Whole-Genome Comparison Reveals Divergent IR Borders and Mutation Hotspots in Chloroplast Genomes of Herbaceous Bamboos (Bambusoideae: Olyreae)

Characterization of the complete chloroplast genome of Rhodiola sachalinensis and comparative analysis with its congeneric plants

Rhodiola, belonging to the Crassulaceae family, is a perennial herbaceous plant genus. There are about 90 Rhodiola species worldwide, some of which have been reported to have medicinal properties. Rhodiola sachalinensis is a perennial medicinal herb within this genus and, in the present study, its chloroplast genome was sequenced, assembled, annotated and compared with 24 other Rhodiola species. The results obtained show that the chloroplast genome of R. sachalinensis is 151 595 bp long and has a CG content of 37.7%. The inverted repeats (IR) region of the Rhodiola chloroplast genome is the most conserved region, with the main differences being observed in the ycf1 and ndhF genes at the IRb-small single copy boundary, and rps19 and trnH genes at the IRa-large single copy boundary. Phylogenetic analysis showed that Rhodiola species form two major clades, and species with recorded medicinal properties, clustered together in one branch except for R. dumulosa. Within the genus, R. sachalinensis is most closely related to Rhodiola rosea, although comparative analyses showed that only R. sachalinensis and Rhodiola subopposita contained the psbZ gene, which encodes a highly conserved protein subunit of the Photosystem II core complex. Overall, the present study contributes to the understanding of the chloroplast genome of Rhodiola species, and provides a theoretical basis for the study of their genetic diversity and possible use as medicinal plants.

Testing plastomes and nuclear ribosomal DNA sequences as the next-generation DNA barcodes for species identification and phylogenetic analysis in Acer

BACKGROUND

Acer is a taxonomically intractable and speciose genus that contains over 150 species. It is challenging to distinguish Acer species only by morphological method due to their abundant variations. Plastome and nuclear ribosomal DNA (nrDNA) sequences are recommended as powerful next-generation DNA barcodes for species discrimination. However, their efficacies were still poorly studied. The current study will evaluate the application of plastome and nrDNA in species identification and perform phylogenetic analyses for Acer.

RESULT

Based on a collection of 83 individuals representing 55 species (c. 55% of Chinese species) from 13 sections, our barcoding analyses demonstrated that plastomes exhibited the highest (90.47%) species discriminatory power among all plastid DNA markers, such as the standard plastid barcodes matK + rbcL + trnH-psbA (61.90%) and ycf1 (76.19%). And the nrDNA (80.95%) revealed higher species resolution than ITS (71.43%). Acer plastomes show abundant interspecific variations, however, species identification failure may be due to the incomplete lineage sorting (ILS) and chloroplast capture resulting from hybridization. We found that the usage of nrDNA contributed to identifying those species that were unidentified by plastomes, implying its capability to some extent to mitigate the impact of hybridization and ILS on species discrimination. However, combining plastome and nrDNA is not recommended given the cytonuclear conflict caused by potential hybridization. Our phylogenetic analysis covering 19 sections (95% sections of Acer) and 128 species (over 80% species of this genus) revealed pervasive inter- and intra-section cytonuclear discordances, hinting that hybridization has played an important role in the evolution of Acer.

CONCLUSION

Plastomes and nrDNA can significantly improve the species resolution in Acer. Our phylogenetic analysis uncovered the scope and depth of cytonuclear conflict in Acer, providing important insights into its evolution.

The first complete chloroplast genome of Thalictrum fargesii: insights into phylogeny and species identification

Introduction

Thalictrum fargesii is a medicinal plant belonging to the genus Thalictrum of the Ranunculaceae family and has been used in herbal medicine in the Himalayan regions of China and India. This species is taxonomically challenging because of its morphological similarities to other species within the genus. Thus, herbal drugs from this species are frequently adulterated, substituted, or mixed with other species, thereby endangering consumer safety.

Methods

The present study aimed to sequence and assemble the entire chloroplast (cp) genome of T. fargesii using the Illumina HiSeq 2500 platform to better understand the genomic architecture, gene composition, and phylogenetic relationships within the Thalictrum.

