The first complete chloroplast genome of the Genistoid legume Lupinus luteus: evidence for a novel major lineage-specific rearrangement and new insights regarding plastome evolution in the legume family

Comparative analysis of chloroplast genomes reveals molecular evolution and phylogenetic relationships within the Papilionoideae of Fabaceae

BACKGROUND

The structure of chloroplast genomes (cpDNAs) in Fabaceae (Fab.) has undergone significant evolutionary modifications. Within the Papilionoideae (Pap.), the emergence of the Inverted Repeat-Lacking Clade (IRLC) represents a major genomic alteration. However, the molecular evolution and phylogenetic relationships within Pap. remain poorly resolved due to limited molecular data and incomplete research, highlighting the need for systematic investigation.

PURPOSE

This study presents an in-depth analysis of the cpDNAs within the Pap., with the aim of unraveling the molecular evolution and phylogenetic interconnections among its species.

METHODS

Complete cpDNAs of 18 Pap. species were sequenced using the Illumina Novaseq 6000 platform, followed by assembly and annotation. Comparative genomic analyses were conducted to elucidate structural variations and phylogenetic relationships.

RESULTS

The research has uncovered significant differences in the structure and characteristics of the cpDNAs within the Pap.. The lengths of the cpDNAs of 18 species range from 121,190 bp to 158,539 bp, and they contain between 107 and 112 unique genes. Five species, namely Desmodium elegans and Indigofera bracteata, exhibit a typical quadripartite structure, while thirteen species from genera such as Astragalus (Ast.), Hedysarum (Hed.), and Caragana (Car.) are grouped within the Inverted Repeat-Lacking Clade (IRLC). Genetic characteristic analysis revealed a plentiful presence of SSR loci, with single-nucleotide repeats and dinucleotide (A/T) repeats being the most predominant. Notably, the cpDNAs of five species including D. elegans have experienced significant rearrangements. For example, an inversion of approximately 23 kilobase (kb) pairs was observed in Pueraria peduncularis and Sophora moorcroftiana. These species exhibit pronounced differences in their non-coding regions. Comparative genomic variations at cpDNA sites were identified. Moreover, by using D. elegans as a reference, six genes (ycf4, clpP, ycf1, trnI-GAU, accD, rpl32) displayed high nucleotide polymorphism (Pi > 0.1), and the Ka/Ks ratio for all protein-coding genes was determined to be less than 1. The topological structure of the constructed phylogenetic tree of 85 species was basically consistent with that of Pap.. Seven main clades were formed and relatively high bootstrap values were exhibited, further clarifying the evolutionary relationships among them.

CONCLUSION

This study provides novel insights into the molecular evolution and phylogeny of Pap., offering a foundational resource for future taxonomic and evolutionary research.

The plastomes of Cypripedium (Orchidaceae: Cypripedioideae) exhibit atypical GC content and genome size based on different sequencing strategies

Most of the sequenced plastomes of photosynthetic angiosperms exhibit conservation in size, gene content, gene order, and GC content. In contrast, the sequenced plastomes of Cypripedium are distinguished by genome size expansion, AT-biased base composition, structural variation, and a low substitution rate. Additionally, the impact of sequencing methods is seldom addressed in prior studies, and the species represented in these studies are underrepresented. These atypical plastome features render the genus an ideal candidate for investigating plastome evolution. Besides, the backbone relationships within the genus remain poorly resolved. In this study, we sequenced twelve Cypripedium plastomes using three distinct sequencing strategies and obtained an additional 27 sequences from GenBank for comparative analysis. We classified the plastomes of the genus into two types: one resembling those of most other angiosperms, and the other characterized by inverted repeat (IR) expansion and small single copy (SSC) contraction. The plastomes within this genus exhibit significant size variations (∼72 kb), variations in GC content, and structural differences at the genus level. Furthermore, our comparative analysis revealed that the choice of sequencing strategy significantly impacts the assembly results. The uncovered regions in samples sequenced with short-read technology are predominantly AT-rich, suggesting that short-read sequencing may lead to assembly errors in plastomes with AT-rich regions and long repeats. Additionally, we have reconstructed the phylogeny of the genus using plastome-level data. However, the phylogenetic relationships within the genus remain partially solved. This study provides new insights into the evolution of plastomes, particularly those with AT-rich base compositions and genomes containing long repeat regions.

The First Complete Chloroplast Genome Sequence of Secale strictum subsp. africanum Stapf (Poaceae), the Putative Ancestor of the Genus Secale

Secale strictum ssp. africanum (synonym Secale africanum), a putative ancestor of the genus Secale, has been classified within Secale strictum, although recent phylogenetic studies suggest that it represents a distinct species. This study reports the first complete chloroplast genome of S. africanum, highlighting its structure, genetic composition, and phylogenetic relationships within Secale and related Triticiceae species. Phylogeny reconstruction based on the maximum-likelihood method reveals notable genetic similarity between S. strictum and S. africanum, supporting their genetic and phylogenetic distinction. Here, we assembled the complete, annotated chloroplast genome sequence of Secale strictum ssp. africanum. The genome is 137,068 base pair (bp) long. It is the first complete chloroplast genome that can be used as a reference genome for further analysis. The genome can be accessed on GenBank with the accession number OQ700974. This work sheds light on the evolutionary history of Secale and contributes to our understanding of chloroplast genomics in cereal ancestors, with potential applications in improving cereal crop resilience, advancing breeding strategies, and informing conservation efforts for genetic diversity.

Characterisation of the complete chloroplast genome of Solanum tuberosum cv. White Lady

Potato (Solanum tuberosum) is considered worldwide as one of the most important non-cereal food crops. As a result of its adaptability and worldwide production area, potato displays a vast phenotypical variability as well as genomic diversity. Chloroplast genomes have long been a core issue in plant molecular evolution and phylogenetic studies, and have an important role in revealing photosynthetic mechanisms, metabolic regulations and the adaptive evolution of plants. We sequenced the complete chloroplast genome of the Hungarian cultivar White Lady, which is 155 549 base pairs (bp) in length and is characterised by the typical quadripartite structure composed of a large- and small single-copy region (85 991 bp and 18 374 bp, respectively) interspersed by two identical inverted repeats (25 592 bp). The genome consists of 127 genes of which 82 are protein-coding, eight are ribosomal RNAs and 37 are transfer RNAs. The overall gene content and distribution of the genes on the White Lady chloroplast was the same as found in other potato chloroplasts. The alignment of S. tuberosum chloroplast genome sequences resulted in a highly resolved tree, with 10 out of the 13 nodes recovered having bootstrap values over 90%. By comparing the White Lady chloroplast genome with available S. tuberosum sequences we found that gene content and synteny are highly conserved. The new chloroplast sequence can support further studies of genetic diversity, resource conservation, evolution and applied agricultural research. The new sequence can support further potato genetic diversity and evolutionary studies, resource conservation, and also applied agricultural research.

Chloroplast genome of Ecbolium viride (Forssk.) Alston: plastome evolution and phylogenomics of Justiceae (Acanthaceae, Acanthoideae)

Justicieae is the most taxonomically complex tribe in Acanthaceae. Here, we sequenced the plastome of Ecbolium viride, a medicinally important species. The genome was analyzed with previously reported plastome of Justiceae. The plastome of E. viride has quadripartite structure with a length of 151 185 bp. The comparative genomic analyses revealed no structural inversion in Justiceae and some regions (rpoC2, ycf2, ycf1, ndhH rps16-trnQ-UGG, and trnL-CAA-ycf15) exhibiting a significant level of nucleotide divergence. The positive selection analyses revealed that some species in the tribe have undergone adaptive evolution. The visualization of the boundaries between the single copy and inverted repeat regions revealed that Justiceae chloroplast genome experienced some levels of variation, which give an insight into the evolution of the species. The longest genome was in the earliest diverged taxa of the tribe Pseuderanthemum haikangense and from this genome, a series of contraction and expansion occurred contributing to the evolution of other lineages. The plastome-based phylogeny revealed and confirmed the monophyly of Justiceae, polyphyly of Justicia and supported the tribal classification Graptophyllinae, Tetrameriinae, and Isoglossinae. We proposed that Declipterinae should be treated as subtribe and the status of Justiciinae can only be confirmed after the resolution of the polyphyletic Justicia.

The complete chloroplast genome sequence and phylogenetic relationship analysis of Eomecon chionantha, one species unique to China

Eomecon chionantha Hance, an endemic species in China, has a long medical history in Chinese ethnic minority medicine and is known for its anti-inflammatory and analgesic effects. However, studies of E. chionantha are lacking. In this study, we investigated the characteristics of the E. chionantha chloroplast genome and determined the taxonomic position of E. chionantha in Papaveraceae via phylogenetic analysis. In addition, we determined molecular markers to identify E. chionantha at the molecular level by comparing the chloroplast genomes of E. chionantha and its closely related species. The complete chloroplast genomic information indicated that E. chionantha chloroplast DNA (178,808 bp) contains 99 protein-coding genes, 8 rRNAs, and 37 tRNAs. Meanwhile, we were able to identify a total of 54 simple sequence repeats through our analysis. Our findings from the phylogenetic analysis suggest that E. chionantha shares a close relationship with four distinct species, namely Macleaya microcarpa, Coreanomecon hylomeconoides, Hylomecon japonica, and Chelidonium majus. Additionally, using the Kimura two-parameter model, we successfully identified five hypervariable regions (ycf4-cemA, ycf3-trnS-GGA, trnC-GCA-petN, rpl32-trnL-UAG, and psbI-trnS-UGA). To the best of our knowledge, this is the first report of the complete chloroplast genome of E. chionantha, providing a scientific reference for further understanding of E. chionantha from the perspective of the chloroplast genome and establishing a solid foundation for the future identification, taxonomic determination and evolutionary analysis of this species.

