Complete chloroplast genome of Fraxinus griffithii C.B. Clarke (Oleaceae): Insights into genome structure and molecular phylogenetics

Eucommia ulmoides is an important traditional medicinal plant that is used for the production of locative Eucommia rubber. In this study, the complete chloroplast (cp) genome sequence of E. ulmoides was obtained by total DNA sequencing; this is the first cp genome sequence of the order Garryales. The cp genome of E. ulmoides was 163,341 bp long and included a pair of inverted repeat (IR) regions (31,300 bp), one large single copy (LSC) region (86,592 bp), and one small single copy (SSC) region (14,149 bp). The genome structure and GC content were similar to those of typical angiosperm cp genomes and contained 115 unique genes, including 80 protein-coding genes, 31 transfer RNA (tRNAs), and four ribosomal RNA (rRNAs). Compared with the entire cp genome sequence, three unique genome rearrangements were observed in the LSC region. Moreover, compared with the Sesamum and Nicotiana cp genomes, E. ulmoides contained no indels in the IR regions, and variable regions were identified in noncoding regions. The E. ulmoides cp genome showed extreme expansion at the IR/SSC boundary owing to the integration of an additional complete gene, ycf1. Twenty-nine simple sequence repeats (SSRs) were identified in the E. ulmoides cp genome. In addition, 36 protein-coding genes were used for phylogenetic inference, supporting a sister relationship between E. ulmoides and Aucuba, which belongs to Euasterids I. In summary, we described the complete cp genome sequence of E. ulmoides; this information will be useful for phylogenetic and evolutionary studies.

Fagopyrum dibotrys, belongs to Polygonaceae family, is one of national key conserved wild plants of China with important medicinal and economic values. Here, the complete chloroplast (cp) genome sequence of F. dibotrys is reported. The cp genome size is 159,919 bp with a typical quadripartite structure and consisting of a pair of inverted repeat regions (30,738 bp) separated by large single copy region (85,134 bp) and small single copy region (13,309 bp). Sequencing analyses indicated that the cp genome encodes 131 genes, including 80 protein-coding genes, 28 tRNA genes and 4 rRNA genes. The genome structure, gene order and codon usage are typical of angiosperm cp genomes. We also identified 48 simple sequence repeats (SSR) loci, fewer of them are distributed in the protein-coding sequences compared to the noncoding regions. Comparison of F. dibotrys cp genome to other Polygonaceae cp genomes indicated the inverted repeats (IRs) and coding regions were more conserved than single copy and noncoding regions, and several variation hotspots were detected. Coding gene sequence divergence analyses indicated that five genes (ndhK, petL rpoC2, ycf1, ycf2) were subject to positive selection. Phylogenetic analysis among 42 species based on cp genomes and 50 protein-coding genes indicated a close relationship between F. dibotrys and F. tataricum. In summary, the complete cp genome sequence of F. dibotrys reported in this study will provide useful plastid genomic resources for population genetics and pave the way for resolving phylogenetic relationships of order Caryophyllales.

This study presents a comprehensive analysis of the chloroplast (cp) genomes of Cornus species, including comparative and phylogenetic evaluations, as well as examinations of their genomic structure and composition. The cp genomes exhibit a typical circular quadripartite structure and demonstrate highly similar gene order and genomic structure. The complete cp genome size of the 10 taxa in this study is 156,965 bp to 157,383 bp, where the length of the large single-copy (LSC) region is 86,296 bp to 86,691 bp, small single-copy (SSC) region is 18,386 bp to 18,454 bp, and inverted repeat (IR) region is 23,143 bp to 26,112 bp. A total of 131 genes were found, including 86 protein-coding genes (PCGs), eight rRNA genes, and 37 tRNA genes. The mean GC content of the 10 taxa is 38.145%, where the LSC region is 36.396%, the SSC region is 32.372%, and the IR region is 43.076%. Despite the relatively conserved nature of the cp genome within the species of Cornus, 25-31 simple sequence repeats (SSRs) were identified in the 10 taxa in our study. The SSRs were found to be distributed in the LSC, SSC, and IR regions in Cornus hongkongensis subsp. hongkongensis, C. hongkongensis subsp. elegans, C. hongkongensis subsp. gigantea, and C. hongkongensis subsp. tonkinensis, while the SSR was not found in the IR region of the other six taxa. Thus, whole cp genomics is a valuable tool for species identification, taxonomic clarification, and genomic evolutionary analysis. Furthermore, our findings reveal that C. hongkongensis and C. hongkongensis subsp. gigantea, along with Cornus kousa and Cornus elliptica, form sister groups. Notably, C. hongkongensis subsp. ferruginea and C. hongkongensis subsp. melanotricha did not exhibit affinity with C. hongkongensis subsp. hongkongensis. Our study furnishes essential data for further research on their classification and provides novel insights into the relationship within Cornus subg. Syncarpea.