Results and discussion

The cp genome was 155,929 bp long and contained large single-copy (85,395 bp) and small single-copy (17,576 bp) regions that were segregated by a pair of inverted repeat regions (26,479 bp) to form a quadripartite structure. The cp genome contains 133 genes, including 88 protein-coding genes (PCGs), 37 tRNA genes, and 8 rRNA genes. Additionally, this genome contains 64 codons that encode 20 amino acids, the most preferred of which are alanine and leucine. We identified 68 SSRs, 27 long repeats, and 242 high-confidence C-to-U RNA-editing sites in the cp genome. Moreover, we discovered seven divergent hotspot regions in the cp genome of T. fargesii, among which ndhD-psaC and rpl16-rps3 may be useful for developing molecular markers for identifying ethnodrug species and their contaminants. A comparative study with eight other species in the genus revealed that pafI and rps19 had highly variable sites in the cp genome of T. fargesii. Additionally, two special features, (i) the shortest length of the ycf1 gene at the IRA-SSC boundary and (ii) the distance between the rps19 fragment and trnH at the IRA-LSC junction, distinguish the cp genome of T. fargesii from those of other species within the genus. Furthermore, phylogenetic analysis revealed that T. fargesii was closely related to T. tenue and T. petaloidium.

Conclusion

Considering all these lines of evidence, our findings offer crucial molecular and evolutionary information that could play a significant role in further species identification, evolution, and phylogenetic studies on T. fargesii.

A new perspective on codon usage, selective pressure, and phylogenetic implications of the plastomes in the Telephium clade (Crassulaceae)

The Telephium clade of the Crassulaceae family contains many medicinal, ornamental, and ecologically restorative plants. However, the phylogenetic relationships within the clade remain debated, and comprehensive analyses of codon usage and selection pressure in Telephium plastomes are limited. In this study, we assembled and annotated four plastomes and performed extensive analyses. The plastomes exhibited a typical quadripartite structure and high conservation. The lengths ranged from 151,357 bp to 151,641 bp with 134 genes identified. The GC content was the highest within IR, followed by LSC, and lowest in the SSC region. Meanwhile, a unique inversion was observed within the LSC region of Meterostachys sikokianus. Polymorphisms analysis revealed minimum nucleotide diversity in the IR regions, with over ten highly polymorphic regions identified. Phylogenetically, two subclades formed within the monophyletic Telephium clade, with Umbilicus as the sister group to the remaining Hylotelephium subclade members. Notably, no significant positive selection was found among the 79 plastid genes, which showed varying evolutionary patterns. However, 19 genes contained codons under positive selection. The specific functions of these sites require further investigation. Synonymous codon usage was biased and conserved across the tested plastomes, shaped by natural selection, mutations and other factors of varying influence. We also identified 34 taxon-specific codon aversion motifs from 49 plastid genes. Our plastomic analyses elucidate phylogenetic relationships and evolutionary patterns in this medicinal clade, providing a foundation for further research on these ecologically and pharmaceutically important plants.

Chloroplast genome assembly of Serjania erecta Raldk: comparative analysis reveals gene number variation and selection in protein-coding plastid genes of Sapindaceae