Plastid phylogenomics and cytonuclear discordance in Rubioideae, Rubiaceae

In this study of evolutionary relationships in the subfamily Rubioideae (Rubiaceae), we take advantage of the off-target proportion of reads generated via previous target capture sequencing projects based on nuclear genomic data to build a plastome phylogeny and investigate cytonuclear discordance. The assembly of off-target reads resulted in a comprehensive plastome dataset and robust inference of phylogenetic relationships, where most intratribal and intertribal relationships are resolved with strong support. While the phylogenetic results were mostly in agreement with previous studies based on plastome data, novel relationships in the plastid perspective were also detected. For example, our analyses of plastome data provide strong support for the SCOUT clade and its sister relationship to the remaining members of the subfamily, which differs from previous results based on plastid data but agrees with recent results based on nuclear genomic data. However, several instances of highly supported cytonuclear discordance were identified across the Rubioideae phylogeny. Coalescent simulation analysis indicates that while ILS could, by itself, explain the majority of the discordant relationships, plastome introgression may be the better explanation in some cases. Our study further indicates that plastomes across the Rubioideae are, with few exceptions, highly conserved and mainly conform to the structure, gene content, and gene order present in the majority of the flowering plants.

Leaf variegation caused by plastome structural variation: an example from Dianella tasmanica

Variegated plants often exhibit plastomic heteroplasmy due to single-nucleotide mutations or small insertions/deletions in their albino sectors. Here, however, we identified a plastome structural variation in albino sectors of the variegated plant Dianella tasmanica (Asphodelaceae), a perennial herbaceous plant widely cultivated as an ornamental in tropical Asia. This structural variation, caused by intermolecular recombination mediated by an 11-bp inverted repeat flanking a 92-bp segment in the large single-copy region (LSC), generates a giant plastome (228 878 bp) with the largest inverted repeat of 105 226 bp and the smallest LSC of 92 bp known in land plants. It also generates an ~7-kb deletion on the boundary of the LSC, which eliminates three protein coding genes (psbA, matK, and rps16) and one tRNA gene (trnK). Albino sectors exhibit dramatic changes in expression of many plastid genes, including negligible expression of psbA, matK, and rps16, reduced expression of photosynthesis-related genes, and increased expression of genes related to the translational apparatus. Microscopic and ultrastructure observations showed that albino tissues were present in both green and albino sectors of the variegated individuals, and chloroplasts were poorly developed in the mesophyll cells of the albino tissues of the variegated individuals. These poorly developed chloroplasts likely carry the large and rearranged plastome, which is likely responsible for the loss of photosynthesis and albinism in the leaf margins. Considering that short repeats are relatively common in plant plastomes and that photosynthesis is not necessary for albino sectors, structural variation of this kind may not be rare in the plastomes of variegated plants.

Complete Chloroplast Genomes of Pterodon emarginatus Vogel and Pterodon pubescens Benth: Comparative and Phylogenetic Analyses

Background

The species Pterodon emarginatus and P. pubescens, popularly known as white sucupira or faveira, are native to the Cerrado biome and have the potential for medicinal use and reforestation. They are sister species with evolutionary proximity.

Objective

Considering that the chloroplast genome exhibits a conserved structure and genes, the analysis of its sequences can contribute to the understanding of evolutionary, phylogenetic, and diversity issues.

Methods

The chloroplast genomes of P. emarginatus and P. pubescens were sequenced on the Illumina MiSeq platform. The genomes were assembled based on the de novo strategy. We performed the annotation of the genes and the repetitive regions of the genomes. The nucleotide diversity and phylogenetic relationships were analyzed using the gene sequences of these species and others of the Leguminosae family, whose genomes are available in databases.

Results

The complete chloroplast genome of P. emarginatus is 159,877 bp, and that of P. pubescens is 159,873 bp. The genomes of both species have circular and quadripartite structures. A total of 127 genes were predicted in both species, including 110 single-copy genes and 17 duplicated genes in the inverted regions. 141 microsatellite regions were identified in P. emarginatus and 140 in P. pubescens. The nucleotide diversity estimates of the gene regions in twenty-one species of the Leguminosae family were 0.062 in LSC, 0.086 in SSC, and 0.036 in IR. The phylogenetic analysis demonstrated the proximity between the genera Pterodon and Dipteryx, both from the clade Dipterygeae. Ten pairs of primers with potential for the development of molecular markers were designed.

Conclusion

The genetic information obtained on the chloroplast genomes of P. emarginatus and P. pubescens presented here reinforces the similarity and evolutionary proximity between these species, with a similarity percentage of 99.8%.

Comparative Analysis of Six Chloroplast Genomes in Chenopodium and Its Related Genera (Amaranthaceae): New Insights into Phylogenetic Relationships and the Development of Species-Specific Molecular Markers

Species within the genus Chenopodium hold significant research interest due to their nutritional richness and salt tolerance. However, the morphological similarities among closely related species and a dearth of genomic resources have impeded their comprehensive study and utilization. In the present research, we conduct the sequencing and assembly of chloroplast (cp) genomes from six Chenopodium and related species, five of which were sequenced for the first time. These genomes ranged in length from 151,850 to 152,215 base pairs, showcased typical quadripartite structures, and encoded 85 protein-coding genes (PCGs), 1 pseudogene, 37 tRNA genes, and 8 rRNA genes. Compared with the previously published sequences of related species, these cp genomes are relatively conservative, but there are also some interspecific differences, such as inversion and IR region contraction. We discerned 929 simple sequence repeats (SSRs) and a series of highly variable regions across 16 related species, predominantly situated in the intergenic spacer (IGS) region and introns. The phylogenetic evaluations revealed that Chenopodium is more closely related to genera such as Atriplex, Beta, Dysphania, and Oxybase than to other members of the Amaranthaceae family. These lineages shared a common ancestor approximately 60.80 million years ago, after which they diverged into distinct genera. Based on InDels and SNPs between species, we designed 12 pairs of primers for species identification, and experiments confirmed that they could completely distinguish 10 related species.

More than a spiny morphology: plastome variation in the prickly pear cacti (Opuntieae)

BACKGROUND

Plastid genomes (plastomes) have long been recognized as highly conserved in their overall structure, size, gene arrangement and content among land plants. However, recent studies have shown that some lineages present unusual variations in some of these features. Members of the cactus family are one of these lineages, with distinct plastome structures reported across disparate lineages, including gene losses, inversions, boundary movements or loss of the canonical inverted repeat (IR) region. However, only a small fraction of cactus diversity has been analysed so far.

METHODS

Here, we investigated plastome features of the tribe Opuntieae, the remarkable prickly pear cacti, which represent one of the most diverse and important lineages of Cactaceae. We assembled de novo the plastome of 43 species, representing a comprehensive sampling of the tribe, including all seven genera, and analysed their evolution in a phylogenetic comparative framework. Phylogenomic analyses with different datasets (full plastome sequences and genes only) were performed, followed by congruence analyses to assess signals underlying contentious nodes.

KEY RESULTS

Plastomes varied considerably in length, from 121 to 162 kbp, with striking differences in the content and size of the IR region (contraction and expansion events), including a lack of the canonical IR in some lineages and the pseudogenization or loss of some genes. Overall, nine different types of plastomes were reported, deviating in the presence of the IR region or the genes contained in the IR. Overall, plastome sequences resolved phylogenetic relationships within major clades of Opuntieae with high bootstrap values but presented some contentious nodes depending on the dataset analysed (e.g. whole plastome vs. genes only). Congruence analyses revealed that most plastidial regions lack phylogenetic resolution, while few markers are supporting the most likely topology. Likewise, alternative topologies are driven by a handful of plastome markers, suggesting recalcitrant nodes in the phylogeny.

CONCLUSIONS

Our study reveals a dynamic nature of plastome evolution across closely related lineages, shedding light on peculiar features of plastomes. Variation of plastome types across Opuntieae is remarkable in size, structure and content and can be important for the recognition of species in some major clades. Unravelling connections between the causes of plastome variation and the consequences for species biology, physiology, ecology, diversification and adaptation is a promising and ambitious endeavour in cactus research. Although plastome data resolved major phylogenetic relationships, the generation of nuclear genomic data is necessary to confront these hypotheses and assess the recalcitrant nodes further.

Molecular structure, comparative and phylogenetic analysis of the complete chloroplast genome sequences of weedy rye Secale cereale ssp. segetale

The complete chloroplast genome of Secale cereale ssp. segetale (Zhuk.) Roshev. (Poaceae: Triticeae) was sequenced and analyzed to better use its genetic resources to enrich rye and wheat breeding. The study was carried out using the following methods: DNA extraction, sequencing, assembly and annotation, comparison with other complete chloroplast genomes of the five Secale species, and multigene phylogeny. As a result of the study, it was determined that the chloroplast genome is 137,042 base pair (bp) long and contains 137 genes, including 113 unique genes and 24 genes which are duplicated in the IRs. Moreover, a total of 29 SSRs were detected in the Secale cereale ssp. segetale chloroplast genome. The phylogenetic analysis showed that Secale cereale ssp. segetale appeared to share the highest degree of similarity with S. cereale and S. strictum. Intraspecific diversity has been observed between the published chloroplast genome sequences of S. cereale ssp. segetale. The genome can be accessed on GenBank with the accession number (OL688773).

