Evolution of Rubioideae: Plastomes Reveal Sweet Secrets of Codon Usage, Diagnostides, and Superbarcoding.

Galium genus belongs to the Rubiaceae family, which consists of approximately 14,000 species. In comparison to its well-known relatives, the plastomes of the Galium genus have not been explored so far. The plastomes of this genus have a typical, quadripartite structure, but differ in gene content, since the infA gene is missing in Galium palustre and Galium trfidum. An evaluation of the effectiveness of using entire chloroplast genome sequences as superbarcodes for accurate plant species identification revealed the high potential of this method for molecular delimitation within the genus and tribe. The trnE-UUC-psbD region showed the biggest number of diagnostides (diagnostic nucleotides) which might be new potential barcodes, not only in Galium, but also in other closely related genera. Relative synonymous codon usage (RSCU) appeared to be connected with the phylogeny of the Rubiaceae family, showing that during evolution, plants started preferring specific codons over others.

Comparative chloroplast genomics and phylogenetic analysis of Oreomecon nudicaulis (Papaveraceae).

Oreomecon nudicaulis, commonly known as mountain poppy, is a significant perennial herb. In 2022, the species O. nudicaulis, which was previously classified under the genus Papaver, was reclassified within the genus Oreomecon. Nevertheless, the phylogenetic status and chloroplast genome within the genus Oreomecon have not yet been reported. This study elucidates the chloroplast genome sequence and structural features of O. nudicaulis and explores its evolutionary relationships within Papaveraceae. Using Illumina sequencing technology, the chloroplast genome of O. nudicaulis was sequenced, assembled, and annotated. The results indicate that the chloroplast genome of O. nudicaulis exhibits a typical circular quadripartite structure. The chloroplast genome is 153,903 bp in length, with a GC content of 38.87%, containing 84 protein-coding genes, 8 rRNA genes, 38 tRNA genes, and 2 pseudogenes. The genome encodes 25,815 codons, with leucine (Leu) being the most abundant codon, and the most frequently used codon is AUU. Additionally, 129 microsatellite markers were identified, with mononucleotide repeats being the most abundant (53.49%). Our phylogenetic analysis revealed that O. nudicaulis has a relatively close relationship with the genus Meconopsis within the Papaveraceae family. The phylogenetic analysis supported the taxonomic status of O. nudicaulis, as it did not form a clade with other Papaver species, consistent with the revised taxonomy of Papaveraceae. This is the first report of a phylogenomic study of the complete chloroplast genome in the genus Oreomecon, which is a significant genus worldwide. This analysis of the O. nudicaulis chloroplast genome provides a theoretical basis for research on genetic diversity, molecular marker development, and species identification, enriching genetic information and supporting the evolutionary relationships among Papaveraceae.

Chloroplast genomes of Caragana tibetica and Caragana turkestanica: structures and comparative analysis.

BACKGROUND: The genus Caragana encompasses multiple plant species that possess medicinal and ecological value. However, some species of Caragana are quite similar in morphology, so identifying species in this genus based on their morphological characteristics is considerably complex. In our research, illumina paired-end sequencing was employed to investigate the genetic organization and structure of Caragana tibetica and Caragana turkestanica, including the previously published chloroplast genome sequence of 7 Caragana plants. RESULTS: The lengths of C. tibetica and C. turkestanica chloroplast genomes were 128,433 bp and 129,453 bp, respectively. The absence of inverted repeat sequences in these two species categorizes them under the inverted repeat loss clade (IRLC). They encode 110 and 111 genes (4 /4 rRNA genes, 30 /31tRNA genes, and 76 /76 protein-coding genes), respectively. Comparison of the chloroplast genomes of C. tibetica and C. turkestanica with 7 other Caragana species revealed a high overall sequence similarity. However, some divergence was observed between certain intergenic regions (matK-rbcL, psbD-psbM, atpA-psbI, and etc.). Nucleotide diversity (π) analysis revealed the detection of five highly likely variable regions, namely rps2-atpI, accD-psaI-ycf4, cemA-petA, psbN-psbH and rpoA-rps11. Phylogenetic analysis revealed that C. tibetica's sister species is Caragana jubata, whereas C. turkestanica's closest relative is Caragana arborescens. CONCLUSIONS: The present study provides worthwhile information about the chloroplast genomes of C. tibetica and C. turkestanica, which aids in the identification and classification of Caragana species.