Serjania erecta Raldk is an essential genetic resource due to its anti-inflammatory, gastric protection, and anti-Alzheimer properties. However, the genetic and evolutionary aspects of the species remain poorly known. Here, we sequenced and assembled the complete chloroplast genome of S. erecta and used it in a comparative analysis within the Sapindaceae family. S. erecta has a chloroplast genome (cpDNA) of 159,297 bp, divided into a Large Single Copy region (LSC) of 84,556 bp and a Small Single Copy region (SSC) of 18,057 bp that are surrounded by two Inverted Repeat regions (IRa and IRb) of 28,342 bp. Among the 12 species used in the comparative analysis, S. erecta has the fewest long and microsatellite repeats. The genome structure of Sapindaceae species is relatively conserved; the number of genes varies from 128 to 132 genes, and this variation is associated with three main factors: (1) Expansion and retraction events in the size of the IRs, resulting in variations in the number of rpl22, rps19, and rps3 genes; (2) Pseudogenization of the rps2 gene; and (3) Loss or duplication of genes encoding tRNAs, associated with the duplication of trnH-GUG in X. sorbifolium and the absence of trnT-CGU in the Dodonaeoideae subfamily. We identified 10 and 11 mutational hotspots for Sapindaceae and Sapindoideae, respectively, and identified six highly diverse regions (tRNA-Lys - rps16, ndhC - tRNA-Val, petA - psbJ, ndhF, rpl32 - ccsA, and ycf1) are found in both groups, which show potential for the development of DNA barcode markers for molecular taxonomic identification of Serjania. We identified that the psaI gene evolves under neutrality in Sapindaceae, while all other chloroplast genes are under strong negative selection. However, local positive selection exists in the ndhF, rpoC2, ycf1, and ycf2 genes. The genes ndhF and ycf1 also present high nucleotide diversity and local positive selection, demonstrating significant potential as markers. Our findings include providing the first chloroplast genome of a member of the Paullinieae tribe. Furthermore, we identified patterns in variations in the number of genes and selection in genes possibly associated with the family's evolutionary history.

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.

Poaceae Chloroplast Genome Sequencing: Great Leap Forward in Recent Ten Years

The first complete chloroplast genome of rice (Oryza sativa) was published in 1989, ushering in a new era of studies of chloroplast genomics in Poaceae. Progresses in Next-Generation Sequencing (NGS) and Third-Generation Sequencing (TGS) technologiesand in the development of genome assembly software, have significantly advanced chloroplast genomics research. Poaceae is one of the most targeted families in chloroplast genome research because of its agricultural, ecological, and economic importance. Over the last 30 years, 2,050 complete chloroplast genome sequences from 40 tribes and 282 genera have been generated, most (97%) of them in the recent ten years. The wealth of data provides the groundwork for studies on species evolution, phylogeny, genetic transformation, and other aspects of Poaceae chloroplast genomes. As a result, we have gained a deeper understanding of the properties of Poaceae chloroplast genomes. Here, we summarize the achievements of the studies of the Poaceae chloroplast genomes and envision the challenges for moving the area ahead.

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.

Sequence Characteristics and Phylogenetic Analysis of the Artemisia argyi Chloroplast Genome

Artemisia argyi Levl. et Van is an important Asteraceae species with a high medicinal value. There are abundant A. argyi germplasm resources in Asia, especially in China, but the evolutionary relationships of these varieties and the systematic localization of A. argyi in the family Asteraceae are still unclear. In this study, the chloroplast (cp) genomes of 72 A. argyi varieties were systematically analyzed. The 72 varieties originated from 47 regions in China at different longitudes, latitudes and altitudes, and included both wild and cultivated varieties. The A. argyi cp genome was found to be ∼151 kb in size and to contain 114 genes, including 82 protein-coding, 28 tRNA, and 4 rRNA genes. The number of short sequence repeats (SSRs) in A. argyi cp genomes ranged from 35 to 42, and most of them were mononucleotide A/T repeats. A total of 196 polymorphic sites were detected in the cp genomes of the 72 varieties. Phylogenetic analysis demonstrated that the genetic relationship between A. argyi varieties had a weak relationship with their geographical distribution. Furthermore, inverted repeat (IR) boundaries of 10 Artemisia species were found to be significantly different. A sequence divergence analysis of Asteraceae cp genomes showed that the variable regions were mostly located in single-copy (SC) regions and that the coding regions were more conserved than the non-coding regions. A phylogenetic tree was constructed using 43 protein-coding genes common to 67 Asteraceae species. The resulting tree was consistent with the traditional classification system; Artemisia species were clustered into one group, and A. argyi was shown to be closely related to Artemisia lactiflora and Artemisia montana. In summary, this study systematically analyzed the cp genome characteristics of A. argyi and compared cp genomes of Asteraceae species. The results provide valuable information for the definitive identification of A. argyi varieties and for the understanding of the evolutionary relationships between Asteraceae species.