Plastome evolution in the East Asian lobelias (Lobelioideae) using phylogenomic and comparative analyses

Lobelia species, as rich source of the alkaloid lobeline which has been shown to have important biological activity, have been used in folk medicine throughout East Asia to treat various diseases. However, Lobelia is a complex and varied genus in East Asia and is thus difficult to identify. Genomic resources would aid identification, however the availability of such information is poor, preventing a clear understanding of their evolutionary history from being established. To close this gap in the available genomic data, in this study, 17 plastomes of East Asian lobelias were newly sequenced and assembled. Although the plastomes of Lobelia sect. Hypsela, L. sect. Speirema, and L. sect. Rhynchopetalum shared the gene structure, the inverted repeat (IR)/large single copy (LSC) boundaries, genome size, and the number of repeats were variable, indicating the non-conservative nature of plastome evolution within these sections. However, the genomes of the Lobelia sect. Delostemon and L. sect. Stenotium showed rearrangements, revealing that these two sections might have undergone different evolutionary histories. We assessed nine hotspot genes and 27-51 simple sequence repeat motifs, which will also serve as valuable DNA barcode regions in future population genetics studies and for the delineation of plant species. Our phylogenetic analysis resolved the evolutionary positions of the five sections in agreement with previous evolutionary trees based on morphological features. Although phylogenetic reconstruction of Lobelioideae based on the rpoC2 gene has rarely been performed, our results indicated that it contains a considerable amount of phylogenetic information and offers great promise for further phylogenetic analysis of Lobelioideae. Our site-specific model identified 173 sites under highly positive selections. The branch-site model exhibited 11 positive selection sites involving four genes in the East Asian branches. These four genes may play critical roles in the adaptation of East Asian taxa to diverse environments. Our study is the first to detect plastome organization, phylogenetic utility, and signatures of positive selection in the plastomes of East Asian lobelias, which will help to further advance taxonomic and evolutionary studies and the utilization of medicinal plant resources.

Analysis of the Chloroplast Genome of Ficus simplicissima Lour Collected in Vietnam and Proposed Barcodes for Identifying Ficus Plants

Ficus simplicissima Lour. is an Asian species of fig tree in the family Moraceae. The chloroplast (cp) genome of F. simplicissima m3 was sequenced using the Pacbio sequel platform. The F. simplicissima cpDNA has a size of 160,321 bp in length, of which GC content accounts for 36.13%. The cp genome of F. simplicissima consists of a single large copy (LSC) with a size of 91,346 bp, a single small copy (SSC) with a size of 20,131 bp, and a pair of inverted repeats with a size of 24,421 to 24,423 bp. The cp genome of F. simplicissima has 127 genes, including 85 protein-coding genes, eight rRNA genes, and 34 tRNA genes; 92 simple sequence repeats and 39 long repeats were detected in the cpDNA of F. simplicissim. A comparative cp genome analysis among six species in the Ficus genus indicated that the genome structure and gene content were highly conserved. The non-coding regions show more differentiation than the coding regions, and the LSC and SSC regions show more differences than the inverted repeat regions. Phylogenetic analysis supported that F. simplicissima m3 had a close relationship with F. hirta. The complete cp genome of F. simplicissima was proposed as a chloroplast DNA barcoding for genus-level in the Moraceae family and the psbA-trnH gene region for species-level identification.

Complete chloroplast genome molecular structure, comparative and phylogenetic analyses of Sphaeropteris lepifera of Cyatheaceae family: a tree fern from China

Sphaeropteris lepifera is a tree fern in the Cyatheaceae, a family that has played an important role in the evolution of plant systems. This study aimed to analyze the complete chloroplast genome of S. lepifera and compared it with previously published chloroplast genomes Cyatheaceae family. The chloroplast genome of S. lepifera comprised 162,114 bp, consisting of a large single copy (LSC) region of 86,327 bp, a small single copy (SSC) region of 27,731 bp and a pair of inverted repeats (IRa and IRb) of 24,028 bp each. The chloroplast genome encoded 129 genes, comprising 32 transfer RNAs, 8 ribosomal RNAs, and 89 protein-coding genes. Comparison of the genomes of 7 Cyatheaceae plants showed that the chloroplast genome of S. lepifera was missing the gene trnV-UAC. Expansion of the SSC region led to the difference in the chloroplast genome size of S. lepifera. Eight genes, atpI, ccsA, petA, psaB, rpl16, rpoA, rpoC1, and ycf2 have high nucleic acid diversity and can be regarded as potential molecular markers. The genes trnG-trnR and atpB were suitable for DNA barcodes between different communities of S. lepifera. The S. lepifera groups in Zhejiang Province probably diffused from Pingtan and Ningde, Fujian. The results will provide a basis for species identification, biological studies, and endangerment mechanism of S. lepifera.

Phylogenetic analysis based on single-copy orthologous proteins in highly variable chloroplast genomes of Corydalis

Corydalis is one of the few lineages that have been reported to have extensive large-scale chloroplast genome (cp-genome) rearrangements. In this study, novel cp-genome rearrangements of Corydalis pinnata, C. mucronate, and C. sheareri are described. C. pinnata is a narrow endemic species only distributed at Qingcheng Mountain in southwest China. Two independent relocations of the same four genes (trnM-CAU-rbcL) were found relocated from the typically posterior part of the large single-copy region to the front of it. A uniform inversion of an 11-14-kb segment (ndhB-trnR-ACG) was found in the inverted repeat region; and extensive losses of accD, clpP, and trnV-UAC genes were detected in all cp-genomes of all three species of Corydalis. In addition, a phylogenetic tree was reconstructed based on 31 single-copy orthologous proteins in 27 cp-genomes. This study provides insights into the evolution of cp-genomes throughout the genus Corydalis and also provides a reference for further studies on the taxonomy, identification, phylogeny, and genetic transformation of other lineages with extensive rearrangements in cp-genomes.

Comparative and Phylogenetic Analysis of Complete Chloroplast Genomes in Leymus (Triticodae, Poaceae)

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.

Comparative Analysis of Chloroplast Genomes of Dalbergia Species for Identification and Phylogenetic Analysis

Dalbergia L.f. is a pantropical genus consisting of 269 species of trees, shrubs, and woody lianas. This genus is listed in CITES Appendices because of illegal logging and trafficking driven by the high economic value of its heartwood. Some species are also used medicinally. Species identification of Dalbergia timber and herbs is challenging but essential for CITES implementation. Molecular methods had been developed for some timber species, mostly from Madagascar and Southeast Asia, but medicinal species in south China were usually not included in those studies. Here, we sequenced and assembled the chloroplast genomes of five Dalbergia species native to Hong Kong, four of which are medicinal plants. Our aim is to find potential genetic markers for the identification of medicinal Dalbergia species based on divergence hotspots detected in chloroplast genomes after comparative and phylogenetic analysis. Dalbergia chloroplast genomes displayed the typical quadripartite structure, with the 50 kb inversion found in most Papilionoideae lineages. Their sizes and gene content are well conserved. Phylogenetic tree of Dalbergia chloroplast genomes showed an overall topology similar to that of ITS sequences. Four divergence hotspots (trnL(UAA)-trnT(UGU), ndhG-ndhI, ycf1a and ycf1b) were identified and candidate markers for identification of several Dalbergia species were suggested.

Plastid Phylogenomic Analysis of Tordylieae Tribe (Apiaceae, Apioideae)

Based on the nrDNA ITS sequence data, the Tordylieae tribe is recognized as monophyletic with three major lineages: the subtribe Tordyliinae, the Cymbocarpum clade, and the Lefebvrea clade. Recent phylogenomic investigations showed incongruence between the nuclear and plastid genome evolution in the tribe. To assess phylogenetic relations and structure evolution of plastomes in Tordylieae, we generated eleven complete plastome sequences using the genome skimming approach and compared them with the available data from this tribe and close relatives. Newly assembled plastomes had lengths ranging from 141,148 to 150,103 base pairs and contained 122-127 genes, including 79-82 protein-coding genes, 35-37 tRNAs, and 8 rRNAs. We observed substantial differences in the inverted repeat length and gene content, accompanied by a complex picture of multiple JLA and JLB shifts. In concatenated phylogenetic analyses, Tordylieae plastomes formed at least three not closely related lineages with plastomes of the Lefebvrea clade as a sister group to plastomes from the Selineae tribe. The newly obtained data have increased our knowledge on the range of plastome variability in Apiaceae.

Phylogenomic and comparative analyses of Coffeeae alliance (Rubiaceae): deep insights into phylogenetic relationships and plastome evolution

BACKGROUND

The large and diverse Coffeeae alliance clade of subfamily Ixoroideae (Rubiaceae) consists of 10 tribes, > 90 genera, and > 2000 species. Previous molecular phylogenetics using limited numbers of markers were often unable to fully resolve the phylogenetic relationships at tribal and generic levels. Also, the structural variations of plastomes (PSVs) within the Coffeeae alliance tribes have been poorly investigated in previous studies. To fully understand the phylogenetic relationships and PSVs within the clade, highly reliable and sufficient sampling with superior next-generation analysis techniques is required. In this study, 71 plastomes (40 newly sequenced and assembled and the rest from the GenBank) were comparatively analyzed to decipher the PSVs and resolve the phylogenetic relationships of the Coffeeae alliance using four molecular data matrices.