Chrysanthemum carinatum Schousb and Kalimeris indica are widely distributed edible vegetables and the sources of the Chinese medicine Asteraceae. The complete chloroplast (cp) genome of Asteraceae usually occurs in the inversions of two regions. Hence, the cp genome sequences and structures of Asteraceae species are crucial for the cp genome genetic diversity and evolutionary studies. Hence, in this paper, we have sequenced and analyzed for the first time the cp genome size of C. carinatum Schousb and K. indica, which are 149,752 bp and 152,885 bp, with a pair of inverted repeats (IRs) (24,523 bp and 25,003) separated by a large single copy (LSC) region (82,290 bp and 84,610) and a small single copy (SSC) region (18,416 bp and 18,269), respectively. In total, 79 protein-coding genes, 30 distinct transfer RNA (tRNA) genes, four distinct rRNA genes and two pseudogenes were found not only in C. carinatum Schousb but also in the K. indica cp genome. Fifty-two (52) and fifty-nine (59) repeats, and seventy (70) and ninety (90) simple sequence repeats (SSRs) were found in the C. carinatum Schousb and K. indica cp genomes, respectively. Codon usage analysis showed that leucine, isoleucine, and serine are the most frequent amino acids and that the UAA stop codon was the significantly favorite stop codon in both cp genomes. The two inversions, the LSC region ranging from trnC-GCA to trnG-UCC and the whole SSC region were found in both of them. The complete cp genome comparison with other Asteraceae species showed that the coding area is more conservative than the non-coding area. The phylogenetic analysis revealed that the rbcL gene is a good barcoding marker for identifying different vegetables. These results give an insight into the identification, the barcoding, and the understanding of the evolutionary model of the Asteraceae cp genome.

Leymus is a perennial genus that belongs to the tribe Triticeae (Poaceae) which has an adaptive capacity to ecological conditions and strong resistance to cold, drought, and salinity. Most Leymus species are fine herbs that can be used for agriculture, conservation, and landscaping. Due to confusion taxonomy within genera, the complete chloroplast (cp) genome of 13 Leymus species was sequenced, assembled, and compared with those of three other previously published Leymus species (Leymus condensatus, Leymus angustus, and Leymus mollis) to clarify the issue. Overall, the whole cp genome size ranged between 135,057 (L. condensatus) and 136,906 bp (Leymus coreanus) and showed a typical quadripartite structure. All studied species had 129 genes, including 83 protein-coding genes, 38 transfer RNAs, and 8 ribosomal RNAs. In total, 800 tandem repeats and 707 SSR loci were detected, most of which were distributed in the large single-copy region, followed by the inverted repeat (IR) and small single-copy regions. The sequence identity of all sequences was highly similar, especially concerning the protein-coding and IR regions; in particular, the protein-coding regions were significantly similar to those in the IR regions, regardless of small sequence differences in the whole cp genome. Moreover, the coding regions were more conserved than the non-coding regions. Comparisons of the IR boundaries showed that IR contraction and expansion events were reflected in different locations of rpl22, rps19, ndhH, and psbA genes. The close phylogenetic relationship of Leymus and Psathyrostachys indicated that Psathyrostachys possibly is the donor of the Ns genome sequence identified in Leymus. Altogether, the complete cp genome sequence of Leymus will lay a solid foundation for future population genetics and phylogeography studies, as well as for the analysis of the evolution of economically valuable plants.