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

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

Comparative plastome analysis of Musaceae and new insights into phylogenetic relationships

Background

Musaceae is an economically important family consisting of 70-80 species. Elucidation of the interspecific relationships of this family is essential for a more efficient conservation and utilization of genetic resources for banana improvement. However, the scarcity of herbarium specimens and quality molecular markers have limited our understanding of the phylogenetic relationships in wild species of Musaceae. Aiming at improving the phylogenetic resolution of Musaceae, we analyzed a comprehensive set of 49 plastomes for 48 species/subspecies representing all three genera of this family.

Results

Musaceae plastomes have a relatively well-conserved genomic size and gene content, with a full length ranging from 166,782 bp to 172,514 bp. Variations in the IR borders were found to show phylogenetic signals to a certain extent in Musa. Codon usage bias analysis showed different preferences for the same codon between species and three genera and a common preference for A/T-ending codons. Among the two genes detected under positive selection (dN/dS > 1), ycf2 was indicated under an intensive positive selection. The divergent hotspot analysis allowed the identification of four regions (ndhF-trnL, ndhF, matK-rps16, and accD) as specific DNA barcodes for Musaceae species.

Bayesian and maximum likelihood phylogenetic analyses using full plastome resulted in nearly identical tree topologies with highly supported relationships between species. The monospecies genus Musella is sister to Ensete, and the genus Musa was divided into two large clades, which corresponded well to the basic number of n = x = 11 and n = x =10/9/7, respectively. Four subclades were divided within the genus Musa. A dating analysis covering the whole Zingiberales indicated that the divergence of Musaceae family originated in the Palaeocene (59.19 Ma), and the genus Musa diverged into two clades in the Eocene (50.70 Ma) and then started to diversify from the late Oligocene (29.92 Ma) to the late Miocene. Two lineages (Rhodochlamys and Australimusa) radiated recently in the Pliocene /Pleistocene periods.

Conclusions

The plastome sequences performed well in resolving the phylogenetic relationships of Musaceae and generated new insights into its evolution. Plastome sequences provided valuable resources for population genetics and phylogenetics at lower taxon.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08454-3.

Development of nuclear and chloroplast polymorphic microsatellites for Crossostephium chinense (Asteraceae)

BACKGROUND

Crossostephium chinense is a traditional Chinese medicinal herb and it is often cultivated as an ornamental plant. Previous studies on this species mainly focused on its chemical composition and it was rarely represented in genetic studies, and thus genomic resources remain scarce.

METHODS AND RESULTS

Both chloroplast and nuclear polymorphic microsatellites of C. chinense were screened from genome skimming data of two individuals. 64 and 63 cpSSR markers were identified from two chloroplast genomes of C. chinense. A total of 133 polymorphic nSSRs were developed. Ten nSSRs were randomly selected to test their transferability across 35 individuals from three populations of C. chinense, and 20 individuals each of Artemisia stolonifera and A. argyi. Cross-amplifications were successfully done for C. chinense and were partially amplified for both Artemisia species. The number of alleles varied from two to nine. The observed heterozygosity and expected heterozygosity per locus ranged from 0.000 to 0.286 and from 0.029 to 0.755, respectively.

CONCLUSIONS

In this study, we developed polymorphic cpSSRs and nSSRs markers for C. chinense based on genome skimming sequencing. These genomic resources will be valuable for population genetics and conservation studies in C. chinense and Artemisia.

Complete Chloroplast Genome Sequence of Fortunella venosa (Champ. ex Benth.) C.C.Huang (Rutaceae): Comparative Analysis, Phylogenetic Relationships, and Robust Support for Its Status as an Independent Species