RESULTS

All plastomes are typically quadripartite with the size ranging from 153,055 to 155,908 bp and contained 111 unique genes. The inverted repeat (IR) regions experienced multiple contraction and expansion; five repeat types were detected but the most abundant was SSR. The size of the Coffeeae alliance clade plastomes and its elements are affected by the IR boundary shifts and the repeat types. However, the emerging PSVs had no taxonomic and phylogenetic implications. Eight highly divergent regions were identified within the plastome regions ndhF, ccsA, ndhD, ndhA, ndhH, ycf1, rps16-trnQ-UUG, and psbM-trnD. These highly variable regions may be potential molecular markers for further species delimitation and population genetic analyses for the clade. Our plastome phylogenomic analyses yielded a well-resolved phylogeny tree with well-support at the tribal and generic levels within the Coffeeae alliance.

CONCLUSIONS

Plastome data could be indispensable in resolving the phylogenetic relationships of the Coffeeae alliance tribes. Therefore, this study provides deep insights into the PSVs and phylogenetic relationships of the Coffeeae alliance and the Rubiaceae family as a whole.

Highly Resolved Papilionoid Legume Phylogeny Based on Plastid Phylogenomics

Comprising 501 genera and around 14,000 species, Papilionoideae is not only the largest subfamily of Fabaceae (Leguminosae; legumes), but also one of the most extraordinarily diverse clades among angiosperms. Papilionoids are a major source of food and forage, are ecologically successful in all major biomes, and display dramatic variation in both floral architecture and plastid genome (plastome) structure. Plastid DNA-based phylogenetic analyses have greatly improved our understanding of relationships among the major groups of Papilionoideae, yet the backbone of the subfamily phylogeny remains unresolved. In this study, we sequenced and assembled 39 new plastomes that are covering key genera representing the morphological diversity in the subfamily. From 244 total taxa, we produced eight datasets for maximum likelihood (ML) analyses based on entire plastomes and/or concatenated sequences of 77 protein-coding sequences (CDS) and two datasets for multispecies coalescent (MSC) analyses based on individual gene trees. We additionally produced a combined nucleotide dataset comprising CDS plus matK gene sequences only, in which most papilionoid genera were sampled. A ML tree based on the entire plastome maximally supported all of the deep and most recent divergences of papilionoids (223 out of 236 nodes). The Swartzieae, ADA (Angylocalyceae, Dipterygeae, and Amburaneae), Cladrastis, Andira, and Exostyleae clades formed a grade to the remainder of the Papilionoideae, concordant with nine ML and two MSC trees. Phylogenetic relationships among the remaining five papilionoid lineages (Vataireoid, Dermatophyllum, Genistoid s.l., Dalbergioid s.l., and Baphieae + Non-Protein Amino Acid Accumulating or NPAAA clade) remained uncertain, because of insufficient support and/or conflicting relationships among trees. Our study fully resolved most of the deep nodes of Papilionoideae, however, some relationships require further exploration. More genome-scale data and rigorous analyses are needed to disentangle phylogenetic relationships among the five remaining lineages.

Extensive reorganization of the chloroplast genome of Corydalis platycarpa: A comparative analysis of their organization and evolution with other Corydalis plastomes

Introduction

The chloroplast (cp) is an autonomous plant organelle with an individual genome that encodes essential cellular functions. The genome architecture and gene content of the cp is highly conserved in angiosperms. The plastome of Corydalis belongs to the Papaveraceae family, and the genome is comprised of unusual rearrangements and gene content. Thus far, no extensive comparative studies have been carried out to understand the evolution of Corydalis chloroplast genomes.

Methods

Therefore, the Corydalis platycarpa cp genome was sequenced, and wide-scale comparative studies were conducted using publicly available twenty Corydalis plastomes.

Results

Comparative analyses showed that an extensive genome rearrangement and IR expansion occurred, and these events evolved independently in the Corydalis species. By contrast, the plastomes of its closely related subfamily Papaveroideae and other Ranunculales taxa are highly conserved. On the other hand, the synapomorphy characteristics of both accD and the ndh gene loss events happened in the common ancestor of the Corydalis and sub-clade of the Corydalis lineage, respectively. The Corydalis-sub clade species (ndh lost) are distributed predominantly in the Qinghai-Tibetan plateau (QTP) region. The phylogenetic analysis and divergence time estimation were also employed for the Corydalis species.

Discussion

The divergence time of the ndh gene in the Corydalis sub-clade species (44.31 - 15.71 mya) coincides very well with the uplift of the Qinghai-Tibet Plateau in Oligocene and Miocene periods, and maybe during this period, it has probably triggered the radiation of the Corydalis species.

Conclusion

To the best of the authors' knowledge, this is the first large-scale comparative study of Corydalis plastomes and their evolution. The present study may provide insights into the plastome architecture and the molecular evolution of Corydalis species.

The Complete Chloroplast Genome Sequences of Eight Fagopyrum Species: Insights Into Genome Evolution and Phylogenetic Relationships

Buckwheat (Fagopyrum genus, Polygonaceae), is an annual or perennial, herbaceous or semi-shrub dicotyledonous plant. There are mainly three cultivated buckwheat species, common buckwheat (Fagopyrum esculentum) is widely cultivated in Asia, Europe, and America, while Tartary buckwheat (F. tataricum) and F. cymosum (also known as F. dibotrys) are mainly cultivated in China. The genus Fagopyrum is taxonomically confusing due to the complex phenotypes of different Fagopyrum species. In this study, the chloroplast (cp) genomes of three Fagopyrum species, F. longistylum, F. leptopodum, F. urophyllum, were sequenced, and five published cp genomes of Fagopyrum were retrieved for comparative analyses. We determined the sequence differentiation, repeated sequences of the cp genomes, and the phylogeny of Fagopyrum species. The eight cp genomes ranged, gene number, gene order, and GC content were presented. Most of variations of Fagopyrum species cp genomes existed in the LSC and SSC regions. Among eight Fagopyrum chloroplast genomes, six variable regions (ndhF-rpl32, trnS-trnG, trnC, trnE-trnT, psbD, and trnV) were detected as promising DNA barcodes. In addition, a total of 66 different SSR (simple sequence repeats) types were found in the eight Fagopyrum species, ranging from 8 to 16 bp. Interestingly, many SSRs showed significant differences especially in some photosystem genes, which provided valuable information for understanding the differences in light adaptation among different Fagopyrum species. Genus Fagopyrum has shown a typical branch that is distinguished from the Rumex, Rheum, and Reynoutria, which supports the unique taxonomic status in Fagopyrum among the Polygonaceae. In addition, phylogenetic analysis based on the cp genomes strongly supported the division of eight Fagopyrum species into two independent evolutionary directions, suggesting that the separation of cymosum group and urophyllum group may be earlier than the flower type differentiation in Fagopyrum plants. The results of the chloroplast-based phylogenetic tree were further supported by the matK and Internal Transcribed Spacer (ITS) sequences of 17 Fagopyrum species, which may help to further anchor the taxonomic status of other members in the urophyllum group in Fagopyrum. This study provides valuable information and high-quality cp genomes for identifying species and evolutionary analysis for future Fagopyrum research.

Plastome Structural Evolution and Homoplastic Inversions in Neo-Astragalus (Fabaceae)

The plastid genomes of photosynthetic green plants have largely maintained conserved gene content and order as well as structure over hundreds of millions of years of evolution. Several plant lineages, however, have departed from this conservation and contain many plastome structural rearrangements, which have been associated with an abundance of repeated sequences both overall and near rearrangement endpoints. We sequenced the plastomes of 25 taxa of Astragalus L. (Fabaceae), a large genus in the inverted repeat-lacking clade of legumes, to gain a greater understanding of the connection between repeats and plastome inversions. We found plastome repeat structure has a strong phylogenetic signal among these closely related taxa mostly in the New World clade of Astragalus called Neo-Astragalus. Taxa without inversions also do not differ substantially in their overall repeat structure from four taxa each with one large-scale inversion. For two taxa with inversion endpoints between the same pairs of genes, differences in their exact endpoints indicate the inversions occurred independently. Our proposed mechanism for inversion formation suggests the short inverted repeats now found near the endpoints of the four inversions may be there as a result of these inversions rather than their cause. The longer inverted repeats now near endpoints may have allowed the inversions first mediated by shorter microhomologous sequences to propagate, something that should be considered in explaining how any plastome rearrangement becomes fixed regardless of the mechanism of initial formation.

Characterization and Comparative Analysis of Complete Chloroplast Genomes of Three Species From the Genus Astragalus (Leguminosae)

Astragalus is the largest genus in Leguminosae. Several molecular studies have investigated the potential adulterants of the species within this genus; nonetheless, the evolutionary relationships among these species remain unclear. Herein, we sequenced and annotated the complete chloroplast genomes of three Astragalus species—Astragalus adsurgens, Astragalus mongholicus var. dahuricus, and Astragalus melilotoides using next-generation sequencing technology and plastid genome annotator (PGA) tool. All species belonged to the inverted repeat lacking clade (IRLC) and had similar sequences concerning gene contents and characteristics. Abundant simple sequence repeat (SSR) loci were detected, with single-nucleotide repeats accounting for the highest proportion of SSRs, most of which were A/T homopolymers. Using Astragalus membranaceus var. membranaceus as reference, the divergence was evident in most non-coding regions of the complete chloroplast genomes of these species. Seven genes (atpB, psbD, rpoB, rpoC1, trnV, rrn16, and rrn23) showed high nucleotide variability (Pi), and could be used as DNA barcodes for Astragalus sp. cemA and rpl33 were found undergoing positive selection by the section patterns in the coded protein. Phylogenetic analysis showed that Astragalus is a monophyletic group closely related to the genus Oxytropis within the tribe Galegeae. The newly sequenced chloroplast genomes provide insight into the unresolved evolutionary relationships within Astragalus spp. and are expected to contribute to species identification.