The size diversity of the Pteridaceae family chloroplast genome is caused by overlong intergenic spacers.

BACKGROUND: While the size of chloroplast genomes (cpDNAs) is often influenced by the expansion and contraction of inverted repeat regions and the enrichment of repeats, it is the intergenic spacers (IGSs) that appear to play a pivotal role in determining the size of Pteridaceae cpDNAs. This provides an opportunity to delve into the evolution of chloroplast genomic structures of the Pteridaceae family. This study added five Pteridaceae species, comparing them with 36 published counterparts. RESULTS: Poor alignment in the non-coding regions of the Pteridaceae family was observed, and this was attributed to the widespread presence of overlong IGSs in Pteridaceae cpDNAs. These overlong IGSs were identified as a major factor influencing variations in cpDNA size. In comparison to non-expanded IGSs, overlong IGSs exhibited significantly higher GC content and were rich in repetitive sequences. Species divergence time estimations suggest that these overlong IGSs may have already existed during the early radiation of the Pteridaceae family. CONCLUSIONS: This study reveals new insights into the genetic variation, evolutionary history, and dynamic changes in the cpDNA structure of the Pteridaceae family, providing a fundamental resource for further exploring its evolutionary research.

Phylogenetic relationships, selective pressure and molecular markers development of six species in subfamily Polygonoideae based on complete chloroplast genomes.

The subfamily Polygonoideae encompasses a diverse array of medicinal and horticultural plants that hold significant economic value. However, due to the lack of a robust taxonomy based on phylogenetic relationships, the classification within this family is perplexing, and there is also a scarcity of reports on the chloroplast genomes of many plants falling under this classification. In this study, we conducted a comprehensive analysis by sequencing and characterizing the complete chloroplast genomes of six Polygonoideae plants, namely Pteroxygonum denticulatum, Pleuropterus multiflorus, Pleuropterus ciliinervis, Fallopia aubertii, Fallopia dentatoalata, and Fallopia convolvulus. Our findings revealed that these six plants possess chloroplast genomes with a typical quadripartite structure, averaging 162,931 bp in length. Comparative chloroplast analysis, codon usage analysis, and repetitive sequence analysis demonstrated a high level of conservation within the chloroplast genomes of these plants. Furthermore, phylogenetic analysis unveiled a distinct clade occupied by P. denticulatum, while P. ciliinrvis displayed a closer relationship to the three plants belonging to the Fallopia genus. Selective pressure analysis based on maximum likelihood trees showed that a total of 14 protein-coding genes exhibited positive selection, with psbB and ycf1 having the highest number of positive amino acid sites. Additionally, we identified four molecular markers, namely petN-psbM, psal-ycf4, ycf3-trnS-GGA, and trnL-UAG-ccsA, which exhibit high variability and can be utilized for the identification of these six plants.

Wasabi Gone Wild? Origin and Characterization of the Complete Plastomes of Ulleung Island Wasabi (Eutrema japonicum; Brassicaceae) and Other Cultivars in Korea.

Korean wasabi occurs naturally on the young oceanic, volcanic Ulleung Island off the east coast of the Korean Peninsula. Although the Ulleung Island wasabi is reported as Eutrema japonicum and has been suggested to be morphologically identical to cultivars in Korea, very little is known about its taxonomic identity and relationship with other cultivars. In this study, we sequenced the complete chloroplast DNA sequences of three naturally occurring Ulleung Island wasabi plants and six cultivars ('Daewang', 'Daruma', 'Micado', 'Orochi', 'Green Thumb', and 'Shogun') from continental Korea and determined the taxonomic identity of Korean wasabi on Ulleung Island. The size and organization of the complete chloroplast genomes of the nine accessions were nearly identical to those of previously reported wasabi cultivars. In addition, phylogenetic analysis based on the complete plastomes suggested that Ulleung Island wasabi most likely comprises various wasabi cultivars with three chlorotypes ('Shogun', 'Green Thumb', and a unique Chusan type). Based on the complete plastomes, we identified eight chlorotypes for the major wasabi cultivars and the Ulleung Island wasabi. Two major groups (1-'Mazuma' and 'Daruma', and 2-'Fujidaruma'/'Shimane No. 3'/Ulleung Island wasabi/five cultivars in Korea) were also identified based on mother line genealogical history. Furthermore, different types of variations (mutations, insertions/deletions (indels), mononucleotide repeats, and inversions) in plastomes were identified to distinguish different cultivar lines and five highly divergent hotspots. The nine newly obtained complete plastomes are valuable organelle genomic resources for species identification and infraspecific phylogeographic studies on wild and cultivated wasabi.