Fortunella venosa (Rutaceae) is an endangered species endemic to China and its taxonomic status has been controversial. The genus Fortunella contains a variety of important economic plants with high value in food, medicine, and ornamental. However, the placement of Genus Fortunella into Genus Citrus has led to controversy on its taxonomy and Systematics. In this present research, the Chloroplast genome of F. venosa was sequenced using the second-generation sequencing, and its structure and phylogenetic relationship analyzed. The results showed that the Chloroplast genome size of F. venosa was 160,265 bp, with a typical angiosperm four-part ring structure containing a large single copy region (LSC) (87,597 bp), a small single copy region (SSC) (18,732 bp), and a pair of inverted repeat regions (IRa\IRb) (26,968 bp each). There are 134 predicted genes in Chloroplast genome, including 89 protein-coding genes, 8 rRNAs, and 37 tRNAs. The GC-content of the whole Chloroplast genome was 43%, with the IR regions having a higher GC content than the LSC and the SSC regions. There were no rearrangements present in the Chloroplast genome; however, the IR regions showed obvious contraction and expansion. A total of 108 simple sequence repeats (SSRs) were present in the entire chloroplast genome and the nucleotide polymorphism was high in LSC and SSC. In addition, there is a preference for codon usage with the non-coding regions being more conserved than the coding regions. Phylogenetic analysis showed that species of Fortunella are nested in the genus of Citrus and the independent species status of F. venosa is supported robustly, which is significantly different from F. japonica. These findings will help in the development of DNA barcodes that can be useful in the study of the systematics and evolution of the genus Fortunella and the family Rutaceae.

Chloroplast genomes in Populus (Salicaceae): comparisons from an intensively sampled genus reveal dynamic patterns of evolution

The chloroplast is one of two organelles containing a separate genome that codes for essential and distinct cellular functions such as photosynthesis. Given the importance of chloroplasts in plant metabolism, the genomic architecture and gene content have been strongly conserved through long periods of time and as such are useful molecular tools for evolutionary inferences. At present, complete chloroplast genomes from over 4000 species have been deposited into publicly accessible databases. Despite the large number of complete chloroplast genomes, comprehensive analyses regarding genome architecture and gene content have not been conducted for many lineages with complete species sampling. In this study, we employed the genus Populus to assess how more comprehensively sampled chloroplast genome analyses can be used in understanding chloroplast evolution in a broadly studied lineage of angiosperms. We conducted comparative analyses across Populus in order to elucidate variation in key genome features such as genome size, gene number, gene content, repeat type and number, SSR (Simple Sequence Repeat) abundance, and boundary positioning between the four main units of the genome. We found that some genome annotations were variable across the genus owing in part from errors in assembly or data checking and from this provided corrected annotations. We also employed complete chloroplast genomes for phylogenetic analyses including the dating of divergence times throughout the genus. Lastly, we utilized re-sequencing data to describe the variations of pan-chloroplast genomes at the population level for P. euphratica. The analyses used in this paper provide a blueprint for the types of analyses that can be conducted with publicly available chloroplast genomes as well as methods for building upon existing datasets to improve evolutionary inference.

The complete chloroplast genome of Photinia davidsoniae: molecular structures and comparative analysis

Photinia davidsoniae is a common ornamental arbor in the genus Photinia (family Rosaceae). Here, we sequenced and assembled the complete plastome of P. davidsoniae using the next-generation DNA sequencing technology. And we then compared it with nine Photinia species using a range of bioinformatics software tools. The ten plastomes had sizes ranging from 159,230 bp for P. beckii to 160,346 bp for P. davidsoniae. They all had a conservative quartile structure. It contained two single-copy regions: a large single-copy (LSC) region, a small single-copy (SSC) region, and a pair of inverted repeat (IR) regions. Each of the plastomes encoded 113 unique genes, including 79 protein-coding genes, four rRNA genes, and 30 tRNA genes. Furthermore, we detected six hypervariable regions (matK-rps16, rpoB-trnC, trnT-psbD, ndhC-trnV, psbE-petL, ndhF-rpl32-trnL), which could be used as potential molecular markers. We constructed two phylogenetic trees with plastomes or concatenated protein sequences of 25 species of 8 genera of Rosaceae. The tree constructed with complete plastomes has much stronger support. The results placed P. davidsoniae in the upper part of the phylogenetic tree. It shows that P. davidsoniae and P. lanuginosa are closely related. In summary, the plastomes of Photinia are conserved overall but carry significant minor variations, as expected. The results will be indispensable for distinguishing species, understanding the interspecific diversity, and elucidating the evolutionary processes of Photinia species.