The chicken or the egg? Plastome evolution and an independent loss of the inverted repeat in papilionoid legumes

The plastid genome (plastome), while surprisingly constant in gene order and content across most photosynthetic angiosperms, exhibits variability in several unrelated lineages. During the diversification history of the legume family Fabaceae, plastomes have undergone many rearrangements, including inversions, expansion, contraction and loss of the typical inverted repeat (IR), gene loss and repeat accumulation in both shared and independent events. While legume plastomes have been the subject of study for some time, most work has focused on agricultural species in the IR-lacking clade (IRLC) and the plant model Medicago truncatula. The subfamily Papilionoideae, which contains virtually all of the agricultural legume species, also comprises most of the plastome variation detected thus far in the family. In this study three non-papilioniods were included among 34 newly sequenced legume plastomes, along with 33 publicly available sequences, to assess plastome structural evolution in the subfamily. In an effort to examine plastome variation across the subfamily, approximately 20% of the sampling represents the IRLC with the remainder selected to represent the early-branching papilionoid clades. A number of IR-related and repeat-mediated changes were identified and examined in a phylogenetic context. Recombination between direct repeats associated with ycf2 resulted in intraindividual plastome heteroplasmy. Although loss of the IR has not been reported in legumes outside of the IRLC, one genistoid taxon was found to completely lack the typical plastome IR. The role of the IR and non-IR repeats in the progression of plastome change is discussed.

Phylogenomic framework of the IRLC legumes (Leguminosae subfamily Papilionoideae) and intercontinental biogeography of tribe Wisterieae

The inverted repeat-lacking clade (IRLC) is one of the most derived clades within the subfamily Papilionoideae of the legume family, and includes various economically important plants, e.g., chickpeas, peas, liquorice, and the largest genus of angiosperms, Astragalus. Tribe Wisterieae is one of the earliest diverged groups of the IRLC, and its generic delimitation and spatiotemporal diversification needs further clarifications. Based on genome skimming data, we herein reconstruct the phylogenomic framework of the IRLC, and infer the inter-generic relationships and historical biogeography of Wisterieae. We redefine tribe Caraganeae to contain Caragana only, and tribe Astragaleae is reduced to the Erophaca-Astragalean clade. The chloroplast capture scenario was hypothesized as the most plausible explanation of the topological incongruences between the chloroplast CDSs and nuclear ribosomal DNA trees in both the Glycyrrhizinae-Adinobotrys-Wisterieae clade and the Chesneyeae-Caraganeae-Hedysareae clade. A new name, Caragana lidou L. Duan & Z.Y. Chang, is proposed within Caraganeae. Thirteen genera are herein supported within Wisterieae, including a new genus, Villosocallerya L. Duan, J. Compton & Schrire, segregated from Callerya. Our biogeographic analyses suggest that Wisterieae originated in the late Eocene and its most recent common ancestor (MRCA) was distributed in continental southeastern Asia. Lineages of Wisterieae remained in the ancestral area from the early Oligocene to the early Miocene. By the middle Miocene, Whitfordiodendron and the MRCA of Callerya-Kanburia-Villosocallerya Clade became disjunct between the Sunda area and continental southeastern Asia, respectively; the MRCA of Wisteria migrated to North America via the Bering land bridge. The ancestor of Austrocallerya and Padbruggea migrated to the Wallacea-Oceania area, which split in the early Pliocene. In the Pleistocene, Wisteria brachybotrys, W. floribunda and Wisteriopsis japonica reached Japan, and Callerya cinerea dispersed to South Asia. This study provides a solid phylogenomic for further evolutionary/biogeographic/systematic investigations on the ecologically diverse and economically important IRLC legumes.

Molecular evolution and SSRs analysis based on the chloroplast genome of Callitropsis funebris

Chloroplast genome sequences have been used to understand evolutionary events and to infer efficiently phylogenetic relationships. Callitropsis funebris (Cupressaceae) is an endemic species in China. Its phylogenetic position is controversial due to morphological characters similar to those of Cupressus, Callitropsis, and Chamaecyparis. This study used next-generation sequencing technology to sequence the complete chloroplast genome of Ca. funebris and then constructed the phylogenetic relationship between Ca. funebris and its related species based on a variety of data sets and methods. Simple sequence repeats (SSRs) and adaptive evolution analysis were also conducted. Our results showed that the monophyletic branch consisting of Ca. funebris and Cupressus tonkinensis is a sister to Cupressus, while Callitropsis is not monophyletic; Ca. nootkatensis and Ca. vietnamensis are nested in turn at the base of the monophyletic group Hesperocyparis. The statistical results of SSRs supported the closest relationship between Ca. funebris and Cupressus. By performing adaptive evolution analysis under the phylogenetic background of Cupressales, the Branch model detected three genes and the Site model detected 10 genes under positive selection; and the Branch-Site model uncovered that rpoA has experienced positive selection in the Ca. funebries branch. Molecular analysis from the chloroplast genome highly supported that Ca. funebris is at the base of Cupressus. Of note, SSR features were found to be able to shed some light on phylogenetic relationships. In short, this chloroplast genomic study has provided new insights into the phylogeny of Ca. funebris and revealed multiple chloroplast genes possibly undergoing adaptive evolution.

Highly variable chloroplast genome from two endangered Papaveraceae lithophytes Corydalis tomentella and Corydalis saxicola

The increasingly wide application of chloroplast (cp) genome super-barcode in taxonomy and the recent breakthrough in cp genetic engineering make the development of new cp gene resources urgent and significant. Corydalis is recognized as the most genotypes complicated and taxonomically challenging plant taxa in Papaveraceae. However, there currently are few reports about cp genomes of the genus Corydalis. In this study, we sequenced four complete cp genomes of two endangered lithophytes Corydalis saxicola and Corydalis tomentella in Corydalis, conducted a comparison of these cp genomes among each other as well as with others of Papaveraceae. The cp genomes have a large genome size of 189,029-190,247 bp, possessing a quadripartite structure and with two highly expanded inverted repeat (IR) regions (length: 41,955-42,350 bp). Comparison between the cp genomes of C. tomentella, C. saxicola, and Papaveraceae species, five NADH dehydrogenase-like genes (ndhF, ndhD, ndhL, ndhG, and ndhE) with psaC, rpl32, ccsA, and trnL-UAG normally located in the SSC region have migrated to IRs, resulting in IR expansion and gene duplication. An up to 9 kb inversion involving five genes (rpl23, ycf2, ycf15, trnI-CAU, and trnL-CAA) was found within IR regions. The accD gene was found to be absent and the ycf1 gene has shifted from the IR/SSC border to the SSC region as a single copy. Phylogenetic analysis based on the sequences of common CDS showed that the genus Corydalis is quite distantly related to the other genera of Papaveraceae, it provided a new clue for recent advocacy to establish a separate Fumariaceae family. Our results revealed one special cp genome structure in Papaveraceae, provided a useful resources for classification of the genus Corydalis, and will be valuable for understanding Papaveraceae evolutionary relationships.

Plastid phylogenomic insights into the evolution of subfamily Dialioideae (Leguminosae)

The subfamily Dialioideae (Leguminosae) consists of 17 genera and about 85 species. Previous studies have detected significant plastid genome (plastome) structure variations in legumes, particularly in subfamilies Papilionoideae and Caesalpinioideae. Hence it is important to investigate plastomes from the newly recognized Dialioideae to better understand the plastome variation across the whole family. Here, we used nine plastomes representing nine genera of Dialioideae to explore plastome structural variation and intergeneric relationships in this subfamily. All plastomes of Dialioideae exhibited a typical quadripartite structure, and had relatively conserved structure compared with other legume subfamilies. However, the genome size ranged from 154,124 bp to 165,973 bp and gene numbers ranged from 129 to 132, mainly due to the expansion and contraction of the inverted repeat (IR) regions. The IR of Distemonanthus benthamianus has experienced two separate expansions into the large single copy (LSC) region and the small single copy (SSC) region, and one contraction from SSC. Poeppigia procera has experienced two separate IR expansions into LSC, while Dicorynia paraensis has experienced an IR contraction from LSC. Highly divergent regions or genes (ndhC-trnV ^UAC ,psbK-trnQ ^UUG,rps19-rps3,rpl33-rps18,accD-psaI,trnG ^UCC -trnS ^GCU ,psbI-trnS ^GCU ,5'rps16-trnQ ^UUG and ycf1) were identified as potential molecular markers for further species delimitation and population genetics analysis in legumes. Phylogenetic analysis based on 77 protein-coding sequences fully resolved the intergeneric relationships among nine genera except a moderately supported sister relationship between Petalostylis labicheoides and Labichea lanceolata. Our study reveals new insights into the structural variations of plastomes in subfamily Dialioideae and advances our understanding of the evolutionary trajectories of legume plastomes.