A High-Quality Assembly and Comparative Analysis of the Mitogenome of Actinidia macrosperma.

The mitochondrial genome (mitogenome) of Actinidia macrosperma, a traditional medicinal plant within the Actinidia genus, remains relatively understudied. This study aimed to sequence the mitogenome of A. macrosperma, determining its assembly, informational content, and developmental expression. The results revealed that the mitogenome of A. macrosperma is circular, spanning 752,501 bp with a GC content of 46.16%. It comprises 63 unique genes, including 39 protein-coding genes (PCGs), 23 tRNA genes, and three rRNA genes. Moreover, the mitogenome was found to contain 63 SSRs, predominantly mono-nucleotides, as well as 25 tandem repeats and 650 pairs of dispersed repeats, each with lengths equal to or greater than 60, mainly comprising forward repeats and palindromic repeats. Moreover, 53 homologous fragments were identified between the mitogenome and chloroplast genome (cp-genome), with the longest segment measuring 4296 bp. This study represents the initial report on the mitogenome of the A. macrosperma, providing crucial genetic materials for phylogenetic research within the Actinidia genus and promoting the exploitation of species genetic resources.

Comparative Analysis of Chloroplast Genomes for the Genus Manglietia Blume (Magnoliaceae): Molecular Structure and Phylogenetic Evolution.

Manglietia Blume, belonging to the Magnoliaceae family and mainly distributed in tropical and subtropical regions of Asia, has great scientific and economic value. In this study, we employed next-generation sequencing followed by de novo assembly to investigate the adaptive evolution of Manglietia using plastid genetic information. We newly sequenced the complete or nearly complete plastomes of four Manglietia species (Manglietia aromatica, Manglietia calcarea, Manglietia kwangtungensis, and Manglietia glauca) and conducted comparative analysis with seventeen published plastomes to examine the evolutionary pattern within this genus. The plastomes of these five newly sequenced Manglietia species range from 157,093 bp (M. calcarea2) to 160,493 bp (M. kwangtungensis), all exhibiting circular structures when mapped. Nucleotide diversity was observed across the plastomes, leading us to identify 13 mutational hotspot regions, comprising eight intergenic spacer regions and five gene regions. Our phylogenetic analyses based on 77 protein-coding genes generated phylogenetic relationships with high support and resolution for Manglietia. This genus can be divided into three clades, and the previously proposed infrageneric classifications are not supported by our studies. Furthermore, the close affinity between M. aromatica and M. calcarea is supported by the present work, and further studies are necessary to conclude the taxonomic treatment for the latter. These results provide resources for the comparative plastome, breeding, and plastid genetic engineering of Magnoliaceae and flowering plants.

Chloroplast genome of Calamus tetradactylus revealed rattan phylogeny.

BACKGROUND: Calamus tetradactylus, a species primarily distributed in Vietnam, Laos, and southern China, is highly valued for its utilization as a small-diameter rattan material. While its physical and mechanical properties have been extensively studied, the genomic characteristics of C. tetradactylus remain largely unexplored. RESULTS: To gain a better understanding of its chloroplast genomic features and evolutionary relationships, we conducted sequencing and assembly of the chloroplast genome of C. tetradactylus. The complete chloroplast genome exhibited the typical highly conserved quartile structure, with specific variable regions identified in the single-copy region (like psbF-psbE, π = 0.10327, ndhF-rpl32, π = 0.10195), as well as genes such as trnT-GGU (π = 0.05764) and ycf1 (π = 0.03345) and others. We propose that these regions and genes hold potential as markers for species identification. Furthermore, phylogenetic analysis revealed that C. tetradactylus formed a distinct clade within the phylogenetic tree, alongside other Calamus species, and C. tetradactylus was most closely related to C. walkeri, providing support for the monophyly of the genus. CONCLUSION: The analysis of the chloroplast genome conducted in this study provides valuable insights that can contribute to the improvement of rattan breeding programs and facilitate sustainable development in the future.