Comparative plastid genomics of four Pilea (Urticaceae) species: insight into interspecific plastid genome diversity in Pilea

BACKGROUND

Pilea is a genus of perennial herbs from the family Urticaceae, and some species are used as courtyard ornamentals or for medicinal purposes. At present, there is no information about the plastid genome of Pilea, which limits our understanding of this genus. Here, we report 4 plastid genomes of Pilea taxa (Pilea mollis, Pilea glauca 'Greizy', Pilea peperomioides and Pilea serpyllacea 'Globosa') and performed comprehensive comparative analysis.

RESULTS

The four plastid genomes all have a typical quartile structure. The lengths of the plastid genomes ranged from 150,398 bp to 152,327 bp, and each genome contained 113 unique genes, including 79 protein-coding genes, 4 rRNA genes, and 30 tRNA genes. Comparative analysis showed a rather high level of sequence divergence in the four genomes. Moreover, eight hypervariable regions were identified (petN-psbM, psbZ-trnG-GCC, trnT-UGU-trnL-UAA, accD-psbI, ndhF-rpl32, rpl32-trnL-UAG, ndhA-intron and ycf1), which are proposed for use as DNA barcode regions. Phylogenetic relationships based on the plastid genomes of 23 species of 14 genera of Urticaceae resulted in the placement of Pilea in the middle and lower part of the phylogenetic tree, with 100% bootstrap support within Urticaceae.

CONCLUSION

Our results enrich the resources concerning plastid genomes. Comparative plastome analysis provides insight into the interspecific diversity of the plastid genome of Pilea. The identified hypervariable regions could be used for developing molecular markers applicable in various research areas.

The Complete Chloroplast Genome Sequencing and Comparative Analysis of Reed Canary Grass (Phalaris arundinacea) and Hardinggrass (P. aquatica)

There are 22 species in the Phalaris genera that distribute almost all over the temperate regions of the world. Among them, reed canary grass (Phalaris arundinacea, tetraploid and hexaploid) and hardinggrass (P. aquatica, tetraploid) have been long cultivated as forage grass and have received attention as bio-energy materials in recent years. We aimed to facilitate inter-species/ploidies comparisons, and to illuminate the degree of sequence variation within existing gene pools, chloroplast (cp) genomes of three Phalaris cytotypes (P. aquatica/4x, P. arundinacea/4x and P. arundinacea/6x) were sequenced and assembled. The result indicated that certain sequence variations existed between the cp genomes of P. arundinacea and P. aquatica. Several hotspot regions (atpI~atpH, trnT-UGU~ndhJ, rbcL~psaI, and ndhF~rpl32) were found, and variable genes (infA, psaI, psbK, etc.) were detected. SNPs (single nucleotide polymorphisms) and/or indels (insertions and deletions) were confirmed by the high Ka/Ks and Pi value. Furthermore, distribution and presence of cp simple sequence repeats (cpSSRs) were identified in the three Phalaris cp genomes, although little difference was found between hexaploid and tetraploid P. arundinacea, and no rearrangement was detected among the three Phalaris cp genomes. The evolutionary relationship and divergent time among these species were discussed. The RNA-seq revealed several differentially expressed genes (DEGs), among which psaA, psaB, and psbB related to leaf color were further verified by leaf color differences.

The complete chloroplast genome sequence of Mangifera sylvatica Roxb. (Anacardiaceae) and its phylogenetic analysis

In this study, we firstly reported the complete chloroplast (cp) genome sequences of the Mangifera sylvatica from Nanning, Guangxi province, China. The complete wild mango cp genome size is 158063 bp with a typical small single-copy region (SSC, 18340 bp), a large single-copy region (LSC, 87008 bp) and a pair of inverted repeats (IRs, 26379 bp and 26379 bp respectively). Out of 112 unique annotated genes in mango cp genome, 78 found to be protein coding, 30 to be tRNA and 4 rRNA genes. Besides, we found 51 microsatellite sequences (SSRs) in the cp genome. Sequence alignment and ML analysis of 29 full plastome data revealed M. sylvatica shares the closest relationship with cultivated mango (M. indica) and form a sister group with Rhus chinensis within Anacardiaceae.