Comparative Chloroplast Genomics of Corydalis Species (Papaveraceae): Evolutionary Perspectives on Their Unusual Large Scale Rearrangements

The chloroplast genome (plastome) of angiosperms (particularly photosynthetic members) is generally highly conserved, although structural rearrangements have been reported in a few lineages. In this study, we revealed Corydalis to be another unusual lineage with extensive large-scale plastome rearrangements. In the four newly sequenced Corydalis plastomes that represent all the three subgenera of Corydalis, we detected (1) two independent relocations of the same five genes (trnV-UAC-rbcL) from the typically posterior part of the large single-copy (LSC) region to the front, downstream of either the atpH gene in Corydalis saxicola or the trnK-UUU gene in both Corydalis davidii and Corydalis hsiaowutaishanensis; (2) relocation of the rps16 gene from the LSC region to the inverted repeat (IR) region in Corydalis adunca; (3) uniform inversion of an 11-14 kb segment (ndhB-trnR-ACG) in the IR region of all the four Corydalis species (the same below); (4) expansions (>10 kb) of IR into the small single-copy (SSC) region and corresponding contractions of SSC region; and (5) extensive pseudogenizations or losses of 13 genes (accD, clpP, and 11 ndh genes). In addition, we also found that the four Corydalis plastomes exhibited elevated GC content in both gene and intergenic regions and high number of dispersed repeats. Phylogenomic analyses generated a well-supported topology that was consistent with the result of previous studies based on a few DNA markers but contradicted with the morphological character-based taxonomy to some extent. This study provided insights into the evolution of plastomes throughout the three Corydalis subgenera and will be of value for further study on taxonomy, phylogeny, and evolution of Corydalis.

Comparative Chloroplast Genomics of Sophora Species: Evolution and Phylogenetic Relationships in the Early-Diverging Legume Subfamily Papilionoideae (Fabaceae)

The taxonomy and evolutionary history of Sophora L., a genus with high economic and medicinal value, remain uncertain due to the absence of genetic resource (especially in China) and low polymorphism of molecular markers. Our aim was to elucidate the molecular evolution and phylogenetic relationships in chloroplast genomes of Sophora species in the early-diverging legume subfamily Papilionoideae (Fabaceae). We reported nine Sophora chloroplast genome from China using Illumina sequencing. We performed a series of analyses with previously published genomes of Sophora species to investigate their genomic characteristics, identified simple sequence repeats, large repeat sequences, tandem repeats, and highly polymorphic loci. The genomes were 152,953-158,087 bp in length, and contained 111-113 unique genes, including 76-78 protein coding, 31 tRNA, and 4 rRNA. The expansion of inverted repeat boundary of Sophora resulted in rps12 entering into the LSC region and loss of trnT-CGU gene in some species. Also, we found an approximately 23 kb inversion between trnC-GCA and trnF-GAA within the genus. In addition, we identified seven highly polymorphic loci (pi (π) > 0.035) suitable for inferring the phylogeny of Sophora species. Among these, three regions also co-occurred with large repeat sequences and support use of repeats as a proxy for the identification of polymorphic loci. Based on whole chloroplast genome and protein-coding sequences data-set, a well-supported phylogenetic tree of Sophora and related taxa showed that this genus is monophyletic, but sect. Disamaea and sect. Sophora, are incongruent with traditional taxonomic classifications based on fruit morphology. Our finding provides significant genetic resources to support further investigation into the phylogenetic relationship and evolution of the genus Sophora.

Phylogenetic and evolutionary features of the plastome of Tropaeolum pentaphyllum Lam. (Tropaeolaceae)

Complete plastome sequence of Tropaeolum pentaphyllum revealed molecular markers, hotspots of nucleotide polymorphism, RNA editing sites and phylogenetic aspects Tropaeolaceae Juss. ex DC. comprises approximately 95 species across North and South Americas. Tropaeolum pentaphyllum Lam. is an unconventional and endangered species with occurrence in some countries of South America. Although this species presents nutritional, medicinal and ornamental uses, genetic studies involving natural populations or promising genotypes are practically non-existent. Here, we report the nucleotide sequence of T. pentaphyllum plastome. It represents the first complete plastome sequence of the family Tropaeolaceae to be fully sequenced and analyzed in detail. The sequencing data revealed that the T. pentaphyllum plastome is highly similar to the plastomes of other Brassicales. Notwithstanding, our analyses detected some specific features concerning events of IR expansion and structural changes in some genes such as matK, rpoA, and rpoC2. We also detected 251 SSR loci, nine hotspots of nucleotide polymorphism, and two specific RNA editing sites in the plastome of T. pentaphyllum. Moreover, plastid phylogenomic inference indicated a closed relationship between the families Tropaeolaceae and Akaniaceae, which formed a sister group to Moringaceae-Caricaceae. Finally, our data bring new molecular markers and evolutionary features to be applied in the natural population, germplasm collection, and genotype selection aiming conservation, genetic diversity evaluation, and exploitation of this endangered species.

The Loss of the Inverted Repeat in the Putranjivoid Clade of Malpighiales

The typical plastid genome (plastome) of photosynthetic angiosperms comprises a pair of Inverted Repeat regions (IRs), which separate a Large Single Copy region (LSC) from a Small Single Copy region (SSC). The independent losses of IRs have been documented in only a few distinct plant lineages. The majority of these taxa show uncommonly high levels of plastome structural variations, while a few have otherwise conserved plastomes. For a better understanding of the function of IRs in stabilizing plastome structure, more taxa that have lost IRs need to be investigated. We analyzed the plastomes of eight species from two genera of the putranjivoid clade of Malpighiales using Illumina paired-end sequencing, the de novo assembly strategy GetOrganelle, as well as a combination of two annotation methods. We found that all eight plastomes of the putranjivoid clade have lost their IRB, representing the fifth case of IR loss within autotrophic angiosperms. Coinciding with the loss of the IR, plastomes of the putranjivoid clade have experienced significant structural variations including gene and intron losses, multiple large inversions, as well as the translocation and duplication of plastome segments. However, Balanopaceae, one of the close relatives of the putranjivoid clade, exhibit a relatively conserved plastome organization with canonical IRs. Our results corroborate earlier reports that the IR loss and additional structural reorganizations are closely linked, hinting at a shared mechanism that underpins structural disturbances.

Unraveling the Chloroplast Genomes of Two Prosopis Species to Identify Its Genomic Information, Comparative Analyses and Phylogenetic Relationship

Genus Prosopis (family Fabaceae) are shrubby trees, native to arid and semi-arid regions of Asia, Africa, and America and known for nitrogen fixation. Here, we have sequenced the complete chloroplast (cp) genomes of two Prosopis species (P. juliflora and P. cineraria) and compared them with previously sequenced P. glandulosa, Adenanthera microsperma, and Parkia javanica belonging to the same family. The complete genome sequences of Prosopis species and related species ranged from 159,389 bp (A. microsperma) to 163,677 bp (P. cineraria). The overall GC contents of the genomes were almost the similar (35.9–36.6%). The P. juliflora and P. cineraria genomes encoded 132 and 131 genes, respectively, whereas both the species comprised of 85 protein-coding genes higher than other compared species. About 140, 134, and 129 repeats were identified in P. juliflora, P. cineraria and P. glandulosa cp genomes, respectively. Similarly, the maximum number of simple sequence repeats were determined in P. juliflora (88), P. cineraria (84), and P. glandulosa (78). Moreover, complete cp genome comparison determined a high degree of sequence similarity among P. juliflora, P. cineraria, and P. glandulosa, however some divergence in the intergenic spacers of A. microsperma and Parkia javanica were observed. The phylogenetic analysis showed that P. juliflora is closer to P. cineraria than P. glandulosa.

Plastome Evolution in Dolomiaea (Asteraceae, Cardueae) Using Phylogenomic and Comparative Analyses

Dolomiaea is a medicinally important genus of Asteraceae endemic to alpine habitats of the Qinghai-Tibet Plateau (QTP) and adjacent areas. Despite significant medicinal value, genomic resources of Dolomiaea are still lacking, impeding our understanding of its evolutionary history. Here, we sequenced and annotated plastomes of four Dolomiaea species. All analyzed plastomes share the gene content and structure of most Asteraceae plastomes, indicating the conservation of plastome evolutionary history of Dolomiaea. Eight highly divergent regions (rps16-trnQ, trnC-petN, trnE-rpoB, trnT-trnL-trnF, psbE-petL, ndhF-rpl32-trnL, rps15-ycf1, and ycf1), along with a total of 51-61 simple sequence repeats (SSRs) were identified as valuable molecular markers for further species delimitation and population genetic studies. Phylogenetic analyses confirmed the evolutionary position of Dolomiaea as a clade within the subtribe Saussureinae, while revealing the discordance between the molecular phylogeny and morphological treatment. Our analysis also revealed that the plastid genes, rpoC2 and ycf1, which are rarely used in Asteraceae phylogenetic inference, exhibit great phylogenetic informativeness and promise in further phylogenetic studies of tribe Cardueae. Analysis for signatures of selection identified four genes that contain sites undergoing positive selection (atpA, ndhF, rbcL, and ycf4). These genes may play important roles in the adaptation of Dolomiaea to alpine environments. Our study constitutes the first investigation on the sequence and structural variation, phylogenetic utility and positive selection of plastomes of Dolomiaea, which will facilitate further studies of its taxonomy, evolution and conservation.