The genus Zygophyllum comprises over 150 species within the plant family Zygophyllaceae. These species predominantly grow in arid and semiarid areas, and about 20 occur in northwestern China. In this study, we sampled 24 individuals of Zygophyllum representing 15 species and sequenced their complete chloroplast (cp) genomes. For comparison, we also sequenced cp genomes of two species of Peganum from China representing the closely allied family, Nitrariaceae. The 24 cp genomes of Zygophyllum were smaller and ranged in size from 104,221 to 106,286 bp, each containing a large single-copy (LSC) region (79,245–80,439 bp), a small single-copy (SSC) region (16,285–17,146 bp), and a pair of inverted repeat (IR) regions (3,792–4,466 bp). These cp genomes contained 111–112 genes each, including 74–75 protein-coding genes (PCGs), four ribosomal RNA genes, and 33 transfer RNA genes, and all cp genomes showed similar gene order, content, and structure. The cp genomes of Zygophyllum appeared to lose some genes such as ndh genes and rRNA genes, of which four rRNA genes were in the SSC region, not in the IR regions. However, the SC and IR regions had greater similarity within Zygophyllum than between the genus and Peganum. We detected nine highly variable intergenic spacers: matK-trnQ, psaC-rps15, psbZ-trnG, rps7-trnL, rps15-trnN, trnE-trnT, trnL-rpl32, trnQ-psbK, and trnS-trnG. Additionally, we identified 156 simple sequence repeat (cpSSR) markers shared among the genomes of the 24 Zygophyllum samples and seven cpSSRs that were unique to the species of Zygophyllum. These markers may be useful in future studies on genetic diversity and relationships of Zygophyllum and closely related taxa. Using the sequenced cp genomes, we reconstructed a phylogeny that strongly supported the division of Chinese Zygophyllum into herbaceous and shrubby clades. We utilized our phylogenetic results along with prior morphological studies to address several remaining taxonomic questions within Zygophyllum. Specifically, we found that Zygophyllum kaschgaricum is included within Zygophyllum xanthoxylon supporting the present treatment of the former genus Sarcozygium as a subgenus within Zygophyllum. Our results provide a foundation for future research on the genetic resources of Zygophyllum.

Sesamum indicum is an important crop plant species for yielding oil. The complete chloroplast (cp) genome of S. indicum (GenBank acc no. JN637766) is 153,324 bp in length, and has a pair of inverted repeat (IR) regions consisting of 25,141 bp each. The lengths of the large single copy (LSC) and the small single copy (SSC) regions are 85,170 bp and 17,872 bp, respectively. Comparative cp DNA sequence analyses of S. indicum with other cp genomes reveal that the genome structure, gene order, gene and intron contents, AT contents, codon usage, and transcription units are similar to the typical angiosperm cp genomes. Nucleotide diversity of the IR region between Sesamum and three other cp genomes is much lower than that of the LSC and SSC regions in both the coding region and noncoding region. As a summary, the regional constraints strongly affect the sequence evolution of the cp genomes, while the functional constraints weakly affect the sequence evolution of cp genomes. Five short inversions associated with short palindromic sequences that form step-loop structures were observed in the chloroplast genome of S. indicum. Twenty-eight different simple sequence repeat loci have been detected in the chloroplast genome of S. indicum. Almost all of the SSR loci were composed of A or T, so this may also contribute to the A-T richness of the cp genome of S. indicum. Seven large repeated loci in the chloroplast genome of S. indicum were also identified and these loci are useful to developing S. indicum-specific cp genome vectors. The complete cp DNA sequences of S. indicum reported in this paper are prerequisite to modifying this important oilseed crop by cp genetic engineering techniques.