Characterization of the complete chloroplast genome of sugar maple (Acer saccharum)

Acer saccharum is one ecologically and economically important tree species cultivated widely across the world. In this study we generated the complete chloroplast (cp) genome of A. saccharum via genome-skimming method. The assembled genome is 155,684 base-pairs (bp) in size, with one large single copy region of 85,393 bp and one small single copy region of 18,033 bp separated by two inverted repeats of 26,129 bp. The genome contains a total of 133 genes, including 85 protein-coding genes, 8 rRNAs and 40 tRNAs. Furthermore, phylogenomic estimation strongly supported A. saccharum as a distinct lineage within the monophyletic Acer.

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

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

Phylogenetic relationships within Parianinae (Poaceae: Bambusoideae: Olyreae) with emphasis on Eremitis: Evidence from nuclear and plastid DNA sequences, macromorphology, and pollen ectexine patterns

Eremitis, Pariana, and Parianella are herbaceous bamboos (tribe Olyreae) included in the subtribe Parianinae, which is characterized by the presence of fimbriae at the apex of the leaf sheaths and exclusively spiciform synflorescences. We analyzed 43 samples of herbaceous and woody bamboos in order to infer relationships within the Parianinae, based on combined data from the nuclear ribosomal internal transcribed spacer (ITS) and plastid DNA (rpl32-trnL and trnD-trnT spacers). Bayesian inference, maximum likelihood, and maximum parsimony methods were applied, and macro- and micromorphological aspects were also analyzed, including the ectexine patterns of pollen grains. Parianinae is represented by three well-supported lineages in our analyses: (1) Parianella, endemic to southern Bahia, Brazil; (2) Pariana sensu stricto with a broad distribution in southern Central America and northern South America, especially in the Amazon region; and (3) Eremitis, endemic to the Brazilian Atlantic Forest, from the states of Pernambuco to Rio de Janeiro, including one species previously described as a member of Pariana. Our molecular phylogeny showed that Pariana, as historically circumscribed, is not monophyletic, by recovering Pariana sensu stricto as strongly supported and sister to Eremitis + Pariana multiflora, with Parianella sister to the Pariana-Eremitis clade. Morphological features of their synflorescences and differences in ectexine patterns characterize each lineage. Based on all these characters and the phylogenetic results, Pariana multiflora, endemic to the state of Espírito Santo, Brazil, is transferred to Eremitis.

Sequencing and Structural Analysis of the Complete Chloroplast Genome of the Medicinal Plant Lycium chinense Mill

Lycium chinense Mill, an important Chinese herbal medicine, is widely used as a dietary supplement and food. Here the chloroplast (CP) genome of L. chinense was sequenced and analyzed, revealing a size of 155,756 bp and with a 37.8% GC content. The L. chinense CP genome comprises a large single copy region (LSC) of 86,595 bp and a small single copy region (SSC) of 18,209 bp, and two inverted repeat regions (IRa and IRb) of 25,476 bp separated by the single copy regions. The genome encodes 114 genes, 16 of which are duplicated. Most of the 85 protein-coding genes (CDS) had standard ATG start codons, while 3 genes including rps12, psbL and ndhD had abnormal start codons (ACT and ACG). In addition, a strong A/T bias was found in the majority of simple sequence repeats (SSRs) detected in the CP genome. Analysis of the phylogenetic relationships among 16 species revealed that L. chinense is a sister taxon to Lycium barbarum. Overall, the complete sequence and annotation of the L. chinense CP genome provides valuable genetic information to facilitate precise understanding of the taxonomy, species and phylogenetic evolution of the Solanaceae family.

The complete chloroplast genome of Bambusa ventricosa (Bambusoideae: Bambuseae)

Bambusa ventricosa is one important ornamental bamboo. In this study, we generated the complete chloroplast (cp) genome of B. ventricosa via genome-skimming method. The complete cp genome is 139,460 base-pairs (bp) in size, with a pair of inverted repeats of 21,794 bp which separate a large single copy region of 82,996 bp and a small single copy region of 12,876 bp. The genome contains a total of 131 genes, including 84 protein-coding genes, 8 ribosomal RNAs and 39 transfer RNAs. The GC content of the cp genome is 38.9%. Moreover, phylogenomic inference robustly placed B. ventricosa in the paleotropical woody bamboos lineage.