New Insights Into the Plastome Evolution of the Millettioid/Phaseoloid Clade (Papilionoideae, Leguminosae)

The Millettioid/Phaseoloid (MP) clade from the subfamily Papilionoideae (Leguminosae) consists of six tribes and ca. 3,000 species. Previous studies have revealed some plastome structural variations (PSVs) within this clade. However, many deep evolutionary relationships within the clade remain unresolved. Due to limited taxon sampling and few genetic markers in previous studies, our understanding of the evolutionary history of this clade is limited. To address this issue, we sampled 43 plastomes (35 newly sequenced) representing all the six tribes of the MP clade to examine genomic structural variations and phylogenetic relationships. Plastomes of the species from the MP clade were typically quadripartite (size ranged from 140,029 to 160,040 bp) and contained 109-111 unique genes. We revealed four independent gene losses (ndhF, psbI, rps16, and trnS-GCU), multiple IR-SC boundary shifts, and six inversions in the tribes Desmodieae, Millettieae, and Phaseoleae. Plastomes of the species from the MP clade have experienced significant variations which provide valuable information on the evolution of the clade. Plastid phylogenomic analyses using Maximum Likelihood and Bayesian methods yielded a well-resolved phylogeny at the tribal and generic levels within the MP clade. This result indicates that plastome data is useful and reliable data for resolving the evolutionary relationships of the MP clade. This study provides new insights into the phylogenetic relationships and PSVs within this clade.

Complete chloroplast genome of Sophora alopecuroides (Papilionoideae): molecular structures, comparative genome analysis and phylogenetic analysis

Sophora alopecuroides belongs to the genus Sophora of the family Papilionoideae. It is mainly distributed in the desert and semidesert areas of northern China, and has high medicinal value and ecological function. Previous studies have reported the chemical composition and ecological functions of S. alopecuroides. However, only a few reports are available on the genomic information of S. alopecuroides, especially the chloroplast genome, which greatly limits the study of the evolutionary relationship between other species of Papilionoideae. Here, we report the complete chloroplast genome of S. alopecuroides. The size of the chloroplast genome is 155,207 bp, and the GC content is 36.44%. The S. alopecuroides chloroplast genome consists of 132 genes, including 83 protein-coding genes, 41 transfer RNA (tRNA) genes,and eight ribosomal RNA (rRNA) genes. Phylogenetic analysis revealed the taxonomic position of S. alopecuroides in Papilionoideae, and the genus Sophora and the genus Ammopiptanthus were highly related. Comparative genomics analysis revealed the gene rearrangement in the evolution of S. alopecuroides. The comparison between S. alopecuroides and the species of the Papilionoideae identified a novel 23 kb inversion between the trnC-GCA and trnF-GAA which occurred before the divergence of Sophora and Ammopiptanthus of Thermopsideae. This study provided an essential data for the understanding of phylogenetic status of S. alopecuroides.

Plastid phylogenomic insights into the evolution of the Caprifoliaceae s.l. (Dipsacales)

The family Caprifoliaceae s.l. is an asterid angiosperm clade of ca. 960 species, most of which are distributed in temperate regions of the northern hemisphere. Recent studies show that the family comprises seven major clades: Linnaeoideae, Zabelia, Morinoideae, Dipsacoideae, Valerianoideae, Caprifolioideae, and Diervilloideae. However, its phylogeny at the subfamily or genus level remains controversial, and the backbone relationships among subfamilies are incompletely resolved. In this study, we utilized complete plastome sequencing to resolve the relationships among the subfamilies of the Caprifoliaceae s.l. and clarify several long-standing controversies. We generated and analyzed plastomes of 48 accessions of Caprifoliaceae s.l., representing 44 species, six subfamilies and one genus. Combined with available Caprifoliaceae s.l. plastomes on GenBank and 12 outgroups, we analyzed a final dataset of 68 accessions. Genome structure was strongly conserved in general, although the boundaries between the Inverted Repeat were found to have contracted across Caprifoliaceae s.l. to exclude rpl2, rps19, and ycf1, all or parts of which are typically present in the IR of most angiosperms. The ndhF gene was found to have been inverted in all plastomes of Adoxaceae. Phylogenomic analyses of 68 complete plastomes yielded a highly supported topology that strongly supported the monophyly of Zabelia and its sister relationship to Morinoideae. Moreover, a clade of Valerianoideae + Dipsacoideae was recovered as sister to a clade of Linnaeoideae + Zabelia + Morinoideae clade, and Heptacodium was sister to remaining Caprifolioideae. The Diervilloideae and Caprifolioideae were successively sister to all other Caprifoliaceae s.l. Major lineages of Caprifoliaceae s.l. were estimated to have diverged from the Upper Cretaceous to the Eocene (50-100 Ma), whereas within-genus diversification was dated to the Oligocene and later, concomitant with global cooling and drying. Our results demonstrate the power of plastid phylogenomics in improving estimates of phylogeny among genera and subfamilies, and provide new insights into plastome evolution across Caprifoliaceae s.l.

The plastomes of Astrocaryum aculeatum G. Mey. and A. murumuru Mart. show a flip-flop recombination between two short inverted repeats

The plastomes of Astrocaryum murumuru and A. aculeatum revealed a lineage-specific structural feature originated by flip-flop recombination, non-synonymous substitutions in conserved genes and several molecular markers. Astrocaryum murumuru Mart. and A. aculeatum G.Mey. are two palm species of Amazon forest that are economically important as source of food, oil and raw material for several applications. Genetic studies aiming to establish strategies for conservation and domestication of both species are still in the beginning given that the exploitation is mostly by extractive activity. The identification and characterization of molecular markers are essential to assess the genetic diversity of natural populations of both species. Therefore, we sequenced and characterized in detail the plastome of both species. We compared both species and identified 32 polymorphic SSR loci, 150 SNPs, 46 indels and eight hotspots of nucleotide diversity. Additionally, we reported a specific RNA editing site found in the ccsA gene, which is exclusive to A. murumuru. Moreover, the structural analysis in the plastomes of both species revealed a 4.6-kb inversion encompassing a set of genes involved in chlororespiration and plastid translation. This 4.6-kb inversion is a lineage-specific structural feature of the genus Astrocaryum originated by flip-flop recombination between two short inverted repeats. Furthermore, our phylogenetic analysis using whole plastomes of 39 Arecaceae species placed the Astrocaryum species sister to Acrocomia within the tribe Cocoseae. Finally, our data indicated substantial changes in the plastome structure and sequence of both species of the genus Astrocaryum, bringing new molecular markers, several structural and evolving features, which can be applied in several areas such as genetic, evolution, breeding, phylogeny and conservation strategies for both species.

Comparative Analysis of two Sugarcane Ancestors Saccharum officinarum and S. spontaneum based on Complete Chloroplast Genome Sequences and Photosynthetic Ability in Cold Stress

Polyploid Saccharum with complex genomes hindered the progress of sugarcane improvement, while their chloroplast genomes are much smaller and simpler. Chloroplast (cp), the vital organelle, is the site of plant photosynthesis, which also evolves other functions, such as tolerance to environmental stresses. In this study, the cp genome of two sugarcane ancestors Saccharum officinarum and S. spontaneum were sequenced, and genome comparative analysis between these two species was carried out, together with the photosynthetic ability. The length is 141,187 bp for S. officinarum and that is 7 bp longer than S. spontaneum, with the same GC content (38.44%) and annotated gene number (134), 13 with introns among them. There is a typical tetrad structure, including LSC, SSC, IRb and IRa. Of them, LSC and IRa/IRb are 18 bp longer and 6 bp shorter than those in S. spontaneum (83,047 bp and 22,795 bp), respectively, while the size of SSC is same (12,544 bp). Five genes exhibit contraction and expansion at the IR junctions, but only one gene ndhF with 29 bp expansion at the border of IRb/SSC. Nucleotide diversity (Pi) based on sliding window analysis showed that the single copy and noncoding regions were more divergent than IR- and coding regions, and the variant hotspots trnG-trnM, psbM-petN, trnR-rps14, ndhC-trnV and petA-psbJ in the LSC and trnL-ccsA in the SSC regions were detected, and petA-psbJ with the highest divergent value of 0.01500. Genetic distances of 65 protein genes vary from 0.00000 to 0.00288 between two species, and the selective pressure on them indicated that only petB was subjected to positive selection, while more genes including rpoC2, rps3, ccsA, ndhA, ndhA, psbI, atpH and psaC were subjected to purifying or very strong purifying selection. There are larger number of codons in S. spontaneum than that in S. officinarum, while both species have obvious codon preference and the codons with highest-(AUG) and lowest frequency (AUA) are same. Whilst, the most abundant amino acid is leucine in both S. officinarum and S. spontaneum, with number of 2175 (10.88% of total) and 2228 (10.90% of total) codons, respectively, and the lowest number is cysteine, with only 221 (1.105%) and 224 (1.096%), respectively. Protein collinearity analysis showed the high collinearity though several divergences were present in cp genomes, and identification of simple sequence repeats (SSRs) were included in this study. In addition, in order to compare cold tolerance and explore the expanding function of this environmental stress, the chlorophyll relative content (SPAD) and chlorophyll fluorescence Fv/Fm were measured. The significantly higher SPAD were observed in S. spontaneum than those in S. officinarum, no matter what the control conditions, exposure to low temperature or during recovery, and so was for Fv/Fm under exposure to low temperature, together with higher level of SPAD in S. spontaneum in each measurement. Aforementioned results suggest much stronger photosynthetic ability and cold tolerance in S. spontaneum. Our findings build a foundation to investigate the biological mechanism of two sugarcane ancestor chloroplasts and retrieve reliable molecular resources for phylogenetic and evolutionary studies, and will be conducive to genetic improvement of photosynthetic ability and cold resistance in modern sugarcane.