Capirona (Calycophyllum spruceanum Benth.) belongs to subfamily Ixoroideae, one of the major lineages in the Rubiaceae family, and is an important timber tree. It originated in the Amazon Basin and has widespread distribution in Bolivia, Peru, Colombia, and Brazil. In this study, we obtained the first complete chloroplast (cp) genome of capirona from the department of Madre de Dios located in the Peruvian Amazon. High-quality genomic DNA was used to construct libraries. Pair-end clean reads were obtained by PE 150 library and the Illumina HiSeq 2500 platform. The complete cp genome of C. spruceanum has a 154,480 bp in length with typical quadripartite structure, containing a large single copy (LSC) region (84,813 bp) and a small single-copy (SSC) region (18,101 bp), separated by two inverted repeat (IR) regions (25,783 bp). The annotation of C. spruceanum cp genome predicted 87 protein-coding genes (CDS), 8 ribosomal RNA (rRNA) genes, 37 transfer RNA (tRNA) genes, and one pseudogene. A total of 41 simple sequence repeats (SSR) of this cp genome were divided into mononucleotides (29), dinucleotides (5), trinucleotides (3), and tetranucleotides (4). Most of these repeats were distributed in the noncoding regions. Whole chloroplast genome comparison with the other six Ixoroideae species revealed that the small single copy and large single copy regions showed more divergence than inverted regions. Finally, phylogenetic analyses resolved that C. spruceanum is a sister species to Emmenopterys henryi and confirms its position within the subfamily Ixoroideae. This study reports for the first time the genome organization, gene content, and structural features of the chloroplast genome of C. spruceanum, providing valuable information for genetic and evolutionary studies in the genus Calycophyllum and beyond.

Quercus litseoides, an endangered montane cloud forest species, is endemic to southern China. To understand the genomic features, phylogenetic relationships, and molecular evolution of Q. litseoides, the complete chloroplast (cp) genome was analyzed and compared in Quercus section Cyclobalanopsis. The cp genome of Q. litseoides was 160,782 bp in length, with an overall guanine and cytosine (GC) content of 36.9%. It contained 131 genes, including 86 protein-coding genes, eight ribosomal RNA genes, and 37 transfer RNA genes. A total of 165 simple sequence repeats (SSRs) and 48 long sequence repeats with A/T bias were identified in the Q. litseoides cp genome, which were mainly distributed in the large single copy region (LSC) and intergenic spacer regions. The Q. litseoides cp genome was similar in size, gene composition, and linearity of the structural region to those of Quercus species. The non-coding regions were more divergent than the coding regions, and the LSC region and small single copy region (SSC) were more divergent than the inverted repeat regions (IRs). Among the 13 divergent regions, 11 were in the LSC region, and only two were in the SSC region. Moreover, the coding sequence (CDS) of the six protein-coding genes (rps12, matK, atpF, rpoC2, rpoC1, and ndhK) were subjected to positive selection pressure when pairwise comparison of 16 species of Quercus section Cyclobalanopsis. A close relationship between Q. litseoides and Quercus edithiae was found in the phylogenetic analysis of cp genomes. Our study provided highly effective molecular markers for subsequent phylogenetic analysis, species identification, and biogeographic analysis of Quercus.