Characterization of the complete chloroplast genome of Wolffia arrhiza and comparative genomic analysis with relative Wolffia species.

Lemnoideae, commonly referred to as the duckweed, are aquatic plants found worldwide. Wolffia species are known for their extreme reduction in size and complexity, lacking both roots and leaves, and they hold the distinction of being the smallest plants among angiosperms. Interestingly, it belongs to the Araceae family, despite its apparent morphological differences from land plants in the same family. Traditional morphological methods have limitations in classifying these plants, making molecular-level information essential. The chloroplast genome of Wolffia arrhiza is revealed that a total length of 169,602 bp and a total GC content of 35.78%. It follows the typical quadripartite structure, which includes a large single copy (LSC, 92,172 bp) region, a small single copy (SSC, 13,686 bp) region, and a pair of inverted repeat (IR, 31,872 bp each) regions. There are 131 genes characterized, comprising 86 Protein-Coding Genes, 37 Transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. Moreover, 48 simple sequence repeats and 32 long repeat sequences were detected. Comparative analysis between W. arrhiza and six other Lemnoideae species identified 12 hotspots of high nucleotide diversity. In addition, a phylogenetic analysis was performed using 14 species belonging to the Araceae family and one external species as an outgroup. This analysis unveiled W. arrhiza and Wolffia globosa as closely related sister species. Therefore, this research has revealed the complete chloroplast genome data of W. arrhiza, offering a more detailed understanding of its evolutionary position and phylogenetic categorization within the Lemnoideae subfamily.

Complete chloroplast genomes of three copal trees (Bursera: Bullockia): comparative analysis and phylogenetic relationships.

BACKGROUND: Bursera trees are conspicuous elements of the tropical dry forests in the Neotropics that have significant cultural value due to their fragrant resins (incense), wood sources (handcrafts), and ecological benefits. Despite their relevance, genetic resources developed for the genus are scarce. METHODS AND RESULTS: We obtained the complete chloroplast (Cp) genome sequence, analyzed the genome structure, and performed functional annotation of three Bursera species of the Bullockia section: Bursera cuneata, B. palmeri, and B. bipinnata. The Cp genome sizes ranged from 159,824 to 159,872 bp in length, including a large single-copy (LSC) region from 87,668 to 87,656 bp, a small single-copy (SSC) from 18,581 to 18,571 bp, and two inverted repeats regions (IRa and IRb) of 26,814 bp each. The three Cp genomes consisted of 135 genes, of which 90 were protein-coding, 37 tRNAs, and 8 rRNAs. The Cp genomes were relatively conserved, with the LSC region exhibiting the greatest nucleotide divergence (psbJ, trnQ-UCC, trnG-UCC, and petL genes), whereas few changes were observed in the IR border regions. Between 589 and 591 simple sequence repeats were identified. Analysis of phylogenetic relationships using our data for each Cp region (LSC, SSC, IRa, and IRb) and of seven species within Burseraceae confirmed that Commiphora is the sister genus of Bursera. Only the phylogenetic trees based on the SSC and LSC regions resolved the close relationship between B. bipinnata and B. palmeri. CONCLUSION: Our work contributes to the development of Bursera's genomic resources for taxonomic, evolutionary, and ecological-genetic studies.

The newly assembled chloroplast genome of Aeluropus littoralis: molecular feature characterization and phylogenetic analysis with related species.