Complete chloroplast genomes of medicinally important Teucrium species and comparative analyses with related species from Lamiaceae

Teucrium is one of the most economically and ecologically important genera in the Lamiaceae family; however, it is currently the least well understood at the plastome level. In the current study, we sequenced the complete chloroplast (cp) genomes of T. stocksianum subsp. stenophyllum R.A.King (TSS), T. stocksianum subsp. stocksianum Boiss. (TS) and T. mascatense Boiss. (TM) through next-generation sequencing and compared them with the cp genomes of related species in Lamiaceae (Ajuga reptans L., Caryopteris mongholica Bunge, Lamium album L., Lamium galeobdolon (L.) Crantz, and Stachys byzantina K.Koch). The results revealed that the TSS, TS and TM cp genomes have sizes of 150,087, 150,076 and 150,499 bp, respectively. Similarly, the large single-copy (LSC) regions of TSS, TS and TM had sizes of 81,707, 81,682 and 82,075 bp, respectively. The gene contents and orders of these genomes were similar to those of other angiosperm species. However, various differences were observed at the inverted repeat (IR) junctions, and the extent of the IR expansion into ψrps19 was 58 bp, 23 bp and 61 bp in TSS, TS and TM, respectively. Similarly, in all genomes, the pbsA gene was present in the LSC at varying distances from the JLA (IRa-LSC) junction. Furthermore, 89, 72, and 92 repeats were identified in the TSS, TM and TS cp genomes, respectively. The highest number of simple sequence repeats was found in TSS (128), followed by TS (127) and TM (121). Pairwise alignments of the TSS cp genome with related cp genomes showed a high degree of synteny. However, relatively lower sequence identity was observed when various coding regions were compared to those of related cp genomes. The average pairwise divergence among the complete cp genomes showed that TSS was more divergent from TM (0.018) than from TS (0.006). The current study provides valuable genomic insight into the genus Teucrium and its subspecies that may be applied to a more comprehensive study.

A strategy for developing high-resolution DNA barcodes for species discrimination of wood specimens using the complete chloroplast genome of three Pterocarpus species

A method for extraction of wood DNA and a strategy for designing high-resolution barcodes for wood were developed. Ycf1b was the prioritized barcode to resolve the Pterocarpus wood species studied. DNA barcoding, an effective tool for wood species identification, mainly focuses on universal barcodes and often lacks high resolution to differentiate species, especially for closely related taxa within the same genus. Therefore, more highly informative DNA barcodes need to be identified. This study is the first to report a strategy for developing specific DNA barcodes of wood tissues. The complete chloroplast genomes of leaf samples of three Pterocarpus species, i.e., P. indicus, P. santalinus, and P. tinctorius, were sequenced, and thereafter, the most variable DNA regions were identified on the scale of the complete chloroplast genomes. Finally, wood DNA was extracted from 30 wood specimens of the three Pterocarpus species, and DNA recovery rates of the selected regions were tested for applicability to verification on the wood specimens studied. The seven regions with the most variation (rpl32-ccsA, rpl20-clpP, trnC-rpoB, ycf1b, accD-ycf4, ycf1a, and psbK-accD) were identified from the chloroplast genome by quantifying nucleotide diversity (Pi > 0.02), which was remarkably higher than that of the plant universal barcodes (rbcL, matK, and trnH-psbA) and the previously reported barcodes (ndhF-rpl32 and trnL-F) used for phylogenetic analysis in Pterocarpus. After comprehensive evaluation of species discrimination ability and applicability, the ycf1b region performed well in terms of the recovery success rate (76.7%) and species identification (100%) for wood specimens of the three Pterocarpus species, and was identified as the preferred high-resolution chloroplast barcode for selected Pterocarpus species. It will offer technical support for curbing illegal timber harvesting activities and for conserving endangered and valuable wood species.

Plastid genome evolution in tribe Desmodieae (Fabaceae: Papilionoideae)

Recent plastid genome (plastome) studies of legumes (family Fabaceae) have shown that this family has undergone multiple atypical plastome evolutions from each of the major clades. The tribe Desmodieae belongs to the Phaseoloids, an important but systematically puzzling clade within Fabaceae. In this study, we investigated the plastome evolution of Desmodieae and analyzed its phylogenetic signaling. We sequenced six complete plastomes from representative members of Desmodieae and from its putative sister Phaseoloid genus Mucuna. Those genomes contain 128 genes and range in size from 148,450 to 153,826 bp. Analyses of gene and intron content revealed similar characters among the members of Desmodieae and Mucuna. However, there were also several distinct characters identified. The loss of the rpl2 intron was a feature shared between Desmodieae and Mucuna, whereas the loss of the rps12 intron was specific to Desmodieae. Likewise, gene loss of rps16 was observed in Mucuna but not in Desmodieae. Substantial sequence variation of ycf4 was detected from all the sequenced plastomes, but pseudogenization was restricted to the genus Desmodium. Comparative analysis of gene order revealed a distinct plastome conformation of Desmodieae compared with other Phaseoloid legumes, i.e., an inversion of an approximately 1.5-kb gene cluster (trnD-GUC, trnY-GUA, and trnE-UUC). The inversion breakpoint suggests that this event was mediated by the recombination of an 11-bp repeat motif. A phylogenetic analysis based on the plastome-scale data set found the tribe Desmodieae is a highly supported monophyletic group nested within the paraphyletic Phaseoleae, as has been found in previous phylogenetic studies. Two subtribes (Desmodiinae and Lespedezinae) of Desmodieae were also supported as monophyletic groups. Within the subtribe Lespedezinae, Lespedeza is closer to Kummerowia than Campylotropis.

Reconfiguration of the plastid genome in Lamprocapnos spectabilis: IR boundary shifting, inversion, and intraspecific variation

We generated a complete plastid genome (plastome) sequence for Lamprocapnos spectabilis, providing the first complete plastome from the subfamily Fumarioideae (Papaveraceae). The Lamprocapnos plastome shows large differences in size, structure, gene content, and substitution rates compared with two sequenced Papaveraceae plastomes. We propose a model that explains the major rearrangements observed, involving at least six inverted repeat (IR) boundary shifts and five inversions, generating a number of gene duplications and relocations, as well as a two-fold expansion of the IR and miniaturized small single-copy region. A reduction in the substitution rates for genes transferred from the single-copy regions to the IR was observed. Accelerated substitution rates of plastid accD and clpP were detected in the Lamprocapnos plastome. The accelerated substitution rate for the accD gene was correlated with a large insertion of amino acid repeat (AAR) motifs in the middle region, but the forces driving the higher substitution rate of the clpP gene are unclear. We found a variable number of AARs in Lamprocapnos accD and ycf1 genes within individuals, and the repeats were associated with coiled-coil regions. In addition, comparative analysis of three Papaveraceae plastomes revealed loss of rps15 in Papaver, and functional replacement to the nucleus was identified.

Plastome characteristics of Cannabaceae

Cannabaceae is an economically important family that includes ten genera and ca. 117 accepted species. To explore the structure and size variation of their plastomes, we sequenced ten plastomes representing all ten genera of Cannabaceae. Each plastome possessed the typical angiosperm quadripartite structure and contained a total of 128 genes. The Inverted Repeat (IR) regions in five plastomes had experienced small expansions (330-983 bp) into the Large Single-Copy (LSC) region. The plastome of Chaetachme aristata has experienced a 942-bp IR contraction and lost rpl22 and rps19 in its IRs. The substitution rates of rps19 and rpl22 decreased after they shifted from the LSC to IR. A 270-bp inversion was detected in the Parasponia rugosa plastome, which might have been mediated by 18-bp inverted repeats. Repeat sequences, simple sequence repeats, and nucleotide substitution rates varied among these plastomes. Molecular markers with more than 13% variable sites and 5% parsimony-informative sites were identified, which may be useful for further phylogenetic analysis and species identification. Our results show strong support for a sister relationship between Gironniera and Lozanell (BS = 100). Celtis, Cannabis-Humulus, Chaetachme-Pteroceltis, and Trema-Parasponia formed a strongly supported clade, and their relationships were well resolved with strong support (BS = 100). The availability of these ten plastomes provides valuable genetic information for accurately identifying species, clarifying taxonomy and reconstructing the intergeneric phylogeny of Cannabaceae.

Sequencing, Characterization, and Comparative Analyses of the Plastome of Caragana rosea var. rosea

To exploit the drought-resistant Caragana species, we performed a comparative study of the plastomes from four species: Caragana rosea, C. microphylla, C. kozlowii, and C. Korshinskii. The complete plastome sequence of the C. rosea was obtained using the next generation DNA sequencing technology. The genome is a circular structure of 133,122 bases and it lacks inverted repeat. It contains 111 unique genes, including 76 protein-coding, 30 tRNA, and four rRNA genes. Repeat analyses obtained 239, 244, 258, and 246 simple sequence repeats in C. rosea, C. microphylla, C. kozlowii, and C. korshinskii, respectively. Analyses of sequence divergence found two intergenic regions: trnI-CAU-ycf2 and trnN-GUU-ycf1, exhibiting a high degree of variations. Phylogenetic analyses showed that the four Caragana species belong to a monophyletic clade. Analyses of Ka/Ks ratios revealed that five genes: rpl16, rpl20, rps11, rps7, and ycf1 and several sites having undergone strong positive selection in the Caragana branch. The results lay the foundation for the development of molecular markers and the understanding of the evolutionary process for drought-resistant characteristics.