The complete chloroplast (cp) genome of Talinum paniculatum (Caryophyllale), a source of pharmaceutical efficacy similar to ginseng, and a widely distributed and planted edible vegetable, were sequenced and analyzed. The cp genome size of T. paniculatum is 156,929 bp, with a pair of inverted repeats (IRs) of 25,751 bp separated by a large single copy (LSC) region of 86,898 bp and a small single copy (SSC) region of 18,529 bp. The genome contains 83 protein-coding genes, 37 transfer RNA (tRNA) genes, eight ribosomal RNA (rRNA) genes and four pseudogenes. Fifty one (51) repeat units and ninety two (92) simple sequence repeats (SSRs) were found in the genome. The pseudogene rpl23 (Ribosomal protein L23) was insert AATT than other Caryophyllale species by sequence alignment, which located in IRs region. The gene of trnK-UUU (tRNA-Lys) and rpl16 (Ribosomal protein L16) have larger introns in T. paniculatum, and the existence of matK (maturase K) genes, which usually located in the introns of trnK-UUU, rich sequence divergence in Caryophyllale. Complete cp genome comparison with other eight Caryophyllales species indicated that the differences between T. paniculatum and P. oleracea were very slight, and the most highly divergent regions occurred in intergenic spacers. Comparisons of IR boundaries among nine Caryophyllales species showed that T. paniculatum have larger IRs region and the contraction is relatively slight. The phylogenetic analysis among 35 Caryophyllales species and two outgroup species revealed that T. paniculatum and P. oleracea do not belong to the same family. All these results give good opportunities for future identification, barcoding of Talinum species, understanding the evolutionary mode of Caryophyllale cp genome and molecular breeding of T. paniculatum with high pharmaceutical efficacy.

Rosa chinensis var. spontanea, an endemic and endangered plant of China, is one of the key ancestors of modern roses and a source for famous traditional Chinese medicines against female diseases, such as irregular menses and dysmenorrhea. In this study, the complete chloroplast (cp) genome of R. chinensis var. spontanea was sequenced, analyzed, and compared to congeneric species. The cp genome of R. chinensis var. spontanea is a typical quadripartite circular molecule of 156,590 bp in length, including one large single copy (LSC) region of 85,910 bp and one small single copy (SSC) region of 18,762 bp, separated by two inverted repeat (IR) regions of 25,959 bp. The GC content of the whole genome is 37.2%, while that of LSC, SSC, and IR is 42.8%, 35.2% and 31.2%, respectively. The genome encodes 129 genes, including 84 protein-coding genes (PCGs), 37 transfer RNA (tRNA) genes, and eight ribosomal RNA (rRNA) genes. Seventeen genes in the IR regions were found to be duplicated. Thirty-three forward and five inverted repeats were detected in the cp genome of R. chinensis var. spontanea. The genome is rich in SSRs. In total, 85 SSRs were detected. A genome comparison revealed that IR contraction might be the reason for the relatively smaller cp genome size of R. chinensis var. spontanea compared to other congeneric species. Sequence analysis revealed that the LSC and SSC regions were more divergent than the IR regions within the genus Rosa and that a higher divergence occurred in non-coding regions than in coding regions. A phylogenetic analysis showed that the sampled species of the genus Rosa formed a monophyletic clade and that R. chinensis var. spontanea shared a more recent ancestor with R. lichiangensis of the section Synstylae than with R. odorata var. gigantea of the section Chinenses. This information will be useful for the conservation genetics of R. chinensis var. spontanea and for the phylogenetic study of the genus Rosa, and it might also facilitate the genetics and breeding of modern roses.

Flemingia prostrata and Flemingia macrophylla, belonging to the genus Flemingia, are ethnomedicinal plants that contain valuable medicinal and nutritional compounds. However, their medicinal materials are frequently confused in the Chinese medicinal materials market. Moreover, molecular genomic resources for this genus remain limited, which hinders phylogenetic studies. In this study, the complete chloroplast (cp) genomes of F. macrophylla and F. prostrata were sequenced to enable genome comparison and phylogenetic analysis. Both cp genomes exhibited typical quadripartite structures, with genome sizes of 152,937 bp for F. macrophylla and 153,033 bp for F. prostrata. Each genome consisted of a large single copy (LSC) region (83,594 and 83,701 bp, respectively), a small single copy (SSC) region (17,773 and 17,776 bp, respectively), and two inverted repeats (IR) regions (50,570 and 51,556 bp, respectively). A total of 129 genes were annotated in each cp genome, including 8 ribosomal RNAs, 83 protein-coding genes, and 37 transfer RNAs. Comparative analysis revealed that although the overall genome structure, codon usage bias, simple sequence repeats (SSRs), and dispersed repetitive sequences were relatively conserved between the two cp genomes, certain genomic variations were present. Specifically, 286 SNPs and 104 indels were identified, and psaJ-rps18 showed the highest variability and could serve as potential DNA barcode regions. Furthermore, phylogenetic analysis supported a close evolutionary relationship between the genus Flemingia and Cajanus. Divergence time estimation suggested that F. macrophylla and F. prostrata diverged approximately 0.26 million years ago (Mya). Finally, we successfully distinguished the two species using SSR markers. This study lays the foundation for enriching the molecular data and phylogenetic insights of this genus, as well as for the safe application of its medicinal materials.