Aeluropus littoralis, a halophyte grass, is widely distributed from the Mediterranean to the Indian subcontinent through the Mongolian Gobi. This model halophyte has garnered increasing attention owing to its use as forage and its high tolerance to environmental stressors. The chloroplast genomes of many plants have been extensively examined for molecular, phylogenetic and transplastomic applications. However, no published research on the A. littoralis chloroplast (cp) genome was discovered. Here, the entire chloroplast genome of A. littoralis was assembled implementing accurate long-read sequences. The entire chloroplast genome, with an estimated length of 135,532 bp (GC content: 38.2%), has a quadripartite architecture and includes a pair of inverted repeat (IR) regions, IRa and IRb (21,012 bp each), separated by a large and a small single-copy regions (80,823 and 12,685 bp, respectively). The features of A. littoralis consist of 133 genes that synthesize 87 peptides, 38 transfer RNAs, and 8 ribosomal RNAs. Of these genes, 86 were unique, whereas 19 were duplicated in IR regions. Additionally, a total of forty-six simple sequence repeats, categorized into 32-mono, four-di, two-tri, and eight-tetranucleotides, were discovered. Furthermore, ten sets of repeats greater than 20 bp were located primarily in the LSC region. Evolutionary analysis based on chloroplast sequence data revealed that A. littoralis with A. lagopoides and A. sinensis belong to the Aeluropodinae subtribe, which is a sister to the Eleusininae in the tribe Cynodonteae and the subfamily Chloridoideae. This subfamily belongs to the PACMAD clade, which contains the majority of the C4 photosynthetic plants in the Poaceae. The newly constructed A. littoralis cp genome offers valuable knowledge for DNA barcoding, phylogenetic, transplastomic research, and other biological studies.

Comparative Analysis of Chloroplast Genomes of "Tiantai Wu-Yao" (Lindera aggregata) and Taxa of the Same Genus and Different Genera.

Lindera aggregata is a species of the Lauraceae family, which has important medicinal, economic and ornamental values. In this study, we sequenced, assembled and annotated the chloroplast genome of L. aggregata and reannotated and corrected eight unverified annotations in the same genus. The chloroplast genomes taxa from Lindera and from different genera of Lauraceae were compared and analyzed, and their phylogenetic relationship and divergence time were speculated. All the 36 chloroplast genomes had typical quadripartite structures that ranged from 150,749 to 154,736 bp in total length. These genomes encoded 111-112 unique genes, including 78-79 protein-coding genes, 29-30 tRNA and 4 rRNA. Furthermore, there were 78-97 SSRs loci in these genomes, in which mononucleotide repeats were the most abundant; there were 24-49 interspersed repeats, and forward repeat types were the most frequent. The codon bias patterns of all species tended to use codons ending with A or U. Five and six highly variable regions were identified within genus and between genera, respectively, and three common regions (ycf1, ndhF-rpl32 and rpl32-trnL) were identified, which can be used as important DNA markers for phylogeny and species identification. According to the evaluation of the Ka/Ks ratio, most of the genes were under purifying selection, and only 10 genes were under positive selection. Finally, through the construction of the evolutionary tree of 39 chloroplast genomes, the phylogenetic relationship of Lauraceae was clarified and the evolutionary relationship of Lindera was revealed. The species of genus Lindera experienced rapid adaptive radiation from Miocene to Pleistocene. The results provided valuable insights for the study of chloroplast genomes in the Lauraceae family, especially in the genus Lindera.

Characterization of Firmiana danxiaensis plastomes and comparative analysis of Firmiana: insight into its phylogeny and evolution.

BACKGROUND: Firmiana danxiaensis is a critically endangered and ecologically important tree currently only found in four locations in Danxia or Karst habitats in northern Guangdong Province, China. The specialized habitat preference makes it an ideal model species for study of adaptive evolution. Meanwhile, the phylogenetic relationships of F. danxiaensis in four locations under two landforms are unclear. Therefore, we sequenced its complete chloroplast (cp.) genomes and conducted comprehensive interspecific and intrageneric plastome studies. RESULTS: The F. danxiaensis plastomes in four locations showed a typical quadripartite and circular structure that ranged from 160,832 to 161,206 bp in size, with 112 unique genes encoded. Comparative genomics showed that the plastomes of F. danxiaensis were relatively conserved with high similarity of genome organization, gene number, GC content and SSRs. While the genomes revealed higher biased codon preferences in Karst habitat than those in Danxia habitats. Eighteen and 11 divergent hotpots were identified at interspecific and intrageneric levels for species identification and further phylogenetic studies. Seven genes (clpP, accD, ccsA, ndhH, rpl20, rpoC2, and rps4) were under positive selection and may be related to adaptation. Phylogenetic analysis revealed that F. danxiaensis is sister to F. major and F. simplex. However, the interspecific relationships are not consistent with the habitat types. CONCLUSIONS: The characteristics and interspecific relationship of F. danxiaensis plastomes provide new insights into further integration of geographical factors, environmental factors, and genetic variations on the genomic study of F. danxiaensis. Together, our study will contribute to the study of species identification, population genetics, and conservation biology of F. danxiaensis.

CLAW: An automated Snakemake workflow for the assembly of chloroplast genomes from long-read data.

Chloroplasts are photosynthetic organelles in algal and plant cells that contain their own genome. Chloroplast genomes are commonly used in evolutionary studies and taxonomic identification and are increasingly becoming a target for crop improvement studies. As DNA sequencing becomes more affordable, researchers are collecting vast swathes of high-quality whole-genome sequence data from laboratory and field settings alike. Whole tissue read libraries sequenced with the primary goal of understanding the nuclear genome will inadvertently contain many reads derived from the chloroplast genome. These whole-genome, whole-tissue read libraries can additionally be used to assemble chloroplast genomes with little to no extra cost. While several tools exist that make use of short-read second generation and third-generation long-read sequencing data for chloroplast genome assembly, these tools may have complex installation steps, inadequate error reporting, poor expandability, and/or lack scalability. Here, we present CLAW (Chloroplast Long-read Assembly Workflow), an easy to install, customise, and use Snakemake tool to assemble chloroplast genomes from chloroplast long-reads found in whole-genome read libraries (https://github.com/aaronphillips7493/CLAW). Using 19 publicly available reference chloroplast genome assemblies and long-read libraries from algal, monocot and eudicot species, we show that CLAW can rapidly produce chloroplast genome assemblies with high similarity to the reference assemblies. CLAW was designed such that users have complete control over parameterisation, allowing individuals to optimise CLAW to their specific use cases. We expect that CLAW will provide researchers (with varying levels of bioinformatics expertise) with an additional resource useful for contributing to the growing number of publicly available chloroplast genome assemblies.

Chloroplast genome analyses of Caragana arborescens and Caragana opulens.

BACKGROUND: Numerous species within the genus Caragana have high ecological and medicinal value. However, species identification based on morphological characteristics is quite complicated in the genus. To address this issue, we analyzed complete plastid genome data for the genus. RESULTS: We obtained chloroplast genomes of two species, Caragana arborescens and Caragana opulens, using Illumina sequencing technology, with lengths of 129,473 bp and 132,815 bp, respectively. The absence of inverted repeat sequences in the two species indicated that they could be assigned to the inverted repeat-lacking clade (IRLC). The genomes included 111 distinct genes (4 rRNA genes, 31 tRNA genes, and 76 protein-coding genes). In addition, 16 genes containing introns were identified in the two genomes, the majority of which contained a single intron. Repeat analyses revealed 129 and 229 repeats in C. arborescens and C. opulens, respectively. C. arborescens and C. opulens genomes contained 277 and 265 simple sequence repeats, respectively. The two Caragana species exhibited similar codon usage patterns. rpl20-clpP, rps19-rpl2, and rpl23-ycf2 showed the highest nucleotide diversity (pi). In an analysis of sequence divergence, certain intergenic regions (matK-rbcL, psbM-petN, atpA-psbI, petA-psbL, psbE-petL, and rps7-rps12) were highly variable. A phylogenetic analysis showed that C. arborescens and C. opulens were related and clustered together with four other Caragana species. The genera Astragalus and Caragana were relatively closely related. CONCLUSIONS: The present study provides valuable information about the chloroplast genomes of C. arborescens and C. opulens and lays a foundation for future phylogenetic research and molecular marker development.