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. 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 159,872bp in length, including a large single-copy (LSC) region from 87,668 to 87,656bp, a small single-copy (SSC) from 18,581 to 18,571bp, and two inverted repeats regions (IRa and IRb) of 26,814bp 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. Our work contributes to the development of Bursera's genomic resources for taxonomic, evolutionary, and ecological-genetic studies.

Background Prinsepia utilis Royle is a wild woody oil species of Rosaceae that yields edible oil which has been proved to possess particular benefits for human health and medical therapy. However, the lack of bred varieties has largely impeded exploiting immense potentials for high quality of its seed oil. It is urgently needed to enlarge the knowledge of genetic basis of the species and develop genetic markers to enhance modern breeding programs.ResultsHere we reported the complete chloroplast (cp) genome of 156,328 bp. Comparative cp sequence analyses of P . utilis along with other four Rosaceae species resulted in similar genome structures, gene orders, and gene contents. Contraction/expansion of inverted repeat regions (IRs) explained part of the length variation in the Rosaceae cp genomes. Genome sequence alignments revealed that nucleotide diversity was associated with AT content, and large single copy regions (LSC) and small single copy regions (SSC) harbored higher sequence variations in both coding and non-coding regions than IRs. Simple sequence repeats (SSRs) were detected in the P . utilis and compared with those of the other four Rosaceae cp genomes. Almost all the SSR loci were composed of A or T, therefore it might contribute to the A-T richness of cp genomes and be associated with AT biased sequence variation. Among all the protein-coding genes, ycf1 showed the highest sequence divergence, indicating that it could accomplish the discrimination of species within Rosaceae as well as within angiosperms better than other genes.ConclusionsWith the addition of this new sequenced cp genome, high nucleotide substitution rate and abundant deletions/insertions were observed, suggesting a greater genomic dynamics than previously explored in Rosaceae. The availability of the complete cp genome of P . utilis will provide chloroplast markers and genetic information to better enhance the conservation and utilization of this woody oil plant.

The complete chloroplast genome sequence of Daphne tangutica Maxim. (Thymelaeaceae), a medicinal plant distributed in northwest alpine region of China, was characterized the complete nucleotide sequence of chloroplast (cp) genome. The total length of cp genome is 169,944 bp, including a large single copy (LSC) region of 84,884 bp, a small single copy (SSC) region of 2248 bp, and a pair of inverted repeats (IRs) of 41,406 bp. The cp genome of D. tangutica contains 137 genes, including 90 protein-coding genes (75 PCG species), 39 transfer RNA genes (31 tRNA species), and eight rRNA genes (four RNA species). A total of 12 genes (tRNA-Lys (UUU), tRNA-Leu (UAA), tRNA-Val (UAC), tRNA-Ile (GAU), tRNA-Ala (UGC), rpl16, rpoC1, petD, rps16, rpl2, ndhB, and ndhA) contains a single intron, and two genes (ycf3 and rps12) contains two introns. The GC content in whole cp genome, LSC region, SSC region, and IR region were 36.8%, 34.8%, 28.6%, and 38.9%, respectively, which are similar to other Thymelaeaceae plants. Phylogenetic analysis suggested that D. tangutica has the closely reltionship with congeneric D. kiusiana.